COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1967 Konkoly Observatory Budapest 1981 May 19 HU ISSN 0374-0676 UBVRI TIMES OF MINIMA OF VW CEPHEI The Automated Filter Photometer at Kitt Peak was used on the number two 0.9 meter telescope during the interval 19-26 August, 1980, for UBVRI observations of VW Cephei. Useful data were obtained on all or parts of four nights. The single comparison star was BD + 74d889, comparison star "a" in the list by Kwee (1966). One second integration times for each filter permitted accumulation of a large body of observational data. The small range in air mass for the comparison star, a result of its large declination, produced a low weight determination of extinction coefficients. Since differential extinction between the variable and comparison star is very small, it was sufficiently accurate to use mean first and second order coefficients in all colors for a first pass extinction correction for both the variable and comparison star. Calculated magnitude residuals, for the comparison star, from predicted constant extra-atmosphere magnitudes and colors then were examined for time-dependent variation. Where appropriate, time-dependent corrections were applied to both variable and comparison star. This procedure will be described in a separate publication. The times of observation received an initial heliocentric correction, followed by a light time correction for orbital motion relative to the close visual companion. The visual binary orbital elements of Hershey (1975) were used for this correction. (See also Linnell (1980)). The correction, added to heliocentric times, was -0.01453 days. The final J.D. times of primary minima are in Table I and secondary minima in Table II, listed by spectral band. The calculated times are among the output of a computer program which will be described in a separate publication. Approximately 150 observations entered the equations of condition for each spectral band in each minimum. Table I Primary Minima, VW Cephei Date Filter Time of Min. Date Filter Time of Min. Aug.19 I 2444470.77895 +-.00017 Aug.25 I 2444476.90234 +-.00024 R 470.77835 +-.00015 R 476.90228 +-.00021 V 470.77840 +-.00015 V 476.90198 +-.00016 B 470.77850 +-.00015 B 476.90179 +-.00015 U 470.77820 +-.00015 U 476.90189 +-.00015 Aug.21 I 2444472.72680 +-.00011 Aug.26 I 2444477.73699 +-.00010 R 472.72667 +-.00011 R 477.73673 +-.00010 V 472.72699 +-.00013 V 477.73661 +-.00010 B 472.72658 +-.00010 B 477.73644 +-.00009 U 472.72666 +-.00010 U 477.73613 +-.00009 Table II Secondary Minima, VW Cephei Date Filter Time of Min. Date Filter Time of Min. Aug.19 No Data V 476.76488 +-.00018 Aug.21 I 2444472.86721 +-.00016 B 476.76516 +-.00014 R 472.86818 +-.00022 U 476.76541 +-.00015 V 472.86813 +-.00018 Aug.26 I 2444477.87697 +-.00018 B 472.86807 +-.00016 R 477.87735 +-.00022 U 472.86834 +-.00018 V 477.87757 +-.00019 Aug.25 I 2444476.76450 +-.00020 B 477.87815 +-.00017 R 476.76495 +-.00018 U 477.87844 +-.00017 An effect is apparent in the solutions which does not appear to have been discussed previously. To within the errors of observation for all nights, the time of primary minimum comes first in U followed successively by B, V, R and I. The total range of times of primary minimum is the same, within the error of determination, on all nights. It is approximately 60 seconds, from U to I. The sequence is reversed for secondary minimum, with earliest minimum occurring in I, followed successively by R, V, B, and U. The time range of secondary minimum approximates 150 seconds. Light asymmetry is such that the higher maximum follows primary minimum. Color data indicate a higher source temperature at the elongation following primary minimum. It is worth noting that the difference in depths of minima precisely equals the difference in heights of the maxima. This rule holds in all color bands even though the differences gradually and monotonically increase from the I band to the U band. A more detailed discussion of these effects will appear in a separate publication. This research was supported by a grant from the National Science Foundation. ALBERT P. LINNELL * Michigan State University East Lansing, MI 48824, USA *Visiting astronomer, Kitt Peak National Observatory, operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. References: Hershey, J.L. 1975, Astron. J. 80, 662. [BIBCODE 1975AJ.....80..662H ] Kwee, K.K. 1966, B.A.N. Suppl. 1, 265. [BIBCODE 1966BANS....1..265K ] Linnell, A.P. 1980, Publ. Astron. Soc. Pacific 92, 202. [BIBCODE 1980PASP...92..202L ]