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Stellar News Feed Archive

Fundamental parameters of RR Lyrae stars from multicolour photometry and Kurucz atmospheric models -- III. SW And, DH Peg, CU Com, DY Peg Monday, May 19, 2014 - 14:44

We report the most comprehensive UBV(RI)_C observations of the bright, radially pulsating field stars SW And, DH Peg, CU Com, DY Peg. Long term variation has been found in the ultraviolet colour curves of SW And and DH Peg. We apply our photometric-hydrodynamic method to determine the fundamental parameters of these stars: metallicity, reddening, distance, mass, radius, equilibrium luminosity and effective temperature. Our method works well for SW And, CU Com and DY Peg. A very small mass 0.26+/-0.04 M_Sun of SW And has been found. The fundamental parameters of CU Com are those of a normal double-mode RR Lyrae (RRd) star. DY Peg has been found to have paradoxical astrophysical parameters: the metallicity, mass and period are characteristic for a high-amplitude Delta Sct star while the luminosity and radius place it in the group of RR Lyrae stars. DH Peg has been found to be peculiar: the definite instability in the colour curves towards ultraviolet, the dynamical variability of the atmosphere during the shocked phases suggests that the main assumptions of our photometric-hydrodynamic method, the quasi-static atmosphere approximation (QSAA) and the exclusive excitation of radial modes are probably not satisfied in this star. The fundamental parameters of all stars studied in this series of papers are summarized in tabular and graphical form.

Authors:  S. Barcza, J. M. Benkő

Read the full paper at astro-ph

AAVSO Acronym of the Day: CHOICE Monday, May 19, 2014 - 13:40

Today's featured acronym is CHOICE – The Carolyn Hurless Online Institute for Continuing Education

CHOICE is an education and outreach initiative of the AAVSO. It is a collection of informal, online short courses on topics chosen to help members of the AAVSO and others contribute more to science. Most CHOICE courses are four weeks long. They are run via the AAVSO web site using private forums and e-mail at a self-directed pace. One of the unique aspects of this program is that courses are peer taught. That is, graduates of one course have the opportunity to teach the next iteration of that course. Those who successfully complete a course are provided with a certificate and a badge displayed on their web site user profile page. We hope to increase the impact of this program by offering many of the courses to non-members.

This is just one example of the 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.
 

Long-term optical and radio variability of BL Lacertae Saturday, May 17, 2014 - 17:28

Well-sampled optical and radio light curves of BL Lacertae in B, V, R, I bands and 4.8, 8.0, 14.5 GHz from 1968 to 2014 were presented in this paper. A possible $1.26 \pm 0.05$ yr period in optical bands and a $7.50 \pm 0.15$ yr period in radio bands were detected based on discrete correlation function, structure function as well as Jurkevich method. Correlations among different bands were also analyzed and no reliable time delay was found between optical bands. Very weak correlations were detected between V band and radio bands. However, in radio bands the variation at low frequency lagged that at high frequency obviously. The spectrum of BL Lacertae turned mildly bluer when the object turned brighter, and stronger bluer-when-brighter trends were found for short flares. A scenario including a precessing helical jet and periodic shocks was put forward to interpret the variation characteristics of BL Lacertae.

Authors:  Y. C. Guo, S. M. Hu, C. Xu, C. Y. Liu, X. Chen, D. F. Guo, F. Y. Meng, M. T. Xu, J. Q. Xu

Read the paper on astro-ph

Pulsing Stars Help Map Milky Way's Outer Reaches Saturday, May 17, 2014 - 13:06

New observations of five young variable stars reveal a strange thickening in farflung regions of the Milky Way galaxy.

Known as Cepheid variables, the stars are positioned above and below the plane of the galaxy's disk. That position, combined with the stars' young age, indicates a warp to the arm that was previously suggested by observations of dust, but had not been shown by the presence of stars.

