GC-IRS13E—A PUZZLING ASSOCIATION OF THREE EARLY-TYPE STARS

Abstract

We present a detailed analysis of high resolution near-infrared imaging and\nspectroscopy of the potential star cluster IRS13E very close to the massive\nblack hole in the Galactic Center. We detect 19 objects in IRS13E from Ks-band\nimages, 15 of which are also detected reliably in H-band. We derive consistent\nproper motions for these objects from the two bands. Most objects share a\nsimilar westward proper motion. We characterize the objects using spectroscopy\n(1.45 to 2.45 micrometer) and (narrow-band) imaging from H- (1.66 mircrometer)\nto L'-band (3.80 micrometer). Nine of the objects detected in both Ks- and\nH-band are very red, and we find that they are all consistent with being warm\ndust clumps. The dust emission may be caused by the colliding winds of the two\nWolf-Rayet stars in the cluster. Three of the six detected stars do not share\nthe motion or spectral properties of the three bright stars. This leaves only\nthe three bright, early-type stars as potential cluster members. It is unlikely\nthat these stars are a chance configuration. Assuming the presence of an IMBH,\na mass of about 14000 solar masses follows from the velocities and positions of\nthese three stars. However, our acceleration limits make such an IMBH nearly as\nunlikely as a chance occurrence of such a star association. Furthermore, there\nis no variable X-ray source in IRS13E despite the high density of dust and gas.\nTherefore, we conclude that is unlikely that IRS13E hosts a black hole massive\nenough to bind the three stars.\n