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Stellar News Feed Archive


A star with a mass of more than eight times of the Sun releases tremendous energy when it is dying and undergoes a supernova explosion. The shockwave caused by the supernova explosion expands, having a strong impact on the composition and physical state of surrounding interstellar materials. It also emits kinetic energy into interstellar space. “Galactic winds” blasting out a large amount of gas are often observed in galaxies where explosively active star formations take place. The energy source of such galactic wind is also thought to be many supernova explosions.

Thus, supernova explosions have an immense influence on interstellar space. Nevertheless, there has been no quantitative research on the expansion velocity and kinetic energy of a supernova shockwave. This is because wide area must be observed in order to study the expansion velocity and kinetic energy of a supernova shockwave. Wide area observations with the existing equipment require quite long observation times. Therefore, observations of interstellar gas influenced by a supernova shockwave have been limited to a narrow area.

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Pulsating Star Sheds Light on Exoplanet Sunday, August 11, 2013 - 11:27

A team of researchers has devised a way to measure the internal properties of stars—a method that offers more accurate assessments of their orbiting planets.

The research, which appears in Proceedings of the National Academy of Sciences, was conducted by a multi-national team of scientists, including physicists at New York University, Princeton University, and the Max Planck Institute for Solar System Research.

The researchers examined HD 52265—a star approximately 92 light years away and nearly 20 percent more massive than our Sun. More than a decade ago, scientists identified an exopanet—a planet outside our Solar System—in the star’s orbit. HD 52265, then, served as an ideal model for both measuring stars’ properties and how such properties can shed light on planetary systems.

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Discovery of the spectroscopic binary nature of three bright southern Cepheids Friday, August 9, 2013 - 08:53

We present an analysis of spectroscopic radial velocity and photometric data of three bright Galactic Cepheids: LR Trianguli Australis (LR TrA), RZ Velorum (RZ Vel), and BG Velorum (BG Vel). Based on new radial velocity data, these Cepheids have been found to be members of spectroscopic binary systems. The ratio of the peak-to-peak radial velocity amplitude to photometric amplitude indicates the presence of a companion for LR TrA and BG Vel. IUE spectra indicate that the companions of RZ Vel and BG Vel cannot be hot stars. The analysis of all available photometric data revealed that the pulsation period of RZ Vel and BG Vel varies monotonically, due to stellar evolution. Moreover, the longest period Cepheid in this sample, RZ Vel, shows period fluctuations superimposed on the monotonic period increase. The light-time effect interpretation of the observed pattern needs long-term photometric monitoring of this Cepheid. The pulsation period of LR TrA has remained constant since the discovery of its brightness variation. Using statistical data, it is also shown that a large number of spectroscopic binaries still remain to be discovered among bright classical Cepheids.

Authors: L. Szabados, R. I. Anderson, A. Derekas, L. L. Kiss, T. Szalai, P. Szekely, J. L. Christiansen

Read the paper at arXiv

Variability of the Spin Period of the White Dwarf in the Magnetic Cataclysmic Binary System EX Hya Friday, August 9, 2013 - 08:07

The observations of the two-periodic magnetic cataclysmic system EX Hya have been carried out, using the telescopes RC16 and TOA-150 of the Tzec Maun observatory. 6 nights of observations were obtained in 2010-2011 (alternatively changing filters VR). Also the databases of WASP, ASAS and AAVSO have been analyzed. Processing time series was carried out using the program MCV. We analyzed changes in the rotation period of the white dwarf, and based on ourm own and previously published moments of maximum. The ephemeris was determined for the maxima of the radiation flux associated with the rotation of the magnetic white dwarf-

Authors: Ivan L. Andronov, Vitalii V. Breus

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KIC 9406652: An Unusual Cataclysmic Variable in the Kepler Field of View Tuesday, August 6, 2013 - 10:47

