TY - JOUR A1 - Martin, Nicolas F. A1 - Nidever, David L. A1 - Besla, Gurtina A1 - Olsen, Knut A1 - Walker, Alistair R. A1 - Vivas, A. Katherina A1 - Gruendl, Robert A. A1 - Kaleida, Catherine C. A1 - Munoz, Ricardo R. A1 - Blum, Robert D. A1 - Saha, Abhijit A1 - Conn, Blair C. A1 - Bell, Eric F. A1 - Chu, You-Hua A1 - Cioni, Maria-Rosa L. A1 - de Boer, Thomas J. L. A1 - Gallart, Carme A1 - Jin, Shoko A1 - Kunder, Andrea A1 - Majewski, Steven R. A1 - Martinez-Delgado, David A1 - Monachesi, Antonela A1 - Monelli, Matteo A1 - Monteagudo, Lara A1 - Noel, Noelia E. D. A1 - Olszewski, Edward W. A1 - Stringfellow, Guy S. A1 - van der Marel, Roeland P. A1 - Zaritsky, Dennis T1 - Hydra II: A faint and compact milky way dwarf galaxy found in the survey of the magellanic stellar history JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters N2 - We present the discovery of a new dwarf galaxy, Hydra II, found serendipitously within the data from the ongoing Survey of the Magellanic Stellar History conducted with the Dark Energy Camera on the Blanco 4 m Telescope. The new satellite is compact (r(h) = 68 +/- 11 pc) and faint (MV = -4.8 +/- 0.3), but well within the realm of dwarf galaxies. The stellar distribution of Hydra II in the color-magnitude diagram is well-described by a metal-poor ([Fe/H] = -2.2) and old (13 Gyr) isochrone and shows a distinct blue horizontal branch, some possible red clump stars, and faint stars that are suggestive of blue stragglers. At a heliocentric distance of 134 +/- 10 kpc, Hydra II is located in a region of the Galactic halo that models have suggested may host material from the leading arm of the Magellanic Stream. A comparison with N-body simulations hints that the new dwarf galaxy could be or could have been a satellite of the Magellanic Clouds. KW - galaxies: individual (Hydra II) KW - Local Group KW - Magellanic Clouds Y1 - 2015 U6 - https://doi.org/10.1088/2041-8205/804/1/L5 SN - 2041-8205 SN - 2041-8213 VL - 804 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Piatti, Andres E. A1 - de Grijs, Richard A1 - Rubele, Stefano A1 - Cioni, Maria-Rosa L. A1 - Ripepi, Vincenzo A1 - Kerber, Leandro T1 - The VMC survey - XV. The Small Magellanic Cloud-Bridge connection history as traced by their star cluster populations JF - Monthly notices of the Royal Astronomical Society N2 - We present results based on YJK(s) photometry of star clusters located in the outermost, eastern region of the Small Magellanic Cloud (SMC). We analysed a total of 51 catalogued clusters whose colour-magnitude diagrams (CMDs), having been cleaned from field-star contamination, were used to assess the clusters' reality and estimate ages of the genuine systems. Based on CMD analysis, 15 catalogued clusters were found to be possible non-genuine aggregates. We investigated the properties of 80 per cent of the catalogued clusters in this part of the SMC by enlarging our sample with previously obtained cluster ages, adopting a homogeneous scale for all. Their spatial distribution suggests that the oldest clusters, log(t yr(-1)) >= 9.6, are in general located at greater distances to the galaxy's centre than their younger counterparts - 9.0 <= log(t yr(-1)) <= 9.4 - while two excesses of clusters are seen at log(t yr(-1)) similar to 9.2 and log(t yr(-1)) similar to 9.7. We found a trail of younger clusters which follow the wing/bridge components. This long spatial sequence does not only harbour very young clusters, log(t yr(-1)) similar to 7.3, but it also hosts some of intermediate ages, log(t yr(-1)) similar to 9.1. The derived cluster and field-star formation frequencies as a function of age are different. The most surprising feature is an observed excess of clusters with ages of log(t yr(-1)) <9.0, which could have been induced by interactions with the LMC. KW - techniques: photometric KW - galaxies: individual: SMC KW - Magellanic Clouds Y1 - 2015 U6 - https://doi.org/10.1093/mnras/stv635 SN - 0035-8711 SN - 1365-2966 VL - 450 IS - 1 SP - 552 EP - 563 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Murray, Claire E. A1 - Stanimirovic, Snezana A1 - McClure-Griffiths, Naomi M. A1 - Putman, Mary E. A1 - Liszt, Harvey S. A1 - Wong, Tony A1 - Richter, Philipp A1 - Dawson, Joanne