Stars/Betelgeuse

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In these three images of Betelgeuse are left: an interferometric image of the photosphere, center: an adaptive optics tricolor composite image, and right: an image at 10.49 μm of the surrounding dust thermal emission. Credit: Yaël Nazé, and Xiao Che, Nick L.J. Cox, José H. Groh, Martin Guerrero, Pierre Kervella, Chien-De Lee, Mikako Matsuura, Sally Oey, Guy S. Stringfellow, Stephanie Wachter.

"Betelgeuse [is] a cool (3600 K), large (700 R), rather massive (10–15 M), luminous (> 105 L), and nearby (150 pc) star."[1]

Notations[edit]

According to SIMBAD, there are a number of catalog entries and notations that refer to Betelgeuse. Some of these are

  1. alf Ori, alpha Orionis, α Ori, 58 Orionis, V* alf Ori
  2. HD 39801,
  3. HR 2061, and
  4. SAO 113271, where SAO stands for Smithsonian Astrophysical Observatory.

Astronomy[edit]

Visibility curves of Betelgeuse. Credit: F. Roddier, C. Roddier, and, R. Petrov, F. Martin, G. Ricort, and C. Aime.
Speckle observation of Betelgeuse uses the Steward Observatory 2.25 m telescope. Credit: M. Karovska, P. Nisenson, and R. Noyes.

The "famous red supergiant has two close companions [...] based on speckle interferometry work done in the early 1980s at Kitt Peak, Arizona, and Cerro Tololo, Chile. It revealed that the inner of the two stars orbits Betelgeuse every two years or so at a mean distance of about 5 astronomical units and little is known about the outer companion except that it lies some 40 or 50 astronomical units from Betelgeuse (December, 1985, Sky and Telescope)."[2]

"A careful look to our visibility curves [on the right, full line is our data and broken line is speckle data from Aime et al. 1985] reveals a small periodic modulation that we have interpreted as possibly due to a stellar companion (Roddier, Roddier, and Karovska 1984). The estimated position angle is 85° ± 5° (mod. 180°). The period of modulation corresponds to an angular distance of 0.4"-0.5" and the depth of modulation to a magnitude difference of the order of 3.5-4."[3]

"Both observations reveal a similar modulation giving confidence about the reality of such a companion. Given its observed distance to the main star, its angular motion is expected to be negligible during the 8 months which separate the two observations."[3]

"The existence of such a companion suggested [...] that another companion might also be present close to the disk. It would explain the bright feature observed by Roddier and Roddier (1983) and Goldberg et al. (1981) as well as the observed rapid rotation of the plane of polarization (Haynes 1980). [...] The existence of both companions has recently been confirmed from speckle observations (Karovska et al. 1985)."[3]

"Detection of two close optical companions to the red supergiant α Ori was accomplished in 1983 November on the Steward Observatory 2.25 m telescope. [...] The closer of the two sources is located at 0.06" ± 0.01" from α Ori (P.A. = 273°), the more distant at 0.51" ± 0.01" (P.A. = 278°)."[4]

"Speckle observation [of Betelgeuse uses the Steward Observatory 2.25 m telescope during November 1983, where] (a) and (b) [are the] recovered power spectrum and phase; (c) and (d) autocorrelation and the reconstructed image for the distant companion; (e) and (f) autocorrelation and image for the close companion."[4]

Meteors[edit]

These graphs include spatially resolved STIS spectra of Si I λ2516 and Si I λ2507 resonance emission lines observed in Betelgeuse out to 1 arcsecond. Credit: A. Lobel, J. Aufdenberg, A. K. Dupree, R. L. Kurucz, R. P. Stefanik, and G. Torres.

The "Si I λ2516 resonance emission line (Lobel & Dupree 2001) [...] has previously been observed by scanning over the inner chromosphere [of Betelgeuse] at 0, 25, 50, and 75 mas, using a slit size of 100 × 30 mas [the left panel in the graphs on the right]."[5]

"The double-peaked line profiles are observed across the inner chromosphere. The central (self-) absorption core results from scattering opacity in the chromosphere. The asymmetry of the emission component intensities probes the chromospheric flow dynamics in our line of sight. The spectra of GO 9369 are observed across the outer chromosphere using a slitsize of 200 × 63 mas [image on the right]. The profiles beyond 200 mas appear red-shifted with a rather weak short-wavelength emission component. It signals substantial wind outflow opacity in the upper chromoshere, which fastly accelerates beyond a radius of ∼8 R."[5]

The set of graphs on the right "compares the profiles of the Si I λ2516 and λ2507 resonance lines (vertical dotted lines are drawn at stellar rest velocity). Both lines share a common upper energy level and their intensities are influenced by pumping through a fluoresced Fe II line. The self-absorption cores of the Si I lines are therefore observed far out, into the upper chromosphere. The shape of these unsaturated emission lines is strongly opacity sensitive to the local chromospheric velocity field. As for the Mg II lines, the outward decreasing intensity of the short-wavelength emission component signals fast acceleration of chromospheric outflow in the upper chromosphere. We also observe this decrease for the resonance line of Mg I λ2852 (not shown). Our previous radiative transfer modeling work based on Si I revealed that α Ori’s inner chromosphere oscillates nonradially, with simultaneous up- and downflows in Sept. 1998."[5]

X-rays[edit]

This is a ROSAT image of the X-ray sky around Orion. Credit: Konrad Dennerl and Wolfgang Voges.
This is the optical sky around Orion. Credit: Konrad Dennerl and Wolfgang Voges.
This is an Aladin sky map of a region(circle,05 55 10.30536 +07 24 25.4304,20m) around Betelgeuse. Credit: Marshallsumter with Aladin at SIMBAD.

