Stellar News Feed Archive
|Dr. George H. Herbig (1920–2013)||Monday, October 14, 2013 - 07:58||
Dr. George H. Herbig, astronomer emeritus at the University of Hawaii at Manoa and a member of the prestigious National Academy of Sciences, has died at the age of 93. He joined the faculty of the UH Institute for Astronomy in 1987 after a long and distinguished career at the Lick Observatory, now part of the University of California, Santa Cruz, and he attained emeritus status at UHM in 2001.
He has been widely acclaimed for his pioneering studies of star formation and the properties and evolution of young stars. His contributions laid the foundation for much of what we know about the birth and early development of stars.
Dr. Herbig’s work on young stars is so fundamental and comprehensive that he is widely seen as the father of the field of star formation studies. He revolutionized the field by identifying and characterizing the physical features of stars that are so young they did not exist when our earliest human ancestors walked the Earth. He recognized that the T Tauri stars, as they are called, have roughly the same mass as our sun, but have much stronger versions of many of the sun’s features, such as magnetic activity, spectral emissions, and lithium content.
|The planets around NN Ser: still there||Tuesday, October 8, 2013 - 11:05||
We present 25 new eclipse times of the white dwarf binary NN Ser taken with the high-speed camera ULTRACAM on the WHT and NTT, the RISE camera on the Liverpool Telescope, and HAWK-I on the VLT to test the two-planet model proposed to explain variations in its eclipse times measured over the last 25 years. The planetary model survives the test with flying colours, correctly predicting a progressive lag in eclipse times of 36 seconds that has set in since 2010 compared to the previous 8 years of precise times. Allowing both orbits to be eccentric, we find orbital periods of 7.9 +/- 0.5 yr and 15.3 +/- 0.3 yr, and masses of 2.3 +/- 0.5 Mjup and 7.3 +/- 0.3 Mjup. We also find dynamically long-lived orbits consistent with the data, associated with 2:1 and 5:2 period ratios. The data scatter by 0.07 seconds relative to the best-fit model, by some margin the most precise of any of the proposed eclipsing compact object planet hosts. Despite the high precision, degeneracy in the orbit fits prevents a significant measurement of a period change of the binary and of N-body effects. Finally, we point out a major flaw with a previous dynamical stability analysis of NN Ser, and by extension, with a number of analyses of similar systems.
Authors: T.R. Marsh, S.G. Parsons, M.C.P. Bours, S.P. Littlefair, C.M. Copperwheat, V.S. Dhillon, E. Breedt, C. Caceres, M.R. Schreiber
|The Runaway Binary LP 400-22 is Leaving the Galaxy||Monday, October 7, 2013 - 08:46||
CfA astronomers Warren Brown and Scott Kenyon and their colleagues decided to investigate the case of the peculiar runaway binary LP400-22. The binary pair was known to consist of two very evolved orbiting stars, so-called white dwarf stars, currently about 1400 light-years away from us. The object is unique in being the only known runaway white dwarf pair, and moreover its velocity is larger than most other runaway stars. The astronomers examined its motion across the sky over a period of five years and conclude from its path in the galaxy that it almost surely was not ejected from the vicinity of the galactic center. Moreover, they report that the supernovae mechanism is also very unlikely because there is no hint at X-ray wavelengths of the remnants of such a supernova. The team concludes that the probable origin of this binary pair is in a dense stellar cluster.
|ALMA Discovers Large 'Hot' Cocoon Around Small Baby Star||Friday, October 4, 2013 - 08:57||
A large hot molecular cloud around a very young star was discovered by ALMA. This hot cloud is about ten times larger than those found around typical solar-mass baby stars, which indicates that the star formation process has more diversity than ever thought. This result was published in Astrophysical Journal Letters on 20 September 2013.
Stars are formed in very cold (-260 degrees Celsius) gas and dust clouds. Infrared dark clouds (IRDCs) are dense regions of such clouds, and thought that in which clusters of stars are formed. Since most of stars are born as members of star clusters, investigating IRDCs has a crucial role in a comprehensive understanding of the star formation process.
|40 Years of Variable Stars: A Celebration of Contributions by Horace A. Smith||Thursday, October 3, 2013 - 08:28||
This online book contains the proceedings of a meeting held at Michigan State University to celebrate the career and contributions of Horace A Smith. The meeting focused on the areas of astronomy which Horace worked on over the years and featured talks on RR Lyrae, Cepheids, and other variable stars. In addition to the direct links to the arXiv articles, I have included a link to download the entire book for free.
Authors: Karen Kinemuchi, Charles A. Kuehn, Nathan De Lee, Horace A. Smith
|Period Changes of Mira Variables, RR Lyrae Stars, and Type II Cepheids||Thursday, October 3, 2013 - 07:48||
Mira variables, RR Lyrae variables, and type II Cepheids all represent evolved states of low-mass stars, and long term observations have revealed that changes in pulsation period occur for each of these classes of variable. Most Mira variables show small or no period changes, but a few show large period changes that can plausibly be associated with thermal pulses on the asymptotic red giant branch. Individual RR Lyrae stars show period changes that do not accord with the predictions of stellar evolution theory. This may be especially true for RR Lyrae stars that exhibit the Blazhko effect. However, the average period changes of all of the RR Lyrae variables within a globular cluster prove a better but still imperfect match for the predictions of evolutionary theory. The observed period changes of short period type II Cepheids (BL Her stars) as well as those of long period type II Cepheids (W Vir stars) are in broad agreement with the rates of period changes expected from their evolutionary motions through the instability strip.
