Ago+2011

=Astro-ph list=

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=30 Aug 2011:= [|arXiv:1108.5548] [[|pdf], [|ps], [|other]] = Title: Early emission from type Ia supernovae= Authors: [|Itay Rabinak], [|Eli Livne], [|Eli Waxman] Comments: 10 pages, 4 figures Subjects: High Energy Astrophysical Phenomena (astro-ph.HE) ; Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA) A unique feature of deflagration-to-detonation (DDT) white dwarf explosion models of SNe of type Ia is the presence of a strong shock wave propagating through the outer envelope. We consider the early emission expected in such models, which is produced by the expanding shock-heated outer part of the ejecta and precedes the emission driven by radioactive decay. We expand on earlier analyses by considering the modification of the pre-detonation density profile by the weak-shocks generated during the deflagration phase, the time evolution of the opacity, and the deviation of the post-shock equation of state from that obtained for radiation pressure domination. A simple analytic model is presented and shown to provide an acceptable approximation to the results of 1D numerical DDT simulations. Our analysis predicts a thousand second long UV/optical flash with a luminosity of ~1 to 3*1e39 erg/s. Lower luminosity corresponds to faster (turbulent) deflagration velocity. The predicted luminosity of the UV flash is an order of magnitude lower than that of earlier estimates, and is expected to be strongly suppressed at times longer than an hour due to the deviation from pure radiation domination. Added by F. Förster

=29 Aug 2011:= [|arXiv:1108.5234] [[|pdf], [|ps], [|other]] = Title: Multidimensional Simulations of Thermonuclear Supernovae from the First Stars= Authors: [|Ke-Jung Chen], [|Alexander Heger], [|Ann Almgren] Comments: 4 pages, 2 figures, to appear in ASPCS: ADVANCES IN COMPUTATIONAL ASTROPHYSICS: METHODS, TOOLS, AND OUTCOME Subjects: High Energy Astrophysical Phenomena (astro-ph.HE) Theoretical models suggest that the first stars in the universe could have been very massive, with typical masses $\gtrsim$ 100 \Msun. Many of them might have died as energetic thermonuclear explosions known as pair-instability supernovae (PSNe). We present multidimensional numerical simulations of PSNe with the new radiation-hydrodynamics code CASTRO. Our models capture all explosive burning and follow the explosion until the shock breaks out from the stellar surface. We find that fluid instabilities driven by oxygen and helium burning arise at the upper and lower boundaries of the oxygen shell $\sim$ 20 - 100 sec after the explosion begins. Later, when the shock reaches the hydrogen envelope a strong reverse shock forms that rapidly develops additional Rayleigh-Taylor instabilities. In red supergiant progenitors, the amplitudes of these instabilities are sufficient to mix the supernova's ejecta and alter its observational signature. Our results provide useful predictions for the detection of PSNe by forthcoming telescopes. Added by F. Förster

=25 Aug 2011:= [|arXiv:1108.4690] [[|pdf], [|ps], [|other]] = Title: Imploding ignition waves: I. one dimensional analysis= Authors: [|Doron Kushnir] (1), [|Eli Livne] (2), [|Eli Waxman] (1) ((1) Weizmann, (2) Hebrew University) Comments: 12 pages, 9 figures Subjects: High Energy Astrophysical Phenomena (astro-ph.HE) ; Solar and Stellar Astrophysics (astro-ph.SR); Fluid Dynamics (physics.flu-dyn) We show that converging spherical and cylindrical shock waves may ignite a detonation wave in a combustible medium, provided the radius at which the shocks become strong exceeds a critical radius, R_c. An approximate analytic expression for R_c is derived for an ideal gas equation of state and a simple (power-law-Arrhenius) reaction law, and shown to reproduce the results of numerical solutions. For typical acetylene-air experiments we find R_c~0.1 mm (spherical) and R_c~1 mm (cylindrical). We suggest that the deflagration to detonation transition (DDT) observed in these systems may be due to converging shocks produced by the turbulent deflagration flow, which reaches sub (but near) sonic velocities on scales >>R_c. Our suggested mechanism differs from that proposed by Zel'dovich et al. (1970), in which a fine tuned spatial gradient in the chemical induction time is required to be maintained within the turbulent deflagration flow. Our analysis may be readily extended to more complicated equations of state and reaction laws. An order of magnitude estimate of R_c within a white dwarf at the pre-detonation conditions believed to lead to type Ia supernova explosions is 0.1 km, suggesting that our proposed mechanism may be relevant for DDT initiation in these systems. The relevance of our proposed ignition mechanism to DDT initiation may be tested by both experiments and numerical simulations. Added by F. Förster

[|arXiv:1108.4849] [[|pdf], [|ps], [|other]] = Title: A Binary Scenario for the Formation of Strongly Magnetized White Dwarfs= Authors: [|J. Nordhaus] (RIT, Princeton) Comments: To appear in the Proceedings of the 2nd International Symposium on Strong Electromagnetic Fields and Neutron Stars, Varadero, Cuba Subjects: Solar and Stellar Astrophysics (astro-ph.SR) ; Earth and Planetary Astrophysics (astro-ph.EP) Since their initial discovery, the origin of isolated white dwarfs (WDs) with magnetic fields in excess of $\sim$1 MG has remained a mystery. Recently, the formation of these high-field magnetic WDs has been observationally linked to strong binary interactions incurred during post-main-sequence evolution. Planetary, brown dwarf or stellar companions located within a few AU of main-sequence stars may become engulfed during the primary's expansion off the main sequence. Sufficiently low-mass companions in-spiral inside a common envelope until they are tidally shredded near the natal white dwarf. Formation of an accretion disk from the disrupted companion provides a source of turbulence and shear which act to amplify magnetic fields and transport them to the WD surface. We show that these disk-generated fields explain the observed range of magnetic field strengths for isolated, high-field magnetic WDs. Additionally, we discuss a high-mass binary analogue which generates a strongly-magnetized WD core inside a pre-collapse, massive star. Subsequent core-collapse to a neutron star may produce a magnetar. Added by F. Förster

[|arXiv:1108.4923] [[|pdf], [|ps], [|other]] = Title: The SDSS-II Supernova Survey: Parameterizing the Type Ia Supernova Rate as a Function of Host Galaxy Properties= Authors: [|Mathew Smith] (ACGC Cape Town, ICG Portsmouth, AIMS), [|Robert C Nichol], [|Benjamin Dilday], [|John Marriner], [|Richard Kessler], [|Bruce Bassett], [|David Cinabro], [|Joshua Frieman], [|Peter Garnavich], [|Saurabh W Jha], [|Hubert Lampeitl], [|Masao Sako], [|Donald P Schneider], [|Jesper Sollerman] Comments: 46 pages, submitted to ApJ Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO) Using data from the Sloan Digital Sky Supernova Survey-II, we measure the rate of Type Ia Supernovae (SNe Ia) as a function of galaxy properties at intermediate redshift. A sample of 342 SNe Ia with 0.05<z<0.25 is constructed. Using broad-band photometry we use the PEGASE spectral energy distributions (SEDs) to estimate host galaxy stellar masses and recent star-formation rates. We find that the rate of SNe Ia per unit stellar mass is significantly higher (by a factor of ~30) in highly star-forming galaxies compared to passive galaxies. When parameterizing the SN Ia rate (SNR_Ia) based on host galaxy properties, we find that the rate of SNe Ia in passive galaxies is not linearly proportional to the stellar mass, instead a SNR_Ia proportional to M^0.68 is favored. However, such a parameterization does not describe the observed SN Ia rate in star-forming galaxies. The SN Ia rate in star-forming galaxies is well fit by SNR_Ia = 1.05\pm0.16x10^{-10} M ^{0.68\pm0.01} + 1.01\pm0.09x10^{-3} SFR^{1.00\pm0.05} (statistical errors only), where M is the host galaxy mass and SFR is the star-formation rate. These results are insensitive to the selection criteria used, redshift limit considered and the inclusion of non-spectroscopically confirmed SNe Ia. We also show there is a dependence between the distribution of the MLCS light-curve decline rate parameter, \Delta, and host galaxy type. Passive galaxies host less luminous SNe Ia than seen in moderately and highly star-forming galaxies, although a population of luminous SNe is observed in passive galaxies, contradicting previous assertions that these SNe Ia are only observed in younger stellar systems. The MLCS extinction parameter, A_V, is similar in passive and moderately star-forming galaxies, but we find indications that it is smaller, on average, in highly star-forming galaxies. We confirm these results using the SALT2 light-curve fitter. Added by F. Förster