Stars on the other side of the galactic center can be challenging for scientists to observe, as the amount of interstellar dust increases at greater distances. A team of astronomers utilized two telescopes at the South African Astronomical Observatory (SAAO) to determine that the five Cepheid variables lie on the far side of the bulge of material in the heart of the Milky Way, above and below the galactic plane.

Read the full story on Space.com

AAVSO Acronym of the Day: VSOTS Saturday, May 17, 2014 - 12:31

Today's acronym is VSOTS – Variable Star of the Season


The “Variable Star of the Season” series of articles originated in 1998 as the "Variable Star of the Month". The articles contain useful and interesting information on individual variable stars. Many of the most popular stars in the AAVSO observing program are featured. From 2002 to 2011, they have all been published as part of the "Variable Star of the Season" collection. Each article is now archived in the VSOTS Archive and available in either .html or .pdf format.

This is another 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.

 

AAVSO Acronym of the Day: CHET Friday, May 16, 2014 - 17:53

CHET – Chart Error Tracking Tool

CHET was created to track of all reported issues with AAVSO variable star charts and sequences and the chart and sequence team’s progress in addressing those issues. Information reported to CHET by observers is used to evaluate and prioritize the work done by the charts and sequences team. When the team makes revisions or corrections, CHET automatically sends an email notification to the observer who reported the issue. The improvement in the quality of charts and sequences, and the speed with which new sequences are created for new transient objects, in the last ten years, is nothing short of amazing.

 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.
 

AAVSO Acronym of the Day: WebObs Wednesday, May 14, 2014 - 09:08

Today's acronym is WebObs – Web-based Observation Submission Tool

WebObs is the tool 99% of our observers use to submit observations to the AID. You can submit observations one at a time using the individual observation form, or you can upload files containing hundreds or thousands of observations all at once using the file upload feature. Files must conform to the AAVSO File Form Specifications which are described in detail on the website.

You can also use WebObs to search for observations of any variable star, or search for your own observations, which you can view, edit or delete. It can be used to download your observations for a specific time frame or all the observations you have ever reported to the AID. Registered photoelectric photometrists may also upload unreduced data to WebObs.

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.
 

Magnetar Formation Mystery Solved? Wednesday, May 14, 2014 - 08:57

Magnetars are the bizarre super-dense remnants of supernova explosions. They are the strongest magnets known in the Universe — millions of times more powerful than the strongest magnets on Earth. A team of European astronomers using ESO’s Very Large Telescope (VLT) now believe they’ve found the partner star of a magnetar for the first time. This discovery helps to explain how magnetars form — a conundrum dating back 35 years — and why this particular star didn’t collapse into a black hole as astronomers would expect.

It seems that being a component of a double star may therefore be an essential ingredient in the recipe for forming a magnetar. The rapid rotation created by mass transfer between the two stars appears necessary to generate the ultra-strong magnetic field and then a second mass transfer phase allows the magnetar-to-be to slim down sufficiently so that it does not collapse into a black hole at the moment of its death.

Read the full story on ESO Science Release 1415

Hidden nurseries in the Milky Way Tuesday, May 13, 2014 - 16:14

The APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) survey has revealed an unprecedented number of cold dense clumps of gas and dust as the cradles of massive stars, thus providing a complete view of their birthplaces in the Milky Way. Based on this census, an international team of scientists led by Timea Csengeri from the Max Planck Institute for Radio Astronomy in Bonn has estimated the time scale for these nurseries to grow stars. This has been found to be a very fast process: with only 75,000 years on average it is much shorter than the corresponding time scales typically found for nurseries of lower mass stars.

Read the press release from Max Plank Institute for Radio Astronomy

Get the pre-print of the research paper-  “The ATLASGAL survey: a catalog of dust condensations in the galactic plane,” T. Csengeri, J. S. Urquhart, F. Schuller, F. Motte, S. Bontemps, F. Wyrowski, K. M. Menten, L. Bronfman, H. Beuther, Th. Henning, L. Testi, A. Zavagno, M. Walmsley, Astronomy & Astrophysics, Vol. 565, A75 (May 2014).
 