"This picture [on the right] shows the (X-ray) sky around midnight at the date [17 December 1994] of the Symposium above Munich, as seen with X-ray sensitive eyes."[6]

"From August 1990 to February 1991 the German X-ray satellite ROSAT performed the first all-sky survey in soft X-rays with an imaging telescope. We have synthesized the point sources found with a preliminary automatic source detection analysis of these data into a colour image which shows the X-ray sky around the Orion region (5228 objects in an area of approximately 50 deg x 75 deg) in a similar way as we perceive the optical sky."[6]

"For this image we have selected that part of the sky which culminated at midnight over Munich during the time of the TEXAS symposium. This is the region around Orion, probably the most beautiful and well-known area of the sky visible from mid-northern latitudes. According to the visual impression, we displayed it in a projection which compresses the areas close to the zenith."[6]

The image on the left is a match in the optical for the X-ray image on the right. Note that Betelgeuse in the optical image on the left is not visible in the ROSAT X-ray image on the right.

"Calculations based on a rather simple theory for quiet coronas (Grasberger and Henyey 1959), indicated that radiation from the chromosphere-corona of at least one of the nearby, bright supergiants (Deneb, Canopus, Betelgeuse, or Rigel) might be bright enough to be observed. [...] a variety of stellar sources can be observed."[7]

According to SIMBAD there is at least one X-ray source at or within 9 arcminutes of the coordinates of Betelgeuse. This source was found using "region(05 55 10.305 +07 24 25.43,9m) & otype='X'". It is 1RXS J055507.1+073007, which is a ROSAT designation. It is 5.74771' from Betelgeuse, which is probably just inside the bow shock.

In the interstellars section below the bow shocks and a linear dust bar are at or within 9 arcmin of Betelgeuse.

On the left is an Aladin sky map of the 27 known astronomical objects listed in SIMBAD as occurring within a 20' circle around Betelgeuse (red + with an arrow showing direction of movement).

Two X-ray (X) sources are present. Eight UV sources (pink *), eleven stars (small red circles), four infrared objects (red diamonds), and two submillimeter sources.

Comparing the locations of the two X-ray sources with their locations in relation to Betelgeuse and its bow shock, the closest is just inside the bow shock and the other is on the other side of the linear bar.

Ultraviolets[edit]

Image shows the red supergiant Betelgeuse that pulsates, swells and shrinks asymmetrically in the UV. Credit: Andrea Dupree, Ronald Gilliland, CfA, STScI, NASA, ESA.

"The photo-montage made in ultraviolet light [on the right] shows the pulsating atmosphere of Betelgeuse. The star is scanned with the Space Telescope Imaging Spectrograph. Seven spectra are recorded through a small field of view shown by the rectangle at different positions on the disk, marked by the crosses. The thick yellow curves show the shape of a double-peaked emission line which emerges from Betelgeuse's chromosphere. The depression between the peaks is formed far out in this warmer envelope. The spectra in the top images of January and March '98 reveal that this outer region collapses since the left-hand peak of the emission line is everywhere stronger than the right. But the STIS scan in the lower left image of September '98 unveils how atmospheric gas begins to move up in the fifth scan position, where the right-hand peak exceeds the left. Here gas streams in opposite directions at the same time through the star's outer atmosphere. The spectral scan in the lower right image of March '99 shows that the expandingtrend proceeds and extends further across the chromosphere. The arrows in the images point North in the plane of the sky and should be aligned when comparing the location of surface details. Note that the mean intensity levels of the four images have been equalized to bring out these details. The top images are actually observed brighter than the lower ones. Note also that some spectral scans are taken a week apart from the images."[8]

"From early 1998 to spring 1999, the Space Telescope Imaging Spectrograph (STIS) was used to scan Betelgeuse's disk four times and to record spectra from small slices cut across its surface."[9]

"We found the upper atmosphere or chromosphere warmer than the region below it and we observed that it also contracted and expanded during this period. But, most surprisingly, a scan in fall 1998 suggests streams of gas that are heading in opposite directions --with velocities of about 10,000 miles per hour."[9]

"Throughout the same period, the Faint Object Camera (FOC) was used to make new images of Betelgeuse's chromosphere in ultraviolet (UV) light. While the intensity of UV emitted by the chromosphere varied with the star's pulsation, brighter and rather subtle intensity patterns appeared at different locations on the stellar disk. Although an FOC observation [...] in 1995 revealed a bright spot-like area on Betelgeuse's surface, the new images -- with their improved resolution -- now also revealed that a bright 'arc-like' structure spanned a large portion of the disk in September 1998."[9]

"As astonishing as these images may be, they also show us that the precise locations of the brighter regions remain unresolved. Sharper and more frequent images obtained during one pulsation cycle are needed to pinpoint their physical origin."[9]

The "new images show that the upper atmosphere changes in a rather unordered manner just like the simultaneous up- and down-flows seen in the STIS spectra."[10]