=24 Aug 2011:= [|arXiv:1108.4600] [[|pdf], [|ps], [|other]] = Title: Post-common-envelope binaries from SDSS. XI: The white dwarf mass distributions of CVs and pre-CVs= Authors: [|M. Zorotovic], [|M.R. Schreiber], [|B.T. Gänsicke] Comments: Accepted for publication in A&amp;A, 18 pages, 9 figures Subjects: Solar and Stellar Astrophysics (astro-ph.SR) We have known for a long time that many of the measured white dwarf (WD) masses in cataclysmic variables (CVs) significantly exceed the mean mass of single WDs. This was thought to be related to observational biases, but recent high-precision measurements of WD masses in a great number of CVs are challenging this interpretation. We review the measured WD masses of CVs, determine the WD-mass distribution of an extensive sample of post-common-envelope binaries (PCEBs) that are representative for the progenitors of the current CV population (pre-CVs) and compare both distributions. We calculate the CV formation time of the PCEBs in our sample by determining the post common-envelope (CE) and the main-sequence evolution of the binary systems and define a pre-CV to be a PCEB that evolves into a semi-detached configuration with stable mass transfer within less than the age of the Galaxy. Possible observational biases affecting the WD-mass distribution for the pre-CV and the CV samples are discussed. The mean WD mass among CVs is =0.83\pm0.23 Msun, much larger than that found for pre-CVs, =0.67\pm0.21 Msun. Selection effects cannot explain the high WD masses observed in CVs and we here suggest two possible explanations, both of which imply substantial revisions to the standard model of CV evolution: either most CVs have formed above the orbital-period gap (which requires a high WD mass to initiate stable mass transfer or a previous phase of thermal-timescale mass transfer), or the mass of the WDs in CVs grows through accretion (which strongly disagrees with the predictions of classical nova models). Both options may imply that CVs contribute to the single-degenerate progenitors of Type Ia supernovae. The number of He-core WDs found in CVs (<=10%) is roughly consistent with the number of He-core WDs in pre-CVs (<=17+-8%), which indicates a low value of the CE efficiency. Added by F. Förster

[|arXiv:1108.4434] [[|pdf], [|ps], [|other]] = Title: Core-collapse supernova enrichment in the core of the Virgo Cluster= Authors: [|E.T. Million], [|N. Werner], [|A. Simionescu], [|S.W. Allen] Comments: 11 pages, 8 figures. Accepted for publication in MNRAS Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO) ; Galaxy Astrophysics (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE) Using a deep (574 ks) Chandra observation of M87, the dominant galaxy of the nearby Virgo Cluster, we present the best measurements to date of the radial distribution of metals in the central intracluster medium (ICM). Our measurements, made in 36 independent annuli with $\sim$250,000 counts each, extend out to a radius r$\sim$40 kpc and show that the abundance profiles of Fe, Si, S, Ar, Ca, Ne, Mg, and Ni are all centrally peaked. Interestingly, the abundance profiles of Si and S - which are measured robustly and to high precision - are even more centrally peaked than Fe, while the Si/S ratio is relatively flat. These measurements challenge the standard picture of chemical enrichment in galaxy clusters, wherein type Ia supernovae (SN Ia) from an evolved stellar population are thought to dominate the central enrichment. The observed abundance patterns are most likely due to one or more of the following processes: continuing enrichment by winds of a stellar population pre-enriched by SNCC products; intermittent formation of massive stars in the central cooling core; early enrichment of the low entropy gas. We also discuss other processes that might have contributed to the observed radial profiles, such as a stellar initial mass function that changes with radius; changes in the pre-enrichment of core-collapse supernova progenitors; and a diversity in the elemental yields of SN Ia. Although systematic uncertainties prevent us from measuring the O abundance robustly, indications are that it is about 2 times lower than predicted by the enrichment models. Added by F. Förster

=23 Aug 2011:= [|arXiv:1108.4036] [[|pdf], [|ps], [|other]] = Title: The Long-Term Evolution of Double White Dwarf Mergers= Authors: [|Ken J. Shen], [|Lars Bildsten], [|Daniel Kasen], [|Eliot Quataert] Comments: Submitted to The Astrophysical Journal; 10 pages, 8 figures Subjects: High Energy Astrophysical Phenomena (astro-ph.HE) ; Solar and Stellar Astrophysics (astro-ph.SR) In this paper, we present a model for the long-term evolution of the merger of two unequal mass C/O white dwarfs (WDs). After the dynamical phase of the merger, magnetic stresses rapidly redistribute angular momentum, leading to nearly solid body rotation on a viscous timescale, 1e4-1e8 s, long before significant cooling can occur. Because of heating during the dynamical and viscous phases, the less massive WD is transformed into a hot radially extended envelope supported by thermal pressure and with the majority of the mass having negligible rotational support. This extended envelope then undergoes Kelvin-Helmholtz contraction on a thermal timescale of ~1e4 yr; during this period, the merger remnant radiates near the Eddington limit. Given the double WD merger rate of a few per 1000 yr, a few dozen of these near-Eddington sources should exist in a Milky Way-type galaxy. In our calculations, the contraction of the cooling envelope is relatively rapid, and the base of the envelope is compressed until off-center convective C-burning begins. As a result, the long-term evolution of the merger remnant is similar to that seen in previous calculations, and a collapse to a neutron star, rather than a Type Ia supernova, is the likely outcome. However, the physical picture and the dynamical state of the matter in our model differ from previous work. Furthermore, substantial remaining uncertainties related to the opacity of the envelope and mass loss during the thermal evolution may significantly affect our conclusions. Thus, future work within the context of the physical model presented here is required to better address the potential of WD mergers as Type Ia supernova progenitors. Added by F. Förster

[|arXiv:1108.4064] [[|pdf], [|other]] = Title: Density Fluctuation Effects on Collective Neutrino Oscillations in O-Ne-Mg Core-Collapse Supernovae= Authors: [|John F. Cherry], [|Meng-Ru Wu], [|Joe Carlson], [|Huaiyu Duan], [|George M. Fuller], [|Yong-Zhong Qian] Comments: 12 pages, 11 figures. This is a pre-submission version of the paper Subjects: High Energy Astrophysical Phenomena (astro-ph.HE) ; Cosmology and Extragalactic Astrophysics (astro-ph.CO); Solar and Stellar Astrophysics (astro-ph.SR); High Energy Physics - Phenomenology (hep-ph) We investigate the effect of matter density fluctuations on supernova collective neutrino flavor oscillations. In particular, we use full multi-angle, 3-flavor, self-consistent simulations of the evolution of the neutrino flavor field in the envelope of an O-Ne-Mg core collapse supernova at shock break-out (neutrino neutronization burst) to study the effect of the matter density "bump" left by the He-burning shell. We find a seemingly counterintuitive increase in the overall electron neutrino survival probability created by this matter density feature. We discuss this behavior in terms of the interplay between the matter density profile and neutrino collective effects. While our results give new insights into this interplay, they also suggest an immediate consequence for supernova neutrino burst detection: it will be difficult to use a burst signal to extract information on fossil burning shells or other fluctuations of this scale in the matter density profile. Consistent with previous studies, our results also show that the interplay of neutrino self-coupling and matter fluctuation could cause a significant increase in the electron neutrino survival probability at very low energy Added by F. Förster

