COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3599 Konkoly Observatory Budapest 7 May 1991 HU ISSN 0374 - 0676 New UBV Light Curves of the Early-Type Eclipsing Binary V1331 Aql New photoelectric UBV light curves and preliminary photometric solutions of the B-type eclipsing binary V1331 Aql (=HD 173198 = SAO 142563 = BD -01d3553; sp=B1V, period = 1.364d, V=7.7m at maximum) are presented. In the past, first photoelectric measurements of V1331 Aql were made by van Leeuwen (1975) with a five-colour Walraven photometer, but the light curves show a considerable scattering. De Freitas Pacheco et al. (1977) published UBV light curves based on a relatively small number of observations and solved it with the Russell-Merrill method and with Wood's WINK code. It is amazing that obviously no further investigations nor observations were dedicated to V1331 Aql until 1990. Within the scope of a research program to determine absolute dimensions of OB-type eclipsing binaries we measured new photoelectric UBV light curves of V1331 Aql during 10 nights between June 15 and 29, 1990 with the single channel photometer at the ESO 0.5m telescope. An uncooled EMI 9789QB photomultiplier tube was attached. More than 500 individual measurements in each colour were achieved and are shown in Fig. 1. As a comparison star, HD 173003 (V=7.7m, sp=B5) was used, which is similar to V1331 Aql in spectral type and magnitude; the non-variability of the comparison was checked with SAO 142571 (V=9.8m, sp=B8). No significant variation in the intensity difference between the comparison and this star was found during the observation time. The differential reduction of the data was made with our own computer code providing relative magnitudes (comparison- variable) and the heliocentric J.D. The transformation in the standard UBV system, which we carried out with a program by L. Kohoutek, yielded the following Johnson magnitudes for the comparison star: U = 7.773 +- 0.018, B = 8.160 +- 0.010, V = 7.699 +- 0.009. Two primary minima and one secondary minimum of V1331 Aql were covered, what doubles the number of minima times published so far. Table 1, Normal points for V1331 Aql. N means the number of individual measurements. Phase U (HD173003-V1331 Aql) N Phase B (HD173003-V1331 Aql) N .00318 -.04811 7 .00372 -.18700 7 .00965 -.04242 13 .01020 -.18125 13 .01655 -.02704 9 .01709 -.17052 9 .02321 -.01395 10 .02375 -.15851 10 .03181 .01691 12 .03235 -.12581 12 .04565 .06506 9 .04619 -.08093 9 .05980 .12074 6 .06034 -.02535 6 .10693 .22640 8 .10747 .07096 8 .14905 .25050 10 .14680 .09047 10 .17772 .26808 12 .17160 .10973 12 .19718 .27279 11 .19205 .11722 11 .23045 .28697 8 .22172 .12562 8 .26848 .29680 12 .26316 .17440 12 .29588 .28071 12 .28999 .12566 12 .31824 .28137 10 .31239 .11690 10 .33987 .27353 11 .33328 .11412 11 .36777 .25263 14 .36309 .09548 14 .38861 .24944 8 .39195 .08714 8 .41172 .23738 8 .41489 .07050 8 .42823 .20254 9 .43007 .03994 9 .44172 .17165 13 .44334 .00809 13 .45407 .14327 15 .45546 -.02255 15 .46756 .12090 17 .46898 -.04403 17 .48001 .10789 10 .48192 -.06321 10 .49114 .09628 7 .49855 -.07589 7 .50862 .09746 8 .51638 -.06060 8 .52947 .12887 10 .53532 -.02842 10 .54422 .15511 8 .55016 .00575 8 .56206 .19205 12 .56763 .04432 12 .58065 .22161 12 .58724 .06850 12 .61562 .25386 13 .62323 .09282 13 .64372 .25878 12 .64271 .09678 12 .69276 .27812 10 .68821 .11220 10 .72628 .28773 13 .72458 .12395 13 .76832 .28977 17 .76376 .12643 17 .82725 .26559 14 .82367 .10870 14 .84871 .29844 14 .84732 .09458 14 .87418 .22823 15 .87291 .07889 15 .89480 .21881 10 .89388 .06748 10 .91082 .20467 9 .90985 .05402 9 .92591 .16144 8 .92409 .01507 8 .94470 .10074 7 .94276 -.03939 7 .95987 .04404 9 .95879 -.09751 9 .97510 -.00599 