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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. 157 — 1 February 2019 http://www.astro.keele.ac.uk/MCnews Editor: Jacco van Loon Editorial Dear Colleagues, It is my pleasure to present you the 157th issue of the Magellanic Clouds Newsletter. Besides a review paper there are many papers on the structure of the Magellanic Clouds, SN 1987A, massive binaries and star clusters... and much more. A great start of the new year! I would like to remind you that besides publications, the newsletter also welcomes ideas, questions, expressions of interest, et cetera, which can be posted under the catch-all ”announcement” category or sent directly to the editor at [email protected] Ultimately, what we all want is for us to better understand the Universe and our place in it, and there is no better way of achieving this than by open discussion and inclusive cooperation. The next issue is planned to be distributed on the 1st of April. Editorially Yours, Jacco van Loon 1 Refereed Journal Papers Search for a metallicity spread in the multiple population Large Magellanic Cloud cluster NGC 1978 Andr´es E. Piatti1 and Jeremy Bailin2 1National Scientific and Technical Research Council, Godoy Cruz 2290, C1425FQB, Buenos Aires, Argentina 2Department of Physics and Astronomy, University of Alabama, Box 870324, Tuscaloosa, AL, 35487-0324 USA We report on the spread of [Fe/H] values in the massive Large Magellanic Cloud cluster NGC1978, recently confirmed to harbor multiple populations of nearly the same age. We used accurate Str¨omgren photometry of carefully selected cluster red giant branch stars along with a high-dispersion spectroscopy-based calibration of the metallicity-sensitive index m1. Once accounting for the photometry quality, assessed from extensive artificial stars tests to trace the photometric uncertainties as a function of the position to the cluster’s center as well as the stellar brightness, and those from the metallicity calibration, we found that NGC1978 exhibits a small metallicity spread of 0.035 dex (±0.019–0.023), depending on whether stars with individual σ[Fe/H] ≤ 0.15 dex or those located in the cluster’s outer areas are considered. Such a spread in [Fe/H] is consistent with a cluster formation model with self-enrichment, if mass loss higher than 90 per cent due to stellar evolutionary and galactic tidal effects is assumed. Nevertheless, scenarios where the apparent [Fe/H] variation reflects CN abundance anomalies or less extreme mass loss models with environmentally-dependent self enrichment should not be ruled out. Accepted for publication in The Astronomical Journal SOFIA mid-infrared observations of Supernova1987A in 2016 – forward shocks and possible dust re-formation in the post-shocked region? M. Matsuura1, James M. De Buizer2, Richard G. Arendt3,4, Eli Dwek3, M.J. Barlow5, Antonia Bevan5, Phil Cigan1, Haley L. Gomez1, Jeonghee Rho2,6, Roger Wesson5, Patrice Bouchet7,8, John Danziger9 and Margaret Meixner10,11 1School of Physics and Astronomy, Cardiff University, Queen’s Buildings, The Parade, Cardiff, CF24 3AA, UK 2Stratospheric Observatory For Infrared Astronomy NASA Ames Research Center, MS 232-12 Moffett Field, CA 94035, USA 3Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 4University of Maryland–Baltimore County, Baltimore, MD 21250, USA 5Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK 6SETI Institute, 189 N. Bernardo Avenue, Mountain View, CA 94043, USA 7DRF/IRFU/DAp, CEA–Saclay, F-91191 Gif-sur-Yvette, France 8NRS/AIM, Universit´eParis Diderot, F-9119, Gif-sur-Yvette, France 9Osservatorio Astronomico di Trieste, Via Tiepolo 11, Trieste, Italy 10Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA 11Department of Physics and Astronomy, The Johns Hopkins University, 366 Bloomberg Center, 3400 N. Charles Street, Baltimore, MD 21218, USA The equatorial ring of Supernova (SN) 1987A has been exposed to forward shocks from the SN blast wave, and it has been suggested that these forward shocks have been causing on-going destruction of dust in the ring. We obtained SOFIA-FORCAST 11.1-, 19.7- and 31.5-µm photometry of SN 1987A in 2016. Compared with Spitzer measurements 10 years earlier, the 31.5-µm flux has significantly increased. The excess at 31.5 µm appears to be related to the Herschel 70-µm excess, which was detected 5 years earlier. The dust mass needed to account for the 31.5–70-µm 2 −4 −5 excess is 3–7 × 10 M⊙, more than ten times larger than the ring dust mass (∼ 1 × 10 M⊙) estimate from the data 10 years earlier. We argue that dust grains are re-formed or grown in the post-shock regions in the ring after forward shocks have destroyed pre-existing dust grains in the ring and released refractory elements into gas. In the post-shock region, atoms can stick to surviving dust grains, and the dust mass may have increased (grain growth), or dust grains might have condensed directly from the gas. An alternative possibility is that the outer part of the expanding ejecta dust might have been heated by X-ray emission from the circumstellar ring. The future development of this excess could reveal whether grains are reformed in the post-shocked region of the ring or eject dust is heated by X-ray. Published in MNRAS Available from http://arxiv.org/abs/1810.03615 and from https://academic.oup.com/mnras/article/482/2/1715/5124393 Stellar streams around the Magellanic Clouds in 4D Camila Navarrete1,2,3, Vasily Belokurov3,4, M´arcio Catelan1,2, Prashin Jethwa5, Sergey E. Koposov3,6, Julio A. Carballo-Bello1,2, Paula Jofr´e3,7, Denis Erkal8, Sonia Duffau9 and Jes´us M. Corral-Santana10 1Instituto de Astrof´ısica, Pontificia Universidad Cat´olica de Chile, Av. Vicu˜na Mackenna 4860, 7820436 Macul, Santiago, Chile 2Millennium Institute of Astrophysics, Av. Vicu˜na Mackenna 4860, 7820436, Macul, Santiago, Chile 3Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK 4Center for Computational Astrophysics, Flatiron Institute, 162 5th Avenue, 10010, New York, NY, USA 5European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei M¨unchen, Germany 6McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA 7Nucleo de Astronom´ıa, Facultad de Ingenier´ıa, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile 8Department of Physics, University of Surrey, Guildford, GU2 7XH, UK 9Universidad Andr´esBello, Departamento de Ciencias F´ısicas, Facultad de Ciencias Exactas, Fern´andez Concha 700, Las Condes, Santiago, Chile 10European Southern Observatory (ESO), Alonso de C´ordova 3107, Vitacura, Casilla 19, Santiago, Chile We carried out a spectroscopic follow-up program of the four new stellar stream candidates detected by Belokurov & Koposov (2016) in the outskirts of the Large Magellanic Cloud (LMC) using FORS2 (VLT). The medium-resolution spectra were used to measure the line-of-sight velocities, estimate stellar metallicities and to classify stars into Blue Horizontal Branch (BHB) and Blue Straggler (BS) stars. Using the 4-D phase-space information, we attribute ap- proximately one half of our sample to the Magellanic Clouds, while the rest is part of the Galactic foreground. Only two of the four stream candidates are confirmed kinematically. While it is impossible to estimate the exact levels of MW contamination, the phase-space distribution of the entire sample of our Magellanic stars matches the expected velocity gradient for the LMC halo and extends as far as 33◦ (angular separation) or 29 kpc from the LMC center. Our detections reinforce the idea that the halo of the LMC seems to be larger than previously expected, and its debris can be spread in the sky out to very large separations from the LMC center. Finally, we provide some kinematic evidence that many of the stars analysed here have likely come from the Small Magellanic Cloud. Accepted for publication in MNRAS Available from http://arxiv.org/abs/1811.11730 and from https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/sty3347/5238734 3 The origins of young stars in the Leading Arm of the Magellanic Stream: abundances, kinematics, and orbits Lan Zhang1, Dana I. Casetti-Dinescu2,3,4, Christian Moni Bidin5, Rene A. Mendez6, Terrence M. Girard7, Katherine Vieira8, Vladimir I. Korchagin9, William F. van Altena10 and Gang Zhao1 1Key Lab of Optical Astronomy, National Astronomical Observatories, CAS, 20A Datun Road, Chaoyang District, 100012 Beijing, China 2Department of Physics, Southern Connecticut State University, 501 Crescent St., New Haven, CT 06515, USA 3Astronomical Institute of the Romanian Academy, str. Cutitul de Argint 5, Bucharest, Romania 4Radiology and Biomedical Imaging, Yale School of Medicine, 300 Cedar Street, New Haven 06519, USA 5Instituto de Astronom´ıa, Universidad Cat´olica del Norte, Av. Angamos 0610, Antofagasta, Chile 6Departamento de Astronom´ıa, Universidad de Chile, Casilla 36-D, Santiago, Chile 714 Dunn Rd., Hamden, Connecticut, CT 06518, USA 8Centro de Investigaciones de Astronom´ıa, Apartado Postal 264, Merida 5101-A, Venezuela 9Institute of Physics, Southern Federal University, Stachki st/194, 344090, Rostov-on-Don, Russia 10Astronomy Department, Yale University, 260 Whitney Ave., New Haven, CT 06511, USA We explore the origins of the young B-type stars found by Casetti–Dinescu et al. (2014) at the outskirts of the Milky- Way disk in the sky region of Leading Arm (LA) of the Magellanic Stream. High-resolution spectroscopic observations made with the MIKE instrument on the Magellan Clay 6.5m telescope for nine stars are added to the previous sample analyzed by Zhang et al. (2017). We compile a sample of fifteen young stars with well-determined stellar types, ages, abundances and kinematics.
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