2008/05/26 by Fabien Grisé, F. Grisé, M. W. Pakull +6
Physics and Astronomy · #Accretion (finance) #Accretion disc #Adaptive optics and wavefront sensing #Amplitude #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Cluster (spacecraft) #Galaxies: Formation, Evolution, Phenomena #Photometry (optics) #Physics #Sky #Stars #astro-ph
paper · pdf · doi:10.1051/0004-6361:200809557
13 pages, 11 figures. Accepted for publication in Astronomy & Astrophysics
arxiv created 2008/05/26 · openalex publication_date 2008/05/27 · arxiv updated 2009/12/01 · openalex created_date 2022/08/13 · openalex updated_date 2026/07/31
NGC 1313 X-2 is one of the brightest ultraluminous X-ray sources in the sky, at both X-ray and optical wavelengths; therefore, quite a few studies of available ESO VLT and HST data have appeared in the literature. Here, we present our analysis of VLT/FORS1 and HST/ACS photometric data, confirming the identification of the B ~ 23 mag blue optical counterpart. We show that the system is part of a poor cluster with an age of 20 Myr, leading to an upper mass limit of some 12 for the mass donor. We attribute the different results with respect to earlier studies to the use of isochrones in the F435W and F555W HST/ACS photometric system that appear to be incompatible with the corresponding Johnson B and V isochrones. The counterpart exhibits significant photometric variability of about 0.2 mag amplitude, both between the two HST observations and during the one month of monitoring with the VLT. This includes variability within one night and suggests that the light is dominated by the accretion disk in the system and not by the mass donor.