COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS NUMBER 696 Konkoly Observatory Budapest 1972 July 12 ROSINO'S OBJECT: EVIDENCE FOR A FOURTH OUTBURST Rosino's object is a peculiar variable star-like object situated about 5 arc minutes from the Sb galaxy NGC 4501 (1). It has been observed at maximum only 3 times. The first maximum was discovered on November 17, 1961 (1), and was monitored by Bertola (2). A second maximum was later found by Zwicky on March 26, 1965 (3). This outburst was also monitored by Bertola (4), who has further reported (2) the object at maximum on a plate taken on April 26, 1892, in the Isaac Robert collection. According to Bertola the variable appears to be an explosive type variable of the U Geminorum type. In an effort to bridge the gap between 1892 and 1961, a search of the plate collection of the Harvard College Observatory was undertaken. The accompanying table is the result of that search. The search was exhaustive in the RH and BM series, and in the MC and MA series the search was thorough for all plates with exposures greater than 30 minutes. In the table M.J.D. (= J.D. -2,400,000), are modified Julian days. The upper magnitude limits come from observing the faintest star visible on each plate using Bertola's comparison sequence (2). In this search, Rosino's object was found at maximum on only 1 plate taken on June 25, 1941. Using Bertola's sequence the plate was measured on an Askania Astrophotometer. The magnitude was mpg =13.84 +- 0.07, well above the plate limit of m_pg ~~ 17.3. An attempt was made to find any plates in the entire Harvard collection taken of the object during the months of June and July, 1941. Three A plates taken at Bloemfontein, South Africa, were catalogued, but all three plates were lost at sea. The following series turned up no information at the suspected time of maximum: AI; AX; AM; C; EE; I; IR; MF; RB; RL; and, X. One fact deserves special attention. An MA plate taken on May 29, 1941, shows no indication of the object. The faintest star of Bertola's sequence visible is m_pg =16.44. The object, therefore, brightened at least 2.5 magnitudes in one month, This is the only reported estimate of a rise-time for Rosino's object. There is very little possibility that the image is a plate defect. The plate for June 25, 1941, is an excellent plate, and the image looks exactly like the images of the other stars. Due to the nearness of Rosino's object to the ecliptic, and the fact that only one plate was found, a normal question arises as to whether merely an asteroid was observed, A quick calculation using results obtained by Kiang (5) Shows that the probability of this is about 1 in 10^4, Furthermore, the plate exposure is 90 minutes which should be long enough to have trailed an asteroid at any point except possibly at a stationary point. The probability of having observed an asteroid in the exact position of Rosino's object and at a stationary point in its orbit is far less than 10^-4. This work was supported in part by a grant from the National Science Foundation. It is a pleasure to thank the staff of the Harvard College Observatory for the hospitality they extended while this work was being done, S.C. LUCCHETTI P.D. USHER Department of Astronomy The Pennsylvania State University University Park., Pa. 16802 U.S.A. June 28, 1972 References 1. Rosino, L. 1961, I.A.U. Circular, No. 1782, 2. Bertola, F. 1964, Ann d' Ap., 27, 298, [BIBCODE 1964AnAp...27..298B ] 3. Zwicky, F. 1965. I.A.U. Circular, No. 1902, 4. Bertola, F. 1965, Comm. 27 I.A.U., Inf. Bull. Var. Stars, No. 103. 