10 .97423 -.14646 10 .98785 -.07601 11 .98738 -.17652 11 .99662 -.04179 7 .99676 -.18782 8 Phase V (HD173003-V1331 Aql) N .00348 -.32952 7 .00992 -.32123 13 .01682 -.31049 9 .02148 -.29479 10 .03208 -.26649 12 .04592 -.22629 9 .06007 -.16968 6 .10720 -.07608 8 .14653 -.05361 10 .17133 -.03627 12 .19178 -.03024 11 .23180 -.01984 12 .27453 -.01473 14 .30539 -.02416 15 .33178 -.02890 12 .36282 -.04675 14 .38118 -.05596 8 .40396 -.06180 8 .42391 -.09075 9 .43874 -.12584 13 .45168 -.15794 15 .46527 -.18588 17 .47752 -.20579 10 .48612 -.21717 7 .50182 -.22225 8 .52349 -.19866 10 .53920 -.16946 8 .55722 -.12149 12 .57614 -.08751 12 .60689 -.05757 13 .63370 -.04515 12 .65601 -.04041 10 .71143 -.02377 13 .75039 -.01670 17 .81052 -.03262 14 .83981 -.04174 14 .86335 -.05891 15 .88652 -.07124 10 .90088 -.08103 9 .91526 -.09957 8 .92940 -.14066 7 .94928 -.20704 9 .96607 -.26456 10 .98118 -.30730 11 .99108 -.32200 7 .99736 -.32964 6 [FIGURE 1] Fig. 1: UBV light curves of V1331 Aql; individual measurements (U top, B middle, V bottom) are differential magnitudes in the sense comparison (HD173003) minus V1331 Aql. Table 2. Typical light curve solution (l_3 means third light contribution) i (deg) q(=M_2/M_3) T_2(K) L_1/L_2 l_3(%) r_1 r_2 (mean Roche radii) ---------------------------------------------------------------------------- 70.259 0.632 19130 U: 0.313 U: 0.00 0.370 0.283 B: 0.340 B: 1.41 V: 0.363 V: 0.06 Fixed parameters: T_1 = 25400 K x_1(U) = 0.315 x_2(U) = 0.340 g_1,2 = A_1,2 = 1.0 x_1(B) = 0.300 x_2(B) = 0.320 x_1(V) = 0.245 x_2(V) = 0.262 Taking all these data into account we calculated a new period giving the improved ephemeris: Pri.Min. = hel.J.D. 2442610.0581 + 1.3641953d E +-1 Our 1990 light curves of V1331 Aql were solved using the Wilson- Devinney approach combined with the Simplex parameter optimization procedure (c.f. Kallrath and Linnell, 1987), which is, according to our experiences, superior to the conventional differential corrections method, especially with respect to the convergence behaviour. As input data we used 46 normal points in each colour, formed from 6 to 17 individual measurements each. These normal points are listed in Table 1. We obtained convergent solutions for several values of q (=M_2/M_1) ranging from about 0.6 to 0.8 with nearly equal fit quality. In all cases the system configuration appears to be detached. As the luminosity ratio L_1/L_2 is always about 0.3 and the temperature of the secondary turns out to be around 19000 K (assuming 25400 K for the primary), the most probable model of V1331 Aql is a detached system with both components not too far from ZAMS. Hence, the spectral type of the secondary should be B2.8, and masses of the primary and secondary amount to 13 and 8 M_Sun, respectively. Then the mass ratio should be about 0.6, a value which is very close to the one we achieved in several light curve solutions (Lorenz et al., 1991). One typical solution is given in Table 2. The final decision about the mass ratio must be delayed until an independent spectroscopic determination will be available. A radial velocity curve of V1331 Aql will be measured by the authors in July 1991 at the ESO 1.52m spectroscopic telescope. REINALD LORENZ PAVEL MAYER HORST DRECHSEL Dr. Remeis-Sternwarte Dept. of Astronomy and Sternwartstr. 7 Astrophysics D-8600 Bamberg, Germany Charles University Prague Svedska 8 CS-150 00 Praha 5 CSFR References: de Freitas Pacheco, J.A., Ritte, C., Damineli Neto, A.: 1977, I.B.V.S., No. 1306. Kallrath, J., Linnell, A.P.: 1987, Astrophys. J. 313, 346. [BIBCODE 1987ApJ...313..346K ] van Leeuwen, F.: 1975, I.B.V.S., No. 1041. Lorenz, R., Drechsel, H., Mayer, P.: 1991, Astron. Ges. Abstract, Ser. 6, 72. [BIBCODE 1991AGAb....6...72L ]