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Stellar News Feed Archive

Ancient story tells of star's variable nature Monday, April 21, 2014 - 14:16

Aboriginal people of central Australia appear to have known about the variable star Betelgeuse, long before modern European astronomers, according to a new study.

The discovery reported in the Journal of Astronomical History and Heritage, was uncovered while examining the records of famous amateur anthropologist Daisy Bates.

Early last century, Bates spent 16 years living among the people of South Australia's Great Victoria Desert, recording their language, customs, and oral traditions, according to one of the study's authors, Dr Duane Hamacher of the University of New South Wales.

Hamacher and co-author Trevor Leaman collected Bates' published accounts and journal entries as part of an ongoing project to develop a complete picture of Aboriginal sky knowledge and star lore.

Read thew full story at ABC Science


The Light Curve Shapes as a Key to Resolving the Origin of Long Secondary Periods in Red Giant Stars Friday, April 18, 2014 - 13:17

We present a study of OGLE light curves of red giant stars exhibiting long secondary periods (LSPs) - an enigmatic phenomenon commonly observed in stars on the upper red giant branch and asymptotic giant branch. We show that the light curves of LSP stars are essentially identical to those of the spotted variables with one dark spot on their photospheres. Such a behavior can be explained by a presence of a dusty cloud orbiting the red giant together with a low-mass companion in a close, circular orbit. We argue that the binary scenario is in agreement with most of the observational properties of LSP variables, including non-sinusoidal shapes of their radial velocity curves.

Authors:  I. Soszynski, A. Udalski

Read the paper on arXiv

Cataclysmic Variables from the Catalina Real-time Transient Survey Wednesday, April 16, 2014 - 13:47

We present 855 cataclysmic variable candidates detected by the Catalina Real-time Transient Survey (CRTS) of which at least 137 have been spectroscopically confirmed and 705 are new discoveries. The sources were identified from the analysis of five years of data, and come from an area covering three quarters of the sky. We study the amplitude distribution of the dwarf novae CVs discovered by CRTS during outburst, and find that in quiescence they are typically two magnitudes fainter compared to the spectroscopic CV sample identified by SDSS. However, almost all CRTS CVs in the SDSS footprint have ugriz photometry. We analyse the spatial distribution of the CVs and find evidence that many of the systems lie at scale heights beyond those expected for a Galactic thin disc population. We compare the outburst rates of newly discovered CRTS CVs with the previously known CV population, and find no evidence for a difference between them. However, we find that significant evidence for a systematic difference in orbital period distribution. We discuss the CVs found below the orbital period minimum and argue that many more are yet to be identified among the full CRTS CV sample. We cross-match the CVs with archival X-ray catalogs and find that most of the systems are dwarf novae rather than magnetic CVs.

Authors:  A.J. Drake, B.T. Gaensicke, S.G. Djorgovski, P. Wils, A.A. Mahabal, M.J. Graham, T-C. Yang, R. Williams, M. Catelan, J.L. Prieto,C. Donalek, S. Larson, E. Christensen

Read the paper on astro-ph

Long-term photometry of the eclipsing dwarf nova V893 Scorpii: Orbital period, oscillations, and a possible giant planet Tuesday, April 15, 2014 - 14:38

The cataclysmic variable V893 Sco is an eclipsing dwarf nova which, apart from outbursts with comparatively low amplitudes, exhibits a particularly strong variability during quiescence on timescales of days to seconds.The present study aims to update the outdated orbital ephemerides published previously, to investigate deviations from linear ephemerides, and to characterize non-random brightness variations in a range of timescales. Light curves of V893 Sco were observed on 39 nights, spanning a total time base of about 14 years. They contain 114 eclipses which were used to significantly improve the precision of the orbital period and to study long-term variations of the time of revolution. Oscillations and similar brightness variations were studied with Fourier techniques in the individual light curves. The orbital period exhibits long-term variations with a cycle time of 10.2 years. They can be interpreted as a light travel time effect caused by the presence of a giant planet with approximately 9.5 Jupiter masses in a 4.5 AU orbit around V893 Sco. On some nights transient semi-periodic variations on timescales of several minutes can be seen which may be identified as quasi-periodic oscillations. However, it is difficult to distinguish whether they are caused by real physical mechanisms or if they are the effect of an accidental superposition of unrelated flickering flares. Simulations to investigate this question are presented.