[|arXiv:1108.4137] [[|pdf], [|ps], [|other]] = Title: Supernova Remnant Shock - Molecular Cloud Interactions: Masers as tracers of hadronic particle acceleration= Authors: [|Dale A. Frail] Comments: Invited review for Cosmic rays and their interstellar medium environment (CRISM-2011). The CRISM meeting proceedings will be published in a special issue of the memoria della societa italiana Subjects: High Energy Astrophysical Phenomena (astro-ph.HE) We review the class of galactic supernova remnants which show strong interactions with molecular clouds, revealed through shock-excited hydroxyl masers. These remnants are preferentially found among the known GeV and TeV detections of supernova remnants. It has been argued that the masers trace out the sites of hadronic particle acceleration. We discuss what is known about the physical conditions of these shocked regions and we introduce a potential new maser tracer for identifying the sites of cosmic ray acceleration. This review includes a reasonably complete bibliography for researchers new to the topic of shock-excited masers and supernova remnants. Added by F. Förster

[|arXiv:1108.4355] [[|pdf], [|ps], [|other]] = Title: Is Strong SASI Activity the Key to Successful Neutrino-Driven Supernova Explosions?= Authors: [|Florian Hanke], [|Andreas Marek], [|Bernhard Mueller], [|Hans-Thomas Janka] (MPI for Astrophysics, Garching) Comments: 19 pages, 14 figures, 26 eps files; submitted to The Astrophysical Journal Subjects: Solar and Stellar Astrophysics (astro-ph.SR) With a numerical approach similar to Nordhaus et al. (2010) but a modified approximation of neutrino effects we explore the viability of the neutrino mechanism of core-collapse supernova explosions in dependence on the spatial dimension of the simulations. We cannot confirm the previous findings. While we also observe that 2D models explode for a lower driving neutrino luminosity than those in 1D, we do not find that explosions in 3D occur easier and earlier than in 2D. Moreover, we find that the average entropy of matter in the gain layer hardly depends on the dimension and thus is not a good diagnostic quantity for the readiness to explode. Instead, the mass, integrated entropy, total neutrino-heating rate, and nonradial kinetic energy in the gain layer turn out to be higher for models that are closer to explosion. Coherent, large-scale mass motions as typically associated with the standing accretion-shock instability (SASI), whose low spherical-harmonics modes have the highest growth rates, are observed to support the explosion because they drive strong shock expansion and thus enlarge the gain layer including its mass and integral values of entropy, neutrino-energy deposition, and nonradial kinetic energy. While 2D models with better angular resolution explode clearly more easily, the opposite trend is seen in 3D. We interpret this as a consequence of the turbulent energy cascade, which transports energy from small to large spatial scales in 2D, thus fostering SASI activity, whereas the energy flow in 3D is in the opposite direction and feeds fragmentation and vortex motions on smaller scales, making the 3D evolution more similar to 1D when finer grid resolution is used. More favorable conditions for explosions in 3D may therefore be tightly linked to efficient growth of low-order SASI modes including nonaxisymmetric ones. Added by F. Förster

=22 Aug 2011:=

[|arXiv:1108.3989] [[|pdf], [|ps], [|other]] = Title: Three-dimensional Hydrodynamic Core-Collapse Supernova Simulations for an $11.2 M_{\odot}$ Star with Spectral Neutrino Transport= Authors: [|Tomoya Takiwaki], [|Kei Kotake], [|Yudai Suwa] Comments: 35 pages, 18 figures, submitted to ApJ Subjects: High Energy Astrophysical Phenomena (astro-ph.HE) We present numerical results on three-dimensional (3D) hydrodynamic core-collapse simulations of an $11.2 M_{\odot}$ star. By comparing one-(1D) and two-dimensional(2D) results with those of 3D, we study how the increasing spacial multi-dimensionality affects the postbounce supernova dynamics. The calculations were performed with an energy-dependent treatment of the neutrino transport that is solved by the isotropic diffusion source approximation scheme. By performing a tracer-particle analysis, we show that the maximum residency time of material in the gain region is shown to be longer for 3D due to non-axisymmetric flow motions than 2D, which is one of advantageous aspects of 3D models to obtain neutrino-driven explosions. Our results show that convective matter motions below the gain radius become much more violent in 3D than 2D, making the neutrino luminosity larger for 3D. Nevertheless the emitted neutrino energies are made smaller due to the enhanced cooling. Our results indicate whether these advantages for driving 3D explosions could or could not overwhelm the disadvantages is sensitive to the employed numerical resolutions. An encouraging finding is that the shock expansion tends to become more energetic for models with finer resolutions. To draw a robust conclusion, 3D simulations with much more higher numerical resolutions and also with more advanced treatment of neutrino transport as well as of gravity is needed, which could be hopefully practicable by utilizing forthcoming Petaflops-class supercomputers. Added by J. Anderson

[|arXiv:1108.3837] [[|pdf], [|ps], [|other]] = Title: Disc instability in RS Ophiuchi: a path to Type Ia supernovae?= Authors: [|R.D.Alexander], [|G.A.Wynn], [|A.R.King], [|J.E.Pringle] Comments: 8 pages, 5 figures. Accepted for publication in MNRAS Subjects: High Energy Astrophysical Phenomena (astro-ph.HE) We study the stability of disc accretion in the recurrent nova RS Ophiuchi. We construct a one-dimensional time-dependent model of the binary-disc system, which includes viscous heating and radiative cooling and a self-consistent treatment of the binary potential. We find that the extended accretion disc in this system is always unstable to the thermal-viscous instability, and undergoes repeated disc outbursts on ~10-20yr time-scales. This is similar to the recurrence time-scale of observed outbursts in the RS Oph system, but we show that the disc's accretion luminosity during outburst is insufficient to explain the observed outbursts. We explore a range of models, and find that in most cases the accretion rate during outbursts reaches or exceeds the critical accretion rate for stable nuclear burning on the white dwarf surface. Consequently we suggest that a surface nuclear burning triggered by disc instability may be responsible for the observed outbursts. This allows the white dwarf mass to grow over time, and we suggest that disc instability in RS Oph and similar systems may represent a path to Type Ia supernovae. Added by J. Anderson

=19 Aug 2011:=

[|arXiv:1108.3576] [[|pdf], [|ps], [|other]] = Title: Supernova Propagation in the Circumstellar and Interstellar Medium= Authors: [|Vikram V. Dwarkadas] Comments: 6 pages, 3 figures. Invited review presented at the conference on Cosmic Rays and the Interstellar Medium (CRISM-2011), Montpellier, France, June 26-July 1. To be published in a special issue of MEMORIE della Societa Astronomica Italiana Subjects: High Energy Astrophysical Phenomena (astro-ph.HE) We describe the propagation of supernova shock waves within the surrounding medium, which may be formed by mass-loss from the progenitor star. The structure and density profile of the ejected material and surrounding medium are considered, and shock wave interaction with clouds or clumps is briefly discussed. Added by F. Förster