"One out of a million stars in our galaxy is a supergiant and fewer yet are cool supergiants. Not only is Betelgeuse a cool supergiant, but it is also the seventh brightest star visible in the northern hemisphere, appearing in the shoulder of the constellation Orion at a distance of 425 light-years from Earth. Because its surface temperature can drop to below 3,000 K degrees, it shines reddish. Its atmosphere is like a big puffy cloud, ten million times less dense than our Sun; and, under such conditions, slight perturbations have dramatic effects on movements of its atmospheric gases."[9]

The "star is wrapped in an even bigger and less dense envelope of warmer gas. Its chromosphere extends up to 5,000 times the radius of our Sun, or out to Neptune's orbit, where the temperature can increase to about 5,000 K degrees. "[9]

Opticals[edit]

Betelgeuse is imaged in ultraviolet light by the Hubble Space Telescope and subsequently enhanced by NASA.[11] Credit: NASA and ESA.

"The yellow/red "image" or "photo" of Betelgeuse usually seen is actually not a picture of the red giant but rather a mathematically generated image based on the photograph. The photograph was actually of much lower resolution: The entire Betelgeuse image fit entirely within a 10x10 pixel area on the Hubble Space Telescopes Faint Object Camera. The actual images were oversampled by a factor of 5 with bicubic spline interpolation, then deconvolved."[11]

Polarized light[edit]

Asymmetric Betelgeuse and its environment is imaged in visible light (top) and polarized visible light (bottom). Credit: P. Kervella, E. Lagadec, M. Montargès, S. T. Ridgway, A. Chiavassa, X. Haubois, H.-M. Schmid, M. Langlois, A. Gallenne, and G. Perrin.

In the image on the right, "Asymmetric Betelgeuse and its environment [are] imaged in visible light (top) and polarized visible light (bottom). Each column is a different filter. The red dashed circle indicates Betelgeuse’s infrared photospheric radius. The light dashed circle is three times this."[12]

"As you can see in the images [on the right], Betelgeuse is not symmetric, and neither is its circumstellar material. The top row shows brightness in different visible-light filters while the bottom row shows degree of polarization (light colors are more polarized than dark)."[12]

"Most of the imaged polarized light is far from the star’s photosphere, and is probably polarized due to dust scattering. However, bits of this dust are close to the star, too! It’s well known that red supergiants like Betelgeuse lose significant amounts of mass. Mass loss seems to be connected to the huge convective cells inside supergiants, because they too are not spherically symmetric, but we don’t know precisely how. We do know the lost mass forms a circumstellar envelope around the star and and provides the material from which dust can form. It follows that if the dust was all far away or all close-in, that would tell us something about how it got there. Instead, at any single distance away from the star, we find different amounts of dust and gas in a range of different temperatures and densities."[12]

Visuals[edit]

This is a visual Hubble Space Telescope image of Betelgeuse with enhancement. Credit: Andrea Dupree (Harvard-Smithsonian CfA), Ronald Gilliland (STScI), NASA and ESA.

"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."[13]

"We do not know why the star is shrinking. Considering all that we know about galaxies and the distant Universe, there are still lots of things we don't know about stars, including what happens as red giants near the ends of their lives."[14]

"Betelgeuse is beyond the death beam distance -- somewhere within 30 light years range -- where it could do ultimate damage to Earth. The explosion won't do the Earth any harm, as a star has to be relatively close -- on the order of 25 light years -- to do that. Betelgeuse is about 600 light years distant."[13]

The image on the right is a visual image using the Hubble Space Telescope with enhancements including a relocation of an apparent hot spot to the right side relative to the image in the Opticals section.

Lights[edit]

This is a long term light curve of Alpha Orionis. Credit: BSJ.

"The light variations of Betelgeuse are not completely understood, however since the star has been studied extensively, there are theories that describe the observed phenomena. Astronomers think the outer layers of the star expand slowly for several years and then shrink again, so the surface area alternately increases and decreases, and the temperature rises and falls, making the star brighten and dim. Red supergiants pulsate this way because their atmospheres are not quite stable. When the star is smallest, the atmosphere absorbs a bit too much of the energy passing through it, so the atmosphere heats and expands. As it expands, it becomes thinner. Energy then passes through the outer layers more easily so the gases cool, and the star shrinks again."[15]

Oranges[edit]

This is a DSS image probably with a Schmidt of Betelgeuse. Credit: Peter Challis.

This visual image of Betelgeuse probably with a Schmidt as part of the DSS shows its orange color.

Reds[edit]

The photo shows the constellation of Orion and the surrounding nebulas of the Orion Molecular Cloud complex. Credit: Rogelio Bernal Andreo.

