COMMISSION 27 OF THE I.A.U. INFORMATION BULLETIN ON VARIABLE STARS Number 2995 Konkoly Observatory Budapest 10 March 1987 HU ISSN 0374 - 0676 SEMIREGULAR VARIATIONS OF NOVA V841 OPH (1848) AT MINIMUM V841 Oph (RA=16h59m30s; D.=-12d53'53"; Equin. 2000) is an old nova which erupted in 1848 reaching at maximum an apparent visual magnitude m_v~4. The star had a moderately fast decline (t2~60; t3~110 days) returning after some years at its normal magnitude m=~12.5. Its amplitude A_v~8.5 is less than normal for a nova, so that the star has been considered as a potential recurrent- one. In the course of a general study of the light curves and spectra of galactic novae, which is being carried out at Asiago, we have collected all the estimates of visual magnitude of V841 Oph published by different Authors (Barnard, Peek, Steavenson) from 1919 to 1947. These magnitudes, although not evenly distributed on the light curve, clearly show the presence of relatively slow brightness fluctuations, between magns. 12 and 13, with a periodicity of the order of 51 days (Fig. 1). Their amplitude, however, is not constant but varies erratically from 0.5 to 1.0 magns. Moreover, at times the fluctuations cease and the star remains more or less constant at m_v~12.5 for weeks or months, perhaps with some flickering of 0.1-0.2 magns. (Fig. 2). [FIGURE 1] Fig. 1. Semiregular maxima in the light curve of V841 Oph [FIGURE 2] Fig. 2. Light curve of V841 Oph in the quiet periods The semiregular periodicity of V841 Oph was noticed by Barnard (1921), Turner (1921) and Steavenson (1923) who proposed different periods, from 27 to 50 days, without coming however to a definite conclusion on the length of the period. Since we dispose now of a much more abundant material (420 visual magnitudes at minimum over an interval of 28 years) we have thought it was worthy to examine better the question of the semiregularity of this old nova. We have therefore selected in the general light curve 17 maxima, fairly well defined, all brighter than m_v 12.3, distributed within the interval 1919-1947, finding, after some tentatives, that the epochs t_M of the maxima were fairly well satisfied by the following elements: t_M = JD 242 7633 + 51d.50 E. The observed J.D. of the selected maxima, the corresponding date, the visual magnitude, the number E of cycles passed from the epoch T_o and the phase (T_o - T_M)/P of each maximum are given in Table I. Table I - Observed maxima and residuals. JD Date m_v (max) E Phase 2400000 22119 1919 Jun 9 12.00 -107 +0.07 22176 Aug 5 12.10 -106 -0.04 22481 1920 Jun 5 12.10 -100 +0.04 22849 1921 Jun 8 12.05 - 93 -0.11 22893 Jul 22 12.30 - 92 +0.04 23199 1922 May 24 12.05 - 86 +0.10 23253 Jul 17 12.10 - 85 +0.05 23978 1924 Jul 11 12.05 - 71 -0.03 24025 Aug 27 12.00 - 70 +0.06 24701 1926 Jul 4 12.10 - 57 -0.07 24750 Aug 22 12.00 - 56 -0.02 24795 Oct 6 12.05 - 55 +0.11 27635 1934 Jul 16 12.20 -- +0.04 28355 1936 Jul 5 12.10 + 14 +0.02 28401 Aug 20 12.10 + 15 -0.09 31962 1946 May 21 12.10 + 84 +0.06 32417 1947 Aug 19 12.30 + 93 -0.11 The mean light curve of the nova at minimum, during the periods of semiregular activity is shown in Fig. 3, the phases having been computed with the precedent elements. Of course the magnitudes of the star observed in its periods of quiescence, as shown in Fig. 2, have not been taken into consideration. [FIGURE 3] Fig. 3. Mean light curve of V841 Oph The mean light curve reproduced in Fig.3 is typical of semiregular variables. The mean amplitude is 0.42, between m_v 12.15 and m_v 12.57, the curve has a sinusoidal-like shape. The relatively high dispersion of the points is mostly due to the variable amplitude of the oscillations and also to the fact that the period, although its average value 51.5d is maintained for 28 years, changes irregularly between 45 and 57 days from cycle to cycle. This very interesting old nova has now been included in a regular programme of spectroscopic and photometric observations at Asiago. M. DELLA VALLE, L. ROSINO Department of Astronomy of the University of Padova. References: Barnard E.E., 1921, Monthly Not. of the RAS 81, 167. [BIBCODE 1921MNRAS..81..167B ] Steavenson W.H., 1923, Monthly Not. of the RAS 83, 160. [BIBCODE 1923MNRAS..83..160S ] Turner, H.H., 1921, Monthly Not. of the RAS 81, 426. [BIBCODE 1921MNRAS..81..426T ]