COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1913 Konkoly Observatory Budapest 1981 January 21 HU ISSN 0374-0676 LIGHT CURVE AND CHARACTERISTIC PHOTOMETRIC PARAMETERS OF NOVA CYGNI 1978 (V 1668 Cyg) 28 photoelectric V observations performed with the 40-cm refractor of the Teramo Observatory are given in Table I. BD +43d4012 with V=9.27 (checked with BD +43d4017) was utilized as comparison star. All the published photoelectric V and B observations together with some visual and photovisual measures which allow to secure the final rise and the epoch of the maximum are listed in Table II. Table I Teramo Observations J.D. V J.D. V 2443771.300 7.87 +-0.01 2443806.292 10.37 +-0.01 772.300 7.82 0.01 807.250 10.46 0.03 774.344 8.03 0.01 810.243 10.54 0.01 775.292 8.17 0.01 811.253 10.52 0.01 776.333 8.18 0.00 813.253 10.75 0.01 777.451 8.38 0.00 823.253 11.10 0.01 778.319 8.40 0.00 829.215 11.19 0.03 779.302 8.53 0.01 832.271 11.24 0.02 781.310 8.61 0.00 833.233 11.24 0.02 788.278 9.28 0.01 835.208 11.20 0.01 789.278 9.26 0.01 837.226 11.32 0.00 793.332 9.77 0.01 838.217 11.35 0.00 804.292 10.19 0.01 843.215 11.41 0.02 805.278 10.27 0.01 849.265 11.47 0.02 The light curve drawn with the data of these two tables appears fairly well outlined up to 35 days after the maximum; thereafter the different series of observations diverge highly owing to the blowing up of the strong emissions in the spectrum of the nova. The same behaviour is, of course shown by the B-V Table II Collected Magnitudes J. D. Magn. B - V S o u r c e 2443759.4 14 Andrews-Lloyd: IAU Circ. 3268 759.84 12 Di Cicco: IAU Circ.3263 760.5 8.7 pg Reginaldo: IAU Circ.3276 761.0 9.0 v Collins: IAU Circ.3263 761.5 6.8 v Morrison: IAU Circ.3264 761.9 6.9-7.0 Reginaldo: IAU Circ.3276 762.0 6.6 v Hiraga: IAU Circ.3267 762.57 6.4 v Bretl: IAU Circ.3263 762.63 6.3 v Morgan: IAU Circ.3263 762.66 6.6 v Harless: IAU Circ.3263 762.67 6.4 v Barstow: IAU Circ.3263 762.69 6.6 v Mayer: IAU Circ.3263 762.78 6.7 v Collins:IAU Circ.3263 763.55 6.0 pv Lloyd: IAU Circ.3268 763.66 6.17 V Mattei: IAU Circ. 3303 763.66 6.2 v Beckman: IAU Circ.3264 764.29 6.4 v Baroni-Cavagna: IAU Circ. 3264 764.34 6.35 V +0.63 Baldinelli: IAU Circ. 3278 764.37 6.38 V +0.68 Lindgren: IBVS 1543 764.45 6.34 V +0.58 Duerbeck: Astron. Astrophys. 81,157 764.58 6.2 pv Stelz: IAU Circ.3268 764.63 6.33 V Mattei: IAU Circ.3303 764.66 6.4 v Ashbrook: IAU Circ.3267 764.75 6.32 V +0.67 de Roux: IBVS 1519 765.41 6.17 V +0.49 Duerbeck: Astron. Astrophys. 81,157 765.53 6.18 V +0.50 Mallama: PASP 91,99 765.54 6.00 V Stelz: IAU Circ.3268 765.66 6.22 V Mattei: IAU Circ.3303 765.88 6.4 v Morris: IAU Circ.3267 766.35 6.66 V +0.50 Baldinelli: IAU Circ.3278 766.41 6.66 v +0.50 Duerbeck: Astron. Astrophys. 81,157 767.47 6.92 V +0.33 " " " " " 767.68 6.90 V +0.36 Mallama: PASP 91,99 768.40 6.83 V +0.35 Duerbeck: Astron. Astrophys.81,157 768.73 7.02 V +0.36 de Roux: IBVS 1519 769.49 7.03 V +0.30 Duerbeck: Astron. Astrophys.81,157 769.67 7.23 V Mattei: IAU Circ.3303 770.35 7.40 V +0.29 Baldinelli: IAU Circ.3278 770.43 7.45 V +0.29 Duerbeck: Astron. Astrophys. 81,157 770.64 7.67 V + Mattei: IAU Circ.3303 770.83 7.71 V +0.18 Margrave: IAU Circ.3316 771.43 7.86 V +0.18 Lindgren: IBVS 1543 771.43 7.69 V +0.26 Duerbeck: Astron. Astrophys.81,157 771.72 7.74 V Mattei: IAU Circ.3303 771.80 7.79 V +0.18 Margrave: IAU Circ.3316 772.29 7.66 V +0.29 Duerbeck: Astron. Astrophys.81,157 772.51 7.72 V +0.24 Mallama: PASP 91,99 774.53 8.02 V +0.34 deRoux: IBVS 1519 775.33 7.97 V +0.29 Duerbeck: Astron. Astrophys.81,157 775.77 8.34 V +0.18 Margrave: IAU Circ.3316 776.29 7.98 V +0.28 Duerbeck: Astron. Astrophys. 81,157 776.81 8.17 V Mattei: IAU Circ.3303 777.29 8.12 V +0.29 Duerbeck: Astron. Astrophys. 81,157 777.52 8.29 V +0.28 Mallama: PASP 91,99 777.55 8.33 V +0.25 deRoux: IBVS 1519 778.31 8.15 V +0.30 Duerbeck: Astron. Astrophys. 