"Cradled in cosmic dust and glowing hydrogen, stellar nurseries in Orion the Hunter lie at the edge of a giant molecular cloud some 1,500 light-years away. Spanning nearly 25 degrees, this breath-taking vista stretches across the well-known constellation from head to toe (left to right). The Great Orion Nebula, the closest large star forming region, is right of center. To its left are the Horsehead Nebula, M78, and Orion's belt stars. Sliding your cursor over the picture will also find red giant Betelgeuse at the hunter's shoulder, bright blue Rigel at his foot, and the glowing Lambda Orionis (Meissa) nebula at the far left, near Orion's head. Of course, the Orion Nebula and bright stars are easy to see with the unaided eye, but dust clouds and emission from the extensive interstellar gas in this nebula-rich complex, are too faint and much harder to record. In this mosaic of broadband telescopic images, additional image data acquired with a narrow hydrogen alpha filter was used to bring out the pervasive tendrils of energized atomic hydrogen gas and the arc of the giant Barnard's Loop."[16]

Infrareds[edit]

This image is from ESO's Very Large Telescope showing not only the stellar disk, but also an extended atmosphere with a previously unknown plume of surrounding gas.[17] Credit: ESO/P. Kervella.
The head (Meissa) and shoulders (Betelgeuse and Bellatrix) of the constellation Orion with surrounding nebulas is depicted in infrared. Credit: NASA/JPL-Caltech/UCLA.
This is an interferometric image of the photosphere of Betelgeuse. Credit: Richard Mushotzky, NASA Goddard Space Flight Center.
This is the surface of Betelgeuse imaged using infrared interferometry at 1.64 µm. Credit: X. Haubois, G. Perrin, S. Lacour, T. Verhoelst, S. Meimon, L. Mugnier, E. Thiebaut, J.P. Berger, S.T. Ridgway, J.D. Monnier, R. Millan-Gabet, and W. Traub.

The image at right is "of the supergiant star Betelgeuse obtained with the NACO adaptive optics instrument on ESO’s Very Large Telescope. The use of NACO combined with a so-called “lucky imaging” technique, allows the astronomers to obtain the sharpest ever image of Betelgeuse, even with Earth’s turbulent, image-distorting atmosphere in the way. The resolution is as fine as 37 milliarcseconds, which is roughly the size of a tennis ball on the International Space Station (ISS), as seen from the ground. The image is based on data obtained in the near-infrared, through different filters. The field of view is about half an arcsecond wide, North is up, East is left."[18]

The image on the left shows the head and shoulders of Orion in the infrared. "In Greek mythology, Orion was a hunter whose vanity was so great that he angered the goddess Artemis. As his punishment, Artemis banished the hunter to the sky where he can be seen as the famous constellation Orion. In the constellation, Orion's head is represented by the star Lamdba Orionis (fuzzy red dot in middle). When viewed in infrared light, NASA's Wide-field Infrared Survey Explorer, or WISE, shows a giant nebula around Lambda Orionis, inflating Orion's head to huge proportions."[19]

"Lambda Orionis is a hot, massive star that is surrounded by several other hot, massive stars, all of which are creating radiation that excites a ring of dust, creating the "Lambda Orionis molecular ring." Also known as SH 2-264, the Lambda Orionis molecular ring is sometimes called the Meissa ring. In Arabic, the star Lambda Orionis is known as "Meissa" or "Al-Maisan," meaning "the shining one." The Meissa Ring is of interest to astronomers because it contains clusters of young stars and proto-stars, or forming stars, embedded within the clouds. With a diameter of approximately 130 light-years, the Lambda Orionis molecular ring is notable for being one of the largest star-forming regions WISE has seen. This is also the largest single image featured by WISE so far, with an area of the sky approximately 10 by 10 degrees in size, equivalent to a grid of 20 by 20 full moons. Nevertheless, at less than one percent of the whole sky's area, it is just a taste of WISE data."[19]

"The bright blue star in the lower left corner of the image is the star Betelgeuse, which represents one shoulder of the hunter Orion. The name Betelgeuse is actually a corruption of the original Arabic phrase "Yad al-Jauza'," meaning "hand of the giant one." Betelgeuse is well known for being a red supergiant star, yet in WISE's infrared view it appears blue, as do most stars in WISE images. This is because most stars, including Betelgeuse, put out more light in the shortest infrared wavelengths of light captured by WISE, and those shorter wavelengths are presented in WISE images as blue and cyan."[19]

"In visible light, Orion's other shoulder is clearly marked by the variable star Bellatrix. In infrared light, however, Bellatrix is a somewhat unremarkable cyan-colored star in the right side of the image. In Latin, Bellatrix means "female warrior," which is perhaps why the name was chosen for a female witch character in the popular Harry Potter books."[19]

"Also seen in this image are two dark nebulae, Barnard 30 and Barnard 35, which are parts of the Meissa ring that are so dense they block out visible light. Barnard 30 is the bright knob of gas and dust in the top center part of the image. Barnard 35 appears as a hook extending towards the center of the ring just above and to the right of the star Betelgeuse. The bright reddish object seen to in the middle right part of the image is the star HR 1763, which is surrounded by another star-forming region, LBN 867."[19]

"Color in this image represents specific wavelengths of infrared light. Blue and cyan represent 3.4- and 4.6-microns, primarily light emitted by hot stars. Green and red represent 12- and 22-micron light, which is mainly radiation from warm dust."[19]

The second image down on the right is an interferometric image of the photosphere of Betelgeuse at 1.64 microns.

The second image down on the left is the unsmoothed infrared interferometry of the surface (photosphere) of Betelgeuse at 1.64 µm.

