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THE MAGELLANIC CLOUDS NEWSLETTER an Electronic Publication Dedicated to the Magellanic Clouds, and Astrophysical Phenomena Therein

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THE MAGELLANIC CLOUDS NEWSLETTER an Electronic Publication Dedicated to the Magellanic Clouds, and Astrophysical Phenomena Therein THE MAGELLANIC CLOUDS NEWSLETTER An electronic publication dedicated to the Magellanic Clouds, and astrophysical phenomena therein No. 129 — 2 June 2014 http://www.astro.keele.ac.uk/MCnews Editor: Jacco van Loon Editorial Dear Colleagues, It is my pleasure to present you the 129th issue of the Magellanic Clouds Newsletter. As always, there is a lot going on in the Magellanic Clouds as well as our research. Star clusters, star formation history, dust production, distance scales, a new look at the Magellanic Stream feeding the Milky Way... and (there is always) more... The next issue is planned to be distributed on the 1st of August. Editorially Yours, Jacco van Loon 1 Refereed Journal Papers Age determination of fifteen old to intermediate-age Small Magellanic Cloud star clusters M.C. Parisi1, D. Geisler2, G. Carraro3, J.J. Clari´a1, E. Costa4, A.J. Grocholski5, A. Sarajedini6, R. Leiton2 and A.E. Piatti1 1Observatorio Astron´omico, Universidad Nacional de C´ordoba, Argentina 2Departamento de Astronom´ıa, Universidad de Concepci´on, Chile 3European Southern Observatory, Chile 4Universidad de Chile, Chile 5Department of Physics and Astronomy, Louisiana State University, USA 6Department of Astronomy, University of Florida, USA We present CMDs in the V and I bands for fifteen star clusters in the Small Magellanic Cloud (SMC) based on data taken with the Very Large Telescope (VLT, Chile). We selected these clusters from our previous work Parisi et al. (2009, AJ, 138, 517), wherein we derived cluster radial velocities and metallicities from Calcium ii infrared triplet (CaT) spectra also taken with the VLT. We discovered that the ages of six of our clusters have been appreciably underestimated by previous studies, which used comparatively small telescopes, graphically illustrating the need for large apertures to obtain reliable ages of old and intermediate-age SMC star clusters. In particular, three of these clusters, L 4, L 6 and L 110, turn out to be amongst the oldest SMC clusters known, with ages of 7.9 ± 1.1, 8.7 ± 1.2 and 7.6 ± 1.0 Gyr, respectively, helping to fill a possible “SMC cluster age gap” (Glatt et al. 2008, AJ, 136, 1703). Using the present ages and metallicities from Parisi et al. (2009), we analyze the age distribution, age gradient and age metallicity relation (AMR) of a sample of SMC clusters measured homogeneously. There is a suggestion of bimodality in the age distribution but it does not show a constant slope for the first 4 Gyr (Piatti et al. 2011, MNRAS, 417, 1559), and we find no evidence for an age gradient. Due to the improved ages of our cluster sample, we find that our AMR is now better represented in the intermediate/old period than that we derived in Parisi et al. (2009), where we simply took ages available in the literature. Additionally, clusters younger than ∼ 4 Gyr now show better agreement with the bursting model of Pagel & Tautvaiˇsien˙e(1998, MNRAS, 299, 535), but we confirm that this model is not a good representation of the AMR during the intermediate-age/old period. A more complicated model is needed to explain the SMC chemical evolution in that period. Published in Astronomical Journal Available from arXiv:1402.1687 Disentangling the physical reality of star cluster candidates projected towards the inner disc of the Large Magellanic Cloud Andr´es E. Piatti1 1Observatorio Astron´omico, Universidad Nacional de C´ordoba, Laprida 854, 5000, C´ordoba, Argentina We have used Washington photometry for 90 star cluster candidates of small angular size – typically ∼ 11′′ in radius – distributed within nine selected regions in the inner disc of the Large Magellanic Cloud (LMC) to disentangle whether they are genuine physical system, and to estimate the ages for the confirmed clusters. In order to avoid a misleading interpretation of the cluster colour–magnitude diagrams (CMDs), we applied a subtraction procedure to statistically clean them from field star contamination. Out of the 90 candidate clusters studied, resulted to be genuine physical systems, whereas the remaining ones were classified as possible non-clusters since either their CMDs and/or the distribution of stars in the respective fields do not resemble those of stellar aggregates. We statistically show that ∼ (13 ± 6) per cent of the catalogued clusters in the inner disc could be possible non-clusters, independently of their deprojected distances. We derived the ages for the confirmed clusters from the fit of theoretical isochrones to the 2 cleaned cluster CMDs. The derived ages resulted to be in the age range 7.8 ≤ log t ≤ 9.2. Finally, we built cluster frequencies (CFs) for the different studied regions and found that there exists some spatial variation of the LMC CF throughout the inner