Showing 1–50 of 51 results for author: Marquette, J -

ExoClock Project IV: A homogeneous catalogue of 620 updated exoplanet ephemerides

Authors: A. Kokori, A. Tsiaras, G. Pantelidou, A. Jones, A. Siakas, B. Edwards, G. Tinetti, A. Wünsche, Y. Jongen, F. Libotte, M. Correa, L. V. Mugnai, A. Bocchieri, A. R. Capildeo, E. Poultourtzidis, C. Sidiropoulos, L. Bewersdorff, G. Lekkas, G. Grivas, R. A. Buckland, S. R. -L. Futcher, P. Matassa, J. -P. Vignes, A. O. Kovacs, M. Raetz , et al. (301 additional authors not shown)

Abstract: The ExoClock project is an open platform aiming to monitor exoplanets by integrating observations from space and ground based telescopes. This study presents an updated catalogue of 620 exoplanet ephemerides, integrating 30000 measurements from ground-based telescopes (the ExoClock network), literature, and space telescopes (Kepler, K2 and TESS). The updated catalogue includes 277 planets from TES… ▽ More The ExoClock project is an open platform aiming to monitor exoplanets by integrating observations from space and ground based telescopes. This study presents an updated catalogue of 620 exoplanet ephemerides, integrating 30000 measurements from ground-based telescopes (the ExoClock network), literature, and space telescopes (Kepler, K2 and TESS). The updated catalogue includes 277 planets from TESS which require special observing strategies due to their shallow transits or bright host stars. This study demonstrates that data from larger telescopes and the employment of new methodologies such as synchronous observations with small telescopes, are capable of monitoring special cases of planets. The new ephemerides show that 45% of the planets required an update while the results show an improvement of one order of magnitude in prediction uncertainty. The collective analysis also enabled the identification of new planets showing TTVs, highlighting the importance of extensive observing coverage. Developed in the context of the ESA's Ariel space mission, with the goal of delivering a catalogue with reliable ephemerides to increase the mission efficiency, ExoClock's scope and service have grown well beyond the remit of Ariel. The ExoClock project has been operating in the framework of open science, and all tools and products are accessible to everyone within academia and beyond, to support efficient scheduling of future exoplanet observations, especially from larger telescopes where the pressure for time allocation efficiency is higher (Ariel, JWST, VLT, ELT, Subaru etc). The inclusion of diverse audiences in the process and the collaborative mode not only foster democratisation of science but also enhance the quality of the results. △ Less

Submitted 18 November, 2025; originally announced November 2025.

Comments: 12 pages of text (104 in total, including the list of authors, acknowledgements, references and data tables), 7 figures, 8 tables. Submitted to ApJS (this version includes the first round of the reviewer's comments). The Data Release is available at: https://doi.org/10.17605/OSF.IO/WPJTN. Machine-readable versions of tables 7 and 8 are included the TeX Source

ExoClock Project III: 450 new exoplanet ephemerides from ground and space observations

Authors: A. Kokori, A. Tsiaras, B. Edwards, A. Jones, G. Pantelidou, G. Tinetti, L. Bewersdorff, A. Iliadou, Y. Jongen, G. Lekkas, A. Nastasi, E. Poultourtzidis, C. Sidiropoulos, F. Walter, A. Wünsche, R. Abraham, V. K. Agnihotri, R. Albanesi, E. Arce-Mansego, D. Arnot, M. Audejean, C. Aumasson, M. Bachschmidt, G. Baj, P. R. Barroy , et al. (192 additional authors not shown)

Abstract: The ExoClock project has been created with the aim of increasing the efficiency of the Ariel mission. It will achieve this by continuously monitoring and updating the ephemerides of Ariel candidates over an extended period, in order to produce a consistent catalogue of reliable and precise ephemerides. This work presents a homogenous catalogue of updated ephemerides for 450 planets, generated by t… ▽ More The ExoClock project has been created with the aim of increasing the efficiency of the Ariel mission. It will achieve this by continuously monitoring and updating the ephemerides of Ariel candidates over an extended period, in order to produce a consistent catalogue of reliable and precise ephemerides. This work presents a homogenous catalogue of updated ephemerides for 450 planets, generated by the integration of $\sim$18000 data points from multiple sources. These sources include observations from ground-based telescopes (ExoClock network and ETD), mid-time values from the literature and light-curves from space telescopes (Kepler/K2 and TESS). With all the above, we manage to collect observations for half of the post-discovery years (median), with data that have a median uncertainty less than one minute. In comparison with literature, the ephemerides generated by the project are more precise and less biased. More than 40\% of the initial literature ephemerides had to be updated to reach the goals of the project, as they were either of low precision or drifting. Moreover, the integrated approach of the project enables both the monitoring of the majority of the Ariel candidates (95\%), and also the identification of missing data. The dedicated ExoClock network effectively supports this task by contributing additional observations when a gap in the data is identified. These results highlight the need for continuous monitoring to increase the observing coverage of the candidate planets. Finally, the extended observing coverage of planets allows us to detect trends (TTVs - Transit Timing Variations) for a sample of 19 planets. All products, data, and codes used in this work are open and accessible to the wider scientific community. △ Less

Submitted 20 September, 2022; originally announced September 2022.

Comments: Recommended for publication to ApJS (reviewer's comments implemented). Main body: 13 pages, total: 77 pages, 7 figures, 7 tables. Data available at http://doi.org/10.17605/OSF.IO/P298N

New limits from microlensing on Galactic Black Holes in the mass range $10M_{\odot}<M<1000M_{\odot}$

Authors: T. Blaineau, M. Moniez, C. Afonso, J. -N. Albert, R. Ansari, E. Aubourg, C. Coutures, J. -F. Glicenstein, B. Goldman, C. Hamadache, T. Lasserre, L. LeGuillou, E. Lesquoy, C. Magneville, J. -B. Marquette, N. Palanque-Delabrouille, O. Perdereau, J. Rich, M. Spiro, P. Tisserand

Abstract: We have searched for long duration microlensing events originating from intermediate mass Black Holes (BH) in the halo of the Milky Way, using archival data from EROS-2 and MACHO photometric surveys towards the Large Magellanic Cloud. We combined data from these two surveys to create a common database of light curves for 14.1 million objects in LMC, covering a total duration of 10.6 years, with fl… ▽ More We have searched for long duration microlensing events originating from intermediate mass Black Holes (BH) in the halo of the Milky Way, using archival data from EROS-2 and MACHO photometric surveys towards the Large Magellanic Cloud. We combined data from these two surveys to create a common database of light curves for 14.1 million objects in LMC, covering a total duration of 10.6 years, with flux series measured through four wide passbands. We have carried out a microlensing search on these light curves, complemented by the light curves of 22.7 million objects, observed by EROS-2 only or MACHO only over about 7 years, with flux series measured through only two passbands. A likelihood analysis, taking into account LMC self lensing and Milky Way disk contributions allows us to conclude that compact objects with masses in the range $10 - 100 M_{\odot}$ cannot make up more than $\sim 15\%$ of a standard halo total mass (at $95\%$ confidence level). Our analysis sensitivity weakens for heavier objects, although we still exclude that $\sim 50\%$ of the halo be made of $\sim 1000 M_{\odot}$ BHs. Combined with previous EROS results, an upper limit of $\sim 15\%$ of the total halo mass can be obtained for the contribution of compact halo objects in the mass range $10^{-6} - 10^2 M_{\odot}$. △ Less

Submitted 9 June, 2022; v1 submitted 28 February, 2022; originally announced February 2022.

Comments: 9 pages, 5 figures, accepted for publication in Astronomy and Astrophysics

Journal ref: A&A 664, A106 (2022)

MagAO observations of the binary microlens OGLE-2014-BLG-1050 prefer the higher-mass solution

Authors: Xiaojia Xie, Subo Dong, Wei Zhu, A. Gould, A. Udalski, J. -P. Beaulieu, L. M. Close, J. R. Males, J. -B. Marquette, K. M. Morzinski, R. W. Pogge, J. C. Yee

Abstract: We report adaptive-optics (AO) follow-up imaging of OGLE-2014-BLG-1050, which is the second binary microlensing event with space-based parallax measurements. The degeneracy in microlens parallax pi_E led to two sets of solutions, either a ~(0.9, 0.35) M_Sun binary at ~3.5 kpc, or a ~(0.2, 0.07) M_Sun binary at ~1.1 kpc. We measure the flux blended with the microlensed source by conducting Magellan… ▽ More We report adaptive-optics (AO) follow-up imaging of OGLE-2014-BLG-1050, which is the second binary microlensing event with space-based parallax measurements. The degeneracy in microlens parallax pi_E led to two sets of solutions, either a ~(0.9, 0.35) M_Sun binary at ~3.5 kpc, or a ~(0.2, 0.07) M_Sun binary at ~1.1 kpc. We measure the flux blended with the microlensed source by conducting Magellan AO observations, and find that the blending is consistent with the predicted lens flux from the higher-mass solution. From the combination of the AO flux measurement together with previous lensing constraints, it is estimated that} the lens system consists of a $1.05^{+0.08}_{-0.07}$ M_Sun primary and a $0.38^{+0.07}_{-0.06}$ M_Sun secondary at $3.43^{+0.19}_{-0.21}$ kpc. △ Less

Submitted 15 December, 2021; originally announced December 2021.

Comments: Published in AJ

Journal ref: 2021, AJ, 161, 113

ExoClock project II: A large-scale integrated study with 180 updated exoplanet ephemerides

Authors: A. Kokori, A. Tsiaras, B. Edwards, M. Rocchetto, G. Tinetti, L. Bewersdorff, Y. Jongen, G. Lekkas, G. Pantelidou, E. Poultourtzidis, A. Wünsche, C. Aggelis, V. K. Agnihotri, C. Arena, M. Bachschmidt, D. Bennett, P. Benni, K. Bernacki, E. Besson, L. Betti, A. Biagini, P. Brandebourg, M. Bretton, S. M. Brincat, M. Caló , et al. (80 additional authors not shown)

Abstract: The ExoClock project is an inclusive, integrated, and interactive platform that was developed to monitor the ephemerides of the Ariel targets to increase the mission efficiency. The project makes the best use of all available resources, i.e., observations from ground telescopes, mid-time values from the literature and finally, observations from space instruments. Currently, the ExoClock network in… ▽ More The ExoClock project is an inclusive, integrated, and interactive platform that was developed to monitor the ephemerides of the Ariel targets to increase the mission efficiency. The project makes the best use of all available resources, i.e., observations from ground telescopes, mid-time values from the literature and finally, observations from space instruments. Currently, the ExoClock network includes 280 participants with telescopes capable of observing 85\% of the currently known Ariel candidate targets. This work includes the results of $\sim$1600 observations obtained up to the 31st of December 2020 from the ExoClock network. These data in combination with $\sim$2350 mid-time values collected from the literature are used to update the ephemerides of 180 planets. The analysis shows that 40\% of the updated ephemerides will have an impact on future scheduling as either they have a significantly improved precision, or they have revealed biases in the old ephemerides. With the new observations, the observing coverage and rate for half of the planets in the sample has been doubled or more. Finally, from a population perspective, we identify that the differences in the 2028 predictions between the old and the new ephemerides have an STD that is double what is expected from gaussian uncertainties. These findings have implications for planning future observations, where we will need to account for drifts potentially greater than the prediction uncertainties. The updated ephemerides are open and accessible to the wider exoplanet community both from our Open Science Framework (OSF) repository and our website. △ Less

Submitted 26 October, 2021; originally announced October 2021.

Comments: 9 pages (47 with appendices and references), 8 figures, 2 tables. Submitted to ApJS. Revised based on the reviewer's comments

OGLE-2017-BLG-1434Lb: Confirmation of a Cold Super-Earth using Keck Adaptive Optics

Authors: J. W. Blackman, J. -P. Beaulieu, A. A. Cole, N. Koshimoto, A. Vandorou, A. Bhattacharya, J. -B. Marquette, D. P. Bennett

Abstract: The microlensing event OGLE-2017-BLG-1434 features a cold super-Earth planet which is one of eleven microlensing planets with a planet-host star mass ratio $q < 1 \times 10^{-4}$. We provide an additional mass-distance constraint on the lens host using near-infrared adaptive optics photometry from Keck/NIRC2. We are able to determine a flux excess of $K_L = 16.96 \pm 0.11$ which most likely comes… ▽ More The microlensing event OGLE-2017-BLG-1434 features a cold super-Earth planet which is one of eleven microlensing planets with a planet-host star mass ratio $q < 1 \times 10^{-4}$. We provide an additional mass-distance constraint on the lens host using near-infrared adaptive optics photometry from Keck/NIRC2. We are able to determine a flux excess of $K_L = 16.96 \pm 0.11$ which most likely comes entirely from the lens star. Combining this with constraints from the large Einstein ring radius, $θ_E=1.40 \pm 0.09\;mas$ and OGLE parallax we confirm this event as a super-Earth with mass $m_p = 4.43 \pm 0.25M_\odot$. This system lies at a distance of $D_L = 0.86 \pm 0.05\,kpc$ from Earth and the lens star has a mass of $M_L=0.234\pm0.012M_\odot$. We confirm that with a star-planet mass ratio of $q=0.57 \times 10^{-4}$, OGLE-2017-BLG-1434 lies near the inflexion point of the planet-host mass-ratio power law. △ Less

Submitted 14 July, 2021; originally announced July 2021.

