THE ASTRONOMER Electronic Circular No 728 1993 Apr 08 19.50UT Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise, Basingstoke, Hants, RG22 4PP,England. Telephone/FAX(0256)471074 Int:+44256471074 TELEX: 9312111261 Answerback: TA G TELECOM GOLD: 10074:MIK2885 GMH at UK.AC.RUTHERFORD.STARLINK.ASTROPHYSICS STARLINK: RLSAC::GMH GMH at UK.AC.CAM.ASTRONOMY.STARLINK STARLINK: CAVAD::GMH ------------------------------------------------------------------- SUPERNOVA 1993J IN NGC 3031 M. Richmond, Princeton University, provides the following J2000.0 position of the supernova, reduced from the Treffers CCD images using the Guide Star Catalogue: R.A. = 9h55m25s.00, Decl. = +69D01'13".3. The corresponding end figures for the position by Hartwick et al. (cf E721) are 25s.00, 13".7. Richmond gives the offset from the mag 14 foreground star (= GSC 4383.0340) as 7".4 east, 24".3 north (7".2 east, 24".3 north at 1950.0). IAUC 5737 A. V. Filippenko, University of California at Berkeley, notes: "The V magnitude and colors (B-V, V-R) of the starlike object reported (E725) at the position of SN 1993J are consistent with those of an unreddened or slightly reddened K0 Ia supergiant at the distance of NGC 3031 (distance modulus 27.5 mag). On page 16 of the Atlas of Galaxies by Sandage and Bedke (1988) the object is clearly visible as a stellar or semistellar condensation in the middle of a spiral arm. An extended progenitor (red supergiant, rather than blue supergiant like that of SN 1987A) is consistent with the fact that SN 1993J is not subluminous in B." IAUC 5737 R. M. Humphreys, G. S. Aldering, C. O. Bryja and P. M. Thurmes, University of Minnesota, communicate: "We have a probable identification of the progenitor star from scans of U,B,V and R Kitt Peak 4-m prime-focus plates with the Automated Plate Scanner at the University of Minnesota. These plates were originally obtained on 1982 Mar. 21-23 by Humphreys and were scanned for a stellar content study of M81 by Zickgraf and Humphreys (1991, A.J. 102, 113). Inspecting these scans and using the astrometric solution from the above survey, we find a mag 21 star at R.A. = 9h51m19s.2s, Decl. = +69D15'26".5 (equinox 1950.0), in agreement with the supernova position. As additional confirmation of this identification, we used an I-band CCD image of SN 1993J, made available by M. Richmond over internet, to measure the positions of six reference stars in the immediate vicinity of SN 1993J using imexamine in IRAF. The corresponding positions on the 4-m plates were determined from the isodensity scans made with the APS. A linear transformation between these sets of coordinates was then calculated. The root-mean-square uncertainty of the transformation was less than 0".15 in each coordinate. The candidate progenitor has a position on all four 4-m plates that is within 0".15 of the position of SN 1993J on the CCD frame. The magnitudes measured from these plates are: V = 20.8 +/- 0.1, B = 21.4 +/- 0.2, R = 19.9 +/- 0.2 and U = 21.7 +/- 0.2. Our V is 0.8 mag fainter than reported by Perelmuter (E725). Thus the star may be variable; all of our photometry is from plates obtained within two days of each other. The colors are consistent with the candidate progenitor being a highly reddened late A or early F-type supergiant. IAUC 5739 EDITORIAL The unprecented volume of e-mail and ordinary post associated with the supernova (more than 200 so far!) has meant it is impossible to answer all but the most urgent queries (discoveries) at the present time. Please continue to e-mail your observations but please remember to include the full estimate,