Nova MUSCAE 1991 (X-Ray Transient in Musca)
Abstract
R. M. West, European Southern Observatory, reports: "M. Della Valle and B. Jarvis (ESO, La Silla) have found the probable optical counterpart of GRS 1121-68 (IAUC 5161) at mag about 17-18, near the edge of the Ginga error box, on a 90-min IIIa-J + GG385 plate taken by G. Pizarro on Jan. 13.25 UT with the 1-m Schmidt telescope. The new object is also visible on a Schmidt plate (45-min exposure) taken Jan. 12.3. On a CCD frame obtained with the 2.2-m telescope on Jan. 15.1, the star was estimated as somewhat brighter, at V about 14.5. Calibrated CCD frames, obtained by Della Valle and Jarvis with the ESO 3.5-m New Technology Telescope and EMMI on Jan. 15.3 (0".94 seeing), indicate a possible further brightening: V = 13.40 +/- 0.03, B-V = +0.25; V-R = -1.04. Two 3-min EMMI spectral exposures (resolution about 0.8 nm, S/N about 110) show a quasi-featureless continuum, particularly strong below 600 nm; there is possibly a narrow H-alpha emission. On one of the NTT frames (5 s in R), transmitted this morning to ESO-Garching, I measured the following position of the starlike object (transfer by 14 secondary PPM-standards from a 2-hr ESO Schmidt plate; estimated accuracy +/- 0".2 in both coordinates): R.A. = 11h24m18s.49; Decl. = -68 24'01".7 (equinox 1950.0). Inspection of the best ESO (R) Schmidt plates (epochs 1984 Jan. 29 and Feb. 22) shows the probable progenitor near the plate limit (R about 21.5); this star is somewhat better visible at the SRC (J) plate (1976 Apr. 3) at J about 21 and barely visible on the ESO (B) plate (1976 Feb. 2) at about the same magnitude; it was therefore blue. The position, measured on the SRC (J) plate, is R.A. = 11h24m18s.51; Decl. = -68 24'01".9; the offsets are 0".14 and 0".19, respectively. It is concluded that the object is likely to be a galactic nova, which has so far brightened by about 7.5 mag and may still be rising. Ground- and space-based observations, especially spectroscopic, are urged."
- Publication:
-
International Astronomical Union Circular
- Pub Date:
- January 1991
- Bibcode:
- 1991IAUC.5165....1W