AAVSO Acronym for the Day: AAVSOnet Tuesday, May 13, 2014 - 09:11

Today's AAVSO Acronym of the Day is AAVSOnet – The AAVSO robotic telescope network

AAVSOnet is a network of remote, robotically controlled, and automatically queued telescopes for the use of AAVSO members. Several telescopes, located worldwide, are currently active and taking data right now. The entire network is founded on the generosity and dedication of AAVSO volunteers, donors and corporate sponsors. 

Even the telescopes in the network have acronyms to describe them!

BSM – Bright Star Monitor, several small (~60mm) telescopes located in Australia and the USA.
C30 – Coker 30cm telescope, located in Sutter Creek, California, donated to the AAVSO by Phillip Coker.
OC61 – Optical Craftsman 61cm telescope, located at the Mount John University Observatory in New Zealand.
SRO – Sonoita Research Observatory, a 50cm telescope located in a private facility in Sonoita, Arizona.
TMO61 – Tortugas Mountain 61cm telescope, part of the new Mexico State University Observatory, located on Tortugas mountain in New Mexico.

This is another 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.

THANK YOU FOR YOUR SUPPORT!

AAVSO Acronym of the Day: VSP Sunday, May 11, 2014 - 23:07

Today's AAVSO Acronym is VSP – Variable Star Plotter.

Variable star charts and sequences are the most essential tools for acquiring accurate variable star measurements. The Variable Star Plotter (VSP) is the AAVSO's online chart plotting program that dynamically plots star charts for any location on the sky, or for any named object currently in the Variable Star Index (VSX). By creating charts this way, every chart utilizes the most current photometric data available. Customizable field of view, print resolution, magnitude limit, and orientation can be set for any chart plotted, or these values can be auto-assigned by selecting from one of the legacy chart scales familiar to many of our long-time observers. The charts produced by this tool include comparison star labels for visual magnitude estimations. You can also call up the photometric data used for the comparison sequence as another option.

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.

Maybe today or this week isn't the best time for you to make a donation. That's okay, make a pledge. We'll take you at your word if you promise to make a donation to the Annual Campaign before June 30, 2014. To make a pledge click here.
 

Sher 25: pulsating but apparently alone Sunday, May 11, 2014 - 22:24

The blue supergiant Sher25 is surrounded by an asymmetric, hourglass-shaped circumstellar nebula, which shows similarities to the triple-ring structure seen around SN1987A. From optical spectroscopy over six consecutive nights, we detect periodic radial velocity variations in the stellar spectrum of Sher25 with a peak-to-peak amplitude of ~12 km/s on a timescale of about 6 days, confirming the tentative detec-tion of similar variations by Hendry et al. From consideration of the amplitude and timescale of the signal, coupled with observed line profile variations, we propose that the physical origin of these variations is related to pulsations in the stellar atmosphere, rejecting the previous hypothesis of a massive, short-period binary companion. The radial velocities of two other blue supergiants with similar bipolar nebulae, SBW1 and HD 168625, were also monitored over the course of six nights, but these did not display any significant radial velocity variations.

Authors: William D. Taylor, Christopher J. Evans, Sergio Sim\'on-D\'iaz, Hugues Sana, Norbert Langer, Nathan Smith and Stephen J. Smartt

Download the paper from astro-ph

Recurrent and symbiotic novae in the OGLE data Friday, May 9, 2014 - 09:55

We analyse long-term optical photometry for two Galactic recurrent novae (V745 Sco, V3890 Sgr) and one LMC object (Nova LMC 1990b) observed over several years by the OGLE sky survey. We do not find variability with previously claimed orbital period of V745 Sco. This voids previous findings based on this value, e.g., the distance determination. The quiescence variability of this object is dominated by semiregular pulsations of the red giant secondary (with periods of 136.5 and 77.4 d). The photometry of Nova LMC 1990b reveals unnoticed eruption in 2010 and eclipse-like variability in quiescence with a period of 1.26432(8) d. The photometric properties make this object very similar to U Sco. Finally, we describe eruptions of two likely symbiotic novae - V5590 Sgr and OGLE-2011-BLG-1444. The progenitor of V5590 Sgr was a Mira star with pulsation period of 236 d.