[|arXiv:1108.3601] [[|pdf], [|ps], [|other]] = Title: Burning Thermals in Type Ia Supernovae= Authors: [|A J Aspden], [|J B Bell], [|S Dong], [|S E Woosley] Journal-ref: Astrophysical Journal, 738, pp. 94-107, (2011) Subjects: High Energy Astrophysical Phenomena (astro-ph.HE) We develop a one-dimensional theoretical model for thermals burning in Type Ia supernovae based on the entrainment assumption of Morton, Taylor and Turner. Extensions of the standard model are required to account for the burning and for the expansion of the thermal due to changes in the background stratification found in the full star. The model is compared with high-resolution three-dimensional numerical simulations, both in a uniform environment, and in a full-star setting. The simulations in a uniform environment present compelling agreement with the predicted power-laws and provide model constants for the full-star model, which then provides excellent agreement with the full-star simulation. The importance of the different components in the model are compared, and are all shown to be relevant. An examination of the effect of initial conditions was then conducted using the one-dimensional model, which would have been infeasible in three dimensions. More mass was burned when the ignition kernel was larger and closer to the center of the star. The turbulent flame speed was found to be important during the early-time evolution of the thermal, but played a diminished role at later times when the evolution is dominated by the large-scale hydrodynamics responsible for entrainment. However, a higher flame speed effectively gave a larger initial ignition kernel and so resulted in more mass burned. This suggests that future studies should focus on the early-time behavior of these thermals (in particular, the transition to turbulence), and that the choice of turbulent flame speed does not play a significant role in the dynamics once the thermal has become established. Added by F. Förster

[|arXiv:1108.3664] [[|pdf], [|ps], [|other]] = Title: Circumstellar Material in Type Ia Supernovae via Sodium Absorption Features= Authors: [|Assaf Sternberg], [|Avishay Gal-Yam], [|Josh D. Simon], [|Douglas C. Leonard], [|Robert M. Quimby], [|Mark M. Phillips], [|Nidia Morrell], [|Ian B. Thompson], [|Inese Ivans], [|Jennifer L. Marshall], [|Alexei V. Filippenko], [|Geoffrey W. Marcy], [|Josh S. Bloom], [|Ferdinando Patat], [|Ryan J. Foley], [|David Yong], [|Bryan E. Penprase], [|Daniel J. Beeler], [|Carlos Allende Prieto], [|Guy S. Stringfellow] Comments: Accepted for publication in Science 5 July 2011 Journal-ref: Science 333, 856 (2011) Subjects: High Energy Astrophysical Phenomena (astro-ph.HE) ; Cosmology and Extragalactic Astrophysics (astro-ph.CO) Type Ia supernovae are key tools for measuring distances on a cosmic scale. They are generally thought to be the thermonuclear explosion of an accreting white dwarf in a close binary system. The nature of the mass donor is still uncertain. In the single-degenerate model it is a main-sequence star or an evolved star, whereas in the double-degenerate model it is another white dwarf. We show that the velocity structure of absorbing material along the line of sight to 35 type Ia supernovae tends to be blueshifted. These structures are likely signatures of gas outflows from the supernova progenitor systems. Thus many type Ia supernovae in nearby spiral galaxies may originate in single-degenerate systems. Added by F. Förster

=18 Aug 2011:=

[|arXiv:1108.3505] [[|pdf], [|ps], [|other]] = Title: The spectroscopic evolution of the recurrent nova T Pyxidis during its 2011 outburst I. The optically thick phase and the origin of moving lines in novae= Authors: [|S. N. Shore] (Univ. di Pisa, INFN-Pisa), [|T. Augusteijn] (Nordic Optical Telescope), [|A. Ederoclite] (IAC de Canarias, Univ.de La Laguna), [|H. Uthas] (Columbia Univ.) Comments: Accepted for publication in Astronomy &amp; Astrophysics Letters (17/8/11) Subjects: Solar and Stellar Astrophysics (astro-ph.SR) ; High Energy Astrophysical Phenomena (astro-ph.HE) The nova T Pyx was observed with high resolution spectroscopy (R ~ 65000) spectroscopy, beginning 1 day after discovery of the outburst and continuing through the last visibility of the star at the end of May 2011. The interstellar absorption lines of Na I, Ca II, CH, CH$^+$, and archival H I 21 cm emission line observations have been used to determine a kinematic distance. Interstellar diffuse absorption features have been used to determine the extinction independent of previous assumptions. Sample Fe-peak line profiles show the optical depth and radial velocity evolution of the discrete components. We propose a distance to T Pyx $\geq$4.5kpc, with a strict lower limit of 3.5 kpc (the previously accepted distance). We derive an extinction, E(B-V)$\approx0.5\pm$0.1, that is higher than previous estimates. The first observation, Apr. 15, displayed He I, He II, C III, and N III emission lines and a maximum velocity on P Cyg profiles of the Balmer and He I lines of $\approx$2500 km s$^{-1}$ characteristic of the fireball stage. These ions were undetectable in the second spectrum, Apr. 23, and we use the recombination time to estimate the mass of the ejecta, $10^{-5}f$M$_\odot$ for a filling factor $f$. Numerous absorption line systems were detected on the Balmer, Fe-peak, Ca II, and Na I lines, mirrored in broader emission line components, that showed an "accelerated" displacement in velocity. We also show that the time sequence of these absorptions, which are common to all lines and arise only in the ejecta, can be described by recombination front moving outward in the expanding gas without either a stellar wind or circumstellar collisions. Added by F. Förster

=17 Aug 2011:=

[|arXiv:1108.3090] [[|pdf], [|ps], [|other]] = Title: Relativistic collapse and explosion of rotating supermassive stars with thermonuclear effects= Authors: [|Pedro J. Montero], [|Hans-Thomas Janka], [|Ewald Mueller] (Max Planck Institute for Astrophysics, Garching) Comments: 12 pages, 8 figures, submitted to the Astrophysical Journal Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO) ; General Relativity and Quantum Cosmology (gr-qc) We present results of general relativistic simulations of collapsing supermassive stars with and without rotation using the two-dimensional general relativistic numerical code Nada, which solves the Einstein equations written in the BSSN formalism and the general relativistic hydrodynamics equations with high resolution shock capturing schemes. These numerical simulations use an equation of state which includes effects of gas pressure, and in a tabulated form those associated with radiation and the electron-positron pairs. We also take into account the effect of thermonuclear energy released by hydrogen and helium burning. We find that objects with a mass of 5x10^{5} solar mass and an initial metallicity greater than Z_{CNO}~0.007 do explode if non-rotating, while the threshold metallicity for an explosion is reduced to Z_{CNO}~0.001 for objects uniformly rotating. The critical initial metallicity for a thermonuclear explosion increases for stars with mass ~10^{6} solar mass. For those stars that do not explode we follow the evolution beyond the phase of black hole formation. We compute the neutrino energy loss rates due to several processes that may be relevant during the gravitational collapse of these objects. The peak luminosities of neutrinos and antineutrinos of all flavors for models collapsing to a BH are ~10^{55} erg/s. The total radiated energy in neutrinos varies between ~10^{56} ergs for models collapsing to a BH, and ~10^{45}-10^{46} ergs for models exploding. Added by F.Förster

[|arXiv:1108.3108] [[|pdf], [|other]] = Title: The Carnegie Supernova Project: Second Photometry Data Release of Low-Redshift Type Ia Supernovae= Authors: [|Maximilian Stritzinger], [|M. M. Phillips], [|Luis Boldt S.], [|Chris Burns], [|Abdo Campillay], [|Carlos Contreras], [|Sergio Gonzalez], [|Gaston Folatelli], [|Nidia Morrell], [|Wojtek Krzeminski], [|Miguel Roth], [|Francisco Salgado], [|Darren L. Depoy], [|Mario Hamuy], [|Wendy L. Freedman], [|Barry Madore], [|Jennifer L. Marshall], [|Sven E. Persson], [|Jean-Philippe Rheault], [|Nicholas Suntzeff], [|Steven Villanueva], [|Weidong Li], [|Alexei V. Filippenko] Comments: 115 pages, 7 figures, 7 tables. To be published in the Astronomical Journal. Comments welcome Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO) The Carnegie Supernova Project (CSP) was a five-year observational survey conducted at Las Campanas Observatory that obtained, among other things, high-quality light curves of ~100 low-redshift Type Ia supernovae (SNe Ia). Presented here is the second data release of nearby SN Ia photometry consisting of 50 objects, with a subset of 45 having near-infrared follow-up observations. Thirty-three objects have optical pre-maximum coverage with a subset of 15 beginning at least 5 days before maximum light. In the near-infrared, 27 objects have coverage beginning before the epoch of B-band maximum, with a subset of 13 beginning at least 5 days before maximum. In addition, we present results of a photometric calibration program to measure the CSP optical (uBgVri)bandpasses with an accuracy of ~1%. Finally, we report the discovery of a second SN Ia, SN 2006ot, similar in its characteristics to the peculiar SN 2006bt. Added by F.Förster