KIC 9406652 is a remarkable variable star in the Kepler field of view that shows both very rapid oscillations and long term outbursts in its light curve. We present an analysis of the light curve over quarters 1 to 15 and new spectroscopy that indicates that the object is a cataclysmic variable with an orbital period of 6.108 hours. However, an even stronger signal appears in the light curve periodogram for a shorter period of 5.753 hours, and we argue that this corresponds to the modulation of flux from the hot spot region in a tilted, precessing disk surrounding the white dwarf star. We present a preliminary orbital solution from radial velocity measurements of features from the accretion disk and the photosphere of the companion. We use a Doppler tomography algorithm to reconstruct the disk and companion spectra, and we also consider how these components contribute to the object's spectral energy distribution from ultraviolet to infrared wavelengths. This target offers us a remarkable opportunity to investigate disk processes during the high mass transfer stage of evolution in cataclysmic variables.

Authors: Douglas R. Gies, Zhao Guo, Steve B. Howell, Martin D. Still, Tabetha S. Boyajian, Abe J. Hoekstra, Kian J. Jek, Daryll LaCourse, Troy Winarski

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Exploring the Variable Sky with LINEAR. III. Classification of Periodic Light Curves Tuesday, August 6, 2013 - 10:36

We describe the construction of a highly reliable sample of approximately 7,000 optically faint periodic variable stars with light curves obtained by the asteroid survey LINEAR across 10,000 sq.deg of northern sky. Majority of these variables have not been cataloged yet. The sample flux limit is several magnitudes fainter than for most other wide-angle surveys; the photometric errors range from ~0.03 mag at r=15 to ~0.20 mag at r=18. Light curves include on average 250 data points, collected over about a decade. Using SDSS-based photometric recalibration of the LINEAR data for about 25 million objects, we selected ~200,000 most probable candidate variables and visually confirmed and classified approximately 7,000 periodic variables using phased light curves. The reliability and uniformity of visual classification across eight human classifiers was calibrated and tested using a SDSS Stripe 82 region variable star catalog, and verified using an unsupervised machine learning approach. The resulting sample of periodic LINEAR variables is dominated by 3,900 RR Lyrae stars and 2,700 eclipsing binary stars of all subtypes, and includes small fractions of relatively rare populations such as asymptotic giant branch stars and SX Phoenicis stars.

Authors: Lovro Palaversa, Željko Ivezić, Laurent Eyer, Domagoj Ruždjak, Davor Sudar, Mario Galin, Andrea Kroflin, Martina Mesarić, Petra Munk, Dijana Vrbanec, Hrvoje Božić, Sarah Loebman, Branimir Sesar, Lorenzo Rimoldini, Nicholas Hunt-Walker, Jacob VanderPlas, David Westman, J. Scott Stuart, Andrew C. Becker, Gregor Srdoč, Przemyslaw Wozniak, Hakeem Oluseyi

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Hubble Finds 'Smoking Gun' After Gamma-Ray Blast Monday, August 5, 2013 - 12:48

NASA's Hubble Space Telescope has provided the strongest evidence yet that short-duration gamma-ray bursts are triggered by the merger of two small, super-dense stellar objects, such as a pair of neutron stars or a neutron star and a black hole.

The definitive evidence came from Hubble observations in near-infrared light of the fading fireball produced in the aftermath of a short gamma-ray burst (GRB). The afterglow reveals for the first time a new kind of stellar blast called a kilonova, an explosion predicted to accompany a short-duration GRB.

Read the full story at HubbleSite

Progenitors of supernova Ibc: a single Wolf-Rayet star as the possible progenitor of the SN Ib iPTF13bvn Friday, August 2, 2013 - 10:03

Core-collapse supernova (SN) explosions mark the end of the tumultuous life of massive stars. Determining the nature of their progenitors is a crucial step towards understanding the properties of SNe. Until recently, no progenitor has been directly detected for SN of type Ibc, which are believed to come from massive stars that lose their Hydrogen envelope through stellar winds and from binary systems where the companion has stripped the H envelope from the primary. Here we analyze recently-reported observations of iPTF13bvn, which could possibly be the first detection of a SN Ib progenitor based on pre-explosion images.