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

Read the paper on astro-ph

AAVSO Acronym of the Day: VStar Friday, May 9, 2014 - 09:07

Today's AAVSO acronym of the day is VStar – Variable Star Analysis Software

VStar is a multi-platform, easy-to-use variable star data visualization and analysis tool that was originally developed as part of the AAVSO's Citizen Sky project. Data for any star can be read from the AAVSO database or from a text file of your own creation. Using VStar you can plot light curves, phase plots, do period analysis, polynomial fits and time frequency analysis. You can even create your own custom plug-ins to perform other analyses. The AAVSO, with support from the National Science Foundation, is delighted to make this powerful software available to anyone, free-of-charge.

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.

Maybe today or this week isn't the best time for you to make a donation. That's okay, make a pledge. We'll take you at your word if you promise to make a donation to the Annual Campaign before June 30, 2014. To make a pledge click here.

Astronomers Find Sun’s ‘Long-Lost Brother,’ Pave Way for Family Reunion Thursday, May 8, 2014 - 17:12

A team of researchers led by University of Texas at Austin astronomer Ivan Ramirez has identified the first “sibling” of the Sun — a star that was almost certainly born from the same cloud of gas and dust as our star. Ramirez’ methods will help other astronomers find other “solar siblings,” work that could lead to an understanding of how and where our Sun formed, and how our solar system became hospitable for life. The work will be published in the June 1 issue of The Astrophysical Journal.

“We want to know where we were born,” Ramirez said. “If we can figure out in what part of the galaxy the Sun formed, we can constrain conditions on the early solar system. That could help us understand why we are here.”

Read the full press release

Read the research paper

AAVSO Acronym of the Day: VSX Thursday, May 8, 2014 - 07:49

Today's AAVSO Acronym is VSX - The International Variable Star Index

Data on variable stars are constantly changing. New and ongoing surveys are locating new variable stars every day. Corrections to errors in the data are always coming in. But all of this work to refine what we know about these stars is happening at different times and in different places. The mission of VSX is to bring all of that new information together in a single data repository, make it accessible to the public via a simple web interface, and provide the tools necessary for the controlled and secure revision of the data. Created by Chris Wayson and maintained by the AAVSO, VSX is now the most accurate and complete variable star catalog on Earth, containing records for 285,745 stars. 

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.

Maybe today or this week isn't the best time for you to make a donation. That's okay, make a pledge. We'll take you at your word if you promise to make a donation to the Annual Campaign before June 30, 2014. To make a pledge click here.
 

NASA's Chandra Delivers New Insight into Formation of Star Clusters Wednesday, May 7, 2014 - 11:32

Using data from NASA’s Chandra X-ray Observatory and infrared telescopes, astronomers have made an important advance in the understanding of how clusters of stars come into being.

The data show early notions of how star clusters are formed cannot be correct. The simplest idea is stars form into clusters when a giant cloud of gas and dust condenses. The center of the cloud pulls in material from its surroundings until it becomes dense enough to trigger star formation. This process occurs in the center of the cloud first, implying that the stars in the middle of the cluster form first and, therefore, are the oldest.

However, the latest data from Chandra suggest something else is happening. Researchers studied two clusters where sun-like stars currently are forming – NGC 2024, located in the center of the Flame Nebula, and the Orion Nebula Cluster. From this study, they discovered the stars on the outskirts of the clusters actually are the oldest.

Read the full Chandra press release

AAVSO Acronym of the Day: AUID Wednesday, May 7, 2014 - 09:24

Today's AAVSO Acronym is AUID – AAVSO Unique Identifier

These combinations of numbers and letters uniquely identify all RA/Dec pairs in VSD, the AAVSO Variable Star Database. They come in the form of triplets ###-XXX-### (101-BCD-854). Triplets are easy for humans to process and they are easy to type. No vowels are used to prevent words. This allows for 10 billion combinations. These identifiers are assigned to variable stars, suspected variables and comparison stars in VSD. Data cannot be submitted to the AID unless an object has been assigned an AUID.