"The image reveals the presence of two giant bright spots, whose size is equivalent to the distance Earth-Sun : they cover a large fraction of the surface. It is a first strong and direct indication of the presence of phenomena of convection, transport of heat by the moving matter, in a star other than the Sun."[20]

"The analysis of the brightness of the spots shows a variation of 500 degrees compared to the average temperature of the star (3 600 Kelvins). The largest of the two structures has a dimension equivalent to the quarter of the star diametre (or one and a half the distance Earth-Sun). This marks a clear difference with the Sun where the cells of convection are much finer and reach hardly 1/20th of the solar radius (a few Earth radius). These characteristics are compatible with the idea of luminous spots produced by the convection."[20]

Radios[edit]

This is a 7 mm radio image of Betelgeuse's atmosphere. Credit: NRAO/AUI and J. Lim, C. Carilli, S.M. White, A.J. Beasley, and R.G. Marson.
The asymmetric structure of Betelgeuse in radio waves is likely due to activity in the outer atmosphere of the star. Credit: NRAO/AUI.

The image on the right is of Betelgeuse at 7 mm (45 Gz) radio waves.

"Close to the star, we find that the atmosphere has an irregular structure, and a temperature (3,450 +/- 850K) consistent with the photospheric temperature but much lower than that of gas in the same region probed by optical and ultraviolet observations. This cooler gas decreases steadily in temperature with radius, reaching 1,370 +/- 330K by seven stellar radii. The cool gas coexists with the hot chromospheric gas, but must be much more abundant as it dominates the radio emission."[21]

The asymmetric structure of Betelgeuse in radio waves shown in the image on the left is likely due to activity in the outer atmosphere of the star.

Dusty regions[edit]

A "constructed [image] of Alpha Orionis [yielded] indications of dust close to the red supergiant star. [Data was] gathered in 1980 with an interferometer and the Canada-France-Hawaii Telescope. To explain Betelgeuse's lopsided appearance, [...] a large fraction of the recorded light comes from an irregular dust envelope close to the stellar disk."[22]

Hydrogens[edit]

These two images show emission and absorption of hydrogen alpha. Credit: P. Kervella, E. Lagadec, M. Montargès, S. T. Ridgway, A. Chiavassa, X. Haubois, H.-M. Schmid, M. Langlois, A. Gallenne, and G. Perrin.

"Two of the filters used to image Betelgeuse are sensitive to the familiar red hydrogen alpha spectral feature. Because one filter is broader than the other, subtracting the light in the narrow filter from the light seen with the broad filter yields a map of where hydrogen gas is emitting or absorbing light. It also turns out to be highly asymmetric. Most of the hydrogen emission is confined within a distance of three times Betelgeuse’s near-infrared radius. It’s a similar distance from the star as most of the polarized dust, but the spatial distributions are different."[12]

In the image on the right, "Left: A map of hydrogen emission (red) and absorption (blue) in the vicinity of Betelgeuse, with the same dashed lines [The red dashed circle indicates Betelgeuse’s infrared photospheric radius. The light dashed circle is three times this.] for reference. Right: Color composite of three of the filters from the first figure (the narrow hydrogen alpha filter is excluded)."[12]

"Betelgeuse’s asymmetries persist in both in dust and gas, with a major interface between the two located around three times the near-infrared stellar radius. These asymmetries agree with different types of past observations and also strongly point toward a connection between supergiant mass loss and vigorous convection."[12]

Ions[edit]

This set of graphs shows spatially resolved chromospheric emission lines of Fe I, Fe II, Al II, and C II. Credit: A. Lobel, J. Aufdenberg, A. K. Dupree, R. L. Kurucz, R. P. Stefanik, and G. Torres.

"[I]on lines of Fe II, Al II, and C II [have been observed] out to 1′′ in the upper chromosphere. [The set of graphs on the right] shows (scaled) emission lines of Fe II λ2716 (UV 62), Al II λ2669 (UV 1), and C II λ2327 (UV 1)."[9]

Spectroscopy[edit]

This is a spectrum of Betelgeuse taken with a SkyWatcher 200p / EQ5 / SynScan Tracking Star Analyser 100. Credit: Raymond Gilchrist.
This spectrum of Betelgeuse ranges from about 520.0 nm (blue-green) to about 640.0 nm (yellow). Credit: Jeremy Sepinsky.

Above is a spectrum of Betelgeuse "taken with a SkyWatcher 200p / EQ5 / SynScan Tracking Star Analyser 100."[23]

The above spectrum of Betelgeuse has magnesium (Mg I) lines and strong titanium oxide (TiO2) bands. Its temperature is between 2,000 to 3,600 K.[23]

The spectrum of Betelgeuse on the right ranges from about 520.0 nm (blue-green) to about 640.0 nm (yellow) on the right end.

Stars[edit]

Def.

  1. any "small luminous dot appearing in the cloudless portion of the night sky, especially with a fixed location relative to other such dots"[24] or
  2. a "luminous celestial body, made up of plasma (particularly hydrogen and helium),[25] and having a spherical shape"[26]

is called a star.

Chromospheres[edit]

This set of graphs shows the detailed profiles of the Mg II h & k lines observed up to 1000 mas. Credit: A. Lobel, J. Aufdenberg, A. K. Dupree, R. L. Kurucz, R. P. Stefanik, and G. Torres.