Author: Albert Bruch

Read the paper on astro-ph

Chandra Resolves the T Tauri Binary System RW Aur Tuesday, April 15, 2014 - 14:32

RW Aur is a multiple T Tauri system consisting of an early-K type primary (A) and a K5 companion (B) at a separation of 1.4 arcsec. RW Aur A drives a bipolar optical jet that is well-characterized optically. We present results of a sensitive Chandra observation whose primary objective was to search for evidence of soft extended X-ray emission along the jet, as has been seen for a few other nearby T Tauri stars. The binary is clearly resolved by Chandra and both stars are detected as X-ray sources. The X-ray spectra of both stars reveal evidence for cool and hot plasma. Suprisingly, the X-ray luminosity of the less-massive secondary is at least twice that of the primary and is variable. The disparity is attributed to the primary whose X-ray luminosity is at the low end of the range for classical T Tauri stars of similar mass based on established correlations. Deconvolved soft-band images show evidence for slight outward elongation of the source structure of RW Aur A along the blueshifted jet axis inside the central arcsecond. In addition, a faint X-ray emission peak is present on the redshifted axis at an offset of 1.2 +- 0.2 arcsec from the star. Deprojected jet speeds determined from previous optical studies are too low to explain this faint emission peak as shock-heated jet plasma. Thus, unless flow speeds in the redshifted jet have been underestimated, other mechanisms such as magnetic jet heating may be involved.

 Authors: Stephen L. Skinner, Manuel Guedel

Read the pre-print on astro-ph

GG Tau: the fifth element Thursday, April 10, 2014 - 08:48

We aim at unveiling the observational imprint of physical mechanisms that govern planetary formation in young, multiple systems. In particular, we investigate the impact of tidal truncation on the inner circumstellar disks. We observed the emblematic system GG Tau at high-angular resolution: a hierarchical quadruple system composed of low-mass T Tauri binary stars surrounded by a well-studied, massive circumbinary disk in Keplerian rotation. We used the near-IR 4-telescope combiner PIONIER on the VLTI and sparse-aperture-masking techniques on VLT/NaCo to probe this proto-planetary system at sub-AU scales. We report the discovery of a significant closure-phase signal in H and Ks bands that can be reproduced with an additional low-mass companion orbiting GG Tau Ab, at a (projected) separation rho = 31.7 +/- 0.2mas (4.4 au) and PA = 219.6 +/- 0.3deg. This finding offers a simple explanation for several key questions in this system, including the missing-stellar-mass problem and the asymmetry of continuum emission from the inner dust disks observed at millimeter wavelengths. Composed of now five co-eval stars with 0.02 <= Mstar <= 0.7 Msun, the quintuple system GG Tau has become an ideal test case to constrain stellar evolution models at young ages (few 10^6yr).

Authors:  E. Di Folco, A. Dutrey, J.-B. Le Bouquin, S. Lacour, J.-P. Berger, R. Köhler, S. Guilloteau, V. Piétu, J. Bary, T. Beck, H. Beust, E. Pantin

Read the pre-print on arXiv

The oEA stars QY Aql, BW Del, TZ Dra, BO Her and RR Lep: Photometric analysis, frequency search and evolutionary status Thursday, April 10, 2014 - 07:38

New and complete multi-band light curves of the oEA stars QY Aql, BW Del, TZ Dra, BO Her and RR Lep were obtained and analysed with the Wilson-Devinney code. The light curves residuals were further analysed with the Fourier method in order to derive the pulsation characteristics of the oscillating components. All the reliable observed times of minimum light were used to examine orbital period irregularities. The orbital period analyses revealed secular changes for QY Aql and BW Del, while the Light-Time Effect seems to be the best explanation for the cyclic period changes in TZ Dra and BO Her. RR Lep has a rather steady orbital period. Light curve solutions provided the means to calculate the absolute parameters of the components of the systems, which subsequently were used to make an estimate of their present evolutionary status.