[|arXiv:1108.3110] [[|pdf], [|ps], [|other]] = Title: Tidal Interactions in Merging White Dwarf Binaries= Authors: [|Anthony L. Piro] (Caltech) Comments: Submitted for publication in The Astrophysical Journal Letters, 5 pages, 2 figures Subjects: Solar and Stellar Astrophysics (astro-ph.SR) ; General Relativity and Quantum Cosmology (gr-qc) The recently discovered system J0651 is the tightest known detached white dwarf (WD) binary. Since it has not yet initiated Roche-lobe overflow, it provides a relatively clean environment for testing our understanding of tidal interactions. I investigate the tidal heating of each WD, parameterized in terms of its tidal Q parameter. Assuming that the heating can be radiated efficiently, the current luminosities are consistent with Q_1=7*10^{10} and Q_2=2*10^7, for the He and C/O WDs, respectively. Conversely, if the observed luminosities are merely from the cooling of the WDs, these estimated values of Q represent upper limits. A large Q_1 for the He WD means its spin velocity will be slower than that expected if it was tidally locked, which, since the binary is eclipsing, may be measurable via the Rossiter-McLaughlin effect. After one year, gravitational wave emission shifts the time of eclipses by 5.5 s, but tidal interactions cause the orbit to shrink more rapidly, changing the time by up to an additional 0.3 s after a year. Future eclipse timing measurements may therefore infer the degree of tidal locking. Added by F. Förster

[|arXiv:1108.3141] [[|pdf], [|ps], [|other]] = Title: First ground-based CCD proper motions for Fornax II: Final results= Authors: [|Rene. A. Mendez], [|Edgardo Costa], [|Carme Gallart], [|Mario H. Pedreros], [|Maximiliano Moyano], [|Martin Altmann] Comments: Accepted by AJ. 25 pages, 9 figures, 9 tables. Interesting conclusions...Enjoy! Subjects: Galaxy Astrophysics (astro-ph.GA) ; Solar and Stellar Astrophysics (astro-ph.SR) We present the first entirely ground-based astrometric determination of the proper motion for the Fornax Local Group Dwarf Spheroidal satellite galaxy of the Milky Way, using CCD data acquired with the ESO 3.5 m NTT telescope at La Silla Observatory in Chile. Our unweighted mean from five Quasar fields in the background of Fornax, used as fiducial reference points, leads to $\mu_\alpha \cos \delta=0.62 \pm 0.16$ $\masy$, and $\mu_\delta=-0.53 \pm 0.15$ $\masy$. A detailed comparison with all previous measurements of this quantity seems to imply that there is still no convincing convergence to a single value, perhaps indicating the existence of unnacounted systematic effects in (some of) these measurements. From all available proper motion and radial velocity measurements for Fornax, we compute Fornax's orbital parameters and their uncertainty using a realistic Galactic potential and a Monte Carlo simulation. Properties of the derived orbits are then compared to main star formation episodes in the history of Fornax.

All published proper motion values imply that Fornax has recently (200-300 Myr ago) approached perigalacticon at a distance of $\sim$150 kpc. However, the derived period exhibits a large scatter, as does the apogalacticon. Our orbit, being the most energetic, implies a very large apogalactic distance of $\sim 950$ kpc. If this were the case, then Fornax would be a representative of an hypervelocity MW satellite in late infall. Added by R. Méndez

=16 Aug 2011:=

[|arXiv:1108.2869v1] =Systematic Blueshift of Line Profiles in the Type IIn Supernova 2010jl: Evidence for Post-Shock Dust Formation?= Authors: [|Nathan Smith], [|Jeffrey M. Silverman], [|Alexei V. Filippenko], [|Michael C. Cooper], [|Thomas Matheson], [|Fuyan Bian], [|Benjamin J. Weiner], [|Julia M. Comerford] (Submitted on 14 Aug 2011) Abstract: Type IIn SNe show spectral evidence for strong interaction between their blast wave and dense circumstellar material (CSM) around the progenitor star. SN2010jl was the brightest core-collapse SN in 2010, and it was a Type IIn explosion with strong CSM interaction. Andrews et al. recently reported evidence for an IR excess in SN2010jl, indicating either new dust formation or the heating of CSM dust in an IR echo. Here we report multi-epoch spectra of SN2010jl that reveal the tell-tale signature of new dust formation: emission-line profiles becoming systematically more blueshifted as the red side of the line is blocked by increasing extinction. The effect is seen clearly in the intermediate-width (400--4000 km/s) component of H$\alpha$ beginning roughly 30d after explosion. Moreover, we present near-IR spectra demonstrating that the asymmetry in the hydrogen-line profiles is wavelength dependent, appearing more pronounced at shorter wavelengths. This evidence suggests that new dust grains had formed quickly in the post-shock shell of SN 2010jl arising from CSM interaction. Since the observed dust temperature has been attributed to an IR echo and not to new dust, either (1) IR excess emission at $\lambda < 5 \mu$m is not a particularly sensitive tracer of new dust formation in SNe, or (2) some assumptions about expected dust temperatures might require further study. Lastly, we discuss one possible mechanism other than dust that might lead to increasingly blueshifted line profiles in SNeIIn, although the wavelength dependence of the asymmetry argues against this hypothesis in the case of SN2010jl. Added by J. Anderson

[|arXiv:1108.2868v1] =SN2010jp (PTF10aaxi): A Jet-Driven Type II Supernova= Authors: [|Nathan Smith], [|S. Bradley Cenko], [|Nat Butler], [|Joshua S. Bloom], [|Mansi M. Kasliwal], [|Assaf Horesh], [|Shrinivas R. Kulkarni], [|Nicholas M. Law], [|Peter E. Nugent], [|Eran O. Ofek], [|Dovi Poznanski], [|Robert M. Quimby], [|Branimir Sesar], [|Sagi Ben-Ami], [|Iair Arcavi], [|Avishay Gal-Yam], [|David Polishook], [|Dong Xu], [|Ofer Yaron], [|Dale A. Frail], [|Mark Sullivan] (Submitted on 14 Aug 2011) Abstract: We present photometry and spectroscopy of the peculiar TypeII supernova (SN) 2010jp, also named PTF10aaxi. The light curve exhibits a linear decline with a relatively low peak absolute magnitude of only -15.9, and a low radioactive decay luminosity at late times that suggests a nickel mass below 0.003 $M_{\odot}$. Spectra of SN2010jp display an unprecedented triple-peaked H$\alpha$ line profile, showing: (1) a narrow (800 km/s) central component that suggests shock interaction with dense CSM; (2) high-velocity blue and red emission features centered at -12600 and +15400 km/s; and (3) broad wings extending from -22000 to +25000 km/s. These features persist during 100 days after explosion. We propose that this line profile indicates a bipolar jet-driven explosion, with the central component produced by normal SN ejecta and CSM interaction at mid latitudes, while the high-velocity bumps and broad line wings arise in a nonrelativistic bipolar jet. Two variations of the jet interpretation seem plausible: (1) A fast jet mixes 56Ni to high velocities in polar zones of the H-rich envelope, or (2) the reverse shock in the jet produces blue and red bumps in Balmer lines when a jet interacts with dense CSM. Jet-driven SNeII are predicted for collapsars resulting from a wide range of initial masses above 25 $M_{\odot}$ at sub-solar metallicity. This seems consistent with the SN host environment, which is either an extremely low-luminosity dwarf galaxy or very remote parts of an interacting pair of star-forming galaxies. It also seems consistent with the low 56Ni mass that may accompany black hole formation. We speculate that the jet survives to produce observable signatures because the star's H envelope was mostly stripped away by previous eruptive mass loss. Added by J. Anderson