Comments: 7 pages, 4 figures

Journal ref: The Astronomical Journal 2021, Volume 161, Issue 6, id.279, 7p The Astronomical Journal, Volume 161, Issue 6, id.279, 7 pp

Combining Spitzer parallax and Keck II adaptive optics imaging to measure the mass of a solar-like star orbited by a cold gaseous planet discovered by microlensing

Authors: J. -P. Beaulieu, V. Batista, D. P. Bennett, J. -B. Marquette, J. W. Blackman, A. A. Cole, C. Coutures, C. Danielski, D. Dominis-Prester, J. Donatowicz, A. Fukui, N. Koshimoto, C. Loncaric, J. C. Morales, T. Sumi, D. Suzuki, C. Henderson, Y. Shvartzvald, C. Beichman

Abstract: To obtain accurate mass measurements for cold planets discovered by microlensing, it is usually necessary to combine light curve modeling with at least two lens mass-distance relations. Often, a constraint on the Einstein ring radius measurement is obtained from the caustic crossing time: This is supplemented by secondary constraints such as precise parallax measurements and/or measures of the len… ▽ More To obtain accurate mass measurements for cold planets discovered by microlensing, it is usually necessary to combine light curve modeling with at least two lens mass-distance relations. Often, a constraint on the Einstein ring radius measurement is obtained from the caustic crossing time: This is supplemented by secondary constraints such as precise parallax measurements and/or measures of the lens luminosity using high angular resolution observations. We resolved the source+lens star from sub-arcsecond blends in H band using adaptive optics (AO) observations with NIRC2 mounted on Keck II telescope. We identify additional flux, coincident with the source to within 160 mas. We estimate the potential contributions to this blended light (chance-aligned star, additional companion to the lens or to the source) and find that 85 % of of the NIR flux is due to the lens star at H_L=16.63 +- 0.06 and K_L=16.46 +- 0.06. We combined the parallax constraint and the AO constraint to derive the physical parameters of the system. The lensing system is composed of a mid-late type G main sequence star of M_L=0.89 +- 0.05 Mo located at D_L = 3.6 +- 0.3 kpc in the Galactic disk. Taking the mass ratio and projected separation from the original study leads to a planet of M_p= 0.64 +- 0.044 M_Jupiter at 3.48 +- 0.22 AU. Excellent parallax measurement from simultaneous ground-space observations have been obtained on the microlensing event OGLE-2014-BLG-0124, but it is only when they are combined with ~ 30 min of Keck II AO observations that the physical parameters of the host star are well measured. △ Less

Submitted 4 September, 2017; originally announced September 2017.

Comments: 5 pages, 4 figures. Submitted to Astrophysical Journal

The First Planetary Microlensing Event with Two Microlensed Source Stars

Authors: D. P. Bennett, A. Udalski, C. Han, I. A. Bond, J. -P. Beaulieu, J. Skowron, B. S. Gaudi, N. Koshimoto, F. Abe, Y. Asakura, R. K. Barry, A. Bhattacharya, M. Donachie, P. Evans, A. Fukui, Y. Hirao, Y. Itow, M. C. A. Li, C. H. Ling, K. Masuda, Y. Matsubara, Y. Muraki, M. Nagakane, K. Ohnishi, H. Oyokawa , et al. (43 additional authors not shown)

Abstract: We present the analysis of microlensing event MOA-2010-BLG-117, and show that the light curve can only be explained by the gravitational lensing of a binary source star system by a star with a Jupiter mass ratio planet. It was necessary to modify standard microlensing modeling methods to find the correct light curve solution for this binary-source, binary-lens event. We are able to measure a stron… ▽ More We present the analysis of microlensing event MOA-2010-BLG-117, and show that the light curve can only be explained by the gravitational lensing of a binary source star system by a star with a Jupiter mass ratio planet. It was necessary to modify standard microlensing modeling methods to find the correct light curve solution for this binary-source, binary-lens event. We are able to measure a strong microlensing parallax signal, which yields the masses of the host star, $M_* = 0.58\pm 0.11 M_\odot$, and planet $m_p = 0.54\pm 0.10 M_{\rm Jup}$ at a projected star-planet separation of $a_\perp = 2.42\pm 0.26\,$AU, corresponding to a semi-major axis of $a = 2.9{+1.6\atop -0.6}\,$AU. Thus, the system resembles a half-scale model of the Sun-Jupiter system with a half-Jupiter mass planet orbiting a half-solar mass star at very roughly half of Jupiter's orbital distance from the Sun. The source stars are slightly evolved, and by requiring them to lie on the same isochrone, we can constrain the source to lie in the near side of the bulge at a distance of $D_S = 6.9 \pm 0.7\,$kpc, which implies a distance to the planetary lens system of $D_L = 3.5\pm 0.4\,$kpc. The ability to model unusual planetary microlensing events, like this one, will be necessary to extract precise statistical information from the planned large exoplanet microlensing surveys, such as the WFIRST microlensing survey. △ Less

Submitted 22 March, 2018; v1 submitted 30 July, 2017; originally announced July 2017.

Comments: Accepted version. Now published in AJ

Journal ref: AJ, 155, 141 (2018)

MOA-2016-BLG-227Lb: A Massive Planet Characterized by Combining Lightcurve Analysis and Keck AO Imaging

Authors: Naoki Koshimoto, Yossi Shvartzvald, David Bennett, Matthew Penny, Markus Hundertmark, Ian A. Bond, Weicheng Zang, Calen Henderson, Daisuke Suzuki, Nicholas J. Rattenbury, Takahiro Sumi, Fumio Abe, Yuichiro Asakura, Aparna Bhattacharya, Akihiko Fukui, Yuki Hirao, Yoshitaka Itow, M. C. A. Li, C. Ling, Kimiaki Masuda, Y. Matsubara, Taro Matsuo, Yasushi Muraki, Masayuki Nagakane, Kouji Ohnishi , et al. (33 additional authors not shown)

Abstract: We report the discovery of a microlensing planet --- MOA-2016-BLG-227Lb --- with a large planet/host mass ratio of $q \simeq 9 \times 10^{-3}$. This event was located near the $K2$ Campaign 9 field that was observed by a large number of telescopes. As a result, the event was in the microlensing survey area of a number of these telescopes, and this enabled good coverage of the planetary light curve… ▽ More We report the discovery of a microlensing planet --- MOA-2016-BLG-227Lb --- with a large planet/host mass ratio of $q \simeq 9 \times 10^{-3}$. This event was located near the $K2$ Campaign 9 field that was observed by a large number of telescopes. As a result, the event was in the microlensing survey area of a number of these telescopes, and this enabled good coverage of the planetary light curve signal. High angular resolution adaptive optics images from the Keck telescope reveal excess flux at the position of the source above the flux of the source star, as indicated by the light curve model. This excess flux could be due to the lens star, but it could also be due to a companion to the source or lens star, or even an unrelated star. We consider all these possibilities in a Bayesian analysis in the context of a standard Galactic model. Our analysis indicates that it is unlikely that a large fraction of the excess flux comes from the lens, unless solar type stars are much more likely to host planets of this mass ratio than lower mass stars. We recommend that a method similar to the one developed in this paper be used for other events with high angular resolution follow-up observations when the follow-up observations are insufficient to measure the lens-source relative proper motion. △ Less

Submitted 11 May, 2017; v1 submitted 6 April, 2017; originally announced April 2017.

Comments: 35 pages, 7 figures, 6 tables, Accepted for publication in AJ

The First Circumbinary Planet Found by Microlensing: OGLE-2007-BLG-349L(AB)c

Authors: D. P. Bennett, S. H. Rhie, A. Udalski, A. Gould, Y. Tsapras, D. Kubas, I. A. Bond, J. Greenhill, A. Cassan, N. J. Rattenbury, T. S. Boyajian, J. Luhn, M. T. Penny, J. Anderson, F. Abe, A. Bhattacharya, C. S. Botzler, M. Donachie, M. Freeman, A. Fukui, Y. Hirao, Y. Itow, N. Koshimoto, M. C. A. Li, C. H. Ling , et al. (57 additional authors not shown)

Abstract: We present the analysis of the first circumbinary planet microlensing event, OGLE-2007-BLG-349. This event has a strong planetary signal that is best fit with a mass ratio of $q \approx 3.4\times10^{-4}$, but there is an additional signal due to an additional lens mass, either another planet or another star. We find acceptable light curve fits with two classes of models: 2-planet models (with a si… ▽ More We present the analysis of the first circumbinary planet microlensing event, OGLE-2007-BLG-349. This event has a strong planetary signal that is best fit with a mass ratio of $q \approx 3.4\times10^{-4}$, but there is an additional signal due to an additional lens mass, either another planet or another star. We find acceptable light curve fits with two classes of models: 2-planet models (with a single host star) and circumbinary planet models. The light curve also reveals a significant microlensing parallax effect, which constrains the mass of the lens system to be $M_L \approx 0.7 M_\odot$. Hubble Space Telescope images resolve the lens and source stars from their neighbors and indicate excess flux due to the star(s) in the lens system. This is consistent with the predicted flux from the circumbinary models, where the lens mass is shared between two stars, but there is not enough flux to be consistent with the 2-planet, 1-star models. So, only the circumbinary models are consistent with the HST data. They indicate a planet of mass $m_c = 80\pm 13\,M_\oplus$, orbiting a pair of M-dwarfs with masses of $M_A = 0.41\pm 0.07 M_\odot$ and $M_B = 0.30\pm 0.07 M_\oplus$, which makes this the lowest mass circumbinary planet system known. The ratio of the separation between the planet and the center-of-mass to the separations of the two stars is $\sim 40$, so unlike most of the circumbinary planets found by Kepler, the planet does not orbit near the stability limit. △ Less

Submitted 3 November, 2016; v1 submitted 21 September, 2016; originally announced September 2016.

Comments: 34 pages, with 9 figures. Published in the Astronomical Journal

Journal ref: Astronomical Journal, 152, 125, 14 pp. (2016)

Revisiting the microlensing event OGLE 2012-BLG-0026: A solar mass star with two cold giant planets

Authors: J. P. Beaulieu, D. P. Bennett, V. Batista, A. Fukui, J. -B. Marquette, S. Brillant, A. A. Cole, L. A. Rogers, T. Sumi, F. Abe, A. Bhattacharya, N. Koshimoto, D. Suzuki, P. J. Tristram, C. Han, A. Gould, R. Pogge, J. Yee

Abstract: Two cold, gas giant planets orbiting a G-type main sequence star in the galactic disk have previously been discovered in the high magnification microlensing event OGLE-2012-BLG-0026 (Han et al. 2013). Here we present revised host star flux measurements and a refined model for the two-planet system using additional light curve data. We performed high angular resolution adaptive optics imaging with… ▽ More Two cold, gas giant planets orbiting a G-type main sequence star in the galactic disk have previously been discovered in the high magnification microlensing event OGLE-2012-BLG-0026 (Han et al. 2013). Here we present revised host star flux measurements and a refined model for the two-planet system using additional light curve data. We performed high angular resolution adaptive optics imaging with the Keck and Subaru telescopes at two epochs while the source star was still amplified. We detected the lens flux, $H=16.39 \pm 0.08$. The lens, a disk star, is brighter than predicted from the modeling in the original study. We revisited the light curve modeling using additional photometric data from the B\&C telescope in New Zealand and CTIO 1.3m H band light curve. We then include the Keck and Subaru adaptive optic observation constraints. The system is composed of a $\sim 4-9$ Gyr lens star of $\rm M_{lens} = 1.06 \pm 0.05~\,M_\odot$ at a distance of $\rm D_{lens} = 4.0 \pm 0.3~$kpc, orbited by two giant planets of $\rm 0.145 \pm 0.008\ M_{\rm Jup}$ and $0.86 \pm 0.06~\rm M_{\rm Jup}$ with projected separations of $4.0 \pm 0.5 $ AU and $4.8 \pm 0.7$ AU respectively. Since the lens is brighter than the source star by $16 \pm 8 \%$ in H, with no other blend within one arcsec, it will be possible to estimate its metallicity by subsequent IR spectroscopy with 8--10~m class telescopes. By adding a constraint on the metallicity it will be possible to refine the age of the system. △ Less

Submitted 8 January, 2016; originally announced January 2016.