Author: Horace A. Smith
|A uniﬁed model for the spectrophotometric development of classical and recurrent novae||Tuesday, October 1, 2013 - 08:48||
There is increasing evidence that the geometry, and not only the ﬁlling factors, of nova ejecta is important in the interpretation of their spectral and photometric developments. Ensembles of spectra and light curves have provided general typographies. This Letter suggests how these can be uniﬁed.The observed spread in the maximum magnitude - rate of decline (MMRD) relation is argued to result from the range of opening angles and inclination of the ejecta, and not only to their masses and velocities. The spectroscopic classes can be similarly explained and linked to the behavior of the light curves. The secondary maximum observed in some dust forming novae is a natural consequence of the asphericity. Neither secondary ejections nor winds are needed to explain the phenomenology. The spectrophotometric development of classical novae can be understood within a single phenomenological model with bipolar, although not jet-like, mass ejecta. High resolution spectropolarimetry will be an essential analytical tool.
Author: Steven N. Shore
|VOLATILE PULSAR REVEALS MILLISECOND MISSING LINK||Monday, September 30, 2013 - 10:11||
For the first time, astronomers have caught a pulsar in a crucial transitional phase that explains the origin of the mysterious millisecond pulsars. These pulsars spin much faster than expected for their old age, and astronomers believe their rotation receives a boost as they accrete matter in a binary system. The newly found pulsar swings back and forth between accretion-powered X-ray emission and rotation-driven radio emission, bringing conclusive evidence for their 'rejuvenation'. The discovery was made possible by the coordinated efforts of ESA's two missions that scan the high-energy sky: INTEGRAL and XMM-Newton.
|PO and PN in the wind of the oxygen-rich AGB star IK Tau||Tuesday, September 24, 2013 - 08:20||
We present the first detections of PN and PO in an O-rich AGB star and estimate abundances X(PN/H2) of about 3x10^-7 and X(PO/H2) in the range 0.5-6.0x10^-7. This is several orders of magnitude higher than what is found for the C-rich AGB star IRC +10216. The diameter (<=0.7") of the PN and PO emission distributions measured in the interferometric data corresponds to a maximum radial extent of about 40 stellar radii. The abundances and the spatial occurrence of the molecules are in very good agreement with the results reported for VY CMa. We did not detect PS or PH3 in the survey. We suggest that PN and PO are the main carriers of phosphorus in the gas phase, with abundances possibly up to several 10^-7. The current chemical models cannot account for this, underlining the strong need for updated chemical models that include phosphorous compounds.
Authors: E. De Beck, T. Kamiński, N. A. Patel, K. H. Young, C. A. Gottlieb, K. M. Menten, L. Decin
|Re-appearance of McNeil's nebula (V1647 Orionis) and its outburst environment||Friday, September 20, 2013 - 11:21||
We present a detailed study of McNeil's nebula (V1647 Ori) in its ongoing outburst phase starting from September 2008 to March 2013. Our 124 nights of photometric observations were carried out in optical V, R, I and near-infrared J, H, K bands, and 59 nights of medium resolution spectroscopic observations were done in 5200 - 9000 Ang wavelength range. All observations were carried out with 2-m Himalayan Chandra Telescope and 2-m IUCAA Girawali Telescope. Our observations show that over last four and a half years, V1647 Ori and the region C near Herbig-Haro object, HH 22A, have been undergoing a slow dimming...
Authors: J.P. Ninan, D.K. Ojha, B.C. Bhatt, S.K. Ghosh, V. Mohan, K.K. Mallick, M. Tamura, Th. Henning
|Pulsation and Mass Loss Across the HR Diagram: From OB stars to Cepheids to Red Supergiants||Wednesday, September 18, 2013 - 09:29||
Both pulsation and mass loss are commonly observed in stars and are important ingredients for understanding stellar evolution and structure, especially for massive stars. There is a growing body of evidence that pulsation can also drive and enhance mass loss in massive stars and that pulsation-driven mass loss is important for stellar evolution. In this review, I will discuss recent advances in understanding pulsation driven mass loss in massive main sequence stars, classical Cepheids and red supergiants and present some challenges remaining.
Author: Hilding R. Neilson
|Young Stars Cooking in the Prawn Nebula||Wednesday, September 18, 2013 - 09:13||
The glowing jumble of gas clouds visible in this new image make up a huge stellar nursery nicknamed the Prawn Nebula. Taken using the VLT Survey Telescope at ESO’s Paranal Observatory in Chile, this may well be the sharpest picture ever taken of this object. It shows clumps of hot new-born stars nestled in among the clouds that make up the nebula.
|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