Cartography of Triangulum-Andromeda using SDSS stars

The outer Galactic halo is home to a number of substructures which still have an uncertain origin, but most likely are remnants of former interactions between the Galaxy and its former satellites. Triangulum-Andromeda (TriAnd) is one of these halo substructures, found as an overdensity of Two Micron All Sky Survey (2MASS) M giants. We analysed the region of TriAnd using photometric data from the Ninth Data Release of Sloan Digital Sky Survey. By comparing the observations with simulations from the TRILEGAL Galactic model, we were able to identify and map several scattered overdensities of main-sequence stars that seem to be associated with TriAnd over a large area covering ∼500 deg2. One of these excesses may represent a new stellar overdensity.We also briefly discuss an alternative hypothesis, according to which TriAnd is one of the troughs of oscillation rings in the Galactic disc

Constraining Mass Loss and Lifetimes of Low Mass, Low Metallicity AGB Stars

The evolution and lifetimes of thermally pulsing asymptotic giant branch (TP-AGB) stars suffer from significant uncertainties. We present a detailed framework for constraining model luminosity functions of TP-AGB stars using resolved stellar populations. We show an example of this method that compares various TP-AGB mass-loss prescriptions that differ in their treatments of mass loss before the onset of dust-driven winds (pre-dust). We find that models with more efficient pre-dust driven mass loss produce results consistent with observations, as opposed to more canonical mass-loss models. Efficient pre-dust driven mass-loss predicts, for [Fe/H] ≲ -1.2, that lower mass TP-AGB stars (M≲ 1 M☉) must have lifetimes less than about 1.2 Myr

The VMC survey - XIV. First results on the look-back time star formation rate tomography of the Small Magellanic Cloud

We analyse deep images from the VISTA survey of the Magellanic Clouds in the YJK(s) filters, covering 14 deg(2) (10 tiles), split into 120 subregions, and comprising the main body and Wing of the Small Magellanic Cloud (SMC). We apply a colour-magnitude diagram reconstruction method that returns their best-fitting star formation rate SFR(t), age-metallicity relation (AMR), distance and mean reddening, together with 68 per cent confidence intervals. The distance data can be approximated by a plane tilted in the East-West direction with a mean inclination of 39 degrees, although deviations of up to +/- 3 kpc suggest a distorted and warped disc. After assigning to every observed star a probability of belonging to a given age-metallicity interval, we build high-resolution population maps. These dramatically reveal the flocculent nature of the young star-forming regions and the nearly smooth features traced by older stellar generations. They document the formation of the SMC Wing at ages <0.2 Gyr and the peak of star formation in the SMC Bar at similar to 40 Myr. We clearly detect periods of enhanced star formation at 1.5 and 5 Gyr. The former is possibly related to a new feature found in the AMR, which suggests ingestion of metal-poor gas at ages slightly larger than 1 Gyr. The latter constitutes a major period of stellar mass formation. We confirm that the SFR(t) was moderately low at even older ages

The 13th Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-IV Survey Mapping Nearby Galaxies at Apache Point Observatory

The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) began observations in July 2014. It pursues three core programs: APOGEE-2,MaNGA, and eBOSS. In addition, eBOSS contains two major subprograms: TDSS and SPIDERS. This paper describes the first data release from SDSS-IV, Data Release 13 (DR13), which contains new data, reanalysis of existing data sets and, like all SDSS data releases, is inclusive of previously released data. DR13 makes publicly available 1390 spatially resolved integral field unit observations of nearby galaxies from MaNGA,the first data released from this survey. It includes new observations from eBOSS, completing SEQUELS. In addition to targeting galaxies and quasars, SEQUELS also targeted variability-selected objects from TDSS and X-ray selected objects from SPIDERS. DR13 includes new reductions ofthe SDSS-III BOSS data, improving the spectrophotometric calibration and redshift classification. DR13 releases new reductions of the APOGEE-1data from SDSS-III, with abundances of elements not previously included and improved stellar parameters for dwarf stars and cooler stars. For the SDSS imaging data, DR13 provides new, more robust and precise photometric calibrations. Several value-added catalogs are being released in tandem with DR13, in particular target catalogs relevant for eBOSS, TDSS, and SPIDERS, and an updated red-clump catalog for APOGEE.This paper describes the location and format of the data now publicly available, as well as providing references to the important technical papers that describe the targeting, observing, and data reduction. The SDSS website, http://www.sdss.org, provides links to the data, tutorials and examples of data access, and extensive documentation of the reduction and analysis procedures. DR13 is the first of a scheduled set that will contain new data and analyses from the planned ~6-year operations of SDSS-IV.PostprintPeer reviewe

The Eleventh and Twelfth Data Releases of the Sloan Digital Sky Survey: Final Data from SDSS-III

