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Stellar News Feed Archive

A Cosmic Bubble That’ll Soon Pop. Hard. Monday, January 27, 2014 - 09:45

 Wolf-Rayet stars lead short, violent lives. They’re so bright that pressure from light itself can blow material off the surface, leading to string winds of gas blasting out from the star. Some time ago, EZ CMa blew out just such a wind, which expanded away from the star in a roughly-spherical manner. It slammed into the gas floating in between the stars, sweeping it up and heating it, creating that magnificent bubble. The gas cloud itself is called Sharpless 2-308.

 It’s when I look at the numbers that this starts to make my brain tingle. The distance to EZ CMa is difficult to determine, but it’s most likely about 5000 light years away. Even from that stunning distance — that’s 50 quadrillion kilometers (30 quadrillion miles) — the star is almost bright enough to be seen with the naked eye. If the Sun were that far away, you’d need a pretty good telescope to see it at all.

Read the whole story from Phil Plait

NASA Spacecraft Take Aim At Nearby Supernova Friday, January 24, 2014 - 18:36

An exceptionally close stellar explosion discovered on Jan. 21 has become the focus of observatories around and above the globe, including several NASA spacecraft. The blast, designated SN 2014J, occurred in the galaxy M82 and lies only about 12 million light-years away. This makes it the nearest optical supernova in two decades and potentially the closest type Ia supernova to occur during the life of currently operating space missions.

To make the most of the event, astronomers have planned observations with the NASA/ESA Hubble Space Telescope and NASA's Chandra X-ray Observatory, Nuclear Spectroscopic Telescope Array (NuSTAR), Fermi Gamma-ray Space Telescope, and Swift missions.

As befits its moniker, Swift was the first to take a look. On Jan. 22, just a day after the explosion was discovered, Swift's Ultraviolet/Optical Telescope (UVOT) captured the supernova and its host galaxy.

Read the full news story at NASA.gov

Accurate Parallax Measurement toward the Symbiotic Star R Aquarii Thursday, January 23, 2014 - 09:43

Multi-epoch phase-referencing VLBI (Very Long Baseline Interferometry) observations with VERA (VLBI Exploration of Radio Astrometry) were performed for the symbiotic star R Aquarii (R Aqr) from September 2005 to Oct 2006. Tracing one of the v=2J=1−0 SiO maser spots, we measured an annual parallax of π=4.59±0.24 mas, corresponding to a distance of 218+12−11 pc. Our result is consistent with earlier distance measurements, but yields the highest accuracy of about 5% level. Applying our distance, we derived an absolute K-band magnitude of MK=−7.71±0.11, which is consistent with the recent Period-Luminosity relation by VLBI parallax measurements for 5 OH-Mira variables. In addition, the expansion age of an inner nebulae around R Aqr is found to be about 240 years, corresponds to about the year 1773.

Authors:  Cheulhong Min, Naoko Matsumoto, Mi Kyoung Kim, Tomoya Hirota, Katsunori M. Shibata, Se-Hyung Cho, Makoto Shizugami and Mareki Honma

Read the paper on astro-ph

UCL telescope spots a supernova Wednesday, January 22, 2014 - 12:47

Supernova in Messier 82 discovered by UCL students

(Press release updated January 23, 2014)

Students and staff at UCL’s teaching observatory, the University of London Observatory, have spotted one of the closest supernova to Earth in recent decades. At 19:20 GMT on 21 January, a team of students – Ben Cooke, Tom Wright, Matthew Wilde and Guy Pollack – assisted by Dr Steve Fossey, spotted the exploding star in nearby galaxy Messier 82 (the Cigar Galaxy).

The discovery was a fluke – a 10 minute telescope workshop for undergraduate students that led to a global scramble to acquire confirming images and spectra of a supernova in one of the most unusual and interesting of our near-neighbour galaxies.

Image Credit: UCL/University of London Observatory/Steve Fossey/Ben Cooke/Guy Pollack/Matthew Wilde/Thomas Wright

 
Spectroscopy of the enigmatic short-period cataclysmic variable IR Com in an extended low state Tuesday, January 21, 2014 - 08:22

We report the occurrence of a deep low state in the eclipsing short-period cataclysmic variable IR Com, lasting more than two years. Spectroscopy obtained in this state shows the system as a detached white dwarf plus low-mass companion, indicating that accretion has practically ceased. The spectral type of the companion is M6-7, suggesting a mass of 0.15-0.20 Msun. Its radial velocity amplitude, K_2=419.6+/-3.4 km/s, together with the inclination of 75deg - 90deg implies 0.91Msun<Mwd<1.05Msun. We estimate the white dwarf temperature to be ~15000K, and the absence of Zeeman splitting in the Balmer lines rules out magnetic fields in excess of ~5MG. While all the binary and stellar parameters are typical for a CV near the lower edge of the orbital period gap, the long-term behaviour of IR Com defies its classification, in particular the occurrence of a deep, long low state is so far unique among short-period CVs that are not strongly magnetic.

Authors:  C.J. Manser, B.T. Gaensicke

Read the paper on arXiv

Subtle flickering in Cepheids Tuesday, January 21, 2014 - 08:15

Fundamental mode classical Cepheids have light curves which repeat accurately enough that we can watch them evolve (change period). The new level of accuracy and quantity of data with the Kepler and MOST satellites probes this further. An intriguing result was found in the long time-series of Kepler data for V1154 Cyg the one classical Cepheid (fundamental mode, P = 4.9d) in the field, which has short term changes in period (≃20 minutes), correlated for ≃10 cycles (period jitter). To follow this up, we obtained a month long series of observations of the fundamental mode Cepheid RT Aur and the first overtone pulsator SZ Tau. RT Aur shows the traditional strict repetition of the light curve, with the Fourier amplitude ratio R1/R2 remaining nearly constant. 

The light curve of SZ Tau, on the other hand, fluctuates in amplitude ratio at the level of approximately 50%. Furthermore prewhitening the RT Aur data with 10 frequencies reduces the Fourier spectrum to noise. For SZ Tau, considerable power is left after this prewhitening in a complicated variety of frequencies.

Authors:  N. R. Evans, R. Szabo, L. Szabados, A. Derekas, L. Kiss, J. Matthews, C. Cameron, the MOST Team

Read the pre-print on arXiv

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

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