[|arXiv:1108.2711] [[|pdf], [|ps], [|other]] = Title: Galaxy pairs in the Sloan Digital Sky Survey - IV: Interactions trigger AGN= Authors: [|Sara L. Ellison], [|David R. Patton], [|J. Trevor Mendel], [|Jillian M. Scudder] Comments: Accepted for publication in MNRAS Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO) Galaxy-galaxy interactions are predicted to cause gas inflows leading to enhanced nuclear star formation. In this paper we test the further prediction that the gas inflows lead to enhanced accretion onto the central supermassive black hole, triggering activity in the nucleus. Based on a sample of 11,060 SDSS galaxies with a close companion (rp < 80 kpc, Delta V < 200 km/s), we classify AGN based either on emission line ratios or on spectral classification as a quasar. The AGN fraction in the close pairs sample is compared to a control sample of 110,600 mass- and redshift-matched control galaxies with no nearby companion. We find a clear increase in the AGN fraction in close pairs of galaxies with projected separations < 40 kpc by up to a factor of 2.5 relative to the control sample (although the enhancement depends on the chosen S/N cut of the sample). The increase in AGN fraction is strongest in equal mass galaxy pairings, and weakest in the lower mass component of an unequal mass pairing. The increased AGN fraction at small separations is accompanied by an enhancement in the number of `composite' galaxies whose spectra are the result of photoionization by both AGN and stars. Our results indicate that AGN activity occurs (at least in some cases) well before final coalescence and concurrently with ongoing star formation. Finally, we find a marked increase at small projected separations of the fraction of pairs in which BOTH galaxies harbour AGN. We demonstrate that the fraction of double AGN exceeds the expected random fraction, indicating that some pairs undergo correlated nuclear activity. Taken together with complimentary studies, we favour an interpretation where interactions trigger AGN, but are not the only cause of nuclear activity. Added by F.Förster

=15 Aug 2011:=

[|arXiv:1108.2508] [[|pdf], [|ps], [|other]] = Title: The Major and Minor Galaxy Merger Rates at z < 1.5= Authors: [|Jennifer M. Lotz] (1,2), [|Patrik Jonsson] (3), [|T.J. Cox] (4), [|Darren Croton] (5), [|Joel R. Primack] (6), [|Rachel S. Somerville] (1,7), [|Kyle Stewart] (8) ((1) STScI, (2) NOAO, (3) Harvard-Smithsonian CfA, (4) Carnegie Observatories, (5) Swinburne University, (6) UC Santa Cruz, (7) JHU, (8) JPL) Comments: accepted by ApJ; 25 pages; 13 figures; 4 tables Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO) Calculating the galaxy merger rate requires both a census of galaxies identified as merger candidates, and a cosmologically-averaged `observability' timescale T_obs(z) for identifying galaxy mergers. While many have counted galaxy mergers using a variety of techniques, T_obs(z) for these techniques have been poorly constrained. We address this problem by calibrating three merger rate estimators with a suite of hydrodynamic merger simulations and three galaxy formation models. We estimate T_obs(z) for (1) close galaxy pairs with a range of projected separations, (2) the morphology indicator G-M20, and (3) the morphology indicator asymmetry A. Then we apply these timescales to the observed merger fractions at z < 1.5 from the recent literature. When our physically-motivated timescales are adopted, the observed galaxy merger rates become largely consistent. The remaining differences between the galaxy merger rates are explained by the differences in the range of mass-ratio measured by different techniques and differing parent galaxy selection. The major merger rate per unit co-moving volume for samples selected with constant number density evolves much more strongly with redshift (~ (1+z)^(+3.0 \pm 1.1)) than samples selected with constant stellar mass or passively evolving luminosity (~ (1+z)^(+0.1 \pm 0.4)). We calculate the minor merger rate (1:4 < M_{sat}/M_{primary} <~ 1:10) by subtracting the major merger rate from close pairs from the `total' merger rate determined by G-M20. The implied minor merger rate is ~3 times the major merger rate at z ~ 0.7, and shows little evolution with redshift. Added by F. Förster

[|arXiv:1108.2645] [[|pdf], [|ps], [|other]] = Title: The Massive Progenitor of the Possible Type II-Linear Supernova 2009hd in Messier 66= Authors: [|Nancy Elias-Rosa] (1,2,3), [|Schuyler D. Van Dyk] (1), [|Weidong Li] (2), [|Jeffrey M. Silverman] (2), [|Ryan J. Foley] (4,5), [|Mohan Ganeshalingam] (2), [|Jon C. Mauerhan] (1), [|Erkki Kankare] (6,7), [|Saurabh Jha] (8), [|Alexei V. Filippenko] (2), [|John E. Beckman] (9,10), [|Edo Berger] (4), [|Jean-Charles Cuillandre] (11), [|Nathan Smith] (2,12) ((1) Spitzer Science Center/Caltech, (2) UC Berkeley, (3) ICE (IEEC-CSIC), (4) CfA, (5) Clay Fellow, (6) Tuorla Observatory, (7) NOT, (8) Rutgers University, (9) IAC, (10) CSIC, (11) IfA/Hawaii, (12) University of Arizona) Comments: 19 pages, 9 figures, 3 tables, accepted for publication in ApJ Subjects: Solar and Stellar Astrophysics (astro-ph.SR) We present observations of SN2009hd in the nearby galaxy M66. This SN is one of the closest to us in recent years but heavily obscured by dust, rendering it unusually faint in the optical, given its proximity. We find that the observed properties of SN2009hd support its classification as a possible Type II-L SN, a relatively rare subclass of CC-SNe. High-precision relative astrometry has been employed to attempt to identify a SN progenitor candidate, based on a pixel-by-pixel comparison between HST F555W and F814W images of the SN site prior to explosion and at late times. A progenitor candidate is identified in the F814W images only; this object is undetected in F555W. Significant uncertainty exists in the astrometry, such that we cannot definitively identify this object as the SN progenitor. Via insertion of artificial stars into the pre-SN HST images, we are able to constrain the progenitor's properties to those of a possible supergiant, with M(F555W)0>-7.6 mag and (V-I) 0>0.99 mag. The magnitude and color limits are consistent with a luminous RSG; however, they also allow for the possibility that the star could have been more yellow than red. From a comparison with theoretical massive-star evolutionary tracks, which include rotation and pulsationally enhanced mass loss, we can place a conservative upper limit on the initial mass for the progenitor of <20 M_sun. If the actual mass of the progenitor is near the upper range allowed by our derived mass limit, then it would be consistent with that for the identified progenitors of the SNII-L 2009kr and the high-luminosity SNII-P 2008cn. The progenitors of these three SNe may possibly bridge the gap between lower-mass RSG that explode as SNeII-P and LBV, or more extreme RSG, from which the more exotic SNeII-n may arise. Very late-time imaging of the SN2009hd site may provide us with more clues regarding the true nature of its progenitor. Added by F.Förster

