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Stellar News Feed Archive

Missing link between turbulence in collapsing star, hypernovae and gamma-ray bursts Monday, November 30, 2015 - 13:01

A supercomputer simulation of a mere 10 milliseconds in the collapse of a massive star into a neutron star proves that these catastrophic events, often called hypernovae, can generate the enormous magnetic fields needed to explode the star and fire off bursts of gamma rays visible halfway across the universe.

The results of the simulation, published online Nov. 30 in advance of publication in the journal Nature, demonstrate that as a rotating star collapses, the star and its attached magnetic field spin faster and faster, forming a dynamo that revs the magnetic field to a million billion times the magnetic field of Earth.

A field this strong is sufficient to focus and accelerate gas along the rotation axis of the star, creating two jets that ultimately can produce oppositely directed blasts of highly energetic gamma rays.

Read the full press release at UC Berkley News

Purchase the article from Nature


Aging Star’s Weight Loss Secret Revealed Wednesday, November 25, 2015 - 11:34

The star VY Canis Majoris is a red hypergiant, one of the largest known stars in the Milky Way. It is 30–40 times the mass of the Sun and 300 000 times more luminous. In its current state, the star would encompass the orbit of Jupiter, having expanded tremendously as it enters the final stages of its life.

New observations of the star using the SPHERE instrument on the VLT have clearly revealed how the brilliant light of VY Canis Majoris lights up the clouds of material surrounding it and have allowed the properties of the component dust grains to be determined better than ever before.

In this very close-up view from SPHERE the star itself is hidden behind an obscuring disc. The crosses are artefacts due to features in the instrument.

Read the full press release from ESO


Forged in the hearts of stars Thursday, November 19, 2015 - 10:34

Apart from hydrogen, as many have heard from the Carl Sagan and Neil deGrasse Tyson "Cosmos" series, every ingredient in the human body is made from elements forged by stars.

The calcium in our bones, the oxygen we breathe, the iron in our blood — all were forged in the element factories of stars. Even the carbon in our apple pie.

Stars are giant element furnaces. Their intense heat can cause atoms to collide, creating new elements — a process known as nuclear fusion. That process is what created chemical elements like carbon or iron, the building blocks that make up life as we know it.

It sounds pretty simple, but it is a very intricate process. And there are still many uncertainties.

Professors Sumner Starrfield and Frank Timmes, both from Arizona State University, and professor Christian Iliadis, from the University of North Carolina at Chapel Hill, hope to resolve some of those uncertainties.

Read the full press release from ASU


Protostar Growth Spurts Thursday, November 5, 2015 - 10:42

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have discovered an adolescent protostar that is undergoing a rapid-fire succession of growth spurts. Evidence for this fitful youth is seen in a pair of intermittent jets streaming away from the star’s poles.

Known as CARMA-7, the protostar is one of dozens of similar objects in the Serpens South star cluster, which is located approximately 1,400 light-years from Earth. This clutch of nascent stellar objects was first detected by and named for the Combined Array for Research in Millimeter-wave Astronomy (CARMA) telescope.

"This young protostar is undergoing periods of rapid growth separated by periods of relative calm,” said Adele Plunkett, previously a National Science Foundation (NSF) graduate research fellow at Yale University and now a fellow at the European Southern Observatory (ESO) in Chile. "This punctuated stellar formation provides important insights into the chaotic interplay within this tightly packed cluster of young stars.”

Read the full story at NRAO News

See also "Growing pains in a cluster of protostars" at Yale News

Mass-loss rate by the Mira in the symbiotic binary V1016 Cygni from Raman scattering Thursday, October 29, 2015 - 11:05





The mass-loss rate from Mira variables represents a key parameter in our understanding of their evolutionary tracks. We introduce a method for determining the mass-loss rate from the Mira component in D-type symbiotic binaries via the Raman scattering of atomic hydrogen in the wind from the giant. Using our method, we investigated Raman HeII 1025\AA\ --> 6545\AA\ conversion in the spectrum of the symbiotic Mira V1016 Cyg. We determined its efficiency to be 0.102 and 0.148, and the corresponding mass-loss rate 2.0 (+0.1/-0.2) x 1E-6 and 2.7 (+0.2/-0.1) x 1E-6 M(Sun)/year, using our spectra from 2006 April and 2007 July,respectively. Our values of the mass-loss rate that we derived from Raman scattering are comparable with those obtained independently by other methods. Applying the method to other Mira-white dwarf binary systems can provide a necessary constraint in the calculation of asymptotic giant branch evolution.

