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Stellar News Feed Archive

Bizarre Star Could Host a Neutron Star in Its Core Monday, January 20, 2014 - 15:54

Astronomers say that they have discovered the first example of a long-sought cosmic oddity: a bloated, dying star with a surprise in its core — an ultra-dense neutron star.

Such entities, known as Thorne-Zytkow objects, are theoretically possible but would alter scientists' understanding of how stars can be powered. Since Thorne-Zytkow objects were first proposed in 1975, researchers have occasionally offered up candidates, but none have been confirmed.

 The latest work, reported on 6 January at a meeting of the American Astronomical Society outside Washington DC, focuses on a red supergiant star in the Small Magellanic Cloud, a neighboring galaxy to the Milky Way. The star is enriched in lithium, rubidium and molybdenum. Elevated amounts of these elements are thought to arise as by-products of Thorne-Zytkow objects, which have to burn through unusual nuclear fusion pathways.
 
Relating jet structure to photometric variability: the Herbig Ae star HD 163296 Friday, January 17, 2014 - 08:47

Herbig Ae/Be stars are intermediate-mass pre-main sequence stars surrounded by circumstellar dust disks. Some are observed to produce jets, whose appearance as a sequence of shock fronts (knots) suggests a past episodic outflow variability. This "jet fossil record" can be used to reconstruct the outflow history. We present the first optical to near-infrared (NIR) VLT/X-shooter spectra of the jet from the Herbig Ae star HD 163296. We determine physical conditions in the knots, as well as their kinematic "launch epochs". Knots are formed simultaneously on either side of the disk, with a regular interval of ~16 yr. The velocity dispersion versus jet velocity and the energy input are comparable in both lobes. However, the mass loss rate, velocity, and shock conditions are asymmetric. We find Mjet/Macc ~ 0.01-0.1, consistent with magneto-centrifugal jet launching models. No evidence for dust is found in the high-velocity jet, suggesting it is launched within the sublimation radius (<0.5 au). The jet inclination measured from proper motions and radial velocities confirms it is perpendicular to the disk. A tentative relation is found between the structure of the jet and the photometric variability of the source. Episodes of NIR brightening were previously detected and attributed to a dusty disk wind. We report for the first time significant optical fadings lasting from a few days up to a year, coinciding with the NIR brightenings. These are likely caused by dust lifted high above the disk plane; this supports the disk wind scenario. The disk wind is launched at a larger radius than the high-velocity atomic jet, although their outflow variability may have a common origin. No significant relation between outflow and accretion variability could be established. Our findings confirm that this source undergoes periodic ejection events, which may be coupled with dust ejections above the disk plane.

Authors:  L. E. Ellerbroek, L. Podio, C. Dougados, S. Cabrit, M. L. Sitko, H. Sana, L. Kaper, A. de Koter, P. D. Klaassen, G. D. Mulders, I. Mendigutia, C. A. Grady, K. Grankin, H. van Winckel, F. Bacciotti, R. W. Russell, D. K. Lynch, H. B. Hammel, L. C. Beerman, A. N. Day, D. M. Huelsman, C. Werren, A. Henden, J. Grindlay

Read the paper on astro-ph

The Double Contact Nature of TT Herculis Thursday, January 16, 2014 - 16:35

We present new radial velocities and photometry of the short-period Algol TT Herculis. Previous attempts to model the light curves of the system have met with limited success, primarily because of the lack of a reliable mass ratio. Our spectroscopic observations are the first to result in radial velocities for the secondary star, and thus provide a spectroscopic mass ratio. Simultaneous analysis of the radial velocities and new photometry shows that the system is a double contact binary, with a rapidly rotating primary that fills its limiting lobe.

