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HIPPI-2: A Versatile High Precision Polarimeter
Authors:
Jeremy Bailey,
Daniel V. Cotton,
Lucyna Kedziora-Chudczer,
Ain De Horta,
Darren Maybour
Abstract:
We describe the High-Precision Polarimetric Instrument-2 (HIPPI-2) a highly versatile stellar polarimeter developed at the University of New South Wales (UNSW). Two copies of HIPPI-2 have been built and used on the 60-cm telescope at Western Sydney University's (WSU) Penrith Observatory, the 8.1-m Gemini North Telescope at Mauna Kea and extensively on the 3.9-m Anglo-Australian Telescope (AAT). Th…
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We describe the High-Precision Polarimetric Instrument-2 (HIPPI-2) a highly versatile stellar polarimeter developed at the University of New South Wales (UNSW). Two copies of HIPPI-2 have been built and used on the 60-cm telescope at Western Sydney University's (WSU) Penrith Observatory, the 8.1-m Gemini North Telescope at Mauna Kea and extensively on the 3.9-m Anglo-Australian Telescope (AAT). The precision of polarimetry, measured from repeat observations of bright stars in the SDSS g' band, is better than 3.5 ppm (parts per million) on the 3.9-m AAT and better than 11 ppm on the 60-cm WSU telescope. The precision is better at redder wavelengths and poorer in the blue. On the Gemini North 8-m telescope the performance is limited by a very large and strongly wavelength dependent telescope polarization that reached 1000's of ppm at blue wavelengths and is much larger than we have seen on any other telescope.
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Submitted 5 November, 2019;
originally announced November 2019.
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The first observed stellar occultations by the irregular satellite (Saturn IX) Phoebe and improved rotational period
Authors:
A. R. Gomes-Júnior,
M. Assafin,
F. Braga-Ribas,
G. Benedetti-Rossi,
B. Morgado,
J. I. B. Camargo,
R. Vieira-Martins,
J. Desmars,
B. Sicardy,
T. Barry,
J. Campbell-White,
E. Fernández-Lajús,
D. Giles,
W. Hanna,
T. Hayamizu,
T. Hirose,
A. De Horta,
R. Horvat,
K. Hosoi,
E. Jehin,
S. Kerr,
D. I. Machado,
L. A. Mammana,
D. Maybour,
M. Owada
, et al. (2 additional authors not shown)
Abstract:
We report six stellar occultations by (Saturn IX) Phoebe, an irregular satellite of Saturn, obtained between mid-2017 and mid-2019. The 2017 July 06 event is the first stellar occultation by an irregular satellite ever observed. The occultation chords were compared to a 3D shape model of the satellite obtained from Cassini observations. The rotation period available in the literature led to a sub-…
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We report six stellar occultations by (Saturn IX) Phoebe, an irregular satellite of Saturn, obtained between mid-2017 and mid-2019. The 2017 July 06 event is the first stellar occultation by an irregular satellite ever observed. The occultation chords were compared to a 3D shape model of the satellite obtained from Cassini observations. The rotation period available in the literature led to a sub-observer point at the moment of the observed occultations where the chords could not fit the 3D model. A procedure was developed to identify the correct sub-observer longitude. It allowed us to obtain the rotation period with improved precision over currently known value from literature. We show that the difference between the observed and the predicted sub-observer longitude suggests two possible solutions for the rotation period. By comparing these values with recently observed rotational light curves and single-chord stellar occultations, we can identify the best solution for Phoebe's rotational period as $9.27365 \pm 0.00002$ h. From the stellar occultations, we also obtained 6 geocentric astrometric positions in the ICRS as realised by the Gaia-DR2 with uncertainties at the 1-mas level.
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Submitted 27 October, 2019;
originally announced October 2019.
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The polarization of the binary system Spica, and the reflection of light from stars
Authors:
Jeremy Bailey,
Daniel. V. Cotton,
Lucyna Kedziora-Chudczer,
Ain De Horta,
Darren Maybour
Abstract:
Close binary systems often show linear polarization varying over the binary period, usually attributed to light scattered from electrons in circumstellar clouds. One of the brightest close binary systems is Spica (Alpha Virginis) consisting of two B type stars orbiting with a period of just over 4 days. Past observations of Spica have shown low polarization with no evidence for variability. Here w…
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Close binary systems often show linear polarization varying over the binary period, usually attributed to light scattered from electrons in circumstellar clouds. One of the brightest close binary systems is Spica (Alpha Virginis) consisting of two B type stars orbiting with a period of just over 4 days. Past observations of Spica have shown low polarization with no evidence for variability. Here we report new high-precision polarization observations of Spica that show variation with an amplitude ~200 parts-per-million (ppm). Using a new modelling approach we show that the phase-dependent polarization is primarily due to reflected light from the primary off the secondary and vice versa. The stars reflect only a few per-cent of the incident light, but the reflected light is very highly polarized. The polarization results show that the binary orbit is clockwise and the position angle of the line of nodes is 130.4 +/- 6.8 degrees in agreement with Intensity Interferometer results. We suggest that reflected light polarization may be much more important in binary systems than has previously been recognized and may be a way of detecting previously unrecognized close binaries.
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Submitted 1 April, 2019;
originally announced April 2019.
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The structure of Chariklo's rings from stellar occultations
Authors:
D. Bérard,
B. Sicardy,
J. I. B. Camargo,
J. Desmars,
F. Braga-Ribas,
J. L. Ortiz,
R. Duffard,
N. Morales,
E. Meza,
R. Leiva,
G. Benedetti-Rossi,
R. Vieira-Martins,
A. R. Gomes-Júnior,
M. Assafin,
F. Colas,
J. L. Dauvergne,
P. Kervella,
J. Lecacheux,
L. Maquet,
F. Vachier,
S. Renner,
B. Monard,
A. A. Sickafoose,
H. Breytenbach,
A. Genade
, et al. (57 additional authors not shown)
Abstract:
Two narrow and dense rings (called C1R and C2R) were discovered around the Centaur object (10199) Chariklo during a stellar occultation observed on 2013 June 3. Following this discovery, we planned observations of several occultations by Chariklo's system in order to better characterize the physical properties of the ring and main body. Here, we use 12 successful occulations by Chariklo observed b…
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Two narrow and dense rings (called C1R and C2R) were discovered around the Centaur object (10199) Chariklo during a stellar occultation observed on 2013 June 3. Following this discovery, we planned observations of several occultations by Chariklo's system in order to better characterize the physical properties of the ring and main body. Here, we use 12 successful occulations by Chariklo observed between 2014 and 2016. They provide ring profiles (physical width, opacity, edge structure) and constraints on the radii and pole position. Our new observations are currently consistent with the circular ring solution and pole position, to within the $\pm 3.3$ km formal uncertainty for the ring radii derived by Braga-Ribas et al. The six resolved C1R profiles reveal significant width variations from $\sim 5$ to 7.5 km. The width of the fainter ring C2R is less constrained, and may vary between 0.1 and 1 km. The inner and outer edges of C1R are consistent with infinitely sharp boundaries, with typical upper limits of one kilometer for the transition zone between the ring and empty space. No constraint on the sharpness of C2R's edges is available. A 1$σ$ upper limit of $\sim 20$ m is derived for the equivalent width of narrow (physical width <4 km) rings up to distances of 12,000 km, counted in the ring plane.
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Submitted 18 September, 2017; v1 submitted 1 June, 2017;
originally announced June 2017.