The spinning-top Be star Achernar from VLTI-VINCI

By A. D. D. Souza, Pierre Kervella, S. Jankov, L. Abe, F. Vakili, E. D. Folco, F. Paresce. 2003

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We report here the first observations of a rapidly rotating Be star, Eridani, using Earth-rotation synthesis on the Very Large Telescope (VLT) Interferometer. Our measures correspond to a 2a=2b= 1:56 0:05 apparent oblate star, 2a and 2b being the equivalent uniform disc angular diameters in the equatorial and polar direction. Considering the presence of a circum- stellar envelope (CSE) we argue that our measurement corresponds to a truly distorted star since Eridani exhibited negligible H emission during the interferometric observations. In this framework we conclude that the commonly adopted Roche approx- imation (uniform rotation and centrally condensed mass) should not apply to Eridani. This result opens new perspectives to basic astrophysical problems, such as rotationally enhanced mass loss and internal angular momentum distribution. In addition to its intimate relation with magnetism and pulsation, rapid rotation thus provides a key to the Be phenomenon: one of the outstanding non-resolved problems in stellar physics.

Subfields: Astronomy and Astrophysics, Education, Instrumentation

View Paper: https://www.semanticscholar.org/paper/e92763365ff76e598f72a19955872a4dc5aa38bd

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Citations in the corpus

Acoustic oscillations of rapidly rotating polytropic stars. II. Effects of the Coriolis and centrifu (2006, background): “For instance, interferometry is starting to give clues as to the shape of these stars and effects such as gravitational darkening (e.g. Domiciano de Souza et al., 2003, 2005, Peterson et al., 2006).”
Be-star rotation: how close to critical? (2003, background): “Recently, Domiciano de Souza et al. (2003) applied this approach to the Be star α Eri; their VLTI observations indicate an aspect ratio entirely consistent with near-critical rotation.”
The angular sizes of dwarf stars and subgiants Surface brightness relations calibrated by interferometry (2004, methodology): “As demonstrated by the VINCI observations of the nearby Be star αEri (Domiciano de Souza et al. 2003), the photosphere of these objects can be deformed by their fast rotation.”
Rotational mixing in massive binaries - Detached short-period systems (2009, background): “Rotation deforms the star to an oblate shape (of which Achernar is an extreme example, see Domiciano de Souza et al. 2003), it interplays with the mass loss from the star (e.g. Friend & Abbott 1986; Langer 1998; Maeder & Meynet 2000a) and it induces instabilities in the interior leading to…”
A STELLAR ROTATION CENSUS OF B STARS: FROM ZAMS TO TAMS (2010, background): “Interferometric observations of Achernar by Domiciano de Souza et al. (2003) showed that the star has an exceptionally large rotational oblateness with Req/Rpolar = 1.56, which is above the value expected (1.5) for a star rotating at the critical rate.”
Evolution towards the critical limit and the origin of Be stars (2007, background): “…observations brought strong support to the idea that these stars are very fast rotators: the oblateness of the Be star Achernar (Domiciano de Souza et al. 2003) suggests indeed that the star is rotating near the critical limit; Meilland et al. (2007) obtained for the first time direct…”
Classical Be stars (2013, background): “Most enigmatically, there is α Eri, for which the photospheric flattening was observed to be 1:1.56, i.e., even more than predicted by the Roche approximation for critical rotation (Domiciano de Souza et al. 2003).”
First Results from the CHARA Array. I. An Interferometric and Spectroscopic Study of the Fast Rotator α Leonis (Regulus) (2005, methodology): “The Very Large Telescope Interferometer (VLTI) has been used by Domiciano de Souza et al. (2003) to study the oblateness of the Be star Achernar (α Eri).”