Authors: Dirk Terrell, Robert H. Nelson

Read the paper on astro-ph

Episodic Accretion in Young Stars Thursday, January 16, 2014 - 16:28

In the last twenty years, the topic of episodic accretion has gained significant interest in the star formation community. It is now viewed as a common, though still poorly understood, phenomenon in low-mass star formation. The FU Orionis objects (FUors) are long-studied examples of this phenomenon. FUors are believed to undergo accretion outbursts during which the accretion rate rapidly increases from typically 10−7 to a few 10−4 M⊙ yr−1, and remains elevated over several decades or more. EXors, a loosely defined class of pre-main sequence stars, exhibit shorter and repetitive outbursts, associated with lower accretion rates. The relationship between the two classes, and their connection to the standard pre-main sequence evolutionary sequence, is an open question: do they represent two distinct classes, are they triggered by the same physical mechanism, and do they occur in the same evolutionary phases? Over the past couple of decades, many theoretical and numerical models have been developed to explain the origin of FUor and EXor outbursts. In parallel, such accretion bursts have been detected at an increasing rate, and as observing techniques improve each individual outburst is studied in increasing detail. We summarize key observations of pre-main sequence star outbursts, and review the latest thinking on outburst triggering mechanisms, the propagation of outbursts from star/disk to disk/jet systems, the relation between classical EXors and FUors, and newly discovered outbursting sources -- all of which shed new light on episodic accretion. We finally highlight some of the most promising directions for this field in the near- and long-term.

Authors: Marc Audard, Péter Ábrahám, Michael M. Dunham, Joel D. Green, Nicolas Grosso, Kenji Hamaguchi, Joel H. Kastner, Ágnes Kóspál, Giuseppe Lodato, Marina Romanova, Stephen L. Skinner, Eduard I. Vorobyov, Zhaohuan Zhu

Read the paper on astro-ph

V1117 Her: A Herbig Ae Star At High Galactic Latitude? Friday, January 10, 2014 - 13:09

Another paper featuring AAVSO observations in the analysis.

Abstract: We examine the long-term light curve, optical spectrum, spectral energy distribution, and Galactic location of V1117 Her in order to establish its nature. V1117 Her is most probably a young intermediate-mass star whose cyclic brightness dimmings are caused by changing circumstellar dust structures.

Authors: M. Kun, M. Rácz, L. Szabados

Read the full paper from arXiv

A Star at the Edge of Eternity Friday, January 10, 2014 - 10:29

A Saturn-size star just 40 light-years away will outlive nearly all of its peers

Every star that now shines will one day die, but some stars live far longer than others. Our 4.6-billion-year-old sun will shrivel into a white dwarf in 7.8 billion years. Now astronomers say a dim red star south of the constellation Orion will outlive any other yet examined. "It actually will live for much longer than the current age of the universe—for literally trillions of years," says Sergio Dieterich, an astronomer at Georgia State University.

Read the full story at Scientific American



 

New Views of Famed Supernova Reveal Cosmic Dust Factory Thursday, January 9, 2014 - 12:56

WASHINGTON — New views from a giant radio telescope in Chile are revealing massive amounts of dust created by an exploding star for the first time.

Scientists used the Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope in Chile to make the discovery while observingsupernova 1987A, an exploded star in the Large Magellanic Cloud — a dwarf galaxy companion of the Milky Way located about 168,000 light-years from Earth.

Astronomers have long thought that supernovas are responsible for creating some of the large amounts of dust found in galaxies around the universe, yet they haven't directly observed the process until now, ALMA officials said.

Read more at Space.com

Chandra Reveals a Black Hole Destroying a Star in a Dwarf Galaxy Thursday, January 9, 2014 - 12:30

A bright, long duration flare may be the first recorded event of a black hole destroying a star in a dwarf galaxy. The evidence comes from two independent studies using data from NASA’s Chandra X-ray Observatory and other telescopes.

As part of an ongoing search of Chandra’s archival data for events signaling the disruption of stars by massive black holes, astronomers found a prime candidate. Beginning in 1999, an unusually bright X-ray source had appeared in a dwarf galaxy and then faded until it was no longer detected after 2005.

“We can’t see the star being torn apart by the black hole,” Peter Maksym of the University of Alabama in Tuscaloosa, Alabama, who led one of the studies, “but we can track what happens to the star’s remains, and compare it with other, similar events. This one fits the profile of ‘death by a black hole.’”

Read the story at SciTechDaily

The Variable Stars In Our Sky Thursday, January 9, 2014 - 08:51

On 14 August 2013 Koichi Itagaki, an amateur astronomer in Yamagata, Japan spotted a “new star”, as people centuries ago would have conceived it, on an image he had taken of the constellation Delphinus, it was in fact a “nova”, eventually earning the catalogue entry V0339 Delphini.

A nova results from a runaway thermonuclear explosion at the surface of a white dwarf star after years of gas exchange from a companion star onto the dwarf. In less than an hour, a shell of material begins to expand at around a thousand kilometres per second. Unlike a supernova, such an event doesn’t destroy the progenitor star system, nor does it release as much energy.

