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Stellar News Feed Archive

The wings of the butterfly Wednesday, August 26, 2015 - 09:59

Ordinary planetary nebulae have one star at their centre, bipolar nebulae have two, in a binary star system. Astronomers have found that the two stars in this pair each have around the same mass as the Sun, ranging from 0.6 to 1.0 solar masses for the smaller star, and from 1.0 to 1.4 solar masses for its larger companion. The larger star is approaching the end of its days and has already ejected its outer layers of gas into space, whereas its partner is further evolved, and is a small white dwarf.

The characteristic shape of the wings of the Twin Jet Nebula is most likely caused by the motion of the two central stars around each other. It is believed that a white dwarf orbits its partner star and thus the ejected gas from the dying star is pulled into two lobes rather than expanding as a uniform sphere.

Read the full story at ESA Hubble News

 

Gaia's First Year of Scientific Observations Tuesday, August 25, 2015 - 10:44

On 21 August 2014, Gaia commenced its main survey operation, employing a scanning law designed to achieve the best possible coverage of the whole sky.

Since the start of its routine phase, the satellite recorded 272 billion positional or astrometric measurements 54.4 billion brightness or photometric data points, and 5.4 billion spectra.

The Gaia team have spent a busy year processing and analysing these data, en route towards the development of Gaia’s main scientific products, consisting of enormous public catalogues of the positions, distances, motions and other properties of more than a billion stars. Because of the immense volumes of data and their complex nature, this requires a huge effort from expert scientists and software developers distributed across Europe, combined in Gaia’s Data Processing and Analysis Consortium (DPAC).

Read the full story at ESA GAIA News

 

Magnetars: The Perpetrators of (Nearly) Everything Thursday, August 20, 2015 - 10:34

Astronomers who study cosmic explosions have a running joke: anything too wild to explain with standard models are probably magnetars. These scapegoats are neutron stars with extremely powerful magnetic fields, like the one shown to the right.

Super-luminous supernovae? Probably a magnetar collapsing. Short, weak gamma ray bursts? Why not magnetar flares. Ultra-long gamma ray bursts? Gotta be magnetars. Magnetars are a popular model due to their natural versatility. In today’s paper, the authors tie together several magnetar theories into a cohesive theoretical explanation of two types of transients, or short cosmic events: super-luminous supernovae (SLSNe) and ultra-long gamma ray bursts (ULGRBs).

Read the full review on Astrobites

 

First Images of Cool Starspots on a Star Other than the Sun: Interferometric Imaging of λ Andromedae Thursday, August 20, 2015 - 10:27

Presented are the first interferometric images of cool starspots on the chromospherically active giant λ Andromedae. These images represent the first model-independent images of cool starspots on a star other than the Sun to date. The interferometric observations, taken with the Michigan Infra-Red Combiner coupled to the Center for High Angular Resolution Astronomy Array, span 26 days from Aug 17th, 2008 to Sep 24th, 2011. The photometric time series acquired at Fairborn Observatory spanning Sep 20th, 2008 to Jan 20th, 2011 is also presented. The angular diameter and power law limb-darkening coefficient of this star are 2.759 ± 0.050 mas and 0.229 ± 0.111, respectively. Starspot properties are obtained from both modeled and SQUEEZE reconstructed images. The images from 2010 through 2011 show anywhere from one to four starspots. The measured properties of identical starspots identified in both the model and reconstructed images are within two σ error bars in 51% of cases. The cadence in the data for the 2010 and 2011 data sets are sufficient to measure a stellar rotation period based on apparent starspot motion. This leads to estimates of the rotation period (P2010= 60 ± 13 days, P2011 = 54.0 ± 7.6 days) that are consistent with the photometrically determined period of 54.8 days. In addition, the inclination and position angle of the rotation axis is computed for both the 2010 and 2011 data sets; values (Ψ¯ = 21.5$\degree$,$\bar{\emph{i}}$ = 78.0$\degree$) for each are nearly identical between the two years.

Authors: J.R. Parks, R.J. White, F. Baron, J.D. Monnier, B. Kloppenborg, G. Henry, G. Scheafer, X. Che, E. Pedretti, N. Thureau, M. Zhao, T. ten Brummelaar, H. McAlister, S.T. Ridgway, N. Turner, J. Sturmann, L. Sturmann

Read the pre-print paper on astro-ph

 

NASA's Hubble Finds Supernovae in 'Wrong Place at Wrong Time' Thursday, August 13, 2015 - 16:40

Scientists have been fascinated by a series of unusual exploding stars-outcasts beyond the typical cozy confines of their galaxies. A new analysis of 13 supernovae — including archived data from NASA's Hubble Space Telescope — is helping astronomers explain how some young stars exploded sooner than expected, hurling them to a lonely place far from their host galaxies.

