@article{MorettiClementiniMarconietal.2016, author = {Moretti, M. I. and Clementini, Gisella and Marconi, V. Ripepi M. and Rubele, S. and Cioni, Maria-Rosa L. and Muraveva, T. and Groenewegen, M. A. T. and Cross, N. J. G. and Ivanov, V. D. and Piatti, A. E. and de Grijs, Richard}, title = {The VMC survey - XX. Identification of new Cepheids in the Small Magellanic Cloud}, series = {Monthly notices of the Royal Astronomical Society}, volume = {459}, journal = {Monthly notices of the Royal Astronomical Society}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0035-8711}, doi = {10.1093/mnras/stw716}, pages = {1687 -- 1697}, year = {2016}, abstract = {We present K-s-band light curves for 299 Cepheids in the Small Magellanic Cloud (SMC) of which 288 are new discoveries that we have identified using multi-epoch near-infrared photometry obtained by the VISTA survey of the Magellanic Clouds system (VMC). The new Cepheids have periods in the range from 0.34 to 9.1 d and cover the magnitude interval 12.9 <= currency sign < K-s > <= currency sign 17.6 mag. Our method was developed using variable stars previously identified by the optical microlensing survey OGLE. We focus on searching new Cepheids in external regions of the SMC for which complete VMC K-s-band observations are available and no comprehensive identification of different types of variable stars from other surveys exists yet.}, language = {en} } @article{ShenarHainichTodtetal.2016, author = {Shenar, Tomer and Hainich, Rainer and Todt, Helge Tobias and Sander, Andreas Alexander Christoph and Hamann, Wolf-Rainer and Moffat, Anthony F. J. and Eldridge, J. J. and Pablo, H. and Oskinova, Lida and Richardson, N. D.}, title = {Wolf-Rayet stars in the Small Magellanic Cloud II. Analysis of the binaries}, series = {American mineralogist : an international journal of earth and planetary materials}, volume = {591}, journal = {American mineralogist : an international journal of earth and planetary materials}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {1432-0746}, doi = {10.1051/0004-6361/201527916}, pages = {25}, year = {2016}, abstract = {Context. Massive Wolf-Rayet (WR) stars are evolved massive stars (M-i greater than or similar to 20 M-circle dot) characterized by strong mass-loss. Hypothetically, they can form either as single stars or as mass donors in close binaries. About 40\% of all known WR stars are confirmed binaries, raising the question as to the impact of binarity on the WR population. Studying WR binaries is crucial in this context, and furthermore enable one to reliably derive the elusive masses of their components, making them indispensable for the study of massive stars. Aims. By performing a spectral analysis of all multiple WR systems in the Small Magellanic Cloud (SMC), we obtain the full set of stellar parameters for each individual component. Mass-luminosity relations are tested, and the importance of the binary evolution channel is assessed. Methods. The spectral analysis is performed with the PotsdamWolf-Rayet (PoWR) model atmosphere code by superimposing model spectra that correspond to each component. Evolutionary channels are constrained using the Binary Population and Spectral Synthesis (BPASS) evolution tool. Results. Significant hydrogen mass fractions (0.1 < X-H < 0.4) are detected in all WN components. A comparison with mass-luminosity relations and evolutionary tracks implies that the majority of the WR stars in our sample are not chemically homogeneous. The WR component in the binary AB6 is found to be very luminous (log L approximate to 6.3 [L-circle dot]) given its orbital mass (approximate to 10 M-circle dot), presumably because of observational contamination by a third component. Evolutionary paths derived for our objects suggest that Roche lobe overflow had occurred in most systems, affecting their evolution. However, the implied initial masses (greater than or similar to 60 M-circle dot) are large enough for the primaries to have entered the WR phase, regardless of binary interaction. Conclusions. Together with the results for the putatively single SMC WR stars, our study suggests that the binary evolution channel does not dominate the formation of WR stars at SMC metallicity.}, language = {en} } @article{PiattiIvanovRubeleetal.2016, author = {Piatti, Andres E. and Ivanov, Valentin D. and Rubele, Stefano and Marconi, Marcella and Ripepi, Vincenzo and Cioni, Maria-Rosa L. and Oliveira, Joana M. and Bekki, Kenji}, title = {The VMC Survey - XXI. New star cluster candidates discovered from infrared photometry in the Small Magellanic Cloud}, series = {Monthly notices of the Royal Astronomical Society}, volume = {460}, journal = {Monthly notices of the Royal Astronomical Society}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0035-8711}, doi = {10.1093/mnras/stw1000}, pages = {383 -- 395}, year = {2016}, language = {en} } @article{MartinJungbluthNideveretal.2016, author = {Martin, Nicolas F. and Jungbluth, Valentin and Nidever, David L. and Bell, Eric F. and Besla, Gurtina and Blum, Robert D. and Cioni, Maria-Rosa L. and Conn, Blair C. and Kaleida, Catherine C. and Gallart, Carme and Jin, Shoko and Majewski, Steven R. and Martinez-Delgado, David and Monachesi, Antonela and Munoz, Ricardo R. and Noel, Noelia E. D. and Olsen, Knut and Stringfellow, Guy S. and van der Marel, Roeland P. and Vivas, A. Katherina and Walker, Alistair R. and Zaritsky, Dennis}, title = {SMASH 1: A VERY FAINT GLOBULAR CLUSTER DISRUPTING IN THE OUTER REACHES OF THE LMC?