Stellar News Feed Archive
|Gigantic ring system around J1407b||Monday, January 26, 2015 - 17:16||
Astronomers at the Leiden Observatory, The Netherlands, and the University of Rochester, USA, have discovered that the ring system that they see eclipse the very young Sun-like star J1407 is of enormous proportions, much larger and heavier than the ring system of Saturn. The ring system – the first of its kind to be found outside our solar system – was discovered in 2012 by a team led by Rochester’s Eric Mamajek.
A new analysis of the data, led by Leiden’s Matthew Kenworthy, shows that the ring system consists of over 30 rings, each of them tens of millions of kilometers in diameter. Furthermore, they found gaps in the rings, which indicate that satellites (“exomoons”) may have formed. The result has been accepted for publication in the Astrophysical Journal.
The researchers encourage amateur astronomers to help monitor J1407, which would help detect the next eclipse of the rings, and constrain the period and mass of the ringed companion. Observations of J1407 can be reported to the American Association of Variable Star Observers (AAVSO). In the meantime the astronomers are searching other photometric surveys looking for eclipses by yet undiscovered ring systems.
|Predicting alpha Comae Berenices Time of Eclipse II: How 3 Faulty Measurements Out of 609 Caused A 26 Year Binary's Eclipse To Be Missed||Friday, January 23, 2015 - 12:10||
The dwarf stars in the 26 year period binary alpha Com were predicted to eclipse each other in early 2015. That prediction was based on an orbit model made with over 600 astrometric observations using micrometers, speckle interferometry, and long baseline optical interferometry. Unfortunately, it has been realized recently that the position angle measurements for three of the observations from ~100 years ago were in error by 180 degrees, which skewed the orbital fit. The eclipse was likely 2 months earlier than predicted, at which point the system was low on the horizon at sunrise.
Authors: Matthew W. Muterspaugh, M.J.P. Wijngaarden, H.F. Henrichs, Benjamin F. Lane, William I. Hartkopf, Gregory W. Henry
|Tau Ceti’s Dust Belt is Huge||Tuesday, January 20, 2015 - 10:28||
Dust arises when asteroids and comets collide, so its location reveals where these dust-creating objects—which are too small to be seen directly—orbit a star. In Tau Ceti's case, “it's quite a wide dust belt,” says Samantha Lawler of the University of Victoria in British Columbia. As her team reported in November, the belt's inner edge is roughly two to three astronomical units (AUs) from the star, which is the position of our own sun's asteroid belt. Tau Ceti's dust belt extends out to 55 AU, which would be just beyond our system's main Edgeworth-Kuiper belt, the zone of small bodies whose largest member is probably Pluto. Presumably full of asteroids and comets, Tau Ceti's dust belt most likely lacks a planet as large as Jupiter, Lawler says. The gravity of such a massive planet would have ejected most small space rocks.
|Classifying the secondary component of the binary star W Aquilae||Tuesday, January 20, 2015 - 10:19||
Aims: The object W Aql is an asymptotic giant branch (AGB) star with a faint companion. By determining more carefully the properties of the companion, we hope to better constrain the properties of the AGB star.
Authors: T. Danilovich, G. Olofsson, J. H. Black, K. Justtanont, H. Olofsson
|Discovery of a Pair of Classical Cepheids in an Invisible Cluster Beyond the Galactic Bulge||Wednesday, January 14, 2015 - 16:54||
We report the discovery of a pair of extremely reddened classical Cepheid variable stars located in the Galactic plane behind the bulge, using near-infrared time-series photometry from the VVV Survey. This is the first time that such objects have ever been found in the opposite side of the Galactic plane. The Cepheids have almost identical periods, apparent brightnesses and colors. From the near-infrared Leavitt law, we determine their distances with ~1.5% precision and ~8% accuracy. We find that they have a same total extinction of A(V)~32 mag, and are located at the same heliocentric distance of <d>=11.4+/-0.9 kpc, and less than 1 pc from the true Galactic plane. Their similar periods indicate that the Cepheids are also coeval, with an age of ~48+/-3 Myr, according to theoretical models. They are separated by an angular distance of only 18.3", corresponding to a projected separation of ~1 pc. Their position coincides with the expected location of the Far 3 kpc Arm behind the bulge. Such a tight pair of similar classical Cepheids indicates the presence of an underlying young open cluster, that is both hidden behind heavy extinction and disguised by the dense stellar field of the bulge. All our attempts to directly detect this "invisible cluster" have failed, and deeper observations are needed.
