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Title: STELLAR DIAMETERS AND TEMPERATURES. II. MAIN-SEQUENCE K- AND M-STARS

Abstract

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 33 K-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 {approx}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 {approx}2%, {approx}5%, and {approx}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 andmore » 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 <5000 K by {approx}3%, and underestimate the radii of stars with radii <0.7 R{sub Sun} by {approx}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 {approx}200 to 300 K. 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.« less

Authors:
; ; ; ; ; ; ;  [1]; ; ;  [2];  [3]; ; ; ;  [4];  [5];  [6];  [7];  [8] more »; « less
  1. Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, P.O. Box 4106, Atlanta, GA 30302-4106 (United States)
  2. NASA Exoplanet Science Institute, California Institute of Technology, MC 100-22, Pasadena, CA 91125 (United States)
  3. Lowell Observatory, Flagstaff, AZ 86001 (United States)
  4. The CHARA Array, Mount Wilson Observatory, Mount Wilson, CA 91023 (United States)
  5. Department of Astronomy, California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, CA 91125 (United States)
  6. Institut de Ciencies de L'Espai (CSIC-IEEC), E-08193 Bellaterra (Spain)
  7. National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726-6732 (United States)
  8. Department of Astrophysics, Division of Physical Sciences, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States)
Publication Date:
OSTI Identifier:
22092211
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 757; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; BINARY STARS; BOLOMETERS; COLOR; DIAGRAMS; DWARF STARS; INDEXES; INTERFEROMETRY; IRON; LUMINOSITY; MAIN SEQUENCE STARS; MASS; POTENTIALS; RESOLUTION; SENSITIVITY; STELLAR ACTIVITY

