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A Near-Infrared and Optical Study of NGC 5822: An Open Cluster Hosting Barium-stars and Lithium-Enriched Giant Stars
Authors:
N. Holanda,
V. Loaiza-Tacuri,
A. Sonally,
S. Bijavara Seshashayana,
M. P. Roriz,
C. F. Martinez,
M. Borges Fernandes,
C. B. Pereira,
O. J. Katime Santrich,
S. Daflon
Abstract:
We present a chemical abundance study of giant stars in the Galactic open cluster NGC 5822, which hosts two barium stars (#002 and #201) and three lithium-enriched giants (#006, #102, and #240). Using high-resolution optical and near-infrared ($H$ and $K$ band) spectra from FEROS and IGRINS, we determine atmospheric parameters and abundances for 23 elements (Li, C, N, O, F, Na, Mg, Al, Si, P, S, K…
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We present a chemical abundance study of giant stars in the Galactic open cluster NGC 5822, which hosts two barium stars (#002 and #201) and three lithium-enriched giants (#006, #102, and #240). Using high-resolution optical and near-infrared ($H$ and $K$ band) spectra from FEROS and IGRINS, we determine atmospheric parameters and abundances for 23 elements (Li, C, N, O, F, Na, Mg, Al, Si, P, S, K, Ca, Sc, Ti, Cr, Fe, Ni, Y, Ce, Nd, Yb, and Pb). This includes species not yet studied in this cluster, such as F, P, K, Yb, and Pb, as well as oxygen isotopic ratios $^{16}$O/$^{17}$O and $^{16}$O/$^{18}$O. Membership was assessed using astrometry and chemical abundances, providing insight into the evolutionary stages of Li-enriched giants and cluster parameters (age, distance, extinction). However, the identification of Ba-stars remains challenging due to their binary nature and less reliable astrometric solutions. The cluster's abundances are broadly consistent with expectations for the Galactic thin disk. The mean fluorine abundance agrees with chemical evolution models predicting that young clusters (<2 Gyr) exhibit elevated [F/Fe], with production from SN II, SN Ia, AGB, and Wolf-Rayet stars. No distinct chemical or rotational features were found to explain the lithium enrichment, likely occurring either during the red clump phase or near the RGB tip. For the Ba-stars, nucleosynthesis models combined with the cluster's turn-off mass suggest polluting companion masses of 3.00 and 3.75 $M_{\odot}$ for stars #002 and #201. These results highlight the importance of open clusters as laboratories for chemically peculiar stars.
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Submitted 24 December, 2025;
originally announced December 2025.
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Chemical Abundances of M and G Dwarfs in the Hyades and Coma Berenices Open Clusters from APOGEE Spectra
Authors:
Deusalete Vilar,
Diogo Souto,
Katia Cunha,
Anderson andrade-silva,
Veronica Loaiza-Tucuri,
Fabio Wanderley,
Verne V. Smith,
Vinicius Grilo,
Cintia F. Martinez,
Barbara Rojas-Ayala,
Zachary Way
Abstract:
Open clusters are one of the best astrophysical laboratories we have available for stellar astrophysics studies. This work presents metallicities and individual abundances for fourteen M dwarfs and six G dwarfs from two well-known open clusters: Hyades and Coma Berenices. Our analysis is based on near-infrared (1.51--1.69 $μ$m), high-resolution ($R \sim 22,500$) spectra obtained from the SDSS IV/A…
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Open clusters are one of the best astrophysical laboratories we have available for stellar astrophysics studies. This work presents metallicities and individual abundances for fourteen M dwarfs and six G dwarfs from two well-known open clusters: Hyades and Coma Berenices. Our analysis is based on near-infrared (1.51--1.69 $μ$m), high-resolution ($R \sim 22,500$) spectra obtained from the SDSS IV/APOGEE Survey. Using one-dimensional, plane-parallel MARCS model atmospheres, the APOGEE line list, and the Turbospectrum radiative transfer code in local thermodynamic equilibrium, we derived spectroscopic stellar parameters for the M dwarfs, along with abundances of 13 elements (C, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, and Fe) for both M and G dwarfs. We find a high degree of chemical homogeneity within each cluster when comparing abundances derived from M and G dwarfs: $δ$[M/H] (M dwarfs -- G dwarfs) of 0.01$\pm$0.04, and 0.02$\pm$0.03 for the Hyades and Coma Berenices, respectively. The overall cluster metallicities derived from M dwarfs (Hyades: 0.16$\pm$0.03 and Coma Berenices: 0.02$\pm$0.06) are consistent with previous literature determinations. Finally, we demonstrate the value of M dwarfs as key tracers in galactic archaeology, emphasizing their potential for studying galactic metallicity gradients and chemical evolution.
