* Astronomy

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RE: Betelgeuse

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Betelgeuse captured with a 100mm f5 Helios achromatic refractor and Canon EOS 350.

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Alpha Orionis

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HD 39801

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Alpha Orion (HD 39801, Betelgeuse): Stack of 2 images captured with a 8" f5 reflector and Canon EOS 350D.

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RE: Betelgeuse

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Title: Direct Ultraviolet Imaging and Spectroscopy of Betelgeuse
Authors: A. K. Dupree, R. P. Stefanik

Direct images of Betelgeuse were obtained over a span of 4 years with the Faint Object Camera on the Hubble Space Telescope. These images reveal the extended ultraviolet continuum emission (about 2 times the optical diameter), the varying overall ultraviolet flux levels and a pattern of bright surface continuum features that change in position and appearance over several months or less. Concurrent photometry and radial velocity measures support the model of a pulsating star, first discovered in the ultraviolet from IUE. Spatially resolved HST spectroscopy reveals a larger extention in chromospheric emissions of Mg II as well as the rotation of the supergiant. Changing localised subsonic flows occur in the low chromosphere that can cover a substantial fraction of the stellar disk and may initiate the mass outflow.

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Title: e-MERLIN resolves Betelgeuse at wavelength 5 cm
Authors: A. M. S. Richards (1), R. J. Davis (1), L. Decin (2), S. Etoka (1,3), G. M. Harper (4) J. J. Lim (5,6), S. T. Garrington (1), M .D. Gray (1), I. McDonald (1), E. O'Gorman (4), M. Wittkowski (7) ((1) JBCA, Dept. Physics and Astronomy, University of Manchester, UK, (2) Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Belgium (3) Hamburger Sternwarte, Germany, (4) School of Physics, Trinity College, Dublin, Ireland, (5) Department of Physics, University of Hong Kong, (6) Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan, (7) ESO, Garching bei Muenchen, Germany)

Convection, pulsation and magnetic fields have all been suggested as mechanisms for the transport of mass and energy from the optical photosphere of red supergiants, out to the region where the stellar wind is launched. We imaged the red supergiant Betelgeuse at 0.06-0.18 arcsec resolution, using e-MERLIN at 5.5--6.0 GHz, with a sensitivity of ~0.01 mJy/beam. Most of the radio emission comes from within an ellipse (0.235 x 0.218) arcsec² (~5x the optical radius), with a flux density of 1.62 mJy, giving an average brightness temperature ~1250 K. This radio photosphere contains two hotspots of 0.53 and 0.79 mJy/beam, separated by 90 milli-arcsec, with brightness temperatures 5400 ±600 K and 3800 ±500 K. Similar hotspots, at more than double the distance from the photosphere of those seen in any other regime, were detected by the less-sensitive `old' MERLIN in 1992, 1995 and 1996 and many exceed the photospheric temperature of 3600 K. Such brightness temperatures are high enough to emanate from pockets of chromospheric plasma. Other possibilities include local shock heating, the convective dredge-up of hot material or exceptionally cool, low density regions, transparent down to the hottest layer at ~40 milliarcsec radius. We also detect an arc 0.2--0.3 arcsec to the SW, brightness temperature ~150 K, in a similar direction to extensions seen on both smaller and larger scales in the infra-red and in CO at mm wavelengths. These preliminary results will be followed by further e-MERLIN, VLA and ALMA observations to help resolve the problem of mass elevation from 1 to 10 R* in red supergiants.

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Title: The past and future evolution of a star like Betelgeuse
Authors: Georges Meynet, Lionel Haemmerle, Sylvia Ekstrom, Cyril Georgy, Jose Groh, Andre Maeder

We discuss the physics and the evolution of a typical massive star passing through an evolutionary stage similar to that of Betelgeuse. After a brief introduction recalling various observed parameters of Betelgeuse, we discuss the Pre-Main-Sequence phase (PMS), the Main-Sequence (MS) phase, the physics governing the duration of the first crossing of the HR diagram, the red supergiant stage (RSG), the post-red supergiant phases and the final fate of solar metallicity stars with masses between 9 and 25 solar masses. We examine the impact of different initial rotation and of various prescriptions for the mass loss rates during the red supergiant phase. We show that, whatever the initial rotation rate (chosen between 0 and 0.7 x \upsilon_{crit}, \upsilon_{crit} being the surface equatorial velocity producing a centrifugal acceleration balancing exactly the gravity) and the mass loss rates during the RSG stage (varied between a standard value and 25 times that value), a 15 solar mass star always ends its lifetime as a RSG and explodes as a type II-P or II-L supernova.

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Title: Betelgeuse and the red supergiants
Authors: Jacco Th. van Loon (Lennard-Jones Laboratories, Keele University, UK)

Betelgeuse is one of the most magnificent stars in the sky, and one of the nearest red supergiants. Astronomers gathered in Paris in the Autumn of 2012 to decide what we know about its structure, behaviour, and past and future evolution, and how to place this in the general context of the class of red supergiants. Here I reflect on the discussions and propose a synthesis of the presented evidence. I believe that, in those four days, we have achieved to solve a few riddles.

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