By 17 August, the nova had peaked in brightness, becoming briefly visible to the unaided eye from a suitably dark location. The rise from pre-nova to peak brightness represents an increase in luminosity of thousands of times that of our Sun.

This relatively rare event went largely unreported in the mainstream media, but to many amateur astronomers, the nova was captivating.

Read the full article from AAVSO member David Benn

Stormy Stars? NASA's Spitzer Probes Weather on Brown Dwarfs Tuesday, January 7, 2014 - 12:02

Swirling, stormy clouds may be ever-present on cool celestial orbs called brown dwarfs. New observations from NASA's Spitzer Space Telescope suggest that most brown dwarfs are roiling with one or more planet-size storms akin to Jupiter's "Great Red Spot."

"As the brown dwarfs spin on their axis, the alternation of what we think are cloud-free and cloudy regions produces a periodic brightness variation that we can observe," said Stanimir Metchev of the University of Western Ontario, Canada. "These are signs of patchiness in the cloud cover."

Read the full NASA JPL press release

Astronomy Image Explorer Puts Scientific Graphics at Your Fingertips Monday, January 6, 2014 - 15:04

IOP Publishing (IOP) and the American Astronomical Society (AAS) are pleased to announce the launch of theAstronomy Image Explorer (AIE). The AIE provides researchers with quick and easy access to hundreds of thousands of images, illustrations, graphs, charts, and videos that have been published in peer-reviewed journals. The AIE has tools designed to aid researchers in their discovery and use of all types of graphic resources and is available free online to scientists and the public alike.

Read the full press release

Mass Accretion Processes in Young Stellar Objects: Role of Intense Flaring Activity Friday, January 3, 2014 - 12:14

According to the magnetospheric accretion scenario, young low-mass stars are surrounded by circumstellar disks which they interact with through accretion of mass. The accretion builds up the star to its final mass and is also believed to power the mass outflows, which may in turn have a significant role in removing the excess angular momentum from the star-disk system. Although the process of mass accretion is a critical aspect of star formation, some of its mechanisms are still to be fully understood. On the other hand, strong flaring activity is a common feature of young stellar objects (YSOs). In the Sun, such events give rise to perturbations of the interplanetary medium. Similar but more energetic phenomena occur in YSOs and may influence the circumstellar environment. In fact, a recent study has shown that an intense flaring activity close to the disk may strongly perturb the stability of circumstellar disks, thus inducing mass accretion episodes (Orlando et al. 2011). Here we review the main results obtained in the field and the future perspectives.

Authors:  S. Orlando, F. Reale, G. Peres, A. Mignone

Download the paper from astro-ph

Fomalhaut’s Little Sibling Has a Debris Disk Too Tuesday, December 31, 2013 - 09:03

The presence of a debris disk around Fomalhaut C is surprising for two reasons. First, this is only the second known example of a multiple star system hosting multiple debris disks. Second, debris disks are very rare around low mass stars — although this may be simply because such stars have low luminosity, leaving their debris cold and faint. The Fomalhaut system is very nearby (only 7.7 parsecs from the sun), making this detection easier. Fomalhaut C may be the best example for studying the properties of debris disks around low mass stars, which could be common but typically undetectable.

Read the full story on astrobites

Astrophoto: Nova Centauri 2013 Turns Pink Saturday, December 28, 2013 - 12:45

A recent naked-eye visible nova that erupted the first week in December 2013 is still showing its stuff, and this new “hot off the press” image from Rolf Wahl Olsen in New Zealand reveals its unusual color. “I managed to grab a close-up of Nova Centauri 2013 with my new 12.5″ f/4 scope,” Rolf said via email to Universe Today. “Curiously, I have only so far seen wide field images of this nova, and none that actually show it’s very unusual strong pink colour.”

Read the full story on Universe Today

Hubble Sees a Stellar "Sneezing Fit" Thursday, December 26, 2013 - 13:42

Look at the bright star in the middle of this image. It appears as if it just sneezed. This sight will only last for a few thousand years — a blink of an eye in the young star's life.

If you could carry on watching for a few years you would realize it's not just one sneeze, but a sneezing fit. This young star is firing off rapid releases of super-hot, super-fast gas, like multiple sneezes, before it finally exhausts itself. These bursts of gas have shaped the turbulent surroundings, creating structures known as Herbig-Haro objects.

