Optical interferometry for astronomy was conceived as early as 1868, succeeded in measuring a stellar diameter in 1920 and was only reborn in 1974. Soon after, several remarkable prototype ...instruments were built, demonstrating the potential power of this technique for stellar studies at visible and near infrared wavelengths. Meanwhile, the physics of the Earth atmosphere, which seriously impacts image quality on ground-based observatories, progressed with the emergence of adaptive optics systems. Then, during the years 1990–2005, ambitious interferometric observatories entered into service, in Europe (VLTI) and in United States (Keck, NPOI, LBT). Today, their results and promises deeply impact stellar studies by providing images of the surface and immediate surrounding of stars, stellar objects and even galactic nuclei.
This chapter describes the methods used to extract closure phase from CLIMB data and visibility amplitude from both the CLASSIC and CLIMB beam combiners. It also includes a rather exhaustive ...description of the theory behind these methods. This high degree of detail is partly because previous publications of this theory contain errors, and partly because having done all this work it*s nice to have it written up in full somewhere, and being slightly beyond the thesis writing stage, this is only possible for me in a chapter like this.
Asteroseismology is a powerful technique that can be employed to determine precise fundamental parameters of stars, such as the radius, mass and age. The data are sensitive to the density structure ...of the star, so if we combine these with an independently measured radius from interferometry, we can determine the mass with high precision. This is one of the only methods for determining masses of single field stars and with high precision – an otherwise unobservable property. Knowing masses of stars has consequences for exoplanetary characterisation, Galactic population studies and for stars themselves, it allows us to constrain stellar model parameters, yields more precise determinations of ages which thus allows us to calibrate age-rotation relations as well as setting stellar constraints on the age of our own Galaxy.
We report on near-IR interferometric observations of the outburst of the recurrent nova T Pyx. We obtained near-IR observations of T Pyx at dates ranging from t=2.37d to t=48.2d 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. Slow expansion velocities were measured (<300km/s) before t=20d (assuming D=3.5kpc). From t=28d 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 700km/s. The expansion of the Brgamma line forming region, as inferred at t=28d and t=35d is slightly larger, implying velocities in the range 500-800km/s, still strikingly lower than the velocities of 1300-1600km/s inferred from the Doppler width of the line. Moreover, a remarkable pattern was observed in the Brgamma 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 P.A.=110° provides a good match to the AMBER observables (spectra, differential visibilities and phases). At t=48d, 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.These observations are most simply interpreted within the frame of a bipolar model, oriented nearly face-on. This finding has profound implications for the interpretation of past, current and future observations of the expanding nebula.
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 ± 0.5 mas), 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.
Stellar rotation is a key in our understanding of both mass-loss and evolution of intermediate and massive stars. It can lead to anisotropic mass-loss in the form of radiative wind or an excretion ...disk. We used the VEGA visible beam combiner installed on the CHARA array that reaches a sub milliarcsecond resolution. We derived, for the first time, the extension and flattening of 51 Oph photosphere. We found an elongated ratio of 1.45 ± 0.12.
This tutorial paper describes the problem of image reconstruction from interferometric data with a particular focus on the specific problems encountered at optical (visible/IR) wavelengths. The ...challenging issues in image reconstruction from interferometric data are introduced in the context of a general inverse problem approach. This framework is then used to describe state-of-the-art image reconstruction algorithms specifically developed for optical interferometry.
We present here two examples of the use of interferometric observations to study stellar rotation effects (flattening and gravity darkening) and spots on the stellar photospheres. From the fit of ...simple geometrical models to two sets of VLTI data (VINCI and AMBER) using the LITpro tool from JMMC we can estimate stellar physical parameters and have insights on the photospheric intensity distribution.
Rotation has a strong influence in the structure of stars. The centrifugal force caused by rotation produces a deformation of the star that also affects the profile of brightness at its surface, this ...is known as gravity darkening. In this chapter we will construct a simple model to predict the shape and surface brightness of a rotating star.
We present in this chapter a description of optical interferometry combining instruments. For that purpose we describe the role of different key functions and give examples of the choice made in ...current and future instruments in particular at VLTI.
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