Authors: Matej Sekeráš, Augustin Skopal

Read the full text from astro-ph 


VISTA Discovers New Component of Milky Way Wednesday, October 28, 2015 - 09:50

“All of the 35 classical Cepheids discovered are less than 100 million years old. The youngest Cepheid may even be only around 25 million years old, although we cannot exclude the possible presence of even younger and brighter Cepheids,” explains the study’s second author Dante Minniti, of the Universidad Andres Bello, Santiago, Chile.

The ages of these classical Cepheids provide solid evidence that there has been a previously unconfirmed, continuous supply of newly formed stars into the central region of the Milky Way over the last 100 million years. But, this wasn’t to be the only remarkable discovery from the survey’s dataset.

Read the full press release from ESO News


The Inner Workings of Red Giant Stars Tuesday, October 27, 2015 - 10:19

Sunspot, filaments, plages, and flares — visible signs of the Sun’s magnetic field riddle its atmosphere. But divining magnetic activity inside the Sun is another matter entirely.

We can’t directly see the magnetic fields within stars, and that makes it difficult to connect a star’s visible tortured gas with the inner workings of its magnetic field. Everything from predicting the strength of the next solar cycle to describing stellar aging hinges on better understanding these fields.

Now, astronomers have found a way to indirectly discern magnetic fields, at least within certain types of stars.

Read the story at Sky & Telescope

Read the original press release

Full text research paper from arXiv


Final Kiss of Two Stars Heading for Catastrophe Wednesday, October 21, 2015 - 10:16

The double star system VFTS 352 is located about 160 000 light-years away in the Tarantula Nebula [1]. This remarkable region is the most active nursery of new stars in the nearby Universe and new observations from ESO’s VLT [2] have revealed that this pair of young stars is among the most extreme and strangest yet found.

VFTS 352 is composed of two very hot, bright and massive stars that orbit each other in little more than a day. The centres of the stars are separated by just 12 million kilometres [3]. In fact, the stars are so close that their surfaces overlap and a bridge has formed between them. VFTS 352 is not only the most massive known in this tiny class of “overcontact binaries” — it has a combined mass of about 57 times that of the Sun — but it also contains the hottest components — with surface temperatures above 40 000 degrees Celsius.

Read the full story at ESO News


First discovery of a magnetic field in a normal delta Scuti star Tuesday, October 20, 2015 - 10:31

Two types of pulsating stars exist among stars with a mass between 1.5 and 2.5 solar masses: the delta Scuti stars and the gamma Dor stars. Theory tells us that, when such stars have a surface temperature between 6900 and 7400 Kelvin, they can have both types of pulsations, i.e. they are called “hybrid stars”. The NASA space mission Kepler provided a wealth of new candidate “hybrid stars”, even outside the theoretically predicted physical parameter range.

Coralie Neiner (LESIA, CNRS / Observatoire de Paris / UPMC / Université Paris Diderot) and Patricia Lampens (Royal Observatory of Belgium) have therefore sought which physical phenomena could mimic the hybrid character in delta Scuti stars. One possibility could be the presence of a magnetic field which would produce spots on the rotating stellar surface and mimic the gamma Dor pulsations. However, no magnetic field had ever been observed in a delta Scuti star until now…

Read the full story at Royal Observatory of Belgium News


The Explosions of Stars Wrapped in Hydrogen Monday, October 19, 2015 - 10:45

The authors of today’s paper are interested in shedding light on what attributes of the star lead to the features we see in these types of supernovae, called Type II-L supernovae (where the “L” stands for “Linear”, as in linear decay).

