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RE: Betelgeuse
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Nearby Star May Be Getting Ready to Explode
The nearby, well-known and very bright star may soon explode in a supernova, according to data released by U.C. Berkeley researchers Tuesday.
The red giant Betelgeuse, once so large it would reach out to Jupiter's orbit if placed in our own solar system, has shrunk by 15 percent over the past decade in a half, although it's just as bright as it's ever been.


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One of the largest known stars in the universe is shrinking rapidly, and astronomers don't know why.
Betelgeuse (pronounced almost like "beetle juice") is a red supergiant star 600 light-years away in the constellation Orion. From Earth the star is clearly visible with the naked eye as the reddish dot that marks Orion's left shoulder.
Researchers at the University of California, Berkeley, first measured the star in 1993 with an infrared instrument on top of Southern California's Mount Wilson. They estimated the star to be as big around as Jupiter's orbit around the sun.
But measurements made since then using the same instrument show that Betelgeuse is now only about as wide as the orbit of Venus - a size reduction of about 15 percent in 15 years.


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Betelgeuse Shrinking
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The red supergiant star Betelgeuse, the bright reddish star in the constellation Orion, has steadily shrunk over the past 15 years, according to University of California, Berkeley, researchers.
Long-term monitoring by UC Berkeley's Infrared Spatial Interferometer (ISI) on the top of Mt. Wilson in Southern California shows that Betelgeuse (bet' el juz), which is so big that in our solar system it would reach to the orbit of Jupiter, has shrunk in diameter by more than 15 percent since 1993.

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Betegeuse
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Space is not empty, and a star ploughing through this ethereally thin gas at dozens of kilometres per second reveals itself. The gas gets compressed ahead of the star, and flows around it in graceful arcs. Like water flowing around the bow of a ship, such a formation is called a bow shock.

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Title: AKARI/FIS Mapping of the ISM-Wind Bow Shock around Alpha Ori
Authors: Toshiya Ueta (U. Denver), Hideyuki Izumiura (OAO/NAOJ), Issei Yamamura (ISAS/JAXA), Yoshikazu Nakada (U. Tokyo/Kiso Obs.), Mikako Matsuura (NAOJ/UCL), Yoshifusa Ita (NAOJ/ISAS), Toshihiko Tanabe (U. Tokyo), Hinako Fukushi (U. Tokyo), Noriyuki Matsunaga (Kyoto U.), Hiroyuki Mito (Kiso Obs.)

We present 10' x 50' scan maps around an M supergiant Alpha Ori at 65, 90, 140 and 160 microns obtained with the AKARI Infrared Astronomy Satellite. Higher spatial resolution data with the exact analytic solution permit us to fit the de-projected shape of the stellar wind bow shock around Alpha Ori to have the stand-off distance of 4.8', position angle of 55 degrees and inclination angle of 56 degrees. The shape of the bow shock suggests that the peculiar velocity of Alpha Ori with respect to the local medium is v_* = 40 (n_H)^(-1/2), where n_H is the hydrogen nucleus density at Alpha Ori. We find that the local medium is of n_H = 1.5 to 1.9 cm^(-3) and the velocity of the local flow is at 11 km s^(-1) by using the most recent astrometric solutions for Alpha Ori under the assumption that the local medium is moving away from the Orion OB 1 association. AKARI images may also reveal a vortex ring due to instabilities on the surface of the bow shock as demonstrated by numerical models. This research exemplifies the potential of AKARI All-Sky data as well as follow-up observations with Herschel Space Telescope and Stratospheric Observatory for Infrared Astronomy for this avenue of research in revealing the nature of interaction between the stellar wind and interstellar medium.

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Betelgeuse the sombre red star in the shoulder of the constellation Orion the Hunter is one of the largest stars visible to the eye alone.
The star Betelgeuse might someday appear as a spectacular explosion in our sky, a supernova.
Brad Schaefer is an astronomer in Baton Rogue, Louisiana. He said Betelgeuse could become a supernova any day now.