The third generation of the Sloan Digital Sky Survey (SDSS-III) took data from 2008 to 2014 using the original SDSS wide-field imager, the original and an upgraded multi-object fiber-fed optical spectrograph, a new near-infrared high-resolution spectrograph, and a novel optical interferometer. All of the data from SDSS-III are now made public. In particular, this paper describes Data Release 11 (DR11) including all data acquired through 2013 July, and Data Release 12 (DR12) adding data acquired through 2014 July (including all data included in previous data releases), marking the end of SDSS-III observing. Relative to our previous public release (DR10), DR12 adds one million new spectra of galaxies and quasars from the Baryon Oscillation Spectroscopic Survey (BOSS) over an additional 3000 deg2 of sky, more than triples the number of H-band spectra of stars as part of the Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE), and includes repeated accurate radial velocity measurements of 5500 stars from the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS). The APOGEE outputs now include the measured abundances of 15 different elements for each star. In total, SDSS-III added 5200 deg2 of ugriz imaging; 155,520 spectra of 138,099 stars as part of the Sloan Exploration of Galactic Understanding and Evolution 2 (SEGUE-2) survey; 2,497,484 BOSS spectra of 1,372,737 galaxies, 294,512 quasars, and 247,216 stars over 9376 deg2; 618,080 APOGEE spectra of 156,593 stars; and 197,040 MARVELS spectra of 5513 stars. Since its first light in 1998, SDSS has imaged over 1/3 of the Celestial sphere in five bands and obtained over five million astronomical spectra. © 2015. The American Astronomical Society

Colour evolution models and the distribution of lmc clusters in the integrated ubv plane

We present a comparison between photometric cluster models, based on classical and with-overshooting stellar tracks, and the enlarged sample of 624 LMC clusters recently gathered in integrated UBV photometry by Bica et al. Models based on Maeder and Meynet's tracks present two temporary red phases: the first at age 10 Myr, caused by a clump of red supergiants; the second at ~ 100 Myr due to the combined effect of both the progressive reduction of the blue loop of core Heburning stars, and their fading relative to top-MS stars. The 100 Myr red phase does not occur in models without overshooting. Taking into account stochastic effects on the mass distribution of stars, the models describe well the general distribution of clusters in the (U – B) vs. (B – V) diagram, except for the oldest, SWB types V-VII, clusters. The dispersion of cluster colours due to stochastic effects is found to be strongly variable along the ageing sequence: the general trend is a decrease with age due to the increasing population of post-MS phases, but the dispersion increases in the temporary red phases and is expected to increase again after the red giant branch phase transition due to the appearance of extended RGBs and carbon stars. We also study the LMC clusters age distribution function, based on the age frequency of clusters of equal initial masses, taking into account different values for the IMF slope

Carbon stars in lmc clusters revisited

Examining the available data for AGB stars in the Large Magellanic Cloud (LMC) clusters, we address the question about the mass interval of low- and intermediate-mass stars which eventually evolve into carbon stars (C stars) during the TP-AGB phase. We combine the data compiled by Frogel, Mould & Blanco (1990) - near infrared photometry and spectral classification for luminous AGB stars in clusters - with the ages for individual clusters derived from independent methods. The resulting distribution of C stars in the Mbol - log(age) plane evidences that the upper and the lower limits of the mass range for the formation of C stars cannot be derived from cluster data. The explanation of this resides in the presence of two different periods of quiescence in the cluster formation history of the LMC, shaping the age (and progenitor mass) distribution of C stars. The most recent of these quiescence episodes could also explain the lack of very luminous AGB stars (with –6 > Mbol > –7) in the clusters, contrary to what observed in the field. Finally we compare the distribution of C stars in the Mbol –log( age) diagram with synthetic models of AGB evolution which were previously constrained to reproduce the observed luminosity function of C stars in the field. These models provide a good description of the relative frequency of M-versus C-type stars

Colour evolution models and the distribution of lmc clusters in the integrated ubv plane

We present a comparison between photometric cluster models, based on classical and with-overshooting stellar tracks, and the enlarged sample of 624 LMC clusters recently gathered in integrated UBV photometry by Bica et al. Models based on Maeder and Meynet's tracks present two temporary red phases: the first at age 10 Myr, caused by a clump of red supergiants; the second at ~ 100 Myr due to the combined effect of both the progressive reduction of the blue loop of core Heburning stars, and their fading relative to top-MS stars. The 100 Myr red phase does not occur in models without overshooting. Taking into account stochastic effects on the mass distribution of stars, the models describe well the general distribution of clusters in the (U – B) vs. (B – V) diagram, except for the oldest, SWB types V-VII, clusters. The dispersion of cluster colours due to stochastic effects is found to be strongly variable along the ageing sequence: the general trend is a decrease with age due to the increasing population of post-MS phases, but the dispersion increases in the temporary red phases and is expected to increase again after the red giant branch phase transition due to the appearance of extended RGBs and carbon stars. We also study the LMC clusters age distribution function, based on the age frequency of clusters of equal initial masses, taking into account different values for the IMF slope

Carbon stars in lmc clusters revisited

Examining the available data for AGB stars in the Large Magellanic Cloud (LMC) clusters, we address the question about the mass interval of low- and intermediate-mass stars which eventually evolve into carbon stars (C stars) during the TP-AGB phase. We combine the data compiled by Frogel, Mould & Blanco (1990) - near infrared photometry and spectral classification for luminous AGB stars in clusters - with the ages for individual clusters derived from independent methods. The resulting distribution of C stars in the Mbol - log(age) plane evidences that the upper and the lower limits of the mass range for the formation of C stars cannot be derived from cluster data. The explanation of this resides in the presence of two different periods of quiescence in the cluster formation history of the LMC, shaping the age (and progenitor mass) distribution of C stars. The most recent of these quiescence episodes could also explain the lack of very luminous AGB stars (with –6 > Mbol > –7) in the clusters, contrary to what observed in the field. Finally we compare the distribution of C stars in the Mbol –log( age) diagram with synthetic models of AGB evolution which were previously constrained to reproduce the observed luminosity function of C stars in the field. These models provide a good description of the relative frequency of M-versus C-type stars