The rotating envelope of the hot star gamma Cassiopeiae resolved by optical interferometry

Mourard, D.; Bosc, I.; Labeyrie, A.; Koechlin, Laurent; Saha, Swapan K.

doi:10.1038/342520a0

Cited by 73 publications

(46 citation statements)

References 4 publications

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“…This emission was expected to be more extended, and thus more easily resolvable, than the tiny photosphere itself. The envelope of γ Cas was first resolved by Thom et al (1986) using the I2T, and Mourard et al (1989) saw evidence for an envelope in rotation by inspecting multiple spectral channels across the line itself using the GI2T. With a good range of baselines, the Mark III was able to detect definite asymmetries in γ Cas and ζ Tau (Quirrenbach et al, 1993a(Quirrenbach et al, , 1994; for the latter, the maximum entropy method was used to visualize the data as a "phase-less" image and this result is shown in Figure 25a.…”

Section: 21mentioning

confidence: 99%

Optical interferometry in astronomy

2003

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Abstract. Here I review the current state of the field of optical stellar interferometry, concentrating on ground-based work although a brief report of space interferometry missions is included. We pause both to reflect on decades of immense progress in the field as well as to prepare for a new generation of large interferometers just now being commissioned (most notably, the CHARA, Keck and VLT Interferometers). First, this review summarizes the basic principles behind stellar interferometry needed by the lay-physicist and general astronomer to understand the scientific potential as well as technical challenges of interferometry. Next, the basic design principles of practical interferometers are discussed, using the experience of past and existing facilities to illustrate important points. Here there is significant discussion of current trends in the field, including the new facilities under construction and advanced technologies being debuted. This decade has seen the influence of stellar interferometry extend beyond classical regimes of stellar diameters and binary orbits to new areas such as mapping the accretion disks around young stars, novel calibration of the Cepheid Period-Luminosity relation, and imaging of stellar surfaces. The third section is devoted to the major scientific results from interferometry, grouped into natural categories reflecting these current developments. Lastly, I consider the future of interferometry, highlighting the kinds of new science promised by the interferometers coming on-line in the next few years. I also discuss the longer-term future of optical interferometry, including the prospects for space interferometry and the possibilities of large-scale ground-based projects. Critical technological developments are still needed to make these projects attractive and affordable. †

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Section: 21mentioning

confidence: 99%

Optical interferometry in astronomy

2003

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“…For about 30 years, Be stars have been favorite targets of optical interferometers (Thom et al 1986;Mourard et al 1989), and Based on observations with MIRC-6T and VEGA-4T instruments on the CHARA Array. Table 2 and Appendix A are available in electronic form at http://www.aanda.org they are important objects to study the role of rotation in the link between a star and its close environment.…”

Section: Introductionmentioning

confidence: 99%

Spectral and spatial imaging of the Be+sdO binaryϕPersei

Mourard

Monnier

Meilland

et al. 2015

A&A

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Aims. The rapidly rotating Be star ϕ Persei was spun up by mass and angular momentum transfer from a now stripped-down, hot subdwarf companion. Here we present the first high angular resolution images of ϕ Persei made possible by new capabilities in longbaseline interferometry at near-IR and visible wavelengths. We analyzed these images to search for the companion, to determine the binary orbit, stellar masses, and fluxes, and to examine the geometrical and kinematical properties of the outflowing disk surrounding the Be star. Methods. We observed ϕ Persei with the MIRC and VEGA instruments of the CHARA Array. MIRC was operated in six-telescope mode, whereas VEGA was configured in four-telescope mode with a change of quadruplets of telescopes during two nights to improve the (u, v) plane coverage. Additional MIRC-only observations were performed to track the orbital motion of the companion, and these were fit together with new and existing radial velocity measurements of both stars to derive the complete orbital elements and distance. We also used the MIRC data to reconstruct an image of the Be disk in the near-IR H-band. VEGA visible broadband and spectro-interferometric Hα observations were fit with analytical models for the Be star and disk, and image reconstruction was performed on the spectrally resolved Hα emission line data. Results. The hot subdwarf companion is clearly detected in the near-IR data at each epoch of observation with a flux contribution of 1.5% in the H band, and restricted fits indicate that its flux contribution rises to 3.3% in the visible. A new binary orbital solution is determined by combining the astrometric and radial velocity measurements. The derived stellar masses are 9.6 ± 0.3 M and 1.2 ± 0.2 M for the Be primary and subdwarf secondary, respectively. The inferred distance (186 ± 3 pc), kinematical properties, and evolutionary state are consistent with membership of ϕ Persei in the α Per cluster. From the cluster age we deduce significant constraints on the initial masses and evolutionary mass transfer processes that transformed the ϕ Persei binary system. The interferometric data place strong constraints on the Be disk elongation, orientation, and kinematics, and the disk angular momentum vector is coaligned with and has the same sense of rotation as the orbital angular momentum vector. The VEGA visible continuum data indicate an elongated shape for the Be star itself, due to the combined effects of rapid rotation, partial obscuration of the photosphere by the circumstellar disk, and flux from the bright inner disk.

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“…These instruments have been intensively used, for example, to study the morphology and kinematic of circumstellar environments (Mourard et al 1989;Berio et al 1999;Meilland et al 2007). A data reduction method was developed to derive these differential measurements for VEGA, which is described in detail in Mourard et al (2009) for two telescope observations.…”

Section: Differential Measurementsmentioning

confidence: 99%

Spatio-spectral encoding of fringes in optical long-baseline interferometry

Mourard

Berio

Perraut

et al. 2011

A&A

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Context. One of the main challenges of optical stellar interferometers is to increase the number of telescopes in the recombining unit to provide a larger number of measurements and an improved imaging capability. At the same time there is a need to preserve the spectroscopic capabilities, which leads to complex recombining schemes that may inhibit development. Aims. We describe the possibilities of combining the spatial and spectral encoding of fringes for the design of more compact beam combiners and for minimizing the number of pixels that must be read. Methods. We establish the formalism of the spatio-spectral fringe encoding, discuss general applications, and describe an implementation in the 3T/4T observing mode of the VEGA (Visible spEctroGraph and polArimeter) instrument installed at the coherent focus of the CHARA Array located on Mt Wilson in California. We finally present the science cases made possible by this instrumental implementation in the case of VEGA/CHARA. Results. We demonstrate the interest in implementing an optimized spatio-spectral encoding of fringes in a multi-telescope beam combiner. On-sky results, obtained with the 3T mode of the VEGA combiner are presented. At visible wavelengths and with the hectometric baselines of CHARA, sub-mas stellar diameters could be determined with a precision of a few percent with a spectral resolution of 5000. Our first estimates of closure phase show that accuracies better than 1 degree can be achieved. Conclusions. The first on-sky results obtained with the 3T-4T VEGA instrument using spatio-spectral fringe encoding show the validity of using this principle in the design of future complex beam combiners.

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The rotating envelope of the hot star gamma Cassiopeiae resolved by optical interferometry

Cited by 73 publications

References 4 publications

Optical interferometry in astronomy

Optical interferometry in astronomy

Spectral and spatial imaging of the Be+sdO binaryϕPersei

Spatio-spectral encoding of fringes in optical long-baseline interferometry

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