Authors: Jose H. Groh (Geneva Observatory, Switzerland), Cyril Georgy (Keele University, UK), Sylvia Ekstrom (Geneva Observatory, Switzerland)

Read the full abstract on arXiv

Under leaden skies - where heavy metal clouds the stars Thursday, August 1, 2013 - 09:01

The team believes that these heavy-metal stars are a crucial link between bright red giants, stars thirty or forty times the size of the Sun, and faint blue subdwarfs, stars one fifth the size, but seven times hotter and seventy times brighter than the Sun. A few red giants lose their thick hydrogen skin and shrink to become hot subdwarfs, or nearly-naked helium stars. As they shrink, conditions become favourable for the pressure of light from the helium stars to act on individual atoms to sort the elements into separate layers, where they are concentrated by a factor of ten thousand or more.

Read the full story from the RAS website

Spitzer Discovers Young Stars with a 'Hula Hoop' Wednesday, July 31, 2013 - 22:55

As the two inner stars whirl around each other, they periodically peek out from the disk that girds them like a hula hoop. The hoop itself appears to be misaligned from the central star pair, probably due to the disrupting gravitational presence of the third star orbiting at the periphery of the system. The whole system cycles through bright and faint phases, with the central stars playing a sort of cosmic peek-a-boo as the tilted disk twirls around them. It is believed that this disk should go on to spawn planets and the other celestial bodies that make up a solar system. 

Spitzer observed infrared light from YLW 16A, emitted by the warmed gas and dust in the disk that still swathes the young stars. Other observations came from the ground-based 2MASS survey, as well as from the NACO instrument at the European Southern Observatory's Very Large Telescope in Chile. 

Read the story from JPL

Powering the Second 2012 Outburst of SN 2009ip by Repeating Binary Interaction Tuesday, July 30, 2013 - 09:02

We propose that the major 2012 outburst of the supernova impostor SN 2009ip was powered by an extended and repeated interaction between the Luminous Blue Variable (LBV) and a more compact companion. Motivated by the recent analysis of Margutti et al. (2013) of ejected clumps and shells we consider two scenarios. In both scenarios the major 2012b outburst of ~5 * 10^{49} erg was powered by accretion of ~ 2-5 solar masses onto the companion during a periastron passage (the first passage) of the binary system approximately 20 days before the observed maximum of the light curve. In the first, the surviving companion scenario, the companion was not destructed and still exists in the system after the outburst. It ejected partial shells (or collimated outflows or clumps) for two consecutive periastron passages after the major one. The orbital period was reduced from ~38 days to ~25 days as a result of the mass transfer process that took place during the first periastron passage. In the second, the merger scenario, some partial shells/clumps were ejected also in a second periastron passage that took place ~20 days after the first one. After this second periastron passage the companion dived too deep into the LBV envelope to launch more outflows, and merged with the LBV.

Authors: Amit Kashi (UNLV), Noam Soker (Technion), Nitsan Moskovitz (Technion)

Download the paper from arXiv

Dynamical Fragmentation of the T Pyxidis Nova Shell During Recurrent Eruptions Tuesday, July 30, 2013 - 07:12

Hubble Space Telescope images of the ejecta surrounding the nova T Pyxidis resolve the emission into more than two thousand bright knots. We simulate the dynamical evolution of the ejecta from T Pyxidis during its multiple eruptions over the last 150 years using the adaptive mesh refinement capability of the gas dynamics code Ramses. We demonstrate that the observed knots are the result of Richtmeyer-Meshkov gas dynamical instabilities (the equivalent of Rayleigh-Taylor instabilities in an accelerated medium). These instabilities are caused by the overrunning of the ejecta from the classical nova of 1866 by fast moving ejecta from the subsequent six recurrent nova outbursts. The model correctly predicts the observed expansion and dimming of the T Pyx ejecta as well as the knotty morphology. The model also predicts that deeper, high resolution imagery will show filamentary structure connecting the knots. We show reprocessed Hubble Space Telescope imagery that shows the first hints of such structure.

