A CLUSTER OF COMPACT RADIO SOURCES IN W40

We present deep 3.6 cm radio continuum observations of the HII region W40 obtained using the Very Large Array in its A and B configurations. We detect a total of 20 compact radio sources in a region of 4 x 4 arcmin, with 11 of them concentrated in a band with 30 arcsec of extent. We also present JHK photometry of the W40 cluster taken with the QUIRC instrument on the University of Hawaii 2.2 meter telescope. These data reveal that 15 of the 20 VLA sources have infrared counterparts, and 10 show radio variability with periods less than 20 days. Based on these combined radio and IR data, we propose that 8 of the radio sources are candidate ultracompact HII regions, 7 are likely to be young stellar objects, and 2 may be shocked interstellar gas.
Comment: Accepted for publication in the Astronomical Journal. 10 pages, 4 figures, plus online table in electronic version