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Stellar News Feed Archive

Face to phase with RU Lupi Monday, November 4, 2013 - 08:42

We present new results on the classical T Tauri star RU Lupi based on three observing runs collecting high-resolution spectra, complementary NIR spectra, multicolour photometric data, and X-ray observations. The photospheric absorption lines are weakened. This veiling becomes extremely strong on occasion, and we show that this effect is due to narrow emission lines that fill in the photospheric lines. The blue-shifted wings in the optical emission lines of He I, attributed to a stellar wind, are remarkably stable in equivalent width. In contrast, the red-shifted wings change dramatically in strength depending on rotational phase. From the pattern of variability we infer that these wings originate in accreting gas close to the star, and that the accretion funnels are bent and trail the hot spot. Forbidden emission lines are very stable over the entire observing period and originate in the disk wind. A system of narrow blue-shifted absorption features seen in lines of Ca II and Na I can be traced to a disk wind as well. Slightly blue-shifted emission components are present in the forbidden lines and might be related to a wide angle molecular disk wind.

Authors: Gösta F. Gahm, Henricus C. Stempels, Frederick M. Walter, Peter P. Petrov, Gregory J. Herczeg

Read the pre-print on arXiv

Could a Milky Way Supernova Be Visible from Earth in Next 50 Years? Friday, November 1, 2013 - 08:02

Astronomers at The Ohio State University have calculated the odds that, sometime during the next 50 years, a supernova occurring in our home galaxy will be visible from Earth.

The good news: they’ve calculated the odds to be nearly 100 percent that such a supernova would be visible to telescopes in the form of infrared radiation.

The bad news: the odds are much lower—dipping to 20 percent or less—that the shining stellar spectacle would be visible to the naked eye in the nighttime sky.

Yet, all this is great news to astronomers, who, unlike the rest of us, have high-powered infrared cameras to point at the sky at a moment’s notice. For them, this study suggests that they have a solid chance of doing something that’s never been done before: detect a supernova fast enough to witness what happens at the very beginning of a star’s demise. A massive star “goes supernova” at the moment when it’s used up all its nuclear fuel and its core collapses, just before it explodes violently and throws off most of its mass into space.

“We see all these stars go supernova in other galaxies, and we don’t fully understand how it happens. We think we know, we say we know, but that’s not actually 100 percent true,” said Christopher Kochanek, professor of astronomy at Ohio State and the Ohio Eminent Scholar in Observational Cosmology. "Today, technologies have advanced to the point that we can learn enormously more about supernovae if we can catch the next one in our galaxy and study it with all our available tools.

Read the full press release

Read the pre-print on arXiv

Nova Aquilae 1918 (V603 Aql) Faded by 0.44 mag/century from 1938-2013 Monday, October 28, 2013 - 08:14

We present the light curve of the old nova V603 Aql (Nova Aql 1918) from 1898-1918 and 1934-2013 using 22,722 archival magnitudes. All of our magnitudes are either in, or accurately transformed into, the Johnson B and V magnitude systems. This is vital because offsets in old sequences and the visual-to-V transformation make for errors from 0.1-1.0 magnitude if not corrected. Our V603 Aql light curve is the first time that this has been done for any nova. Our goal was to see the evolution of the mass accretion rate on the century time scale, and to test the long-standing prediction of the Hibernation model that old novae should be fading significantly in the century after their eruption is long over. The 1918 nova eruption was completely finished by 1938 when the nova decline stopped, and when the star had faded to fainter than its pre-nova brightness of B=11.43±0.03 mag. We find that the nova light from 1938-2013 was significantly fading, with this being seen consistently in three independent data sets (the Sonneberg plates in B, the AAVSO V light curve, and the non-AAVSO V light curve). We find that V603 Aql is declining in brightness at an average rate of 0.44±0.04 mag per century since 1938. This work provides remarkable confirmation of an important prediction of the Hibernation model. However, our result does not uniquely point to the Hibernation model because other models of novae evolution are now making similar predictions.