Authors: Jayashree Toraskr, Mordecai-Mark Mac Low, Michael M. Shara, David R. Zurek

Download the paper from arXiv

Binary Cepheids: Separations and Mass Ratios in 5 Solar Mass Binaries Tuesday, July 30, 2013 - 07:00

Deriving the distribution of binary parameters for a particular class of stars over the full range of orbital separations usually requires the combination of results from many different observing techniques (radial velocities, interferometry, astrometry, photometry, direct imaging), each with selection biases. However, Cepheids---cool, evolved stars of 5 Mdot---are a special case because ultraviolet spectra will immediately reveal any companion star hotter than early type A, regardless of the orbital separation. We have used  International Ultraviolet Explorer (IUE) UV spectra of a complete sample of all 76 Cepheids brighter than V=8 to create a list of all 18 Cepheids with companions more massive than 2.0 Mdot. Orbital periods of many of these binaries are available from radial-velocity studies, or can be estimated for longer-period systems from detected velocity variability. In an imaging survey with the Hubble Space Telescope Wide Field Camera 3, we resolved three of the companions (those of eta Aql, S Nor, and V659 Cen), allowing us to make estimates of the periods out to the long-period end of the distribution. Combining these separations with orbital data in the literature, we derive an unbiased distribution of binary separations, orbital periods, and mass ratios. The distribution of orbital periods shows that the 5 Mdot binaries have systematically shorter periods than do 1 Mdot stars. Our data also suggest that the distribution of mass ratios depends both on binary separation and system multiplicity. The distribution of mass ratios as a function of orbital separation, however, does not depend on whether a system is a binary or a triple.

Authors: Nancy Remage Evans (SAO), Howard E. Bond (PSU, STScI), Gail H. Schaefer (The CHARA Array, GSU), Brian D. Mason (USNO), Margarita Karovska (SAO), Evan Tingle (SAO)

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"The Dark Cloud"--Emergence of a Monster Star: Largest Ever Observed in the Milky Way Monday, July 29, 2013 - 14:01

“The remarkable observations from ALMA allowed us to get the first really in-depth look at what was going on within this cloud,” says Nicolas Peretto, of Cardiff University and CEA/AIM Parsis-Saclay. “We wanted to see how monster stars form and grow, and we certainly achieved our aim! One of the sources we have found is an absolute giant — the largest protostellar core ever spotted in the Milky Way."

Read the entire article at The Daily Galaxy

Third Bright Supernova Discovered In Spiral Galaxy M74 Sunday, July 28, 2013 - 09:31

I love this galaxy. Not only does M74 display a near perfect spiral form but if this latest supernova is the third to “go boom” in the galaxy in just 11 years. The new object, designated PSN J01364816+1545310, was discovered blazing near 12.4 magnitude by the Lick Observatory Supernova Search at Lick Observatory near San Jose, Calif. “PSN” stands for “possible supernova” and the long string of numbers give the object’s position in the sky using the celestial equivalents of latitude and longitude.

Read the full article by AAVSO member Bob King at Universe Today

Kepler observations of the eclipsing cataclysmic variable KIS J192748.53+444724.5 Saturday, July 27, 2013 - 10:06

We present results from long cadence Kepler observations covering 97.6 days of the newly discovered eclipsing cataclysmic variable KIS J192748.53+444724.5/KIC 8625249. We detect deep eclipses of the accretion disk by the donor star every 3.97 hours. Additionally, the Kepler observations also cover a full outburst for this cataclysmic variable, making KIS J192748.53+444724.5 the second known eclipsing cataclysmic variable system in the Kepler field of view. We show how in quiescence a significant component associated to the hot-spot is visible preceding the eclipse, and that this component is swamped by the brightness increase during the outburst, potentially associated with the accretion disk. Furthermore we present evidence for accretion disk radius changes during the outburst by analysing the out-of-eclipse light levels and eclipse depth through each orbital cycle. We show how these parameters are linearly correlated in quiescence, and discuss how their evolution during the outburst is suggesting disk radius changes and/or radial temperature gradient variations in the disk.

