COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3309 Konkoly Observatory Budapest 20 March 1989 HU ISSN 0374 - 0676 V398 Cyg: PERIOD DETERMINATION FOR AN UNUSUAL EA SYSTEM V398 Cyg is a so far quite ignored variable star. The GCVS lists it as an EA eclipsing system with a possible period of 9.2122d and a photographic magnitude range of 12.5 - >15.0. V398 Cyg belongs to the field of Nova Cygni 1970, on which many plates have been exposed at Asiago Astrophysical Observatory with the two Schmidt telescopes. On all available, good quality B (103a-O + GG13) and V (103a-D + GG14) plates, we have estimated the magnitude of V398 Cyg with respect to the photometric sequence given by Kohoutek (1969) for the nearby slow nova V1329 Cyg. The results are given in Table I, where heliocentric Julian days are used. We have examined the data in Table I with a Deeming code (Barbieri et al. 1977) to determine the eclipse, period. The only admitted period is 2.4481d. The following ephemeris gives the instants of minima in our B light curve: B_min = 2445227.396+2.4481d*E (1) Linking our minimum to that listed in the GCVS should result in: B_min = 2425157.27+2.4481735d*E (2) A plot of the data in Tab. I with the period listed in the GCVS (9.2122d) shows the points defining the B minimum uniformly distributed in phases. The B and V light curves, using Tab. I and ephemeris (2), are presented in Fig. 1. The eclipse in the B band is well defined. Its amplitude could be as large as 5 magn. In fact, the B>18.0 point comes from a good plate with no emulsion defect on the V398 Cyg expected position. The eclipse in the V band is much less well defined. Anyway it appears to be of much lower amplitude than the B one. Out of eclipse the B-V index is about 0.0, in agreement with a B&C+CCD red spectrum taken for us by J. Hron of Astron. Inst. of Vienna, showing an early type star. In eclipse the B-V color index largely increases, but no spectra are available for this phase. Table I. B, V photographic photometry of V 398 Cyg H.J.D. B V H.J.D B V H.J.D. B V 2440508.341 13.2 41657.256 13.2 43753.472 13.2 40508.351 13.2 41658.260 13.2 43789.387 13.1 40748.535 13.0 41919.479 13.0 43805.484 13.2 40748.547 13.1 41919.490 13.2 43806.414 13.1 40749.553 13.3 41924.459 13.1 44015.532 13.9 40763.472 13.2 41924.474 13.1 44015.550 15.2 40773.470 13.2 41927.384 13.3 44022.541 13.1 40778.517 13.0 41927.400 14.0 44022.566 13.2 40778.532 13.1 42190.463 13.2 44023.517 13.2 40794.498 13.2 42713.303 13.2 44023.539 13.3 40796.442 13.2 42713.315 13.2 44044.491 13.2 40804.442 13.2 42716.396 13.2 44044.508 13.2 40804.458 13.2 43127.267 13.2 44136.466 13.2 40824.406 13.1 43127.283 13.1 44166.366 13.1 40824.419 13.2 43259.569 13.3 44198.329 13.2 40836.507 13.0 43284.567 13.3 44221.316 13.8 40839.415 13.1 43313.473 13.2 44461.556 13.3 40839.427 13.2 43337.522 14.2 44461.572 13.1 40916.276 16.5 43394.366 13.1 44812.517 13.2 40918.270 13.2 43398.378 13.3 44912.363 13.2 40918.286 13.0 43405.411 13.2 44928.278 13.2 41068.549 13.2 43420.379 13.2 44928.301 13.2 41099.559 13.2 43429.304 13.1 45118.541 13.2 41099.572 13.0 43433.398 13.1 45118.573 13.2 41135.491 13.3 43433.490 13.2 45148.508 13.2 41163.519 16.6 43452.302 13.3 45148.536 13.2 41178.439 13.2 43453.299 13.2 45201.368 13.2 41178.453 13.1 43454.395 13.3 45201.389 13.2 41217.336 14.8 43456.393 13.3 45227.375 14.2 41245.385 13.3 43459.303 13.2 45227.396 >18.0 41272.218 13.2 43462.346 14.8 45258.375 13.1 41296.289 13.3 43462.399 14.0 45259.378 13.5 41486.550 13.3 43464.401 13.2 45315.325 13.2 41572.371 16.6 43480.226 13.3 45383.399 13.2 41595.367 13.2 43480.301 13.0 45551.441 13.2 41616.250 13.3 43482.228 13.3 45617.359 13.2 41623.280 13.3 43483.270 13.1 45620.460 13.2 41624.282 13.2 43732.557 13.2 45640.411 13.0 41651.341 13.3 [FIGURE 1] Figure 1. (top) Phase plot according to the ephemeris (2) of the V data in Table I. (bottom) Phase plot according to the ephemeris (2) of the B data in Table I. Note the "fainter than" mark on JD 2445227.396 near phase 0.0 . A further puzzling feature comes from the analysis of 9 infrared plates (I-N + RG5). Only one of these plates has been exposed during a light minimum (HJD= 2444015.569, phase 0.008). On the V398 Cyg expected position on this plate no emulsion defect is visible and the star presents a deep minimum, while out of eclipse the star is bright and constant. A marked fall in the blue and in the infrared, while the visual is little affected, points towards a very strange eclipsing system. Due to the very deep B minimum (5 magn. ?) this system should deserve further attention by the observers. Particularly useful should be an optical spectrum secured during a light minimum, to investigate the nature of the eclipsing star. R. MARGONI U. MUNARI A. MAMMANO R. STAGNI Dept. of Mathematics Astrophysical Observatory University of Messina I-36012 Asiago (VI), Italy I-98100 Messina, Italy References: Barbieri, C., Romano, G., di Serego, A.S., Zambon, M.: 1977 Astron. Astrophys. 59, 419. [BIBCODE 1977A&A....59..419B ] Kohoutek, L.: 1969 IBVS 384.