|Fourteen new eclipsing white dwarf plus main-sequence binaries from the SDSS and Catalina surveys||Monday, February 23, 2015 - 07:51||
We report on the search for new eclipsing white dwarf plus main-sequence (WDMS) binaries in the light curves of the Catalina surveys. We use a colour selected list of almost 2000 candidate WDMS systems from the Sloan Digital Sky Survey, specifically designed to identify WDMS systems with cool white dwarfs and/or early M type main-sequence stars. We identify a total of 17 eclipsing systems, 14 of which are new discoveries. We also find 3 candidate eclipsing systems, 2 main-sequence eclipsing binaries and 22 non-eclipsing close binaries. Our newly discovered systems generally have optical fluxes dominated by the main-sequence components, which have earlier spectral types than the majority of previously discovered eclipsing systems. We find a large number of ellipsoidally variable binaries with similar periods, near 4 hours, and spectral types M2--3, which are very close to Roche-lobe filling. We also find that the fraction of eclipsing systems is lower than found in previous studies and likely reflects a lower close binary fraction among WDMS binaries with early M-type main-sequence stars due to their enhanced angular momentum loss compared to fully convective late M type stars, hence causing them to become cataclysmic variables quicker and disappear from the WDMS sample. Our systems bring the total number of known detached, eclipsing WDMS binaries to 71.
Authors: S. G. Parsons, C. Agurto-Gangas, B. T. Gaensicke, A. Rebassa-Mansergas, M. R. Schreiber, T. R. Marsh, V. S. Dhillon, S. P. Littlefair, A. J. Drake, M. C. P. Bours, E. Breedt, C. M. Copperwheat, L. K. Hardy, C. Buisset, P. Prasit, J. J. Ren
|Every interacting double white dwarf binary may merge||Friday, February 20, 2015 - 10:45||
Interacting double white dwarf binaries can give rise to a wide variety of astrophysical outcomes ranging from faint thermonuclear and Type Ia supernovae to the formation of neutron stars and stably accreting AM Canum Venaticorum systems. One key factor affecting the final outcome is whether mass transfer remains dynamically stable or instead diverges, leading to the tidal disruption of the donor and the merger of the binary. It is typically thought that for low ratios of the donor mass to the accretor mass, mass transfer remains stable, especially if accretion occurs via a disk. In this Letter, we examine disk-accreting binaries with extremely low mass ratios and find that the initial phase of hydrogen-rich mass transfer leads to a classical nova-like outburst on the accretor. Dynamical friction within the expanding nova shell shrinks the orbit and causes the mass transfer rate to increase dramatically above the accretor's Eddington limit, resulting in a binary merger. While further calculations are necessary to confirm this outcome for the entire range of binaries previously thought to be dynamically stable, it appears likely that most, if not all, interacting double white dwarf binaries will merge during the course of their evolution.
Author: Ken J. Shen
|'Golden stars' pulsate in a strange, non-chaotic way||Tuesday, February 17, 2015 - 14:22||
This star – called KIC 5520878 – is a type of periodic variable star known as an "RRc Lyrae" variable. It pulsates at a large number of frequencies that are all related to two frequencies – f1 and f2 – that have a golden ratio. The golden ratio or "golden mean" is an irrational number that has significance in geometry, biology and art. Its presence in a dynamical system can mean that the system behaves as a "strange non-chaotic attractor". In this case, "strange" means that the system can be characterized as fractal, and "non-chaotic" means that the dynamics falls in the middle ground between order and chaos.
Read the article in physicsworld.com News
|Stars akin to the sun also explode when they die||Tuesday, February 17, 2015 - 12:10||
IRAS 15103-5754 stands out because it has been observed that the velocity of the material inside the jet increases in proportion to the distance from the central star. "Water molecules are generally destroyed soon after the planetary nebula is formed, and in the rare cases where a maser emission has been detected, the velocity has always been very low”, says Luis F. Miranda (IAA-CSIC, University of Vigo). “In IRAS 15103-5754 we are seeing for the first time a water maser emission at velocities of hundreds of kilometers per second. We are witnessing the transition of a star into a planetary nebula in real time".
“The high velocity can only be explained by the occurrence of an explosion”.
Read the full press release from the Institute of Astrophysics of Andalusia (IAA-CSIC)
|Astronomers Catch Multiple-Star System in First Stages of Formation||Friday, February 13, 2015 - 22:48||
For the first time, astronomers have caught a multiple-star system in the beginning stages of its formation, and their direct observations of this process give strong support to one of several suggested pathways to producing such systems.
When the research team used the VLA to map radio emission from methane molecules, they discovered that filaments of gas in B5 are fragmenting, and the fragments are beginning to form into additional stars that will become a multiple-star system.
