The close circumstellar environment of Betelgeuse

Context. 55 Cancri hosts five known exoplanets, most notably the hot super-Earth 55 Cnc e, which is one of the hottest known transiting super-Earths. Aims. Because of the short orbital separation and host star brightness, 55 Cnc e provides one of the best opportunities for studying star-planet interactions (SPIs). We aim to understand possible SPIs in this system, which requires a detailed understanding of the stellar magnetic field and wind impinging on the planet. Methods. Using spectropolarimetric observations and Zeeman Doppler Imaging, we derived a map of the large-scale stellar magnetic field. We then simulated the stellar wind starting from the magnetic field map, using a 3D magneto-hydrodynamic model. Results. The map of the large-scale stellar magnetic field we derive has an average strength of 3.4 G. The field has a mostly dipolar geometry; the dipole is tilted by 90° with respect to the rotation axis and the dipolar strength is 5.8 G at the magnetic pole. The wind simulations based on this magnetic geometry lead us to conclude that 55 Cnc e orbits inside the Alfvén surface of the stellar wind, implying that effects from the planet on the wind can propagate back to the stellar surface and result in SPI.

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The circumstellar environment of the B[e] star GG Car: an interferometric modeling

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314006966 ◽

2014 ◽

Vol 9 (S307) ◽

pp. 291-292

Author(s):

A. Domiciano de Souza ◽

M. Borges Fernandes ◽

A. C. Carciofi ◽

O. Chesneau

Keyword(s):

Binary System ◽

Primary Component ◽

Compact Ring ◽

Hot Stars ◽

Self Consistent ◽

Grain Formation ◽

Formation And Evolution ◽

Circumstellar Environments ◽

Consistent Treatment ◽

Circumstellar Environment

AbstractThe research of stars with the B[e] phenomenon is still in its infancy, with several unanswered questions. Physically realistic models that treat the formation and evolution of their complex circumstellar environments are rare. The code HDUST (developed by A. C. Carciofi and J. Bjorkman) is one of the few existing codes that provides a self-consistent treatment of the radiative transfer in a gaseous and dusty circumstellar environment seen around B[e] supergiant stars. In this work we used the HDUST code to study the circumstellar medium of the binary system GG Car, where the primary component is probably an evolved B[e] supergiant. This system also presents a disk (probably circumbinary), which is responsible for the molecular and dusty signatures seen in GG Car spectra. We obtained VLTI/MIDI data on GG~Car at eight baselines, which allowed to spatially resolve the gaseous and dusty circumstellar environment. From the interferometric visibilities and SED modeling with HDUST, we confirm the presence of a compact ring, where the hot dust lies. We also show that large grains can reproduce the lack of structure in the SED and visibilities across the silicate band. We conclude the dust condensation site is much closer to the star than previously thought. This result provides stringent constraints on future theories of grain formation and growth around hot stars.

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Radio Supernovae as Direct Evidence of Stellar Evolution in Real Time

Highlights of Astronomy ◽

10.1017/s1539299600021171 ◽

1998 ◽

Vol 11 (1) ◽

pp. 367-367

Author(s):

S.D. Van Dyk ◽

M.J. Montes ◽

K.W. Weiler ◽

R.A. Sramek ◽

N. Panagia

Keyword(s):

Mass Loss ◽

Stellar Evolution ◽

Loss Rate ◽

Direct Evidence ◽

Mass Loss Rate ◽

X Ray ◽

Stringent Constraint ◽

Clear Change ◽

Late Stages ◽

Circumstellar Environment

The radio emission from supernovae provides a direct probe of a supernova’s circumstellar environment, which presumably was established by mass-loss episodes in the late stages of the progenitor’s presupernova evolution. The observed synchrotron emission is generated by the SN shock interacting with the relatively high-density circumstellar medium which has been fully ionized and heated by the initial UV/X-ray flash. The study of radio supernovae therefore provides many clues to and constraints on stellar evolution. We will present the recent results on several cases, including SN 1980K, whose recent abrupt decline provides us with a stringent constraint on the progenitor’s initial mass; SN 1993J, for which the profile of the wind matter supports the picture of the progenitor’s evolution in an interacting binary system; and SN 1979C, where a clear change in presupernova mass-loss rate occurred about 104 years before explosion. Other examples, such as SNe 19941 and 1996cb, will also be discussed.

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