The aim of this project is to determine a population of Luminous Blue Variable stars (LBVs) in external galaxies in the Local Group. This is important as this phase of Post Main Sequence (PMS) life is critical in determining the mass of the relativistic remnant left behind after the supernova event. To accomplish this, we will obtain photometric observations of spectroscopic candidates identified in e.g. Massey et al (2007).
Initial target selection will include spectroscopically classified LBVs, with a supplemental list drawn from point sources with the appropriate colours etc. (to appear in the final published ApJ paper). Massey et al. (2007) identify 24 known or suspected LBVs in M31, 37 in M33, 1 in NGC6822 and 3 in IC10.
In addition, these observations will also identify variability amongst a wide variety of other objects within the host galaxy, including other massive variables such as Be and Wolf-Rayet stars.
Observing Strategy:
The timescale of variability for LBVs is typically years-to-decades, with a magnitude range of typically 1-2 in V band, with an associated colour change as the star expands and cools. We thus require broadband photometry with a sampling frequency of once per month to identify any variables. Subsequent to this, we will require multi-wavelength observations to characterise colour (temperature) changes in the candidate variables stars. The typical target magnitudes are V~19-20, with a required photometric accuracy of +/-0.05.
Outputs:
Photometric variability study of massive variables in the target galaxies – identification of LBVs, assisting with characterisation of range/duration of active behaviour, hence determination of mass loss to star during this phase.
Identification (and characterisation?) of other variables in the field (possibly including novae in M31, M33?), such as Be and Wolf-Rayet stars.
Future:
Request spectroscopic follow-up of targets identified in first year of survey (prioritising LBV candidates).
DIRECT survey data is sampling over several months, rather than several years – could repeat a survey of the DIRECT fields to search for long timescale variability (e.g. LBVs) that could have been missed. Check when DIRECT observations were obtained, confirm that timescale of variability being sampled is only ~4 months. DIRECT studied a few specific areas within the target galaxies – we could repeat these and/or image new areas not previously studied.