Authors: S. Scaringi, P.J. Groot, M. Still

Download the paper from arXiv

New discoveries about quasars Friday, July 26, 2013 - 12:48

Dartmouth astrophysicists Ryan Hickox and Kevin Hainline and colleagues have a paper scheduled for publication in The Astrophysical Journal, detailing discoveries based upon observations of 10 quasars. They documented the immense power of quasar radiation, which reaches out for many thousands of light years to the limits of the quasar’s galaxy.

“For the first time, we are able to see the actual extent to which these quasars and their black holes can affect their galaxies, and we see that it is limited only by the amount of gas in the galaxy,” says Hainline, a Dartmouth postdoctoral research associate. “The radiation excites gas all the way to the margins of the galaxy and stops only when it runs out of gas.”


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WZ Sge-type dwarf novae with multiple rebrightenings: MASTER OT J211258.65+242145.4 and MASTER OT J203749.39+552210.3 Friday, July 26, 2013 - 08:49

From the abstract: We have made a survey of WZ Sge-type dwarf novae with multiple rebrightenings, and confirmed that the superhump periods of WZ Sge-type dwarf novae with multiple rebrightenings were longer than those of WZ Sge-type dwarf novae without a rebrightening. Although WZ Sge-type dwarf novae with multiple rebrightenings have been thought to be the good candidates for period bouncers based on their low mass ratio (q) from inferred from the period of fully grown (stage B) superhumps, our new method using the period of growing superhumps (stage A superhumps), however, implies higher q than those expected from stage B superhumps. These q values appear to be consistent with the duration of the stage A superoutbursts, which likely reflects the growth time of the 3:1 resonance. We present a working hypothesis that the small fractional superhump excesses for stage B superhumps in these systems may be explained as a result that a higher gas pressure effect works in these systems than in ordinary SU UMa-type dwarf novae. This result leads to a new picture that WZ Sge-type dwarf novae with multiple rebrightenings and SU UMa-type dwarf novae without a rebrightening (they are not period bouncers) are located in the same place on the evolutionary track.

Authors: Chikako Nakata, Tomohito Ohshima, Taichi Kato, Daisaku Nogami, Gianluca Masi, Enrique de Miguel, Joseph Ulowetz, Colin Littlefield, William N. Goff, Thomas Krajci, Hiroyuki Maehara, William Stein, Richard Sabo, Ryo Noguchi, Rikako Ono, Miho Kawabata, Hisami Furukawa, Katsura Matsumoto, Takehiro Ishibashi, Pavol A. Dubovsky, Igor Kudzej, Shawn Dvorak, Franz-Josef Hambsch, Roger D. Pickard, Etienne Morelle, Eddy Muyllaert, Stefano Padovan, Arne Henden

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Orbital, Superhump, and Superorbital Periods in the Cataclysmic Variables AQ Mensae and IM Eridani Thursday, July 25, 2013 - 09:45

This paper features AAVSO observers as co-authors.

Abstract: We report photometric detections of orbital and superorbital signals, and negative orbital sidebands, in the light curves of the nova-like cataclysmic variables AQ Mensae and IM Eridani. The frequencies of the orbital, superorbital, and sideband signals are 7.0686 (3), 0.263 (3), and 7.332 (3) cycles per day (c/d) in AQ Mensae, and 6.870 (1), 0.354 (7), and 7.226 (1) c/d in IM Eridani. We also find a spectroscopic orbital frequency in IM Eridani of 6.86649 (2) c/d. These observations can be reproduced by invoking an accretion disc that is tilted with respect to the orbital plane. This model works well for X-ray binaries, in which irradiation by a primary neutron star can account for the disc's tilt. A likely tilt mechanism has yet to be identified in CVs, yet the growing collection of observational evidence indicates that the phenomenon of tilt is indeed at work in this class of object. The results presented in this paper bring the number of CVs known to display signals associated with retrograde disc precession to twelve. 

