Mount Hermon, CA, United States
Mount Hermon, CA, United States

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Mourard D.,French National Center for Scientific Research | Harmanec P.,Charles University | Stencel R.,University of Denver | Berio P.,French National Center for Scientific Research | And 15 more authors.
Astronomy and Astrophysics | Year: 2012

The enigmatic binary, ε Aur, is yielding its parameters as a result of new methods applied to the recent eclipse, including optical spectro-interferometry with the VEGA beam combiner at the CHARA Array. VEGA/CHARA visibility measurements from 2009 to 2011 indicate the formation of emission wings of Hα in an expanding zone almost twice the photospheric size of the F star, namely, in a stellar wind. These may be caused by shocks in the atmosphere from large scale convective or multi-periodic pulsation modes emerging from the star. During the total eclipse phase in 2010, when the disk was in the line of sight, we saw broadening of the Hα absorption and a less steep drop of the visibility curve, consistent with the addition of neutral hydrogen in the line of sight but extended above and below the plane of the interferometrically imaged disk itself. This provides a unique constraint on the scale height of the gaseous component of the disk material, and, based on some additional assumptions, points to a mass of the central object being 2.4 to 5.5 M ⊙ for a distance of 650 pc or 3.8 to 9.1 M ⊙ for a distance of 1050 pc. These results can be tested during coming observing seasons as the star moves from eclipse phase toward quadrature. © 2012 ESO.


Ten Brummelaar T.A.,CHARA Array | McAlister H.A.,Georgia State University | Ridgway S.,National Optical Astronomy Observatory
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

The CHARA Array has been a PI led, low budget, and low manpower operation, and has followed a fairly unconventional path in its development. In this, the third paper of a series of three, we discuss some of the engineering and design decisions made along the way, some right and some wrong, with a focus on the choice between in-house development and the purchase of pre-built, or sub-contracted, subsystems. Along with these issues we will also address a few parts of the system that we might have done differently given our current knowledge, and those that somehow turned out very well. © 2014 SPIE.


Bigot L.,University of Nice Sophia Antipolis | Mourard D.,University of Nice Sophia Antipolis | Berio P.,University of Nice Sophia Antipolis | Thevenin F.,University of Nice Sophia Antipolis | And 20 more authors.
Astronomy and Astrophysics | Year: 2011

Context. The interpretation of stellar pulsations in terms of internal structure depends on the knowledge of the fundamental stellar parameters. Long-base interferometers permit us to determine very accurate stellar radii, which are independent constraints for stellar models that help us to locate the star in the HR diagram. Aims. Using a direct interferometric determination of the angular diameter and advanced three-dimensional (3D) modeling, we derive the radius of the CoRoT target HD  49933 and reduce the global stellar parameter space compatible with seismic data. Methods. The VEGA/CHARA spectro-interferometer is used to measure the angular diameter of the star. A 3D radiative hydrodynamical simulation of the surface is performed to compute the limb darkening and derive a reliable diameter from visibility curves. The other fundamental stellar parameters (mass, age, and Teff) are found by fitting the large and small p-mode frequency separations using a stellar evolution model that includes microscopic diffusion. Results. We obtain a limb-darkened angular diameter of θLD = 0.445 ± 0.012 mas. With the Hipparcos parallax, we obtain a radius of R = 1.42 ± 0.04 Rȯ. The corresponding stellar evolution model that fits both large and small frequency separations has a mass of 1.20 ± 0.08 M ȯ and an age of 2.7 Gy. The atmospheric parameters are T eff = 6640 ± 100 K, log g = 4.21 ± 0.14, and [Fe/H] =-0.38. © 2011 ESO.


Meilland A.,Max Planck Institute for Radio Astronomy | Delaa O.,French National Center for Scientific Research | Stee P.,French National Center for Scientific Research | Kanaan S.,University of Valparaíso | And 17 more authors.
Astronomy and Astrophysics | Year: 2011

Context. Classical Be stars are hot non-supergiant stars surrounded by a gaseous circumstellar disk that is responsible for the observed IR-excess and emission lines. The influence of binarity on these phenomena remains controversial. Aims.δ Sco is a binary system whose primary suddenly began to exhibit the Be phenomenon at the last periastron in 2000. We want to constrain the geometry and kinematics of its circumstellar environment. Methods. We observed the star between 2007 and 2010 using spectrally-resolved interferometry with the VLTI/AMBER and CHARA/VEGA instruments. Results. We found orbital elements that are compatible with previous estimates. The next periastron should take place around July 5, 2011 (± 4 days). We resolved the circumstellar disk in the Hα (FWHM = 4.8 ± 1.5 mas), Brγ (FWHM = 2.9 ± 0.5mas), and the 2.06 μm He i (FWHM = 2.4 ± 0.3 mas) lines, as well as in the K band continuum (FWHM 2.4 mas). The disk kinematics are dominated by the rotation, with a disk expansion velocity on the order of 0.2 km s-1. The rotation law within the disk is compatible with Keplerian rotation. Conclusions. As the star probably rotates at about 70% of its critical velocity, the ejection of matter does not seem to be dominated by rotation. However, the disk geometry and kinematics are similar to the previously studied quasi-critically rotating Be stars, α Ara, ψ Per and 48 Per. © 2011 ESO.