Authors: I. Dékány, D. Minniti, G. Hajdu, J. Alonso-García, M. Hempel, T. Palma, M. Catelan, W. Gieren, D. Majaess
|Unusual Light Signal Yields Clues About Elusive Black Hole Merger||Wednesday, January 7, 2015 - 16:51||
"Quasars are valuable probes of the evolution of galaxies and their central black holes," saysGeorge Djorgovski, professor of astronomy and director of the Center for Data-Driven Discovery at Caltech.
In the January 7 issue of the journal Nature, Djorgovski and his collaborators report on an unusual repeating light signal from a distant quasar that they say is most likely the result of two supermassive black holes in the final phases of a merger—something that is predicted from theory but which has never been observed before. The discovery could help shed light on a long-standing conundrum in astrophysics called the "final parsec problem," which refers to the failure of theoretical models to predict what the final stages of a black hole merger look like or even how long the process might take. "The end stages of the merger of these supermassive black hole systems are very poorly understood," says the study's first author, Matthew Graham, a senior computational scientist at Caltech. "The discovery of a system that seems to be at this late stage of its evolution means we now have an observational handle on what is going on."
|Where Did All the Stars Go?||Wednesday, January 7, 2015 - 10:50||
Astronomers studying star formation in LDN 483 have discovered some of the youngest observable kinds of baby stars buried in LDN 483’s shrouded interior. These gestating stars can be thought of as still being in the womb, having not yet been born as complete, albeit immature, stars.
In this first stage of stellar development, the star-to-be is just a ball of gas and dust contracting under the force of gravity within the surrounding molecular cloud. The protostar is still quite cool — about –250 degrees Celsius — and shines only in long-wavelength submillimetre light. Yet temperature and pressure are beginning to increase in the fledgling star’s core.
Read the full story at ESO News
|Stars' Spins Reveal Their Ages||Monday, January 5, 2015 - 16:08||
"Our goal is to construct a clock that can measure accurate and precise ages of stars from their spins. We've taken another significant step forward in building that clock," says Soren Meibom of the Harvard-Smithsonian Center for Astrophysics (CfA).
Meibom presented his team's findings today in a press conference at a meeting of the American Astronomical Society. Their results mark the first extension of such observations to stars with ages beyond 1 billion years, and toward the 4.6-billion-year age of the Sun.
Being able to tell the ages of stars is the basis for understanding how astronomical phenomena involving stars and their companions unfold over time.
Knowing a star's age is particularly relevant to the search for signs of alien life outside our solar system. It has taken a long time for life on Earth to attain the complexity we find today. With an accurate stellar clock, astronomers can identify stars with planets that are as old as our Sun or older.
Read the full article at CfA News
|Mid-Infrared Variations of R Coronae Borealis Stars||Saturday, December 27, 2014 - 11:23||
Mid-infrared photometry of R Coronae Borealis stars obtained from various satellites from IRAS to WISE has been utilized in studying the variations of the circumstellar dust's contributions to the spectral energy distribution of these stars. The variation of the fractional coverage (R) of dust clouds and their blackbody temperatures (T) have been used in trying to understand the dust cloud evolution over the three decades spanned by the satellite observations. In particular, it is shown that a relation of R to T developed in this paper is satisfied, especially by those stars for which a single collection of cloud dominates the IR fluxes. Correlations of R with photospheric abundance and luminosity of the stars are explored.