}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, volume = {830}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {2041-8205}, doi = {10.3847/2041-8205/830/1/L10}, pages = {92 -- 98}, year = {2016}, language = {en} } @article{MartinNideverBeslaetal.2015, author = {Martin, Nicolas F. and Nidever, David L. and Besla, Gurtina and Olsen, Knut and Walker, Alistair R. and Vivas, A. Katherina and Gruendl, Robert A. and Kaleida, Catherine C. and Munoz, Ricardo R. and Blum, Robert D. and Saha, Abhijit and Conn, Blair C. and Bell, Eric F. and Chu, You-Hua and Cioni, Maria-Rosa L. and de Boer, Thomas J. L. and Gallart, Carme and Jin, Shoko and Kunder, Andrea and Majewski, Steven R. and Martinez-Delgado, David and Monachesi, Antonela and Monelli, Matteo and Monteagudo, Lara and Noel, Noelia E. D. and Olszewski, Edward W. and Stringfellow, Guy S. and van der Marel, Roeland P. and Zaritsky, Dennis}, title = {Hydra II: A faint and compact milky way dwarf galaxy found in the survey of the magellanic stellar history}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, volume = {804}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {2041-8205}, doi = {10.1088/2041-8205/804/1/L5}, pages = {6}, year = {2015}, abstract = {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.}, language = {en} } @article{PiattideGrijsRubeleetal.2015, author = {Piatti, Andres E. and de Grijs, Richard and Rubele, Stefano and Cioni, Maria-Rosa L. and Ripepi, Vincenzo and Kerber, Leandro}, title = {The VMC survey - XV. The Small Magellanic Cloud-Bridge connection history as traced by their star cluster populations}, series = {Monthly notices of the Royal Astronomical Society}, volume = {450}, journal = {Monthly notices of the Royal Astronomical Society}, number = {1}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0035-8711}, doi = {10.1093/mnras/stv635}, pages = {552 -- 563}, year = {2015}, abstract = {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.}, language = {en} } @article{MuravevaPalmerClementinietal.2015, author = {Muraveva, Tatiana and Palmer, Max and Clementini, Gisella and Luri, Xavier and Cioni, Maria-Rosa L. and Moretti, Maria Ida and Marconi, Marcella and Ripepi, Vincenzo and Rubele, Stefano}, title = {New near-infrared period-luminosity-metallicity relations for RR lyrae stars and the outlock for GAIA}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {807}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, number = {2}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0004-637X}, doi = {10.1088/0004-637X/807/2/127}, pages = {17}, year = {2015}, abstract = {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.}, language = {en} } @article{MurrayStanimirovicMcClureGriffithsetal.2015, author = {Murray, Claire E. and Stanimirovic, Snezana and McClure-Griffiths, Naomi M. and Putman, Mary E. and Liszt, Harvey S. and Wong, Tony and Richter, Philipp and Dawson, Joanne R. and Dickey, John M. and Lindner, Robert R. and Babler, Brian L. and Allison, James R.}, title = {First detection of HCO+ absorption in the magellanic system}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {808}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0004-637X}, doi = {10.1088/0004-637X/808/1/41}, pages = {6}, year = {2015}, abstract = {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.}, language = {en} } @article{HainichPasemannTodtetal.2015, author = {Hainich, Rainer and Pasemann, Diana and Todt, Helge Tobias and Shenar, Tomer and Sander, Andreas Alexander Christoph and Hamann, Wolf-Rainer}, title = {Wolf-Rayet stars in the Small Magellanic Cloud I. Analysis of the single WN stars}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {581}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {1432-0746}, doi = {10.1051/0004-6361/201526241}, pages = {30}, year = {2015}, abstract = {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.}, language = {en} } @article{PiattideGrijsRipepietal.2015, author = {Piatti, Andres E. and de Grijs, Richard and Ripepi, Vincenzo and Ivanov, Valentin D. and Cioni, Maria-Rosa L. and Marconi, Marcella and Rubele, Stefano and Bekki, Kenji and For, Bi-Qing}, title = {The VMC survey - XVI. Spatial variation of the cluster formation activity in the innermost regions of the Large Magellanic Cloud}, series = {Monthly notices of the Royal Astronomical Society}, volume = {454}, journal = {Monthly notices of the Royal Astronomical Society}, number = {1}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0035-8711}, doi = {10.1093/mnras/stv2054}, pages = {839 -- 848}, year = {2015}, language = {en} }