Ten Brummelaar T.A.,CHARA Array | Sturmann J.,CHARA Array | McAlister H.A.,Georgia State University | Sturmann L.,CHARA Array | And 5 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

The CHARA Array1 is a six telescope optical/IR interferometer run by the Center for High Angular Resolution Astronomy of Georgia State University and is located at Mount Wilson Observatory just to the north of Los Angeles California. The CHARA Array has the largest operational baselines in the world and has been in regular use for scientific observations since 2004. Our most sensitive beam combiner capable of measuring closure phases is the CLassic Interferometry with Multiple Baselines beam combiner known as CLIMB. In this paper we discuss the design and layout of CLIMB with a particular focus on the data analysis methodology. This analysis is presented in a very general form and will have applications in many other beam combiners. We also present examples of on sky data showing the precision and stability of both amplitude and closure phase measurements. © 2012 SPIE.


Perraut K.,CNRS Grenoble Institute for Particle Astrophysics and Cosmology Laboratory | Borgniet S.,CNRS Grenoble Institute for Particle Astrophysics and Cosmology Laboratory | Cunha M.,University of Porto | Bigot L.,French National Center for Scientific Research | And 11 more authors.
Astronomy and Astrophysics | Year: 2013

Context. Owing to the strong magnetic field and related abnormal surface layers existing in rapidly oscillating Ap (roAp) stars, systematic errors are likely to be present when determining their effective temperatures, which potentially compromises asteroseismic studies of this class of pulsators. Aims. Using the unique angular resolution provided by long-baseline visible interferometry, our goal is to determine accurate angular diameters of a number of roAp targets, so as to derive unbiased effective temperatures (T eff) and provide a Teff calibration for these stars. Methods. We obtained long-baseline interferometric observations of 10 Aql with the visible spectrograph VEGA at the combined focus of the CHARA array. We derived the limb-darkened diameter of this roAp star from our visibility measurements. Based on photometric and spectroscopic data available in the literature, we estimated the star's bolometric flux and used it, in combination with its parallax and angular diameter, to determine the star's luminosity and effective temperature. Results. We determined a limb-darkened angular diameter of 0.275 ± 0.009 mas and deduced a linear radius of R = 2.32 ± 0.09 R⊙. For the bolometric flux we considered two datasets, leading to an effective temperature of Teff = 7800 ± 170 K and a luminosity of L/L⊙ = 18 ± 1 or Teff = 8000 ± 210 K and L/L ⊙ = 19 ± 2. Finally we used these fundamental parameters together with the large frequency separation determined by asteroseismic observations to constrain the mass and the age of 10 Aql, using the CESAM stellar evolution code. Assuming a solar chemical composition and ignoring all kinds of diffusion and settling of elements, we obtained a mass M/M⊙ ~ 1.92 and an age of ~780 Gy or a mass M/M⊙ ~ 1.95 and an age of ~740 Gy, depending on the derived value of the bolometric flux. Conclusions. For the first time, thanks to the unique capabilities of VEGA, we managed to determine an accurate angular diameter for a star smaller than 0.3 mas and to derive its fundamental parameters. In particular, by only combining our interferometric data and the bolometric flux, we derived an effective temperature that can be compared to those derived from atmosphere models. Such fundamental parameters can help for testing the mechanism responsible for the excitation of the oscillations observed in the magnetic pulsating stars. © 2013 ESO.


Chesneau O.,University of Nice Sophia Antipolis | Meilland A.,University of Nice Sophia Antipolis | Banerjee D.P.K.,Physical Research Laboratory | Le Bouquin J.-B.,CNRS Grenoble Institute for Particle Astrophysics and Cosmology Laboratory | And 19 more authors.
Astronomy and Astrophysics | Year: 2011

Aims.T Pyx is the first recurrent nova ever historically studied. It was seen in outburst six times between 1890 and 1966 and then not for 45 years. We report on near-IR interferometric observations of the recent outburst of 2011. Methods.We obtained near-IR observations of T Pyx at dates ranging from t = 2.37 d to t = 48.2 d after the outburst, with the CLASSIC recombiner located at the CHARA array and with the PIONIER and AMBER recombiners located at the VLTI array. These data are supplemented with near-IR photometry and spectra obtained at Mount Abu, India. We compare expansion of the H and K band continua and the Br? emission line, and infer information on the kinematics and morphology of the early ejecta. Results. Slow expansion velocities were measured (≤300 km s-1) before t = 20 d. From t = 28 d on, the AMBER and PIONIER continuum visibilities (K and H band, respectively) are best simulated with a two-component model consisting of an unresolved source plus an extended source whose expansion velocity onto the sky plane is lower than ∼700 km s -1. The expansion of the Bry lineforming region, as inferred at t = 28 d and t = 35 d, is slightly larger, implying velocities in the range 500-800 km s-1, which is still strikingly lower than the velocities of 1300-1600 km s-1 inferred from the Doppler width of the line. Moreover, a remarkable pattern was observed in the Bry differential phases. A semi-quantitative model using a bipolar flow with a contrast of 2 between the pole and equator velocities, an inclination of i = 15°, and a position angle PA = 110° provides a good match to the AMBER observables. At t = 48 d, a PIONIER dataset confirms the two-component nature of the H band emission, consisting of an unresolved stellar source and an extended region whose appearance is circular and symmetric within error bars. Conclusions. These observations are most simply interpreted within the frame of a bipolar model, oriented nearly face-on. This finding has profound implications for interpreting past, current, and future observations of the expanding nebula. © 2011 ESO.