5. Kiang, T. 1939, M.N., 123, 509, [BIBCODE 1962MNRAS.123..509K ] Plate M.J.D. m_pg Plate M.J.D. m_pg MC 21795 24199 >15.15 RM 855 29022 >15.15 RH 4860 27104 >15.15 BM 1136 29289 >15.15 RH 5026 27183 >14.28 BM 1180 29311 >15.15 RH 5760 27478 >16.44 MA 7521 29318 >17.50 MC 27128 27511 >18.43(a)MA 7523 29319 >17.30 RH 5823 27512 >15.15 BM 1209 29319 >15.15 RH 5830 27515 >15.15 BM 1250 29333 >14.28 RH 5978 27574 >14.28 BM 1268 29339 >15.15 RH 5980 27574 >15.02 MA 7574 29344 >17.30 RH 6013 27595 >12.63 BM 1298 29361 >14.28 RH 6023 27596 >14.28 RH 8805 29377 >15.15 RH 6392 27808 >16.44 BM 1317 29096 >15.15 RH 6396 27813 >16.44 BM 1327 29397 >15.15 RH 6424 27832 >16.44 BM 1949 29638 >14.28 BM 364 27834 >14.28 BM 2124 29671 >15.15 RH 6445 27840 >17.23 BM 2204 ?9698 >15.15 RH 7087 28554 >15.15 RH 9641 29708 >14.28 RH 7131 28293 >14.28 RH 9665 29726 >17.23 RH 7580 28600 >16.44 MA 8242 29726 >17.30 BM 499 28624 >12.63 BM 2304 29730 >14.28 BM 510 28636 >15.15 BM 2322 29734 >14.28 RH 7646 28653 >16.44 BM 2337 29748 >14.28 RH 8006 28898 >16.44 BM 2370 29760 >15.15 RH 8013 28904 >16.44 BM 3120 30002 >15.15 BM 804 28982 >15.15 BM 3172 30018 >14.28 RH 8234 28993 >15.15 RH 10182 30020 >16.44 BM 825 28993 >15.02 BM 3209 3U030 >14.28 BM 845 29013 >14.28 MA 8753 30049 >17.50 RH 8272 29016 >15.15 MA 8783 30105 >16.44 RH 8281 29020 >15.15 MA 8811 30134 >16.44 Plate M.J.D. m_pg Plate M.J.D. m_pg MA 8819 30144 >16.44 RH 15253 33301 >16.44 MA 8853 30171 13.84(c) MC 36778 33388 >16.44 RH 11005 30438 >15.15 RH 15635 33768 >15.15 MC 33435 31176 >16.44 MC 37233 34045 >18.43(a) RH 12922 31523 >15.15 MC 37919 34834 >17.50 MC 34483 31859 >17.50 MC 37921 34834 >18.05 MC 34535 31907 >18.43 MC 37924 34836 >18.43(b) RH 13841 31911 >16.44 MC 37926 34836 >18.05 MC 34544 31930 >18.43 MC 37933 34837 >18.43(a) MC 34576 31976 >18.43 MC 37935 34837 >18.05(a) MC 35259 32213 >16.44 MC 37939 34854 >17.50 MC 35328 32264 >18.43 MC 37941 34855 >17.50 MC 35354 32285 >18.43(a) MC 37942 34855 >18.43(b) MC 35362 32293 >18.43 MC 37943 34855 >16.44 MC 35941 32623 >18.43 MC 37944 34857 >16.44 MC 35948 32628 >17.50(b) MC 37946 34857 >16.44 MC 35962 32645 >18.43(b) MC 37956 34862 >17.50 MC 35968 32648 >17.50 MC 38158 35163 >17.50 MC 35985 32668 >18.43(a) MC 38166 35181 >17.50 MC 36287 32955 >18.43(b) MC 38176 35186 >17.50 MC 36307 32969 >17.50 MC 38178 35186 >17.50 RH 14936 32979 >16.44 MC 38189 35195 >17.50 MC 36338 32996 >18.43(a) MC 38196 35214 >17.50 MC 36359 33028 >17.50 MC 38199 35216 >17.50 MC 36702 33036 >18.05 MC 38200 35216 >17.50 MC 38201 35216 >17.50 Notes a. Rosino's object is possibly barely visible by eye. b. Rosino's object is barely visible by eye. Probably on the order of m_pg~~ 18.5 as a star with m_pg ~~ 18.5 was not observed. c. See text.