It's a complicated mystery of double-star systems, merging galaxies, and twin black holes that began in 2000 when the first such supernova was discovered, according to study leader Ryan Foley, University of Illinois at Urbana-Champaign. "This story has taken lots of twists and turns, and I was surprised every step of the way," he said. "We knew these stars had to be far from the source of their explosion as supernovae and wanted to find out how they arrived at their current homes."

Read the full story at HubbleSite News

 

Neutron Stars Strike Back at Black Holes in Jet Contest Tuesday, August 4, 2015 - 10:02

Previously, black holes were the undisputed kings of forming powerful jets. Even when only nibbling on a small amount of material, the radio emission that traces the jet outflow from the black hole was relatively bright. In comparison, neutron stars seemed to make relatively puny jets -- the radio emission from their jets was only bright enough to see when they were gobbling material from their companion at a very high rate. A neutron star sedately consuming material was therefore predicted to form only very weak jets, which would be too faint to observe.

Recently, however, combined radio and X-ray observations of the neutron star PSR J1023+0038 completely contradicted this picture.

Read the full press release at NRAO News

 

The circumstellar dust of “Born-Again” stars Monday, July 27, 2015 - 15:02

We describe the evolution of the carbon dust shells around Very Late Thermal Pulse (VLTP) objects as seen at infrared wavelengths. This includes a 20-year overview of the evolution of the dust around Sakurai’s object (to which Olivier made a seminal contribution) and FG Sge. VLTPs may occur during the endpoint of as many as 25% of solar mass stars, and may therefore provide a glimpse of the possible fate of the Sun.

Authors: A. Evans, R. D. Gehrz, L. A. Helton and C. E. Woodward

Read the paper from astro-ph

 

Brown Dwarfs, Stars Share Formation Process, New Study Indicates Thursday, July 23, 2015 - 13:53


Astronomers using the Karl G. Jansky Very Large Array (VLA) have discovered jets of material ejected by still-forming young brown dwarfs. The discovery is the first direct evidence that brown dwarfs, intermediate in mass between stars and planets, are produced by a scaled-down version of the same process that produces stars.


The astronomers studied a sample of still-forming brown dwarfs in a star-forming region some 450 light-years from Earth in the constellation Taurus, and found that four of them have the type of jets emitted by more-massive stars during their formation.

"This is the first time that such jets have been found coming from brown dwarfs at such an early stage of their formation, and shows that they form in a way similar to that of stars," said Oscar Morata, of the Institute of Astronomy and Astrophysics of the Academia Sinica in Taiwan. 

Read the full story at NRAO News

 

Gaia satellite and amateur astronomers spot one in a billion star Saturday, July 18, 2015 - 15:24

Gaia14aae contains large amounts of helium, but no hydrogen, which is highly unusual as hydrogen is the most common element in the Universe. The lack of hydrogen allowed them to classify Gaia14aae as a very rare type of system known as an AM Canum Venaticorum (AM CVn), a type of Cataclysmic Variable system where both stars have lost all of their hydrogen. This is the first known AM CVn system where one star totally eclipses the other.

“It’s really cool that the first time that one of these systems was discovered to have one star completely eclipsing the other, that it was amateur astronomers who made the discovery and alerted us,” said Campbell. “This really highlights the vital contribution that amateur astronomers make to cutting edge scientific research.”

Read the full news article

Read the research paper from the MNRAS

 

ASASSN-15lh: The Most Luminous Supernova Ever Discovered Thursday, July 16, 2015 - 10:49

We report the discovery and early evolution of ASASSN-15lh, the most luminous supernova ever found. At redshift z=0.2326, ASASSN-15lh reached an absolute magnitude of M_{u,AB} ~ -23.5 and bolometric luminosity L_bol ~ 2.2x10^45 ergs/s, which is >~ 2 times more luminous than any previously known supernova. Its spectra match the hydrogen-poor sub-class of super-luminous supernovae (SLSNe-I), whose energy sources and progenitors are poorly understood. In contrast to known SLSNe-I, most of which reside in star-forming, dwarf galaxies, its host appears to be a luminous galaxy (M_V ~ -22; M_K ~ -25.1) with little star formation. In the two months since its first detection, ASASSN-15lh has radiated ~7.5x10^51 ergs, challenging the popular magnetar model for the engine of SLSNe-I.

