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Stellar News Feed Archive

One thousand cataclysmic variables from the Catalina Real-time Transient Survey Wednesday, July 9, 2014 - 08:58

Over six years of operation, the Catalina Real-time Transient Survey (CRTS) has identified 1043 cataclysmic variable (CV) candidates --- the largest sample of CVs from a single survey to date. Here we provide spectroscopic identification of 85 systems fainter than g<19, including three AMCVn binaries, one helium-enriched CV, one polar and one new eclipsing CV. We analyse the outburst properties of the full sample and show that it contains a large fraction of low accretion rate CVs with long outburst recurrence times. We argue that most of the high accretion rate dwarf novae in the survey footprint have already been found and that future CRTS discoveries will be mostly low accretion rate systems. We find that CVs with white dwarf dominated spectra have significantly fewer outbursts in their CRTS light curves compared to disc-dominated CVs, reflecting the difference in their accretion rates. Comparing the CRTS sample to other samples of CVs, we estimate the overall external completeness to be 23.6 per cent, but show that as much as 56 per cent of CVs have variability amplitudes that are too small to be selected using the transient selection criteria employed by current ground-based surveys. The full table of CRTS CVs, including their outburst and spectroscopic properties examined in this paper, is provided in the online materials.

Authors: E. Breedt (1), B.T. Gaensicke (1), A.J. Drake (2), P. Rodriguez-Gil (3 and 4), S.G. Parsons (5), T.R. Marsh (1), P. Szkody (6), M.R. Schreiber (5), S.G. Djorgovski (2) ((1) University of Warwick, UK, (2) California Institute of Technology, USA, (3) Instituto de Astrofisica de Canarias, Spain, (4) Universidad de La Laguna, Spain, (5) Universidad de Valparaiso, Chile, (6) University of Washington, USA)

Read the paper on arXiv

 

Astronomers Bring The Third Dimension To A Doomed Star's Outburst Wednesday, July 9, 2014 - 08:03

In the middle of the 19th century, the massive binary system Eta Carinae underwent an eruption that ejected at least 10 times the sun's mass and made it the second-brightest star in the sky. Now, a team of astronomers has used extensive new observations to create the first high-resolution 3-D model of the expanding cloud produced by this outburst.

"Our model indicates that this vast shell of gas and dust has a more complex origin than is generally assumed," said Thomas Madura, a NASA Postdoctoral Program fellow at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and a member of the study team. "For the first time, we see evidence suggesting that intense interactions between the stars in the central binary played a significant role in sculpting the nebula we see today."

Read the full press release at nasa.gov

 

The 2014 Eclipse of EE Cep- Announcement for a Third International Observational Campaign Tuesday, July 8, 2014 - 08:33

EE Cep is a unique system in which a Be star is eclipsed by a dark dusty disk, making this star similar to the famous epsilon Aur in many respects. The depth and the duration of the EE Cep eclipses change to a large extent. The last two eclipses were observed in the framework of extensive international campaigns. The joint analysis of these campaigns data and historical photometry, enabled us to propose a model of this system, which implies a disk precession with a period approximately 11-12 times larger than the orbital period. This model predicts that the forthcoming eclipse should be among the deepest observed, reaching about 2 mag. The next eclipse approaches - the photometric minimum should occur around August 23, 2014. Here we would like to announce a new, third international campaign with purpose to verify the disk precession model and to put more constraints on the physical parameters of this system.

Authors: C. Galan, P. Wychudzki, M. Mikolajewski, T. Tomov, D. Dimitrov

Read the paper on astro-ph

 

New Technique Provides a Clear and Rapid Means of Classifying Supernova Remnants Friday, July 4, 2014 - 09:10

An international team of astronomers using data from the Japan-led Suzaku X-ray observatory has developed a powerful technique for analyzing supernova remnants, the expanding clouds of debris left behind when stars explode. The method provides scientists with a way to quickly identify the type of explosion and offers insights into the environment surrounding the star before its destruction.

“Supernovae imprint their remnants with X-ray evidence that reveals the nature of the explosion and its surroundings,” said lead researcher Hiroya Yamaguchi, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Thanks to Suzaku, we are now learning how to interpret these signals.”

