ooPQ 00 : THE ASTRONOMICAL JOURNAL VOLUME 83, NUMBER 1 JANUARY 1978 SUPERNOVAE IN THE COMA CLUSTER OF GALAXIES 1978AJ. Roberto Barbon Asiago Astrophysical Observatory and University of Trieste, Trieste, Italy Received 7 September 1977 ABSTRACT All the supernovae so far discovered in the Coma cluster have been identified and their light curves reanalyzed. Unpublished observations are reported for SN 1963c, SN 1963m, and SN 1962i, which is found to belong to a background galaxy. For type I supernovae, comparison with the average light curve provided a mean magnitude at maximum m0= 15.5 ±0.2, corresponding to an absolute magnitude Mp= —18.7 if a distance modulus of 34.2 for the cluster is used. The location of the parent galaxies within the cluster may appear peculiar if compared with the distribution of the cluster members. A reliable sample of cluster members has been isolated and an observed rate of supernova production of one SN per 1O average galaxy per 600 yr has been found. The rate per unit luminosity (1O L0) appears significantly lower than that previously derived for E and SO galaxies. h m I. INTRODUCTION and centered at coordinate 12 57 , +28° 15' was in- spected. All the SNe occurring in galaxies belonging to The Coma cluster, one of the nearest regular clusters this region are listed in Table I. The successive columns of galaxies, has been extensively searched for supernovae give relevant data on type and magnitude of the SNe and (SNe) since 1958. Because of its position near the north their parent galaxies as reported in the SN catalog. galactic pole it suffers a minimum of local obscuration Different morphological types are given by other au- and, as Zwicky (1961) pointed out, it can be observed thors: NGC 4874 is classified E by Gregory (1975) and in the more favorable conditions by some of the major Maza and van den Bergh (1976), whereas NGC 4944 northern observatories. Due to its large population, the is considered by the respective authors to be E and Sa. cluster should exhibit a high rate of SN production and, The recession velocities in column 9 are mainly from as a result of the uniformity of the morphological types Gregory (1975). Other sources are given as footnotes to of the member galaxies, it should also provide a better the table. The last column identifies cluster members on sample for studying the SN phenomenon than those the basis of Coma having a mean recession velocity of derived by collecting data from randomly chosen gal- 6946 km/s with a dispersion of 896 km/s (Gregory axies of different types and origin. 1975). For SN 1963m, no velocity is available and the In recent years the Coma cluster has been exhaustively membership of its parent galaxy is proved only by the investigated by many authors (see Rood et al. 1972; discussion of the photometric material as given in Sec. Gregory 1975 and references therein) who have assem- III. By the same token, SN 1962i has been found not to bled a complete sample of radial velocities and mor- belong to the cluster. phological types for a large number of cluster members. No other SNe occurring in Coma galaxies have been These studies have contributed to a good understanding discovered in the vicinity of the inspected area except of the structure of the cluster and of the distribution of perhaps SN 1960j in NGC 4375, which has a velocity its members according to type and luminosity. In the of 9165 km/s (Zwicky 1965). This value fits to the tail light of this knowledge, it appears of interest to study the of the velocity distribution of the cluster members but, properties of the cluster and its members also as con- owing to the large distance (7.°5) of NGC 4375 from the tributors of SNe. cluster center, its membership may be questioned, since large velocity dispersions are likely to be found only near the center (Rood et al. 1972; Gregory 1975). II. SUPERNOVAE AND THEIR PARENT GALAXIES Table I also shows that most of the SNe found in Coma galaxies are of type I. For these, and for the re- An updated copy of the SN catalog (Sargent et al. maining unclassified SNe, a comparison between the 1974), complete through August 1976 and kindly made available photometric data and the average light curves available to us by C. Kowal, was used as the reference given by Barbon et al. (1973a) can be made. A reliable for SNe