We report on K-band interferometric observations of the bright, rapidly rotating star Regulus (type B7 V) made with the CHARA Array on Mount Wilson, California. Through a combination of ...interferometric and spectroscopic measurements, we have determined for Regulus the equatorial and polar diameters and temperatures, the rotational velocity and period, the inclination and position angle of the spin axis, and the gravity darkening coefficient. These first results from the CHARA Array provide the first interferometric measurement of gravity darkening in a rapidly rotating star and represent the first detection of gravity darkening in a star that is not a member of an eclipsing binary system.
We present new near-infrared interferometric data from the CHARA array and the Keck Interferometer on the circumstellar disk of the young star, TW Hya, a proposed 'transition disk.' We use these ...data, as well as previously published, spatially resolved data at 10 Delta *mm and 7 mm, to constrain disk models based on a standard flared disk structure. We find that we can match the interferometry data sets and the overall spectral energy distribution with a three-component model, which combines elements at spatial scales proposed by previous studies: optically thin, emission nearest the star, an inner optically thick ring of emission at roughly 0.5 AU followed by an opacity gap and, finally, an outer optically thick disk starting at ~4 AU. The model demonstrates that the constraints imposed by the spatially resolved data can be met with a physically plausible disk but this requires a disk containing not only an inner gap in the optically thick disk as previously suggested, but also a gap between the inner and outer optically thick disks. Our model is consistent with the suggestion by Calvet et al. of a planet with an orbital radius of a few AU. We discuss the implications of an opacity gap within the optically thick disk.
Context. The parallax of pulsation, and its implementations such as the Baade-Wesselink method and the infrared surface brightness technique, is an elegant method to determine distances of pulsating ...stars in a quasi-geometrical way. However, these classical implementations in general only use a subset of the available observational data. Aims. Freedman & Madore (2010, ApJ, 719, 335) suggested a more physical approach in the implementation of the parallax of pulsation in order to treat all available data. We present a global and model-based parallax-of-pulsation method that enables including any type of observational data in a consistent model fit, the SpectroPhoto-Interferometric modeling of Pulsating Stars (SPIPS). Methods. We implemented a simple model consisting of a pulsating sphere with a varying effective temperature and a combination of atmospheric model grids to globally fit radial velocities, spectroscopic data, and interferometric angular diameters. We also parametrized (and adjusted) the reddening and the contribution of the circumstellar envelopes in the near-infrared photometric and interferometric measurements. Results. We show the successful application of the method to two stars: δ Cep and η Aql. The agreement of all data fitted by a single model confirms the validity of the method. Derived parameters are compatible with publish values, but with a higher level of confidence. Conclusions. The SPIPS algorithm combines all the available observables (radial velocimetry, interferometry, and photometry) to estimate the physical parameters of the star (ratio distance/p-factor, Teff, presence of infrared excess, color excess, etc). The statistical precision is improved (compared to other methods) thanks to the large number of data taken into account, the accuracy is improved by using consistent physical modeling and the reliability of the derived parameters is strengthened thanks to the redundancy in the data.
We present the results of long-baseline interferometric observations of the classical Cepheids Polaris and delta Cep in the near infrared K' band (1.9-2.3 mu m), using the FLUOR instrument of the ...CHARA Array. Following our previous detection of a circumstellar envelope (CSE) around Car (Kervella et al. 2006), we report similar detections around Polaris and delta Cep. Owing to the large data set acquired on Polaris, in both the first and second lobes of visibility function, we have detected the presence of a circum-stellar envelope (CSE), located at 2.4 plus or minus 0.1 stellar radii, accounting for 1.5 plus or minus 0.4% of the stellar flux in the K band. A similar model is applied to the delta Cep data, which shows improved agreement compared to a model without CSE. Finally, we find that the bias in estimating the angular diameter of delta Cep in the framework of the Baade-Wesselink method (Merand et al. 2005b) is of the order of 1% or less in the K band. A complete study of the influence of the CSE is proposed in this context, showing that at the optimum baseline for angular diameter variation detection, the bias is of the order of the formal precision in the determination of the delta Cep pulsation amplitude (1.6%).