The technique involves observing specific X-ray emissions from iron atoms in the core of supernova remnants. Even after thousands of years, these atoms remain extremely hot, stripped of most of the 26 electrons that accompany iron atoms under normal conditions on Earth. The metal is formed in the centers of shattered stars toward the end of their energy-producing lives and in their explosive demise, which makes it a key witness to stellar death.

Read the full press release with links to the paper here.

 

Luminous Blue Variables are Antisocial: Their Isolation Implies that they are Kicked Mass Gainers in Binary Evolution Tuesday, July 1, 2014 - 07:17

Based on their relatively isolated environments, we argue that LBVs must be primarily the product of binary evolution, challenging the traditional single-star view wherein LBVs mark a brief transition between massive O stars and Wolf-Rayet (WR) stars. If the latter were true, then LBVs should be concentrated in young clusters and found alongside main-sequence stars with similarly high inferred initial mass. This is decidedly not the case. Examining locations of LBVs compared to O stars in our Galaxy and the Magellanic Clouds reveals that LBVs systematically avoid clusters of O stars, and many reside over 100 pc from any O star. In the LMC, LBVs are statistically much more isolated than O-type stars, and (perhaps most surprisingly) even more isolated than most WR stars. This makes it impossible for LBVs to be massive stars in transition to WR stars. Instead, we propose that massive stars and supernova (SN) subtypes are dominated by bifurcated evolutionary paths in interacting binaries, wherein most WR stars and SNeIbc correspond to the mass donors, while LBVs (and their lower-mass analogs like B[e] supergiants, which we show to be even more isolated) are the mass gainers. LBVs are essentially the late evolutionary stage of massive blue stragglers. Through binary mass transfer, rejuvinated mass gainers get enriched, spun up, and sometimes kicked far from their clustered birthsites by their companion's SN. This scenario agrees better with LBVs exploding as SNeIIn and the observed isolation of SNe~IIn and SN impostors. We argue that environmental trends of various SN subtypes are influenced more by binarity and SN kicks, rather than tracing initial mass as is generally assumed. Mergers or Thorne-Zykow objects might also give rise to LBVs, but these scenarios may have a harder time explaining why LBVs avoid clusters.

Authors: Nathan Smith, Ryan Tombleson

Read the paper on astro-ph

 

Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae. VI: The Sixth Year (2013-2014) Thursday, June 26, 2014 - 12:56

Continuing the project described by Kato et al. (2009, PASJ, 61, S395, arXiv:0905.1757), we collected times of superhump maxima for 56 SU UMa-type dwarf novae mainly observed during the 2013-2014 season and characterized these objects. We detected negative superhumps in VW Hyi and indicated that the low number of normal outbursts in some supercycle can be interpreted as a result of the disk tilt. This finding, combined with the Kepler observation of V1504 Cyg and V344 Lyr, suggests that the disk tilt is responsible for modulating the outburst pattern in SU UMa-type dwarf novae. We also studied the deeply eclipsing WZ Sge-type dwarf nova MASTER OT J005740.99+443101.5 and found evidence of a sharp eclipse during the phase of early superhumps. The profile can be reproduced by a combination of the eclipse of the axisymmetric disk and the uneclipsed light source of early superhumps. This finding confirms the lack of evince of a greatly enhanced hot spot during the early stage of WZ Sge-type outburst. We detected growing (stage A) superhumps in MN Dra and give a suggestion that some of SU UMa-type dwarf novae situated near the critical condition of tidal instability may show long-lasting stage A superhumps. The large negative period derivatives reported in such systems can be understood a result of the combination of stage A and B superhumps. The WZ Sge-type dwarf novae AL Com and ASASSN-13ck showed a long-lasting (plateau-type) rebrightening. In the early phase of the rebrightening, both objects showed a precursor-like outburst, suggesting that the long-lasting rebrightening is triggered by a precursor outburst.