Comments: 6 pages, 4 figures, submitted to ApJ

Campaign 9 of the $K2$ Mission: Observational Parameters, Scientific Drivers, and Community Involvement for a Simultaneous Space- and Ground-based Microlensing Survey

Authors: Calen B. Henderson, Radosław Poleski, Matthew Penny, Rachel A. Street, David P. Bennett, David W. Hogg, B. Scott Gaudi, W. Zhu, T. Barclay, G. Barentsen, S. B. Howell, F. Mullally, A. Udalski, M. K. Szymański, J. Skowron, P. Mróz, S. Kozłowski, Ł. Wyrzykowski, P. Pietrukowicz, I. Soszyński, K. Ulaczyk, M. Pawlak, T. Sumi, F. Abe, Y. Asakura , et al. (96 additional authors not shown)

Abstract: $K2$'s Campaign 9 ($K2$C9) will conduct a $\sim$3.7 deg$^{2}$ survey toward the Galactic bulge from 7/April through 1/July of 2016 that will leverage the spatial separation between $K2$ and the Earth to facilitate measurement of the microlens parallax $π_{\rm E}$ for $\gtrsim… ▽ More $K2$'s Campaign 9 ($K2$C9) will conduct a $\sim$3.7 deg$^{2}$ survey toward the Galactic bulge from 7/April through 1/July of 2016 that will leverage the spatial separation between $K2$ and the Earth to facilitate measurement of the microlens parallax $π_{\rm E}$ for $\gtrsim$127 microlensing events. These will include several that are planetary in nature as well as many short-timescale microlensing events, which are potentially indicative of free-floating planets (FFPs). These satellite parallax measurements will in turn allow for the direct measurement of the masses of and distances to the lensing systems. In this white paper we provide an overview of the $K2$C9 space- and ground-based microlensing survey. Specifically, we detail the demographic questions that can be addressed by this program, including the frequency of FFPs and the Galactic distribution of exoplanets, the observational parameters of $K2$C9, and the array of resources dedicated to concurrent observations. Finally, we outline the avenues through which the larger community can become involved, and generally encourage participation in $K2$C9, which constitutes an important pathfinding mission and community exercise in anticipation of $WFIRST$. △ Less

Submitted 7 March, 2016; v1 submitted 30 December, 2015; originally announced December 2015.

Comments: 19 pages, 11 figures, 3 tables; submitted to PASP

Red noise versus planetary interpretations in the microlensing event OGLE-2013-BLG-446

Authors: E. Bachelet, D. M. Bramich, C. Han, J. Greenhill, R. A. Street, A. Gould, G. D Ago, K. AlSubai, M. Dominik, R. Figuera Jaimes, K. Horne, M. Hundertmark, N. Kains, C. Snodgrass, I. A. Steele, Y. Tsapras, M. D. Albrow, V. Batista, J. -P. Beaulieu, D. P. Bennett, S. Brillant, J. A. R. Caldwell, A. Cassan, A. Cole, C. Coutures , et al. (76 additional authors not shown)

Abstract: For all exoplanet candidates, the reliability of a claimed detection needs to be assessed through a careful study of systematic errors in the data to minimize the false positives rate. We present a method to investigate such systematics in microlensing datasets using the microlensing event OGLE-2013-BLG-0446 as a case study. The event was observed from multiple sites around the world and its high… ▽ More For all exoplanet candidates, the reliability of a claimed detection needs to be assessed through a careful study of systematic errors in the data to minimize the false positives rate. We present a method to investigate such systematics in microlensing datasets using the microlensing event OGLE-2013-BLG-0446 as a case study. The event was observed from multiple sites around the world and its high magnification (A_{max} \sim 3000) allowed us to investigate the effects of terrestrial and annual parallax. Real-time modeling of the event while it was still ongoing suggested the presence of an extremely low-mass companion (\sim 3M_\oplus ) to the lensing star, leading to substantial follow-up coverage of the light curve. We test and compare different models for the light curve and conclude that the data do not favour the planetary interpretation when systematic errors are taken into account. △ Less

Submitted 28 October, 2015; v1 submitted 9 October, 2015; originally announced October 2015.

Comments: accepted ApJ 2015

Confirmation of the OGLE-2005-BLG-169 planet signature and characteristics with lens-source proper motion detection

Authors: V. Batista, J. -P. Beaulieu, D. P. Bennett, A. Gould, J. -B. Marquette, A. Fukui, A. Bhattacharya

Abstract: We present Keck NIRC2 high angular resolution adaptive optics observations of the microlensing event OGLE-2005-BLG-169, taken 8.21 years after the discovery of this planetary system. For the first time for a microlensing planetary event, the source and the lens are completely resolved, providing a precise measurement of their heliocentric relative proper motion,… ▽ More We present Keck NIRC2 high angular resolution adaptive optics observations of the microlensing event OGLE-2005-BLG-169, taken 8.21 years after the discovery of this planetary system. For the first time for a microlensing planetary event, the source and the lens are completely resolved, providing a precise measurement of their heliocentric relative proper motion, $μ_{\rm{rel},\rm{helio}}=7.44 \pm 0.17$ mas yr$^{-1}$. This confirms and refines the initial model presented in the discovery paper and rules out a range of solutions that were allowed by the microlensing light curve. This is also the first time that parameters derived from a microlensing planetary signal are confirmed, both with Keck measurements, presented in this paper, and independent measurements obtained with the Hubble Space Telescope in I, V and B bands, presented in a companion paper. Hence, this new measurement of $μ_{\rm{rel},\rm{helio}}$, as well as the measured brightness of the lens in H band, enabled the mass and distance of the system to be updated: a Uranus-mass planet ($m_\rm{p}=13.2\pm 1.3 M_\oplus$) orbiting a K5-type main sequence star ($M_*=0.65\pm 0.05 M_\odot$) separated by $a_\perp=3.4\pm 0.3$ AU, at the distance $D_\rm{L}=4.0\pm 0.4$ kpc from us. △ Less

Submitted 31 July, 2015; originally announced July 2015.

Comments: 9 pages, 5 figures

Journal ref: ApJ, 808, 170, 2015

MOA-2007-BLG-197: Exploring the brown dwarf desert

Authors: C. Ranc, A. Cassan, M. D. Albrow, D. Kubas, I. A. Bond, V. Batista, J. -P. Beaulieu, D. P. Bennett, M. Dominik, Subo Dong, P. Fouqué, A. Gould, J. Greenhill, U. G. Jørgensen, N. Kains, J. Menzies, T. Sumi, E. Bachelet, C. Coutures, S. Dieters, D. Dominis Prester, J. Donatowicz, B. S. Gaudi, C. Han, M. Hundertmark , et al. (26 additional authors not shown)

Abstract: We present the analysis of MOA-2007-BLG-197Lb, the first brown dwarf companion to a Sun-like star detected through gravitational microlensing. The event was alerted and followed-up photometrically by a network of telescopes from the PLANET, MOA, and uFUN collaborations, and observed at high angular resolution using the NaCo instrument at the VLT. From the modelling of the microlensing light curve,… ▽ More We present the analysis of MOA-2007-BLG-197Lb, the first brown dwarf companion to a Sun-like star detected through gravitational microlensing. The event was alerted and followed-up photometrically by a network of telescopes from the PLANET, MOA, and uFUN collaborations, and observed at high angular resolution using the NaCo instrument at the VLT. From the modelling of the microlensing light curve, we derived the binary lens separation in Einstein radius units (s~1.13) and a mass ratio of (4.732+/-0.020)x10^{-2}. Annual parallax, lens orbital motion and finite source effects were included in the models. To recover the lens system's physical parameters, we combined the resulting light curve best-fit parameters with (J,H,Ks) magnitudes obtained with VLT NaCo and calibrated using IRSF and 2MASS data. We derived a lens total mass of 0.86+/-0.04 Msun and a lens distance of 4.2+/-0.3 kpc. We find that the companion of MOA-2007-BLG-197L is a brown dwarf of 41+/-2 Mjup observed at a projected separation of 4.3+/-0.1 AU, and orbits a 0.82+/-0.04 Msun G-K dwarf star. We study the statistical properties of this population of brown dwarfs detected by microlensing, transit, radial velocity, and direct imaging (most of these objects orbit solar-type stars), and we performed a two-dimensional, non-parametric probability density distribution fit to the data, which draws a structured brown dwarf landscape. We confirm the existence of a region that is strongly depleted in objects at short periods and intermediate masses (P<30 d, M~30-60 Mjup), but also find an accumulation of objects around P~500 d and M~20 Mjup, as well as another depletion region at long orbital periods (P>500 d) and high masses (M>50 Mjup). While these data provide important clues on mechanisms of brown dwarfs formation, more data are needed to establish their relative importance, in particular as a function of host star mass. △ Less

Submitted 22 May, 2015; originally announced May 2015.

Comments: 16 pages, 12 figures

Journal ref: A&A 580, A125 (2015)

Reanalyses of Anomalous Gravitational Microlensing Events in the OGLE-III Early Warning System Database with Combined Data

Authors: J. Jeong, H. Park, C. Han, A. Gould, A. Udalski, M. K. Szymański, G. Pietrzyński, I. Soszyński, R. Poleski, K. Ulaczyk, Ł. Wyrzykowski, F. Abe, D. P. Bennett, I. A. Bond, C. S. Botzler, M. Freeman, A. Fukui, D. Fukunaga, Y. Itow, N. Koshimoto, K. Masuda, Y. Matsubara, Y. Muraki, S. Namba, K. Ohnishi , et al. (73 additional authors not shown)

Abstract: We reanalyze microlensing events in the published list of anomalous events that were observed from the OGLE lensing survey conducted during 2004-2008 period. In order to check the existence of possible degenerate solutions and extract extra information, we conduct analyses based on combined data from other survey and follow-up observation and consider higher-order effects. Among the analyzed event… ▽ More We reanalyze microlensing events in the published list of anomalous events that were observed from the OGLE lensing survey conducted during 2004-2008 period. In order to check the existence of possible degenerate solutions and extract extra information, we conduct analyses based on combined data from other survey and follow-up observation and consider higher-order effects. Among the analyzed events, we present analyses of 8 events for which either new solutions are identified or additional information is obtained. We find that the previous binary-source interpretations of 5 events are better interpreted by binary-lens models. These events include OGLE-2006-BLG-238, OGLE-2007-BLG-159, OGLE-2007-BLG-491, OGLE-2008-BLG-143, and OGLE-2008-BLG-210. With additional data covering caustic crossings, we detect finite-source effects for 6 events including OGLE-2006-BLG-215, OGLE-2006-BLG-238, OGLE-2006-BLG-450, OGLE-2008-BLG-143, OGLE-2008-BLG-210, and OGLE-2008-BLG-513. Among them, we are able to measure the Einstein radii of 3 events for which multi-band data are available. These events are OGLE-2006-BLG-238, OGLE-2008-BLG-210, and OGLE-2008-BLG-513. For OGLE-2008-BLG-143, we detect higher-order effect induced by the changes of the observer's position caused by the orbital motion of the Earth around the Sun. In addition, we present degenerate solutions resulting from the known close/wide or ecliptic degeneracy. Finally, we note that the masses of the binary companions of the lenses of OGLE-2006-BLG-450 and OGLE-2008-BLG-210 are in the brown-dwarf regime. △ Less

Submitted 2 March, 2015; v1 submitted 23 February, 2015; originally announced February 2015.

Comments: 10 pages, 4 tables, 9 figures. Accepted in ApJ, Author list updated

The EChO science case

Authors: Giovanna Tinetti, Pierre Drossart, Paul Eccleston, Paul Hartogh, Kate Isaak, Martin Linder, Christophe Lovis, Giusi Micela, Marc Ollivier, Ludovic Puig, Ignasi Ribas, Ignas Snellen, Bruce Swinyard. France Allard, Joanna Barstow, James Cho, Athena Coustenis, Charles Cockell, Alexandre Correia, Leen Decin, Remco de Kok, Pieter Deroo, Therese Encrenaz, Francois Forget, Alistair Glasse, Caitlin Griffith , et al. (326 additional authors not shown)

Abstract: The discovery of almost 2000 exoplanets has revealed an unexpectedly diverse planet population. Observations to date have shown that our Solar System is certainly not representative of the general population of planets in our Milky Way. The key science questions that urgently need addressing are therefore: What are exoplanets made of? Why are planets as they are? What causes the exceptional divers… ▽ More The discovery of almost 2000 exoplanets has revealed an unexpectedly diverse planet population. Observations to date have shown that our Solar System is certainly not representative of the general population of planets in our Milky Way. The key science questions that urgently need addressing are therefore: What are exoplanets made of? Why are planets as they are? What causes the exceptional diversity observed as compared to the Solar System? EChO (Exoplanet Characterisation Observatory) has been designed as a dedicated survey mission for transit and eclipse spectroscopy capable of observing a large and diverse planet sample within its four-year mission lifetime. EChO can target the atmospheres of super-Earths, Neptune-like, and Jupiter-like planets, in the very hot to temperate zones (planet temperatures of 300K-3000K) of F to M-type host stars. Over the next ten years, several new ground- and space-based transit surveys will come on-line (e.g. NGTS, CHEOPS, TESS, PLATO), which will specifically focus on finding bright, nearby systems. The current rapid rate of discovery would allow the target list to be further optimised in the years prior to EChO's launch and enable the atmospheric characterisation of hundreds of planets. Placing the satellite at L2 provides a cold and stable thermal environment, as well as a large field of regard to allow efficient time-critical observation of targets randomly distributed over the sky. A 1m class telescope is sufficiently large to achieve the necessary spectro-photometric precision. The spectral coverage (0.5-11 micron, goal 16 micron) and SNR to be achieved by EChO, thanks to its high stability and dedicated design, would enable a very accurate measurement of the atmospheric composition and structure of hundreds of exoplanets. △ Less

Submitted 19 February, 2015; originally announced February 2015.

