Spectral energy distribution of M-subdwarfs: A study of their atmospheric properties

Rajpurohit, A. S.; Reylé, C.; Allard, F.; Homeier, D.; Bayo, A.; Mousis, O.; Rajpurohit, Sangeeta; Fernández-Trincado, J. G.

doi:10.1051/0004-6361/201526776

Cited by 22 publications

(26 citation statements)

References 42 publications

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“…Exact values of these physical parameters could not be determined until recently because model atmospheres still could not reproduce many of the molecular features present in the atmospheres of cool stars. However, Rajpurohit et al (2014Rajpurohit et al ( , 2016 found that the recently updated PHOENIX stellar atmosphere models (Allard et al 2012) successfully reproduced many of the features in low metallicity stars and were therefore able to make estimates of the metallicity, surface gravity and temperature of a limited sample of M subdwarfs.…”

Section: Introductionmentioning

confidence: 99%

Radii of 88 M Subdwarfs and Updated Radius Relations for Low-metallicity M-dwarf Stars

Kesseli

Kirkpatrick

Fajardo-Acosta

et al. 2019

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M subdwarfs are low-metallicity M dwarfs that typically inhabit the halo population of the Galaxy. Metallicity controls the opacity of stellar atmospheres; in metal poor stars, hydrostatic equilibrium is reached at a smaller radius, leading to smaller radii for a given effective temperature. We compile a sample of 88 stars that span spectral classes K7 to M6 and include stars with metallicity classes from solar-metallicity dwarf stars to the lowest metallicity ultra-subdwarfs to test how metallicity changes the stellar radius. We fit models to Palomar Double Spectrograph (DBSP) optical spectra to derive effective temperatures (T eff ) and we measure bolometric luminosities (L bol ) by combining broad wavelength-coverage photometry with Gaia parallaxes. Radii are then computed by combining the T eff and L bol using the Stefan-Boltzman law. We find that for a given temperature, ultra-subdwarfs can be as much as five times smaller than their solar-metallicity counterparts. We present color-radius and color-surface brightness relations that extend down to [Fe/H] of −2.0 dex, in order to aid the radius determination of M subdwarfs, which will be especially important for the WFIRST exoplanetary microlensing survey.

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Section: Introductionmentioning

confidence: 99%

Radii of 88 M Subdwarfs and Updated Radius Relations for Low-metallicity M-dwarf Stars

Kesseli

Kirkpatrick

Fajardo-Acosta

et al. 2019

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“…The effect of non-LTE is generally taken into account where it matters most (e.g., hot stars and metal-poor stars Lanz & Hubeny 2003;Lind et al 2012) and some 3D theoretical models (e.g, Magic et al 2013) have begun to emerge but these techniques have not been widely adopted due to the fact that they are very computationally expensive. Theoretical stellar spectra are most unreliable for very cool stars and very hot stars (Allard et al 1997;Martins & Coelho 2007;Bertone et al 2008;Allard et al 2013;Rajpurohit et al 2014Rajpurohit et al , 2016. The former is a particularly acute problem for both exoplanet and galaxy studies.…”

Section: Introductionmentioning

confidence: 99%

The Extended IRTF Spectral Library: Expanded Coverage in Metallicity, Temperature, and Surface Gravity

Villaume

Conroy

Johnson

et al. 2017

ApJS

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We present a 0.7 − 2.5µm spectral library of 284 stars observed with the medium-resolution infrared spectrograph, SpeX, at the 3.0 meter NASA Infrared Telescope Facility (IRTF) on Maunakea, Hawaii. This library extends the metallicity range of the IRTF Cool Star library beyond solar metallicity to −1.7 < [Fe/H] < 0.6. All of the observed stars are also in the MILES optical stellar library, providing continuous spectral coverage for each star from 0.35 − 2.5µm. The spectra are absolute flux calibrated using Two Micron All Sky Survey photometry and the continuum shape of the spectra is preserved during the data reduction process. Synthesized JHK S colors agree with observed colors at the 1 − 2% level, on average. We also present a spectral interpolator that uses the library to create a datadriven model of spectra as a function of T eff , log g, and [Fe/H]. We use the library and interpolator to compare empirical trends with theoretical predictions of spectral feature behavior as a function of stellar parameters. These comparisons extend to the previously difficult to access low-metallicity and cool dwarf regimes, as well as the previously poorly sampled super-solar metallicity regime. The library and interpolator are publicly available.

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“…The log g of M dwarfs can be determined with the help of high-resolution spectra (Passegger et al 2016;Rajpurohit et al 2016). Passegger et al (2016); Rajpurohit et al (2016) used gravity-sensitive features such as Na I, K I and Ca I lines to determine the surface gravity in the optical. Other authors used interferometry to determine the angular diameter of the M dwarfs, together with mass-luminosity relations to derive the mass and log g (e.g.…”

Section: Introductionmentioning

confidence: 99%

Photospheric properties and fundamental parameters of M dwarfs

Rajpurohit

Allard

Teixeira

et al. 2018

A&A

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Context. M dwarfs are an important source of information when studying and probing the lower end of the Hertzsprung-Russell (HR) diagram, down to the hydrogen-burning limit. Being the most numerous and oldest stars in the galaxy, they carry fundamental information on its chemical history. The presence of molecules in their atmospheres, along with various condensed species, complicates our understanding of their physical properties and thus makes the determination of their fundamental stellar parameters more challenging and difficult. Aims. The aim of this study is to perform a detailed spectroscopic analysis of the high-resolution H-band spectra of M dwarfs in order to determine their fundamental stellar parameters and to validate atmospheric models. The present study will also help us to understand various processes, including dust formation and depletion of metals onto dust grains in M dwarf atmospheres. The high spectral resolution also provides a unique opportunity to constrain other chemical and physical processes that occur in a cool atmosphere.Methods. The high-resolution APOGEE spectra of M dwarfs, covering the entire H-band, provide a unique opportunity to measure their fundamental parameters. We have performed a detailed spectral synthesis by comparing these high-resolution H-band spectra to that of the most recent BT-settl model and have obtained fundamental parameters such as effective temperature, surface gravity, and metallicity (T eff , log g and [Fe/H], respectively). Results. We have determined T eff , log g and [Fe/H] for 45 M dwarfs using high-resolution H-band spectra. The derived T eff for the sample ranges from 3100 to 3900 K, values of log g lie in the range 4.5 ≤ log g ≤ 5.5, and the resulting metallicities lie in the range -0.5 ≤ [Fe/H] ≤ +0.5. We have explored systematic differences between effective temperature and metallicity calibrations with other studies using the same sample of M dwarfs. We have also shown that the stellar parameters determined using the BT-Settl model are more accurate and reliable compared to other comparative studies using alternative models.

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Spectral energy distribution of M-subdwarfs: A study of their atmospheric properties

Cited by 22 publications

References 42 publications

Radii of 88 M Subdwarfs and Updated Radius Relations for Low-metallicity M-dwarf Stars

Radii of 88 M Subdwarfs and Updated Radius Relations for Low-metallicity M-dwarf Stars

The Extended IRTF Spectral Library: Expanded Coverage in Metallicity, Temperature, and Surface Gravity

Photospheric properties and fundamental parameters of M dwarfs

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