Authors: Subo Dong (KIAA-PKU), B. J. Shappee (Carnegie), J. L. Prieto (UDP), S. W. Jha (Rutgers), K. Z. Stanek (Ohio State), T. W.-S. Holoien (Ohio State), C. S. Kochanek (Ohio State), T. A. Thompson (Ohio State), N. Morrell (LCO), I. B. Thompson (Carnegie), U. Basu, J. F. Beacom, D. Bersier, J. Brimacombe, J. S. Brown, Ping Chen, E. Conseil, A. B. Danilet, E. Falco, D. Grupe, S. Kiyota, G. Masi, B. Nicholls, F. Olivares, G. Pignata, G. Pojmanski, G. V. Simonian, D. M. Szczygiel, P. R. Wozniak

Download the pre-print from astro-ph

 

Colliding red giant prime suspect for luminous red nova outburst Thursday, July 9, 2015 - 08:14

Observations of a rare astronomical phenomenon, called a luminous red nova, suggest that this bright outburst was caused by a red giant colliding with another star. Astronomers used the Liverpool Telescopeto track the outburst over several months and hunted through the Hubble Space Telescope archive to identify possible progenitors. Dr Steven Williams will present the results at the National Astronomy Meeting 2015 in Llandudno on Thursday 9th July.

“We found that our observations of M31LRN 2015 showed strong similarities to other objects classified as luminous red novae. If a single mechanism is responsible for all these rare events, the evidence suggests merging stars as the cause,” said Williams. He added, “Further observations of this and other systems are certainly needed. Astronomers have some way to go before these enigmatic objects are fully understood.”

Read the full press release at RAS News

 

Biggest Explosions in the Universe Powered by Strongest Magnets Wednesday, July 8, 2015 - 14:16

Observations from ESO’s La Silla and Paranal Observatories in Chile have for the first time demonstrated a link between a very long-lasting burst of gamma rays and an unusually bright supernova explosion. The results show that the supernova was not driven by radioactive decay, as expected, but was instead powered by the decaying super-strong magnetic fields around an exotic object called a magnetar.

GRBs usually only last a few seconds, but in very rare cases the gamma rays continue for hours. One such ultra-long duration GRB was picked up by the Swift satellite on 9 December 2011 and named GRB 111209A. It was both one of the longest and brightest GRBs ever observed.

As the afterglow from this burst faded it was studied using both the GROND instrument on the MPG/ESO 2.2-metre telescope at La Silla and also with the X-shooter instrument on the Very Large Telescope (VLT) at Paranal. The clear signature of a supernova, later named SN 2011kl, was found. This is the first time that a supernova has been found to be associated with an ultra-long GRB.

Read the press release at ESO News

Download the research paper to appear in Nature

 

A five star, doubly-eclipsing star system Wednesday, July 8, 2015 - 09:33

Astronomers at the Open University have discovered the first quintuple star system containing two eclipsing binary stars. Details of the five star system, the first of its kind to be found, will be presented by Marcus Lohr of the Open University in a talk on Wednesday 8 July at the National Astronomy Meeting at Venue Cymru, Llandudno, Wales.

The light curve of the new quintuple system, designated as 1SWASP J093010.78+533859.5, initially revealed the presence of a contact eclipsing binary - a system in which the two stars are orbiting so close together that they share an outer atmosphere. Contact binaries are quite common, but this particular system is notable because its orbital period - the time the two stars take to complete one orbital cycle - is so short, just under six hours.

Then it was spotted that the light curve contained some additional unexpected eclipses, and the data were reanalysed to reveal a second eclipsing binary at the same location on the sky.  The new binary is detached - its component stars are well-separated by a distance of about 3 million km, or about twice the size of the Sun - and it has a longer orbital period of one and a third days.

Read the full press release

 

Transition Disks Tuesday, July 7, 2015 - 12:51

A star is typically born with a disk of gas and dust encircling it, from which planets develop as dust grains in the disk collide, stick together and grow. These disks, warmed by the star to a range of temperatures above the cold, ambient interstellar material, can be detected at infrared or millimeter wavelengths, and their infrared color used to characterize their properties. Stars older than about five million years lack evidence for these disks, however, suggesting that by this age most of the disk material has either been converted into planets or smaller bodies, accreted onto the star, or dispersed from the system. Transition disks bridge this period in disk evolution: They have not yet been disbursed, but although they are present they emit only slightly in the infrared. Their emission shows characteristically cooler temperatures, and signs that the innermost (hottest) regions have already disappeared and left a gap (or cavity) in the ring.

