ISOLATED WOLF–RAYET STARS AND O SUPERGIANTS IN THE GALACTIC CENTER REGION IDENTIFIED VIA PASCHEN-α EXCESS

Abstract

We report the discovery of 19 hot, evolved, massive stars near the Galactic center region (GCR). These objects were selected for spectroscopy owing to their detection as strong sources of Paschen-α emission-line excess, following a narrowband imaging survey of the central 0. • 65 × 0. • 25 (l, b) around Sgr A * with the Hubble Space Telescope. Discoveries include five carbon-type (WC) and six nitrogen-type (WN) Wolf-Rayet stars, six O supergiants, and two B supergiants. Two of the O supergiants have X-ray counterparts, the properties of which are broadly consistent with colliding-wind binaries and solitary O stars. The infrared photometry of 17 stars is consistent with the Galactic center distance, but two of them are located in the foreground. Several WC stars exhibit a relatively large infrared excesses, which is possibly the signature of thermal emission from hot dust. Most of the stars appear scattered throughout the GCR, with no relation to the three known massive young clusters; several others lie near the Arches and Quintuplet clusters and may have originated within one of these systems. The results of this work bring the total sample of Wolf-Rayet stars in the GCR to 92. All sources of strong Pα excess have been identified in the area surveyed with HST, which implies that the sample of WN stars in this region is near completion, and is dominated by late (WNL) subtypes. The current WC sample, although probably not complete, is almost exclusively dominated by late (WCL) subtypes. The observed Wolf-Rayet subtype distribution in the GCR is a reflection of the intrinsic rarity of early subtypes (WNE and WCE) in the inner Galaxy, an effect that is driven by metallicity.

An interesting candidate for isolated massive-star formation in the Small Magellanic Cloud

“…This means that a small percentage, about 5%, of high mass stars may form in isolation, in very good agreement with the finding by Parker & Goodwin (2007). Even in the Galactic center region, a number of Wolf-Rayet stars and O supergiants might have formed in isolation (Mauerhan et al 2010). Lamb et al (2010) observed eight apparently isolated O stars in the SMC.…”

First detections of FS Canis Majoris stars in clusters

“…Interestingly, the discovery we present below is carried out through observations in the Paschen-α line that were initially aimed at finding hot massive evolved cluster members. P α observations have been already proven to be very effective to find such stars in clusters (Davies et al 2012a,b) or in the central region of the Milky Way (Mauerhan et al 2010a;Dong et al 2011), however this method has never been used to locate lower luminosity emission-line objects like FS CMa stars.…”

Unveiling the massive stars in the Galactic center

“…Because P100 and P107 are relatively older than the Arches cluster (Dong et al, in preparation), future proper motion are needed to confirm their relationship. Combined with three WNh stars within 1-2 pc of the Arches cluster suggested by Mauerhan et al (2010), there are five 'field' EMSs which could have been ejected from the Arches cluster.…”