81,157 778.60 8.24 V +0.27 Mallama: PASP 91,99 778.70 8.30 V +0.21 Margrave: IAU Circ.3316 779.40 8.34 V +0.30 Duerbeck: Astron. Astrophys. 81,157 780.58 8.62 V +0.31 Mallama: PASP 91,99 780.69 8.68 V +0.27 deRoux: IBVS 1519 781.80 8.68 V +0.22 Margrave: IAU Circ.3316 783.41 8.53 V +0.28 Duerbeck: Astron. Astrophys. 81,157 783.63 8.80 V Mattei: IAU Circ.3303 784.62 8.79 V " " " " 785.64 8.87 V " " " " 786.52 9.00 V +0.21 deRoux: IBVS 1519 786.57 8.94.V +0.22 Mallama: PASP 91,99 786.72 9.00 V Mattei: IAU Circ.3303 786.85 9.11 V +0.22 Margrave: IAU Circ.3296 787.76 9.32 V +0.24 " " " " 788.76 9.37 V +0.21 " " " " 789.32 9.06 V +0.29 Hopp: IBVS 1633 790.26 9.08 V +0.34 " " " 790.83 9.18 V +0.23 Margrave: IAU Circ.3296 791.53 9.30 V +0.25 Mallama: PASP 91,99 791.76 9.47 V +0.19 Margrave: IAU Circ. 3296 792.44 9.32 V +0.28 Duerbeck: Astron. Astrophys. 81,157 792.70 9.71 V +0.11 deRoux: IBVS 1519 793.27 9.15 V +0.16 Hopp: IBVS 1633 793.36 9.47 V +0.29 Duerbeck: Astron. Astrophys. 81,157 794.26 9.62 V +0.33 " " " " " 794.31 9.67 V +0.40 Hopp: IBVS 1633 795.31 9.64 V +0.20 " " " 795.72 9.81 V +0.19 Margrave: IAU Circ. 3299 796.27 9.42 V +0.33 Duerbeck: Astron. Astrophys. 81, 157 796.78 9.92 V +0.19 Margrave: IAU Circ. 3299 797.25 9.70 V +0.09 Bruch: IBVS 1567 798.20 9.81 V +0.09 " " " 799.20 9.70 V +0.04 " " " 799.76 9.90 V +0.17 Margrave: IAU Circ. 3299 800.19 9.81 V +0.04 Bruch: IBVS 1567 800.38 9.68 V +0.22 Hopp: IBVS 1633 801.14 9.71 V +0.05 Bruch: IBVS 1567 801.25 9.66 V +0.21 Duerbeck: Astron. Astrophys. 81,157 801.78 9.89 V +0.14 Margrave: IAU Circ.3299 802.53 9.95 V +0.27 Mallama: PASP 91,99 803.22 9.91 V +0.06 Bruch: IBVS 1567 803.35 9.83 V +0.22 Duerbeck: Astron. Astrophys. 81,157 803.85 10.17 V +0.12 Margrave: IAU Circ.3299 804.44 9.80 V -0.02 Bruch: IBVS 1567 805.30 9.95 V +0.18 Duerbeck: Astron. Astrophys. 81,157 807.31 9.90 V +0.47 Hopp: IBVS 1633 808.34 10.10 V +0.24 " " " 809.56 10.16 V +0.20 Mallama: PASP 91,99 814.21 10.44 V +0.52 Hopp: IBVS 1633 814.37 10.35 V +0.32 Duerbeck: Astron. Astrophys. 81,157 815.23 10.36 V +0.41 Hopp: IBVS 1633 818.26 10.41 V +0.35 Duerbeck: Astron. Astrophys. 81,157 825.21 10.54 V +0.31 " " " " 828.25 10.51 V +0.29 Hopp: IBVS 1633 829.27 10.51 V +0.41 " " " 832.26 10.61 V +0.25 " " " 833.25 10.63 V +0.24 " " " 847.25 10.90 V +0.16 " " " 848.25 10.83 V +0.31 " " " 849.37 10.97 V +0.43 Duerbeck: Astron. Astrophys. 81,157 850.19 10.99 V +0.23 Hopp: IBVS 1633 862.24 10.93 V +0.33 " " " values after J.D. 43800 appear tremendously scattered, in accordance with the fact that the standard colours are meaningless for an emission object. A characteristic feature of this nova, already pointed out by other observers, is the complicated structure of the maximum: it appears to have been two maxima, at J.D. 2443763.7 and at J.D. 2443765.5; the first maximum time relies largely on the photoelectric observation made by Mattei on J.D. 2443763.66: the reliability of this datum has been checked considering the good agreement of the remaining observations of Mattei with those of other observers. This structure of the maximum, which looks like a miniature version of the complicated structure of some slow novae such HR Del, is rather surprising in a fast nova such Nova Cyg 1978. From the V light curve and the B-V colour displayed in Fig.1 the photometric values and the characteristic times of the decline [FIGURE 1] Fig. 1. At the top: the V light curve (triangle) : visual or photovisual observations, (circle) : photoelectric observations. The lower branch after J.D. 3805 is formed by Teramo observations only; the upper branch is formed by the observations of Duerbeck and of Hopp. At the bottom: the B-V curve (only photoelectric measures). are derived: t_2= 12d t_3= 23d (V light) t_2= 15d t_3= 30d (B light) M_Vmax= 6.1 (B-V)_max=+0.68 According to the standard criterion, V 1668 Cyg may be