First stellar spectroscopy in Leo P

¹ UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
e-mail: chris.evans@stfc.ac.uk
² Department of Astronomy, University of Michigan, 1085 S. University Avenue, Ann Arbor, MI 48109-1107, USA
³ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁴ Centro de Astrobiología, CSIC-INTA, Ctra. Torrejón a Ajalvir km.4, 28850 Torrejón de Ardoz, Madrid, Spain
⁵ Astrophysics Research Institute, Liverpool John Moores University, Liverpool L3 5RF, UK
⁶ Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
⁷ Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
⁸ ESA, European Space Astronomy Centre, Apdo. de Correos 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁹ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
¹⁰ Universidad de La Laguna, Dpto. Astrofísica, 38206 La Laguna, Tenerife, Spain
¹¹ Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, UK
¹² Department of Astronomy, University of California Berkeley, Berkeley, CA 94720, USA

Received: 27 August 2018
Accepted: 21 December 2018

Abstract

We present the first stellar spectroscopy in the low-luminosity (M_V ∼ −9.3 mag), dwarf galaxy Leo P. Its significantly low oxygen abundance (3% solar) and relative proximity (∼1.6 Mpc) make it a unique galaxy in which to investigate the properties of massive stars with near-primordial compositions akin to those in the early Universe. From our VLT-MUSE spectroscopy we find the first direct evidence for an O-type star in the prominent H II region, providing an important test case to investigate the potential environmental dependence of the upper end of the initial mass function in the dwarf galaxy regime. We classify 14 further sources as massive stars (and 17 more as candidate massive stars), most likely B-type objects. From comparisons with published evolutionary models we argue that the absolute visual magnitudes of massive stars in very metal-poor systems such as Leo P and I Zw 18 may be fainter by ∼0.5 mag compared to Galactic stars. We also present spectroscopy of two carbon stars identified previously as candidate asymptotic-giant-branch stars. Two of three further candidate asymptotic-giant-branch stars display Ca II absorption, confirming them as cool, evolved stars; we also recover Ca II absorption in the stacked data of the next brightest 16 stars in the upper red giant branch. These discoveries will provide targets for future observations to investigate the physical properties of these objects and to calibrate evolutionary models of luminous stars at such low metallicity. The MUSE data also reveal two 100 pc-scale ring structures in Hα emission, with the H II region located on the northern edge of the southern ring. Lastly, we report serendipitous observations of 20 galaxies, with redshifts ranging from z = 0.39, to a close pair of star-forming galaxies at z = 2.5.