Read the full NASA press release

Photometry of the progenitor of Nova Del 2013 (V339 Del) and calibration of a deep BVRI photometric Monday, December 23, 2013 - 23:25

The Asiago plate archive has been searched for old plates covering the region of the sky containing Nova Del 2013 (V339 Del). The brightness of the progenitor was measured against a deep BVRI photometric sequence that we calibrated on purpose. The mean brightness of the progenitor on Asiago plates is <B>=17.27 and <V>=17.6, for a mean color (B-V) = -0.33. The recorded total amplitude of variation in B band is 0.9 mag. Color and variability are in agreement with a progenitor dominated by the emission from an accretion disc. The progenitor was marginally detected also by the APASS all sky survey on April 2012. We have stacked the CCD images from three individual visits and measured the progenitor at B=17.33+/-0.09 and V=17.06+/-0.10 mag.

Authors:  Ulisse Munari, Arne Henden

Get the pre-print from astro-ph

Powerful Ancient Explosions Explain New Class of Supernovae Thursday, December 19, 2013 - 10:05

The new study finds that the supernovae are likely powered by the creation of a magnetar, an extraordinarily magnetized neutron star spinning hundreds of times per second. Magnetars have the mass of the sun packed into a star the size of a city and have magnetic fields a hundred trillion times that of the Earth. While a handful of these superluminous supernovae have been seen since they were first announced in 2009, and the creation of a magnetar had been postulated as a possible energy source, the work of Howell and his colleagues is the first to match detailed observations to models of what such an explosion might look like.

Read the full press release 

The Magnetospheric Boundary in Cataclysmic Variables Tuesday, December 17, 2013 - 22:56

The magnetic cataclysmic variables (MCVs) present a wealth of observational diagnostics for studying accretion flows interacting with a magnetosphere. Spin-period pulsations from the rotation of the white dwarf are seen in optical light, in the UV and X-ray bands, and in polarimetry, and modelling these can constrain the size and location of the accretion footprints on the white-dwarf surface. Tracing these back along field lines can tell us about the transition region between the stream or disk and the magnetosphere. Further, optical emission lines give us velocity information, while analysis of eclipses gives spatial information. 

Author: Coel Hellier

Read the full abstract

J075141 and J174140: Doubling Down With Rare White Dwarf Systems Tuesday, December 17, 2013 - 16:59

Despite being known for almost 50 years, the question has remained: where do AM CVn systems come from? New X-ray and optical observations have begun to answer that with the discovery of the first known systems of double stars that astronomers think will evolve into AM CVn systems.

AM CVn systems are of interest to scientists because they are predicted to be sources of gravitational waves. This is important because even though such waves have yet to be detected, many scientists and engineers are working on instruments that should be able to detect them in the near future. This will open a significant new observational window to the universe.

The paper reporting these results is available online and is published in the Monthly Notices of the Royal Astronomical Society Letters. The authors are Mukremin Kilic, from the University of Oklahoma in Norman, OK; J.J. Hermes from the University of Texas at Austin in TX; Alexandros Gianninas from the University of Oklahoma; Warren Brown from Smithsonian Astrophysical Observatory in Cambridge, MA; Craig Heinke from University of Alberta, in Edmonton, Canada; Marcel Agüeros from Columbia University in New York, NY; Paul Chote and Denis Sullivan from Victoria University of Wellington, New Zealand; and Keaton Bell and Samuel Harrold from University of Texas at Austin.

Read the full press release from Chandra

RS Puppis puts on a spectacular light show Tuesday, December 17, 2013 - 11:09

The NASA/ESA Hubble Space Telescope has observed the variable star RS Puppis over a period of five weeks, showing the star growing brighter and dimmer as it pulsates. These pulsations have created a stunning example of a phenomenon known as a light echo, where light appears to reverberate through the murky environment around the star.

RS Puppis is unusual as it is shrouded by a nebula — thick, dark clouds of gas and dust. Hubble observed this star and its murky environment over a period of five weeks in 2010, capturing snapshots at different stages in its cycle and enabling scientists to create a time-lapse video of this ethereal object (heic1323a).