Authors: Alexios Liakos and Panagiotis Niarchos

Read the pre-print on arXiv

Light Echoes of Historic Transients Thursday, April 3, 2014 - 13:50

AAVSO councilor, Doug Welch, co-authors an interesting paper on light echoes of historic transients.

Light echoes, light from a variable source scattered off dust, have been observed for over a century. The recent discovery of light echoes around centuries-old supernovae in the Milky Way and the Large Magellanic Cloud have allowed the spectroscopic characterization of these events, even without contemporaneous photometry and spectroscopy using modern instrumentation. Here we review the recent scientific advances using light echoes of ancient and historic transients, and focus on our latest work on SN 1987A's and Eta Carinae's light echoes.

Authors: A. Rest, B. Sinnott, D. L. Welch, J. L. Prieto, F. Bianco

Read the pre-print from astro-ph

Also see the article in Astrobites discussing the paper

NOAO/Gemini: Sakurai's Object - Stellar Evolution in Real Time Thursday, April 3, 2014 - 06:39

Stellar lifetimes are measured in billions of years, so changes in their appearance rarely take place on a human timescale. Thus an opportunity to observe a star passing from one stage of life to another on a timescale of months to years is very exciting, as there are only a very few examples known. One such star is Sakurai’s Object (V4334 Sgr). First reported by a Japanese amateur astronomer in 1996 as a “nova-like object,” Sakurai’s Object had been only a few years before the faint central star of a planetary nebula. In the 1990’s Sakurai’s Object brightened by a factor of 10000. This brightening has been attributed to a final helium shell flash. In this process the burned out core of the star at the center of the planetary nebula re-ignites.

The final helium shell flash is violent, ejecting a cloud of dust and gas that forms a thick cocoon around the star blocking all visible light. By 2000 the dust cloud was so thick that Sakurai’s Object was not visible even with the Hubble Space Telescope (HST). Scientists at the National Optical Astronomy Observatory (NOAO) have been observing the sky in the area of Sakurai’s Object waiting for infrared radiation to break through the dust cloud. Infrared radiation penetrates dust much more efficiently than optical light. A detection of the infrared light would mean that the dust cloud is breaking apart, ultimately permitting light from the star to escape.

Read the full story at either Gemini or NOAO

A Mystery Star Wrapped in a Stingray Tuesday, April 1, 2014 - 12:19

SAO 244567 is nestled in the heart of the Stingray Nebula, a tiny planetary nebula. Planetary nebulae are formed when an intermediate mass (roughly 0.6–10 solar masses) star enters the last stages of stellar evolution.

Observations of the Stingray Nebula in 1989 led astronomers to conclude that SAO 244567 was a post-AGB star, since it had already produced a planetary nebula.

But spectra taken in 1971 and analyzed in 1995 indicated the star was still evolving at the time, meaning it would have made the transition from giant to post-AGB in twenty years, which is far too fast for any known evolutionary models.  Further, the 1971 observations yielded an effective temperature of 21,000 K for the star, but in 2002 different observations found the star to be at 60,000 K. Spectral observations in between those times support the star growing steadily hotter, though it appears lately (since 2006) to be cooling again slightly. That is a massive change in temperature in roughly thirty years.