Direct detection of thermal emission from nearby hot Jupiters has greatly advanced our knowledge of extrasolar planets in recent years. Since hot Jupiter systems can be regarded as analogs of ...high-contrast binaries, ground-based infrared long-baseline interferometers have the potential to resolve them and detect their thermal emission with precision closure phase—a method that is immune to the systematic errors induced by the Earth’s atmosphere. In this work, we present closure-phase studies toward direct detection of nearby hot Jupiters using the CHARA interferometer array outfitted with the MIRC instrument. We carry out closure-phase simulations and conduct a large number of observations for the best candidate υ And. Our experiments suggest that the method is feasible with highly stable and precise closure phases. However, we also find much larger systematic errors than expected in the observations, most likely caused by dispersion across different wavelengths. We find that using higher spectral resolution modes (e.g.,
R = 150
R
=
150
) can significantly reduce the systematics. By combining all calibrators in an observing run together, we are able to roughly recalibrate the lower spectral resolution data, allowing us to obtain upper limits of the star-planet contrast ratios of υ And b across the
H
H
band. The data also allow us to get a refined stellar radius of1.625 ± 0.011 R
⊙
1.625
±
0.011
R
⊙
. Our best upper limit corresponds to a contrast ratio of2.1 × 103 : 1
2.1
×
10
3
:
1
with 90% confidence level at 1.52 μm, suggesting that we are starting to have the capability of constraining atmospheric models of hot Jupiters with interferometry. With recent and upcoming improvements of CHARA/MIRC, the prospect of detecting emission from hot Jupiters with closure phases is promising.
Context. The prospects for using the asteroseismology of rapidly oscillating Ap (roAp) stars are hampered by the large uncertainty in fundamental stellar parameters. Results in the literature for the ...effective temperature (Teff) often span a range of 1000 K. Aims. Our goal is to reduce systematic errors and improve the Teff calibration of Ap stars based on new interferometric measurements. Methods. We obtained long-baseline interferometric observations of β CrB using the CHARA/FLUOR instrument. To disentangle the flux contributions of the two components of this binary star, we obtained VLT/NACO adaptive optics images. Results. We determined limb-darkened angular diameters of 0.699±0.017 mas for β CrB A (from interferometry) and 0.415±0.017 mas for β CrB B (from surface brightness-colour relations), corresponding to radii of 2.63±0.09 ${R}_\odot$ (3.4% uncertainty) and 1.56±0.07 ${R}_\odot$ (4.5%). The combined bolometric flux of the A+B components was determined from satellite UV data, spectrophotometry in the visible, and broadband data in the infrared. The flux from the B component constitutes 16±4% of the total flux and was determined by fitting an ATLAS9 model atmosphere to the broad-band NACO J and K magnitudes. By combining the flux of the A component with its measured angular diameter, we determined the effective temperature Teff (A) = 7980±180 K (2.3%). Conclusions. Our new interferometric and imaging data enable nearly model-independent determination of the effective temperature of β CrB A. Including our recent study of α Cir, we now have direct Teff measurements of two of the brightest roAp stars, providing a strong benchmark for improved calibration of the Teff scale for Ap stars. This will support the use of potentially strong constraints imposed by asteroseismic studies of roAp stars.
We present observations of the A7 IV-V star Alderamin (a Cep, HR 8162, HD 203280) from the Georgia State University CHARA Array. These infrared interferometric angular size measurements indicate a ...noncircular projected disk brightness distribution for this known rapid rotator. The interferometric observations are modeled as arising from an elongated rigid atmosphere, with apparent polar and equatorial radii of r sub(p) = 0.6753 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(0) sub(0) super(1) sub(1) super(1) sub(3) super(9) sub(5) and r sub(e) = 0.8767 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(0) sub(0) super(2) sub(1) super(9) sub(8) super(3) sub(3) mas, respectively, for a difference of 201 c 32 kas, and with an axial ratio of r sub(e)/r sub(p) = 1.298 c 0.051. Using the Hipparcos distance of 14.96 c 0.11 pc, these angular measures translate to 2.18 c 0.05 and 2.82 c 0.10 R sub( )The inclination of + 1.S Alderamin to the line of sight indicated by this modeling is effectively edge-on (i = 88.2 super(+) sub(-) super(1) sub(1) super(.) sub(3) super(8) sub(.3) deg). The star has a true rotational velocity of 283 c10 km s super(-1) (683% of breakup velocity) and a polar temperature of roughly 8400 K. Significantly, a necessary aspect of this modeling is a determination of the gravity-darkening coefficient, which at a value of b = 0.084 -0.049 is consistent with a convective photosphere, as expected for an A7 IV-V star. Our detailed characterization of this object allows us to investigate various scenarios for the angular momentum history of Alderamin and the appropriateness of certain stellar evolution models.
We present the first K'-band, long-baseline interferometric observations of the northern Be stars g Cas, h 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 Ha and continuum polarimetric observations. We find that the angular size of the K' disk emission is smaller than that determined for the Ha emission, and we argue that the difference is the result of a larger Ha 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 h Per and Dra. We also present contemporaneous observations of the Ha, Hg, and Brg 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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