XMM-Newton imaging of V1818 Ori: a young stellar group on the eastern edge of the Kappa Ori ring

We present the results of a 40 ks XMM-Newton observation centered on the variable star V1818 Ori. Using a combination of the XMM-Newton and AllWISE catalog data, we identify a group of about 31 young stellar objects around V1818 Ori. This group is coincident with the eastern edge of the dust ring surrounding Kappa Ori. Previously, we concluded that the young stellar objects on the western side of ring were formed in an episode of star formation that started 3-5 Myr ago, and are at a distance similar to that of kappa Ori (250-280 pc) and in the foreground to the Orion A cloud. Here we use the XMM-Newton observation to calculate X-ray fluxes and luminosities of the young stars around V1818 Ori. We find that their X-ray luminosity function (XLF), calculated for a distance of ~270 pc, matches the XLF of the YSOs west of Kappa Ori. We rule out that this group of young stars is associated to Mon R2 as assumed in the literature, but rather they are part of the same Kappa Ori's ring stellar population.Comment: 4 pages, 4 figures, 1 table. Accepted for publication to A&

Hubble Space Telescope NICMOS Imaging of W3 IRS 5: A Trapezium in the Making?

We present Hubble Space Telescope NICMOS imaging of W3 IRS 5, a binary high-mass protostar. In addition to the two protostars, NICMOS images taken in the F222M and F160W filters show three new 2.22 micron sources with very red colors; these sources fall within a region 5600 AU in diameter, and are coincident with a 100 solar mass dense molecular clump. Two additional point sources are found within 0.4'' (800 AU) of one of the high-mass protostars; these may be stellar companions or unresolved emission knots from an outflow. We propose that these sources constitute a nascent Trapezium system in the center of the W3 IRS 5 cluster containing as many as five proto OB stars. This would be the first identification of a Trapezium still deeply embedded in its natal gas.Comment: accepted to ApJ letter