Read the rest of the story on Astrobites

Novalike Cataclysmic Variables in the Infrared Tuesday, April 1, 2014 - 12:07

Novalike cataclysmic variables have persistently high mass transfer rates and prominent steady state accretion disks. We present an analysis of infrared observations of twelve novalikes obtained from the Two Micron All Sky Survey, the Spitzer Space Telescope, and the Wide-field Infrared Survey Explorer All Sky Survey. The presence of an infrared excess at >3-5 microns over the expectation of a theoretical steady state accretion disk is ubiquitous in our sample. The strength of the infrared excess is not correlated with orbital period, but shows a statistically significant correlation (but shallow trend) with system inclination that might be partially (but not completely) linked to the increasing view of the cooler outer accretion disk and disk rim at higher inclinations. We discuss the possible origin of the infrared excess in terms of emission from bremsstrahlung or circumbinary dust, with either mechanism facilitated by the mass outflows (e.g., disk wind/corona, accretion stream overflow, and so on) present in novalikes. Our comparison of the relative advantages and disadvantages of either mechanism for explaining the observations suggests that the situation is rather ambiguous, largely circumstantial, and in need of stricter observational constraints.

Authors:  D. W. Hoard, Knox S. Long, Steve B. Howell, Stefanie Wachter, Carolyn S. Brinkworth, Christian Knigge, J. E. Drew, Paula Szkody, S. Kafka, Kunegunda Belle, David R. Ciardi, Cynthia S. Froning, Gerard T. van Belle, M. L. Pretorius

Read the pre-print on astro-ph

New SDO Image of X-Class Solar Flare Tuesday, April 1, 2014 - 11:57

From SciTech Daily

This new image of an X-class solar flare was captured by NASA’s Solar Dynamics Observatory on March 29, 2014.

The sun emitted a significant solar flare, peaking at 1:48 p.m. EDT March 29, 2014, and NASA’s Solar Dynamics Observatory captured images of the event. Solar flares are powerful bursts of radiation. Harmful radiation from a flare cannot pass through Earth’s atmosphere to physically affect humans on the ground, however — when intense enough — they can disturb the atmosphere in the layer where GPS and communications signals travel.

To see how this event impacted Earth, please visit NOAA’s Space Weather Prediction Center at, the U.S. government’s official source for space weather forecasts, alerts, watches and warnings.

This flare is classified as an X.1-class flare. X-class denotes the most intense flares, while the number provides more information about its strength. An X2 is twice as intense as an X1, an X3 is three times as intense, etc.

Source: Karen C. Fox, NASA’s Goddard Space Flight Center


Theory suggests source of white dwarf pollution … and ominous fate for Earth Thursday, March 27, 2014 - 08:38

Hot, young, white dwarfs – the super-dense remains of sunlike stars – have atmospheres made essentially of pure hydrogen or pure helium. But these stars’ atmospheres are contaminated by other elements, too – for example, carbon, silicon and iron – known to astronomers as metals. A decades-old space mystery is how the metals came to be in white dwarf atmospheres. And now an international team of astronomers led by Professor Martin Barstow of the University of Leicester in the U.K. say they have solved the mystery. Their solution points to an ominous fate for planet Earth. Professor Barstow said in a press release:

The mystery of the composition of these stars is a problem we have been trying to solve for more than 20 years. It is exciting to realize that they are swallowing up the leftovers from planetary systems, perhaps like our own.

Read the full story on

OGLE-BLG-RRLYR-12245: An RR Lyrae Star that Switched from a Double to Single-mode Pulsation Thursday, March 27, 2014 - 07:40

We report the discovery of an RR Lyrae star that experienced a switching of its pulsation mode. OGLE-BLG-RRLYR-12245 was discovered as a double-mode RRd star from the observations conducted in years 2001-2006 during the third phase of the Optical Gravitational Lensing Experiment (OGLE-III). The OGLE-IV observations carried out since 2010 reveal that this object is now a fundamental-mode RRab star, with no sign of the first-overtone pulsation. The analysis of the OGLE photometry shows that the final stage of the mode switching occurred on a relatively short timescale of a few months in 2005. We study the behavior of the star during this process, showing changes of the pulsational amplitudes and periods. We also discuss possible causes for the mode switching in RR Lyr stars.