We also find AQ Mensae to be an eclipsing system. The eclipse depths are highly variable, which suggests that the eclipses are grazing. This finding raises the possibility of probing variations in disc tilt by studying systematic variations in the eclipse profile.

Download the paper from arXiv

The Weakest Solar Cycle in 100 Years Wednesday, July 24, 2013 - 16:54

The Sun is acting weird. It typically puts on a pageant of magnetic activity every 11 years for aurora watchers and sungazers alike, but this time it overslept. When it finally woke up (a year late), it gave the weakest performance in 100 years.

Read the full story at Sky & Telescope

Starburst to Star Bust: ALMA Sheds Light on Mystery of Missing Massive Galaxies Wednesday, July 24, 2013 - 13:33

New observations from the ALMA telescope in Chile have given astronomers the best view yet of how vigorous star formation can blast gas out of a galaxy and starve future generations of stars of the fuel they need to form and grow. The dramatic images show enormous outflows of molecular gas ejected by star-forming regions in the nearby Sculptor Galaxy. These new results help to explain the strange paucity of very massive galaxies in the Universe. The study is published in the journal Nature on 25 July 2013.

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Variability of the Spin Period of the White Dwarf in the Intermediate Polar V405 Aur Wednesday, July 24, 2013 - 10:35

We present the results of photometric CCD observations of the magnetic cataclysmic variable V405 Aurigae obtained using different instruments. We analysed variability of the spin period of the white dwarf in the V405 Aur system using our observations and previously published maxima timings. The spin period of the system in 2010-2012 is P=545.4558163(94)s. As we have gaps in observational data, we present 2 hypotheses of the spin period variability of this system - a cubic ephemeris which may be interpreted by a precession of the magnetic white dwarf or a periodic change with a period of 6.2 years and semi-amplitude of 17.2\pm1.8 sec. The periodic variations may be interpreted by a light-time effect caused by a low-mass star. In this case, the system belongs to a rare class of cataclysmic variables with a third body.

Image credit Mark Garlick

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Metal Abundances, Radial Velocities and other Physical Characteristics for the RR Lyrae Stars in the Kepler Field Wednesday, July 24, 2013 - 10:08

Spectroscopic iron-to-hydrogen ratios, radial velocities, atmospheric parameters, and new photometric analyses are presented for 41 RR Lyrae stars (and one probable high-amplitude delta Scuti star) located in the field-of-view of the Kepler space telescope. Thirty-seven of the RR Lyrae stars are fundamental-mode pulsators (i.e., RRab stars) of which 16 exhibit the Blazhko effect. Four of the stars are multiperiodic RRc pulsators oscillating primarily in the first-overtone mode.

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The discovery of gamma-ray emission from Nova Sco 2012 Wednesday, July 24, 2013 - 10:02

In March 2010 the Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope discovered for the first time >100 MeV gamma-ray emission from a nova within our galaxy, V407 Cyg. The high-energy spectrum and light curve was explained as a consequence of shock acceleration in the nova shell as it interacts with the local ambient medium. It was suspected that the necessary conditions for high-energy emission from novae would be rare. In June 2012 the LAT detected a new flaring source, Fermi J1750-3243, that is spatially coincident and contemporaneous with a new nova, Nova Sco 2012. We report on the exciting discovery of this new 'gamma-ray' nova and present a detailed analysis of its high-energy properties.

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Supernova Explosions of Super-Asymptotic Giant Branch Stars Wednesday, July 24, 2013 - 09:56

An electron-capture supernova (ECSN) is a core-collapse supernova (CCSN) explosion of a super-asymptotic giant branch (SAGB) star with a main-sequence mass 7-9.5 that of the Sun. The explosion takes place in accordance with core bounce and subsequent neutrino heating and is a unique example successfully produced by first-principle simulations. This allows us to derive a first self-consistent multicolor light curves of a CCSN.  

Image credit: Argonne National Laboratory via Flickr (Creative Commons license); Image courtesy Hongfeng Yu

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