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Stellar News Feed Archive

The evolution of triples with a Roche-lobe filling outer star Monday, September 9, 2013 - 10:43

Some fascinating results from simulations of triple star systems undergoing mass transfer, during which stellar evolution, gravitational dynamics and hydrodynamics all play an important role.

In neither of the cases studied an accretion disk formed, not even a circumbinary disk. The mass that leaves the outer star is funnelled through the first Lagrangian point of the outer orbit to land very near the inner binary system. The interaction between the gas and the inner binary causes the former to be ejected from the binary system like in a common envelope.

Authors: Nathan de Vries, Simon Portegies Zwart, Joana Figueira

Read the abstract on arXiv

Double mode radial pulsations among RR Lyrae stars Friday, September 6, 2013 - 13:50

The detection of a second radial mode in the RR Lyr type star puts strong constrain on its internal structure. We present 59 new Galactic double mode RR Lyr stars found in the LINEAR survey data with the fundamental radial mode and the first overtone exited (RRd stars). These stars may be useful for constraining the mass-metallicity relation for field horizontal branch stars. We present the updated Petersen diagram and the distribution of the fundamental mode periods in the Galactic RRd stars.

Author: R. Poleski

Read the paper on arXiv

Hubble Space Telescope and Ground-Based Observations of V455 Andromedae Post-Outburst Friday, September 6, 2013 - 13:40

Hubble Space Telescope spectra obtained in 2010 and 2011, three and four years after the large amplitude dwarf nova outburst of V455 And, were combined with optical photometry and spectra to study the cooling of the white dwarf, its spin, and possible pulsation periods after the outburst. The modeling of the ultraviolet (UV) spectra show that the white dwarf temperature remains ~600 K hotter than its quiescent value at three years post outburst, and still a few hundred degrees hotter at four years post outburst. The white dwarf spin at 67.6 s and its second harmonic at 33.8 s are visible in the optical within a month of outburst and are obvious in the later UV observations in the shortest wavelength continuum and the UV emission lines, indicating an origin in high temperature regions near the accretion curtains. The UV light curves folded on the spin period show a double-humped modulation consistent with two-pole accretion. The optical photometry two years after outburst shows a group of frequencies present at shorter periods (250-263 s) than the periods ascribed to pulsation at quiescence, and these gradually shift toward the quiescent frequencies (300-360 s) as time progresses past outburst. The most surprising result is that the frequencies near this period in the UV data are only prominent in the emission lines, not the UV continuum, implying an origin away from the white dwarf photosphere. Thus, the connection of this group of periods with non-radial pulsations of the white dwarf remains elusive.

Authors: Paula Szkody, Anjum S. Mukadam, Boris T. Gaensicke, Arne Henden, Edward M. Sion, Dean M. Townsley, Damian Christian, Ross E. Falcon, Stylianos Pyrzas, Justin Brown, Kelsey Funkhouser

 http://arxiv.org/pdf/1309.1217v1.pdfhttp://arxiv.org/pdf/1309.1217v1.pdf

Bizarre Alignment of Planetary Nebulae Wednesday, September 4, 2013 - 12:03

Astronomers have used ESO's New Technology Telescope and the NASA/ESA Hubble Space Telescope to explore more than 100 planetary nebulae in the central bulge of our galaxy. They have found that butterfly-shaped members of this cosmic family tend to be mysteriously aligned — a surprising result given their different histories and varied properties.

Read the entire press release

The Carina Project. VI. The helium burning variable stars Friday, August 30, 2013 - 08:59

We present new optical (BVI) time-series data for the evolved variable stars in the Carina dwarf spheroidal galaxy. The quality of the data and the observing strategy allowed us to identify 14 new variable stars. Eight out of the 14 are RR Lyrae (RRL) stars, four are Anomalous Cepheids (ACs) and two are geometrical variables. Comparison of the period distribution for the entire sample of RRLs with similar distributions in nearby dSphs and in the Large Magellanic Cloud indicates that the old stellar populations in these systems share similar properties. This finding is also supported by the RRL distribution in the Bailey diagram. On the other hand, the period distribution and the Bailey diagram of ACs display significant differences among the above stellar systems. This evidence suggests that the properties of intermediate-age stellar populations might be affected both by environmental effects and structural parameters.

Authors: G. Coppola, P.B. Stetson, M. Marconi, G. Bono, V. Ripepi, M. Fabrizio, M. Dall'Ora, I. Musella, R. Buonanno, I. Ferraro, G. Fiorentino, G. Iannicola, M. Monelli, M. Nonino, I. Pulone, F. Thévenin, A.R. Walker

Read the full abstract and paper on arXiv

Oldest Solar Twin Identified Wednesday, August 28, 2013 - 09:52

An international team led by astronomers in Brazil has used ESO’s Very Large Telescope to identify and study the oldest solar twin known to date. Located 250 light-years from Earth, the star HIP 102152 is more like the Sun than any other solar twin — except that it is nearly four billion years older. This older, but almost identical, twin gives us an unprecedented chance to see how the Sun will look when it ages. The new observations also provide an important first clear link between a star’s age and its lithium content, and in addition suggest that HIP 102152 may be host to rocky terrestrial planets.

Read the full ESO press release

Zeta Puppis --"A Monster Star Recycling the Cosmos" Wednesday, August 28, 2013 - 08:15

Massive stars like Zeta Puppis are relatively rare, but play a very important role in recycling materials in the Universe. They burn their nuclear fuel much more rapidly than stars like the Sun, living only for millions of years before exploding as a supernova and returning most of their matter to space. But during their brief lives, they lose a significant fraction of their mass through fierce winds of gas driven off their surfaces by the intense light emitted from the star. The fierce wind from a giant star like Zeta Puppis, an extreme blue supergiant, one of the most luminous stars in the Milky Way, 12,500 times more powerful than the Sun, is not a uniform breeze but is fragmented into hundreds of thousands of pieces, according to a study by the ESA’s XMM-Newtonspace observatory.

Read the full story 

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

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