A search for pulsations in the HgMn star HD 45975 with CoRoT photometry and ground-based spectroscopy^⋆

¹ Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août, Bât. B5c, 4000 Liège, Belgium
e-mail: morel@astro.ulg.ac.be
² LESIA, Observatoire de Paris, CNRS, 5 place J. Janssen, 92190 Meudon, France
³ LUTH, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place J. Janssen, 92190 Meudon, France
⁴ Byurakan Astrophysical Observatory, Aragatzotn Province, 0213 Byurakan, Armenia
⁵ Astronomical Institute, Wrocław University, Kopernika 11, 51-622 Wrocław, Poland
⁶ Argelander-Institut für Astronomie der Universität Bonn, auf dem Hügel 71, 53121 Bonn, Germany
⁷ Thüringer Landessternwarte Tautenburg (TLS), Sternwarte 5, 07778 Tautenburg, Germany
⁸ Leibniz-Institut für Astrophysik Potsdam (AIP), an der Sternwarte 16, 14482 Potsdam, Germany
⁹ College of Graduate Studies, University of South Africa, PO Box 392, UNISA 0003 Johannesburg, South Africa
¹⁰ Centre de Recherche en Astronomie, Astrophysique et Géophysique (CRAAG), route de l’Observatoire, BP 63 Bouzareah, 16340 Alger, Algeria
¹¹ INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate ( LC), Italy
¹² Dipartimento di Scienza e Alta Tecnologia, Università dell’Insubria, via Valleggio 11, 22100 Como, Italy
¹³ Instituut voor Sterrenkunde, K.U. Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
¹⁴ Centro de Astrofísica e Faculdade de Ciências da Universidade do Porto, rua das Estrelas, 4150-762 Porto, Portugal
¹⁵ Astronomical Observatory Institute, Faculty of Physics, A. Mickiewicz University, Słoneczna 36, 60-286 Poznań, Poland
¹⁶ Royal Observatory of Belgium, 3 avenue Circulaire, 1180 Brussels, Belgium
¹⁷ Institut d’Astronomie et d’Astrophysique, Université libre de Bruxelles, Boulevard du Triomphe CP 226, 1050 Bruxelles, Belgium

Received: 16 July 2013
Accepted: 28 October 2013

Abstract

The existence of pulsations in HgMn stars is still being debated. To provide the first unambiguous observational detection of pulsations in this class of chemically peculiar objects, the bright star HD 45975 was monitored for nearly two months by the CoRoT satellite. Independent analyses of the light curve provide evidence of monoperiodic variations with a frequency of 0.7572 d^-1 and a peak-to-peak amplitude of ~2800 ppm. Multisite, ground-based spectroscopic observations overlapping the CoRoT observations show the star to be a long-period, single-lined binary. Furthermore, with the notable exception of mercury, they reveal the same periodicity as in photometry in the line moments of chemical species exhibiting strong overabundances (e.g., Mn and Y). In contrast, lines of other elements do not show significant variations. As found in otherHgMn stars, the pattern of variability consists in an absorption bump moving redwards across the line profiles. We argue that the photometric and spectroscopic changes are more consistent with an interpretation in terms of rotational modulation of spots at the stellar surface. In this framework, the existence of pulsations producing photometric variations above the ~50 ppm level is unlikely in HD 45975. This provides strong constraints on the excitation/damping of pulsation modes in this HgMn star.