Spectro-interferometric observations of interacting massive stars with VEGA/CHARA

We obtained spectro-interferometric observations in the visible of $\beta$ Lyrae and $\upsilon$ Sgr using the instrument VEGA of the CHARA interferometric array. For $\beta$ Lyrae, the dispersed fringe visibilities and differential phases were obtained in spectral regions containing the H$\alpha$ and HeI 6678 lines and the H$\beta$ and HeI 4921 lines. Whereas the source is unresolved in the continuum, the source of the emission lines is resolved and the photocenter of the bulk of the H$\alpha$ emission exhibits offsets correlated with the orbital phase. For $\upsilon$ Sgr, both the continuum and H$\alpha$ sources are resolved, but no clear binary signal is detected. The differential phase shift across the line reveals that the bulk of the H$\alpha$ emission is clearly offset from the primary

The operation of VEGA/CHARA : from the scientific idea to the final products

We describe the data flow in the operation of the VEGA/CHARA instrument. After a brief summary of the main characteristics and scientific objectives of the VEGA instrument, we explain the standard procedure from the scientific idea up to the execution of the observation. Then, we describe the different steps done after the observation, from the raw data to the archives and the final products. Many tools are used and we show how the Virtual Observatory principles have been implemented for the interoperability of these software and databases.Comment: 9 pages, 3 figure

Planet transit and stellar granulation detection with interferometry

Aims. We used realistic three-dimensional (3D) radiative hydrodynamical (RHD) simulations from the Stagger-grid and synthetic images computed with the radiative transfer code Optim3D to provide interferometric observables to extract the signature of stellar granulation and transiting planets. Methods. We computed intensity maps from RHD simulations for twelve interferometric instruments covering wavelengths ranging from optical to infrared. The stellar surface asymmetries in the brightness distribution mostly affect closure phases. We compared the closure phases of the system star with a transiting planet and the star alone and considered the impact of magnetic spots constructing a hypothetical starspots image. Results. All the simulations show departure from the axisymmetric case at all wavelengths. We presented two possible targets (Beta Com and Procyon) and found that departures up to 16 deg can be detected on the 3rd lobe and higher. In particular, MIRC is the most appropriate instrument because it combines good UV coverage and long baselines. Moreover, we explored the impact of convection on interferometric planet signature for three prototypes of planets. It is possible to disentangle the signature of the planet at particular wavelengths (either in the infrared or in the optical) by comparing the closure phases of the star at difference phases of the planetary transit. Conclusions. The detection and characterisation of planets must be based on a comprehensive knowledge of the host star; this includes the detailed study of the stellar surface convection with interferometric techniques. In this context, RHD simulations are crucial to reach this aim. We emphasize that interferometric observations should be pushed at high spatial frequencies by accumulating observations on closure phases at short and long baselines.Comment: accepted in Astronomy and Astrophysics, 13 pages. Some figures have reduced resolution to decrease the size of the output file. Please contact [email protected] to have the high resolution version of the pape

High spatial resolution monitoring of the activity of BA supergiant winds

There are currently two optical interferometry recombiners that can provide spectral resolutions better than 10000, AMBER/VLTI operating in the H-K bands, and VEGA/CHARA, recently commissioned, operating in the visible. These instruments are well suited to study the wind activity of the brightest AB supergiants in our vicinity, in lines such as H$\alpha$ or BrGamma. We present here the first observations of this kind, performed on Rigel (B8Ia) and Deneb (A2Ia). Rigel was monitored by AMBER in two campaigns, in 2006-2007 and 2009-2010, and observed in 2009 by VEGA; whereas Deneb was monitored in 2008-2009 by VEGA. The extension of the Halpha and BrGamma line forming regions were accurately measured and compared with CMFGEN models of both stars. Moreover, clear signs of activity were observed in the differential visibility and phases. These pioneer observations are still limited, but show the path for a better understanding of the spatial structure and temporal evolution of localized ejections using optical interferometry.Comment: Proceedings of conf. IAUS272 - Active OB stars - Paris, July 19-23, 201

Radii, masses, and ages of 18 bright stars using interferometry and new estimations of exoplanetary parameters