Authors: Taichi Kato (Kyoto U), Pavol A. Dubovsky, Igor Kudzej, Franz-Josef Hambsch, Ian Miller, Tomohito Ohshima, Chikako Nakata, Miho Kawabata, Hirochika Nishino, Kazunari Masumoto, Sahori Mizoguchi, Masayuki Yamanaka, Katsura Matsumoto, Daisuke Sakai, Daiki Fukushima, Minami Matsuura, Genki Bouno, Megumi Takenaka, Shinichi Nakagawa, Ryo Noguchi, Eriko Iino, Roger D. Pickard, Yutaka Maeda, Arne Henden, Kiyoshi Kasai, Seiichiro Kiyota, Hidehiko Akazawa, Kazuyoshi Imamura, Enrique de Miguel, Hiroyuki Maehara, Berto Monard, Elena P. Pavlenko, Kirill Antonyuk, Nikolaj Pit, Oksana I. Antonyuk, Aleksei V. Baklanov, Javier Ruiz, Michael Richmond, Arto Oksanen, Caisey Harlingten, Sergey Yu. Shugarov, Drahomir Chochol, Gianluca Masi, Francesca Nocentini, Patrick Schmeer, Greg Bolt, Peter Nelson, Joseph Ulowetz, Richard Sabo, William N. Goff, William Stein, Raul Michel, Shawn Dvorak, Irina B. Voloshina, Vladimir Metlov, Natalia Katysheva, Vitaly V. Neustroev, George Sjoberg, Colin Littlefield, Bartlomiej Debski, Paulina Sowicka, Marcin Klimaszewski, Malgorzata Curylo, Etienne Morelle, Ivan A. Curtis, Hidetoshi Iwamatsu, Neil D. Butterworth, Maksim V. Andreev, Nikolai Parakhin, Aleksandr Sklyanov, Kazuhiko Shiokawa, Rudolf Novak, Tat'yana R. Irsmambetova, Hiroshi Itoh, Yoshiharu Ito, Kenji Hirosawa, Denis Denisenko, Christopher S. Kochanek, Benjamin Shappee, Krzysztof Z. Stanek, Jose L. Prieto, Koh-ichi Itagaki, Rod Stubbings, Jose Ripero, Eddy Muyllaert, Gary Poyner

Read the paper on arXiv

 

Outburst activity of symbiotic system AG Dra Wednesday, June 25, 2014 - 11:23

AG Dra is a well known bright symbiotic binary with a white dwarf and a pulsating red giant. The long-term photometry monitoring and a new behaviour of the system are presented. The detailed period analysis of photometry as well as spectroscopy was carried out. In the system of AG Dra, two periods of variability are detected. The longer one around 550 days is related to the orbital motion, and the shorter one around 355 days is interpreted as pulsations of the red giant in our older paper. In addition the active stages change distinctively, but the outbursts are repeated with the periods from 359 to 375 days.

Authors: Ladislav Hric, Rudolf Galis, Laurits Leedjärv, Mari Burmeister, Emil Kundra

Read the pre-print on arXiv

 

Remarkable White Dwarf Star Possibly Coldest, Dimmest Ever Detected Monday, June 23, 2014 - 14:30

A team of astronomers has identified possibly the coldest, faintest white dwarf star ever detected. This ancient stellar remnant is so cool that its carbon has crystallized, forming -- in effect -- an Earth-size diamond in space.

“It’s a really remarkable object,” said David Kaplan, a professor at the University of Wisconsin-Milwaukee. “These things should be out there, but because they are so dim they are very hard to find.” 

Read the full press release from the National Radio Astronomy Observatory.
 

On the Effect of Explosive Thermonuclear Burning on the Accreted Envelopes of White Dwarfs in Cataclysmic Variables Monday, June 23, 2014 - 01:21

The detection of heavy elements at suprasolar abundances in the atmospheres of some accreting white dwarfs in cataclysmic variables, coupled with the high temperatures needed to produce these elements requires explosive thermonuclear burning. The central temperatures of any formerly more massive secondary stars in CVs undergoing hydrostatic CNO burning are far too low to produce these elements. Evidence is presented that at least some cataclysmic variables contain donor secondaries that have been contaminated by repeated novae ejecta and are transferring this material back to the white dwarf. This scenario does not exclude the channel in which formerly more massive donor stars underwent CNO processing in ystems that underwent thermal timescale mass transfer. Implications for the progenitors of CVs are discussed.

