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Stellar News Feed Archive

Astronomers Observe a Possible Planet-Forming Disk around the Young Star RY Tau Monday, August 26, 2013 - 10:08

An international team of astronomers that are members of the Strategic Exploration of Exoplanets and Disks with Subaru Telescope (SEEDS) Project has used Subaru Telescope’s High Contrast Instrument for the Subaru Next Generation Adaptive Optics (HiCIAO) to observe a disk around the young star RY Tau (Tauri). The team’s analysis of the disk shows that a “fluffy” layer above it is responsible for the scattered light observed in the infrared image. Detailed comparisons with computer simulations of scattered light from the disk reveal that this layer appears to be a remnant of material from an earlier phase of stellar and disk development, when dust and gas were falling onto the disk.

Read the full story at SciTechDaily

On the nature of CP Pup Monday, August 26, 2013 - 08:49

We present new X-ray and optical spectra of the old nova CP Pup (nova Pup 1942) obtained with Chandra and the CTIO 4m telescope. These new observational facts add further support to CP Pup as a magnetic cataclysmic variable (mCV).

We compare the mCV and the non-mCV scenarios and while we cannot conclude whether CP Pup is a long period system, all observational evidences point at an intermediate polar (IP) type CV.

Authors:  Elena Mason, Marina Orio, Koji Mukai, Antonio Bianchini, Domitilla de Martino, Francesco di Mille, Robert E. Williams, Timothy Abbot, Roberto de Propris

Read the full abstract and paper on arXiv

Old, Fat Stars Flicker Wednesday, August 21, 2013 - 22:06

Observing the pattern of flickers in a star’s light offers a new way for astronomers to measure one of the basic properties of stars — and any exoplanets they might host.

Astronomers can tell the difference between dwarfs and giants by measuring the strength of the star’s gravity at its surface. High surface gravity indicates a stable, healthy star in the prime of its life. Low surface gravity means the star has swollen in old age.
 

Unfortunately, surface gravity is devilishly difficult to measure. One hint is the width of dark lines imprinted in a star’s spectrum by elements in the stellar atmosphere as they absorb certain wavelengths of outgoing light. (Wider lines means a higher surface gravity: the higher pressure jostles the atoms, which can then absorb a broader range of light due to one of quantum physics’ many bizarre effects.) However, this method is only accurate to about 25–50%. Another rough estimate comes from a star’s mass and radius, which in turn are estimates from measurements of the star’s brightness. But like a passing phrase in a game of telephone, this chain can result in errors as large as the measurements themselves. It’s possible to measure gravity via “starquakes” — which can give accuracy to within 2%! — but this method only works for the very brightest stars.

Read the full article at Sky & Telescope

What's in store for Nova Del 2013? Tuesday, August 20, 2013 - 13:08

There are some tantalizing similarities between Nova Del 2013 and HR Del, another bright slow nova discovered by George Alcock in 1967. If they turn out to be anything alike, we are in for a wild ride.

Read the rest of the story

ALMA Takes Close Look at the Drama of Starbirth Tuesday, August 20, 2013 - 11:27

Young stars are violent objects that eject material at speeds as high as one million kilometres per hour. When this material crashes into the surrounding gas it glows, creating a Herbig-Haro object. A spectacular example is named Herbig-Haro 46/47 and is situated about 1400 light-years from Earth in the southern constellation of Vela (The Sails). This object was the target of a study using ALMA during the Early Science phase, whilst the telescope was still under construction and well before the array was completed.

The new images reveal fine detail in two jets, one coming towards Earth and one moving away. The receding jet was almost invisible in earlier pictures made in visible light, due to obscuration by the dust clouds surrounding the new-born star. ALMA has not only provided much sharper images than earlier facilities but also allowed astronomers to measure how fast the glowing material is moving through space.

Read the full press release

Naked-eye Nova in Delphinus: A Joint Sky & Telescope and AAVSO Press Release Tuesday, August 20, 2013 - 10:51

"It’s easily visible in the eastern sky in the early evening, so it can be followed for many hours. This means that amateur skygazers and professional scientists alike can continue monitoring it for months to come,” adds Arne Henden, director of the American Association of Variable Star Observers (AAVSO). “The nova can be seen with binoculars even from light-polluted metropolitan areas. Hundreds of observers, many for the first time, have submitted brightness estimates of the nova to the AAVSO.”

Read the full story at Sky & Telescope

 

 

The peculiar light curve of the Symbiotic Star AX Per of the last 125 years Monday, August 19, 2013 - 08:06

We analyze the last 125 years optical light curve of the symbiotic star AX Per through some remarkable correlations that we discovered in its power spectrum. The data were assembled from the literature and from the AAVSO database. We suggest, following others, that the major outbursts of the system result from events of intense mass loss from the giant star.

Authors: Elia M. Leibowitz and Liliana Formiggini

Read the full abstract

Download paper at arXiv

Everybody's Doing It, Even Arne! Friday, August 16, 2013 - 12:20

If you haven't had a chance to observe Nova Del 2013 yet, don't worry, it appears to still be on the rise. According to the latest AAVSO data, Nova Del 2013 was last seen over Australia at magnitude 4.4 visual, and the trend is upward. This places Nova Del 2013 in the top 30 brightest novae in recorded history. 

If you can get out under the stars in the next few days you may be able to see the first naked eye nova in quite some time. The last one I remember was Nova Sco 2007 (V1280 Sco).

If you look closely at this light curve, you will see observer HQA highlighted with a blue crosshair. This is Arne Henden's first visual observation ever submitted to the International Database!

Nice Color Photo of the Nova in Delphinus Thursday, August 15, 2013 - 08:59


From John Chumack
www.galacticimages.com

Nova in Delphinus - PNV J20233073+2046041 at Mag. 6.1

Here is a nice image of the New Nova in Delphinus, visible in binoculars…..hard to see naked eye unless you are in a very dark sky….and know exactly where to look, but this is a very bright Nova…most don’t get above 8th magnitude.

QHY8 Cooled Color CCD Camera + Homemade 16" Newtonian scope.  30 minute exposure. 
At my observatories at JBSPO in Yellow Springs , Ohio USA

Bright New Nova In Delphinus — You Can See it Tonight With Binoculars Wednesday, August 14, 2013 - 20:34

Looking around for something new to see in your binoculars or telescope tonight? How about an object whose name literally means “new”. Japanese amateur astronomer Koichi Itagaki of Yamagata discovered an apparent nova or “new star” in the constellation Delphinus the Dolphin just today, August 14. He used a small 7-inch (.18-m) reflecting telescope and CCD camera to nab it. Let’s hope its mouthful of a temporary designation, PNVJ20233073+2046041, is soon changed to Nova Delphini 2013!

Read the full story at Universe Today

WEAKLING MAGNETAR REVEALS HIDDEN STRENGTH Wednesday, August 14, 2013 - 14:28

Astronomers using ESA's XMM-Newton have measured the magnetic field in a small surface feature of a magnetar - a highly magnetised pulsar - for the first time. Until now, only the dipolar magnetic field of magnetars had been measured. With a new technique, the astronomers have now revealed a strong, localised surface magnetic field in the magnetar that had the lowest measured dipolar field. The discovery yields conclusive proof that magnetars conceal some of the strongest magnetic fields in the Universe.

Read the full article at the ESA XMM-Newton site

PRECISELY MEASURING VELOCITY OF SUPERNOVA SHOCKWAVE Wednesday, August 14, 2013 - 06:59

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.

Read the full press release

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.

Read the full story

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

Read the full abstract

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

Read the full paper

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

Read the full abstract

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)

Download the paper from arXiv

"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

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