CIT6 - uncertainty in its position

CIT6 is a.k.a. RW LMi, IRC+30219, AFGL 1403.

Its positions are quoted variously as :

The current (J2000) coordinates being used at JCMT are odd in their apparent coarseness in RA and specificity in Dec. However, inaccurate precession is not the cause of any error. It is unclear at this stage where our 1950 coordinates came from, but the precessed-to-2000 version seems to suffer some typographical contraction, and it would seem prudent to adopt the interferometric measures in preference.

The fixed difference in (RA,Dec) between the (coarse) JCMT position and the Carlstrom position generates the (az,el) error pattern shown below :

It resembles the transit effect although is of an amplitude somewhat smaller than that observed Nov 04 & 05. However, it seems reasonable to conclude that an erroneous position of the magnitude suggested in the table above is substantially the cause of these recent events.

The behaviour on 05/06 May 2001 was described in the fault report as tolerable. Actually, CIT6 is deviant by about 7" in elevation on the 05th in the sense seen above (my mitsake). On the 06th one measurement of two was made at a time when the errors would be small anyhow, and the other, if corrected according to the curves above, would still not seem too deviant in the context of the other systematics pervading these data.

08 Nov 2001The JCMT catalog entry for CIT6 is updated to reflect the Carlstom coordinates.

The precision (and accuracy) of other sources in our catalog - particularly the 'spectral line' sources - will be examined soon, although at first glance none seems so egregious as CIT6.