Completing the K-band Celestial Reference Frame in the North
Résumé
22 GHz (K-band) radio observations have the potential to form the basis for the most accurate celestial reference frame ever constructed. Relative to the standard 2.3/8.4 GHz (S/X) observing bands, K-band is expected to exhibit a reduction in extended source morphology and core-shift. This reduction in astrophysical systematics should allow for a more stable celestial reference frame at K-band and should also be advantageous in tying the VLBI radio frame to the Gaia optical frame. The current K-band catalog consists of only 279 sources from ten Very Long Baseline Array (VLBA) sessions producing uncertainties in source positions at the ˜100 μas level. Given that southern K-band observations in the mid-south and over the south polar cap are under way, this paper returns attention back to the north. Further, given that the VLBA's 2 Gbps data rate is now 16 times better than that used in the original northern K-band observations, the resulting four-fold increase in sensitivity makes now an opportune time to re-visit K-band celestial frame work in the north. Therefore, we have initiated a new program of astrometric and imaging observations in the north using the VLBA to improve K-band astrometric precision and spatial coverage as well as to map the intrinsic source structure so that their astrometric quality can be evaluated. Our goal is to have at least 500 sources in the final K-band reference frame. This paper discusses the initial results from the first two of four approved K-band VLBA sessions.