Baade’s window and APOGEE

Metallicities, ages, and chemical abundances

¹ Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Bd de l’Observatoire, 06304 Nice, France
e-mail: mathias.schultheis@oca.eu
² Departamento de Fisica, Facultad de Ciencias Exactas, Universidad Andres Bello Av. Fernandez Concha 700, 7591538 Las Condes, Santiago, Chile
³ Millennium Institute of Astrophysics, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
⁴ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
⁵ Universidad de La Laguna, Dpto. Astrofísica, 38206 La Laguna, Tenerife, Spain
⁶ Observatório Nacional, 20921-400 Sao Cristóvao, Rio de Janeiro, Brazil
⁷ New Mexico State University, Las Cruces, NM 88003, USA
⁸ Department of Physics and JINA Center for the Evolution of the Elements, Univ. of Notre Dame, Notre Dame, IN 46556, USA
⁹ Apache Point Observatory and New Mexico State University, PO Box 59, Sunspot, NM 88349-0059, USA
¹⁰ Sternberg Astronomical Institute, Moscow State University, 119991 Moscow, Russia
¹¹ Departamento de Astronomía, Casilla 160-C, Universidad de Concepción, Concepción, Chile
¹² Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802, USA
¹³ The Observatoire des sciences de l’Univers de Besançon, 41 avenue de l’Observatoire, 25000 Besançon, France
¹⁴ ICG-University of Portsmouth, Dennis Sciama Building, Burnaby Rd., Portsmouth, PO13 FX, UK
¹⁵ Vatican Observatory, V 00120 Vatican City State, Italy
¹⁶ Unidad de Astronomía, Universidad de Antofagasta, Avenida Angamos 601, 1270300 Antofagasta, Chile
¹⁷ Departamento de Física, Facultad de Ciencias, Universidad de La Serena, Cisternas 1200, La Serena, Chile
¹⁸ Institute for Gravitation and the Cosmos, The Pennsylvania State University, University Park, PA 16802, USA
¹⁹ Center for Astrophysical Sciences, Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
²⁰ Department of Physics & Astronomy, University of Utah, 115 S. 1400 E., Salt Lake City, UT 84112, USA
²¹ Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA
²² Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile

Received: 28 November 2016
Accepted: 5 February 2017

Abstract

Context. Baade’s window (BW) is one of the most observed Galactic bulge fields in terms of chemical abundances. Owing to its low and homogeneous interstellar absorption it is considered the perfect calibration field for Galactic bulge studies.

Aims. In the era of large spectroscopic surveys, calibration fields such as BW are necessary for cross calibrating the stellar parameters and individual abundances of the APOGEE survey.

Methods. We use the APOGEE BW stars to derive the metallicity distribution function (MDF) and individual abundances for α- and iron-peak elements of the APOGEE ASPCAP pipeline (DR13), as well as the age distribution for stars in BW.

Results. We determine the MDF of APOGEE stars in BW and find a remarkable agreement with that of the Gaia-ESO survey (GES). Both exhibit a clear bimodal distribution. We also find that the Mg-metallicity planes of the two surveys agree well, except for the metal-rich part ([Fe/H] > 0.1), where APOGEE finds systematically higher Mg abundances with respect to the GES. The ages based on the [C/N] ratio reveal a bimodal age distribution, with a major old population at ~ 10 Gyr, with a decreasing tail towards younger stars. A comparison of stellar parameters determined by APOGEE and those determined by other sources reveals detectable systematic offsets, in particular for spectroscopic surface gravity estimates. In general, we find a good agreement between individual abundances of O, Na, Mg, Al, Si, K, Ca, Cr, Mn, Co, and Ni from APOGEE with that of literature values.

Conclusions. We have shown that in general APOGEE data show a good agreement in terms of MDF and individual chemical abundances with respect to literature works. Using the [C/N] ratio we found a significant fraction of young stars in BW.