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Submitted 15 September, 2025;
originally announced September 2025.
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Correlation between activity indicators: H$α$ and Ca II lines in M-dwarf stars
Authors:
R. V. Ibañez Bustos,
A. P. Buccino,
M. Flores,
C. F. Martinez,
P. J. D. Mauas
Abstract:
Different approaches have been adopted to study short- and long-term stellar magnetic activity, and although the mechanisms by which low-mass stars generate large-scale magnetic fields are not well understood, it is known that stellar rotation plays a key role. There are stars that show a cyclical behaviour in their activity which can be explained by solar dynamo or $αΩ$ dynamo models. However, wh…
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Different approaches have been adopted to study short- and long-term stellar magnetic activity, and although the mechanisms by which low-mass stars generate large-scale magnetic fields are not well understood, it is known that stellar rotation plays a key role. There are stars that show a cyclical behaviour in their activity which can be explained by solar dynamo or $αΩ$ dynamo models. However, when studying late-type dwarf stars, it is necessary to implement other indicators to analyse their magnetic activity. In the present work, we perform a comparative study between the best-known activity indicators so far defined from the Ca II and H$α$ lines to analyse M-dwarf stars. We studied a sample of 29 M stars with different chromospheric activity levels and spectral classes ranging from dM0 to dM6. To do so, we employed 1796 wide range spectra from different instruments with a median time span of observations of 21 yr. In addition, we complemented our data with photometric observations from the TESS space mission for better stellar characterisation and short-term analysis. We obtained a good and significant correlation ($rho = 0.91$) between the indexes defined from the two lines for the whole set of stars in the sample. However, we found that there is a deviation for faster rotators (with $P_{rot} < 4$ days) and higher flare activity (at least one flare per day). There is an overall positive correlation between Ca II and H$α$ emission in dM stars, except during flare events. In particular, we found that low-energy high-frequency flares could be responsible for the deviation in the linear trend in fast-rotator M dwarfs. This implies that the rotation period could be a fundamental parameter to study the stellar activity and that the rotation could drive the magnetic dynamo in low-mass active stars.
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Submitted 30 March, 2023;
originally announced March 2023.
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A Spectroscopic Analysis of a Sample of K2 Planet-Host Stars: Stellar Parameters, Metallicities and Planetary Radii
Authors:
V. Loaiza-Tacuri,
Katia Cunha,
Verne V. Smith,
Cintia F. Martinez,
Luan Ghezzi,
Simon C. Schuler,
Johanna Teske,
Steve B. Howell
Abstract:
The physical properties of transiting exoplanets are connected with the physical properties of their host stars. We present a homogeneous spectroscopic analysis based on spectra of FGK-type stars observed with the Hydra spectrograph on the WIYN telescope. We derived effective temperatures, surface gravities, and metallicities, for 81 stars observed by K2 and 33 from Kepler 1. We constructed an Fe…
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The physical properties of transiting exoplanets are connected with the physical properties of their host stars. We present a homogeneous spectroscopic analysis based on spectra of FGK-type stars observed with the Hydra spectrograph on the WIYN telescope. We derived effective temperatures, surface gravities, and metallicities, for 81 stars observed by K2 and 33 from Kepler 1. We constructed an Fe I and II line list that is adequate for the analysis of R$\sim$18,000 spectra covering 6050-6350 Å and adopted the spectroscopic technique based on equivalent width measurements. The calculations were done in LTE using Kurucz model atmospheres and the qoyllur-quipu (q$^2$) package. We validated our methodology via analysis of a benchmark solar twin and solar proxies, which are used as the solar reference. We estimated the effects that including Zeeman sensitive Fe I lines have on the derived stellar parameters for young and possibly active stars in our sample and found it not to be significant. Stellar masses and radii were derived by combining the stellar parameters with Gaia EDR3 and V magnitudes and isochrones. The measured stellar radii have 4.2\% median internal precision, leading to a median internal uncertainty of 4.4\% in the derived planetary radii. With our sample of 83 confirmed planets orbiting K2 host stars, the radius gap near R$_{planet}1.9R{_\plus}$ is detected, in agreement with previous findings. Relations between the planetary radius, orbital period and metallicity are explored and these also confirm previous findings for Kepler 1 systems.
