Stellar Diameters and Temperatures. I. Main-Sequence A, F, and G Stars

Abstract

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 fortyfour stars with an average precision of ∼ 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 model atmospheres and evolutionary isochrones. We find that for most cases, the models overestimate the effective temperature by ∼ 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 ∼ 1.3 M ⊙ . 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) color as well as spectral type showing that calibration of effective temperatures with errors ∼ 1% is now possible from interferometric angular diameters of stars.1 The average precision of these angular diameter determinations depended primarily on the brightness of the object, and was ≈ 6.5% for the 32 stars measured. 8 (Toyota et al. 2009) comment that the V r trend is not attributed to the visual companion, HD 162004 ∼ 30 ′′ away. 9 which coincidentally has been assigned the name Chara (Hoffleit & Jaschek 1991). 10 distance of the furthest star is ∼ 30 parsecsIn Figure 13, we show our data and the solution for the fit. We also show the solution from several other sources, Code et al. (1976); Gray (1992) and Lejeune et al. (1998). All the solutions shown here are approximately identical in the range of (B − V ) > 0.45.Similar to our work, the results from Code et al. (1976) are derived solely on empirical measurements. In that milestone paper, Code et al. (1976) measure the diameters of 32 stars using the Narrabri Stellar Intensity Interferometer (NSII), all being objects hotter than the Sun and most having evolved luminosity classes. We show in Figure 13 the 9 data points from Code et al. (1976) that have a (B − V ) > 0 (∼A-type and later) that are luminosity class V or IV (8 A-type objects and 1 F-type object), as well as the fit from Code et al. (1976). Comparing this fit to ours, we note that it is a few hundred Kelvin hotter than our own for 0.05 < (B − V ) < 0.3, converging at the bluest range of (B − V ) ∼ 0, as well as the reddest range (B − V ) ∼ 0.4. The offset is likely strongly connected to the fit's dependence on the sparse amount of data in this intermediate range.The function presented in Gr...

Calibrating theαparameter of convective efficiency using observed stellar properties

“…The available interferometric observations provide accurate bolometric fluxes (F BOL ) with typical uncertainties of ∼2% (e.g., Boyajian et al 2012). Combined with the interferometrically measured stellar angular diameter (θ) measurements with typical relative uncertainties of 1 ∼ 3% for our samples, the uncertainties of T eff = 2341(F BOL /θ 2 ) 1/4 are lower than 1.5%, which is precise enough as cross-validations of the spectroscopic data.…”

GaiaFGK benchmark stars: Effective temperatures and surface gravities

“…For that star (HD 145607), they assumed slightly different angular diameters, but they agree within the uncertainties. In any case, the measurements by Bazot et al (2011) show a much smaller scatter, and the model curve using their θ LD value passes through a few of the points by Boyajian et al (2012a), while the opposite case is not true.…”

“…2.2 in Boyajian et al 2013). Bazot et al (2011) and Boyajian et al (2012a) used three and two calibrator stars, respectively, with one star in common. For that star (HD 145607), they assumed slightly different angular diameters, but they agree within the uncertainties.…”

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