Citation Formats

Boyajian, Tabetha S., McAlister, Harold A., Jones, Jeremy, White, Russel, Henry, Todd, Gies, Douglas, Jao, Wei-Chun, Parks, J. Robert, Von Braun, Kaspar, Kane, Stephen R., Ciardi, David, Van Belle, Gerard, Ten Brummelaar, Theo A., Schaefer, Gail, Sturmann, Laszlo, Sturmann, Judit, Muirhead, Philip S., Lopez-Morales, Mercedes, Ridgway, Stephen, Rojas-Ayala, Barbara, and and others. STELLAR DIAMETERS AND TEMPERATURES. II. MAIN-SEQUENCE K- AND M-STARS. United States: N. p., 2012. Web. doi:10.1088/0004-637X/757/2/112.
Boyajian, Tabetha S., McAlister, Harold A., Jones, Jeremy, White, Russel, Henry, Todd, Gies, Douglas, Jao, Wei-Chun, Parks, J. Robert, Von Braun, Kaspar, Kane, Stephen R., Ciardi, David, Van Belle, Gerard, Ten Brummelaar, Theo A., Schaefer, Gail, Sturmann, Laszlo, Sturmann, Judit, Muirhead, Philip S., Lopez-Morales, Mercedes, Ridgway, Stephen, Rojas-Ayala, Barbara, & and others. STELLAR DIAMETERS AND TEMPERATURES. II. MAIN-SEQUENCE K- AND M-STARS. United States. doi:10.1088/0004-637X/757/2/112.
Boyajian, Tabetha S., McAlister, Harold A., Jones, Jeremy, White, Russel, Henry, Todd, Gies, Douglas, Jao, Wei-Chun, Parks, J. Robert, Von Braun, Kaspar, Kane, Stephen R., Ciardi, David, Van Belle, Gerard, Ten Brummelaar, Theo A., Schaefer, Gail, Sturmann, Laszlo, Sturmann, Judit, Muirhead, Philip S., Lopez-Morales, Mercedes, Ridgway, Stephen, Rojas-Ayala, Barbara, and and others. 2012. "STELLAR DIAMETERS AND TEMPERATURES. II. MAIN-SEQUENCE K- AND M-STARS". United States. doi:10.1088/0004-637X/757/2/112.
@article{osti_22092211,
title = {STELLAR DIAMETERS AND TEMPERATURES. II. MAIN-SEQUENCE K- AND M-STARS},
author = {Boyajian, Tabetha S. and McAlister, Harold A. and Jones, Jeremy and White, Russel and Henry, Todd and Gies, Douglas and Jao, Wei-Chun and Parks, J. Robert and Von Braun, Kaspar and Kane, Stephen R. and Ciardi, David and Van Belle, Gerard and Ten Brummelaar, Theo A. and Schaefer, Gail and Sturmann, Laszlo and Sturmann, Judit and Muirhead, Philip S. and Lopez-Morales, Mercedes and Ridgway, Stephen and Rojas-Ayala, Barbara and and others},
abstractNote = {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 33 K-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 {approx}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 {approx}2%, {approx}5%, and {approx}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 <5000 K by {approx}3%, and underestimate the radii of stars with radii <0.7 R{sub Sun} by {approx}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 {approx}200 to 300 K. 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.},
doi = {10.1088/0004-637X/757/2/112},
journal = {Astrophysical Journal},
number = 2,
volume = 757,
place = {United States},
year = 2012,
month =
}
  • We have executed a survey of nearby, main-sequence A-, F-, and G-type stars with the CHARA Array, successfully measuring the angular diameters of forty-four stars with an average precision of {approx}1.5%. We present new measures of the bolometric flux, which in turn leads to an empirical determination of the effective temperature for the stars observed. In addition, these CHARA-determined temperatures, radii, and luminosities are fit to Yonsei-Yale model isochrones to constrain the masses and ages of the stars. These results are compared to indirect estimates of these quantities obtained by collecting photometry of the stars and applying them to modelmore » atmospheres and evolutionary isochrones. We find that for most cases, the models overestimate the effective temperature by {approx}1.5%-4% when compared to our directly measured values. The overestimated temperatures and underestimated radii in these works appear to cause an additional offset in the star's surface gravity measurements, which consequently yield higher masses and younger ages, in particular for stars with masses greater than {approx}1.3 M{sub Sun }. Additionally, we compare our measurements to a large sample of eclipsing binary stars, and excellent agreement is seen within both data sets. Finally, we present temperature relations with respect to (B - V) and (V - K) colors as well as spectral type, showing that calibration of effective temperatures with errors {approx}1% is now possible from interferometric angular diameters of stars.« less
  • Based on CHARA Array measurements, we present the angular diameters of 23 nearby, main-sequence stars, ranging from spectral types A7 to K0, 5 of which are exoplanet host stars. We derive linear radii, effective temperatures, and absolute luminosities of the stars using Hipparcos parallaxes and measured bolometric fluxes. The new data are combined with previously published values to create an Angular Diameter Anthology of measured angular diameters to main-sequence stars (luminosity classes V and IV). This compilation consists of 125 stars with diameter uncertainties of less than 5%, ranging in spectral types from A to M. The large quantity ofmore » empirical data is used to derive color-temperature relations to an assortment of color indices in the Johnson (BVR{sub J} I{sub J} JHK), Cousins (R{sub C} I{sub C}), Kron (R{sub K} I{sub K}), Sloan (griz), and WISE (W{sub 3} W{sub 4}) photometric systems. These relations have an average standard deviation of {approx}3% and are valid for stars with spectral types A0-M4. To derive even more accurate relations for Sun-like stars, we also determined these temperature relations omitting early-type stars (T{sub eff} > 6750 K) that may have biased luminosity estimates because of rapid rotation; for this subset the dispersion is only {approx}2.5%. We find effective temperatures in agreement within a couple of percent for the interferometrically characterized sample of main-sequence stars compared to those derived via the infrared flux method and spectroscopic analysis.« less
  • The number of stellar angular diameter measurements has greatly increased over the past few years due to innovations and developments in the field of long baseline optical interferometry. We use a collection of high-precision angular diameter measurements for nearby, main-sequence stars to develop empirical relations that allow the prediction of stellar angular sizes as a function of observed photometric color. These relations are presented for a combination of 48 broadband color indices. We empirically show for the first time a dependence on metallicity of these relations using Johnson (B – V) and Sloan (g – r) colors. Our relations aremore » capable of predicting diameters with a random error of less than 5% and represent the most robust and empirical determinations of stellar angular sizes to date.« less