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 contributiong 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.

Maybe today or this week isn't the best time for you to make a donation. That's okay, make a pledge. We'll take you at your word if you promise to make a donation to the Annual Campaign before June 30, 2014. To make a pledge click here.
 

The Strange Naming Conventions of Astronomy Wednesday, May 7, 2014 - 09:16

If you’ve spent time around the astronomical literature, you’ve probably heard at least one term that made you wonder “why did astronomers do that?” G-type stars, early/late type galaxies, magnitudes, population I/II stars, sodium “D” lines, and the various types of supernovae are all members of the large, proud family of astronomy terms that are seemingly backwards, unrelated to the underlying physics, or annoyingly complicated. While it may seem surprising now, the origins of these terms were logical at the time of their creation. Today, let’s look at the history of a  couple of these terms, to figure out why astronomers did that.

Read the article on Astrobites

Recent outburst of the young star V1180 Cas Tuesday, May 6, 2014 - 09:48

We report on the ongoing outburst of the young variable V1180 Cas, which is known to display characteristics in common with EXor eruptive variables. We present results that support the scenario of an accretion-driven nature of the brightness variations of the object and provide the first evidence of jet structures around the source. We monitored the recent flux variations of the target in the Rc, J, H, and K bands. New optical and near-IR spectra taken during the current high state of V1180 Cas are presented, in conjunction with H2 narrow-band imaging of the source. Observed near-IR colour variations are analogous to those observed in EXors and consistent with excess emission originating from an accretion event. The spectra show numerous emission lines, which indicates accretion, ejection of matter, and an active disc. Using optical and near-IR emission features we derive a mass accretion rate of ~3 E-8 Msun/yr, which is an order of magnitude lower than previous estimates. In addition, a mass loss rate of ~4 E-9 and ~4 E-10 Msun/yr are estimated from atomic forbidden lines and H2, respectively. Our H2 imaging reveals two bright knots of emission around the source and the nearby optically invisible star V1180 Cas B, clearly indicative of mass-loss phenomena. Higher resolution observations of the detected jet will help to clarify whether V1180 Cas is the driving source and to determine the relation between the observed knots.

Authors:  S. Antoniucci, A.A.Arkharov, A. Di Paola, T. Giannini, A. Harutyunyan, E. N. Kopatskaya, V.M Larionov, G. Li Causi, D. Lorenzetti, D. Morozova, B. Nisini, F. Vitali

Read the paper on astro-ph

AAVSO Acronym of the Day: AID Tuesday, May 6, 2014 - 09:27

Today's featured AAVSO Acronym is AID – The AAVSO International Database

The AAVSO International Database has over 25 million variable star observations going back over one hundred years. It is the largest and most comprehensive digital variable star database in the world. Over 1,000,000 new variable star brightness measurements are added to the database every year by observers from all over the world. Professional astronomers, educators, students and amateur researchers around the globe use these data.

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.

Maybe today or this week isn't the best time for you to make a donation. That's okay, make a pledge. We'll take you at your word if you promise to make a donation to the Annual Campaign before June 30, 2014. To make a pledge click here.
 

AAVSO Acronym of the Day: APASS Monday, May 5, 2014 - 07:19

Today we begin a series of short informational pieces, highlighting some of the tools, projects and programs we know by their acronym names.

Our first featured acronym is APASS- The AAVSO Photometric All Sky Survey.

Through a grant from the Robert Martin Ayers Sciences Fund, the AAVSO is performing an all-sky photometric survey. This survey is conducted in five filters: Johnson B and V, plus Sloan g’, r’, i’. It is valid from approximately 10th magnitude to 17th magnitude. Precise, reliable standardized photometry in this magnitude range is in high demand, both from our observers and from the professional community. This survey will have an impact on the astronomical community for decades to come.