CfA astronomer Sean Andrews and his colleagues have been studying transition disks in nearby star-forming regions located in constellations of Taurus and Ophiuchus. The astronomers note that the gaps in transition disks they see might have been caused by one or more of three processes: grain growth and planet formation that depleted the material, a giant planet in the vicinity that swept the region clean, or a stellar wind that blew away or evaporated the dust.

See more at: CfA News

Read the pre-print on astro-ph

 

MONSTER BLACK HOLE WAKES UP AFTER 26 YEARS Thursday, June 25, 2015 - 14:25

On 15 June 2015, a long-time acquaintance of X-ray and gamma ray astronomers made its comeback to the cosmic stage: V404 Cygni, a system comprising a black hole and a star orbiting one another. It is located in our Milky Way galaxy, almost 8000 light-years away in the constellation Cygnus, the Swan.

In this type of binary system, material flows from the star towards the black hole and gathers in a disc, where it is heated up, shining brightly at optical, ultraviolet and X-ray wavelengths before spiralling into the black hole.

The V404 Cygni black hole system has not been this bright and active since 1989, when it was observed with the Japanese X-ray satellite Ginga and high-energy instruments on board the Mir space station. 

Read the full story at the ESA Intregal site

 

Intense radio emission from tiny binary star Monday, June 22, 2015 - 09:33

The small binary star known as AB Doradus B is located in the AB Doradus star system, consisting of two pairs of stars. Stars normally emit light that can be seen with the naked eye or through telescopes, but some also emit radio waves, similar to those from televisions, mobile phones or microwave ovens.

These emissions have made it possible to calculate the mass of the star, which is usually complex, but "when the star is accompanied by another, its orbital motion gives us an accurate way to determine it, as Kepler's laws establish," says the director of the Astronomical Observatory, José Carlos Guirado, co-author of the study. "The mass of these stars cannot be reproduced by the current models of stellar evolution, so we require a major overhaul of these theories," adds the scientist in the Department of Astronomy and Astrophysics.

Read the full story at Science Daily

 

Voracious vortexes in cataclysmic variables. Multi-epoch tomographic study of HT Cassiopeia Wednesday, June 17, 2015 - 10:20

We present multi-epoch, time-resolved optical spectroscopic observations of the dwarf nova HT Cas, obtained during 1986, 1992, 1995 and 2005 with the aim to study the properties of emission structures in the system. We determined that the accretion disc radius, measured from the double-peaked emission line profiles, is persistently large and lies within the range of 0.45-0.52a, where a is the binary separation. This is close to the tidal truncation radius r_max=0.52a. This result contradicts with previous radius measurements. An extensive set of Doppler maps has revealed a very complex emission structure of the accretion disc. Apart from a ring of disc emission, the tomograms display at least three areas of enhanced emission: the hot spot from the area of interaction between the gas stream and the disc, which is superposed on the elongated spiral structure, and the extended bright region on the leading side of the disc, opposite to the location of the hot spot. The position of the hot spot in all the emission lines is consistent with the trajectory of the gas stream. However, the peaks of emission are located in the range of distances 0.22-0.30a, which are much closer to the white dwarf than the disc edge. This suggests that the outer disc regions have a very low density, allowing the gas stream to flow almost freely before it starts to be seen as an emission source. We have found that the extended emission region in the leading side of the disc is always observed at the very edge of the large disc. Observations of other cataclysmic variables, which show a similar emission structure in their tomograms, confirm this conclusion. We propose that the leading side bright region is caused by irradiation of tidally thickened sectors of the outer disc by the white dwarf and/or hot inner disc regions.

Authors: V. V. Neustroev, S. V. Zharikov, N. V. Borisov

Read the paper on astro-ph

 

A Celestial Butterfly Emerges from its Dusty Cocoon Wednesday, June 10, 2015 - 10:33

Astronomers found the dust disc to begin about 900 million kilometres from the star — slightly farther than the distance from the Sun to Jupiter — and discovered that it flares outwards, creating a symmetrical, funnel-like shape surrounding the star. The team also observed a second source of light about 300 million kilometres — twice the distance from Earth to the Sun — from L2 Puppis. This very close companion star is likely to be another red giant of slightly lower mass, but less evolved.