The set of graphs on the right "shows the detailed profiles of the Mg II h & k lines observed up to 1000 mas. The emission line intensities decrease by a factor of ∼700 from chromospheric disk center (TP 0) to 1′′. These optically thick chromospheric lines show remarkable changes of their detailed shapes when scanning off-limb. The full width across both emission components at half intensity maximum decreases by ∼20%, while the broad and saturated central absorption core narrows by more than 50%. Beyond 600 mas the central core assumes a constant width which results from absorption contributions by the local interstellar medium (d≃132 pc). We observe a strong increase of the (relative) intensity of the long-wavelength emission component in both lines beyond 200 mas. It signals fast wind acceleration beyond this radius. Note that the short-wavelength emission components of the k and h lines are blended with chomospheric Mn I lines (decreasing the k- and increasing the h-component), but that become much weaker in the outer chromosphere."[5]

Interstellars[edit]

These are Herschel PACS and SPIRE images of Betelgeuse. Credit: L. Decin, N.L.J. Cox, P. Royer, A.J. Van Marle, B. Vandenbussche, D. Ladjal, F. Kerschbaum, R. Ottensamer, M.J. Barlow, J.A.D.L. Blommaert, H.L. Gomez, M.A.T. Groenewegen, T. Lim, B.M. Swinyard, C. Waelkens, and A.G.G.M. Tielens.
This is an image in the far infrared of the bow shock preceding Betelgeuse. Credit: Leen Decin.

In the image above there are "Herschel [Photodetector Array Camera and Spectrometer] PACS and [Spectral and Photometric Imaging Receiver on board the Herschel satellite] SPIRE images of Betelgeuse. North is up, east to the left. The field-of-view (FOV) is ∼49′ ×29′."[27] The grid overlain is J2000.0 RA and Dec.

"For both instruments, the ‘scan map’ observing mode was used with medium (20′′/s) scan speed in the PACS 70, 100, and 160μm filter settings and 30′′/s for the SPIRE 250, 350, and 500 μm filters. To create a uniform cover- age, avoid striping artefacts, and increase redundancy, two ob- servations at orthogonal scan directions were concatenated. The PACS images were obtained on September 13, 2010 (OBSIDS 1342204435 and 1342204436) and on March 29, 2012 (OBSIDS 1342242656 and 1342242657), the SPIRE images on March 11, 2010 (OBSID 1342192099)."[27]

"The individual scan maps are plotted [in the image above] a multiple arc-like structure is detected at ∼6-7′ away from the central star, together with an enigmatic linear bar-like structure at ∼9′. [...] The inner radius of the closest arc is at 280′′ (as measured from the central target). The other most prominent arcs have an inner radius at 280′′, 310′′, 350′′ and 375′′. The brightest parts of the arcs are reasonably well fitted by concentric ellipses [...] The width of the arcs is typically ∼20′′. Clearly, substructures of the size of several arcseconds, probably related to density differences, are seen in the arcs. The arc-like structure is probably related to the [circumstellar matter-interstellar matter] CSM-ISM interaction phase, when the circumstellar material collides at a wind speed of ∼15 km/s with the ISM, creating a bow shock [...] The inner ridge of the linear bar is at 535′′ from the central star. The length is ∼1600′′. The width is ∼30′′ in the northern part; moving down towards the south-east, the bar widens and splits into two parts. The angle between the direction of space velocity [...] and the linear bar is ∼80°."[27]

"Multiple arcs are revealed around Betelgeuse, the nearest red supergiant star to Earth, in [the second image down on the right] from ESA’s Herschel space observatory. The star and its arc-shaped shields [or bow shock] could collide with an intriguing dusty ‘wall’ in 5000 years."[28]

The "far-infrared view from Herschel shows how the star’s winds are crashing against the surrounding interstellar medium, creating a bow shock as the star moves through space at speeds of around 30 km/s."[28]

"A series of broken, dusty arcs ahead of the star’s direction of motion testify to a turbulent history of mass loss."[28]

"Closer to the star itself, an inner envelope of material shows a pronounced asymmetric structure. Large convective cells in the star’s outer atmosphere have likely resulted in localised, clumpy ejections of dusty debris at different stages in the past."[28]

"An intriguing linear structure is also seen further away from the star, beyond the dusty arcs. While some earlier theories proposed that this bar was a result of material ejected during a previous stage of stellar evolution, analysis of the new image suggests that it is either a linear filament linked to the Galaxy’s magnetic field, or the edge of a nearby interstellar cloud that is being illuminated by Betelgeuse."[28]

"The infrared Herschel images of the environment around Betelgeuse [show] the occurrence of multiple arcs at 6-7 arcmin from the central target and the presence of a linear bar at 9 arcmin."[27]

Betelgeuse "should be spinning slowly, since rotation rate decreases as size increases. [...] But that's not the case with Betelgeuse, which is rotating at a blazing 33,500 mph (53,900 km/h)"[29]

"We cannot account for the rotation of Betelgeuse. It's spinning 150 times faster than any plausible single star just rotating and doing its thing."[30]

"Betelgeuse's puzzling spin could be explained if the giant gobbled up a companion roughly the same mass as the sun 100,000 years or so ago. (The angular momentum of the companion's orbit would be transferred to Betelgeuse, speeding up the giant's rotation to its current rate.)"[29]

"This act of cannibalism likely would have spurred a cosmic belch of sorts, causing Betelgeuse to blast a cloud of material out into space at about 22,400 mph (36,000 km/h). Indeed, [there is] a shell of matter at roughly the distance from Betelgeuse that this scenario predicts. [See the image on the right.] "[30]

Nebulas[edit]

This picture of the dramatic nebula around the bright red supergiant star Betelgeuse was created from images taken with the VISIR infrared camera on ESO’s Very Large Telescope (VLT). Credit: ESO/P. Kervella.