Accurate stellar parameters are needed in numerous domains of astrophysics. The position of stars on the H-R diagram is an important indication of their structure and evolution, and it helps improve stellar models. Furthermore, the age and mass of stars hosting planets are required elements for studying exoplanetary systems. We aim at determining accurate parameters of a set of 18 bright exoplanet host and potential host stars from interferometric measurements, photometry, and stellar models. Using the VEGA/CHARA interferometer, we measured the angular diameters of 18 stars, ten of which host exoplanets. We combined them with their distances to estimate their radii. We used photometry to derive their bolometric flux and, then, their effective temperature and luminosity to place them on the H-R diagram. We then used the PARSEC models to derive their best fit ages and masses, with error bars derived from MC calculations. Our interferometric measurements lead to an average of 1.9% uncertainty on angular diameters and 3% on stellar radii. There is good agreement between measured and indirect estimations of angular diameters (from SED fitting or SB relations) for MS stars, but not as good for more evolved stars. For each star, we provide a likelihood map in the mass-age plane; typically, two distinct sets of solutions appear (an old and a young age). The errors on the ages and masses that we provide account for the metallicity uncertainties, which are often neglected by other works. From measurements of its radius and density, we also provide the mass of 55 Cnc independently of models. From the stellar masses, we provide new estimates of semi-major axes and minimum masses of exoplanets with reliable uncertainties. We also derive the radius, density, and mass of 55 Cnc e, a super-Earth that transits its stellar host. Our exoplanetary parameters reflect the known population of exoplanets.Comment: 23 pages, 9 figures, published in A&A. (This version includes proof corrections.

Separated Fringe Packet Observations with the CHARA Array II: ω\omega Andromeda, HD 178911, and {\xi} Cephei

When observed with optical long-baseline interferometers (OLBI), components of a binary star which are sufficiently separated produce their own interferometric fringe packets; these are referred to as Separated Fringe Packet (SFP) binaries. These SFP binaries can overlap in angular separation with the regime of systems resolvable by speckle interferometry at single, large-aperture telescopes and can provide additional measurements for preliminary orbits lacking good phase coverage, help constrain elements of already established orbits, and locate new binaries in the undersampled regime between the bounds of spectroscopic surveys and speckle interferometry. In this process, a visibility calibration star is not needed, and the separated fringe packets can provide an accurate vector separation. In this paper, we apply the SFP approach to {\omega} Andromeda, HD 178911, and {\xi} Cephei with the CLIMB three-beam combiner at the CHARA Array. For these systems we determine component masses and parallax of 0.963${\pm}$0.049 $M_{\odot}$ and 0.860${\pm}$0.051 $M_{\odot}$ and 39.54${\pm}$1.85 milliarcseconds (mas) for {\omega} Andromeda, for HD 178911 of 0.802${\pm}$0.055 $M_{\odot}$ and 0.622${\pm}$0.053 $M_{\odot}$ with 28.26${\pm}$1.70 mas, and masses of 1.045${\pm}$0.031 $M_{\odot}$ and 0.408${\pm}$0.066 $M_{\odot}$ and 38.10${\pm}$2.81 mas for {\xi} Cephei.Comment: 28 pages, 4 tables, 6 figures, accepted to AJ May 201

Spectroscopic and interferometric approach for differential rotation in massive fast rotators

The coupling between the convective region in the envelope and rotation can produce a surface latitudinal differential rotation that may induce changes of the stellar geometry and on the spectral line profiles that it may be scrutinized spectroscopically and by interferometry.Facultad de Ciencias Astronómicas y Geofísica

Discretized aperture mapping with a micro-lenses array for interferometric direct imaging

Discretized Aperture Mapping (DAM) appears as an original filtering technique easy to play with existing adaptive optics (AO) systems. In its essential DAM operates as an optical passive filter removing part of the phase residuals in the wavefront without introducing any difficult-to-align component in the Fourier conjugate of the entrance pupil plane. DAM reveals as a new interferometric technique combined with spatial filtering allowing direct imaging over a narrow field of view (FOV). In fact, the entrance pupil of a single telescope is divided into many sub-pupils so that the residual phase in each sub-pupil is filtered up to the DAM cut-off frequency. DAM enables to smooth the small scale wavefront defects which correspond to high spatial frequencies in the pupil plane and to low angular frequencies in the image plane. Close to the AO Nyquist frequency, such pupil plane spatial frequencies are not well measured by the wavefront sensor (WFS) due to aliasing. Once bigger than the AO Nyquist frequency, they are no more measured by the WFS due to the fitting limit responsible for the narrow AO FOV. The corresponding image plane angular frequencies are not transmitted by DAM and are useless to image small FOVs, as stated by interferometry. That is why AO and DAM are complementary assuming that the DAM cut-off frequency is equal to the AO Nyquist frequency. Here we describe the imaging capabilities when DAM is placed downstream an AO system, over a convenient pupil which precedes the scientific detector. We show firstly that the imaging properties are preserved on a narrow FOV allowing direct imaging throughout interferometry. Then we show how the residual pupil plane spatial frequencies bigger than the AO Nyquist one are filtered out, as well as the residual halo in the image is dimmed