Author: Edward M. Sion

Read the paper on astro-ph
 

Ultra-short Period Binaries from the Catalina Surveys Thursday, June 19, 2014 - 08:44

We investigate the properties of 367 ultra-short period binary candidates selected from 31,000 sources recently identified from Catalina Surveys data. Based on light curve morphology, along with WISE, SDSS and GALEX multi-colour photometry, we identify two distinct groups of binaries with periods below the 0.22 day contact binary minimum. In contrast to most recent work, we spectroscopically confirm the existence of M-dwarf+M-dwarf contact binary systems. By measuring the radial velocity variations for five of the shortest-period systems, we find examples of rare cool-white dwarf+M-dwarf binaries. Only a few such systems are currently known. Unlike warmer white dwarf systems, their UV flux and their optical colours and spectra are dominated by the M-dwarf companion. We contrast our discoveries with previous photometrically-selected ultra-short period contact binary candidates, and highlight the ongoing need for confirmation using spectra and associated radial velocity measurements. Overall, our analysis increases the number of ultra-short period contact binary candidates by more than an order of magnitude.

Authors: A.J. Drake, S.G. Djorgovski, D. Garcia-Alvarez, M.J. Graham, M. Catelan, A.A. Mahabal, C. Donalek, J.L. Prieto, G. Torrealba, S. Abraham, R. Williams, S. Larson, E. Christensen

Read the paper on astro-ph
 

The puzzling new class of variable stars in NGC 3766 : old friend pulsators? Thursday, June 19, 2014 - 08:37

The recent variability survey of the NGC 3766 cluster revealed a considerable number of periodic variable stars in a region of the H-R diagram where no pulsation is expected. This region lies between the instability strips of the delta Scuti and SPB stars. Moreover the periods of the new phenomenon, P~0.1-0.7 d, do not allow to associate it a priori to either of these two types of pulsations. Stars in the NGC 3766 cluster are known as fast rotators with rotational velocities typically larger than half of their critical velocity. Rotation can affect both the geometrical properties and period domain of pulsations. It also alters the apparent stellar luminosity through gravity darkening, effect seldom taken considered in theoretical studies of the rotation-pulsation interaction. We explore if both of these effects are able to deliver a consistent interpretation for the observed properties of the "new variables" in NGC 3766: explaining their presence outside the known instability strips and their variability periods. We carry out an instability analysis of SPB models within the framework of the Traditional Approximation of Rotation and study the visibility of modes according to the angle of view and rotation. We also check how gravity darkening affects the effective temperature and luminosity of stellar models for different angles of view and rotation velocities. At the red (cold) border of the instability strip, prograde sectoral modes are preferentially excited and their visibilities are maximum when seen equator-on. Furthermore low-mass SPB models seen equator-on can appear in the gap between non-rotating SPB and delta Scuti stars due to gravity darkening. In that case, periods of these most visible modes are shifted to the 0.2-0.5 d range due to the effects of the Coriolis force. We hence suggest that the new variable stars observed in NGC 3766 are actually fast rotating SPB pulsators.

Authors: S. J. A. J. Salmon, J. Montalbàn, D. R. Reese, M.-A. Dupret, P. Eggenberger

Read the paper on astro-ph
 

The asynchronous polar V1432 Aquilae and its path back to synchronism Tuesday, June 17, 2014 - 14:36

A paper from the Society for Astronomical Sciences 33rd Annual Symposium on Telescope Science held last week in Ontario, California.

V1432 Aquilae is the only known eclipsing asynchronous polar. In this respect it is unique and therefore merits our attention. We report the results of a 15-year campaign by the globally distributed Center for Backyard Astrophysics to observe V1432 Aql and investigate its return to synchronism. Originally knocked out of synchrony by a nova explosion before observing records began, the magnetic white dwarf in V1432 Aql is currently rotating slower than the orbital period but is gradually catching up. The fortuitously high inclination of the binary orbit affords us the bonus of eclipses providing a regular clock against which these temporal changes can be assessed. At the present rate, synchronism should be achieved around 2100. The continually changing trajectory of the accretion stream as it follows the magnetic field lines of the rotating white dwarf produces a complex pattern of light emission which we have measured and documented, providing comprehensive observational evidence against which physical models of the system can be tested.

