Stellar News Feed Archive
|Resolving the stellar activity of the Mira AB binary with ALMA||Saturday, March 28, 2015 - 09:44||
We present the size, shape and flux densities at millimeter continuum wavelengths, based on ALMA science verification observations in Band 3 (~94.6 GHz) and Band 6 (~228.7 GHz), from the binary Mira A (o Ceti) and Mira B. The Mira AB system has been observed with ALMA at a spatial resolution of down to ~25 mas. The extended atmosphere of Mira A and the wind around Mira B sources are resolved and we derive the size of Mira A and of the ionized region around Mira B. The spectral indices within Band 3 (between 89-100 GHz) and between Band 3 and Band 6 are also derived. The spectral index of Mira A is found to change from 1.71+-0.05 within Band 3 to 1.54+-0.04 between Band 3 and 6. The spectral index of Mira B is 1.3+-0.2 in Band 3, in good agreement with measurements at longer wavelengths. However it rises to 1.72+-0.11 between the bands. For the first time the extended atmosphere of a star is resolved at these frequencies and for Mira A the diameter is ~3.7x2.9 AU in Band 3 (with brightness temperature Tb~6000 K) and ~4.0x3.6 AU in Band 6 (Tb~2500 K). Additionally, a bright hotspot of ~0.4 AU and with Tb~10000 K is found on the stellar disc of Mira A. The size of the ionized region around the accretion disk of Mira B is found to be ~2.4 AU. The emission around Mira B is consistent with that from a partially ionized wind of gravitationally bound material from Mira A close to the accretion disk of Mira B. The Mira A atmosphere does not fully match predictions, with brightness temperatures in Band 3 significantly higher than expected, potentially due to shock heating. The hotspot is likely due to magnetic activity and could be related to the previously observed X-ray flare of Mira A.
Authors: W.H.T. Vlemmings, S. Ramstedt, E. O'Gorman, E.M.L. Humphreys, M. Wittkowski, A. Baudry, M. Karovska
|This International Year of Light, Switch Off the Lights for the Planet||Friday, March 27, 2015 - 09:03||
This International Year of Light, as we celebrate the role of light and light-based technology in sustainable development, let us also pledge to take action for a sustainable future with the flick of a light switch. Celebrate your commitment to our planet by switching off the lights on Saturday 28 March at 8:30 PM local time.
|Colliding Stars Explain Enigmatic Seventeenth Century Explosion||Monday, March 23, 2015 - 12:11||
New observations made with APEX and other telescopes reveal that the star that European astronomers saw appear in the sky in 1670 was not a nova, but a much rarer, violent breed of stellar collision. It was spectacular enough to be easily seen with the naked eye during its first outburst, but the traces it left were so faint that very careful analysis using submillimetre telescopes was needed before the mystery could finally be unravelled more than 340 years later.
The lead author of the new study, Tomasz Kamiński (ESO and the Max Planck Institute for Radio Astronomy, Bonn, Germany) explains: “For many years this object was thought to be a nova, but the more it was studied the less it looked like an ordinary nova — or indeed any other kind of exploding star.”
The results appear online in the journal Nature on 23 March 2015.
|Spectacular aurora from severe solar storm light up northern skies||Saturday, March 21, 2015 - 08:41||
The St. Patrick’s Day geomagnetic storm, the most intense since fall of 2013, spurred dazzling aurora before and after sunset, and then finally faded.
On Tuesday evening, forecasts indicated a slight chance aurora would be viewable as far south as the Mid-Atlantic, but the farthest south we’ve seen reports were in Illinois, Ohio and northern New Jersey – which is nonetheless quite unusual.
Pictures from the Washington Post article.
Cloud camera YouTube video from Hankasalmi Observatory, compliments of Arto Okasanen.
