COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3644 Konkoly Observatory Budapest 18 July 1991 HU ISSN 0374 - 0676 ON THE X-RAY STAR WW Ari = EXO 020528+1454.8 WW Ari, consisting of a pair of dMe stars (dM4.5e+dM4.5e), is identical with Lowell's proper motion star G035-027. First results about the behaviour of the total light of the system in the optical range were given by Hudec et al. (1988) and Gotz (1987). To complete and supplement the study of the optical behaviour, the star was measured on 101 blue-sensitive plates (ORWO ZU21+ GG13+BG12) from 54 nights obtained with the Schmidt camera 50/70/172 cm of Sonneberg Observatory, covering the time interval between October 2 1987 and February 2 1991. The observations are linked to the sequence of comparison stars given by Götz (1987). The light curve in B is given in Figure 1; it shows the individual observations and, in addition, the series of the season 1986/87. It turns out that the two series differ. While in the season 1986/87 most of the observations are brighter than m = 16.0m, in the season 1987-91 a remarkable number of observations are fainter than m = 16.0m. The star is scattering nearly over the whole range of amplitude and the light curve is characterized by short-term flares and depressions starting from a mean level. This fact is also confirmed by the histogram given in Figure 2, where the brightness distributions of observations published by Hudec et al. (1988) and Gotz (1987) (clear areas) and those of the new series are shown. Remarkable brightness changes of the star are listed in Table I. Considering all observations of the star, the total amplitude of the system in B amounts to 1.2 mag (15.3m - 16.5m). On 3 plates of the new series the two components of the system are isolated and separate. The individual magnitudes of the eastern and western components of WW Ari are given in Table II, where [FIGURE 1] [FIGURE 2] Table I J.D.hel m_B Delta t Delta m_B 244.... 7205.261 15.62m 0.015d +0.88m 276 16.50 7413.537 15.75 0.021 +0.51 558 16.26 7414.521 16.41 0.020 -0.83 541 15.58 7471.348 16.47 0.016 -0.71 364 15.76 J.D.hel m_B Delta t Delta m_B 244... 7823.447 15.86m 0.017d +0.46m 464 16.32 8220.462 16.18 0.017 -0.49 479 15.69 8274.238 15.80 0.038 -0.43 276 15.38 0.019 +0.45 295 15.82 Table II J.D.hel m_B distance 244.... eastern/western component 7415.548 16.43m 16.40m 3.32" 8274.238 15.99: 16.02: 2.93 8274.276 15.76: 15.87: 3.16 the measured angular distances of the two stars have also been listed. In this connection it should be mentioned that the brightness and distance measurements were difficult. As can be seen from Table II, both objects are variable nearly of the same order and in the same manner. On the best plate, from J.D.hel 244 7415.548, the two dM4.5e stars show nearly the same brightness of m = 16.4m. Considering an absolute magnitude of M_v = 11.8 and a colour index of (B-V) = 1.59 according to data given by Schmidt-Kaler (1982), one finds that the distance to the earth is D = 40 pc. This value is at the upper margin of that given by Hudec et al. (1988) with D = 25 pc+- 15 pc, who worked with an average absolute magnitude of M_v = 13.2 for dM4-5 stars of the solar neighbourhood. Considering the mean brightness of the stars on the other plates, one obtains distances of D = 33 pc and D = 30.5 pc. From the largest and the smallest distances to the earth on the basis of the angular distances the distances between the two stars can be determined. These results are given in Table III, where the values of the individual observations and the mean distances averaged over all observations are shown. There is no doubt that the system WW Ari is a close pair of stars between which interaction by means of X-rays is possible. Table III Angular distances between both components distance in Astronomical Units D = 25 pc D = 40 pc 3.32" 83.0 132.8 2.93 73.3 117.2 3.16 79.0 126.2 3.14 78.5 125.6 W. GOTZ, K. HEILAND Sonneberg Observatory References: Hudec, R. et al., 1988, BAC 39,296-302 [BIBCODE 1988BAICz..39..296H ] Gotz, W., 1987, Inf.Bull.Var.Stars No. 3045 Schmidt-Kaler, Th., 1982, Landolt-Bornstein, Group VI Vol. 2b, 15-18, Springer-Verlag Berlin, Heidelberg, New York