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 contributiong 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.
 

Identifying and Quantifying Recurrent Novae Masquerading as Classical Novae Thursday, May 1, 2014 - 21:45

Recurrent novae (RNe) are cataclysmic variables with two or more nova eruptions within a century. Classical novae (CNe) are similar systems with only one such eruption. Many of the so-called 'CNe' are actually RNe for which only one eruption has been discovered. Since RNe are candidate Type Ia supernova progenitors, it is important to know whether there are enough in our galaxy to provide the supernova rate, and therefore to know how many RNe are masquerading as CNe. To quantify this, we collected all available information on the light curves and spectra of a Galactic, time-limited sample of 237 CNe and the 10 known RNe, as well as exhaustive discovery efficiency records. We recognize RNe as having (a) outburst amplitude smaller than 14.5 - 4.5 * log(t_3), (b) orbital period >0.6 days, (c) infrared colors of J-H > 0.7 mag and H-K > 0.1 mag, (d) FWHM of H-alpha > 2000 km/s, (e) high excitation lines, such as Fe X or He II near peak, (f) eruption light curves with a plateau, and (g) white dwarf mass greater than 1.2 M_solar. Using these criteria, we identify V1721 Aql, DE Cir, CP Cru, KT Eri, V838 Her, V2672 Oph, V4160 Sgr, V4643 Sgr, V4739 Sgr, and V477 Sct as strong RN candidates. We evaluate the RN fraction amongst the known CNe using three methods to get 24% +/- 4%, 12% +/- 3%, and 35% +/- 3%. With roughly a quarter of the 394 known Galactic novae actually being RNe, there should be approximately a hundred such systems masquerading as CNe.

Authors:  Ashley Pagnotta, Bradley E. Schaefer

Read this paper on astro-ph

Diversity Of Short Gamma-Ray Burst Afterglows From Compact Binary Mergers Hosting Pulsars Thursday, May 1, 2014 - 21:33

Short gamma-ray bursts (sGRBs) are widely believed to result from the mergers of compact binaries. This model predicts an afterglow that bears the characteristic signatures of a constant, low density medium, including a smooth prompt-afterglow transition, and a simple temporal evolution. However, these expectations are in conflict with observations for a non-negligible fraction of sGRB afterglows. In particular, the onset of the afterglow phase for some of these events appears to be delayed and, in addition, a few of them exhibit late-time rapid fading in their lightcurves. These facts have prompted speculation that the central engine activity continues to operate effectively for tens of seconds following the prompt emission. We show that these peculiar observations can be explained independently of ongoing central engine activity if some sGRB progenitors are compact binaries hosting at least one pulsar. The Poynting flux emanating from the pulsar companion can excavate a bow-shock cavity surrounding the binary. If this cavity is larger than the shock deceleration length scale in the undisturbed interstellar medium, then the onset of the afterglow will be delayed. Should the deceleration occur entirely within the swept-up thin shell, a rapid fade in the lightcurve will ensue. We identify two types of pulsar that can achieve the conditions necessary for altering the afterglow: low field, long lived pulsars, and high field pulsars. We find that a sizable fraction (2050%) of low field pulsars are likely to reside in neutron star binaries based on observations, while their high field counterparts are not.

Authors:  Cole Holcomb, Enrico Ramirez-Ruiz, Fabio De Colle, Gabriela Montes

Read the preprint on astro-ph

Massive Stars Don’t Make Good Neighbors Wednesday, April 30, 2014 - 06:38

Big stars are bullies. When one dies, it does so spectacularly, exploding in a supernova with energy output equal to that of the Sun over its entire lifetime. However, a massive star’s mischief starts much sooner. As it is born, it can steal gas from its neighbors. During its life, its strong radiation and winds plow through the neighborhood, wreaking havoc and disrupting the births of other stars. Is this feedback enough to explain why we see such a small fraction of the gas in stellar nurseries ending up in stars? New analysis using simulations investigates the details.

Read the full story on Astrobites

 

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