Authors: N. Kameswara Rao, David L. Lambert
|Watching a Quasar Shut Down||Saturday, December 27, 2014 - 11:01||
The first spectrum, measured in 2000 with the Sloan Digital Sky Survey, resembled a classic quasar: blue in color with broad emission lines. But the second spectrum, measured in 2010 as part of the BOSS Survey, didn’t exhibit those same emission lines. The broad component of one emission line, known as H-beta, had disappeared entirely, and another, known as H-alpha, had become only weakly visible.
Spectral lines aside, the object had dimmed to one-tenth its former brightness; once identified as a quasar, the object now looked almost like a galaxy.
So the million-dollar question became: what caused such a drastic and immediate change?
|Surprising Theorists, Stars Within Middle-Aged Clusters Are of Similar Age||Wednesday, December 17, 2014 - 19:19||
“NGC 1651 is the best example found to date of a truly single-age stellar population,” said Richard de Grijs, a faculty member at KIAA involved in the study. “We have since identified a handful of other middle-aged clusters that appear to show similar features.”
The research suggests that, for middle-aged clusters at least, today’s conventional wisdom may be wrong and it might be common for all stars in a single cluster to be of approximately the same age.
A decade ago, astronomers actually thought that the stars within any cluster should all be about the same age, but that idea fell out of favor when clear evidence of the presence of stars of different ages within a single cluster was discovered, at least for the oldest and most populous clusters in our Milky Way. Based on today’s Nature paper, a reverse shift looks necessary.
|Characterizing Cepheid Light Curves||Tuesday, December 16, 2014 - 20:12||
Measuring the mean magnitude or period of a Cepheid, however, can be a pretty demanding task in its own right. A Cepheid’s light curve looks different in different wavelengths (as shown in Figure 1, taken from Madore and Freedman 1991). The shorter-wavelength bands like the B and V-bands have light curves with larger amplitudes of variation and more asymmetry than the light curves in longer-wavelength near-infrared bands like J, H, and K. This makes it easier to detect and characterize the Cepheids in the B and V bands, but harder to accurately determine the mean magnitude of a Cepheid in those wavelengths, since we have to know accurately what phase of the light curve we are observing in order to get a good measurement of the mean magnitude. In practice, we often want to use measure the periods using light curves from shorter wavelengths and measure the mean magnitudes using light curves from longer wavelengths.
Read the paper "New NIR light-curve templates for classical Cepheids" on astro-ph
|The occurrence of classical Cepheids in binary systems||Thursday, December 11, 2014 - 22:42||
Classical Cepheids, like binary stars, are laboratories for stellar evolution and Cepheids in binary systems are especially powerful ones. About one-third of Galactic Cepheids are known to have companions and Cepheids in eclipsing binary systems have recently been discovered in the Large Magellanic Cloud. However, there are no known Galactic binary Cepheids with orbital periods less than one year. We compute population synthesis models of binary Cepheids to compare to the observed period and eccentricity distributions of Galactic Cepheids as well as to the number of observed eclipsing binary Cepheids in the LMC. We find that our population synthesis models are consistent with observed binary properties of Cepheids. Furthermore, we show that binary interaction on the red giant branch prevents some red giant stars from becoming classical Cepheids. Such interactions suggest that the binary fraction of Cepheids should be significantly less than that of their main-sequence progenitors, and that almost all binary Cepheids have orbital periods longer than one year. If the Galactic Cepheid spectroscopic binary fraction is about 35%, then the spectroscopic binary fraction of their intermediate mass main sequence progenitors is about 40-45%.