appearing in the region of the Coma cluster. value of the apparent magnitude attained at maximum Since the actual area covered by the cluster extends by SNe I in the Coma cluster may be inferred, which is beyond the contour line given in the Catalogue of Gal- important in the problem of the calibration of SNe as axies and of Clusters of Galaxies (Zwicky and Herzog distance indicators. To this end, besides presenting new 1963), hereafter CGCG, a circular region 5° in radius data on the light curves of SNe 1962i, 1963c, and 13 Astron.J. 83(1), Jan. 1978 0004-6256/78/8301-0013Í00.90 © 1978 Am. Astron. Soc. 13 © American Astronomical Society • Provided by the NASA Astrophysics Data System ooPQ 00 14 R BARBON: SUPERNOVAE 14 Table I. Supernovae in the field of the Coma cluster. Cluster 1978AJ. SN Galaxy R.A. Dec. me. WSN Typec TypesN Vo member 1940b N 4725 \2h48™0 +25°46/ 10.2 12.8 SBb 1109 1969h N 4725 12 48.0 +25 46 10.2 15.0: SBb 1109 1961d Anon 12 48.3 +28 06 14.8 v\6.5 EO 7473 1963c Anon 12 55.3 +28 09 15.3 15.7 E 6044 1963m Anon 12 55.5 +28 20 16.3 v 15.9: SOp 1968h Anon 12 55.9 +27 24 16.6 16.6 Sb 12 050 1968b N 4874 12 57.2 +28 14 13.7 17.4 SO 7181 1950a 1 4051 12 58.5 +28 17 14.8 17.7 El 4945 1959b N 4921 12 59.0 +28 08 13.7 18.5 Sa pec 5472 19621 Anon 13 00.5 +27 47 19.0 17.2 I: 1973f N 4944 13 01.5 +28 28 13.3 v\6.2 SO I: 7009 1962a Anon 13 04.3 +28 08 16.0 15.6 E/SO I 6137 1976a Anon 13 08.7 +29 50 15.3 16.5 S 7190 Notes to Table I v means a visual magnitude. Sources of the velocities other than Gregory (1975) are Rood et al. (1972) for NGC 4725 and Anon 1308.7 + 29; Zwicky et al. (1969) for Anon 1255.9+27; and Zwicky and Barbon (1967) for Anon 1304.3+28. 1963m, a rediscussion of the photometry of the individ- imum occurs 2 or 3 days later than the blue one. With ual SNe is given in the Sec. III. the adopted conversion procedure, we found that this difference has negligible effect on the fitting to the av- erage blue light curves. It is important to stress that these HE THE LIGHT CURVES OF THE COMA CLUSTER curves, and not the average visual, have to be used to SUPERNOVAE draw the final results. They have a higher statistical Table II lists all the photometric data available for significance and, due to the rather constant rate of de- bona fide Coma cluster SNe. Before comparing the cline which is present in the latter, they are more useful observed magnitudes with the average light curves of when only fragmentary light curves are available. SN 1961 d. This object appeared exceedingly far out Barbon et al. (1973a), a conversion to the mPg system has to be made, since most of the observations were made of the nucleus of an anonymous E0 galaxy, in a region in the F band. Rust (1974) discussed extensively several in which the galaxy contribution is no longer detected. conversion methods for type I SNe based primarily on It was caught before maximum and the light curve Pskowski’s (B — V)q, t relation (Pskowski 1971). In the (Zwicky 1961) sets ¿o on 16 January. After processing Zwicky’s photovisual observations as outlined previously, case of a K mPg transformation, an analogous (mpg — F)o, t relation has to be used once the epoch of the a good fit to the average blue curve for the “fast” subtype maximum is known. When this quantity is not avail- can be reached yielding apparent magnitude at maxi- able a long iterative procedure, based on a first guess of mum mo = 16.2 and zero reddening. As an example of the degree of accuracy possible, the fitting procedure is ¿o, must be applied to the data in order to convert the V shown schematically in Fig. 1. For this object, as for the magnitudes to the mpg system. In these cases we used a more straightforward method that gives /q by comparing following ones, zero galactic obscuration has been as- directly the visual magnitudes with an “average V light sumed (Sandage 1973). The value of mo for SN 1961d, curve” built up from data available in the literature for as also noted by Kowal (1968), is low if compared with the following six well-observed type I SNe: 196Id, the maxima of the other SNe found in the cluster. 1962a, 1970j, 1971g, 1971i, and 1972h. Then, at each SN 1963c. This SN occurred on the boundary region of an anonymous elliptical galaxy. Observations were date of a visual observation, (mpg — F)o may be read from Rust’s diagram.