On the population of galactic Luminous Blue Variables

¹ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK e-mail: jsc@star.ucl.ac.uk
² Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
³ Astronomical Institute of St. Petersburg University, St. Petersburg, Petrodvorets, Universitetsky pr. 28, 198504 St. Petersburg, Russia
⁴ Isaac Newton Institute of Chile, St. Petersburg Branch
⁵ Central Astronomical Observatory, 196140 St. Petersburg, Russia

Received: 17 December 2004
Accepted: 28 January 2005

Abstract

We report the first results of a long term infrared monitoring campaign of known and candidate galactic Luminous Blue Variables (LBVs). In particular, we are able to confirm the LBV nature of G24.73+0.69, a luminous mid-B supergiant associated with a dusty ejection nebula. We find that prior to 2003 September G24.73+0.69 exhibited low amplitude ( mag) variability, but in the ~200 day period between 2003 September–2004 April it abruptly brightened by ~0.7 mag in the broadband J filter. Subsequently, a further ~0.4 mag increase was observed between 2004 April–October, resulting in an overall difference of ~1.1 mag between (current) photometric mimimum and maximum; similar variability also being observed in the H and K bands. In light of the numerous recent IR studies of the galactic hot star population we also compile an updated census of confirmed and candidate galactic LBVs, reporting 12 and 23 members respectively for each class. Finally, we utilise this new census to construct an H-R diagram for the galactic LBV population, resulting in a striking confirmation of the LBV-minimum light strip.