Authors: David Boyd, Joseph Patterson, William Allen, Greg Bolt, Michel Bonnardeau, Tut, Jeannie Campbell, David Cejudo, Michael Cook, Enrique de Miguel, Claire Ding, Shawn Dvorak, Jerrold Foote, Robert Fried, Franz-Josef Hambsch, Jonathan Kemp,Thomas Krajci, Berto Monard, Yenal Ogmen, Robert Rea, George Roberts, David Skillman, Donn Starkey, Joseph Ulowetz, Helena Uthas, Stan Walker

Read the paper on astro-ph

The Smallest Star Friday, June 13, 2014 - 10:21

Astronomers may have identified what may be the smallest known star. And not just the smallest known star but quite possibly the smallest possible star. If it were any smaller, it might not even be a star anymore.

The star in question is called 2MASS J05233822-1403022, but I’ll call it J0523 for short (the name comes from its discovery in the 2-Micron All Sky Survey (2MASS), together with its coordinates on the sky). As weaklings go, it’s just about the weakest: It shines only 1/8,000th as brightly as the Sun, has a temperature of 1,800° C (compared with the Sun’s 5,600°), and a diameter a mere 0.09 times the Sun’s—smaller than Jupiter!

Read the full article on Bad Astronomy
 

Accretion in Young Stars Friday, June 13, 2014 - 10:17

Previous observations of T Tauri stars have found that the accretion rate declines with age. Accretion rates have been observed as high as 10-4 solar masses per year for young T Tauri stars. Older T Tauri stars have been observed with accretion rates as low as 10-10 solar masses per year. There are a couple reasons why this happens. First, as material from the inner part of the disk accretes onto the star, the accretion disk is depleted in that region. If the disk does not evolve and move in to fill that region with more material, the accretion rate will drop. Alternatively, radiation from the newly-formed star could blow away the inner parts of the accretion disk, reducing the overall accretion rate. Once the accretion rate drops, astronomers refer to the systems as weak T Tauri stars. Classical T Tauri stars are those with higher accretion rates.

A few T Tauri stars have been found with high accretion rates up to 10 Myr, well after the accretion rate typically drops. Since not many of these systems have been observed, it is unclear whether they are anomalous or represent a different evolutionary path. In this paper, the authors look at eight T Tauri stars to measure their ages and mass accretion rates. They find seven systems which have accretion rates higher than would be expected.

Read the rest of this interesting story on Astrobites.
 

Astronomers discover first Thorne-Zytkow object, a bizarre type of hybrid star Friday, June 6, 2014 - 08:16

In a discovery decades in the making, scientists have detected the first of a “theoretical” class of stars first proposed in 1975 by physicist Kip Thorne and astronomer Anna Żytkow. Thorne-Żytkow objects (TŻOs) are hybrids of red supergiant and neutron stars that superficially resemble normal red supergiants, such as Betelgeuse in the constellation Orion. They differ, however, in their distinct chemical signatures that result from unique activity in their stellar interiors.

TŻOs are thought to be formed by the interaction of two massive stars―a red supergiant and a neutron star formed during a supernova explosion―in a close binary system. While the exact mechanism is uncertain, the most commonly held theory suggests that, during the evolutionary interaction of the two stars, the much more massive red supergiant essentially swallows the neutron star, which spirals into the core of the red supergiant.

Read the joint press release from CU-Boulder and Lowell Observatory

 

V473 Lyrae, a unique second-overtone Cepheid with two modulation cycles Wednesday, June 4, 2014 - 10:05

V473 Lyrae is the only Galactic Cepheid with confirmed periodic amplitude and phase variations similar to the Blazhko effect observed in RR Lyrae stars. We collected all available photometric data and some radial velocity measurements to investigate the nature of the modulation. The comparison of the photometric and radial velocity amplitudes confirmed that the star pulsates in the second overtone. The extensive data set, spanning more than 40 years, allowed us to detect a secondary modulation cycle with a period of approximately 5300 days or 14.5 years. The secondary variations can be detected in the period of the primary modulation, as well. 
Phenomenologically, the light variations are analogous to the Blazhko effect. To find a physical link, we calculated linear hydrodynamic models to search for potential mode resonances that could drive the modulation and found two viable half-integer (n:2) and three n:4 resonances between the second overtone and other modes. If any of these resonances will be confirmed by non-linear models, it may confirm the mode resonance model, a common mechanism that can drive modulations both in RR Lyrae and Cepheid stars.

