THE MAGELLANIC CLOUDS NEWSLETTER an Electronic Publication Dedicated to the Magellanic Clouds, and Astrophysical Phenomena Therein
Total Page：16
File Type：pdf, Size：1020Kb
THE MAGELLANIC CLOUDS NEWSLETTER An electronic publication dedicated to the Magellanic Clouds, and astrophysical phenomena therein No. 104 — 2 April 2010 http://www.astro.keele.ac.uk/MCnews Editor: Jacco van Loon Editorial Dear Colleagues, It is my pleasure to present you the 104th issue of the Magellanic Clouds Newsletter. Marvel at the MAD images of the heart of the Tarantula Nebula’s nest of massive stars, or be amazed by the three (sic!) papers on SN 1987 A alone (plus one about its surrounding field) and the two papers on supernova remnants and their progenitors by Maoz & Badenes (and Draine). The PDF version of this newsletter contains a two-page advertisement for a special issue of the Royal Society’s Philo- sophical Transactions, on the topic of star clusters. There is an attractive discount being offered on buying this book. This issue does not feature a cover picture as no suggestions were received. They remain very welcome for future issues. The next issue is planned to be distributed on the 1st of June 2010. Editorially Yours, Jacco van Loon 1 Refereed Journal Papers VLT-MAD observations of the core of 30 Doradus M.A. Campbell1, C.J. Evans2,1, A.D. Mackey1, M. Gieles3, J. Alves4, J. Ascenso5, N. Bastian6 and A.J. Longmore2 1Institute for Astronomy, The University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK 2UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK 3European Southern Observatory, Casilla 19001, Santiago 19, Chile 4Calar Alto Observatory-Centro Astron´omico Hispano-Alem´an, C/ Jes´us Durb´an Rem´on 2-2, 04004 Almeria, Spain 5Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA 6Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK We present H- and Ks-band imaging of three fields at the centre of 30 Doradus in the Large Magellanic Cloud, obtained as part of the Science Demonstration programme with the Multi-conjugate Adaptive optics Demonstrator (MAD) at the Very Large Telescope. Strehl ratios of 15–30% were achieved in the Ks-band, yielding near-infrared images of this dense and complex region at unprecedented angular resolution at these wavelengths. The MAD data are used to construct a near-infrared luminosity profile for R 136, the cluster at the core of 30 Dor. Using cluster profiles of the form used by Elson et al., we find the surface brightness can be fit by a relatively shallow power-law function (γ ∼ 1.5–1.7) over the full extent of the MAD data, which extends to a radius of ∼ 40′′ (∼ 10 pc). We do not see compelling evidence for a break in the luminosity profile as seen in optical data in the literature, arguing that cluster asymmetries are the dominant source, although extinction effects and stars from nearby triggered star-formation likely also contribute. These results highlight the need to consider cluster asymmetries and multiple spatial components in interpretation of the luminosity profiles of distant unresolved clusters. We also investigate seven candidate young stellar objects reported by Gruendl & Chu from Spitzer observations, six of which have apparent counterparts in the MAD images. The most interesting of these (GC09 053839.24−690552.3) appears related to a striking bow-shock–like feature, orientated away from both R 136 and the Wolf-Rayet star Brey 75, at distances of 19.5′′ and 8′′ (4.7 and 1.9 pc in projection), respectively. Accepted for publication in MNRAS Available from arXiv:1002.0288 New tests for disruption mechanisms of star clusters: The Large and Small Magellanic Clouds Rupali Chandar1, S. Michael Fall2 and Bradley C. Whitmore2 1Department of Physics & Astronomy, University of Toledo, Toledo, OH 43606, USA 2Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA We compare the observed bivariate distribution of masses (M) and ages (t) of star clusters in the Large Magellanic Cloud (LMC) with the predicted distributions g(M, t) from three idealized models for the disruption of star clusters: (1) sudden mass-dependent disruption; (2) gradual mass-dependent disruption; and (3) gradual mass-independent disruption. The model with mass-independent disruption provides a good, first-order description of these cluster populations, with g(M, t) ∝ M βtγ , β = −1.8 ± 0.2 and γ = −0.8 ± 0.2, at least for clusters with ages t< 109 yr and 3 7 2 1.3 masses M < few ×10 M⊙ (more specifically, t< 10 (M/10 M⊙) yr). This model predicts that the clusters should have a power-law luminosity function, dN/dL ∝ L−1.8, in agreement with the observations. The first two models, on the other hand, fare poorly when describing the observations, refuting previous claims that mass-dependent disruption of star clusters is observed in the LMC over the studied M–t domain. Clusters in the SMC can be described by the same g(M, t) distribution as for the LMC, but with smaller