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Submitted 10 January, 2023;
originally announced January 2023.
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A Spectroscopic Analysis of the California-Kepler Survey Sample: II. Correlations of Stellar Metallicities with Planetary Architectures
Authors:
Luan Ghezzi,
Cintia F. Martinez,
Robert F. Wilson,
Katia Cunha,
Verne V. Smith,
Steven R. Majewski
Abstract:
We present independent and self-consistent metallicities for a sample of 807 planet-hosting stars from the California-Kepler Survey from an LTE spectroscopic analysis using a selected sample of Fe I and Fe II lines. Correlations between host-star metallicities, planet radii, and planetary architecture (orbital periods - warm or hot - and multiplicity - single or multiple), were investigated using…
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We present independent and self-consistent metallicities for a sample of 807 planet-hosting stars from the California-Kepler Survey from an LTE spectroscopic analysis using a selected sample of Fe I and Fe II lines. Correlations between host-star metallicities, planet radii, and planetary architecture (orbital periods - warm or hot - and multiplicity - single or multiple), were investigated using non-parametric statistical tests. In addition to confirming previous results from the literature, e.g., that overall host star metallicity distributions differ between hot and warm planetary systems of all types, we report on a new finding that when comparing the median metallicities of hot versus warm systems, the difference for multiple Super-Earths is considerably larger when compared to that difference in single Super-Earths. The metallicity CDFs of hot single Super-Earths versus warm single Super-Earths indicate different parent stellar populations, while for Sub-Neptunes this is not the case. The transition radius between Sub-Neptunes and Sub-Saturns was examined by comparing the APOGEE metallicity distribution for the Milky Way thin disk in the solar neighborhood with metallicity distributions of host stars segregated based upon the largest known planet in their system. These comparisons reveal increasingly different metallicity distributions as the radius of the largest planet in the systems increases, with the parent stellar metallicities becoming significantly different for R$_{p}>$ 2.7 R$_{\oplus}$. The behavior of the p-values as a function of planet radius undergoes a large slope change at R$_{p}$ = 4.4 $\pm$ 0.5 R$_{\oplus}$, indicating the radius boundary between small and large planets.
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Submitted 8 July, 2021;
originally announced July 2021.
