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We present the first release of the MaNGA Stellar Library (MaStar), which is a large, well-calibrated, high-quality empirical library covering the wavelength range 3622-10354 Å at a resolving power of R ∼ 1800. The spectra were obtained using the same instrument as used by the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) project, by piggybacking on the Sloan Digital Sky Survey (SDSS-IV)/Apache Point Observatory Galaxy Evolution Experiment 2-N (APOGEE-2N) observations. Compared to previous empirical libraries, the MaStar library will have a higher number of stars and a more comprehensive stellar-parameter coverage, especially of cool dwarfs, low-metallicity stars, and stars with different [α/Fe], achieved by a sophisticated target-selection strategy that takes advantage of stellar-parameter catalogs from the literature. This empirical library will provide a new basis for stellar-population synthesis and is particularly well suited for stellar-population analysis of MaNGA galaxies. The first version of the library contains 8646 high-quality per-visit spectra for 3321 unique stars. Compared to photometry, the relative flux calibration of the library is accurate to 3.9% in g-r, 2.7% in r-i, and 2.2% in i-z. The data are released as part of SDSS Data Release 15. We expect the final release of the library to contain more than 10,000 stars.

We have computed the Galactic Habitable Zones (GHZs) of the Andromeda galaxy (M31) based on the probability of terrestrial planet formation, which depends on the metallicity (Z) of the interstellar medium, and the number of formed stars per surface unit. The GHZ was therefore obtained from a chemical evolution model built to reproduce a precise metallicity gradient in the galactic disk, [O/H](r) $ = -0.015 \pm 0.003 dex kpc^{-1} x r(kpc) + 0.44 \pm 0.04 dex $. This gradient is the most probable when intrinsic scatter is present in the observational data. The chemical evolution model predicted a higher star formation history in both the halo and disk components of M31 and a less efficient inside-out galactic formation, compared to those of the Milky Way. If we assumed that Earth-like planets form with a probability law that follows the Z distribution shown by stars with detected planets and the SFH predicted by the CEM, the most probable GHZ per pc$^2$ is located between 3 and 7 kpc for planets with ages between 6 and 7 Gy, approximately. But the highest number of stars with habitable planets is in a ring located between 12 and 14 kpc with mean age of $\sim$7 Gy. 11 % and 6.5 % of the all formed stars in M31 may have planets with basic and complex life, respectively., Comment: 33 pages. 9 Figures. Accepted by Revista Mexicana de Astronomia y Astrofisica

Stellar spectral libraries play a pivotal role in astrophysics, helping us to understand the physics of stars and build models of stellar populations in order to study distant star clusters and galaxies. Aspects of current stellar spectral libraries that require improvement are: better calibrations, more stars, higher spectral resolution and broader wavelength coverage. The X-shooter spectrograph is well suited to the task, and we are building the X-shooter Spectral Library (XSL) of more than 700 stars covering the entire Hertzsprung-Russell diagram in the wavelength range 300-2480 nm at a mean resolving power of 10 000. Here we describe the sample, observations and reduction of the data, concentrating on the flux-calibrated, telluric-corrected near-ultraviolet and optical spectra of the first 237 unique stars observed in the first year of the survey. These spectra, the first data release, are now available at http://xsl.u-strasbg.fr/.