Comments: 50 pages, 30 figures. Experimental Astronomy

New RR Lyrae variables in binary systems

Authors: G. Hajdu, M. Catelan, J. Jurcsik, I. Dékány, A. J. Drake, J. -B. Marquette

Abstract: Despite their importance, very few RR Lyrae (RRL) stars have been known to reside in binary systems. We report on a search for binary RRL in the OGLE-III Galactic bulge data. Our approach consists in the search for evidence of the light-travel time effect in so-called observed minus calculated ($O-C$) diagrams. Analysis of 1952 well-observed fundamental-mode RRL in the OGLE-III data revealed an in… ▽ More Despite their importance, very few RR Lyrae (RRL) stars have been known to reside in binary systems. We report on a search for binary RRL in the OGLE-III Galactic bulge data. Our approach consists in the search for evidence of the light-travel time effect in so-called observed minus calculated ($O-C$) diagrams. Analysis of 1952 well-observed fundamental-mode RRL in the OGLE-III data revealed an initial sample of 29 candidates. We used the recently released OGLE-IV data to extend the baselines up to 17 years, leading to a final sample of 12 firm binary candidates. We provide $O-C$ diagrams and binary parameters for this final sample, and also discuss the properties of 8 additional candidate binaries whose parameters cannot be firmly determined at present. We also estimate that $\gtrsim 4$ per cent of the RRL reside in binary systems. △ Less

Submitted 4 February, 2015; originally announced February 2015.

Comments: MNRAS Letters, in press

OGLE-2011-BLG-0265Lb: a Jovian Microlensing Planet Orbiting an M Dwarf

Authors: J. Skowron, I. -G. Shin, A. Udalski, C. Han, T. Sumi, Y. Shvartzvald, A. Gould, D. Dominis-Prester, R. A. Street, U. G. Jørgensen, D. P. Bennett, V. Bozza, M. K. Szymański, M. Kubiak, G. Pietrzyński, I. Soszyński, R. Poleski, S. Kozłowski, P. Pietrukowicz, K. Ulaczyk, Ł. Wyrzykowski, F. Abe, A. Bhattacharya, I. A. Bond, C. S. Botzler , et al. (99 additional authors not shown)

Abstract: We report the discovery of a Jupiter-mass planet orbiting an M-dwarf star that gave rise to the microlensing event OGLE-2011-BLG-0265. Such a system is very rare among known planetary systems and thus the discovery is important for theoretical studies of planetary formation and evolution. High-cadence temporal coverage of the planetary signal combined with extended observations throughout the even… ▽ More We report the discovery of a Jupiter-mass planet orbiting an M-dwarf star that gave rise to the microlensing event OGLE-2011-BLG-0265. Such a system is very rare among known planetary systems and thus the discovery is important for theoretical studies of planetary formation and evolution. High-cadence temporal coverage of the planetary signal combined with extended observations throughout the event allows us to accurately model the observed light curve. The final microlensing solution remains, however, degenerate yielding two possible configurations of the planet and the host star. In the case of the preferred solution, the mass of the planet is $M_{\rm p} = 0.9\pm 0.3\ M_{\rm J}$, and the planet is orbiting a star with a mass $M = 0.22\pm 0.06\ M_\odot$. The second possible configuration (2$σ$ away) consists of a planet with $M_{\rm p}=0.6\pm 0.3\ M_{\rm J}$ and host star with $M=0.14\pm 0.06\ M_\odot$. The system is located in the Galactic disk 3 -- 4 kpc towards the Galactic bulge. In both cases, with an orbit size of 1.5 -- 2.0 AU, the planet is a "cold Jupiter" -- located well beyond the "snow line" of the host star. Currently available data make the secure selection of the correct solution difficult, but there are prospects for lifting the degeneracy with additional follow-up observations in the future, when the lens and source star separate. △ Less

Submitted 23 February, 2015; v1 submitted 30 October, 2014; originally announced October 2014.

Comments: 10 pages, 2 tables, 5 figures. Accepted in ApJ

The VMC ESO Public Survey

Authors: M. -R. L. Cioni, P. Anders, G. Bagheri, K. Bekki, G. Clementini, J. P. Emerson, C. J. Evans, B. -Q. For, R. de Grijs, B. Gibson, L. Girardi, M. A. T. Groenewegen, R. Guandalini, M. Gullieuszik, V. D. Ivanov, D. Kamath, M. Marconi, J. -B. Marquette, B. Miszalski, B. Moore, M. I. Moretti, T. Muraveva, R. Napiwotzki, J. M. Oliveira, A. E. Piatti , et al. (9 additional authors not shown)

Abstract: The VISTA near-infrared YJKs survey of the Magellanic Clouds system (VMC) has entered its core phase: about 40% of the observations across the Large and Small Magellanic Clouds (LMC, SMC), the Magellanic Bridge and Stream have already been secured and the data are processed and analysed regularly. The initial analyses, concentrated in the first two completed tiles in the LMC (6_6 including 30 Dora… ▽ More The VISTA near-infrared YJKs survey of the Magellanic Clouds system (VMC) has entered its core phase: about 40% of the observations across the Large and Small Magellanic Clouds (LMC, SMC), the Magellanic Bridge and Stream have already been secured and the data are processed and analysed regularly. The initial analyses, concentrated in the first two completed tiles in the LMC (6_6 including 30 Doradus and 8_8 including the South Ecliptic Pole), show the superior quality of the data. The depth of the VMC survey allows the derivation of the star formation history (SFH) with unprecedented quality compared to previous wide-area surveys while reddening maps of high angular resolution are constructed using red clump stars. The multi-epoch Ks-band data reveal tight period-luminosity relations for variable stars and they permit the measurement of accurate proper motions of the stellar populations. The VMC survey continues to acquire data that will address many issues in the field of star and galaxy evolution. △ Less

Submitted 27 June, 2014; originally announced June 2014.

Comments: 3 pages, 4 figures

Journal ref: ESO Messenger 154, (2013), 23-25

A Sub-Earth-Mass Moon Orbiting a Gas Giant Primary or a High Velocity Planetary System in the Galactic Bulge

Authors: D. P. Bennett, V. Batista, I. A. Bond, C. S. Bennett, D. Suzuki, J. -P. Beaulieu, A. Udalski, J. Donatowicz, F. Abe, C. S. Botzler, M. Freeman, D. Fukunaga, A. Fukui, Y. Itow, N. Koshimoto, C. H. Ling, K. Masuda, Y. Matsubara, Y. Muraki, S. Namba, K. Ohnishi, N. J. Rattenbury, To. Saito, D. J. Sullivan, T. Sumi , et al. (68 additional authors not shown)

Abstract: We present the first microlensing candidate for a free-floating exoplanet-exomoon system, MOA-2011-BLG-262, with a primary lens mass of M_host ~ 4 Jupiter masses hosting a sub-Earth mass moon. The data are well fit by this exomoon model, but an alternate star+planet model fits the data almost as well. Nevertheless, these results indicate the potential of microlensing to detect exomoons, albeit one… ▽ More We present the first microlensing candidate for a free-floating exoplanet-exomoon system, MOA-2011-BLG-262, with a primary lens mass of M_host ~ 4 Jupiter masses hosting a sub-Earth mass moon. The data are well fit by this exomoon model, but an alternate star+planet model fits the data almost as well. Nevertheless, these results indicate the potential of microlensing to detect exomoons, albeit ones that are different from the giant planet moons in our solar system. The argument for an exomoon hinges on the system being relatively close to the Sun. The data constrain the product M pi_rel, where M is the lens system mass and pi_rel is the lens-source relative parallax. If the lens system is nearby (large pi_rel), then M is small (a few Jupiter masses) and the companion is a sub-Earth-mass exomoon. The best-fit solution has a large lens-source relative proper motion, mu_rel = 19.6 +- 1.6 mas/yr, which would rule out a distant lens system unless the source star has an unusually high proper motion. However, data from the OGLE collaboration nearly rule out a high source proper motion, so the exoplanet+exomoon model is the favored interpretation for the best fit model. However, the alternate solution has a lower proper motion, which is compatible with a distant (so stellar) host. A Bayesian analysis does not favor the exoplanet+exomoon interpretation, so Occam's razor favors a lens system in the bulge with host and companion masses of M_host = 0.12 (+0.19 -0.06) M_solar and m_comp = 18 (+28 -100 M_earth, at a projected separation of a_perp ~ 0.84 AU. The existence of this degeneracy is an unlucky accident, so current microlensing experiments are in principle sensitive to exomoons. In some circumstances, it will be possible to definitively establish the low mass of such lens systems through the microlensing parallax effect. Future experiments will be sensitive to less extreme exomoons. △ Less

Submitted 13 December, 2013; originally announced December 2013.

Comments: 32 pages with 9 included figures

A Super-Jupiter orbiting a late-type star: A refined analysis of microlensing event OGLE-2012-BLG-0406

Authors: Y. Tsapras, J. -Y. Choi, R. A. Street, C. Han, V. Bozza, A. Gould, M. Dominik, J. -P. Beaulieu, A. Udalski, U. G. Jørgensen, T. Sumi, D. M. Bramich, P. Browne, K. Horne, M. Hundertmark, S. Ipatov, N. Kains, C. Snodgrass, I. A. Steele, K. A. Alsubai, J. M. Andersen, S. Calchi Novati, Y. Damerdji, C. Diehl, A. Elyiv , et al. (100 additional authors not shown)

Abstract: We present a detailed analysis of survey and follow-up observations of microlensing event OGLE-2012-BLG-0406 based on data obtained from 10 different observatories. Intensive coverage of the lightcurve, especially the perturbation part, allowed us to accurately measure the parallax effect and lens orbital motion. Combining our measurement of the lens parallax with the angular Einstein radius deter… ▽ More We present a detailed analysis of survey and follow-up observations of microlensing event OGLE-2012-BLG-0406 based on data obtained from 10 different observatories. Intensive coverage of the lightcurve, especially the perturbation part, allowed us to accurately measure the parallax effect and lens orbital motion. Combining our measurement of the lens parallax with the angular Einstein radius determined from finite-source effects, we estimate the physical parameters of the lens system. We find that the event was caused by a $2.73\pm 0.43\ M_{\rm J}$ planet orbiting a $0.44\pm 0.07\ M_{\odot}$ early M-type star. The distance to the lens is $4.97\pm 0.29$\ kpc and the projected separation between the host star and its planet at the time of the event is $3.45\pm 0.26$ AU. We find that the additional coverage provided by follow-up observations, especially during the planetary perturbation, leads to a more accurate determination of the physical parameters of the lens. △ Less

Submitted 5 December, 2013; v1 submitted 9 October, 2013; originally announced October 2013.

Comments: 9 pages, 4 figures, accepted by ApJ

MOA-2010-BLG-328Lb: a sub-Neptune orbiting very late M dwarf ?

Authors: K. Furusawa, A. Udalski, T. Sumi, D. P. Bennett, I. A. Bond, A. Gould, U. G. Jorgensen, C. Snodgrass, D. Dominis Prester, M. D. Albrow, F. Abe, C. S. Botzler, P. Chote, M. Freeman, A. Fukui, P. Harris, Y. Itow, C. H. Ling, K. Masuda, Y. Matsubara, N. Miyake, Y. Muraki, K. Ohnishi, N. J. Rattenbury, To. Saito , et al. (97 additional authors not shown)

Abstract: We analyze the planetary microlensing event MOA-2010-BLG-328. The best fit yields host and planetary masses of Mh = 0.11+/-0.01 M_{sun} and Mp = 9.2+/-2.2M_Earth, corresponding to a very late M dwarf and sub-Neptune-mass planet, respectively. The system lies at DL = 0.81 +/- 0.10 kpc with projected separation r = 0.92 +/- 0.16 AU. Because of the host's a-priori-unlikely close distance, as well as… ▽ More We analyze the planetary microlensing event MOA-2010-BLG-328. The best fit yields host and planetary masses of Mh = 0.11+/-0.01 M_{sun} and Mp = 9.2+/-2.2M_Earth, corresponding to a very late M dwarf and sub-Neptune-mass planet, respectively. The system lies at DL = 0.81 +/- 0.10 kpc with projected separation r = 0.92 +/- 0.16 AU. Because of the host's a-priori-unlikely close distance, as well as the unusual nature of the system, we consider the possibility that the microlens parallax signal, which determines the host mass and distance, is actually due to xallarap (source orbital motion) that is being misinterpreted as parallax. We show a result that favors the parallax solution, even given its close host distance. We show that future high-resolution astrometric measurements could decisively resolve the remaining ambiguity of these solutions. △ Less

Submitted 9 October, 2013; v1 submitted 29 September, 2013; originally announced September 2013.

Comments: 30 pages, 6 figures. accepted for publication in ApJ. Figure 1 and 2 are updated

Interpretation of a Short-Term Anomaly in the Gravitational Microlensing Event MOA-2012-BLG-486

Authors: K. -H. Hwang, J. -Y. Choi, I. A. Bond, T. Sumi, C. Han, B. S. Gaudi, A. Gould, V. Bozza, J. -P. Beaulieu, Y. Tsapras, F. Abe, D. P. Bennett, C. S. Botzler, P. Chote, M. Freeman, A. Fukui, D. Fukunaga, P. Harris, Y. Itow, N. Koshimoto, C. H. Ling, K. Masuda, Y. Matsubara, Y. Muraki, S. Namba , et al. (56 additional authors not shown)

Abstract: A planetary microlensing signal is generally characterized by a short-term perturbation to the standard single lensing light curve. A subset of binary-source events can produce perturbations that mimic planetary signals, thereby introducing an ambiguity between the planetary and binary-source interpretations. In this paper, we present analysis of the microlensing event MOA-2012-BLG-486, for which… ▽ More A planetary microlensing signal is generally characterized by a short-term perturbation to the standard single lensing light curve. A subset of binary-source events can produce perturbations that mimic planetary signals, thereby introducing an ambiguity between the planetary and binary-source interpretations. In this paper, we present analysis of the microlensing event MOA-2012-BLG-486, for which the light curve exhibits a short-lived perturbation. Routine modeling not considering data taken in different passbands yields a best-fit planetary model that is slightly preferred over the best-fit binary-source model. However, when allowed for a change in the color during the perturbation, we find that the binary-source model yields a significantly better fit and thus the degeneracy is clearly resolved. This event not only signifies the importance of considering various interpretations of short-term anomalies, but also demonstrates the importance of multi-band data for checking the possibility of false-positive planetary signals. △ Less

Submitted 27 August, 2013; originally announced August 2013.

