The local stellar population of nova regions in the Large Magellanic Cloud

Abstract

This study aims at identifying and understanding the parent population of novae in the Large Magellanic Cloud (LMC) by studying the local, projected, stellar population. The star formation history of the local environment around novae is studied based on photometric data of stars and star clusters in the nova neighbourhood, available in the OGLE II survey and star cluster catalogues. The age of the stellar population within a few arcmin around nova regions are estimated using isochrone fits to the V vs. (V-I) colour-magnitude diagrams. The fraction of stars in various evolutionary states are compared using luminosity functions of the main-sequence stars and the red giant stars. The age, density and luminosity function of the stellar population are estimated around 15 novae. The upper limit of the age of the intermediate stellar population is found to be 4 Gyr in all the regions, excepting the region around the slow nova LMC 1948. Star formation in these regions is found to have started between 4-2.0 Gyr ago, with a majority of the regions starting star formation at 3.2 Gyr. This star formation event lasted upto 1.6-0.8 Gyr. The star formation history of the underlying population of both the fast and moderately fast novae indicate their parent population to be similar and likely to be in the age range 3.2-1.0 Gyr. This is in good agreement with the theoretical age estimates for Galactic cataclysmic variables. The region around the slow nova shows a stellar population in the age range 1-10 Gyr, with a good fraction older than 4 Gyr. This indicates that the progenitor might belong to an older population, consistent with the idea that the progenitors of slow novae belong to older population.