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Register a new userAngular Diameters and Effective Temperatures of Twenty-five K Giant Stars from the CHARA Array
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Using Georgia State Universitys CHARA Array interferometer, we measured angular diameters for 25 giant stars, six of which host exoplanets. The combination of these measurements and Hipparcos parallaxes produce physical linear radii for the sample. Except for two outliers, our values match angular diameters and physical radii estimated using photometric methods to within the associated errors with the advantage that our uncertainties are significantly lower. We also calculated the effective temperatures for the stars using the newly-measured diameters. Our values do not match those derived from spectroscopic observations as well, perhaps due to the inherent properties of the methods used or because of a missing source of extinction in the stellar models that would affect the spectroscopic temperatures.
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We present interferometric observations of six O-type stars that were made with the Precision Astronomical Visible Observations (PAVO) beam combiner at the Center for High Angular Resolution Astronomy (CHARA) Array. The observations include multiple brackets for three targets, $lambda$~Ori~A, $zeta$~Oph, and 10~Lac, but there are only preliminary, single observations of the other three stars, $xi$~Per, $alpha$~Cam, and $zeta$~Ori~A. The stellar angular diameters range from 0.55 milliarcsec for $zeta$~Ori~A down to 0.11 mas for 10~Lac, the smallest star yet resolved with the CHARA Array. The rotational oblateness of the rapidly rotating star $zeta$ Oph is directly measured for the first time. We assembled ultraviolet to infrared flux measurements for these stars, and then derived angular diameters and reddening estimates using model atmospheres and an effective temperature set by published results from analysis of the line spectrum. The model-based angular diameters are in good agreement with observed angular diameters. We also present estimates for the effective temperatures of these stars derived by setting the interferometric angular size and fitting the spectrophotometry.
We measured the angular diameter of the lithium-rich K giant star HD 148293 using Georgia State Universitys Center for High Angular Resolution Astronomy (CHARA) Array interferometer. We used our measurement to calculate the stars effective temperature, which allowed us to place it on an H-R diagram to compare it with other Li-rich giants. Its placement supports the evidence presented by Charbonnel & Balachandran that it is undergoing a brief stage in its evolution where Li is being created.
Debate over the planet occurrence rates around intermediate-mass stars has hinged on the accurate determination of masses of evolved stars, and has been exacerbated by a paucity of reliable, directly-measured fundamental properties for these stars. We present long-baseline optical interferometry of five evolved intermediate-mass ($sim,1.5,mathrm{M}_odot$) planet-hosting stars using the PAVO beam combiner at the CHARA Array, which we combine with bolometric flux measurements and parallaxes to determine their radii and effective temperatures. We measured the radii and effective temperatures of 6 Lyncis ($5.12pm0.16,mathrm{R}_odot$, $4949pm58,mathrm{K}$), 24 Sextantis ($5.49pm0.18,mathrm{R}_odot$, $4908pm65,mathrm{K}$), $kappa$ Coronae Borealis ($4.77pm0.07,mathrm{R}_odot$, $4870pm47,mathrm{K}$), HR 6817 ($4.45pm0.08,mathrm{R}_odot$, $5013pm59,mathrm{K}$), and HR 8641 ($4.91pm0.12,mathrm{R}_odot$, $4950pm68,mathrm{K}$). We find disagreements of typically 15 per cent in angular diameter and $sim$200 K in temperature compared to interferometric measurements in the literature, yet good agreement with spectroscopic and photometric temperatures, concluding that the previous interferometric measurements may have been affected by systematic errors exceeding their formal uncertainties. Modelling based on BaSTI isochrones using various sets of asteroseismic, spectroscopic, and interferometric constraints tends to favour slightly ($sim$15 per cent) lower masses than generally reported in the literature.
We present interferometric diameter measurements of 21 K- and M- dwarfs made with the CHARA Array. This sample is enhanced by literature radii measurements to form a data set of 33 K-M dwarfs with diameters measured to better than 5%. For all 33 stars, we compute absolute luminosities, linear radii, and effective temperatures (Teff). We develop empirical relations for simK0 to M4 main- sequence stars between the stellar Teff, radius, and luminosity to broad-band color indices and metallicity. These relations are valid for metallicities between [Fe/H] = -0.5 and +0.1 dex, and are accurate to ~2%, ~5%, and ~4% for Teff, radius, and luminosity, respectively. Our results show that it is necessary to use metallicity dependent transformations to convert colors into stellar Teffs, radii, and luminosities. We find no sensitivity to metallicity on relations between global stellar properties, e.g., Teff-radius and Teff-luminosity. Robust examinations of single star Teffs and radii compared to evolutionary model predictions on the luminosity-Teff and luminosity-radius planes reveals that models overestimate the Teffs of stars with Teff < 5000 K by ~3%, and underestimate the radii of stars with radii < 0.7 Rodot by ~5%. These conclusions additionally suggest that the models overestimate the effects that the stellar metallicity may have on the astrophysical properties of an object. By comparing the interferometrically measured radii for single stars to those of eclipsing binaries, we find that single and binary star radii are consistent. However, the literature Teffs for binary stars are systematically lower compared to Teffs of single stars by ~ 200 to 300 K. Lastly, we present a empirically determined HR diagram 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. [abridged]
We measured the angular diameter of the exoplanet host star iota Dra with Georgia State Universitys Center for High Angular Resolution Astronomy (CHARA) Array interferometer, and, using the stars parallax and photometry from the literature, calculated its physical radius and effective temperature. We then combined our results with stellar oscillation frequencies from Zechmeister et al. (2008) and orbital elements from Kane et al. (2010) to determine the masses for the star and exoplanet. Our value for the central stars mass is 1.82 +/- 0.23 M_Sun, which means the exoplanets minimum mass is 12.6 +/- 1.1 M_Jupiter. Using our new effective temperature, we recalculated the habitable zone for the system, though it is well outside the star-planet separation.
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