Stellar News Feed Archive
|Blazhko effect in Cepheids and RR Lyrae stars||Tuesday, September 17, 2013 - 08:58||
The Blazhko effect is the conspicuous amplitude and phase modulation of the pulsation of RR Lyrae stars that was discovered in the early 20th century. The field of study of this mysterious modulation has recently been invigorated thanks to the space photometric missions providing long, uninterrupted, ultra-precise time series data. In this paper I give a brief overview of the new observational findings related to the Blazhko effect, like extreme modulations, irregular modulation cycles and additional periodicities. I argue that these findings together with dedicated ground-based efforts now provide us with a fairly complete picture and a good starting point to theoretical investigations. Indeed, new, unpredicted dynamical phenomena have been discovered in Blazhko RR Lyrae stars, such as period doubling, high-order resonances, three-mode pulsation and low-dimensional chaos. These led to the proposal of a new explanation to this century-old enigma, namely a high-order resonance between radial modes. Along these lines I present the latest efforts and advances from the theoretical point of view. Lastly, amplitude variations in Cepheids are discussed.
Author: R. Szabo
|Magnetic jet shows how stars begin their final transformation||Monday, September 16, 2013 - 09:13||
Astronomers have for the first time found a jet of high-energy particles from a dying star. The discovery, by a team including Chalmers scientists, is a crucial step in explaining how some of the most beautiful objects in space are formed – and what happens when stars like the sun reach the end of their lives.
At the end of their lives, stars like the sun transform into some of the most beautiful objects in space: amazing symmetric clouds of gas called planetary nebulae. But how planetary nebulae get their strange shapes has long been a mystery to astronomers.
Chalmers University of Technology scientists have together with colleagues from Germany and Australia discovered what could be the key to the answer: a high-speed, magnetic jet from a dying star.
Read the Chalmers press release here
Read the CSIRO press release here
|Study of Superoutbursts and Superhumps in SU UMa Stars by the Kepler Light Curves of V344 Lyrae and V1504 Cygni||Monday, September 16, 2013 - 09:01||
We have studied the short-cadence Kepler public light curves of SU UMa stars, V344 Lyr and V1504 Cyg extending over a period of more than two years by using power spectral analysis. We determined the orbital period of V344 Lyr to be Porb=0.087903(1) d. We also reanalyzed the frequency variation of the negative superhump in a complete supercycle of V1504 Cyg with additional data of the O-C diagram, confirming that its characteristic variation is in accordance with the thermal-tidal instability model.
Authors: Yoji Osaki (U. of Tokyo), Taichi Kato (Kyoto U.)
|Newly identified YSO candidates towards the LDN 1188||Monday, September 16, 2013 - 08:34||
We present an analysis of Young Stellar Object (YSO) candidates towards the LDN 1188 molecular cloud. The YSO candidates were selected from the WISE all-sky catalogue, based on a statistical method. We found 601 candidates in the region, and classified them as Class I, Flat and Class II YSOs. Groups were identified and described with the Minimal Spanning Tree (MST) method. Previously identified molecular cores show evidence of ongoing star formation at different stages throughout the cloud complex.
Authors: Gábor Marton, Erika Verebélyi, Csaba Kiss, József Smidla
|Asteroseismic Investigation of two Algol-type systems V1241 Tau and GQ Dra||Friday, September 13, 2013 - 08:43||
We present new photometric observations of eclipsing binary systems V1241 Tau and GQ Dra. We use the following methodology: Initially, WD code is applied to the light curves, in order to determine the photometric elements of the systems. Then the residuals are analysed using Fourier Transformation techniques. The results show that one frequency can be barely attributed to the residual light variation of V1241 Tau, while there is no evidence of pulsation on the light curve of GQ Dra.
Authors: Burak Ulaş, Ceren Ulusoy, Kosmas Gazeas, Naci Erkan, Alexios Liakos
|The Milky Way has a crunchy peanut center||Thursday, September 12, 2013 - 09:04||
Two groups of astronomers have used data from ESO telescopes to make the best three-dimensional map yet of the central parts of the Milky Way. They have found that the inner regions take on a peanut-like, or X-shaped, appearance from some angles. This odd shape was mapped by using public data from ESO’s VISTA survey telescope along with measurements of the motions of hundreds of very faint stars in the central bulge.
|Astronomy Picture of the Day, RS Puppis||Tuesday, September 10, 2013 - 11:30||
It is one of the most important stars in the sky. This is partly because, by coincidence, it is surrounded by a dazzling reflection nebula. Pulsating RS Puppis, the brightest star in the image center, is some ten times more massive than our Sun and on average 15,000 times more luminous. In fact, RS Pup is a Cepheid type variable star, a class of stars whose brightness is used to estimate distances to nearby galaxies as one of the first steps in establishing the cosmic distance scale. As RS Pup pulsates over a period of about 40 days, its regular changes in brightness are also seen along the nebula delayed in time, effectively a light echo. Using measurements of the time delay and angular size of the nebula, the known speed of light allows astronomers to geometrically determine the distance to RS Pup to be 6,500 light-years, with a remarkably small error of plus or minus 90 light-years.
Read the full explanation and see the full scale image at APOD
|One, two or three stars? An investigation of an unusual eclipsing binary candidate undergoing dramatic period changes||Monday, September 9, 2013 - 10:55||
More triple stars in the news!
We report our investigation of 1SWASP J234401.81-212229.1, a variable with a 18461.6 s period. After identification in a 2011 search of the SuperWASP archive for main-sequence eclipsing binary candidates near the distribution's short-period limit of approx. 0.20 d, it was measured to be undergoing rapid period decrease in our earlier work, though later observations supported a cyclic variation in period length. Spectroscopic data obtained in 2012 with the Southern African Large Telescope did not, however, support the interpretation of the object as a normal eclipsing binary. Here, we consider three possible explanations consistent with the data: a single-star oblique rotator model in which variability results from stable cool spots on opposite magnetic poles; a two-star model in which the secondary is a brown dwarf; and a three-star model involving a low-mass eclipsing binary in a hierarchical triple system. We conclude that the latter is the most likely model.
Authors: M. E. Lohr, A. J. Norton, U. C. Kolb, D. R. S. Boyd
|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
|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
|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
|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.
|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
|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.
|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.
|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.
|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
|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.
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.
|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.
|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.
|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.”
|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
|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||
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.
|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!