Hα emission-line stars in molecular clouds

Abstract

A deep objective-prism survey for Hα emission stars towards the Canis Major star-forming clouds was performed. A total of 398 Hα emitters were detected, 353 of which are new detections. There is a strong concentration of these Hα emitters towards the molecular clouds surrounding the CMa OB1 association, and it is likely that these stars are young stellar objects recently born in the clouds. An additional population of Hα emitters is scattered all across the region, and probably includes unrelated foreground dMe stars and background Be stars. About 90% of the Hα emitters are detected by WISE, of which 75 % was detected with usable photometry. When plotted in a WISE colour-colour diagram it appears that the majority are Class II YSOs. Coordinates and finding charts are provided for all the new stars, and coordinates for all the detections. We searched the Gaia-DR2 catalogue and from 334 Hα emission stars with useful parallaxes, we selected a subset of 98 stars that have parallax errors of less than 20% and nominal distances in the interval 1050 to 1350 pc that surrounds a strong peak at 1185 pc in the distance distribution. Similarly, Gaia distances were obtained for 51 OB-stars located towards Canis Major and selected with the same parallax errors as the Hα stars. We find a median distance for the OB stars of 1182 pc, in excellent correspondence with the distance from the Hα stars. Two known runaway stars are confirmed as members of the association. Finally, two new Herbig-Haro objects are identified.

OB Associations and their origins

“…Recent surveys have begun to uncover the low-mass population of the association. Fischer et al (2016), Santos-Silva et al 2018and Pettersson & Reipurth (2019) used infrared, X-ray and Hα observations, respectively, to uncover hundreds of YSOs across the association and in nearby star forming regions. Fischer et al (2016) find the spatial distribution of young stars in the association to be highly clumpy, with multiple groups and clusters within it.…”

The New EXor Outburst of ESO-Hα 99 Observed by Gaia ATLAS and TESS

“…It appears that RCW 27 is a particularly fertile star-forming region. Pettersson & Reipurth (1994) carried out a large survey for Hα emission stars towards RCW 27, 32, and 33, many of which have subsequently been identified as T Tauri stars, e.g., by Prizinzano et al (2018). One of these young emission-line stars is ESO-Hα 99, the object of this paper.…”

“…As part of a spectroscopic survey of the brighter stars of the sample of Hα emission line stars in the VMR-D region of Pettersson & Reipurth (1994) a spectrum of ESO-Hα 99 was obtained on February 22, 1993 at the ESO 3.6m telescope with the OPTOPUS multi-object spectrograph and an exposure time of 2 × 30 min. The original data are no longer available, but a plot of the spectrum is.…”

Low-mass star formation and subclustering in the H II regions RCW 32, 33, and 27 of the Vela Molecular Ridge

“…The Vela Molecular Ridge (VMR) is a large molecular cloud complex, revealed by four strong emission peaks observed in the 1→0 transition of 12 CO (Murphy & May, 1991), indicating that active SF is taking place (Pettersson, 2008). It is located in the constellations of Puppis and Vela and it is part of a complex region including the very large H II Gum Nebula, the Vela supernova remnant and also a remarkable annular system of cometary globules (Pettersson, 2008). Murphy & May (1991) identified four main clouds within the VMR, named A, B, C and D, with the clouds A, C and D located at 0.7±0.2 kpc and the B cloud located a 2 kpc.…”

“…Other surveys based on NIR and CO observations have been conducted in the whole VMR region with the aim of finding signs of embedded YSOs. A detailed review is given in Pettersson (2008).…”