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A super-Earth and a mini-Neptune around Kepler-59
Authors:
X. Saad-Olivera,
C. F. Martinez,
A. Costa de Souza,
F. Roig 1,
D. Nesvorný
Abstract:
We characterize the radii and masses of the star and planets in the Kepler-59 system, as well as their orbital parameters. The star parameters are determined through a standard spectroscopic analysis, resulting in a mass of $1.359\pm 0.155\,M_\odot$ and a radius of $1.367\pm 0.078\,R_\odot$. The planetary radii obtained are $1.5\pm 0.1\,R_\oplus$ for the inner and $2.2\pm 0.1\,R_\oplus$ for the ou…
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We characterize the radii and masses of the star and planets in the Kepler-59 system, as well as their orbital parameters. The star parameters are determined through a standard spectroscopic analysis, resulting in a mass of $1.359\pm 0.155\,M_\odot$ and a radius of $1.367\pm 0.078\,R_\odot$. The planetary radii obtained are $1.5\pm 0.1\,R_\oplus$ for the inner and $2.2\pm 0.1\,R_\oplus$ for the outer planet. The orbital parameters and the planetary masses are determined by the inversion of Transit Timing Variations (TTV) signals. For this, we consider two different data sets, one provided by Holczer et al. 2016, with TTVs only for the planet Kepler-59c, and the other provided by Rowe et al. 2015, with TTVs signals for both planets. The inversion method is carried out by applying an algorithm of Bayesian inference (MultiNest) combined with an efficient N-body integrator (Swift). For each of the data sets, two possible solutions are found, both having the same probability according to their corresponding Bayesian evidences. All four solutions appear to be indistinguishable within their 2-$σ$ uncertainties. Nevertheless, statistical analyses show that the solutions from Rowe et al. 2015 data better characterize the data. The first and second solutions identify masses of $5_{-2}^{+4}~M_{\mathrm{\oplus}}$ and $4.6_{-2.0}^{+3.6}~M_{\mathrm{\oplus}}$, and $3.0^{+0.8}_{-0.8}~M_{\mathrm{\oplus}}$ and $2.6^{+1.9}_{-0.8}~M_{\mathrm{\oplus}}$ for the inner and outer planet, respectively. This points to a system with an inner super-Earth and an outer mini-Neptune. Dynamical studies show the planets have almost co-planar orbits with small eccentricities ($e<0.1$), close but not into the 3:2 mean motion resonance. Stability analysis indicates that this configuration is stable over million years of evolution.
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Submitted 18 October, 2019;
originally announced October 2019.
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A Spectroscopic Analysis of the California-Kepler Survey Sample: I. Stellar Parameters, Planetary Radii and a Slope in the Radius Gap
Authors:
Cintia F. Martinez,
Katia Cunha,
Luan Ghezzi,
Verne V. Smith
Abstract:
We present results from a quantitative spectroscopic analysis conducted on archival Keck/HIRES high-resolution spectra from the California-$Kepler$ Survey (CKS) sample of transiting planetary host stars identified from the $Kepler$ mission. The spectroscopic analysis was based on a carefully selected set of Fe I and Fe II lines, resulting in precise values for the stellar parameters of effective t…
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We present results from a quantitative spectroscopic analysis conducted on archival Keck/HIRES high-resolution spectra from the California-$Kepler$ Survey (CKS) sample of transiting planetary host stars identified from the $Kepler$ mission. The spectroscopic analysis was based on a carefully selected set of Fe I and Fe II lines, resulting in precise values for the stellar parameters of effective temperature (T$_{\rm eff}$) and surface gravity (log $g$). Combining the stellar parameters with $Gaia$ DR2 parallaxes and precise distances, we derived both stellar and planetary radii for our sample, with a median internal uncertainty of 2.8$\%$ in the stellar radii and 3.7$\%$ in the planetary radii. An investigation into the distribution of planetary radii confirmed the bimodal nature of this distribution for the small radius planets found in previous studies, with peaks at: $\sim$1.47 $\pm$ 0.05 R$_{\oplus}$ and $\sim$2.72 $\pm$ 0.10 R$_{\oplus}$, with a gap at $\sim$ 1.9R$_{\oplus}$. Previous studies that modeled planetary formation that is dominated by photo-evaporation predicted this bimodal radii distribution and the presence of a radius gap, or photo-evaporation valley. Our results are in overall agreement with these models. The high internal precision achieved here in the derived planetary radii clearly reveal the presence of a slope in the photo-evaporation valley for the CKS sample, indicating that the position of the radius gap decreases with orbital period; this decrease was fit by a power law of the form R$_{pl}$ $\propto$ P$^{-0.11}$, which is consistent with photo-evaporation and Earth-like core composition models of planet formation.
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Submitted 1 March, 2019;
originally announced March 2019.