Image above taken by Marketa Murray on March 17, 2015 @ Dalton HWY , Alaska
|Another deep dimming of the classical T Tauri star RW Aur A||Monday, March 16, 2015 - 09:07||
Context. RW Aur A is a classical T Tauri star (CTTS) with an unusually rich emission line spectrum. In 2014 the star faded by ~ 3 magnitudes in the V band and went into a long-lasting minimum. In 2010 the star suffered from a similar fading, although less deep. These events in RW Aur A are very unusual among the CTTS, and have been attributed to occultations by passing dust clouds. Aims. We want to find out if any spectral changes took place after the last fading of RW Aur A with the intention to gather more information on the occulting body and the cause of the phenomenon. Methods. We collected spectra of the two components of RW Aur. Photometry was made before and during the minimum. Results. The overall spectral signatures reflecting emission from accretion flows from disk to star did not change after the fading. However, blue-shifted absorption components related to the stellar wind had increased in strength in certain resonance lines, and the profiles and strengths, but not fluxes, of forbidden lines had become drastically different. Conclusions. The extinction through the obscuring cloud is grey indicating the presence of large dust grains. At the same time, there are no traces of related absorbing gas. The cloud occults the star and the interior part of the stellar wind, but not the wind/jet further out. The dimming in 2014 was not accompanied by changes in the accretion flows at the stellar surface. There is evidence that the structure and velocity pattern of the stellar wind did change significantly. The dimmings could be related to passing condensations in a tidally disrupted disk, as proposed earlier, but we also speculate that large dust grains have been stirred up from the inclined disk into the line-of-sight through the interaction with an enhanced wind.
Authors: P. P. Petrov, G. F. Gahm, A. A. Djupvik, E. V. Babina, S. A. Artemenko, K. N. Grankin
|Revealing δ Cephei's Secret Companion and Intriguing Past||Monday, March 16, 2015 - 08:27||
Classical Cepheid variable stars are crucial calibrators of the cosmic distance scale thanks to a relation between their pulsation periods and luminosities. Their archetype, δ Cephei, is an important calibrator for this relation. In this paper, we show that δ Cephei is a spectroscopic binary based on newly-obtained highprecision radial velocities. We combine these new data with literature data to determine the orbit, which has period 2201 days, semi-amplitude 1.5 km s−1 , and high eccentricity (e = 0.647). We re-analyze Hipparcos intermediate astrometric data to measure δ Cephei’s parallax ($ = 4.09 ± 0.16 mas) and find tentative evidence for an orbital signature, although we cannot claim detection. We estimate that Gaia will fully determine the astrometric orbit. Using the available information from spectroscopy, velocimetry, astrometry, and Geneva stellar evolution models (MδCep ∼ 5.0 − 5.25 M ), we constrain the companion mass to within 0.2 < M2 < 1.2 M . We discuss the potential of ongoing and previous interactions between the companion and δ Cephei near pericenter passage, informing reported observations of circumstellar material and bow-shock. The orbit may have undergone significant changes due to a Kozai-Lidov mechanism driven by the outer (visual and astrometric) companion HD 213307. Our discovery of δ Cephei’s nature as a spectroscopic binary exposes a hidden companion and reveals a rich and dynamical history of the archetype of classical Cepheid variables.
Authors: Richard I. Anderson, Johannes Sahlmann, Berry Holl, Laurent Eyer, Lovro Palaversa, Nami Mowlavi, Maria Süveges, Maroussia Roelens
|How old is the Hyades?||Monday, March 9, 2015 - 10:40||
The Hyades cluster forms the head of Taurus the bull in the zodiac constellation. It is one of the most famous open clusters—a group of stars that all formed at the same time from the same cloud of gas. This cluster was thought to be 625 million years old, however new research suggests that the Hyades is much older. This makes for a slightly awkward situation; the Hyades underpins our understanding of stellar ages. If its age is wrong then a lot of other ages are wrong too.
This conflict may be resolved soon—the Kepler spacecraft (now reincarnated as K2) is currently observing the Hyades. It will be able to detect asteroseismic oscillations in some of its stars, revealing their true ages. Hundreds of inferences rely on the age of this cluster—unveiling the mystery will be an exciting moment for stellar astronomy!
Read the story on Astrobites
|A young star takes centre stage||Wednesday, March 4, 2015 - 09:44||
What makes V1331Cyg special is the fact that we look almost exactly at one of its poles. Usually, the view of a young star is obscured by the dust from the circumstellar disc and the envelope that surround it. However, with V1331Cyg we are actually looking in the exact direction of a jet driven by the star that is clearing the dust and giving us this magnificent view.
Image credit: ESA/Hubble, NASA, Karl Stapelfeldt (GSFC), B. Stecklum and A. Choudhary (Thüringer Landessternwarte Tautenburg, Germany)
Read the full press release from ESA Hubble Images
|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."