Bonneau D.,University of Nice Sophia Antipolis | Chesneau O.,University of Nice Sophia Antipolis | Mourard D.,University of Nice Sophia Antipolis | Berio P.,University of Nice Sophia Antipolis | And 15 more authors.
Astronomy and Astrophysics | Year: 2011

Aims. This study aims at constraining the properties of two interacting binary systems by measuring their continuum-forming region in the visible and the forming regions of some emission lines, in particular Hα, using optical interferometry. Methods. We have obtained visible medium (R ∼ 1000) spectral resolution interferometric observations of α Lyr and of υ Sgr using the VEGA instrument of the CHARA array. For both systems, visible continuum (520/640 nm) visibilities were estimated and differential interferometry data were obtained in the Hα emission line at several epochs of their orbital period. For β Lyr, dispersed visibilities and phases were also obtained in the Hα and the HeI 6678 A lines. Results. As expected, for baselines shorter than 60 m, the system of β Lyr is unresolved in the visible continuum, but the source associated with the H¥ á, the Hα and the HeI 6678 A lines appears to be well resolved at any orbital phase. The differential visibilities through these lines are lower during eclipses, indicating that significant emission originates close to the stars. The Hα line forming region appears to be made up of a compact source located near the orbital plane (possibly linked with the "hot point") and an extended source (i.e. ≥2mas, i.e. 125 R⊙) out of the orbital plane (possibly associated to the "jet-like feature"). The υ Sgr continuum visibilities are at a similar level for short (20.25 m) and long (90.110 m) baselines. This is interpreted as the presence of an extended structure surrounding a compact bright source. No binary signal was detected, excluding a flux ratio between the stellar components of the system larger than 0.1 from 500 to 700 nm. The radius of the brightest star is estimated to be 0.33 ± 0.16 mas, i.e. 21 ± 10 R ⊙ using the latest Hipparcos distance. By contrast, the Hα line forming region is very extended (i.e. ≥6 mas, i.e. 400 R ⊙) and found to be off-center from the brightest star, following the orbital motion of the hidden companion. Conclusions. In both cases, the extension of the H¥ á line forming region is much larger than the size of the system, which is indicative of a non-conservative evolution. Although a large circumbinary disk surrounds the evolved system υ Sgr, storing a considerable part of the lost material, a substantial part of the Hα, Hβ, and the HeI 6678 A line emission derives from regions perpendicular to the orbital plane of β Lyr. © 2011 ESO.


Perraut K.,Joseph Fourier University | Brandao I.,University of Porto | Mourard D.,French National Center for Scientific Research | Cunha M.,University of Porto | And 19 more authors.
Astronomy and Astrophysics | Year: 2011

Context. A precise comparison of the predicted and observed locations of stars in the H-R diagram is needed when testing stellar interior theoretical models. For doing this, one must rely on accurate, observed stellar fundamental parameters (mass, radius, luminosity, and abundances). Aims. We determine the angular diameter of the rapidly oscillating Ap star, γ Equ, and derive its fundamental parameters from this value. Methods. We observed γ Equ with the visible spectro-interferometer VEGA installed on the optical CHARA interferometric array, and derived both the uniform-disk angular diameter and the limb-darkened diameter from the calibrated squared visibility. We then determined the luminosity and the effective temperature of the star from the whole energy flux distribution, the parallax, and the angular diameter. Results. We obtained a limb-darkened angular diameter of 0.564 ± 0.017 mas and deduced a radius of R = 2.20 ± 0.12 R⊙. Without considering the multiple nature of the system, we derived a bolometric flux of (3.12 ± 0.21) × 10-7 erg cm-2 s-1 and an effective temperature of 7364 ± 235 K, which is below the previously determined effective temperature. Under the same conditions we found a luminosity of L = 12.8 ± 1.4 L⊙. When the contribution of the closest companion to the bolometric flux is considered, we found that the effective temperature and luminosity of the primary star can reach ∼100 K and ∼0.8 L⊙ lower than the values mentioned above. Conclusions. For the first time, and thanks to the unique capabilities of VEGA, we managed to constrain the angular diameter of a star as small as 0.564 mas with an accuracy of about 3% and to derive its fundamental parameters. In particular the new values of the radius and effective temperature should bring further constraints on the asteroseismic modeling of the star. © 2011 ESO.

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