2007/07/13 by Pavel K. Abolmasov, Douglas A. Swartz, S. Fabrika +3 · 1 citation
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #Cluster (spacecraft) #Emission spectrum #Line (geometry) #Nebula #Photoionization #Solar mass #Spectral line #Star cluster #Stars #Stellar, planetary, and galactic studies #Supernova #astro-ph
paper · pdf · doi:10.1086/520828
17 pages, accepted to ApJ
arxiv created 2007/07/13 · openalex publication_date 2007/10/10 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
Optical photometric and spectroscopic data are presented that show an association of an ultraluminous X-ray source in NGC 7331 with a young star cluster of mass M = (1.1 ± 0.2) × 10 5 M ☉ and age t c = 4.25 ± 0.25 Myr. If the ULX is part of the bright stellar cluster, then the mass of the progenitor of the compact accretor must have been ≳40-50 M ☉ in order to already have evolved through the supernova stage into a compact object. The companion star is also probably an evolved massive star. The emission-line spectrum of the nebula surrounding the cluster can be interpreted as being a result of photoionization by the cluster OB stars with an additional source of shock excitation producing strong [S II], [O I], and N II lines. This additional source appears to be as much as 5 times more powerful than the supernovae and stellar winds in the cluster can provide for. Additional mechanical energy input associated with the ULX itself can help explain the residual shock-excited line luminosities of the emission region.