Authors:  I. Soszynski, W. A. Dziembowski, A. Udalski, M. K. Szymanski, M. Kubiak, G. Pietrzynski, L. Wyrzykowski, K. Ulaczyk, R. Poleski, S. Kozlowski, P. Pietrukowicz, J. Skowron, P. Mroz

Read the paper on arXiv


Type Ia supernovae are among the best tools to measure cosmological distances. Thanks to their consistent peak brightness, these ”standard candles” are used to map the expansion history of the Universe. In 1998 distance measurements using supernovae lead to the a paradigm shift in cosmology and fundamental physics: the expansion of the Universe is speeding up, contrary to the expectations from the attractive nature of gravitational forces: a mysterious new cosmic component, ”dark energy”, has been invoked to explain this unexpected phenomenon. This discovery was awarded the 2011 Nobel Prize in physics.

“Since Type Ia supernovae are very rare, occurring only once every several hundred years in a galaxy like ours, there have been very few opportunities to study these explosions in great detail. SN2014J in the nearby galaxy M82 is a very welcome exception”, says Rahman Amanullah a researcher at OKC.

Read the full press release at The Oscar Klein Centre blog

Download the paper (paywall) from IOP Science

HD 54272, a classical lambda Bootis star and gamma Doradus pulsator Thursday, March 20, 2014 - 14:40

Another remarkable star, formerly misclassified as a lambda Bootis and RR Lyrae star,  featured in a pre-print on arXiv

We detect the second known lambda Bootis star (HD 54272) which exhibits gamma Doradus-type pulsations. The star was formerly misidentified as a RR Lyrae variable. The lambda Bootis stars are a small group (only 2 per cent) of late B to early F-type, Population I stars which show moderate to extreme (up to a factor 100) surface underabundances of most Fe-peak elements and solar abundances of lighter elements (C, N, O, and S). The photometric data from the Wide Angle Search for Planets (WASP) and All Sky Automated Survey (ASAS) projects were analysed. They have an overlapping time base of 1566 d and 2545 d, respectively. Six statistically significant peaks were identified (f1 = 1.410 116 c/d, f2 = 1.283 986 c/d, f3 = 1.293 210 c/d, f4 = 1.536 662 c/d, f5 = 1.157 22 c/d and f6 = 0.226 57 c/d). The spacing between f1 and f2, f1 and f4, f5 and f2 is almost identical. Since the daily aliasing is very strong, the interpretation of frequency spectra is somewhat ambiguous. From spectroscopic data, we deduce a high rotational velocity (250+-25 km/s) and a metal deficiency of about -0.8 to -1.1 dex compared to the Sun. A comparison with the similar star, HR 8799, results in analogous pulsational characteristics but widely different astrophysical parameters. Since both are lambda Bootis-type stars, the main mechanism of this phenomenon, selective accretion, may severely influence gamma Doradus-type pulsations.

Authors: E. Paunzen, M. Skarka, D.L. Holdsworth, B. Smalley, R. G. West

Read the abstract and paper on arXiv

An exotic eclipsing binary system composed of two classical overtone Cepheids in a 413-day orbit. Tuesday, March 18, 2014 - 12:10

We have obtained extensive high-quality spectroscopic observations of the OGLE-LMC-CEP-1718 eclipsing binary system in the Large Magellanic Cloud which Soszynski et al. (2008) had identified as a candidate system for containing two classical Cepheids in orbit. Our spectroscopic data clearly demonstrate binary motion of the Cepheids in a 413-day eccentric orbit, rendering this eclipsing binary system the first ever known to consist of two classical Cepheid variables. After disentangling the four different radial velocity variations in the system we present the orbital solution and the individual pulsational radial velocity curves of the Cepheids. We show that both Cepheids are extremely likely to be first overtone pulsators and determine their respective dynamical masses, which turn out to be equal to within 1.5 %. Since the secondary eclipse is not observed in the orbital light curve we cannot derive the individual radii of the Cepheids, but the sum of their radii derived from the photometry is consistent with overtone pulsation for both variables.