"This picture [on the right] of the dramatic nebula around the bright red supergiant star Betelgeuse was created from images taken with the VISIR infrared camera on ESO’s Very Large Telescope (VLT). This structure, resembling flames emanating from the star, forms because the behemoth is shedding its material into space. The earlier NACO observations of the plumes are reproduced in the central disc. The small red circle in the middle has a diameter about four and half times that of the Earth’s orbit and represents the location of Betelgeuse’s visible surface. The black disc corresponds to a very bright part of the image that was masked to allow the fainter nebula to be seen."[31]

"The VLT image shows the surrounding nebula, which is much bigger than the supergiant itself, stretching 37 billion miles (60 billion kilometers) away from the star’s surface – about 400 times the distance of Earth from the Sun."[32]

In theory, "Red supergiants like Betelgeuse represent one of the last stages in the life of a massive star. In this short-lived phase, the star increases in size and expels material into space at a tremendous rate — it sheds immense quantities of material (about the mass of the Sun) in just 10,000 years. [...] the plumes seen close to the star are probably connected to structures in the outer nebula now imaged in the infrared with VISIR. The nebula cannot be seen in visible light, as the very bright Betelgeuse completely outshines it. The irregular, asymmetric shape of the material indicates that the star did not eject its material in a symmetric way. The bubbles of stellar material and the giant plumes they originate may be responsible for the clumpy look of the nebula."[32]

"The small red circle in the middle has a diameter about 4.5 times that of Earth’s orbit and represents the location of Betelgeuse’s visible surface. The black disk corresponds to a bright part of the image that was masked to allow the fainter nebula to be seen. The VISIR images were taken through infrared filters sensitive to radiation of different wavelengths, with blue corresponding to shorter wavelengths and red to longer. The field of view is 5.63 by 5.63 arcseconds."[32]

Bright nebulas[edit]

This is a radio image taken with the e-MERLIN radio telescope array operated from the Jodrell Bank Observatory in Cheshire. Credit: Anita Richards, The University of Manchester.

"The image [on the right] shows Betelgeuse’s atmosphere extending out to five times the size of the visual surface of the star. It also reveals two hot spots within the outer atmosphere and a faint arc of cool gas even farther out beyond the radio surface of the star. The arc of cool gas extends about as far away as Pluto is from our Sun."[33]

"The hot spots have a temperature of about 6,740 to 8,540 degrees Fahrenheit [4000 to 5000 K], which is much higher than the average temperature of the radio surface of the star and even higher than the visual surface."[33]

The photosphere of the Sun is at 5778 K.

"This is the first image showing hot spots this far away from the center of the star."[33]

"The new image, taken by the e-MERLIN radio telescope array operated from the Jodrell Bank Observatory in Cheshire, also shows regions of surprisingly hot gas in the star’s outer atmosphere and a cooler arc of gas weighing almost as much as the Earth."[33]

Red supergiants[edit]

Red supergiants (RSGs) are supergiant stars (luminosity class I) of spectral type K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive. Betelgeuse and Antares are the best known examples of a red supergiant. These stars have very cool surface temperatures (3500–4500 K), and enormous radii. The five largest known red supergiants in the Galaxy are VY Canis Majoris, VV Cephei A, V354 Cephei, RW Cephei and KW Sagittarii, which all have radii about 1500 times that of the Sun (about 7 astronomical units, or 7 times as far as the Earth is from the Sun). The radius of most red giants is between 200 and 800 times that of the [S]un. Absolute luminosities may reach -10 magnitude compared to +5 for our Sun.

Stellar astrophysics[edit]

These three images show the shrinking surface of Betelgeuse. Credit: C. H. Townes, E. H. Wishnow, D. D. S. Hale, and B. Walp.
The graph shows the changes in Betelgeuse's diameter, but the changes appear bigger than they actually are. Credit: C. H. Townes, E. H. Wishnow, D. D. S. Hale, and B. Walp.

"The two images on the right were reconstructed using data from the Cambridge Optical Aperture Synthesis Telescope (COAST), and the image on the left with data from the William Herschel Telescope (WHT). Each image has a side length corresponding to 100 mas, and one sees big differences in the diameter of the star, and of its surface features, depending of the wavelength at which it is observed."[34]

"This fact makes it difficult to compare directly angular diameters of Betelgeuse obtained with different instruments at different wavelengths."[34]

"Using the Infrared Spatial Interferometer (ISI) on Mount Wilson, [data was collected at a wavelength of around 11000 nanometres over the last 15 years.]"[34]

"The diameters measured by the ISI are not particularly inconsistent with previous measurements, are rather accurate, and show clearly that the star has systematically decreased in size by about 15% over the past 15 years."[35]

"Betelgeuse has been known to be a star with variability, but it seems that this change in size is odd and unexpected, even more so as its luminosity has been roughly constant."[34]

"ISI measurements over the last 15 years clearly show a systematic change in the diameter of α Ori. This change may or may not be periodic; if it is, the period is likely rather long, perhaps a few decades. [...] It should be valuable to continue accurate measurements of α Ori's size and other characteristics in order to understand the dynamics involved in this striking change, and to have systematic long-term measurements of similar stars."[35]

Orion[edit]

This is the IAU sky chart for the constellation Orion. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg).
This Hubble Space Telescope image shows the position of Betelgeuse in the constellation of Orion. Credit: Akira Fujii.