Comments: 5 pages, 4 figures and ApJ submitted

Gravitational Binary-lens Events with Prominent Effects of Lens Orbital Motion

Authors: H. Park, A. Udalski, C. Han, A. Gould, J. -P. Beaulieu, Y. Tsapras, M. K. Szymański, M. Kubiak, I. Soszyński, G. Pietrzyński, R. Poleski, K. Ulaczyk, P. Pietrukowicz, S. Kozłowski, J. Skowron, Ł. Wyrzykowski, J. -Y. Choi, D. L. Depoy, Subo Dong, B. S. Gaudi, K. -H. Hwang, Y. K. Jung, A. Kavka, C. -U. Lee, L. A. G. Monard , et al. (36 additional authors not shown)

Abstract: Gravitational microlensing events produced by lenses composed of binary masses are important because they provide a major channel to determine physical parameters of lenses. In this work, we analyze the light curves of two binary-lens events OGLE-2006-BLG-277 and OGLE-2012-BLG-0031 for which the light curves exhibit strong deviations from standard models. From modeling considering various second-o… ▽ More Gravitational microlensing events produced by lenses composed of binary masses are important because they provide a major channel to determine physical parameters of lenses. In this work, we analyze the light curves of two binary-lens events OGLE-2006-BLG-277 and OGLE-2012-BLG-0031 for which the light curves exhibit strong deviations from standard models. From modeling considering various second-order effects, we find that the deviations are mostly explained by the effect of the lens orbital motion. We also find that lens parallax effects can mimic orbital effects to some extent. This implies that modeling light curves of binary-lens events not considering orbital effects can result in lens parallaxes that are substantially different from actual values and thus wrong determinations of physical lens parameters. This demonstrates the importance of routine consideration of orbital effects in interpreting light curves of binary-lens events. It is found that the lens of OGLE-2006-BLG-277 is a binary composed of a low-mass star and a brown dwarf companion. △ Less

Submitted 17 June, 2013; originally announced June 2013.

Comments: 6 pages and 4 figures

A Giant Planet beyond the Snow Line in Microlensing Event OGLE-2011-BLG-0251

Authors: N. Kains, R. Street, J. -Y. Choi, C. Han, A. Udalski, L. A. Almeida, F. Jablonski, P. Tristram, U. G. Jorgensen, M. K. Szymanski, M. Kubiak, G. Pietrzynski, I. Soszynski, R. Poleski, S. Kozlowski, P. Pietrukowicz, K. Ulaczyk, L. Wyrzykowski, J. Skowron, K. A. Alsubai, V. Bozza, P. Browne, M. J. Burgdorf, S. Calchi Novati, P. Dodds , et al. (106 additional authors not shown)

Abstract: We present the analysis of the gravitational microlensing event OGLE-2011-BLG-0251. This anomalous event was observed by several survey and follow-up collaborations conducting microlensing observations towards the Galactic Bulge. Based on detailed modelling of the observed light curve, we find that the lens is composed of two masses with a mass ratio q=1.9 x 10^-3. Thanks to our detection of highe… ▽ More We present the analysis of the gravitational microlensing event OGLE-2011-BLG-0251. This anomalous event was observed by several survey and follow-up collaborations conducting microlensing observations towards the Galactic Bulge. Based on detailed modelling of the observed light curve, we find that the lens is composed of two masses with a mass ratio q=1.9 x 10^-3. Thanks to our detection of higher-order effects on the light curve due to the Earth's orbital motion and the finite size of source, we are able to measure the mass and distance to the lens unambiguously. We find that the lens is made up of a planet of mass 0.53 +- 0.21,M_Jup orbiting an M dwarf host star with a mass of 0.26 +- 0.11 M_Sun. The planetary system is located at a distance of 2.57 +- 0.61 kpc towards the Galactic Centre. The projected separation of the planet from its host star is d=1.408 +- 0.019, in units of the Einstein radius, which corresponds to 2.72 +- 0.75 AU in physical units. We also identified a competitive model with similar planet and host star masses, but with a smaller orbital radius of 1.50 +- 0.50 AU. The planet is therefore located beyond the snow line of its host star, which we estimate to be around 1-1.5 AU. △ Less

Submitted 5 March, 2013; originally announced March 2013.

Comments: 12 pages, 7 figures, 3 tables; A&A in press

Microlensing Discovery of a Population of Very Tight, Very Low-mass Binary Brown Dwarfs

Authors: J. -Y. Choi, C. Han, A. Udalski, T. Sumi, B. S. Gaudi, A. Gould, D. P. Bennett, M. Dominik, J. -P. Beaulieu, Y. Tsapras, V. Bozza, F. Abe, I. A. Bond, C. S. Botzler, P. Chote, M. Freeman, A. Fukui, K. Furusawa, Y. Itow, C. H. Ling, K. Masuda, Y. Matsubara, N. Miyake, Y. Muraki, K. Ohnishi , et al. (99 additional authors not shown)

Abstract: Although many models have been proposed, the physical mechanisms responsible for the formation of low-mass brown dwarfs are poorly understood. The multiplicity properties and minimum mass of the brown-dwarf mass function provide critical empirical diagnostics of these mechanisms. We present the discovery via gravitational microlensing of two very low-mass, very tight binary systems. These binaries… ▽ More Although many models have been proposed, the physical mechanisms responsible for the formation of low-mass brown dwarfs are poorly understood. The multiplicity properties and minimum mass of the brown-dwarf mass function provide critical empirical diagnostics of these mechanisms. We present the discovery via gravitational microlensing of two very low-mass, very tight binary systems. These binaries have directly and precisely measured total system masses of 0.025 Msun and 0.034 Msun, and projected separations of 0.31 AU and 0.19 AU, making them the lowest-mass and tightest field brown-dwarf binaries known. The discovery of a population of such binaries indicates that brown dwarf binaries can robustly form at least down to masses of ~0.02 Msun. Future microlensing surveys will measure a mass-selected sample of brown-dwarf binary systems, which can then be directly compared to similar samples of stellar binaries. △ Less

Submitted 20 March, 2013; v1 submitted 18 February, 2013; originally announced February 2013.

Comments: 7 pages, 5 figures, 3 tables, ApJ submitted

MOA-2010-BLG-073L: An M-Dwarf with a Substellar Companion at the Planet/Brown Dwarf Boundary

Authors: R. A. Street, J. -Y. Choi, Y. Tsapras, C. Han, K. Furusawa, M. Hundertmark, A. Gould, T. Sumi, I. A. Bond, D. Wouters, R. Zellem, A. Udalski, C. Snodgrass, K. Horne, M. Dominik, P. Browne, N. Kains, D. M. Bramich, D. Bajek, I. A. Steele, S. Ipatov, F. Abe, D. P. Bennett, C. S. Botzler, P. Chote , et al. (107 additional authors not shown)

Abstract: We present an analysis of the anomalous microlensing event, MOA-2010-BLG-073, announced by the Microlensing Observations in Astrophysics survey on 2010-03-18. This event was remarkable because the source was previously known to be photometrically variable. Analyzing the pre-event source lightcurve, we demonstrate that it is an irregular variable over time scales >200d. Its dereddened color,… ▽ More We present an analysis of the anomalous microlensing event, MOA-2010-BLG-073, announced by the Microlensing Observations in Astrophysics survey on 2010-03-18. This event was remarkable because the source was previously known to be photometrically variable. Analyzing the pre-event source lightcurve, we demonstrate that it is an irregular variable over time scales >200d. Its dereddened color, $(V-I)_{S,0}$, is 1.221$\pm$0.051mag and from our lens model we derive a source radius of 14.7$\pm$1.3 $R_{\odot}$, suggesting that it is a red giant star. We initially explored a number of purely microlensing models for the event but found a residual gradient in the data taken prior to and after the event. This is likely to be due to the variability of the source rather than part of the lensing event, so we incorporated a slope parameter in our model in order to derive the true parameters of the lensing system. We find that the lensing system has a mass ratio of q=0.0654$\pm$0.0006. The Einstein crossing time of the event, $T_{\rm{E}}=44.3$\pm$0.1d, was sufficiently long that the lightcurve exhibited parallax effects. In addition, the source trajectory relative to the large caustic structure allowed the orbital motion of the lens system to be detected. Combining the parallax with the Einstein radius, we were able to derive the distance to the lens, $D_L$=2.8$\pm$0.4kpc, and the masses of the lensing objects. The primary of the lens is an M-dwarf with $M_{L,p}$=0.16$\pm0.03M_{\odot}$ while the companion has $M_{L,s}$=11.0$\pm2.0M_{\rm{J}}$ putting it in the boundary zone between planets and brown dwarfs. △ Less

Submitted 11 December, 2012; v1 submitted 15 November, 2012; originally announced November 2012.

Comments: 24 pages, 8 figures, best viewed in colour, accepted by ApJ

MOA-2010-BLG-523: "Failed Planet" = RS CVn Star

Authors: A. Gould, J. C. Yee, I. A. Bond, A. Udalski, C. Han, U. G. Jorgensen, J. Greenhill, Y. Tsapras, M. H. Pinsonneault, T. Bensby, W. Allen, L. A. Almeida, M. Bos, G. W. Christie, D. L. DePoy, Subo Dong, B. S. Gaudi, L. -W. Hung, F. Jablonski, C. -U. Lee, J. McCormick, D. Moorhouse, J. A. Munoz, T. Natusch, M. Nola , et al. (94 additional authors not shown)

Abstract: The Galactic bulge source MOA-2010-BLG-523S exhibited short-term deviations from a standard microlensing lightcurve near the peak of an Amax ~ 265 high-magnification microlensing event. The deviations originally seemed consistent with expectations for a planetary companion to the principal lens. We combine long-term photometric monitoring with a previously published high-resolution spectrum taken… ▽ More The Galactic bulge source MOA-2010-BLG-523S exhibited short-term deviations from a standard microlensing lightcurve near the peak of an Amax ~ 265 high-magnification microlensing event. The deviations originally seemed consistent with expectations for a planetary companion to the principal lens. We combine long-term photometric monitoring with a previously published high-resolution spectrum taken near peak to demonstrate that this is an RS CVn variable, so that planetary microlensing is not required to explain the lightcurve deviations. This is the first spectroscopically confirmed RS CVn star discovered in the Galactic bulge. △ Less

Submitted 26 October, 2012; v1 submitted 22 October, 2012; originally announced October 2012.

Comments: 29 pp, 6 figs, submitted to ApJ

MOA-2010-BLG-311: A planetary candidate below the threshold of reliable detection

Authors: J. C. Yee, L. -W. Hung, I. A. Bond, W. Allen, L. A. G. Monard, M. D. Albrow, P. Fouque, M. Dominik, Y. Tsapras, A. Udalski, A. Gould, R. Zellem, M. Bos, G. W. Christie, D. L. DePoy, Subo Dong, J. Drummond, B. S. Gaudi, E. Gorbikov, C. Han, S. Kaspi, N. Klein, C. -U. Lee, D. Maoz, J. McCormick , et al. (101 additional authors not shown)

Abstract: We analyze MOA-2010-BLG-311, a high magnification (A_max>600) microlensing event with complete data coverage over the peak, making it very sensitive to planetary signals. We fit this event with both a point lens and a 2-body lens model and find that the 2-body lens model is a better fit but with only Delta chi^2~80. The preferred mass ratio between the lens star and its companion is $q=10^(-3.7+/-… ▽ More We analyze MOA-2010-BLG-311, a high magnification (A_max>600) microlensing event with complete data coverage over the peak, making it very sensitive to planetary signals. We fit this event with both a point lens and a 2-body lens model and find that the 2-body lens model is a better fit but with only Delta chi^2~80. The preferred mass ratio between the lens star and its companion is $q=10^(-3.7+/-0.1), placing the candidate companion in the planetary regime. Despite the formal significance of the planet, we show that because of systematics in the data the evidence for a planetary companion to the lens is too tenuous to claim a secure detection. When combined with analyses of other high-magnification events, this event helps empirically define the threshold for reliable planet detection in high-magnification events, which remains an open question. △ Less

Submitted 10 October, 2013; v1 submitted 22 October, 2012; originally announced October 2012.

