High‐Resolution Continuum Imaging at 1.3 and 0.7 Centimeters of the W3 IRS 5 Region

High-resolution images of the hypercompact HII regions (HCHII) in W3 IRS 5taken with the Very Large Array (VLA) at 1.3 and 0.7 cm are presented. FourHCHII regions were detected with sufficient signal-to-noise ratios to allow thedetermination of relevant parameters such as source position, size and fluxdensity. The sources are slightly extended in our ~0.2 arcsecond beams; thedeconvolved radii are less than 240 AU. A comparison of our data with VLAimages taken at epoch 1989.1 shows proper motions for sources IRS 5a and IRS5f. Between 1989.1 and 2002.5, we find a proper motion of 210 mas at a positionangle of 12 deg for IRS 5f and a proper motion of 190 mas at a position angleof 50 deg for IRS 5a. At the assumed distance to W3 IRS 5, 1.83 +/- 0.14 kpc,these offsets translate to proper motions of ~135 km/s and ~122 km/s$respectively. These sources are either shock ionized gas in an outflow orionized gas ejected from high mass stars. We find no change in the positions ofIRS 5d1/d2 and IRS 5b; and we show through a comparison with archival NICMOS2.2 micron images that these two radio sources coincide with the infrareddouble constituting W3 IRS 5. These sources contain B or perhaps O stars. Theflux densities of the four sources have changed compared to the epoch 1989.1results. In our epoch 2002.5 data, none of the spectral indicies obtained fromflux densities at 1.3 and 0.7 cm are consistent with optically thin free-freeemission; IRS 5d1/d2 shows the largest increase in flux density from 1.3 cm to0.7 cm. This may be an indication of free-free optical depth within an ionizedwind, a photoevaporating disk, or an accretion flow. It is less likely thatthis increase is caused by dust emission at 0.7 cm.Comment: 13 pages, 3 figures To be published in The Astrophysical Journa