COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 4066 Konkoly Observatory Budapest 12 August 1994 HU ISSN 0374 - 0676 PHOTOMETRY OF THE ACTIVE STARS HD 127535 AND HD 202077 In this paper we present new photometry for the two southern active late-type stars HD 127535 and HD 202077 from June to July 1994. HD 127535 = V841 Cen (alpha = 14h34m16s, delta = -60d24'27", 2000.0, V = 8.5 mag) is a rapidly rotating, single-lined spectroscopic binary with an active K1 subgiant as the primary component (Collier et al. 1982). The star exhibits strong CaII H&K and Halpha emission (Houk & Cowley 1975, Weiler & Stencel 1979, Collier et al. 1982), it shows high X-ray flux in the ROSAT 0.1-2.4 keV energy range (Dempsey et al. 1993) and also very high radio- flux densities (Slee & Stewart 1989). The orbital period is 5.998 days with zero eccentricity (Collier 1982a) while the photometric (= rotational) period of the K1 subgiant is 5.929+/-0.024 days (Cutispoto 1990). Thus, the orbital motion and the stellar rotation are bound but not quite exactly synchronous. Previous photometry of HD 127535 was presented by Collier (1982b) from 1980-81, by Innis et al. (1985) from 1981, by Udalski & Geyer (1984) from 1984, by Bopp et al. (1986) from 1985, by Mekkaden & Geyer (1988) from April 1987 and Cutispoto (1990) from February 1987, and most recently by Cutispoto (1993) from 1989. Randich et al. (1993) determined the Lithium abundance and the v sin i. HD 127535 is listed as star number 118 in the "Catalog of Chromospherically Active Binary Stars" (Strassmeier et al. 1993). HD 202077 = BM Mic (alpha = 21h14m31s, delta = -30d45'24", 2000.0, V = 8.3 mag) is an apparently single G6 IV/V star (Houk 1982) with CaII H&K in emission (Lloyd-Evans & Koen 1987). Extensive photometry was presented by Lloyd-Evans & Koen (1987) for the observing period 1979-1981 who also determined the photometric period of HD 202077 of 14.5 days. With this period, the star showed a sinusoidal light curve with a full amplitude of 0.2 mag in Johnson V in 1979-1981. Otherwise there is nothing known about this star. The new data in this paper were obtained on 15 nights at the 70-cm Swiss-telescope at ESO La Silla in Chile between June 24th and July 15th, 1994. All seven Geneva-colours were measured almost simultaneously. For a description of the Geneva-system see Rufener & Nicolet (1988). The observers were P. North and E. Paunzen. For the reduction we used the Geneva [U], [B] and [V] filters which are similiar to Johnson U, B and V (for relations see Cramer 1984). Every light-curve point for the two stars is the average of ten individual 60 sec measures taken within 10 minutes. The data were corrected for sky background and extinction. Tables 1 and 2 list the differential [V], [U - B] and [B - V] magnitudes for HD 127535 and HD 202077, respectively. Their respective comparison stars were HD 128227 (V =8.350 mag; e.g. Collier-Cameron 1987) and HD202540 (V = 6.551 mag, Lloyd-Evans et al. 1983). [FIGURE 1] Figure 1: Periodograms from the [V] data of HD 127535 (left panels) and HD 202077 (right panels). The upper graph shows the window function and the lower graph is the periodogram for the two stars, respectively. The "best" periods are indicated and are 5.86 days for HD 127535 and 14.3 days for HD 202077. [FIGURE 2] Figure 2: [UBV] light and color curves for HD 127535 (left panels) and HD 202077 (right panels). The HD 127535 data are plotted with the ephemeris JD 2,445,804.1+ 5.929xE and for HD 202077 with JD 2,449,000.0+14.3xE. Table 1: Geneva [UBV] photometry of HD 127535 and HD 202077 HD 127535-HD 128227 HD 202077-HD 202540 HJD Delta[V] Delta[U-B] Delta[B-V] HJD Delta[V] Delta[U-B] Delta[B-V] 244+ (mag) (mag) (mag) 244+ (mag) (mag) (mag) 9528.0285 0.325 -0.026 +0.021 9528.3764 1.428 -0.782 -0.445 9529.1118 0.302 +0.012 -0.013 9529.3403 1.419 -0.798 -0.446 9530.0944 0.143 -0.009 +0.004 9530.3319 1.410 -0.771 -0.438 9534.0465 0.325 -0.013 +0.025 9534.3174 1.459 -0.769 -0.440 9535.0250 0.298 -0.004 +0.038 9535.3056 1.467 -0.778 -0.442 9536.0847 0.131 -0.031 -0.002 9537.3167 1.510 -0.790 -0.445 9537.1632 0.101 -0.029 -0.009 9538.2792 1.445 -0.789 -0.442 9538.0736 0.177 -0.009 +0.006 9539.2486 1.427 -0.771 -0.448 9539.0701 0.263 -0.015 +0.015 9540.2799 1.425 -0.798 -0.442 9541.0208 0.290 +0.014 +0.039 9541.2361 1.421 -0.770 -0.440 9542.0132 0.129 -0.024 +0.006 9543.1917 1.439 -0.779 -0.439 9543.0146 0.092 -0.011 -0.006 9544.3264 1.439 -0.785 -0.437 9544.0215 0.181 -0.025 +0.009 9545.3458 1.425 -0.820 -0.441 9548.1410 0.119 -0.006 -0.002 9548.2847 1.433 -0.785 -0.440 9549.0028 0.105 -0.033 -0.005 9549.2708 1.465 -0.799 -0.432 Our data were examined for periodicity with a standard period-finding program, and we obtained the greatest reduction of the sum of the squares of the residuals at a period of 5.86+/-0.10 days for HD 127535 and 14.3+/-0.5 days for HD 202077, in agreement with previous determinations. Figure 1 shows periodograms for both stars and their respective window functions. The full amplitudes in [V], [U-B] and [B-V] are 0.23+/-0.02, 0.035+/-0.010, and 0.050+/-0.007 mag, respectively for HD 127535 and 0.060+/-0.015, <=0.05, and <=0.015 mag, respectively for HD 202077. The light and color curves are plotted in Fig. 2 versus rotational phase (data were phased with the photometric periods cited in the caption of Fig. 2). As compared to earlier observations, HD 202077 seems to be in a low-amplitude state in mid 1994, while the light curve amplitude of HD 127535 is at the previously observed maximum of 0.25 mag from 1984 (Udalski & Geyer 1984). If we assume that the photometric period of HD 127535 is the rotation period, the v sin i measure of 33+/-2(?) kms^-1 (Randich et al. 1993) leads to a minimum radius of 3.8+/-0.3 R_sun. Several sources quote a typical radius of ~0.8 R_sun for a K1 dwarf, and ~17 R_sun for a K1 class III giant. 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