Comments: 29 pages, 6 Figures, 3 Tables. For a brief video presentation on this paper, please see http://www.youtube.com/user/OSUAstronomy 10/25/2012 - Updated author list. Replaced 10/10/13 to reflect the version published in ApJ

Microlensig Binaries with Candidate Brown Dwarf Companions

Authors: I. -G. Shin, C. Han, A. Gould, A. Udalski, T. Sumi, M. Dominik, J. -P. Beaulieu, Y. Tsapras, V. Bozza, M. K. Szymański, M. Kubiak, I. Soszyński, G. Pietrzyński, R. Poleski, K. Ulaczyk, P. Pietrukowicz, S. Kozłowski, J. Skowron, Ł. Wyrzykowski, F. Abe, D. P. Bennett, I. A. Bond, C. S. Botzler, M. Freeman, A. Fukui , et al. (130 additional authors not shown)

Abstract: Brown dwarfs are important objects because they may provide a missing link between stars and planets, two populations that have dramatically different formation history. In this paper, we present the candidate binaries with brown dwarf companions that are found by analyzing binary microlensing events discovered during 2004 - 2011 observation seasons. Based on the low mass ratio criterion of q < 0.… ▽ More Brown dwarfs are important objects because they may provide a missing link between stars and planets, two populations that have dramatically different formation history. In this paper, we present the candidate binaries with brown dwarf companions that are found by analyzing binary microlensing events discovered during 2004 - 2011 observation seasons. Based on the low mass ratio criterion of q < 0.2, we found 7 candidate events, including OGLE-2004-BLG-035, OGLE-2004-BLG-039, OGLE-2007-BLG-006, OGLE-2007-BLG-399/MOA-2007-BLG-334, MOA-2011-BLG-104/OGLE-2011-BLG-0172, MOA-2011-BLG-149, and MOA-201-BLG-278/OGLE-2011-BLG-012N. Among them, we are able to confirm that the companions of the lenses of MOA-2011-BLG-104/OGLE-2011-BLG-0172 and MOA-2011-BLG-149 are brown dwarfs by determining the mass of the lens based on the simultaneous measurement of the Einstein radius and the lens parallax. The measured mass of the brown dwarf companions are (0.02 +/- 0.01) M_Sun and (0.019 +/- 0.002) M_Sun for MOA-2011-BLG-104/OGLE-2011-BLG-0172 and MOA-2011-BLG-149, respectively, and both companions are orbiting low mass M dwarf host stars. More microlensing brown dwarfs are expected to be detected as the number of lensing events with well covered light curves increases with new generation searches. △ Less

Submitted 2 October, 2012; v1 submitted 11 August, 2012; originally announced August 2012.

Comments: 10 pages, 9 figures, 4 tables

A New Type of Ambiguity in the Planet and Binary Interpretations of Central Perturbations of High-Magnification Gravitational Microlensing Events

Authors: J. -Y. Choi, I. -G. Shin, C. Han, A. Udalski, T. Sumi, A. Gould, V. Bozza, M. Dominik, P. Fouqué, K. Horne, M. K. Szymański, M. Kubiak, I. Soszyński, G. Pietrzyński, R. Poleski, K. Ulaczyk, P. Pietrukowicz, S. Kozłowski, J. Skowron, Ł. Wyrzykowski, F. Abe, D. P. Bennett, I. A. Bond, C. S. Botzler, P. Chote , et al. (96 additional authors not shown)

Abstract: High-magnification microlensing events provide an important channel to detect planets. Perturbations near the peak of a high-magnification event can be produced either by a planet or a binary companion. It is known that central perturbations induced by both types of companions can be generally distinguished due to the basically different magnification pattern around caustics. In this paper, we pre… ▽ More High-magnification microlensing events provide an important channel to detect planets. Perturbations near the peak of a high-magnification event can be produced either by a planet or a binary companion. It is known that central perturbations induced by both types of companions can be generally distinguished due to the basically different magnification pattern around caustics. In this paper, we present a case of central perturbations for which it is difficult to distinguish the planetary and binary interpretations. The peak of a lensing light curve affected by this perturbation appears to be blunt and flat. For a planetary case, this perturbation occurs when the source trajectory passes the negative perturbation region behind the back end of an arrowhead-shaped central caustic. For a binary case, a similar perturbation occurs for a source trajectory passing through the negative perturbation region between two cusps of an astroid-shaped caustic. We demonstrate the degeneracy for 2 high-magnification events of OGLE-2011-BLG-0526 and OGLE-2011-BLG-0950/MOA-2011-BLG-336. For OGLE-2011-BLG-0526, the $χ^2$ difference between the planetary and binary model is $\sim$ 3, implying that the degeneracy is very severe. For OGLE-2011-BLG-0950/MOA-2011-BLG-336, the stellar binary model is formally excluded with $Δχ^2 \sim$ 105 and the planetary model is preferred. However, it is difficult to claim a planet discovery because systematic residuals of data from the planetary model are larger than the difference between the planetary and binary models. Considering that 2 events observed during a single season suffer from such a degeneracy, it is expected that central perturbations experiencing this type of degeneracy is common. △ Less

Submitted 25 April, 2012; v1 submitted 21 April, 2012; originally announced April 2012.

Comments: 8 pages, 8 figures

Characterizing Low-Mass Binaries From Observation of Long Time-scale Caustic-crossing Gravitational Microlensing Events

Authors: I. -G. Shin, C. Han, J. -Y. Choi, A. Udalski, T. Sumi, A. Gould, V. Bozza, M. Dominik, P. Fouqué, K. Horne, M., K. Szymański, M. Kubiak, I. Soszyński, G. Pietrzyński, R. Poleski, K. Ulaczyk, P. Pietrukowicz, S. Kozłowski, J. Skowron, Ł. Wyrzykowski, F. Abe, D. P. Bennett, I. A. Bond, C. S. Botzler , et al. (97 additional authors not shown)

Abstract: Despite astrophysical importance of binary star systems, detections are limited to those located in small ranges of separations, distances, and masses and thus it is necessary to use a variety of observational techniques for a complete view of stellar multiplicity across a broad range of physical parameters. In this paper, we report the detections and measurements of 2 binaries discovered from obs… ▽ More Despite astrophysical importance of binary star systems, detections are limited to those located in small ranges of separations, distances, and masses and thus it is necessary to use a variety of observational techniques for a complete view of stellar multiplicity across a broad range of physical parameters. In this paper, we report the detections and measurements of 2 binaries discovered from observations of microlensing events MOA-2011-BLG-090 and OGLE-2011-BLG-0417. Determinations of the binary masses are possible by simultaneously measuring the Einstein radius and the lens parallax. The measured masses of the binary components are 0.43 $M_{\odot}$ and 0.39 $M_{\odot}$ for MOA-2011-BLG-090 and 0.57 $M_{\odot}$ and 0.17 $M_{\odot}$ for OGLE-2011-BLG-0417 and thus both lens components of MOA-2011-BLG-090 and one component of OGLE-2011-BLG-0417 are M dwarfs, demonstrating the usefulness of microlensing in detecting binaries composed of low-mass components. From modeling of the light curves considering full Keplerian motion of the lens, we also measure the orbital parameters of the binaries. The blended light of OGLE-2011-BLG-0417 comes very likely from the lens itself, making it possible to check the microlensing orbital solution by follow-up radial-velocity observation. For both events, the caustic-crossing parts of the light curves, which are critical for determining the physical lens parameters, were resolved by high-cadence survey observations and thus it is expected that the number of microlensing binaries with measured physical parameters will increase in the future. △ Less

Submitted 12 June, 2012; v1 submitted 12 April, 2012; originally announced April 2012.

Comments: 8 pages, 5 figures, 4 tables

OGLE-2008-BLG-510: first automated real-time detection of a weak microlensing anomaly - brown dwarf or stellar binary?

Authors: V. Bozza, M. Dominik, N. J. Rattenbury, U. G. Joergensen, Y. Tsapras, D. M. Bramich, A. Udalski, I. A. Bond, C. Liebig, A. Cassan, P. Fouque, A. Fukui, M. Hundertmark, I. -G. Shin, S. H. Lee, J. -Y. Choi, S. -Y. Park, A. Gould, A. Allan, S. Mao, L. Wyrzykowski, R. A. Street, D. Buckley, T. Nagayama, M. Mathiasen , et al. (81 additional authors not shown)

Abstract: The microlensing event OGLE-2008-BLG-510 is characterised by an evident asymmetric shape of the peak, promptly detected by the ARTEMiS system in real time. The skewness of the light curve appears to be compatible both with binary-lens and binary-source models, including the possibility that the lens system consists of an M dwarf orbited by a brown dwarf. The detection of this microlensing anomaly… ▽ More The microlensing event OGLE-2008-BLG-510 is characterised by an evident asymmetric shape of the peak, promptly detected by the ARTEMiS system in real time. The skewness of the light curve appears to be compatible both with binary-lens and binary-source models, including the possibility that the lens system consists of an M dwarf orbited by a brown dwarf. The detection of this microlensing anomaly and our analysis demonstrates that: 1) automated real-time detection of weak microlensing anomalies with immediate feedback is feasible, efficient, and sensitive, 2) rather common weak features intrinsically come with ambiguities that are not easily resolved from photometric light curves, 3) a modelling approach that finds all features of parameter space rather than just the `favourite model' is required, and 4) the data quality is most crucial, where systematics can be confused with real features, in particular small higher-order effects such as orbital motion signatures. It moreover becomes apparent that events with weak signatures are a silver mine for statistical studies, although not easy to exploit. Clues about the apparent paucity of both brown-dwarf companions and binary-source microlensing events might hide here. △ Less

Submitted 6 March, 2012; originally announced March 2012.

Comments: 17 pages with 8 figures, MNRAS submitted

One or more bound planets per Milky Way star from microlensing observations

Authors: A. Cassan, D. Kubas, J. -P. Beaulieu, M. Dominik, K. Horne, J. Greenhill, J. Wambsganss, J. Menzies, A. Williams, U. G. Jorgensen, A. Udalski, D. P. Bennett, M. D. Albrow, V. Batista, S. Brillant, J. A. R. Caldwell, A. Cole, Ch. Coutures, K. H. Cook, S. Dieters, D. Dominis Prester, J. Donatowicz, P. Fouque, K. Hill, N. Kains , et al. (17 additional authors not shown)

Abstract: Most known extrasolar planets (exoplanets) have been discovered using the radial velocity$^{\bf 1,2}$ or transit$^{\bf 3}$ methods. Both are biased towards planets that are relatively close to their parent stars, and studies find that around 17--30% (refs 4, 5) of solar-like stars host a planet. Gravitational microlensing$^{\bf 6\rm{\bf -}\bf 9}$, on the other hand, probes planets that are further… ▽ More Most known extrasolar planets (exoplanets) have been discovered using the radial velocity$^{\bf 1,2}$ or transit$^{\bf 3}$ methods. Both are biased towards planets that are relatively close to their parent stars, and studies find that around 17--30% (refs 4, 5) of solar-like stars host a planet. Gravitational microlensing$^{\bf 6\rm{\bf -}\bf 9}$, on the other hand, probes planets that are further away from their stars. Recently, a population of planets that are unbound or very far from their stars was discovered by microlensing$^{\bf 10}$. These planets are at least as numerous as the stars in the Milky Way$^{\bf 10}$. Here we report a statistical analysis of microlensing data (gathered in 2002--07) that reveals the fraction of bound planets 0.5--10 AU (Sun--Earth distance) from their stars. We find that 17$_{\bf -9}^{\bf +6}$% of stars host Jupiter-mass planets (0.3--10 $\MJ$, where $\MJ {\bf = 318}$ $\Mearth$ and $\Mearth$ is Earth's mass). Cool Neptunes (10--30 $\Mearth$) and super-Earths (5--10 $\Mearth$) are even more common: their respective abundances per star are 52$_{\bf -29}^{\bf +22}$% and 62$_{\bf -37}^{\bf +35}$%. We conclude that stars are orbited by planets as a rule, rather than the exception. △ Less

Submitted 4 February, 2012; originally announced February 2012.

Comments: Letter, 2 figures

Journal ref: Nature 481, 167-169 (2012)

Long Period Variables in the Large Magellanic Cloud from the EROS-2 survey

Authors: M. Spano, N. Mowlavi, L. Eyer, G. Burki, J. -B. Marquette, I. Lecoeur-Taïbi, P. Tisserand

Abstract: Context. The EROS-2 survey has produced a database of millions of time series from stars monitored for more than six years, allowing to classify some of their sources into different variable star types. Among these, Long Period Variables (LPVs), known to follow sequences in the period-luminosity diagram, include long secondary period variables whose variability origin is still a matter of debate.… ▽ More Context. The EROS-2 survey has produced a database of millions of time series from stars monitored for more than six years, allowing to classify some of their sources into different variable star types. Among these, Long Period Variables (LPVs), known to follow sequences in the period-luminosity diagram, include long secondary period variables whose variability origin is still a matter of debate. Aims.We use the 856 864 variable stars available from the Large Magellanic Cloud (LMC) in the EROS-2 database to detect, classify and characterize LPVs. Methods. Our method to extract LPVs is based on the statistical Abbe test. It investigates the regularity of the light curve with respect to the survey duration in order to extract candidates with long-term variability. The period search is done by Deeming, Lomb-Scargle and generalized Lomb-Scargle methods, combined with Fourier series fit. Color-magnitude, period-magnitude and period-amplitude diagrams are used to characterize our candidates. Results. We present a catalog of 43 551 LPV candidates for the Large Magellanic Cloud. For each of them, we provide up to five periods, mean magnitude in EROS-2, 2MASS and Spitzer bands, BE-RE color, RE amplitude and spectral type.We use infrared data to make the distinction between RGB, O-rich, C-rich and extreme AGB stars. Properties of our LPV candidates are investigated by analyzing period-luminosity and period-amplitude diagrams. △ Less

Submitted 12 October, 2011; v1 submitted 28 September, 2011; originally announced September 2011.

