Short-term variability and mass loss in Be stars

IV. Two groups of closely spaced, approximately equidistant frequencies in three decades of space photometry of ν Puppis (B7-8 IIIe)^{⋆,⋆⋆,⋆⋆⋆}

¹ European Organisation for Astronomical Research in the Southern Hemisphere (ESO), Karl-Schwarzschild-Str. 2, 85748, Garching
e-mail: dbaade@eso.org
² Astronomical Institute, Wrocław University, Kopernika 11, Wrocław 51-622, Poland
³ European Organisation for Astronomical Research in the Southern Hemisphere (ESO), Santiago 19, Casilla 19001, Chile
⁴ Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, GA 30302-5060, Atlanta PO Box 5060, USA
⁵ Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, Warsaw 00-716, Poland
⁶ Observatório Nacional, Rua General José Cristino 77, São Cristóvão, Rio de Janeiro 20921-400, Brazil
⁷ Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Cidade Universitária, Rua do Matão 1226, São Paulo, SP 05508-900, Brazil
⁸ Institut für Kommunikationsnetze und Satellitenkommunikation, Technical University Graz, Inffeldgasse 12, Graz 8010, Austria
⁹ Département de physique and Centre de Recherche en Astrophysique du Québec (CRAQ), Université de Montréal, CP 6128, Succ. Centre-Ville, Montréal Québec H3C 3J7, Canada
¹⁰ AAVSO Headquarters, 49 Bay State Rd., Cambridge, MA 02138, USA
¹¹ Department of Astronomy and Astrophysics, University of Toronto, 50 St. George St., Toronto, Ontario M5S 3H4, Canada
¹² Department of Physics and Space Science, Royal Military College of Canada, Stn Forces, Ontario K7K 7B4, , Kingston PO Box 17000, Canada
¹³ Institute of Astrophysics, University of Vienna, Universitätsring 1, Vienna 1010, Austria
¹⁴ Universität Innsbruck, Institut für Astro- und Teilchenphysik, Technikerstrasse 25, Innsbruck 6020, Austria

Received: 30 August 2018
Accepted: 13 October 2018

Abstract

Context. In early-type Be stars, groups of nonradial pulsation (NRP) modes with numerically related frequencies may be instrumental for the release of excess angular momentum through mass-ejection events. Difference and sum/harmonic frequencies often form additional groups.

Aims. The purpose of this study is to find out whether a similar frequency pattern occurs in the cooler third-magnitude B7-8 IIIe shell star ν Pup.

Methods. Time-series analyses were performed of space photometry with BRITE-Constellation (2015, 2016/17, and 2017/18), SMEI (2003–2011), and HIPPARCOS (1989–1993). Two IUE SWP and 27 optical echelle spectra spanning 20 years were retrieved from various archives.

Results. The optical spectra exhibit no anomalies or well-defined variabilities. A magnetic field was not detected. All three photometry satellites recorded variability near 0.656 c/d which is resolved into three features separated by ∼0.0021 c/d. Their first harmonics and two combination frequencies form a second group, whose features are similarly spaced by 0.0021 c/d. The frequency spacing is very nearly but not exactly equidistant. Variability near 0.0021 c/d was not detected. The long-term frequency stability could be used to derive meaningful constraints on the properties of a putative companion star. The IUE spectra do not reveal the presence of a hot subluminous secondary.

Conclusions. ν Pup is another Be star exhibiting an NRP variability pattern with long-term constancy and underlining the importance of combination frequencies and frequency groups. This star is a good target for efforts to identify an effectively single Be star.