disc. Particularly, the innermost field contains a handful of clusters older than ∼ 2 Gyr, while the wider spread between different CFs has taken place during the most recent 50 Myr of the galaxy lifetime. Accepted for publication in MNRAS Available from arXiv:1403.3561 CCD SDSS gr photometry of poorly studied star clusters in the Large Magellanic Cloud Andr´es E. Piatti1 1Observatorio Astron´omico, Universidad Nacional de C´ordoba, Laprida 854, 5000, C´ordoba, Argentina We present for the first time CCD SDSS gr photometry, obtained at the Gemini South telescope with the GMOS attached, of stars in the field of the poorly studied star clusters NGC 1768, HS 85, SL 676, NGC 2107, NGC 2190, and SL 866, which are distributed in the main body of the Large Magellanic Cloud. We applied a subtraction procedure to statistically clean the cluster CMDs from field star contamination. In order to disentangle cluster features from those belonging to their surrounding fields, we applied a subtraction procedure which makes use of variable cells to reproduce the field star Color–Magnitude Diagrams (CMDs) as closely as possible. We then traced their stellar density radial profiles from star counts performed over the cleaned field stars dataset and derived their radii. Using the cleaned cluster CMDs, we estimated ages and metallicities from matching theoretical isochrones computed for the SDSS system. The studied star clusters have ages from 0.1 up to 2.0 Gyr and are of slightly metal-poor metal content ([Fe/H] ≈ −0.4 dex). Accepted for publication in ISRN Astronomy and Astrophysics Available from arXiv:1403.4519 Dissecting the Spitzer color–magnitude diagrams of extreme LMC AGB stars F. Dell’Agli1,2, P. Ventura1, D.A. Garc´ıa-Hern´andez3,4, R. Schneider1, M. Di Criscienzo1, E. Brocato1, F. D’Antona1 and C. Rossi2 1INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00040, Monte Porzio Catone (RM), Italy 2Dipartimento di Fisica, Universit`adi Roma “La Sapienza”, P.le Aldo Moro 5, 00143, Roma, Italy 3Instituto de Astrof´ısica de Canarias, V´ıaL´actea s/n, E-38200 La Laguna, Tenerife, Spain 4Dept. Astrof´ısica, Universidad de La Laguna (ULL), E-38206 La Laguna, Tenerife, Spain We trace the full evolution of low- and intermediate-mass stars (1 M⊙ ≤ M ≤ 8 M⊙) during the Asymptotic Giant Branch (AGB) phase in the Spitzer two-color and color–magnitude diagrams. We follow the formation and growth of dust particles in the circumstellar envelope with an isotropically expanding wind, in which gas molecules impinge upon pre-existing seed nuclei, favour their growth. These models are the first able to identify the main regions in the Spitzer data occupied by AGB stars in the Large Magellanic Cloud (LMC). The main diagonal sequence traced by LMC extreme stars in the [3.6]–[4.5] vs. [5.8]–[8.0] and [3.6]–[8.0] vs. [8.0] planes are nicely fit by carbon stars models; it results to be an evolutionary sequence with the reddest objects being at the final stages of their AGB evolution. The most extreme stars, with [3.6] − [4.5] > 1.5 mag and [3.6] − [8.0] > 3 mag, are 2.5–3 M⊙ stars surrounded by solid carbon grains. In higher mass (> 3 M⊙) models dust formation is driven by the extent of Hot Bottom Burning (HBB) – most of the dust formed is in the form of silicates and the maximum obscuration phase by dust particles occurs when the HBB experienced is strongest, before the mass of the envelope is considerably reduced. Accepted for publication in Monthly Notices of the Royal Astronomical Society Available from arXiv:1403.7340 3 The COS/UVES absorption survey of the Magellanic Stream. III: Ionization, total mass, and inflow rate onto the Milky Way Andrew J. Fox1, Bart P. Wakker2, Kathleen A. Barger3, Audra K. Hernandez2, Philipp Richter4, Nicolas Lehner3, Joss Bland-Hawthorn5, Jane C. Charlton6, Tobias Westmeier7, Christopher Thom1, Jason Tumlinson1, Toru Misawa8, J. Christopher Howk3, L. Matthew Haffner2, Justin Ely1, Paola Rodriguez-Hidalgo9,10 and Nimisha Kumari11 1Space Telescope Science Institute, USA 2University of Wisconsin-Madison, USA 3University of Notre Dame, USA 4University of Potsdam, Germany 5University of Sydney, Australia 6Pennsylvania State University, USA 7ICRAR, University of Western Australia, Australia 8Shinshu University, Japan 9York University, Canada 10University of Toronto, Canada 11Ecole´ Polytechnique, France Dynamic interactions between the two Magellanic Clouds have flung large quantities of gas into the halo of the Milky Way, creating the Magellanic Stream, the Magellanic Bridge, and the Leading Arm (collectively referred to as the Magellanic System). In this third paper of a series studying the Magellanic gas in absorption, we analyze the gas ionization level using a sample of 69 Hubble Space Telescope/Cosmic Origins Spectrograph sightlines that pass through or within 30◦ of the 21 cm-emitting regions. We find that 81% (56/69) of the sightlines show UV absorption at Magellanic velocities, indicating that the total cross section of the Magellanic System is ∼ 11 000 square degrees, or around a quarter of the entire sky.
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