The existence of two equal-mass Cepheids in a binary system having different pulsation periods (1.96 and 2.48 days, respectively) may pose an interesting challenge to stellar evolution and pulsation theories, and a more detailed study of this system using additional datasets should yield deeper insight about the physics of stellar evolution of Cepheid variables. Future analysis of the system using additional near-infrared photometry might also lead to a better understanding of the systematic uncertainties in current Baade-Wesselink techniques of distance determinations to Cepheid variables.

Authors: W. Gieren, B. Pilecki, G. Pietrzynski, D. Graczyk, I.B. Thompson, I. Soszynski, P. Konorski, R. Smolec, A. Udalski, N. Nardetto, G. Bono, P.G. Prada Moroni, J. Storm, A. Gallenne

Read the pre-print paper

Discovery of an SU UMa-type eclipsing cataclysmic variable star inside the CV "period gap'' Monday, March 17, 2014 - 08:48

IBVS 6097 on a recently discovered eclipsing cataclysmic variable

We report the discovery of CzeV404 - eclipsing SU UMa-type cataclysmic variable star with an orbital period inside the period gap. Using photometric observations taken during 15 nights from June to September 2012 and 8 nights from July to August 2013 we determined an orbital period of 2.35 hours and superhump period of 2.50 hours. From the observed period excess, theestimated mass ratio of the system is q = 0.30.

Authors:  Cagas, Pavel; Cagas, Petr

Read IBVS 6097

Stellar luminosity: The true brightness of stars Thursday, March 13, 2014 - 05:24

Nearly every star that you see with the unaided eye is larger and more luminous than our sun. Astronomers speak of a star’s true brightness as its “luminosity.”

Some stars look bright because they’re near Earth. Others are truly extremely bright members of our Milky Way galaxy. Astronomers call the true, intrinsic brightness of a star its luminosity. The luminosity of any star depends on size and surface temperature. Some extremely large and hot stars blaze away with the luminosity of a million suns!

Read the full explanation at


VLT Spots Largest Yellow Hypergiant Star Wednesday, March 12, 2014 - 06:38

ESO’s Very Large Telescope Interferometer has revealed the largest yellow star — and one of the ten largest stars found so far. This hypergiant has been found to measure more than 1300 times the diameter of the Sun, and to be part of a double star system, with the second component so close that it is in contact with the main star. Observations spanning over sixty years, some from amateur observers, also indicate that this rare and remarkable object is changing very rapidly and has been caught during a very brief phase of its life.

Read the full press release from ESO

Towards a Determination of Definitive Parameters for the Long Period Cepheid S Vulpeculae Tuesday, March 11, 2014 - 14:05

AAVSO Councilor, David G. Turner, utilizes APASS data to expand on an oral paper given at the spring meeting of the AAVSO held in Boone, North Carolina, May 17–18, 2013.

A new compilation of UBV data for stars near the Cepheid S Vul incorporates BV observations from APASS and NOMAD to augment UBV observations published previously. A reddening analysis yields mean colour excesses and distance moduli for two main groups of stars in the field: the sparse cluster Turner 1 and an anonymous background group of BA stars. The former appears to be 1.07+-0.12 kpc distant and reddened by E(B-V)=0.45+-0.05, with an age of 10^9 yrs. The previously overlooked latter group is 3.48+-0.19 kpc distant and reddened by E(B-V)=0.78+-0.02, with an age of 1.3x10^7 yrs. Parameters inferred for S Vul under the assumption that it belongs to the distant group, as also argued by 2MASS data, are all consistent with similar results for other cluster Cepheids and Cepheid-like supergiants.

Read the paper on arXiv

The 2011 Outburst of Recurrent Nova T Pyx: Radio Observations Reveal the Ejecta Mass and Hint at Complex Mass Loss Friday, March 7, 2014 - 09:34

An updated version of this paper appeared on arXiv March 5, 2014.

