Interesting Astrophysics: Mar 16 to Mar 20

An unusually large crop of interesting star/supernova/star cluster related preprints attracted my attention this week. From the largest (radius) star in the LMC through photon-tiring in radiation driven winds, super-hard X-ray emission from Eta Carinae, to an anomaly with the classic wind-blown bubble, the "Bubble Nebula."

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Galaxies and Starbursts

The Relationship Between Intergalactic HI/OVI and Nearby (z<0.017) Galaxies
B.P. Wakker, B.D. Savage, arXiv:0903.2259 [ps, pdf, other]
Comments: ApJ Supplement, in press

On the massive star content of the nearby dwarf irregular Wolf-Rayet galaxy IC 4662
P.A. Crowther, J.L. Bibby, arXiv:0903.2288 [ps, pdf, other]
Comments: 10 pages, 4 figures, accepted for Astronomy & Astrophysics

The Vela Cloud: A Giant HI Anomaly in the NGC 3256 Group
Jayanne English, Baerbel Koribalski, Joss Bland-Hawthorn, Ken Freeman, Claudia McCain, arXiv:0903.2690 [ps, pdf, other]
Comments: 46 pages, 11 figures, submitted to AJ

The chemical evolution of galaxies within the IGIMF theory: the [alpha/Fe] ratios and downsizing
Simone Recchi, Francesco Calura, Pavel Kroupa, arXiv:0903.2395 [ps, pdf, other]
Comments: 13 pages, 18 figures, accepted for publication in Astronomy and Astrophysics

The Star Formation Law at Low Surface Density
Ted K. Wyder, et al, arXiv:0903.3015 [ps, pdf, other]
Comments: 53 pages, 21 Figures, accepted for publication in the ApJ

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Black Holes and AGN

X-ray Properties of Intermediate-Mass Black Holes in Active Galaxies. II. X-ray-Bright Accretion and Possible Evidence for Slim Disks
Louis-Benoit Desroches, Jenny E. Greene, Luis C. Ho, arXiv:0903.2257 [ps, pdf, other]
Comments: 11 pages, 6 figures, submitted to ApJ, emulateapj

The Suzaku View of the Swift/BAT AGNs (II): Time Variability and Spectra of Five "Hidden" AGNs
Lisa Winter, Richard Mushotzky, Yuichi Terashima, Yoshihiro Ueda, arXiv:0903.2802 [ps, pdf, other]
Comments: 45 pages, 16 figures, 10 tables, accepted to ApJ

Journey to the $M_{\rm BH} - \sigma$ relation: the fate of low mass black holes in the Universe
Marta Volonteri, Priyamvada Natarajan, arXiv:0903.2262 [pdf, other]
Comments: 8 pages, 5 figures, submitted to MNRAS

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Numerical Astrophysics and Hydrodynamics

Simulating Magnetohydrodynamical Flow with Constrained Transport and Adaptive Mesh Refinement; Algorithms & Tests of the AstroBEAR Code
Andrew J. Cunningham, Adam Frank, Peggy Varniere, Sorin Mitran, Thomas W. Jones, arXiv:0710.0424 (replaced) [ps, pdf, other]
Comments: Additional Tests shown. Accepted to ApJS

Includes some images showing the interaction between a cylindrical cloud moving though an ambient medium with a magnetic field oriented in various directions w.r.t the cloud motion. B fields at 45 or 90 degree to the cloud motion/axis lead to less cloud disruption than if the B field is parallel to the cloud axis/motion.

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Stars, Supernovae and Planets

The Physical Properties of the Red Supergiant WOH G64: The Largest Star Known?
Emily M. Levesque, Philip Massey, Bertrand Plez, Knut A. G. Olsen, arXiv:0903.2260 [ps, pdf, other]
Comments: 25 pages, 5 figures; accepted for publication in The Astronomical Journal

Super-hard X-Ray Emission from eta Carinae Observed with Suzaku
Akiko Sekiguchi, Masahiro Tsujimoto, Shunji Kitamoto, Manabu Ishida, Kenji Hamaguchi, Hideyuki Mori, Yohko Tsuboi, arXiv:0903.3307 [ps, pdf, other]
Comments: Accepted for publication in PASJ (10 pages, 7 Postscript figures)

Interestingly they argue that the 15-50 keV emission is either Inverse Compton emission arising between stellar UV photons and non-thermal electrons "or to the thermal bremsstrahlung of very hot plasma, and not to the bremsstrahlung by non-thermal electrons colliding with cold ambient matter."

On the behaviour of stellar winds that exceed the photon-tiring limit
Allard Jan van Marle, Stanley P. Owocki, Nir J. Shaviv, MNRAS, 2009, 394, 595
Full Text: HTML, PDF (Size: 9132K)

A steady-state continuum radiation-driven wind not have a mechanical luminosity exceeding the radiative luminosity at its base (the photon tiring limit). This paper explores non-steady state winds beyond the photon tiring limit. Interesting also w.r.t radiation-driven winds from AGN perhaps?

Unsolved Problems about Supernovae
Nino Panagia, arXiv:0903.3378 [ps, pdf, other]
Comments: 7 pages, Proceedings of 'Probing Stellar Populations out to the Distant Universe', Cefalu, Italy, Sep 7-19, 2008, AIP Conf. Proc. Series

Three-dimensional numerical model of the Omega Nebula (M17): simulated thermal X-ray emission
J. Reyes-Iturbide, P. F. Velázquez, M. Rosado, A. Rodríguez-González, R. F. González, A. Esquivel, 2009, MNRAS, 394, 1009
Full Text: HTML, PDF (Size: 4758K)

Study of Bubble Nebula using IUE high resolution Spectra
M. Y. Anand, B. A. I Kagali, Jayant Murthy, arXiv:0903.2828 [ps, pdf, other]
Comments: 9 pages, 6 figures, accepted in BASI

Interesting. Yet another expansion velocity - bubble size - stellar age anomaly, and this time in a spherical bubble around a main sequence star that really should follow the Weaver bubble model. The dynamical age of a wind blown bubble t_bub = 0.6*R_bub/v_bub, in this case ~3e4 years, which is much smaller than the age of the main sequence O star thought to have blown the bubble (~2e6 years). Yet the expansion velocity of v_bub ~ 36 km/s is high enough that there is no reason to suspect the bubble has stalled, and its near perfect shape does not suggest irregular expansion.