Authors:  Christopher B. Johnson (LSU), Bradley E. Schaefer (LSU), Peter Kroll (Sonneberg Observatory), Arne Henden (AAVSO)

Read the pre-print on arXiv

Amplitude Variations in Pulsating Red Supergiants Thursday, October 24, 2013 - 07:55

We have used long-term AAVSO visual observations and Fourier and wavelet analysis to identify periods and study long-term amplitude variations in 44 red supergiants. Of these, 12 stars had data which were too sparse and/or had low amplitude and/or were without conspicuous peaks in the Fourier spectrum; 6 stars had only long (2500-4000 days) periods without significant amplitude variation. The other 26 stars had one or two periods, either "short" (hundreds of days) or "long" (thousands of days), whose amplitudes varied by up to a factor of 8, but more typically 2-4. The median timescale of the amplitude variation was 18 periods. We interpret the shorter periods as due to pulsation, and the longer periods as analogous to the "long secondary periods" found in pulsating red giants.

Authors:  John R. Percy and Viraja C. Khatu

Read the pre-print paper from arXiv

Origin of W UMa-type contact binaries - age and orbital evolution Tuesday, October 22, 2013 - 14:49

Recently, our understanding of the origin of W UMa-type contact binaries has become clearer. Initial masses of their components were successfully estimated by Yildiz and Dougan using a new method mainly based on observational properties of overluminous secondary components. In this paper, we continue to discuss the results and make computations for age and orbital evolution of these binaries. It is shown that the secondary mass, according to its luminosity, also successfully predicts the observed radius. While the current mass of the primary component is determined by initial masses, the current secondary mass is also a function of initial angular momentum. We develop methods to compute the age of A- and W-subtype W UMa-type contact binaries {in terms of} initial masses and mass according to the luminosity of the secondaries. 

Author:  Mutlu Yildiz

Read the full abstract and pre-print paper on arXiv

Astronomers Shed New Light on the Rarest and Brightest Exploding Stars Thursday, October 17, 2013 - 12:52

The research is published on Thursday (17 October) in Nature Magazine – one of the world’s most prestigious science publications. It proposes that the most luminous supernovae – exploding stars – are powered by small and incredibly dense neutron stars, with gigantic magnetic fields that spin hundreds of times a second.

Scientists at Queen’s Astrophysics Research Center observed two super-luminous supernovae – two of the Universe’s brightest exploding stars – for more than a year. Contrary to existing theories, which suggested that the brightest supernovae are caused by super-massive stars exploding, their findings suggest that their origins may be better explained by a type of explosion within the star’s core which creates a smaller but extremely dense and rapidly spinning magnetic star.

Read the full press release

Read the abstract and pre-print on arXiv

Multi-Longitude Observation Campaign of KV Cancri: an RR Lyrae star with irregular Blazhko modulations Thursday, October 17, 2013 - 09:20

We present the results of multi-longitude observations of KV Cancri, an RR Lyrae star showing an irregular Blazhko effect. With a pulsation period of 0.50208 day, the times of light curve maxima are delayed by 6 minutes per day. This daily delay regularly leads to long periods of time without maximum light curve observations for a given site. To cope with this observing time window problem, we have organized a multi-longitude observation campaign including a telescope of the AAVSONet. From the observed light curves, 92 pulsation maxima have been measured covering about six Blazhko periods. The Fourier analysis of magnitudes at maximum light has revealed a main Blazhko period of 77.6 days and also a secondary period of 40.5 days. A Fourier analysis of (O-C) values did not show the secondary Blazhko period. The frequency spectrum of the complete light curve, from a Fourier analysis and successive pre-whitening with PERIOD04, has shown triplet structures around the two Blazhko modulation frequencies but with slightly different periods (77.8 and 42.4 days). The second Blazhko frequency is statistically not a harmonic of the main Blazhko frequency. Besides the two Blazhko modulations KV Cnc presents other particularities like irregularities from Blazhko cycle to cycle and very fast magnitude variations which can reach a maximum of 2.5 magnitudes per hour over a period of 15 minutes. This campaign shows that regular observations by amateur astronomers remain important. Indeed such a detailed characterization of the Blazhko effect could not be obtained from large-scale surveys, as cooperative long time-series observations are needed.

Authors: Pierre de Ponthiere, Michel Bonnardeau, Franz-Joseph Hambsch, Tom Krajci, Kenneth Menzies, Richard Sabo

Read the paper on arXiv

Variable Stars and Galactic Structure Wednesday, October 16, 2013 - 15:16

Variable stars have a unique part to play in Galactic astronomy. Among the most important of these variables are the Cepheids (types I and II), the RR Lyraes and the Miras (O- and C-rich). The current status of the basic calibration of these stars in their roles as distance, structure and population indicators is outlined and some examples of recent applications of these stars to Galactic and extragalactic problems is reviewed. The expected impact of Gaia on this type of work is discussed and the need for complementary ground based observations, particularly large scale near-infrared photometry, is stressed.

