The X-shooter Spectral Library (XSL): Data release 2 A. Gonneau, M. Lyubenova, A. Lançon, S. Trager, R. Peletier, A. Arentsen, Y.-P. Chen, P. Coelho, M. Dries, J. Falcón-Barroso, et al. To cite this version: A. Gonneau, M. Lyubenova, A. Lançon, S. Trager, R. Peletier, et al.. The X-shooter Spectral Library (XSL): Data release 2. Astronomy and Astrophysics - A&A, EDP Sciences, 2020, 634, pp.A133. 10.1051/0004-6361/201936825. hal-03152017 HAL Id: hal-03152017 https://hal.archives-ouvertes.fr/hal-03152017 Submitted on 28 Feb 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. A&A 634, A133 (2020) Astronomy https://doi.org/10.1051/0004-6361/201936825 & c ESO 2020 Astrophysics The X-shooter Spectral Library (XSL): Data release 2?,?? A. Gonneau1,2,4 , M. Lyubenova3,2, A. Lançon4, S. C. Trager2, R. F. Peletier2, A. Arentsen7,2, Y.-P. Chen6, P. R. T. Coelho11, M. Dries2, J. Falcón-Barroso8,9, P. Prugniel5, P. Sánchez-Blázquez10, A. Vazdekis8,9, and K. Verro2 1 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK e-mail: [email protected] 2 Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands 3 ESO, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany 4 Observatoire Astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de l’Université, 67000 Strasbourg, France 5 CRAL-Observatoire de Lyon, Université de Lyon, Lyon I, CNRS, UMR 5574, Lyon, France 6 New York University Abu Dhabi, PO Box 129188, Abu Dhabi, UAE 7 Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany 8 Instituto de Astrofísica de Canarias, Vía Láctea s/n, La Laguna, Tenerife, Spain 9 Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain 10 Departamento de Física de la Tierra y Astrofísica, UCM, 28040 Madrid, Spain 11 Universidade de São Paulo, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Rua do Matão 1226, 05508-090 São Paulo, Brazil Received 1 October 2019 / Accepted 29 December 2019 ABSTRACT We present the second data release (DR2) of the X-shooter Spectral Library (XSL), which contains all the spectra obtained over the six semesters of that program. This release supersedes our first data release from Chen et al. (2014, A&A, 565, A117), with a larger number of spectra (813 observations of 666 stars) and with a more extended wavelength coverage as the data from the near- infrared arm of the X-shooter spectrograph are now included. The DR2 spectra then consist of three segments that were observed simultaneously and, if combined, cover the range between ∼300 nm and ∼2.45 µm at a spectral resolving power close to R = 10 000. The spectra were corrected for instrument transmission and telluric absorption, and they were also corrected for wavelength-dependent flux-losses in 85% of the cases. On average, synthesized broad-band colors agree with those of the MILES library and of the combined IRTF and Extended IRTF libraries to within ∼1%. The scatter in these comparisons indicates typical errors on individual colors in the XSL of 2−4%. The comparison with 2MASS point source photometry shows systematics of up to 5% in some colors, which we attribute mostly to zero-point or transmission curve errors and a scatter that is consistent with the above uncertainty estimates. The final spectra were corrected for radial velocity and are provided in the rest-frame (with wavelengths in air). The spectra cover a large range of spectral types and chemical compositions (with an emphasis on the red giant branch), which makes this library an asset when creating stellar population synthesis models or for the validation of near-ultraviolet to near-infrared theoretical stellar spectra across the Hertzsprung-Russell diagram. Key words. Hertzsprung-Russell and C-M diagrams – catalogs 1. Introduction new instrumentation1 (e.g., Coelho 2009; Husser et al. 2013; Allende Prieto et al. 2018 for the theoretical side and Vazdekis Stellar spectral libraries are fundamental resources that shape et al. 2016; Villaume et al. 2017 for the empirical side). our understanding of stellar astrophysics and allow us to study For the purpose of building stellar population synthesis mo- the stellar populations of galaxies across the Universe. These dels, a good stellar library should have four key properties, as libraries come in two flavors: empirical, which are composed highlighted by Trager(2012): an exhaustive coverage of all stel- of a well-defined set of stars with certain stellar atmospheric lar evolutionary phases and chemical compositions to represent parameters coverage, and theoretical where stellar spectra are as well as possible the integrated light of real stellar systems; computed for