Authors: Hilding R. Neilson, Fabian R.N. Schneider, Robert G. Izzard, Nancy R. Evans, Norbert Langer
|Astronomers observe two stars so close to each other that they will end up merging into a supermassive star||Monday, December 8, 2014 - 16:27||
This article concludes that MY Cam is the most massive binary star observed and its components, two stars of spectral type O (blue, very hot and bright), 38 and 32 times the Sun's mass, are still on the main sequence and are very close to each other, with an orbital period of less than 1.2 days, in other words, the shortest orbital period in this type of stars. This indicates that the binary was virtually formed as it is now: the stars were almost in contact at the time they were formed.
The expected development is the merger of both components into a single object over 60 solar masses before any of them have time to evolve significantly. Hence, these results demonstrate the viability of some theoretical models suggesting that most massive stars are formed by merging less massive stars.
Read the paper "MY Camelopardalis, a very massive merger progenitor" on astro-ph
|Twinkle, Twinkle New-Born Star||Sunday, December 7, 2014 - 21:34||
Stars are born in dense, cool clouds of molecular gas and dust. When the local density is high enough, the matter can gravitationally collapse to form a new star, a so-called young stellar object (YSO). In its early phases, a thick envelope dominates the infrared emission from the YSO, hiding what is going on within, but eventually the envelope flattens out into a warm circumstellar accretion disk. The disk emits more infrared than does the young star, and that excess radiation can be used to distinguish young stars from more mature stars whose disks and envelopes have disappeared. In recent years it has become possible to investigate these envelopes and disks in more detail, and astronomers have been building on these studies to address how planetary systems develop.
|Making Order Out of Chaos||Wednesday, December 3, 2014 - 13:25||
Today’s paper looks at this phenomenon with a telescope that is normally associated with exoplanets—Kepler. In order to fully understand the chaotic nature of RR Lyrae stars, the authors needed a long, continuous data set and an aperture capable of capturing the full light curve of the stars in question. Kepler is great at the former, but it is designed to search for small dips of light to detect exoplanets. Because of this, the “optimal” apertures used to detect exoplanets cut out a small fraction of the host star’s light. Removing RR Lyrae light, however, would lead to an inaccurate light curve. To complete this study, the authors created larger, specialized aperture masks to capture the full light curve of the RR Lyrae stars.
Read the full paper summary on Astrobites
|Keck Interferometer Reveals Sun-Like Stars Not All That Dusty||Wednesday, December 3, 2014 - 13:18||
Planet hunters received some good news recently. A new study concluded that, on average, sun-like stars aren’t all that dusty. Less dust means better odds of snapping clear pictures of the stars’ planets in the future.
These results come from surveying nearly 50 stars from 2008 to 2011 using the Keck Interferometer, a former NASA key science project that combined the power of the twin W. M. Keck Observatory telescopes atop Mauna Kea, Hawaii.
“Dust is a double-edged sword when it comes to imaging distant planets,” explained Bertrand Mennesson of NASA’s Jet Propulsion Laboratory, Pasadena, California, lead author of an Astrophysical Journal report to be published online December 8. “The presence of dust is a signpost for planets, but too much dust can block our view.”
Read the full story at SciTechDaily
|A Colourful Gathering of Middle-aged Stars||Wednesday, November 26, 2014 - 10:04||
This grouping of stars is about 300 million years old. This makes it middle-aged by open star cluster standards. The cluster stars that started off with moderate masses are still shining brightly with blue-white colours, but the more massive ones have already exhausted their supplies of hydrogen fuel and have become red giant stars. As a result the cluster appears rich in both blue and orange stars. The most massive stars in the original cluster will have already run through their brief but brilliant lives and exploded as supernovae long ago. There are also numerous less conspicuous fainter stars of lower mass that have longer lives and shine with yellow or red hues. NGC 3532 consists of around 400 stars in total.
