Stellar diameters and temperatures. II. Main-sequence K- and M-stars

Boyajian, Tabetha S. and von Braun, Kaspar and van Belle, Gerard and McAlister, Harold A. and ten Brummelaar, Theo A. and Kane, Stephen R. and Muirhead, Philip S. and Jones, Jeremy and White, Russel and Schaefer, Gail and Ciardi, David and Henry, Todd and Lopez-Morales, Mercedes and Ridgway, Stephen and Gies, Douglas and Jao, Wei Chun and Rojas-Ayala, Barbara and Parks, J. Robert and Sturmann, Laszlo and Sturmann, Judit and Turner, Nils H. and Farrington, Chris and Goldfinger, P. J. and Berger, David H. (2012) Stellar diameters and temperatures. II. Main-sequence K- and M-stars. The Astrophysical Journal, 757 (2). pp. 112-142. ISSN 0004-637X


We present interferometric angular diameter measurements of 21 low-mass, K- and M-dwarfs made with the CHARA Array. This sample is enhanced by adding a collection of radius measurements published in the literature to form a total data set of 33K-M-dwarfs with diameters measured to better than 5%. We use these data in combination with the Hipparcos parallax and new measurements of the star's bolometric flux to compute absolute luminosities, linear radii, and effective temperatures for the stars. We develop empirical relations for K0 to M4 main-sequence stars that link the stellar temperature, radius, and luminosity to the observed (B - V), (V - R), (V - I), (V - J), (V - H), and (V - K) broadband color index and stellar metallicity [Fe/H]. These relations are valid for metallicities ranging from [Fe/H] = -0.5 to +0.1 dex and are accurate to 2%, 5%, and 4% for temperature, radius, and luminosity, respectively. Our results show that it is necessary to use metallicity-dependent transformations in order to properly convert colors into stellar temperatures, radii, and luminosities. Alternatively, we find no sensitivity to metallicity on relations we construct to the global properties of a star omitting color information, e.g., temperature-radius and temperature-luminosity. Thus, we are able to empirically quantify to what order the star's observed color index is impacted by the stellar iron abundance. In addition to the empirical relations, we also provide a representative look-up table via stellar spectral classifications using this collection of data. Robust examinations of single star temperatures and radii compared to evolutionary model predictions on the luminosity-temperature and luminosity-radius planes reveal that models overestimate the temperatures of stars with surface temperatures <5000K by 3%, and underestimate the radii of stars with radii <0.7 R ⊙ by 5%. These conclusions additionally suggest that the models over account for the effects that the stellar metallicity may have on the astrophysical properties of an object. By comparing the interferometrically measured radii for the single star population to those of eclipsing binaries, we find that for a given mass, single and binary star radii are indistinguishable. However, we also find that for a given radius, the literature temperatures for binary stars are systematically lower compared to our interferometrically derived temperatures of single stars by 200 to 300K. The nature of this offset is dependent on the validation of binary star temperatures, where bringing all measurements to a uniform and correctly calibrated temperature scale is needed to identify any influence stellar activity may have on the physical properties of a star. Lastly, we present an empirically determined H-R diagram using fundamental properties presented here in combination with those in Boyajian et al. for a total of 74 nearby, main-sequence, A- to M-type stars, and define regions of habitability for the potential existence of sub-stellar mass companions in each system.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Files associated with this item cannot be displayed due to copyright restrictions.
Faculty / Department / School: No Faculty
Date Deposited: 05 Jun 2017 21:45
Last Modified: 27 Jun 2017 04:46
Uncontrolled Keywords: Hertzsprung-Russell and C-M diagrams; infrared: stars; planetary systems; tmospheres;fundamental parameters; stars: general; ate-type stars: low-mass stars;high angular resolution; interferometric;
Fields of Research : 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Socio-Economic Objective: E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Identification Number or DOI: 10.1088/0004-637X/757/2/112

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