COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1845 Konkoly Observatory Budapest 1980 September 19 HU ISSN 0374-0676 A PHOTOGRAPHIC LIGHT CURVE OF NOVA V1668 CYGNI AND SOME OBSERVATIONS OF SS CYGNI V1668 Cyg (Nova Cygni 1978) is a relatively faint, but well investigated nova. It was discovered on 1978 September 10.0 (UT) by Morrison (1978) and Collins (1978). Reginaldo (1978) published two pre-discovery magnitudes. At Hoher List Observatory, spectroscopic, photoelectric and photographic observations were carried out. In this note, we present a light curve based on the photographic observations of the field of V1668 Cyg between 1978 September 12.87 and 1979 October 24. As a by-product of this study, several outbursts of the nearby dwarf nova SS Cyg were also observed. The series of photographic plates was obtained with the 30 cm f/5 four-lens astrograph. 70 plates are available, 12 of them were taken a few weeks before the brightening of the nova. All plates were measured with a Becker iris diaphragm photometer. Photographic magnitudes of the comparison stars and the sources from which they were taken are given in Table I. A critical review of m_pg of those stars which form the comparison sequence of SS Cyg was recently given by Lukas (1979). The magnitudes of the fainter stars were derived through comparison with a sequence in the open cluster IC 5146 (Walker 1959). An identification chart of the fainter stars is given in Fig. 1a,b, which is the reproduction of a POSS chart. The photographic magnitudes of V1668 Cyg and SS Cyg are given in Table II.The plates were taken by the following observers: D = Duerbeck, H = Hopp, Ha = Hanel, K = Kiehl, Ka = Karimie, L = Lukas, Le = Lentes, S = Schumann, W = Witzigmann. On the plates taken before 1978 September 10, V1668 Cyg is not visible. One of the deepest plates is A3171, taken 18 days before outburst, which has a limiting magnitude m_pg of about 17m, and does not show the image of the nova. [FIGURE 1a] Fig. 1a. Field of Nova V1668 Cyg (=N) and SS Cyg (=SS); some of the fainter comparison stars are identified. North is to the left [FIGURE 1b] Fig. 1b. The field of Nova V1668 Cyg. The position of the nova (=N) is marked by a circle; some comparison stars are identified. North is to the left Table I List of comparison stars No. BD No. m_pg ref. No. BD No. m_pg ref. 1 +44^o 3865 4.91 3,5 15 - 11.35 1,2,4,6,8 2 +44 3889 6.39 4 16 - 12.04 6 3 +43 4002 6.66 4 17 - 12.07 1,6,7 4 +42 4204 6.86 2 18 - 12.28 I 5 +43 4048 7.94 1,7 19 - 12.48 1,6,7 6 +42 4197 8.74 1 20 - 12.91 1,6,7 7 +43 4037 9.12 1 21 - 13.78 9 8 +43 4030 9.18 1 22 - 13.93 9 9 +43 4017 9.36 4 23 - 14.02 9 10 +42 4190 9.76 1,4,6,7,8 24 - 14.58 9 11 +43 4020 10.19 1,2,4,6,7,8 25 - 14.69 9 12 - 10.55 1,4,6,8 26 - 14.88 9 13 - 10.62 1,6,7 27 - 16.34 9 14 - 11.05 1,6,7,8 References: 1. Bell, B., Harvard Bull. 919, 19 (1950) 2. Grant, G., Abt, H.A., Astrophys. J. 129, 323 (1959) 3. Hoffleit, D., Catalogue of Bright Stars, New Haven: Yale Univ. Press (1964) 4. Hopp, U., Inf. Bull. Var. Stars 1633 (1979) 5. Iriate, B., Johnson, H.L., Mitchell, R.I., Wisniewski, W.K., Sky Telesc. 30, 21 (1965) 6. Lenouvel, F., Daguillon, J., J. Observateurs 39, 9 (1956) 7. Sokolova, I.A., Per. Zvezdy 13, 273 (1961) 8. Zuckermann, M.F., Ann. Astrophys. 24, 431 (1961) 9. Walker, M.F., Astrophys. J. 130, 57 (1959) Table II Photographic observations of V1668 Cyg and SS Cyg Plate No. Date Exposure Emulsion Observer V1668 Cyg SS Cyg A JD 2440000+ (min) 3135 3718.414 10 ZU-2 H,K,W 8.91 3141 19.385 10 " " 9.12 3145 19.531 10 " " 9.47 3146 20.486 9 " " 9.85 3147 23.483 10 " " 11.11 3150 24.442 6 " " 11.50 3151 25.451 10 " " 11.67 3158 38.452 5 IIa-O L 12.15 3161 40.450 9 " " 12.57 3165 41.477 5 " " 12.75 3169 42.478 7 " " 12.30 3171 47.459 15 ZU-2 Ka 12.27 3172 64.373 5 " D 6.82 12.45 3173 64.380 5 " " 6.80 12.43 3174 64.399 5 " " 6.53 12.37 3175 64.446 5 " " 6.44 12.55 3176 64.536 13 " " 6.48 12.47 3177 65.310 5 " " 6.03 12.12 3178 65.332 6 " " 6.06 12.04 3179 66.476 5 " " 6.71 11.69 3180 66.483 5 " " 6.85 11.86 3181 67.479 5 " " 6.88 9.06 3182 67.483 5 " " 7.04 8.82 3183 68.289 5 " " 6.68 8.19 3184 68.293 5 " " 6.51 8.07 3185 69.307 5 " " 6.38 - 3186 69.342 8 " " 6.37 8.16 3187 70.331 6 " " 7.12 8.23 3188 70.337 8 " " 7.03 8.40 3189 71.391 6 " " 7.22 7.95 3190 71.397 8 " " 7.46 8.15 3191 72.327 10 " " 7.63 8.22 3192 72.336 13 " " 7.39 7.94 3193 73.337 9 " " 7.50 8.30 3194 73.351 10 " " 7.67 8.51 Table II (cont.) Plat No. JD 244000+ Exposure Emulsion Observer V1668 Cyg SS Cyg (min) 3195 3775.465 8 ZU-2 D 7.74 8.37 3196 75.471 10 " Ha 7.56 8.14 3198 78.347 6 " " 8.04 8.86 3199 83.434 10 " D 8.30 11.07 3200 83.441 10 IIa-O " 8.23 11.26 3201 85.333 15 " Ha 8.17 11.67 3202 85.353 8 " " 8,82 11.48 3204 88.430 23 " S 9.17 12.22 3212 91.350 10 " Ha 9.07 12.16 3213 92.343 10 " " 9.77 12.32 3214 93.489 10 " D 9.81 12.44 3215 94.382 10 " " 9.65 12.49 3216 96.404 8 " " 9.70 12.08 3217 3801.365 10 " " 9.82 12.31 3218 03.382 10 " " 10.02 12.33 3219 22.333 10 " " 10.75 12.51 3220 25.396 10 " " 10.68 12.40 3221 28.435 10 " " 10.73 11.79 3222 49.237 10 " " 11.26 12.42 3257 4040.463 20 " " 14.64 12.57 3263 90.523 15 " " 15.80 8.35 3272 4100.469 20 " " 15.84 8.89 3285 28.394 20 " " 15.55 12.38 3289 33.338 30 " Le 15.80 12.38 3293 39.488 15 " H 15.81 12.15 3297 40.343 30 103a-0 " 15.50 12.37 3305 42,411 30 " " 15.86 12.11 3311 43.344 30 " " 16.02 12.26 3320 46.481 30 " " 15.96 12.46 3322 47.463 10 " " 15.86 12.60 3330 70.381 20 IIa-0 D 16.29 8.98 3331 70.364 20 " " 16.01 8.99 3332 71.301 10 " " 16.20 8.99 3333 71.309 5 " " 16.40 9.10 3334 71.318 13 " " 16.07 9.39 [FIGURE 2] Fig.2. Photographic (upper) and photoelectric V (lower) light curves of V1668 Cyg. On the log t axis (number of days elapsed since JD 2 443 761.0), several Julian days are indicated. Three brightness maxima are labeled by numbers 1,2,3 (see text). In Fig. 2, the photographic light curve and the photoelectric V light curve compiled by Duerbeck et al. (1980) are compared. The construction of a nova light curve from photoelectric data of different observers is somewhat problematic: UBV observations obtained with various instruments of different sensitivity functions exhibit systematic differences because of the influence of emission lines in the spectrum of the nova after maximum. Therefore, a series of photographic observations obtained with a single telescope is important to check the reality of some fluctuations in the light curve of V1668 Cyg which were reported in the paper by Duerbeck et al. (1980). A logarithmic time scale is used in Fig. 2 in order to display the fluctuations in the early stages as well as the brightness decline in the late stages of the outburst. The time t = 0 was set to JD 2 443 761.0, as proposed by Gallagher et al. (1980). The maximum of the nova has a complicated structure, three brightness maxima occurred on JD 2 443 763, 765 and 769. They are present in the V light curve, yet more pronounced in the photographic light curve. The photographic light curve supports the fact that the light curve of V1668 Cyg deviates markedly from those of the fast, intrinsically bright novae, like V1500 Cyg, Q Cyg, CP Lac etc. It is more like that of the somewhat slower, intrinsically fainter nova LV Vul. The finding of Duerbeck et al. (1980) that V1668 Cyg is subluminous for its fast evolution is thus confirmed and leads to the conclusion that the t_3 - time is not as good a luminosity indicator as hitherto assumed. A thorough discussion of the problem of nova luminosities is the subject of a forthcoming paper (Duerbeck 1980). Acknowledgements: We thank Drs. and Messrs. A. Hanel, U. Hopp, M.T. Karimie, M. Kiehl, F.T. Lentes, R. Lukas, J.D. Schumann and S. Witzigmann for obtaining some of the plates used in this study. H. W. DUERBECK Observatorium Hoher List 5568 Daun Federal Republic of Germany H. POLLOK Astronomisches Institut der Universitat Munster Corrensstrasse 4400 Munster Federal Republic of Germany References: Collins, P.L., 1978, IAU Circ. 3263 [BIBCODE 1978IAUC.3263....1C ] Duerbeck, H.W., 1980, in preparation Duerbeck, H.W., Rindermann, K., Seitter, W.C., 1980, Astr. Astrophys. 81, 157 [BIBCODE 1980A&A....81..157D ] Gallagher, J.S., Kaler, J.B., Olson, E.C., Hartkopf, W.I., Hunter, D.A., 1980, Publ. Astr. Soc. Pacific 92, 46 [BIBCODE 1980PASP...92...46G ] Lukas, R., 1979, Sterne 55, 119 Morrison, W., 1978, IAU Circ. 3264 [BIBCODE 1978IAUC.3264....3M ] Reginaldo, R. 1978, IAU Circ. 3276 [BIBCODE 1978IAUC.3276....1R ] Walker, M.F., 1959, Astrophys. J. 130, 57 [BIBCODE 1959ApJ...130...57W ]