|Discovery of ZZ Cetis in detached white dwarf plus main-sequence binaries||Sunday, November 23, 2014 - 10:15||
We present the first results of a dedicated search for pulsating white dwarfs (WDs) in detached white dwarf plus main-sequence binaries. Candidate systems were selected from a catalogue of WD+MS binaries, based on the surface gravities and effective temperatures of the WDs. We observed a total of 26 systems using ULTRACAM mounted on ESO's 3.5m New Technology Telescope (NTT) at La Silla. Our photometric observations reveal pulsations in seven WDs of our sample, including the first pulsating white dwarf with a main-sequence companion in a post common envelope binary, SDSSJ1136+0409. Asteroseismology of these new pulsating systems will provide crucial insight into how binary interactions, particularly the common envelope phase, affect the internal structure and evolution of WDs. In addition, our observations have revealed the partially eclipsing nature of one of our targets, SDSSJ1223-0056.
Authors: S. Pyrzas, B. T. Gaensicke, J. J. Hermes, C. M. Copperwheat, A. Rebassa-Mansergas, V. S. Dhillon, S. P. Littlefair, T. R. Marsh, S. G. Parsons, C. D. J. Savoury, M. R. Schreiber, S. C. C. Barros, J. Bento, E. Breedt, P. Kerry
|Doppler images of the eclipsing binary ER Vulpeculae||Sunday, November 23, 2014 - 10:07||
We present Doppler images of both components of the eclipsing binary system ER Vul, based on the spectra obtained in 2004 November, 2006 September and 2008 November. The least-squares deconvolution technique is used for enhancing the signal-to-noise ratios of the observed profiles. The new surface images reveal that both stars of ER Vul show strong starspot activities and the starspots appear at various latitudes. The surface maps of 2006 and 2008 both show the presence of large high-latitude starspots on each component of ER Vul. We find no obvious phase shift of the active regions during our observations. The longitude distributions of starspots are non-uniform on both stars. At low-to-mid latitudes, the active regions are almost exclusively found in the hemisphere facing the other star. However, we find no pronounced concentration of spots at the sub-stellar points.
Authors: Yue Xiang, Shenghong Gu, A. Collier Cameron, J. R. Barnes
|Real-Time Stellar Evolution||Saturday, November 22, 2014 - 10:38||
To get an idea of how stars live and die, we can’t just pick one and watch its life unfold in real time. Most stars live for billions of years! So instead, we do a population census of sorts. Much like you can study how humans age by taking a “snapshot” of individuals ranging from newborn to elderly, so too can we study the lives of stars.
But like all good things in life (and stars), there are exceptions. Sometimes, stellar evolution happens on more human timescales—tens to hundreds of years rather than millions or billions. One such exception is the topic of today’s paper: planetary nebulae, and the rapidly dying stellar corpses responsible for all that glowing gas.
All stars similar to our Sun, or up to about eight times as massive, will end their lives embedded in planetary nebulae like these. The name is a holdover from their discovery and general appearance—we have long known that planetary nebulae have nothing to do with planets. Instead, they are the former outer layers of a star: an envelope of material hastily ejected when gravity can no longer hold a star together. In its final death throes, what’s left of the star rapidly heats up and begins to ionize gas in the nebula surrounding it.
|NASA's Swift Mission Probes an Exotic Object: ‘Kicked’ Black Hole or Mega Star?||Wednesday, November 19, 2014 - 16:21||
An international team of researchers analyzing decades of observations from many facilities, including NASA's Swift satellite, has discovered an unusual source of light in a galaxy some 90 million light-years away.
The object's curious properties make it a good match for a supermassive black hole ejected from its home galaxy after merging with another giant black hole. But astronomers can't yet rule out an alternative possibility. The source, called SDSS1133, may be the remnant of a massive star that erupted for a record period of time before destroying itself in a supernova explosion.
