YOUNG STELLAR POPULATIONS IN MYStIX STAR-FORMING REGIONS: CANDIDATE PROTOSTARS

Abstract

The Massive Young Star Forming Complex in Infrared and X-ray (MYStIX) project provides a new census on stellar members of massive star forming regions within 4 kpc. Here the MYStIX Infrared Excess catalog (MIRES) and Chandra-based X-ray photometric catalogs are mined to obtain high-quality samples of Class I protostars using criteria designed to reduce extragalactic and Galactic field star contamination. A total of 1,109 MYStIX Candidate Protostars (MCPs) are found in 14 star forming regions. Most are selected from protoplanetary disk infrared excess emission, but 20% are found from their ultrahard X-ray spectra from heavily absorbed magnetospheric flare emission. Two-thirds of the MCP sample is newly reported here. The resulting samples are strongly spatially associated with molecular cores and filaments on Herschel far-infrared maps. This spatial agreement and other evidence indicate that the MCP sample has high reliability with relatively few 'false positives' from contaminating populations. But the limited sensitivity and sparse overlap among the infrared and X-ray subsamples indicate that the sample is very incomplete with many 'false negatives'. Maps, tables, and source descriptions are provided to guide further study of star formation in these regions. In particular, the nature of ultrahard X-ray protostellar candidates without known infrared counterparts needs to be elucidated.

IRAS 09002-4732: A Laboratory for the Formation of Rich Stellar Clusters

“…Our follow-up study found a rich group of 24 candidate Class 0/I protostars in the region 09 h 01 m 12 s < α < 09 • 02 24 and -47:40< δ <-47:45 (Romine et al 2016). They lie along a dusty filament seen in Herschel infrared maps that is oriented northwest to southeast, bifurcated by the older IRAS 09002-4732 star cluster.…”

Candidate X-Ray-emitting OB Stars in MYStIX Massive Star-forming Regions

“…This is not surprising, given that no large H II region is present in DR21 (Figure 2h), and the most luminous IR point sources are protostars and pre-main sequence stars with dusty disks Romine et al 2016). Bright, extended MIR emission associated with embedded massive stars also foils the MYStIX MIR point-source photometry.…”

Star Formation In Nearby Clouds (SFiNCs): X-Ray and Infrared Source Catalogs and Membership

“…Complementary to the MYStIX sample of >30,000 probable cluster members , Romine et al (2016) provide the catalog of >1000 MYStIX candidate ClassI protostars. The science studies on stellar mass segregation (M. A.…”

“…Since the J−H color is also a surrogate for spectral type, its values for many known lightly/moderately absorbed OB-type members are shifted downwards with respect to the PMS locus. In their MYStIX science study of new protostellar objects in the MYStIX regions, Romine et al (2016) usedX-ray median energy >4.5 keV as a strict criterion to discriminate ClassI protostars from ClassII-III systems.…”