Authors: László MolnárLászló Szabados

Read the paper on astro-ph
 

Astronomers View Pulsar Encased in Supernova Bubble Tuesday, June 3, 2014 - 10:14

Massive stars end their lives with a bang: exploding as spectacular supernovas, they release huge amounts of mass and energy into space. These explosions sweep up any surrounding material, creating bubble remnants that expand into interstellar space. At the heart of bubbles like these are small, dense neutron stars or black holes, the remains of what once shone brightly as a star.

Since supernova-carved bubbles shine for only a few tens of thousands of years before dissolving, it is rare to come across neutron stars or black holes that are still enclosed within their expanding shell. This image captures such an unusual scene, featuring both a strongly magnetized, rotating neutron star – known as a pulsar – and its cosmic cloak, the remains of the explosion that generated it.

Read the full story at SciTechDaily.com
 

How Many Stars Are In The Universe? Tuesday, June 3, 2014 - 10:09

Looking up into the night sky, it's challenging enough for an amateur astronomer to count the number of naked-eye stars that are visible. With bigger telescopes, more stars become visible, making counting impossible because of the amount of time it would take. So how do astronomers figure out how many stars are in the universe?

The first sticky part is trying to define what "universe" means. Even if we narrow down the definition to the "observable" universe — what we can see — estimating the number of stars within it requires knowing just how big the universe is. The first complication is that the universe itself is expanding, and the second complication is that space-time is curved.

Read the rest of the story at Space.com
 

Does the Period of a Pulsating Star Depend on its Amplitude? Friday, May 30, 2014 - 10:00

Several classes of pulsating stars are now known to undergo slow changes in amplitude; these include pulsating red giants and supergiants, and yellow supergiants. We have used visual observations from the AAVSO International Database, and wavelet analysis of 39 red giants, 7 red supergiants, and 3 yellow supergiants, to test the hypothesis that an increase in amplitude would result in an increase in period, because of non-linear effects in the pulsation. For most of the stars, the results are complex and/or indeterminate, due to the limitations of the data, the small amplitude or amplitude variation, or other processes such as random cycle-to-cycle period fluctuations. For the dozen stars which have substantial amplitude variation, and reasonably simple behavior, there is a 75-80% tendency to show a positive correlation between amplitude and period.

Authors: John R. Percy, Jeong Yeon (JY) Yook

Read the paper on astro-ph
 

AAVSO Acronym of the Day: VPhot Friday, May 30, 2014 - 09:45

Today's acronym of the day is VPhot – Variable Star Photometry Software

                      

VPhot is an online tool for photometric analysis. You can upload your own FITS images to VPhot or have images taken via AAVSOnet automatically sent to your VPhot account. All VPhot processing is done via a web browser. All of the basic photometry tools exist (stacking, time series analysis, control of annulus', transformation, etc.) and the algorithms have been rigorously checked and confirmed to be of the highest quality. Results of the processing are automatically exported in AAVSO Extended Format, meaning you can directly load them into our database via WebObs without having to make any changes to the data file. VPhot is only available to AAVSO members.

This is just one example of the tools and programs the AAVSO provides to its members, observers and the astronomical community. Please help support these services by contributing to this year's Annual Campaign.

You can mail a check to AAVSO headquarters, or you can make a donation online. Just click the Donate Now button on our home page and select Annual Campaign in the drop down menu.
 

A new method for cosmic distances: using active galactic nuclei Thursday, May 29, 2014 - 13:07

Adam Riess, co-discoverer of the accelerating expansion of the Universe due to dark energy, visited Harvard last year, where he told me a story about his time in grad school there.  He recalled hearing a lecture on the uncertainty in the rate at which the Universe is expanding and thinking, “That problem will never be solved.”  Twenty years on, we know the local expansion rate (called the Hubble constant, or H0) to about 4% precision, and many different, independent techniques find mutually consistent values. However, measuring the Hubble constant remains one of the most important problems in cosmology because it is intimately connected to the Universe’s contents.  In particular, General Relativity means that the Universe’s contents set its expansion rate, and so precise measurement of the expansion rate can probe the amount and evolution of different components of the Universe.