Authors:  Michael W. Feast, Patricia A. Whitelock

Read the pre-print paper on arXiv

How The Largest Star Known Is Tearing Itself Apart Wednesday, October 16, 2013 - 08:43

When astronomers studied the images of Westerlund 1 they spotted something truly unique. Around one of the stars, known as W26, they saw a huge cloud of glowing hydrogen gas, shown as green in this new image. Such glowing clouds are ionized, meaning that the electrons have been stripped away from the atoms of hydrogen gas.

Clouds of this type are rarely found around massive stars and are even rarer around red supergiant stars such as W26 -- this is the first ionized nebula ever discovered around such a star. W26 itself would be too cool to make the gas glow; the astronomers speculate that the source of the ionizing radiation may be either hot blue stars elsewhere in the cluster, or possibly a fainter, but much hotter, companion star to W26. The fact that the nebula is ionized will make it considerable easier to study in the future than if it were not ionized.

On investigating the star W26 in more detail the researchers realized that the star is probably the largest star ever discovered, with a radius 1,500 times larger than the Sun and is also one of the most luminous red supergiants known. Such large and luminous massive stars are believed to be highly evolved, all of which suggests that W26 is coming towards the end of its life and will eventually explode as a supernova.

The nebula observed around W26 is very similar to the nebula surrounding SN 1987A, the remnant of a star that exploded as a supernova in 1987. SN 1987A was the closest observed supernova to Earth since 1604 and as such it gave astronomers a chance to better study the properties of these explosions. Studying objects like the new nebula around W26 will help astronomers to understand the mass loss processes around these massive stars, which eventually lead to their explosive demise.

Read the pre-print on arXiv

Read the press release at ESO

Dr. George H. Herbig (1920–2013) Monday, October 14, 2013 - 06:58

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.

Read the full press release

The planets around NN Ser: still there Tuesday, October 8, 2013 - 10:05

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

Read the paper and abstract on arXiv

The Runaway Binary LP 400-22 is Leaving the Galaxy Monday, October 7, 2013 - 07:46

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.

Read the full press release

Read the abstract and paper on arXiv

ALMA Discovers Large 'Hot' Cocoon Around Small Baby Star Friday, October 4, 2013 - 07:57

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.

Read the full press release

40 Years of Variable Stars: A Celebration of Contributions by Horace A. Smith Thursday, October 3, 2013 - 07:28

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

http://arxiv.org/abs/1310.0149

Period Changes of Mira Variables, RR Lyrae Stars, and Type II Cepheids Thursday, October 3, 2013 - 06:48

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

Download the paper from arXiv

A unified model for the spectrophotometric development of classical and recurrent novae Tuesday, October 1, 2013 - 07:48

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

Read the paper on arXiv

VOLATILE PULSAR REVEALS MILLISECOND MISSING LINK Monday, September 30, 2013 - 09:11

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.

Read the full story at ESA

PO and PN in the wind of the oxygen-rich AGB star IK Tau Tuesday, September 24, 2013 - 07:20

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

Read the full abstract on arXiv

Re-appearance of McNeil's nebula (V1647 Orionis) and its outburst environment Friday, September 20, 2013 - 10:21

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

Read the full abstract and paper at arXiv

Pulsation and Mass Loss Across the HR Diagram: From OB stars to Cepheids to Red Supergiants Wednesday, September 18, 2013 - 08:29

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

Read the review paper from arXiv

Young Stars Cooking in the Prawn Nebula Wednesday, September 18, 2013 - 08:13

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.

Read the full press release

Blazhko effect in Cepheids and RR Lyrae stars Tuesday, September 17, 2013 - 07:58

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

Read the paper at arXiv

Magnetic jet shows how stars begin their final transformation Monday, September 16, 2013 - 08:13

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 - 08:01

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.)

Read the full abstract at arXiv

Newly identified YSO candidates towards the LDN 1188 Monday, September 16, 2013 - 07:34

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

Read the paper on arXiv

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