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Title: Dark Supergiant: Chandra's Limits on X-rays from Betelgeuse
Authors: Jennifer Posson-Brown, Vinay L. Kashyap, Deron O. Pease, Jeremy J. Drake
(Version v2)

We have analysed Chandra calibration observations of Betelgeuse (alpha Ori, M2Iab, m_V=0.58, 131 pc) obtained at the aimpoint locations of the HRC-I (8 ks), HRC-S (8 ks), and ACIS-I (5 ks). Betelgeuse is undetected in all the individual observations as well as cumulatively. We derive upper limits to the X-ray count rates and compute the corresponding X-ray flux and luminosity upper limits for coronal plasma that may potentially exist in the atmosphere of Betelgeuse over a range of temperatures, T=0.3-10 MK. We place a flux limit at the telescope of fx ~ 4x10^(-15) ergs s^(-1) cm^(-2) at T=1 MK. The upper limit is lowered by a factor of ~3 at higher temperatures, roughly an order of magnitude lower than that obtained previously. Assuming that the entire stellar surface is active, these fluxes correspond to a surface flux limit that ranges from 30-7000 ergs s^(-1) cm^(-2) at T=1 MK, to ~1 ergs s^(-1) cm^(-2) at higher temperatures, five orders of magnitude below the quiet Sun X-ray surface flux. We discuss the implications of our analysis in the context of models of a buried corona and a pervasive magnetic carpet. We rule out the existence of a solar-like corona on Betelgeuse, but cannot rule out the presence of low-level emission on the scale of coronal holes.

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Title: The molecular and dusty composition of Betelgeuses inner circumstellar environment
Authors: G. Perrin, T. Verhoelst, S.T. Ridgway, J. Cami, Q.N. Nguyen, O. Chesneau, B. Lopez, Ch. Leinert, and A. Richichi

Context. The study of the atmosphere of red supergiant stars in general and of Betelgeuse ( Orionis) in particular is of prime importance to understand dust formation and how mass is lost to the interstellar medium in evolved massive stars.   
Aims. A molecular shell, the MOLsphere (Tsuji, 2000a), in the atmosphere of Betelgeuse has been proposed to account for the near and mid-infrared spectroscopic observations of Betelgeuse. The goal is to further test this hypothesis and to identify some of the molecules in this MOLsphere.
Methods. We report on measurements taken with the mid-infrared two-telescope beam combiner of the VLTI,MIDI, operated between 7.5 and 13.5 m. The data are compared to a simple geometric model of a photosphere surrounded by a warm absorbing and emitting shell. Physical characteristics of the shell are derived: size, temperature and optical depth. The chemical constituents are determined with an analysis consistent with available infrared spectra and interferometric data.
Results. The MIDI data are well modeled with a geometrically thin shell whose radius varies from 1.31 to 1.43 R across the N band with a typical temperature of 1550 K. We are able to account for the measured optical depth of the shell in the N band, the ISO-SWS spectrum and K and L band interferometric data with a shell whose inner and outer radii are given by the above range and with the following species and densities: H2O (7.1 ± 4.7 x 10^19 cm^-2), SiO (4.0 ± 1.1 x 10^20 cm^-2), Al2O3 (2.4 ± 0.5 x 10^15 cm^-2).
Conclusions. These results confirm the MOLsphere model. We bring evidence for more constituents and for the presence of species participating in the formation of dust grains in the atmosphere of the star, i.e. well below the distance at which the dust shell is detected. We believe these results bring key elements to the understanding of mass loss in Betelgeuse and red supergiants in general and bring support to the dust-driven scenario.

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What causes Betelgeuse to vary in brightness? Like many red supergiants it changes slowly and irregularly, sometimes differing by a half magnitude or more from one year to the next enough for a careful naked-eye starwatcher to recognise.
New measurements taken with the Very Large Telescope interferometer in Chile may help to answer why and also why red supergiants have bigger atmospheres than astronomers can explain. Some researchers have thought a changing dust envelope might be veiling light from below. Others, looking at the star's ultraviolet light, thought a totally new phenomenon could be responsible. At least one team proposed the idea of colossal convective cells. But new high-resolution data collected with the multi-telescope interferometer is allowing astronomers to characterise Betelgeuse and its immediate surroundings in greater detail than ever before.

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Each star has a personality. Go ahead, look closely. They vary in brightness, size, distance and especially colour.
Stars can be blue, white, yellow, orange or red. Colour is an indication of a star's temperature - blue being the hottest and red being the coldest.
The constellation Orion shows off an outstanding variety of stars. Betelgeuse, marking the hunter's armpit, is a cool, red giant star. Fluctuating in size and brightness, Betelgeuse is nearing the end of its lifetime and will "soon" explode in a violent supernova. "Soon," to astronomers, may be thousands to millions of years.

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