R. A1 - Dickey, John M. A1 - Lindner, Robert R. A1 - Babler, Brian L. A1 - Allison, James R. T1 - First detection of HCO+ absorption in the magellanic system JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We present the first detection of HCO+ absorption in the Magellanic System. Using the ATCA, we observed nine extragalactic radio continuum sources behind the Magellanic System and detected HCO+ absorption toward one source located behind the leading edge of the Magellanic Bridge. The detection is located at an LSR velocity of v = 214.0 +/- 0.4 km s(-1), with an FWHM of Delta v = 4.5 +/- 1.0 km s(-1), and an optical depth of tau (HCO+) = 0.10 +/- 0.02. Although there is abundant neutral hydrogen (H I) surrounding the sight line in position-velocity space, at the exact location of the absorber the H I column density is low, <10(20) cm(-2), and there is little evidence for dust or CO emission from Planck observations. While the origin and survival of molecules in such a diffuse environment remain unclear, dynamical events such as H I flows and cloud collisions in this interacting system likely play an important role. KW - ISM: molecules KW - ISM: structure KW - Magellanic Clouds Y1 - 2015 U6 - https://doi.org/10.1088/0004-637X/808/1/41 SN - 0004-637X SN - 1538-4357 VL - 808 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Muraveva, Tatiana A1 - Palmer, Max A1 - Clementini, Gisella A1 - Luri, Xavier A1 - Cioni, Maria-Rosa L. A1 - Moretti, Maria Ida A1 - Marconi, Marcella A1 - Ripepi, Vincenzo A1 - Rubele, Stefano T1 - New near-infrared period-luminosity-metallicity relations for RR lyrae stars and the outlock for GAIA JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We present results of the analysis of 70 RR Lyrae stars located in the bar of the Large Magellanic Cloud (LMC). Combining the spectroscopically determined metallicity of these stars from the literature with precise periods from the OGLE III catalog and multi-epoch K-s photometry from the VISTA survey of the Magellanic Clouds system, we derive a new near-infrared period-luminosity-metallicity (PLKsZ) relation for RR Lyrae variables. In order to fit the relation we use a fitting method developed specifically for this study. The zero-point of the relation is estimated two different ways: by assuming the value of the distance to the LMC and by using Hubble Space Telescope parallaxes of five RR Lyrae stars in the Milky Way (MW). The difference in distance moduli derived by applying these two approaches is similar to 0.2 mag. To investigate this point further we derive the PL(Ks)Z relation based on 23 MW RR Lyrae stars that had been analyzed in Baade-Wesselink studies. We compared the derived PL(Ks)Z relations for RR Lyrae stars in the MW and LMC. Slopes and zero-points are different, but still consistent within the errors. The shallow slope of the metallicity term is confirmed by both LMC and MW variables. The astrometric space mission Gaia is expected to provide a huge contribution to the determination of the RR Lyrae PL(Ks)Z relation; however, calculating an absolute magnitude from the trigonometric parallax of each star and fitting a PL(Ks)Z relation directly to period and absolute magnitude leads to biased results. We present a tool to achieve an unbiased solution by modeling the data and inferring the slope and zero-point of the relation via statistical methods. KW - astrometry KW - distance scale KW - Magellanic Clouds KW - methods: data analysis KW - stars: statistics KW - stars: variables: RR Lyrae Y1 - 2015 U6 - https://doi.org/10.1088/0004-637X/807/2/127 SN - 0004-637X SN - 1538-4357 VL - 807 IS - 2 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Piatti, Andres E. A1 - de Grijs, Richard A1 - Ripepi, Vincenzo A1 - Ivanov, Valentin D. A1 - Cioni, Maria-Rosa L. A1 - Marconi, Marcella A1 - Rubele, Stefano A1 - Bekki, Kenji A1 - For, Bi-Qing T1 - The VMC survey - XVI. Spatial variation of the cluster formation activity in the innermost regions of the Large Magellanic Cloud JF - Monthly notices of the Royal Astronomical Society KW - techniques: photometric KW - galaxies: individual: LMC KW - Magellanic Clouds Y1 - 2015 U6 - https://doi.org/10.1093/mnras/stv2054 SN - 0035-8711 SN - 