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...

We present the first K 0 -band, long-baseline interferometric observations of the northern Be stars Cas, Per, Tau, and Dra. The measurements were made with multiple telescope pairs of the CHARA Array interferometer and in every case the observations indicate that the circumstellar disks of the targets are resolved. We fit the interferometric visibilities with predictions from a simple disk model that assumes an isothermal gas in Keplerian rotation. We derive fits of the four model parameters (disk base density, radial density exponent, disk normal inclination, and position angle) for each of the targets. The resulting densities are in broad agreement with prior studies of the IR excess flux, and the resulting orientations generally agree with those from interferometric H and continuum polarimetric observations. We find that the angular size of the K 0 disk emission is smaller than that determined for the H emission, and we argue that the difference is the result of a larger H opacity and the relatively larger neutral hydrogen fraction with increasing disk radius. All the targets are known binaries with faint companions, and we find that companions appear to influence the interferometric visibilities in the cases of Per and Dra. We also present contemporaneous observations of the H, H, and Br emission lines. Synthetic model profiles of these lines that are based on the same disk inclination and radial density exponent as derived from the CHARA Array observations match the observed emission line strength if the disk base density is reduced by %1.7 dex.

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Using CHARA and VLTI near-infrared spectro-interferometry with hectometric baseline lengths (up to 330 m) and with high spectral resolution (up to λ/Δλ = 12, 000), we studied the gas distribution and kinematics around two classical Be stars. The combination of high spatial and spectral resolution achieved allows us to constrain the gas velocity field on scales of a few stellar radii and to obtain, for the first time in optical interferometry, a dynamical mass estimate using the position-velocity analysis technique known from radio astronomy. For our first target star, β Canis Minoris, we model the H + K-band continuum and Brγ-line geometry with a near-critical rotating stellar photosphere and a geometrically thin equatorial disk. Testing different disk rotation laws, we find that the disk is in Keplerian rotation (v(r) ∝ r −0.5±0.1) and derive the disk position angle (140 • ± 1. • 7), inclination (38. • 5 ± 1 •), and the mass of the central star (3.5 ± 0.2 M). As a second target star, we observed the prototypical Be star ζ Tauri and spatially resolved the Brγ emission as well as nine transitions from the hydrogen Pfund series (Pf 14-22). Comparing the spatial origin of the different line transitions, we find that the Brackett (Brγ), Pfund (Pf 14-17), and Balmer (Hα) lines originate from different stellocentric radii (R cont < R Pf < R Brγ ∼ R Hα), which we can reproduce with an LTE line radiative transfer computation. Discussing different disk-formation scenarios, we conclude that our constraints are inconsistent with wind compression models predicting a strong outflowing velocity component, but support viscous decretion disk models, where the Keplerian-rotating disk is replenished with material from the near-critical rotating star.

The emission-line Be star HD 215227 lies within the positional error circle of the newly identified gamma-ray source AGL J2241+4454. We present new blue spectra of the star, and we point out the morphological and variability similarities to other Be binaries. An analysis of the available optical photometry indicates a variation with a period of 60.37 ± 0.04 d, which may correspond to an orbital modulation of the flux from the disk surrounding the Be star. The distance to the star of 2.6 kpc and its relatively large Galactic latitude suggest that the binary was ejected from the plane by a supernova explosion that created the neutron star or black hole companion. The binary and runaway properties of HD 215227 make it an attractive candidate as the optical counterpart of AGL J2241+4454 and as a new member of the small class of gamma-ray emitting binaries.