Despite being the prototype of its class, T Pyx is arguably the most unusual and poorly understood recurrent nova. Here, we use radio observations from the Karl G. Jansky Very Large Array to trace the evolution of the ejecta over the course of the 2011 outburst of T Pyx. The radio emission is broadly consistent with thermal emission from the nova ejecta. However, the radio flux began rising surprisingly late in the outburst, indicating that the bulk of the radio-emitting material was either very cold, or expanding very slowly, for the first ~50 days of the outburst. Considering a plausible range of volume filling factors and geometries for the ejecta, we find that the high peak flux densities of the radio emission require a massive ejection of 1-30 x 10^{-5} solar masses. This ejecta mass is much higher than the values normally associated with recurrent novae, and is more consistent with a nova on a white dwarf well below the Chandrasekhar limit.

Authors: Thomas Nelson, Laura Chomiuk, Nirupam Roy, J. L. Sokoloski, Koji Mukai, Miriam I. Krauss, Amy J. Mioduszewski, Michael P. Rupen, Jennifer Weston

Read the pre-print on astro-ph

OQ Carinae: A New Southern Z Cam Type Dwarf Nova Tuesday, March 4, 2014 - 21:49

Rod Stubbings has discovered a new southern Z Cam hiding in the weeds, disguised as an ordinary dwarf nova no one has paid attention to in years.

Congratulations to Rod. His story is a testament to the value of patience, persistence and visual observations.

Abstract: Long term optical monitoring of the dwarf nova OQ Car has been conducted to study the previously unknown behaviour of this star system. The observations have shown OQ Car to have frequent dwarf nova outbursts and revealed the first recorded standstill of this star system. Based on this, we conclude that OQ Car is a new member of the Z Cam type dwarf novae.

Authors: Rod Stubbings and Mike Simonsen

Read the pre-print paper on arXiv

GALEX J194419.33+491257.0: An Unusually Active SU UMa-Type Dwarf Nova with a Very Short Orbital Period in the Kepler Data Tuesday, March 4, 2014 - 08:57

We studied the background dwarf nova of KIC 11412044 in the Kepler public data and identified it with GALEX J194419.33+491257.0. This object turned out to be a very active SU UMa-type dwarf nova having a mean supercycle of about 150 d and frequent normal outbursts having intervals of 4-10 d. The object showed strong persistent signal of the orbital variation with a period of 0.0528164(4) d (76.06 min) and superhumps with a typical period of 0.0548 d during superoutbursts. Most of the superoutbursts were accompanied by a precursor outburst. All these features are unusual for this very short orbital period. We succeeded in detecting the evolving stage of superhumps (stage A superhumps) and obtained a mass ratio of 0.141(2), which is unusually high for this orbital period. We suggest that the unusual outburst properties are a result of this high mass ratio. We suspect that this object is a member of the recently recognized class of cataclysmic variables (CVs) with a stripped core evolved secondary which are evolving toward AM CVn-type CVs. The present determination of the mass ratio using stage A superhumps makes the first case in such systems.

Authors:  Taichi Kato (Kyoto U.), Yoji Osaki (U. of Tokyo)

Dowload the pre-print from arXiv

Standard-Candle Supernovae are Still Standard, but Why? Monday, March 3, 2014 - 15:40

The Nearby Supernova Factory based at Berkeley Lab shows that Type Ia supernovae have a surprisingly large range of masses

Until recently, scientists thought they knew why Type Ia supernovae are all so much alike. But their favorite scenario was wrong.

The assumption was that carbon-oxygen white dwarf stars, the progenitors of the supernovae, capture additional mass by stripping it from a companion star or by merging with another white dwarf; when they approach the Chandrasekhar limit (40 percent more massive than our sun) they experience thermonuclear runaway. Type Ia brightnesses were so similar, scientists thought, because the amounts of fuel and the explosion mechanisms were always the same.

Greg Aldering summarizes the most basic result of the new analysis: “The white dwarfs exploding as Type Ia supernovae have a range of masses, and the resulting light-curve width is directly proportional to the total mass involved in the explosion.”

Read the full press release at Berkley Lab

Read the pre-print paper on astro-ph 

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