Read the full story at NRAO News
|Mining R Coronae Borealis stars from Catalina surveys||Tuesday, February 10, 2015 - 10:13||
This study presents the results of 26 RCB candidates from the Catalina surveys, where five of them are spectroscopically confirmed RCBs and seven of them are previously known carbon stars. This demonstrates the efficacy of this kind of an approach and the potential to discover uncharted RCBs in ongoing and future synoptic surveys.
Author: C.-H. Lee
Read the paper on Astronomy & Astrophysics (register and download for FREE)
|Stellar Partnership Doomed to End in Catastrophe||Monday, February 9, 2015 - 11:40||
A team of astronomers has discovered a close pair of white dwarf stars — tiny, extremely dense stellar remnants — that have a total mass of about 1.8 times that of the Sun. This is the most massive such pair yet found and when these two stars merge in the future they will create a runaway thermonuclear explosion leading to a Type Ia supernova.
Read the full story at ESO News
|New RR Lyrae variables in binary systems||Thursday, February 5, 2015 - 10:09||
Despite their importance, very few RR Lyrae (RRL) stars have been known to reside in binary systems. We report on a search for binary RRL in the OGLE-III Galactic bulge data. Our approach consists in the search for evidence of the light-travel time effect in so-called observed minus calculated (
Authors: G. Hajdu, M. Catelan, J. Jurcsik, I. Dékány, A. J. Drake, J.-B. Marquette
|New infrared view of the Trifid Nebula reveals new variable stars far beyond||Wednesday, February 4, 2015 - 14:17||
Apparently close to the Trifid Nebula in the sky, but in reality about seven times more distant, a newly discovered pair of variable stars has been found in the VISTA data. These are Cepheid variables, a type of bright star that is unstable and slowly brightens and then fades with time. This pair of stars, which the astronomers think are the brightest members of a cluster of stars, are the only Cepheid variables detected so far that are close to the central plane, but on the far side of the galaxy. They brighten and fade over a period of eleven days.
|Nobel laureate and laser inventor Charles Townes dies at 99||Wednesday, January 28, 2015 - 15:04||
BERKELEY — Charles Hard Townes, a professor emeritus of physics at the University of California, Berkeley, who shared the 1964 Nobel Prize in Physics for invention of the laser and subsequently pioneered the use of lasers in astronomy, died early Tuesday, Jan. 27, in Oakland. He was 99 and in failing health, and died on his way to the hospital.
“Charles Townes embodies the best of Berkeley; he’s a great teacher, great researcher and great public servant,” said UC Berkeley Chancellor Nicholas Dirks on the occasion of a campuswide celebration of Townes’ 99th birthday last July 28. “As we celebrate this 99-year milestone and a career spanning nearly 80 years, we can only be impressed by the range of his intellectual curiosity, his persistence and his pioneering spirit.”
Until last year, Townes visited the campus daily, working either in his office in the physics department or at the Space Sciences Laboratory.
“Charlie was a cornerstone of the Space Sciences Laboratory for almost 50 years,” said Stuart Bale, director of the lab and a UC Berkeley professor of physics. “He trained a great number of excellent students in experimental astrophysics and pioneered a program to develop interferometry at short wavelengths. He was a truly inspiring man and a nice guy. We’ll miss him.”
|ASASSN-14cc: Likely Helium Analog of RZ Leonis Minoris||Wednesday, January 28, 2015 - 07:39||
We identified that ASASSN-14cc is a very active dwarf nova spending approximately 60% of the time in outburst. Our long-term photometry revealed that the object shows long outbursts recurring with a period of 21-33 d and very brief short outbursts lasting less than 1 d. The maximum decline rate exceeds 2.8 mag/d. The duration of long outbursts is 9-18 d, comprising 50-60% of the recurrence time of long outbursts. We detected 0.01560-0.01562 d (22.5 min) modulations during long outbursts, which we identified to be superhumps. These features indicate that ASASSN-14cc has outburst parameters very similar to the extreme dwarf nova RZ LMi but with a much shorter superhump period. All the observations can be naturally understood considering that this object is a helium analog (AM CVn-type object) of RZ LMi. The highest outburst activity among AM CVn-type objects can be understood as the high-mass transfer rate expected for the orbital period giving a condition close to the stability limit of the accretion disk. In contrast to RZ LMi, this object shows little evidence for premature quenching of the superoutburst, which has been proposed to explain the unusual outburst parameters in RZ LMi.
Authors: Taichi Kato, Franz-Josef Hambsch, Berto Monard
|Gigantic ring system around J1407b||Monday, January 26, 2015 - 16:16||
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 - 11:10||
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 - 09:28||
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 - 09:19||
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 - 15:54||
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 - 15:51||
"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 - 09:50||
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 - 15:08||
"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 - 10:23||
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 - 10:01||
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 - 18:19||
“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 - 19:12||
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 - 21:42||
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 - 15:27||
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