The combination of a large amount of dust surrounding a slowly dying star, along with the presence of a companion star, mean that this is exactly the type of system expected to create a bipolar planetary nebula. These three elements seem to be necessary, but a considerable amount of good fortune is also still required if they are to lead to the subsequent emergence of a celestial butterfly from this dusty chrysalis.

Read the press release

 

A new sdO+dM binary with extreme eclipses and reflection effect Wednesday, June 3, 2015 - 09:48

We report the discovery of a new totally-eclipsing binary (RA=06:40:29.11; Dec=+38:56:52.2; J=2000.0; Rmax=17.2 mag) with an sdO primary and a strongly irradiated red dwarf companion. It has an orbital period of Porb=0.187284394(11) d and an optical eclipse depth in excess of 5 magnitudes.

Astronomers Observe Rare Stellar Eclipse Tuesday, June 2, 2015 - 15:48

A team of professional and amateur astronomers has succeeded in observing a distant companion as it eclipsed the bright variable star b Persei (not to be confused with Beta Persei) in a rare event.

The b Persei system was already known as a binary, with two stars that orbit each other every 1.5 days. But a suspected third companion popped up during a survey of radio-emitting stars. The Navy Precision Optical Interferometer (NPOI) began to trace out the companion’s orbit, and what began as routine observations turned into a rare eclipse prediction: the distant companion was set to cross in front of the other two stars in February 2013, and then again in January 2015.

- See more at: http://www.skyandtelescope.com/astronomy-news/astronomers-observe-rare-stellar-eclipse-0602201503/

 

Searching for nova shells around cataclysmic variables Sunday, May 31, 2015 - 11:33

We present the results of a search for nova shells around 101 cataclysmic variables (CVs), using Halpha images taken with the 4.2-m William Herschel Telescope (WHT) and the 2.5-m Isaac Newton Telescope Photometric Halpha Survey of the Northern Galactic Plane (IPHAS). Both telescopes are located on La Palma. We concentrated our WHT search on nova-like variables, whilst our IPHAS search covered all CVs in the IPHAS footprint. We found one shell out of the 24 nova-like variables we examined. The newly discovered shell is around V1315 Aql and has a radius of approx.2.5 arcmin, indicative of a nova eruption approximately 120 years ago. This result is consistent with the idea that the high mass-transfer rate exhibited by nova-like variables is due to enhanced irradiation of the secondary by the hot white dwarf following a recent nova eruption. The implications of our observations for the lifetime of the nova-like variable phase are discussed. We also examined 4 asynchronous polars, but found no new shells around any of them, so we are unable to confirm that a recent nova eruption is the cause of the asynchronicity in the white dwarf spin. We find tentative evidence of a faint shell around the dwarf nova V1363 Cyg. In addition, we find evidence for a light echo around the nova V2275 Cyg, which erupted in 2001, indicative of an earlier nova eruption approx.300 years ago, making V2275 Cyg a possible recurrent nova. 

Authors: D. I. Sahman, V. S. Dhillon, C. Knigge, T. R. Marsh

Read the pre-print on astro-ph

 

Resolving the stellar activity of the Mira AB binary with ALMA Friday, May 29, 2015 - 09:31

We present the size, shape and flux densities at millimeter continuum wavelengths, based on ALMA science verification observations in Band 3 (~94.6 GHz) and Band 6 (~228.7 GHz), from the binary Mira A (o Ceti) and Mira B. The Mira AB system has been observed with ALMA at a spatial resolution of down to ~25 mas. The extended atmosphere of Mira A and the wind around Mira B sources are resolved and we derive the size of Mira A and of the ionized region around Mira B. The spectral indices within Band 3 (between 89-100 GHz) and between Band 3 and Band 6 are also derived. The spectral index of Mira A is found to change from 1.71+-0.05 within Band 3 to 1.54+-0.04 between Band 3 and 6. The spectral index of Mira B is 1.3+-0.2 in Band 3, in good agreement with measurements at longer wavelengths. However it rises to 1.72+-0.11 between the bands. For the first time the extended atmosphere of a star is resolved at these frequencies and for Mira A the diameter is ~3.8x3.2 AU in Band 3 (with brightness temperature Tb~5300 K) and ~4.0x3.6 AU in Band 6 (Tb~2500 K). Additionally, a bright hotspot of ~0.4 AU and with Tb~10000 K is found on the stellar disc of Mira A. The size of the ionized region around the accretion disk of Mira B is found to be ~2.4 AU. The emission around Mira B is consistent with that from a partially ionized wind of gravitationally bound material from Mira A close to the accretion disk of Mira B. The Mira A atmosphere does not fully match predictions, with brightness temperatures in Band 3 significantly higher than expected, potentially due to shock heating. The hotspot is likely due to magnetic activity and could be related to the previously observed X-ray flare of Mira A.

