UBV observations of V1500 Cyg.

Abstract

The brightness of V1500 Cyg (nova Cygni 1975) was monitored in UBV light from Fernbank Observatory between September 1975 and June 1976. Short-term brightness fluctuations were observed on 1976 June 6, corresponding to a binary period of 0^139.

The UBV Color Evolution of Classical Novae. III. Time-stretched Color–Magnitude Diagram of Novae in Outburst

“…• 75, 0. • 00) The BV data of V1500 Cyg are taken from Williamon (1977), Tempesti (1979), Pfau (1976), and Arkhipova & Zaitseva (1976).…”

The Ubv Color Evolution of Classical Novae. Ii. Color–magnitude Diagram

“…The orbital period of 3.35 hr was detected by Tempesti (1975). We already analyzed the nova light curves in Paper I, and determined the reddening to be E ( Arkhipova & Zaitseva (1976), Pfau (1976), Kiselev & Narizhnaia (1977), and Williamon (1977).…”

The lightcurve of nova cygni 1975 (V 1500 Cyg) from the outburst to July 1977

“…The equipment, an E M 1 9502 photomultiplier with 2-mm Schott GG14 + GG13 filter combination, is the same employed for the already published observations of the nova (ROSINO and TEMPESTI 1977) and the same comparison star, BD +48"3340 with assumed V magnitude 84143, was used throughout for the new observations here presented in Tables I and 2 The detailed study of the photometric behaviour of the nova near maximum has already been published (YOUNG et al 1978;1978;ROSINO and TEMPESTI 1977); therefore the observations have been plotted in Figure I on a logarithmic scale suitable for a representation of the general lightcurve. The decline appears to be quite smooth, the scattering of the observations in some stretches of the lightcurve being largely t o be ascribed to the well known 3.3-hour light variation, and since 3 days after maximum thereafter, the fading results to follow constantly the law V = 2.5 + 3.9 lg t. The A 3.5-hour night run on 1976, December 13, shows that 500 days after maximum the short-period light variation was acting with an amplitude much greater than before observed in V light (ROSINO and TEMPESTI 1977;AMBRUSTER et al 1977;SEMENIUK 1975;LINDGREN and LINDGREN 1975;WILLIAMON 1977). Since this light variation arises esseutially from the continuum ) and considering that the emission of the green 0111 lines is by far the dominant feature in the V band, it may be inferred that the amplitude in the continuum was much greater than that observed in V light : a rough estimate from the published spectroscopic data yields the ratio 10: I for the flux in the 0111 lines to that on the continuum within the V band; allowance made for the response curve of the photometer, one can safely assume for the amplitude in the continuum within the V band the value 1.2 magnitudes.…”

“…Present paper. The detailed study of the photometric behaviour of the nova near maximum has already been published (YOUNG et al 1978;1978;ROSINO and TEMPESTI 1977); therefore the observations have been plotted in Figure I A 3.5-hour night run on 1976, December 13, shows that 500 days after maximum the short-period light variation was acting with an amplitude much greater than before observed in V light (ROSINO and TEMPESTI 1977;AMBRUSTER et al 1977;SEMENIUK 1975;LINDGREN and LINDGREN 1975;WILLIAMON 1977). Since this light variation arises esseutially from the continuum ) and considering that the emission of the green 0111 lines is by far the dominant feature in the V band, it may be inferred that the amplitude in the continuum was much greater than that observed in V light : a rough estimate from the published spectroscopic data yields the ratio 10: I for the flux in the 0111 lines to that on the continuum within the V band; allowance made for the response curve of the photometer, one can safely assume for the amplitude in the continuum within the V band the value 1.2 magnitudes.…”

“…The presence of secondary waves gives little significance to the different shape of the two maxima observed on Decembre 13, 1976, as regards the (MARCOCCI et al 1976;PROKOFIEVA and ABRAMENKO 1976;SEMENIUK 1975;YOUNG et al 1977), nevertheless the reality of the modulation appearing in Figure 2 may be questioned, especially considering that the brightness of the nova was rather close to the limit of the telescope power. Unfortunately no suitable check star could be used thoroughly along the night run; however a plot of the measures on the comparison star (see Figure 2) shows no fluctuations greater than 0.02 mag and there appears only the steady decline caused by the increasing of the zenithal distance; the constancy of this star has been moreover tested by WILLIAMON (1977). The possibility remains of the presence of sky fluctuations, which although largely ineffective for the eight magnitude comparison star could be very effective for the twelfth magnitude nova; however tests on the sky, performed every five to six measures on the nova, showed no fluctuation adeguate for accounting spurious star brightness variations greater than 0.03 mag; concluding, a fairly good reliance may be placed upon the reality of the half-hour time scale fluctuations.…”