1365-2966 VL - 454 IS - 1 SP - 839 EP - 848 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Evans, Chris J. A1 - van Loon, Jacco Th A1 - Hainich, Rainer A1 - Bailey, M. T1 - 2dF-AAOmega spectroscopy of massive stars in the Magellanic Clouds The north-eastern region of the Large Magellanic Cloud JF - Astronomy and astrophysics : an international weekly journal N2 - We present spectral classifications from optical spectroscopy of 263 massive stars in the north-eastern region of the Large Magellanic Cloud. The observed two-degree field includes the massive 30 Doradus star-forming region, the environs of SN1987A, and a number of star-forming complexes to the south of 30 Dor. These are the first classifications for the majority (203) of the stars and include eleven double-lined spectroscopic binaries. The sample also includes the first examples of early OC-type spectra (AA Omega 30 Dor 248 and 280), distinguished by the weakness of their nitrogen spectra and by C IV lambda 4658 emission. We propose that these stars have relatively unprocessed CNO abundances compared to morphologically normal O-type stars, indicative of an earlier evolutionary phase. From analysis of observations obtained on two consecutive nights, we present radial-velocity estimates for 233 stars, finding one apparent single-lined binary and nine (>3 sigma) outliers compared to the systemic velocity; the latter objects could be runaway stars or large-amplitude binary systems and further spectroscopy is required to investigate their nature. KW - Magellanic Clouds KW - stars: early-type KW - stars: fundamental parameters KW - open clusters and associations: general Y1 - 2015 U6 - https://doi.org/10.1051/0004-6361/201525882 SN - 1432-0746 VL - 584 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Hainich, Rainer A1 - Pasemann, Diana A1 - Todt, Helge Tobias A1 - Shenar, Tomer A1 - Sander, Andreas Alexander Christoph A1 - Hamann, Wolf-Rainer T1 - Wolf-Rayet stars in the Small Magellanic Cloud I. Analysis of the single WN stars JF - Astronomy and astrophysics : an international weekly journal N2 - Context. Wolf-Rayet (WR) stars have a severe impact on their environments owing to their strong ionizing radiation fields and powerful stellar winds. Since these winds are considered to be driven by radiation pressure, it is theoretically expected that the degree of the wind mass-loss depends on the initial metallicity of WR stars. Aims. Following our comprehensive studies of WR stars in the Milky Way, M31, and the LMC, we derive stellar parameters and mass-loss rates for all seven putatively single WN stars known in the SMC. Based on these data, we discuss the impact of a low-metallicity environment on the mass loss and evolution of WR stars. Methods. The quantitative analysis of the WN stars is performed with the Potsdam Wolf-Rayet (PoWR) model atmosphere code. The physical properties of our program stars are obtained from fitting synthetic spectra to multi-band observations. Results. In all SMC WN stars, a considerable surface hydrogen abundance is detectable. The majority of these objects have stellar temperatures exceeding 75 kK, while their luminosities range from 10(5.5) to 10(6.1) L-circle dot. The WN stars in the SMC exhibit on average lower mass-loss rates and weaker winds than their counterparts in the Milky Way, M31, and the LMC. Conclusions. By comparing the mass-loss rates derived for WN stars in different Local Group galaxies, we conclude that a clear dependence of the wind mass-loss on the initial metallicity is evident, supporting the current paradigm that WR winds are driven by radiation. A metallicity effect on the evolution of massive stars is obvious from the HRD positions of the SMC WN stars at high temperatures and high luminosities. Standard evolution tracks are not able to reproduce these parameters and the observed surface hydrogen abundances. Homogeneous evolution might provide a better explanation for their evolutionary past. KW - stars: Wolf-Rayet KW - Magellanic Clouds KW - stars: early-type KW - stars: atmospheres KW - stars: winds, outflows KW - stars: mass-loss Y1 - 2015 U6 - https://doi.org/10.1051/0004-6361/201526241 SN - 1432-0746 VL - 581 PB - EDP Sciences CY - Les Ulis ER -