Authors: W.H.T. Vlemmings, S. Ramstedt, E. O'Gorman, E.M.L. Humphreys, M. Wittkowski, A. Baudry, M. Karovska

Read the paper on asdtro-ph

 

The inner environment of Z Canis Majoris: High-contrast imaging polarimetry with NaCo Tuesday, May 26, 2015 - 10:05

Abstract
Context. Z CMa is a binary composed of an embedded Herbig Be and an FU Ori class star separated by ~100 au. Observational evidence indicates a complex environment in which each star has a circumstellar disk and drives a jet, and the whole system is embedded in a large dusty envelope.
Aims. We aim to probe the circumbinary environment of Z CMa in the inner 400 au in scattered light.
Methods. We use high-contrast imaging polarimetry with VLT/NaCo at the H and Ks bands.
Results. The central binary is resolved in both bands. The polarized images show three bright and complex structures: a common dust envelope, a sharp extended feature previously reported in direct light, and an intriguing bright clump located  south of the binary, which appears spatially connected to the sharp extended feature.
Conclusions. We detect orbital motion when compared to previous observations, and report a new outburst driven by the Herbig star. Our observations reveal the complex inner environment of Z CMa in unprecedented detail and contrast.


Authors: H. Canovas, S. Perez, C. Dougados, J. de Boer, F. Ménard, S. Casassus, M. R. Schreiber, L. A. Cieza, C. Caceres and J. H. Girard

Recently published in A&A, read the pre-print from astro-ph

 

Supernova Hits Star, Results Shocking Thursday, May 21, 2015 - 10:48

The origin of type Ia supernovae, the standard candles used to reveal the presence of dark energy in the universe, is one of astronomy’s most beguiling mysteries. Astronomers know they occur when a white dwarf explodes in a binary system with another star, but the properties of that second star — and how it triggers the explosion — have remained elusive for decades. 

Now, a team of astronomers from the intermediate Palomar Transient Factory (iPTF), including those associated with UC Santa Barbara, have witnessed a supernova smashing into a nearby star, shocking it, and creating an ultraviolet glow that reveals the size of the companion. The discovery involved the rapid response and coordination of iPTF, NASA’s Swift satellite and the new capabilities of the Las Cumbres Observatory Global Telescope Network (LCOGT).

- See more at: http://www.news.ucsb.edu/2015/015447/supernova-hits-star-results-shocking#sthash.ppQknp9D.dpuf

 

What is the Shell Around R Coronae Borealis? Monday, May 18, 2015 - 09:52

The hydrogen-deficient, carbon-rich R Coronae Borealis (RCB) stars are known for being prolific producers of dust which causes their large iconic declines in brightness. Several RCB stars, including R CrB, itself, have large extended dust shells seen in the far-infrared. The origin of these shells is uncertain but they may give us clues to the evolution of the RCB stars. The shells could form in three possible ways. 1) they are fossil Planetary Nebula (PN) shells, which would exist if RCB stars are the result of a final, helium-shell flash, 2) they are material left over from a white-dwarf merger event which formed the RCB stars, or 3) they are material lost from the star during the RCB phase. Arecibo 21-cm observations establish an upper limit on the column density of H I in the R CrB shell implying a maximum shell mass of less than 0.3 solar masses. A low-mass fossil PN shell is still a possible source of the shell although it may not contain enough dust. The mass of gas lost during a white-dwarf merger event will not condense enough dust to produce the observed shell, assuming a reasonable gas-to-dust ratio. The third scenario where the shell around R CrB has been produced during the star's RCB phase seems most likely to produce the observed mass of dust and the observed size of the shell. But this means that R CrB has been in its RCB phase for approximately 10^4 yrs.

Authors: Edward J. Montiel, Geoffrey C. Clayton, Dominic C. Marcello, Felix J. Lockman

Read the paper on atro-ph

 

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