At right is the IAU sky chart for Orion with notable sources including Betelgeuse indicated.

On the left is a full color image of the constellation of Orion with an arrow pointing to Betelgeuse.

Mythology[edit]

"There is [...] another figure in Greek mythology who does fit in with [Betelgeuse being a very bright, prominent star that undergoes striking changes in intensity, occasionally becoming extremely bright, other times dwindling in intensity, with no clearly discernable period, that represents the shoulder of a large figure] very nicely. That figure is Pelops, son of Tantalus. According to his myth (recounted most notably in Pindar’s first Olympian Ode, although referred to several times in ancient literature (Ganz 1993)) Pelops was killed by his father and cut up into a stew served to the gods. The gods immediately knew what the banquet was and refused to eat it, except for one goddess—Demeter, in most sources—who ate what turned out to be his shoulder. Tantalus was cast into Hades to atone perpetually for his crime, and Pelops was restored by being boiled in a cauldron. His missing shoulder was replaced by a piece of ivory."[36]

"Pelops later defeated king Oenomaus of Pisa in a chariot race, killing the king in the process and winning his daughter Hippodameia as a wife. He later became ruler of the Pelopponese, which he renamed after himself (“Pelops’ Island” = “ Pelopponese”), and was esteemed a great ruler, although his line was notably cursed."[36]

There "is a Hungarian myth of a warrior whose shoulder is replaced by one of ivory (Frazer 1935), although this is not explicitly connected with a constellation. In Egypt, the constellation of Orion was associated with the god Osiris. It is significant, I think, that Osiris was also said to have been dismembered, then re-assembled and brought back to life. Again, one part was missing and had to be replaced."[36]

"The constellation of Orion is associated with myths of dismemberment elsewhere in the world. Among the Taulipang of Brazil, it is said to represent a man named Zililkawai whose wife hacked off his leg, represented by Betelgeuse (Staal 1988; Werner 1961; Koch-Grünberg 1923). Staal, who recounts this, associates the redness of Betelgeuse with the bloody stump, but I note that the variations in brightness could give the impression of the leg being “hacked off.” The Taulipang live in northern Brazil, near or below the equator, where the constellation of Orion appears to be sideways (relative to its orientation in the northern hemisphere) when it rises, and Betelgeuse can plausibly be interpreted as a leg rather than a shoulder. (I must note, in fairness, that the parallel myth among the nearby Warao concerns a man named Nohi-Abassi, who also loses a leg. The Warao say the leg is the “belt” of Orion (Wilbert 1970)."[36]

Among "the Lakota of the North American Plains the constellation represents the arm of a Lakota chief which was ripped off as punishment. Again, in this case Betelgeuse is not explicitly even named (the belt is the wrist and thumb, Rigel the index finger) (Goodman 1992a, 1992b)."[36]

"The existence of so many myths of removed and replaced body parts that can be plausibly connected with the constellation of Orion suggests that knowledge of the variability of alpha Ori was known in several parts of the world."[36]

Classical history[edit]

A segment of the Dunhuang star map, with the constellation of Orion to the left. Credit: Unknown.

The classical history period dates from around 2,000 to 1,000 b2k.

Around 150 AD, the Hellenistic astronomer Claudius Ptolemy described Sirius as reddish, along with five other stars, Betelgeuse, Antares, Aldebaran, Arcturus and Pollux, all of which are clearly of orange or red hue.[37]

A segment of the Dunhuang star map from around 700 AD (1,300 b2k) on the right contains the constellation of Orion to the left. Betelgeuse is the star at the top of Orion.

Recent history[edit]

The view is mirrored following the tradition of celestial globes, showing the celestial sphere in a view from "ouside", with Betelgeuse in the right shoulder of Orion. Credit: Johannes Hevelius.
This map of the celestial dome shows stars and constellations near Betelgeuse. Credit: Agnes Giberne (from an old catalog).

The recent history period dates from around 1,000 b2k to present.

On the upper right is a celestial map of the constellations near or around Taurus, including Orion with Betelgeuse the star in Orion's right shoulder. This image is from 1690 (310 b2k).

On the lower right is a celestial map of the stars and constellations near to Betelgeuse from 1898 (102 b2k).

"Among colored stars, single and double, a few maybe mentioned by name as examples. Sirius, as already observed, is a brilliant white sun; and brilliant white also are Vega, Altair, Regulus, Spica, and many others. Capella, Procyon, the Pole star, and our own sun, are examples of yellow stars. Aldebaran, Betelgeuse, and Pollux, are ruby-red. Antares is a red star."[38]

Temperatures[edit]

Reconstructed from interference patterns this false-color image of Betelgeuse reveals a "hot spot" that could correspond to a huge column of upwelling gas. Credit: David Busher.

On the right is a false-color image of Betelgeuse that reveals a "hot spot" that could correspond to a huge column of upwelling gas.

Hypotheses[edit]

  1. Betelgeuse has a low-temperature photosphere relative to the Sun because the interstellar electron influx is much less intense.
  2. Betelgeuse is a young star being compressed by interstellar electron influx.

See also[edit]

References[edit]

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External links[edit]

{{Charge ontology}}{{Radiation astronomy resources}}