[|arXiv:1108.2692] [[|pdf], [|ps], [|other]] = Title: Radio Emission from SN 1994I in NGC 5194 (M 51) - The Best Studied Type Ib/c Radio Supernova= Authors: [|Kurt W. Weiler], [|Nino Panagia], [|Christopher Stockdale], [|Michael Rupen], [|Richard A. Sramek], [|Christopher L. Williams] Comments: 43 pages, 5 figures Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO) We present the results of detailed monitoring of the radio emission from the Type Ic supernova SN 1994I from 3 days after optical discovery on 1994 March 31 until eight years later at age 2927 days on 2002 April 05. The data were mainly obtained using the Very Large Array at the five wavelengths, 1.3, 2.0, 3.6, 6.2, and 21 cm, and from the Cambridge 5 km Ryle Telescope at 2.0 cm. Two additional measurements were obtained at millimeter wavelengths. This data set represents the most complete, multifrequency radio observations ever obtained for a Type Ib/c supernova. The radio emission evolves regularly in both time and frequency and is well described by established SN emission/absorption models. It is the first radio supernova with sufficient data to show that it is clearly dominated by the effects of synchrotron self-absorption at early times. Added by F.Förster

=11 Aug 2011:=

[|arXiv:1108.2257] [[|pdf], [|ps], [|other]] = Title: Formation of Bipolar Planetary Nebulae by Intermediate-Luminosity Optical Transients= Authors: [|Noam Soker], [|Amit Kashi] (Technion, Israel) Comments: Submitted Subjects: Solar and Stellar Astrophysics (astro-ph.SR) We present surprising similarities between some bipolar planetary nebulae (PNe) and eruptive objects with peak luminosity between novae and supernovae. The later group is termed ILOT for intermediate luminosity optical transients (other terms are intermediate luminosity red transients and red novae). In particular we compare the PN NGC 6302 and the pre-PNe OH231.8+4.2, M1-92 and IRAS 22036+5306 with the ILOT NGC 300OT2008-1. These similarities lead us to propose that the lobes of some (but not all) PNe and pre-PNe were formed in an ILOT event (or several close sub-events). We suggest that in both types of objects the several months long outbursts are powered by mass accretion onto a main-sequence companion to an AGB (or extreme-AGB) star. Jets launched by an accretion disk around the main-sequence companion shape the bipolar lobes. Some of the predictions that result from our comparison is that the ejecta of some ILOTs will have morphologies similar to those of bipolar PNe, and that the central stars of the PNe that were shaped by ILOTs should have a main-sequence binary companion with an eccentric orbit of several years long period. Added by F.Förster

=10 Aug 2011:=

[|arXiv:1108.1792] [[|pdf], [|other]] = Title: Magnetohydrodynamics on an unstructured moving grid= Authors: [|Ruediger Pakmor], [|Andreas Bauer], [|Volker Springel] Comments: 11 pages, 9 figures, accepted by MNRAS Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM) Magnetic fields play an important role in astrophysics on a wide variety of scales, ranging from the Sun and compact objects to galaxies and galaxy clusters. Here we discuss a novel implementation of ideal magnetohydrodynamics (MHD) in the moving mesh code AREPO which combines many of the advantages of Eulerian and Lagrangian methods in a single computational technique. The employed grid is defined as the Voronoi tessellation of a set of mesh-generating points which can move along with the flow, yielding an automatic adaptivity of the mesh and a substantial reduction of advection errors. Our scheme solves the MHD Riemann problem in the rest frame of the Voronoi interfaces using the HLLD Riemann solver. To satisfy the divergence constraint of the magnetic field in multiple dimensions, the Dedner divergence cleaning method is applied. In a set of standard test problems we show that the new code produces accurate results, and that the divergence of the magnetic field is kept sufficiently small to closely preserve the correct physical solution. We also apply the code to two first application problems, namely supersonic MHD turbulence and the spherical collapse of a magnetized cloud. We verify that the code is able to handle both problems well, demonstrating the applicability of this MHD version of AREPO to a wide range of problems in astrophysics. Added by F.Förster

=9 Aug 2011:=

[|arXiv:1108.1415] [[|pdf], [|other]] = Title: Simulations of Accretion Powered Supernovae in the Progenitors of Gamma Ray Bursts= Authors: [|Christopher C. Lindner], [|Milos Milosavljevic], [|Rongfeng Shen], [|Pawan Kumar] Comments: 20 Pages, 15 Figures, Submitted to ApJ Subjects: High Energy Astrophysical Phenomena (astro-ph.HE) Observational evidence suggests a link between long duration gamma ray bursts (LGRBs) and Type Ic supernovae. Here, we propose a potential mechanism for Type Ic supernovae in LGRB progenitors powered solely by accretion energy. We present spherically-symmetric hydrodynamic simulations of the long-term accretion of a rotating gamma-ray burst progenitor star, a "collapsar," onto the central compact object, which we take to be a black hole. The simulations were carried out with the adaptive mesh refinement code FLASH in one spatial dimension and with rotation, an explicit shear viscosity, and convection in the mixing length theory approximation. Once the accretion flow becomes rotationally supported outside of the black hole, an accretion shock forms and traverses the stellar envelope. Energy is carried from the central geometrically thick accretion disk to the stellar envelope by convection. Energy losses through neutrino emission and nuclear photodisintegration are calculated but do not seem important following the rapid early drop of the accretion rate following circularization. We find that the shock velocity, energy, and unbound mass are sensitive to convective efficiency, effective viscosity, and initial stellar angular momentum. Our simulations show that given the appropriate combinations of stellar and physical parameters, explosions with energies ~0.5 Bethes, velocities ~3000 km/s, and unbound material masses > 5 solar masses are possible in a rapidly rotating 16 solar mass main sequence progenitor star. Further work is needed to constrain the values of these parameters, to identify the likely outcomes in more plausible and massive LRGB progenitors, and to explore nucleosynthetic implications. Added by F.Förster

[|arXiv:1108.1604] [[|pdf], [|ps], [|other]] = Title: Solar differential rotation: origin, models, and implications for dynamo= Authors: [|L. L. Kitchatinov] Comments: 10 pages, 5 figures, Proceedings of 1st Asia-Pacific Solar Physics Meeting Subjects: Solar and Stellar Astrophysics (astro-ph.SR) Helioseismology shows that the regions occupied by convection and differential rotation inside the sun almost coincide. This supports the leading theoretical concept for the origin of differential rotation as a result of interaction between convection and rotation. This talk outlines the current state of the differential rotation theory. Numerical models based on the theory reproduce the observed solar rotation quite closely. The models also compute meridional flow and predict that the flow at the bottom of the convection zone is not small compared to the surface. Theoretical predictions for stellar differential rotation as a function of the stellar mass and rotation rate are discussed and compared with observations. The implications of the differential rotation models for solar and stellar dynamos are briefly discussed. Added by F.Förster

=8 Aug 2011:=

[|arXiv:1108.1207] [[|pdf], [|ps], [|other]] = Title: RCW 86: A Type Ia Supernova in a Wind-Blown Bubble= Authors: [|Brian J. Williams], [|William P. Blair], [|John M. Blondin], [|Kazimierz J. Borkowski], [|Parviz Ghavamian], [|Knox S. Long], [|John C. Raymond], [|Stephen P. Reynolds], [|Jeonghee Rho], [|P. Frank Winkler] Comments: Accepted for publication in ApJ. 50 pages, 9 figures Subjects: Galaxy Astrophysics (astro-ph.GA) We report results from a multi-wavelength analysis of the Galactic SNR RCW 86, the proposed remnant of the supernova of 185 A.D. We report new infrared observations from {\it Spitzer} and {\it WISE}, where the entire shell is detected at 24 and 22 $\mu$m. We fit the infrared flux ratios with models of collisionally heated ambient dust, finding post-shock gas densities in the non-radiative shocks of 2.4 and 2.0 cm$^{-3}$ in the SW and NW portions of the remnant, respectively. The Balmer-dominated shocks around the periphery of the shell, large amount of iron in the X-ray emitting ejecta, and lack of a compact remnant support a Type Ia origin for this remnant. From hydrodynamic simulations, the observed characteristics of RCW 86 are successfully reproduced by an off-center explosion in a low-density cavity carved by the progenitor system. This would make RCW 86 the first known case of a Type Ia supernova in a wind-blown bubble. The fast shocks ($> 3000$ km s$^{-1}$) observed in the NE are propagating in the low-density bubble, where the shock is just beginning to encounter the shell, while the slower shocks elsewhere have already encountered the bubble wall. The diffuse nature of the synchrotron emission in the SW and NW is due to electrons that were accelerated early in the lifetime of the remnant, when the shock was still in the bubble. Electrons in a bubble could produce gamma-rays by inverse-Compton scattering. The wind-blown bubble scenario requires a single-degenerate progenitor, which should leave behind a companion star. Added by F.Förster