Comments: Accepted for publication in A&A

Long Period Variables in the Magellanic Clouds with EROS-2 survey

Authors: M. Spano, N. Mowlavi, L. Eyer, J. -B. Marquette, G. Burki

Abstract: We use the EROS-2 database to analyze Long Period Variables (LPVs) in the Magellanic Clouds. It results in the creation of a catalog of more than 40 000 LPV candidates which is briefly introduced here. We use the EROS-2 database to analyze Long Period Variables (LPVs) in the Magellanic Clouds. It results in the creation of a catalog of more than 40 000 LPV candidates which is briefly introduced here. △ Less

Submitted 22 September, 2011; originally announced September 2011.

Comments: To appear in the proceedings of the conference "Why Galaxies Care About AGB Stars II", Vienna, August 16-20, 2010, ASP Conference Series

Microlensing Binaries Discovered through High-Magnification Channel

Authors: I. -G. Shin, J. -Y. Choi, S. -Y. Park, C. Han, A. Gould, T. Sumi, A. Udalski, J. -P. Beaulieu, M. Dominik, W. Allen, M. Bos, G. W. Christie, D. L. Depoy, S. Dong, J. Drummond, A. Gal-Yam, B. S. Gaudi, L. -W. Hung, J. Janczak, S. Kaspi, C. -U. Lee, F. Mallia, D. Maoz, A. Maury, J. McCormick , et al. (127 additional authors not shown)

Abstract: Microlensing can provide a useful tool to probe binary distributions down to low-mass limits of binary companions. In this paper, we analyze the light curves of 8 binary lensing events detected through the channel of high-magnification events during the seasons from 2007 to 2010. The perturbations, which are confined near the peak of the light curves, can be easily distinguished from the central p… ▽ More Microlensing can provide a useful tool to probe binary distributions down to low-mass limits of binary companions. In this paper, we analyze the light curves of 8 binary lensing events detected through the channel of high-magnification events during the seasons from 2007 to 2010. The perturbations, which are confined near the peak of the light curves, can be easily distinguished from the central perturbations caused by planets. However, the degeneracy between close and wide binary solutions cannot be resolved with a $3σ$ confidence level for 3 events, implying that the degeneracy would be an important obstacle in studying binary distributions. The dependence of the degeneracy on the lensing parameters is consistent with a theoretic prediction that the degeneracy becomes severe as the binary separation and the mass ratio deviate from the values of resonant caustics. The measured mass ratio of the event OGLE-2008-BLG-510/MOA-2008-BLG-369 is $q\sim 0.1$, making the companion of the lens a strong brown-dwarf candidate. △ Less

Submitted 28 November, 2011; v1 submitted 15 September, 2011; originally announced September 2011.

Comments: 10 figures, 6 tables, 26 pages

Discovery and Mass Measurements of a Cold, 10-Earth Mass Planet and Its Host Star

Authors: Y. Muraki, C. Han, D. P. Bennett, D. Suzuki, L. A. G. Monard, R. Street, U. G. Jorgensen, P. Kundurthy, J. Skowron, A. C. Becker, M. D. Albrow, P. Fouque, D. Heyrovsky, R. K. Barry, J. -P. Beaulieu, D. D. Wellnitz, I. A. Bond, T. Sumi, S. Dong, B. S. Gaudi, D. M. Bramich, M. Dominik, F. Abe, C. S. Botzler, M. Freeman , et al. (103 additional authors not shown)

Abstract: We present the discovery and mass measurement of the cold, low-mass planet MOA-2009-BLG-266Lb, made with the gravitational microlensing method. This planet has a mass of m_p = 10.4 +- 1.7 Earth masses and orbits a star of mass M_* = 0.56 +- 0.09 Solar masses at a semi-major axis of a = 3.2 (+1.9 -0.5) AU and an orbital period of P = 7.6 (+7.7 -1.5} yrs. The planet and host star mass measurements a… ▽ More We present the discovery and mass measurement of the cold, low-mass planet MOA-2009-BLG-266Lb, made with the gravitational microlensing method. This planet has a mass of m_p = 10.4 +- 1.7 Earth masses and orbits a star of mass M_* = 0.56 +- 0.09 Solar masses at a semi-major axis of a = 3.2 (+1.9 -0.5) AU and an orbital period of P = 7.6 (+7.7 -1.5} yrs. The planet and host star mass measurements are enabled by the measurement of the microlensing parallax effect, which is seen primarily in the light curve distortion due to the orbital motion of the Earth. But, the analysis also demonstrates the capability to measure microlensing parallax with the Deep Impact (or EPOXI) spacecraft in a Heliocentric orbit. The planet mass and orbital distance are similar to predictions for the critical core mass needed to accrete a substantial gaseous envelope, and thus may indicate that this planet is a "failed" gas giant. This and future microlensing detections will test planet formation theory predictions regarding the prevalence and masses of such planets. △ Less

Submitted 10 June, 2011; originally announced June 2011.

Comments: 38 pages with 7 figures

Binary microlensing event OGLE-2009-BLG-020 gives a verifiable mass, distance and orbit predictions

Authors: J. Skowron, A. Udalski, A. Gould, Subo Dong, L. A. G. Monard, C. Han, C. R. Nelson, J. McCormick, D. Moorhouse, G. Thornley, A. Maury, D. M. Bramich, J. Greenhill, S. Kozlowski, I. Bond, R. Poleski, L. Wyrzykowski, K. Ulaczyk, M. Kubiak, M. K. Szymanski, G. Pietrzynski, I. Soszynski, B. S. Gaudi, J. C. Yee, L. -W. Hung , et al. (77 additional authors not shown)

Abstract: We present the first example of binary microlensing for which the parameter measurements can be verified (or contradicted) by future Doppler observations. This test is made possible by a confluence of two relatively unusual circumstances. First, the binary lens is bright enough (I=15.6) to permit Doppler measurements. Second, we measure not only the usual 7 binary-lens parameters, but also the 'mi… ▽ More We present the first example of binary microlensing for which the parameter measurements can be verified (or contradicted) by future Doppler observations. This test is made possible by a confluence of two relatively unusual circumstances. First, the binary lens is bright enough (I=15.6) to permit Doppler measurements. Second, we measure not only the usual 7 binary-lens parameters, but also the 'microlens parallax' (which yields the binary mass) and two components of the instantaneous orbital velocity. Thus we measure, effectively, 6 'Kepler+1' parameters (two instantaneous positions, two instantaneous velocities, the binary total mass, and the mass ratio). Since Doppler observations of the brighter binary component determine 5 Kepler parameters (period, velocity amplitude, eccentricity, phase, and position of periapsis), while the same spectroscopy yields the mass of the primary, the combined Doppler + microlensing observations would be overconstrained by 6 + (5 + 1) - (7 + 1) = 4 degrees of freedom. This makes possible an extremely strong test of the microlensing solution. We also introduce a uniform microlensing notation for single and binary lenses, we define conventions, summarize all known microlensing degeneracies and extend a set of parameters to describe full Keplerian motion of the binary lenses. △ Less

Submitted 17 January, 2011; originally announced January 2011.

Comments: 51 pages, 8 figures, 2 appendices. Submitted to ApJ. Fortran codes for Appendix B are attached to this astro-ph submission and are also available at http://www.astronomy.ohio-state.edu/~jskowron/OGLE-2009-BLG-020/

The VMC Survey - I. Strategy and First Data

Authors: M. -R. L. Cioni, G. Clementini, L. Girardi, R. Guandalini, M. Gullieuszik, B. Miszalski, M. -I. Moretti, V. Ripepi, S. Rubele, G. Bagheri, K. Bekki, N. Cross, W. J. G. de Blok, R. de Grijs, J. P. Emerson, C. J. Evans, B. Gibson, E. Gonzales-Solares, M. A. T. Groenewegen, M. Irwin, V. D. Ivanov, J. Lewis, M. Marconi, J. -B. Marquette, C. Mastropietro , et al. (9 additional authors not shown)

Abstract: The new VISual and Infrared Telescope for Astronomy (VISTA) has started operations. Over its first five years it will be collecting data for six public surveys, one of these is the near-infrared YJKsVISTA survey of the Magellanic Clouds system (VMC). This survey comprises the LMC, the SMC, the Bridge connecting the two galaxies and two fields in the Stream. This paper provides an overview of the V… ▽ More The new VISual and Infrared Telescope for Astronomy (VISTA) has started operations. Over its first five years it will be collecting data for six public surveys, one of these is the near-infrared YJKsVISTA survey of the Magellanic Clouds system (VMC). This survey comprises the LMC, the SMC, the Bridge connecting the two galaxies and two fields in the Stream. This paper provides an overview of the VMC survey strategy and presents first science results. The main goals of the VMC survey are the determination of the spatially resolved SFH and 3D structure of the Magellanic system. Therefore, the VMC survey is designed to reach stars as faint as the oldest main sequence turn-off point and to constrain the mean magnitude of pulsating variable stars such as RR Lyrae stars and Cepheids. This paper focuses on observations of VMC fields in the LMC obtained between November 2009 and March 2010. These observations correspond to a 7% completeness of the LMC fields. The VMC observations consist of multi-epoch measurements organised following a specific structure. The data were reduced using the VISTA Data Flow System pipeline whose source catalogues were produced and made available via the VISTA Science Archive. The analysis of the data shows that the sensitivity in each wave band agrees with expectations. Uncertainties and completeness of the data are also derived. The first science results, aimed at assessing the science quality of the VMC data, include an overview of the distribution of stars in colour-magnitude and colour-colour diagrams, the detection of planetary nebulae and of stellar clusters, and the Ks band light-curve of variable stars. The VMC survey represents a tremendous improvement, in spatial resolution and sensitivity, on previous panoramic observations of the Magellanic system in the near-infrared and complements nicely the deep observations at other wavelengths. (Abridged) △ Less

Submitted 4 February, 2011; v1 submitted 22 December, 2010; originally announced December 2010.

Comments: 25 pages, 20 figures, accepted for publication by Astronomy & Astrophysics, high resolution version available at http://star.herts.ac.uk/~mcioni/vmc/

Journal ref: Astronomy & Astrophysics, vol. 527, 2011

OGLE-2005-BLG-153: Microlensing Discovery and Characterization of A Very Low Mass Binary

Authors: K. -H. Hwang, A. Udalski, C. Han, Y. -H. Ryu, I. A. Bond, J. -P. Beaulieu, M. Dominik, K. Horne, A. Gould, B. S. Gaudi, M. Kubiak, M. K. Szymanski, G. Pietrzynski, I. Soszynski, O. Szewczyk, K. Ulaczyk, L. Wyrzykowski, F. Abe, C. S. Botzler, J. B. Hearnshaw, Y. Itow, K. Kamiya, P. M. Kilmartin, K. Masuda, Y. Matsubara , et al. (55 additional authors not shown)

Abstract: The mass function and statistics of binaries provide important diagnostics of the star formation process. Despite this importance, the mass function at low masses remains poorly known due to observational difficulties caused by the faintness of the objects. Here we report the microlensing discovery and characterization of a binary lens composed of very low-mass stars just above the hydrogen-burnin… ▽ More The mass function and statistics of binaries provide important diagnostics of the star formation process. Despite this importance, the mass function at low masses remains poorly known due to observational difficulties caused by the faintness of the objects. Here we report the microlensing discovery and characterization of a binary lens composed of very low-mass stars just above the hydrogen-burning limit. From the combined measurements of the Einstein radius and microlens parallax, we measure the masses of the binary components of $0.10\pm 0.01\ M_\odot$ and $0.09\pm 0.01\ M_\odot$. This discovery demonstrates that microlensing will provide a method to measure the mass function of all Galactic populations of very low mass binaries that is independent of the biases caused by the luminosity of the population. △ Less

Submitted 25 April, 2012; v1 submitted 2 September, 2010; originally announced September 2010.

Comments: 6 pages, 3 figures, 1 table

OGLE 2008--BLG--290: An accurate measurement of the limb darkening of a Galactic Bulge K Giant spatially resolved by microlensing

Authors: P. Fouque, D. Heyrovsky, S. Dong, A. Gould, A. Udalski, M. D. Albrow, V. Batista, J. -P. Beaulieu, D. P. Bennett, I. A. Bond, D. M. Bramich, S. Calchi Novati, A. Cassan, C. Coutures, S. Dieters, M. Dominik, D. Dominis Prester, J. Greenhill, K. Horne, U. G. Jorgensen, S. Kozlowski, D. Kubas, C. -H. Lee, J. -B. Marquette, M. Mathiasen , et al. (93 additional authors not shown)

Abstract: Gravitational microlensing is not only a successful tool for discovering distant exoplanets, but it also enables characterization of the lens and source stars involved in the lensing event. In high magnification events, the lens caustic may cross over the source disk, which allows a determination of the angular size of the source and additionally a measurement of its limb darkening. When such exte… ▽ More Gravitational microlensing is not only a successful tool for discovering distant exoplanets, but it also enables characterization of the lens and source stars involved in the lensing event. In high magnification events, the lens caustic may cross over the source disk, which allows a determination of the angular size of the source and additionally a measurement of its limb darkening. When such extended-source effects appear close to maximum magnification, the resulting light curve differs from the characteristic Paczynski point-source curve. The exact shape of the light curve close to the peak depends on the limb darkening of the source. Dense photometric coverage permits measurement of the respective limb-darkening coefficients. In the case of microlensing event OGLE 2008-BLG-290, the K giant source star reached a peak magnification of about 100. Thirteen different telescopes have covered this event in eight different photometric bands. Subsequent light-curve analysis yielded measurements of linear limb-darkening coefficients of the source in six photometric bands. The best-measured coefficients lead to an estimate of the source effective temperature of about 4700 +100-200 K. However, the photometric estimate from colour-magnitude diagrams favours a cooler temperature of 4200 +-100 K. As the limb-darkening measurements, at least in the CTIO/SMARTS2 V and I bands, are among the most accurate obtained, the above disagreement needs to be understood. A solution is proposed, which may apply to previous events where such a discrepancy also appeared. △ Less

Submitted 6 May, 2010; originally announced May 2010.