Thus, it is exciting when a new, independent method of measuring the expansion rate (H0) is proposed—and even more exciting when it works. In the short paper I discuss today, the authors show that time delays in the light emitted from distant, violently variable galactic centers (“active galactic nuclei”, or AGN) can probe H0 with precision similar to that of the Hubble Space Telescope—and out to about twice the distance.

Read the rest on Astrobites
 

AAVSO Acronym of the Day: LCG Thursday, May 29, 2014 - 10:18

The AAVSO Acronym of the Day today is LCG – The AAVSO Light Curve Generator

Observations of variable stars are plotted on a graph called a light curve as the apparent brightness (magnitude) versus time, usually in Julian Date (JD). The light curve is the single most important graph in variable star astronomy. Light curves allow astronomers to unlock some of the secrets of variable stars. The AAVSO Light Curve Generator allows anyone to plot light curves using data on thousands of stars stored in the AAVSO International Database. It is one of the most popular tools on the AAVSO website. 

This is another example of the tools the AAVSO provides to its members, observers and the astronomical community. Please help support these services by contributing to this year's Annual Campaign.

You can mail a check to AAVSO headquarters, or you can make a donation online. Just click the Donate Now button on our home page and select Annual Campaign in the drop down menu.

 

The M4.5V flare star AF Psc as seen in K2 engineering data Thursday, May 29, 2014 - 10:09

We present the light curve of the little studied flare star AF Psc (M4.5V) obtained using engineering data from the K2 mission. Data were obtained in Long Cadence mode giving an effective exposure of 29 min and nearly 9 d of coverage. A clear modulation on a period of 1.08 d was seen which is the signature of the stellar rotation period. We identify 14 flares in the light curve, with the most luminous flares apparently coming from the same active region. We compare the flare characteristics of AF Psc to two M4V flare stars studied using kepler data. The K2 mission, if given approval, will present a unique opportunity to study the rotation and flare properties of late type dwarf stars with different ages and mass.

Authors: Gavin Ramsay, J. Gerry Doyle (Armagh Observatory) 

Read the paper on astro-ph
 

Revised age for CM Draconis and WD 1633+572: Toward a resolution of model-observation radius discrepancies Thursday, May 29, 2014 - 09:55

We report an age revision for the low-mass detached eclipsing binary CM Draconis and its common proper motion companion, WD 1633+572. An age of 10±2 Gyr is found by combining an age estimate for the lifetime of WD 1633+572 and an estimate from galactic space motions. The revised age is greater than a factor of two older than previous estimates. Our results provide consistency between the white dwarf age and the system's galactic kinematics, which reveal the system is a highly probable member of the galactic thick disk. We find the probability that CM Draconis and WD 1633+572 are members of the thick disk is 8500 times greater than the probability that they are members of the thin disk and 170 times greater than the probability they are halo interlopers. If CM Draconis is a member of the thick disk, it is likely enriched in α-elements compared to iron by at least 0.2 dex relative to the Sun. This leads to the possibility that previous studies under-estimate the [Fe/H] value, suggesting the system has a near-solar [Fe/H]. Implications for the long-standing discrepancies between the radii of CM Draconis and predictions from stellar evolution theory are discussed. We conclude that CM Draconis is only inflated by about 2% compared to stellar evolution predictions.

Authors: Gregory A. Feiden and Brian Chaboyer

Read the paper on astro-ph
 

AAVSO Acronym of the Day: SeqPlot Wednesday, May 28, 2014 - 08:08

Today's acronym of the day features one of the AAVSO's tools, SeqPlot – The AAVSO Sequence Plotter.

SeqPlot is a platform independent Java Web Start application. It accesses an on-line MySQL database that contains more than 47 million stars that have been calibrated through the AAVSO Photometric All-Sky Survey (APASS), USNO-Flagstaff, Sonoita, and other AAVSOnet telescopes. The General Catalogue of Photometric Data (GCPD) and Tycho-2 catalogs are also included. You can plot fields using either a field name or by coordinates and field size. Users can select stars for a sequence and write them to a text file in the correct format for uploading to VSD.

This is just one example of the tools the AAVSO provides to its members, observers and the astronomical community. Please help support these services by contributing to this year's Annual Campaign.

You can mail a check to AAVSO headquarters, or you can make a donation online. Just click the Donate Now button on our home page and select Annual Campaign in the drop down menu.
 

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