classified as a fast nova. It has not been possible to check the reliability of the highest observed photoelectric brightness (V=6.00; Stelz, 1978); therefore we have assumed for the magnitude at maximum the conservative value V=6.1. By means of the well known relation of Schmidt as revised by Pfau (1976), M_B=-10.67+-0.30+1.80(+-0.20) log t_3, the absolute magnitude at maximum MB=-8.0+-0.6 is derived. Assuming the Schmidt value +0.35 for the intrinsic B-V colour at maximum, the absolute V magnitude results M_Vmax=-8.4+-0.6 (from the rate of decline). With this assumption, the observed B-V give the value +0.33 for the reddening of the nova. This result is in good agreement with the value M_Vmax=-8.3 found by Mallama and Skillman (1979) using the same criterion. The method of the rate of decline 2/t2 as calibrated by Rosino (1964) confirms this result giving V_0=-8.0. The method of the light curve crossing point t=95 days (Buscombe and Vaucouleurs, 1955; Pfau, 1976) gives V=-8.2+-0.6. The absolute magnitude found by various observers with criteria independent from the rate of decline results much fainter: -7.5+-0.5 from the interstellar K I line (Slovak and Vogt, 1979); -6.8+-0.7 from the colour excess and the assumed reddening law (Duerbeck at al., 1980). The disagreement between the results obtained using the rate-of-decline criterion and those obtained using other criteria appears confirmed and the doubt that the t_3-time is not so good luminosity indicator for all novae as hitherto assumed (Duerbeck and Pollok, 1980) would appear therefore strengthened. We think, however, that the methods based on the interstellar absorption are of very little weight in this region of the sky where the absorption is so erratic. A two hours monitoring on October 11, 1978, shows a maximum [FIGURE 2] Fig. 2: The structure of the maximum: (open circle) visual or photovisual observations, (filled circle) photoelectric observations. [FIGURE 3] Fig. 3: The short period light variation on October 11, 1978. of the short period regular oscillation found in the nova light curve shortly after the maximum by Campolongo et al., (1980). The amplitude and the shape of the observed stretch agree with the amplitude and the period (respectively 0.15m and 10.54h) found by the quoted authors. The statement of Mallama and Skillmann that a two-hour monitoring on September, 27, 1978, showed no short- time variation is not surprising: owing to the length of the cycle the monitoring may have fallen on an almost constant phase. The presence of short-period regular oscillation in the very proximity of the maximum light was discovered for the first time in Nova Cyg 1975 (=V 1500 Cyg); the occurrence that the first monitoring of a nova thereafter expressly carried out has given a positive result seems to indicate that such a phenomenon is rather general feature. Photoelectric monitoring for several hours during the first decline of the novae is therefore highly recommended. DI PAOLANTONIO, A., PATRIARCA, R., TEMPESTI, P. Osservatorio Astronomico di Collurania I - 64100 Teramo References: Buscombe, W., de Vaucouleurs, G., 1955, The Observatory, 75, 170 [BIBCODE 1955Obs....75..170B ] Campolongo, F., Gilmozzi, R., Guidoni, U., Messi, R., Natali, G., Wells, J., 1980, Astron. and Astrophys. 85, L4 [BIBCODE 1980A&A....85L...4C ] Duerbeck, H.W., Rindermann, K., Seitter, W.C., 1980, Astron. and Astrophys. 81, 157 [BIBCODE 1980A&A....81..157D ] Duerbeck, H.W., Pollok, H., 1980, I.B.V.S. No. 1845 Mallama, A.D., Skillman, D.R., 1979, P.A.S.P. 91, 99 [BIBCODE 1979PASP...91...99M ] Pfau, W., 1976, Astron. and Astrophys., 50, 113 [BIBCODE 1976A&A....50..113P ] Rosino, L., 1964, Ann. d'Astrophys., 27, 497 [BIBCODE 1964AnAp...27..497R ] Slovak, M.H., Vogt, S., 1979, Nature, 277, 114 [BIBCODE 1979Natur.277..114S ] Stelz, 1978, IAU Circ. 3268 [BIBCODE 1978IAUC.3268....1A ]