[|arXiv:1108.1226] [[|pdf], [|ps], [|other]] = Title: Common envelope: the progress and the pitfalls= Authors: [|Natalia Ivanova] Comments: 15 pages, 2 figures, invited review talk. To appear in the proceedings for the ESO Conference, the workshop 'Evolution of Compact Binaries', 6-11 March 2011, Vi\~na del Mar, Chile, edited by L. Schmidtobreick, M. R. Schreiber, C. Tappert, ASP conference series Subjects: Solar and Stellar Astrophysics (astro-ph.SR) ; High Energy Astrophysical Phenomena (astro-ph.HE)The common envelope event is one of the most important and uncertain evolutionary stages that lead to formation of compact binaries. While the problem is almost 30 years old, its theoretical foundation did not progress much from the first proposed consideration. For many years, the simple estimate provided by \alpha \lambda-formalism has been intensively used by population synthesis studies and, not surprisingly, frequently contradicted observations. In recent years, the advancements in our studies of stellar structure, progress of the numerical techniques for hydrodynamical simulations as well as increase of the computer power and new observations started to bring improvements to our understanding of the common envelope phase. We review main physical processes taking place during the common envelope phase from the theoretical point of view and how they affect the values of classical formal parameters. In particular, we discuss the energy budget problem -- what are the energy sources, sinks and what is the condition for the envelope to disperse, as well as the importance of choosing the definition of the remnant core to the common envelope outcome. Added by F.Förster

=5 Aug 2011:=

[|arXiv:1108.0946] [[|pdf], [|ps], [|other]] = Title: On the Radial Stellar Content of Early-Type Galaxies as a Function of Mass and Environment= Authors: [|F. La Barbera], [|I. Ferreras], [|R.R. de Carvalho], [|P.A.A. Lopes], [|A. Pasquali], [|I.G. de la Rosa], [|G. De Lucia] Comments: 2 figures, accepted for publication on ApJL Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO) Using optical-optical and optical-NIR colors, we analyze the radial dependence of age and metallicity inside massive (M* > 10^10.5 MSun), low-redshift (z<0.1), early-type galaxies (ETGs), residing in both high-density group regions and the field. On average, internal color gradients of ETGs are mainly driven by metallicity, consistent with previous studies. However, we find that group galaxies feature positive age gradients, Nabla_t, i.e. a younger stellar population in the galaxy center, and steeper metallicity gradients, compared to the field sample, whose Nabla_t ranges from negative in lower mass galaxies, to positive gradients at higher mass. These dependencies yield new constraints to models of galaxy formation and evolution. We speculate that age and metallicity gradients of group ETGs result from (either gas-rich or minor-dry) mergers and/or cold-gas accretion, while field ETGs exhibit the characteristic flatter gradients expected from younger, more metal-rich, stars formed inside--out by later gas-cooling. Added by F.Förster

=4 Aug 2011:=

[|arXiv:1108.0681] [[|pdf], [|ps], [|other]] = Title: On The Formation of Double White Dwarfs: Reevaluating How We Parametrize the Common Envelope Phase= Authors: [|T.E. Woods], [|N. Ivanova], [|M. van der Sluys], [|S. Chaichenets] Comments: 6 pages, 2 figures. Proceedings for the ESO Conference, the workshop 'Evolution of Compact Binaries', 6-11 March 2011, Vi\~na del Mar, Chile, edited by L. Schmidtobreick, M. R. Schreiber, C. Tappert, ASP conference series Subjects: Solar and Stellar Astrophysics (astro-ph.SR) One class of compact binaries of special interest is that of double white dwarfs (DWDs). For many of these systems, the exact nature of the evolutionary channels by which they form remains uncertain. The canonical explanation calls for the progenitor binary system to undergo two subsequent mass-transfer events, both of which are unstable and lead to a common envelope (CE) phase. However, it has been shown that if both CE events obey the standard alpha prescription, it is not possible to reproduce all of the observed systems. As an alternative prescription, the gamma-formalism was proposed, which parametrizes the fraction of angular momentum carried away with mass loss, in contrast to the alpha prescription, which parametrizes energy loss. We demonstrate that the gamma-prescription is also inadequate in describing the evolution of an arbitrary DWD binary; clearly we require a deeper understanding of the physical mechanisms underlying their formation. We then present a detailed model for the evolution of Red Giant -- Main Sequence binaries during the first episode of mass transfer, and demonstrate that their evolution into DWDs need not arise through two phases of dynamical mass loss. Instead, the first episode of dramatic mass loss may be stable, non-conservative mass transfer. The second phase is then well described by the alpha prescription. We find that the considered progenitors can reproduce the properties of the observed helium DWDs in which the younger component is the more massive. Added by F.Förster

[|arXiv:1108.0663] [[|pdf], [|ps], [|other]] = Title: The Angular Momentum of Disk Galaxies: Implications for Gas Accretion, Outflows, and Dynamical Friction= Authors: [|Aaron A. Dutton] (Victoria), [|Frank C. van den Bosch] (Yale) Comments: 14 pages, 11 figures, submitted to MNRAS Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO) ; Galaxy Astrophysics (astro-ph.GA) We combine constraints on the galaxy-dark matter connection with structural and dynamical scaling relations to investigate the angular momentum content of disk galaxies. For haloes with masses in the interval 10^{11.3}M_sun < M_vir < 10^{12.7}M_sun we find that the galaxy spin parameters are basically independent of halo mass with <\lambda'_gal> (J_gal/M_gal) / (\sqrt{2} R_vir V_vir) 0.019^{+0.004}_{-0.003} (1sigma). This is significantly lower than for relaxed LCDM haloes, which have an average spin parameter <\lambda'_halo> 0.031. The average ratio between the specific angular momentum of disk galaxies and their host dark matter haloes is therefore R_{j} \lambda'_gal/\lambda'_halo = 0.61^{+0.13}_{-0.10}. This calls into question a standard assumption made in the majority of all (semi-analytical) models for (disk) galaxy formation, namely that R_{j}=1. Using simple disk formation models we show that it is particularly challenging to understand why R_{j} is independent of halo mass, while the galaxy formation efficiency (\epsilon_{GF}, proportional to the ratio of galaxy mass to halo mass) reveals a strong halo mass dependence. We argue that the empirical scaling relations between \epsilon_{GF}, R_{j} and halo mass require both feedback (i.e., galactic outflows) and angular momentum transfer from the baryons to the dark matter (i.e., dynamical friction). The efficiency of angular momentum loss need to decrease with increasing halo mass. Such a mass dependence may reflect a bias against forming stable disks in high mass, low spin haloes or a transition from cold-mode accretion in low mass haloes to hot-mode accretion at the massive end. However, current hydrodynamical simulations of galaxy formation, which should include these processes, seem unable to reproduce the empirical relation between \epsilon_{GF} and R_{j}. We conclude that the angular momentum build-up of galactic disks remains poorly understood. Added by A. Escala