"With the data we have in hand, we can't yet distinguish between these two scenarios," said lead researcher Michael Koss, an astronomer at ETH Zurich, the Swiss Federal Institute of Technology. "One exciting discovery made with NASA's Swift is that the brightness of SDSS1133 has changed little in optical or ultraviolet light for a decade, which is not something typically seen in a young supernova remnant."
|GSC 4560--02157: a New Long-period Eclipsing Cataclysmic Variable Star||Tuesday, November 18, 2014 - 11:49||
Abstract: We study the newly discovered variable star GSC 4560--02157. CCD photometry was performed in 2013--2014, and a spectrum was obtained with the 6-m telescope in June, 2014. GSC 4560--02157 is demonstrated to be a short-period (P=0.265359d) eclipsing variable star. All its flat-bottom primary minima are approximately at the same brightness level, while the star's out-of-eclipse brightness and brightness at secondary minimum varies considerably (by up to 0.6m) from cycle to cycle. Besides, there are short-term (time scale of 0.03-0.04 days) small-amplitude brightness variations out of eclipse. This behavior suggests cataclysmic nature of the star, confirmed with a spectrum taken on June 5, 2014. The spectrum shows numerous emissions of the hydrogen Balmer series, HeI, HeII.
Authors: A.V. Khruslov, A.V. Kusakin, E.A. Barsukova, V.P. Goranskij, A.F. Valeev, N.N. Samus
|ASASSN-13co: A Type-Defying Supernova||Tuesday, November 18, 2014 - 09:46||
There are arguably a lot of things defy categorization, but it’s not everyday that we find something that suggests we do away with our categories altogether. The authors of today’s paper believe that the recently-discovered Type II supernova ASASSN-13co — read that as “assassin”, please — might just be one of the latter. Its unusual characteristics call into question the validity of the two classes (II-P and II-L, more on that later) into which we usually group Type II supernovae. As a result, they suggest that we treat Type II supernovae properties as a continuum, rather than the discrete designations we’ve become accustomed to assigning.
Death Throes of Massive Stars
Type II supernovae are identified by the hydrogen in their spectra (meaning that they still have a hydrogen envelope when they die). They are formed when a star with mass of 8-50 times that of the sun dies through core-collapse.
All stars produce energy through nuclear fusion, but massive stars can fuse much heavier nuclei than stars the size of our sun – all the way to nickel and iron, which have the highest binding energy of all elements. While the fusion of the lighter elements is an exothermic process, fusing iron uses up energy instead, so fusing elements heavier than iron isn’t energetically favorable. As a result, a core of iron and nickel (which then decays into iron) builds up in the center of a massive star. The core is supported by electron degeneracy pressure. When the mass of the iron-nickel core exceeds the Chandrasekhar limit (about 1.4 solar masses), however, electron degeneracy pressure is not enough to stop the core from collapsing. As the core collapses, the protons and electrons in the core of the star merge to form neutrons and neutrinos. The neutrinos can escape and carry away energy. At the same time, the outer layers of the star fall inward until neutrondegeneracy pressure kicks in, stopping the collapse and causing the outer layers to rebound. The combination of the pressure from the neutrinos and the rebound of the outer layers off of the core causes the star to be torn apart in a huge explosion – a core-collapse supernovae.
|Astrochemical Dating of a Stellar Nursery||Monday, November 17, 2014 - 22:33||
An international research team led by scientists from the Coordinated Research Center (CRC) 956 “Conditions and Impact of Star Formation” at the University of Cologne has used observations made with the GREAT instrument on board the SOFIA aircraft observatory and the APEX telescope to date the core of an interstellar cloud that is forming a group of Sun-like stars.
The age of this star-forming cloud, which is located in the Ophiuchus constellation at a distance of around 400 light years, was determined by comparing the data from the telescopes with extensive computer simulations of the chemistry that is changing with time. “The simulations allow us a detailed look at the movement of our H2D+ clock,” explains Jorma Harju of the University of Helsinki. “We find that our new chemical clock is more precise than any of those used previously. Even more importantly, it keeps running when other clocks have already stopped working.” The team is confident that their new method will help to date other stellar birthplaces.