Comments: Astronomy & Astrophysics in press

Limb-darkening measurements for a cool red giant in microlensing event OGLE 2004-BLG-482

Authors: M. Zub, A. Cassan, D. Heyrovsky, P. Fouque, H. C. Stempels, M. D. Albrow, J. -P. Beaulieu, S. Brillant, G. W. Christie, N. Kains, S. Kozlowski, D. Kubas, J. Wambsganss, V. Batista, D. P. Bennett, K. Cook, C. Coutures, S. Dieters, M. Dominik, D. Dominis Prester, J. Donatowicz, J. Greenhill, K. Horne, U. G. Jorgensen, S. R. Kane , et al. (25 additional authors not shown)

Abstract: Aims: We present a detailed analysis of OGLE 2004-BLG-482, a relatively high-magnification single-lens microlensing event which exhibits clear extended-source effects. These events are relatively rare, but they potentially contain unique information on the stellar atmosphere properties of their source star, as shown in this study. Methods: Our dense photometric coverage of the overall light curve… ▽ More Aims: We present a detailed analysis of OGLE 2004-BLG-482, a relatively high-magnification single-lens microlensing event which exhibits clear extended-source effects. These events are relatively rare, but they potentially contain unique information on the stellar atmosphere properties of their source star, as shown in this study. Methods: Our dense photometric coverage of the overall light curve and a proper microlensing modelling allow us to derive measurements of the OGLE 2004-BLG-482 source star's linear limb-darkening coefficients in three bands, including standard Johnson-Cousins I and R, as well as in a broad clear filter. In particular, we discuss in detail the problems of multi-band and multi-site modelling on the expected precision of our results. We also obtained high-resolution UVES spectra as part of a ToO programme at ESO VLT from which we derive the source star's precise fundamental parameters. Results: From the high-resolution UVES spectra, we find that OGLE 2004-BLG-482's source star is a red giant of MK type a bit later than M3, with Teff = 3667 +/- 150 K, log g = 2.1 +/- 1.0 and an assumed solar metallicity. This is confirmed by an OGLE calibrated colour-magnitude diagram. We then obtain from a detailed microlensing modelling of the light curve linear limb-darkening coefficients that we compare to model-atmosphere predictions available in the literature, and find a very good agreement for the I and R bands. In addition, we perform a similar analysis using an alternative description of limb darkening based on a principal component analysis of ATLAS limb-darkening profiles, and also find a very good agreement between measurements and model predictions. △ Less

Submitted 28 September, 2010; v1 submitted 11 December, 2009; originally announced December 2009.

Comments: Accepted in A&A

Difference imaging photometry of blended gravitational microlensing events with a numerical kernel

Authors: M. D. Albrow, K. Horne, D. M. Bramich, P. Fouqué, V. R. Miller, J. -P. Beaulieu, C. Coutures, J. Menzies, A. Williams, V. Batista, D. P. Bennett, S. Brillant, A. Cassan, S. Dieters, D. Dominis Prester, J. Donatowicz, J. Greenhill, N. Kains, S. R. Kane, D. Kubas, J. -B. Marquette, K. R. Pollard, K. C. Sahu, Y. Tsapras, J. Wambsganss , et al. (1 additional authors not shown)

Abstract: The numerical kernel approach to difference imaging has been implemented and applied to gravitational microlensing events observed by the PLANET collaboration. The effect of an error in the source-star coordinates is explored and a new algorithm is presented for determining the precise coordinates of the microlens in blended events, essential for accurate photometry of difference images. It is s… ▽ More The numerical kernel approach to difference imaging has been implemented and applied to gravitational microlensing events observed by the PLANET collaboration. The effect of an error in the source-star coordinates is explored and a new algorithm is presented for determining the precise coordinates of the microlens in blended events, essential for accurate photometry of difference images. It is shown how the photometric reference flux need not be measured directly from the reference image but can be obtained from measurements of the difference images combined with knowledge of the statistical flux uncertainties. The improved performance of the new algorithm, relative to ISIS2, is demonstrated. △ Less

Submitted 18 May, 2009; originally announced May 2009.

Comments: Accepted by MNRAS, 8 pages, 4 figures

The EROS2 search for microlensing events towards the spiral arms: the complete seven season results

Authors: Y. R. Rahal, C. Afonso, J. -N. Albert, J. Andersen, R. Ansari, E. Aubourg, P. Bareyre, J. -P. Beaulieu, X. Charlot, F. Couchot, C. Coutures, F. Derue, R. Ferlet, P. Fouqué, J. -F. Glicenstein, B. Goldman, A. Gould, D. Graff, M. Gros, J. Haissinski, C. Hamadache, J. de Kat, E. Lesquoy, C. Loup, L. Le Guillou , et al. (14 additional authors not shown)

Abstract: The EROS-2 project has been designed to search for microlensing events towards any dense stellar field. The densest parts of the Galactic spiral arms have been monitored to maximize the microlensing signal expected from the stars of the Galactic disk and bulge. 12.9 million stars have been monitored during 7 seasons towards 4 directions in the Galactic plane, away from the Galactic center. A tot… ▽ More The EROS-2 project has been designed to search for microlensing events towards any dense stellar field. The densest parts of the Galactic spiral arms have been monitored to maximize the microlensing signal expected from the stars of the Galactic disk and bulge. 12.9 million stars have been monitored during 7 seasons towards 4 directions in the Galactic plane, away from the Galactic center. A total of 27 microlensing event candidates have been found. Estimates of the optical depths from the 22 best events are provided. A first order interpretation shows that simple Galactic models with a standard disk and an elongated bulge are in agreement with our observations. We find that the average microlensing optical depth towards the complete EROS-cataloged stars of the spiral arms is $\barτ =0.51\pm .13\times 10^{-6}$, a number that is stable when the selection criteria are moderately varied. As the EROS catalog is almost complete up to $I_C=18.5$, the optical depth estimated for the sub-sample of bright target stars with $I_C<18.5$ ($\barτ=0.39\pm >.11\times 10^{-6}$) is easier to interpret. The set of microlensing events that we have observed is consistent with a simple Galactic model. A more precise interpretation would require either a better knowledge of the distance distribution of the target stars, or a simulation based on a Galactic model. For this purpose, we define and discuss the concept of optical depth for a given catalog or for a limiting magnitude. △ Less

Submitted 9 January, 2009; originally announced January 2009.

Comments: 22 pages submitted to Astronomy & Astrophysics

Journal ref: Astronomy and Astrophysics 500 (2009) 1027-1044

A large-scale survey for variable stars in M33

Authors: D. Bersier, J. D. Hartman, K. Z. Stanek, J. -P. Beaulieu, J. Kaluzny, J. -B. Marquette, A. Schwarzenberg-Czerny, V. Scowcroft, P. B. Stetson

Abstract: We have started a survey of M 33 in order to find variable stars and Cepheids in particular. We have obtained more than 30 epochs of g'r'i' data with the CFHT and the one-square-degree camera MegaCam. We present first results from this survey, including the search for variable objects and a basic characterization of the various groups of variable stars. We have started a survey of M 33 in order to find variable stars and Cepheids in particular. We have obtained more than 30 epochs of g'r'i' data with the CFHT and the one-square-degree camera MegaCam. We present first results from this survey, including the search for variable objects and a basic characterization of the various groups of variable stars. △ Less

Submitted 13 March, 2008; originally announced March 2008.

Comments: To appear in the proceedings of the "Nonlinear stellar hydrodynamics", conference in honor of Robert Buchler's 65th birthday, July 2007, Paris

Detection of Beat Cepheids in M33 and Their Use as a Probe of the M33 Metallicity Distribution

Authors: J. -P. Beaulieu, J. Robert Buchler, J. -B. Marquette, J. D. Hartman, A. Schwarzenberg-Czerny

Abstract: Our analysis of the Deep CFHT M33 variability survey database has uncovered 5 Beat Cepheids (BCs) that are pulsating in the fundamental and first overtone modes. With {\it only} the help of stellar pulsation theory and of mass--luminosity (M-L) relations, derived from evolutionary tracks, we can accurately determine the metallicities Z of these stars. The [O/H] metallicity gradient of -0.16 dex/… ▽ More Our analysis of the Deep CFHT M33 variability survey database has uncovered 5 Beat Cepheids (BCs) that are pulsating in the fundamental and first overtone modes. With {\it only} the help of stellar pulsation theory and of mass--luminosity (M-L) relations, derived from evolutionary tracks, we can accurately determine the metallicities Z of these stars. The [O/H] metallicity gradient of -0.16 dex/kpc that is inferred from the M33 galacto-centric distances of these Cepheids and from their 'pulsation' metallicities is in excellent agreement with the standard spectroscopic metallicity gradients that are determined from H II regions, early B supergiant stars and planetary nebulae. Beat Cepheids can thus provide an additional, independent probe of galactic metallicity distributions. △ Less

Submitted 25 October, 2006; originally announced October 2006.

Comments: 5 pages, 2 figs

Journal ref: Astrophys.J.653:L101-L104,2006

OGLE 2004-BLG-254: a K3 III Galactic Bulge Giant spatially resolved by a single microlens

Authors: A. Cassan, J. -P. Beaulieu, P. Fouque, S. Brillant, M. Dominik, J. Greenhill, D. Heyrovsky, K. Horne, U. G. Jorgensen, D. Kubas, H. C. Stempels, C. Vinter, M. D. Albrow, D. Bennett, J. A. R. Caldwell, J. J. Calitz, K. Cook, C. Coutures, D. Dominis, J. Donatowicz, K. Hill, M. Hoffman, S. Kane, J. -B. Marquette, R. Martin , et al. (15 additional authors not shown)

Abstract: We present an analysis of OGLE 2004-BLG-254, a high-magnification and relatively short duration microlensing event in which the source star, a Bulge K3-giant, has been spatially resolved by a point-like lens. We have obtained dense photometric coverage of the event light curve with OGLE and PLANET telescopes, as well as a high signal-to-noise ratio spectrum taken while the source was still magni… ▽ More We present an analysis of OGLE 2004-BLG-254, a high-magnification and relatively short duration microlensing event in which the source star, a Bulge K3-giant, has been spatially resolved by a point-like lens. We have obtained dense photometric coverage of the event light curve with OGLE and PLANET telescopes, as well as a high signal-to-noise ratio spectrum taken while the source was still magnified by 20, using the UVES/VLT spectrograph. Our dense coverage of this event allows us to measure limb darkening of the source star in the I and R bands. We also compare previous measurements of linear limb-darkening coefficients involving GK-giant stars with predictions from ATLAS atmosphere models. We discuss the case of K-giants and find a disagreement between limb-darkening measurements and model predictions, which may be caused by the inadequacy of the linear limb-darkening law. △ Less

Submitted 11 September, 2006; originally announced September 2006.

Comments: 14 pages, 8 figures, accepted for publication in A&A (04/09/2006)

Deep CFHT Photometric Survey of the Entire M33 Galaxy I: Catalogue of 36000 Variable Point Sources

Authors: J. D. Hartman, D. Bersier, K. Z. Stanek, J. -P. Beaulieu, J. Kaluzny, J. -B. Marquette, P. B. Stetson

Abstract: We have conducted a variability survey of the local group galaxy M33 using g', r', and i' observations from 27 nights spanning 17 months made with the MegaPrime/MegaCam instrument on the 3.6 m CFHT telescope. We identify more than 36000 variable sources with g',r',i' < 24 out of approximately 2 million point sources in a one square degree field of view. This increases the number of known variabl… ▽ More We have conducted a variability survey of the local group galaxy M33 using g', r', and i' observations from 27 nights spanning 17 months made with the MegaPrime/MegaCam instrument on the 3.6 m CFHT telescope. We identify more than 36000 variable sources with g',r',i' < 24 out of approximately 2 million point sources in a one square degree field of view. This increases the number of known variables in this galaxy by more than a factor of 20. In this paper we provide a brief description of the data and a general overview of the variable star population which includes more than 800 candidate variable blue and red supergiant stars, more than 2000 Cepheids, and more than 19000 long period variable AGB and RGB stars. △ Less

Submitted 20 March, 2006; originally announced March 2006.

Comments: Submitted to MNRAS. 20 pages, 16 figures. Catalogue and light curves are available at http://www.astro.livjm.ac.uk/~dfb/M33/ animations associated with this paper are available at http://www.cfa.harvard.edu/~jhartman/M33_Movie.html a version of the paper with full-resolution images is available at http://www.astro.livjm.ac.uk/~dfb/M33/M33_fullres.ps.gz

Journal ref: Mon.Not.Roy.Astron.Soc.371:1405,2006