The authors combine two popular programs to generate fake supernova light curves. First, they generate a progenitor star using the a program called MESAstar. Using this simulation, they’re able to change the amount of mass a star loses over its lifetime to beef-up that star’s outer hydrogen envelope. When their stars are ready to explode, they pass them off to another program known as STELLA. STELLA follows packets of atoms to see how they mix and heat during the supernova explosion. STELLA lets astronomers see these interactions at different frequencies, so they can map the results onto filters we can observe, like the V-band. Figure 2 shows some of the light curves the authors get from STELLA and how they compare with real Type II-L supernovae.

Read the full article in Astrobites


Shedding light on the growth of stars and black holes Wednesday, October 14, 2015 - 09:30

Christian Knigge, Professor in Physics and Astronomy, worked with colleagues from around the world to study one of the most important, but least understood processes in astronomy – accretion, where the mass of an object grows by gravitationally collecting material from nearby.

The article Accretion-induced variability links young stellar objects, white dwarfs, and black holes has been published in the latest edition of the journal Science Advances.

The paper reveals a close relationship between the way in which different types of accreting objects vary in brightness over time. Their results connect proto-stars resembling our Sun at the time of its birth, to accreting white dwarfs, to supermassive black holes with a billion times the mass of the Sun, located in galaxies millions of light years away.

Read the full press release here.


Mysterious Ripples Found Racing Through Planet-forming Disc Wednesday, October 7, 2015 - 13:38

AU Microscopii, or AU Mic for short, is a young, nearby star surrounded by a large disc of dust [1]. Studies of suchdebris discs can provide valuable clues about how planets, which form from these discs, are created.

Astronomers have been searching AU Mic’s disc for any signs of clumpy or warped features, as such signs might give away the location of possible planets. And in 2014 they used the  powerful high-contrast imaging capabilities of ESO’s newly installed SPHERE instrument, mounted on the Very Large Telescope for their search — and discovered something very unusual.

“The images from SPHERE show a set of unexplained features in the disc which have an arch-like, or wave-like, structure, unlike anything that has ever been observed before.”

Read the full story at Hubble Space Telescope News


Searching for Orphan Stars Amid Starbirth Fireworks Wednesday, September 30, 2015 - 10:24

Gemini Observatory has released one of the most detailed images ever obtained of emerging gas jets streaming from a region of newborn stars. The region, known as the Herbig-Haro 24 (HH 24) Complex, contains no less than six jets streaming from a small cluster of young stars embedded in a molecular cloud in the direction of the constellation of Orion.

Reipurth along with co-researcher, Colin Aspin, also at the IfA, are using the Gemini North data from the Gemini Multi-Object Spectrograph (GMOS), as well as the Gemini Near-Infrared Imager, to study the region which was discovered in 1963 by George Herbig and Len Kuhi. Located in the Orion B cloud, at a distance of about 400 parsecs, or about 1,300 light-years from our Solar System, this region is rich in young stars and has been extensively studied in all types of light, from radio waves to X-rays.

"The Gemini data are the best ever obtained from the ground of this remarkable jet complex and are showing us striking new detail," says Aspin. Reipurth and Aspin add that they are particularly interested in the fine structure and "excitation distribution" of these jets.

Read the full story at Gemini Observatory News


Discovery of an “Eclipse” in the WC9d-Type Wolf-Rayet Star, WR 53 Wednesday, September 30, 2015 - 10:16

AAVSO observer extraordinaire flies the flag for visual observers proudly with yet another independent discovery.

Abstract: The WC9d-type Wolf-Rayet star WR 53 was observed visually entering into an “eclipse” with a depth of 1.2 magnitude. Subsequent visual and CCD data showed a steady linear rise over 10 days to recover and return to its normal brightness level. This is the first-ever recorded “eclipse” of this star which has previously shown no photometric variability. 

Author: Rod Stubbings

Read the pre-print on astro-ph


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


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