Read the full press release

Also see the NASA press release

Fast Radio Bursts Might Come From Nearby Stars Thursday, December 12, 2013 - 12:22

First discovered in 2007, "fast radio bursts" continue to defy explanation. These cosmic chirps last for only a thousandth of a second. The characteristics of the radio pulses suggested that they came from galaxies billions of light-years away. However, new work points to a much closer origin - flaring stars within our own galaxy.

"We propose that fast radio bursts aren't as exotic as astronomers first thought," says lead author Avi Loeb of the Harvard-Smithsonian Center for Astrophysics (CfA).

Fast radio bursts are both brief and bright, packing a lot of energy into a short time. Only six have been discovered to date, all of them in archival data. Each was detected only once, making follow-up studies difficult.

NOAO/SOAR: Where do stars end and brown dwarfs begin? Monday, December 9, 2013 - 15:15

Stars come in a tremendous size range, from many tens of times bigger than the Sun to a tiny fraction of its size. But the answer to just how small an astronomical body can be, and still be a star, has never been known. What is known is that objects below this limit are unable to ignite and sustain hydrogen fusion in their cores: these objects are referred to as brown dwarfs.

 “We can now point to a temperature (2100K), radius (8.7% that of our Sun), and luminosity (1/8000 of the Sun) and say ‘the main sequence ends there’ and we can identify a particular star (with the designation 2MASS J0513-1403) as a representative of the smallest stars.”

Read the full press release

Observing the Next Galactic Supernova Saturday, December 7, 2013 - 16:46

The last time a supernova was observed within the Milky Way was in 1604 by Johannes Kepler, and was only appreciated by the human eye, since optical telescopes and other measurement devices had not yet been invented. Despite a lack of hard observational data, astronomers have a theoretical framework to describe the processes that occur during a supernova, and numerical simulations are always growing more detailed and sophisticated. Still, without observation, neither theory nor numerical result can be put to the test.

While supernovae in our galaxy are relatively rare, extragalactic supernovae are not. That is because there are countless galaxies that have supernova rates similar to that of the Milky Way. But, due to their distance from Earth are not resolvable and offer little insight into the mechanisms at work during the explosion. Although astronomers haven’t observed supernovae in the Milky Way for several hundred years (read on to find out why this may be), the good news here is that astronomers are developing methods to be ready when the next one happens...

Read the summary on Astrobites

Read the paper from arXiv

Explosive growth of young star Wednesday, December 4, 2013 - 10:03


A star is formed when a large cloud of gas and dust condenses and eventually becomes so dense that it collapses into a ball of gas, where the pressure heats the matter, creating a glowing gas ball – a star is born. New research from the Niels Bohr Institute, among others, shows that a young, newly formed star in the Milky Way had such an explosive growth, that it was initially about 100 times brighter than it is now. The results are published in the scientific journal, Astrophysical Journal Letters.

Read the full press release from the Niels Bohr Institute

Read the pre-print paper from arXiv

Authors: Jes K. Jorgensen, Ruud Visser, Nami Sakai, Edwin A. Bergin, Christian Brinch, Daniel Harsono, Johan E. Lindberg, Ewine F. van Dishoeck, Satoshi Yamamoto, Suzanne E. Bisschop, Magnus V. Persson

The Star of Bethlehem is Not the Nova DO Aquilae (Nor Any Other Nova, Supernova, or Comet) Monday, December 2, 2013 - 09:56

The Star of Bethlehem is only known from a few verses in the Gospel of Matthew, with the Star inspiring and leading the Magi (i.e., Persian astrologers) to Jerusalem and ultimately worshipping the young Jesus Christ in Bethlehem. In the last four centuries, astronomers have put forth over a dozen greatly different naturalistic explanations, all involving astronomical events, often a bright nova, supernova, or comet. This paper will evaluate one prominent recent proposal, that the Star was a 'recurrent nova' now catalogued as DO Aquilae, and provide three refutations. In particular, (1) DO Aql is certainly not a recurrent nova, but rather an ordinary nova with a recurrence time scale of over a million years, (2) in its 1925 eruption, DO Aql certainly never got brighter than 8.5 mag, and the physics of the system proves that it could never get to the required luminosity of a supernova, and (3) the Magi were astrologers who had no recognition or interpretation for novae (or supernovae or comets) so any such event is completely irrelevant and meaningless to them.

Author: Bradley Schaefer

Read the paper on arXiv

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