samples and hence larger uncertainties. The successful g(M, t) model for clusters in the Magellanic Clouds is virtually the same as the one for clusters in the merging Antennae galaxies, but extends the domain of validity to lower masses and to older ages. This indicates that the dominant 2 disruption processes are similar in these very different galaxies over at least t < 108 yr and possibly t < 109 yr. The mass functions for young clusters in the LMC are power-laws, while that for ancient globular clusters is peaked. Ancient clusters in the LMC have a higher mean density than clusters with ages between t = 108–109 yr. We show that the observed shapes of the mass functions are consistent with expectations from the simple evaporation model presented by McLaughlin & Fall. Accepted for publication in Astrophysical Journal Available from arXiv:1002.0779 The column density towards LMC X-1 Manfred Hanke1, J. Wilms1, Michael A. Nowak2, Laura Barrag´an1 and Norbert S. Schulz2 1Dr. Karl Remeis-Observatory / ECAP, University of Erlangen-Nuremberg, Sternwartstr. 7, 96049 Bamberg, Germany 2MIT Kavli Institute for Astrophysics and Space Research, NE80-6077, 77 Mass. Ave., Cambridge, MA 02139, USA We measure the neutral absorption towards the black hole X-ray binary system LMC X-1 from six archival soft X-ray spectra obtained with the gratings and/or CCD detectors on Chandra, XMM-Newton, and Swift. Four spectral models for the soft continuum are investigated. While the powerlaw model may overestimate NH considerably, the others give consistent results. Taking the lower metalicity of the Large Magellanic Cloud into account, we find equivalent 22 −2 hydrogen column densities of NH = (1.0 − 1.3) × 10 cm , with a systematic dependence on the orbital phase. This variation in the neutral absorption can nearly explain the orbital modulation of the soft X-ray flux recently detected with the All Sky Monitor (ASM) on the Rossi X-ray Timing Explorer (RXTE). Published in Astronomy and Astrophysics, 509, L8 (2010) Available from arXiv:0912.3719 High Resolution X-Ray Spectroscopy of SN1987A: Monitoring with XMM-Newton Richard Sturm1, Frank Haberl1, Bernd Aschenbach1 and G¨unther Hasinger1,2 1Max-Planck-Institut f¨ur extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany 2Max-Planck-Institut f¨ur Plasmaphysik, Boltzmannstraße 2, 85748 Garching, Germany We report the results of our XMM-Newton monitoring of SN 1987 A. The ongoing propagation of the supernova blast wave through the inner circumstellar ring caused a drastic increase in X-ray luminosity during the last years, enabling detailed high resolution X-ray spectroscopy with the Reflection Grating Spectrometer. The observations can be used to follow the detailed evolution of the arising supernova remnant. The fluxes and broadening of the numerous emission lines seen in the dispersed spectra provide information on the evolution of the X-ray emitting plasma and its dynamics. These were analyzed in combination with the EPIC-pn spectra, which allow a precise determination of the higher temperature plasma. We modeled individual emission lines and fitted plasma emission models. Especially from the observations between 2003 and 2007 we can see a significant evolution of the plasma parameters and a deceleration of the radial velocity of the lower temperature plasma regions. We found an indication (3σ-level) of an iron K feature in the co-added EPIC-pn spectra. The comparison with Chandra grating observations in 2004 yields a clear temporal coherence of the spectral evolution and the sudden deceleration of the expansion velocity seen in X-ray images ∼6100 days after the explosion. Accepted for publication in A&A Available from arXiv:1002.1865 3 Observational constraints on the modified gravity model (MOG) proposed by Moffat: using the Magellanic System Hosein Haghi1 and Sohrab Rahvar2,3 1Institute for Advanced Studies in Basic Sciences (IASBS), P.O. Box 45195-1159, Zanjan, Iran 2Department of Physics, Sharif University of Technology, P.O. Box 11365-9161, Tehran, Iran 3School of Astronomy and Astrophysics, Institute for Research in Fundamental Sciences, (IPM), P.O. Box 19395-5531, Tehran, Iran A simple model for the dynamics of the Magellanic Stream (MS), in the framework of modified gravity models is investigated. We assume that the galaxy is made up of baryonic matter out of context of dark matter scenario. The model we used here is named Modified Gravity (MOG) proposed by Moffat (2005). In order to examine the compatibility of the overall properties of the MS under the MOG theory, the observational radial velocity profile of the MS is compared with the numerical results using the 2 fit method. In order to obtain the best model parameters, a maximum likelihood analysis is performed. We also compare the results of this model with the Cold Dark Matter (CDM) halo model and the other alternative gravity model that proposed by Bekenstein (2004), so called TeVeS.