an arbitrarily large set of parameters and extensive a broad wavelength coverage since not all stellar phases con- wavelength coverage. The list of empirical and theoretical spec- tribute equally at all wavelengths; simultaneous observations at tral libraries grows continuously due to their versatile usage in all wavelengths to avoid issues due to temporal stellar spectral modern astrophysics and they are boosted by developments of variations; and good calibration of the individual stars in terms of flux and wavelength calibration as well as high-precision stellar atmospheric parameters. This latter point requires com- ? Table C.1 and the spectra are only available at the CDS via anony- mous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http: parison with synthetic stellar spectra, which highlights another //cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/634/A133 ?? Based on observations collected at ESO Paranal La Silla Obser- 1 For an extensive list of stellar spectral libraries see David Montes’ vatory, Chile, Prog. IDs 084.B-0869, 085.B-0751, and 189.B-0925 (PI web collection at https://webs.ucm.es/info/Astrof/invest/ Trager). actividad/spectra.html and references therein. Article published by EDP Sciences A133, page 1 of 20 A&A 634, A133 (2020) important application of libraries with the above properties: the 75° validation and improvement of theoretical stellar models across 60° 45° the Hertzsprung-Russell (HR) diagram and across wavelengths. These were the goals of the X-shooter Spectral Library 30° (XSL), which is a moderate-resolution (R ∼ 10 000) spectral 15° library that was designed to cover most of the HR diagram. The 14h 0h 10h 0° observations were carried out with the X-shooter three-arm spec- DEC trograph on ESO’s VLT (Vernet et al. 2011) in two phases, a -15° pilot and an ESO Large Program, spanning six semesters in total. -30° In our first data release (hereafter DR1, Chen et al. 2014), we present spectra of 237 unique stars, which were observed during -45° -60° the pilot program, for a wavelength range that was restricted to -75° RA the two optical arms of X-shooter (300–1024 nm). In the current data release (DR2), we present our full set Fig. 1. Positions of XSL stars in the sky (Aitoff projection). of 813 observations of 666 stars, now also including data from the near-infrared (NIR) arm of X-shooter. This NIR exten- with a wide range of chemical compositions. Our original sam- sion is undoubtedly one of the main advantages of XSL over ple consists of 679 unique stars. The primary references for the other empirical spectral libraries in the literature. Empirical NIR construction of the XSL target list were existing spectral libraries libraries for a relatively wide range of stellar parameters have or compilations of stellar parameter measurements. In particular, been constructed in the past, first at very low spectral resolution the XSL sample has a strong overlap with the MILES spectral (e.g., Johnson & Méndez 1970; Lançon & Rocca-Volmerange library (142 stars, Sánchez-Blázquez et al. 2006; Cenarro et al. 1992), then progressively at intermediate resolution (e.g., Lançon 2007) and the NGSL library (135 stars, Gregg et al. 2006). We & Wood 2000; Ivanov et al. 2004; Rayner et al. 2009; Villaume completed the list with objects from the parameter compilation et al. 2017), or at higher spectral resolution but in restricted wave- PASTEL (Soubiran et al. 2010, 2016) and from a variety of more length ranges (e.g., Cenarro et al. 2001; Majewski et al. 2017). We specialised catalogs (see Table A.1 for details and corresponding note that some of these libraries did not attempt to preserve the references). In Fig.1 we plot the distribution of the selected XSL shapes of the stellar continua across the wavelengths observed. stars on the sky. Only some have been combined with optical libraries for the pur- More than half of the stars in the XSL library are red giants pose of calculating the spectra of synthetic stellar populations in the broad sense, which includes red supergiants or asymptotic (e.g., Pickles 1998; Lançon et al. 1999, 2008; Vazdekis et al. giant branch stars. These stars provide strong (age-dependent) 2003; Maraston 2005; Röck et al. 2016; Conroy et al. 2018). In contributions to the NIR emission of galaxies (e.g., Lançon et al. these efforts, the need to merge optical and NIR observations 1999; Maraston 2005; Melbourne et al. 2012). The luminous red of distinct samples of stars is an inevitable cause of system- stars in XSL are located in star clusters, in the field, in the Galac- atic errors.