COMMISSION 27 OF THE I. A. U.
INFORMATION BULLETIN ON VARIABLE STARS
Number 1694
Konkoly Observatory
Budapest
1979 October 23
PHOTOELECTRIC TIMES OF MINIMA FOR SELECTED
ECLIPSING BINARIES AND UPDATED EPHEMERIDES
The following times of minima are derived from photoelectric
V-filter observations during August-September of 1979 with the 40-cm
reflector of the University of Montana. The observing procedure
was identical to that described in IBVS No. 1478 (Margrave et al.,
1978).
Each time of primary minimum in Table 1 was determined by the
least-squares fitting of a parabola to the observations. Table 1
lists the heliocentric Julian Date for each primary minimum observed,
the epoch number E, the O-C value, and N, the number of observations
used in the determination (each observation is the average of three
10-second integrations). The ephemerides used to calculate the O-C
values are given in Table 2.
Table 1. Heliocentric Times of Primary Minima
Star Hel. JD - 2,440,000 E O-C N
KO Aql 4135.7568 785 +0.0218d 36
RZ Cas 4096.7410 11,893 -0.0016 33
4121.8392 11,919 -0.0036 52
4127.8151 11,924 -0.0039 45
TV Cas 4094.9219 580 -0.0164 53
4114.8601 591 -0.0169 70
TW Cas 4110.8729 1,472 -0.0109 32
4123.7296 1,481 -0.0092 32
4130.8694 1,486 -0.0110 42
DO Cas 4095.7981 14,853 -0.0026 66
XX Cep 4133.9256 2,495 +0.0162 52
AT Peg 4089.8201 3,186 -0.0534 76
4128.7853 3,220 -0.0558 51
4136.8079 3,227 -0.0559 32
Table 2. Ephemerides for Program Stars
Star Hel. JD Period (days) Source
KO Aql 2,441,887.4714 2.86403 SAC 49
RZ Cas 2,429,875.6902 1.1952473 Herczeg
and Friboes-Conde
TV Cas 2,443,043.6265 1.8126066 SAC 50
TW Cas 2,442,008.3850 1.428328 SAC 50
DO Cas 2,433,926.4573 0.68466595 SAC 50
XX Cep 2,438,302.3209 2.33731 SAC 50
AT Peg 2,440,438.383 1.146105 SAC 50
The residual of KO Aql has increased steadily since August 1975.
A linear fit to the epoch given in SAC 50, the IBVS No. 1478 minimum,
and that of this note yields
Hel. JD (Min) = 2,441,887.4733 + 2.864055d*E
which fits these minima with residuals of -0.0019d, +0.0001d, and +0.0003d,
respectively, Thus it appears that there has been an increase of
2.5d x 10^-5 in the period of KO Aql since 1973.
The residual behavior of RZ Cas will be discussed elsewhere,
insofar as it is linked to the question of sudden period changes
versus light travel time effects (Doolittle, 1976).
The provisional new ephemeris for TV Cas given by Margrave (1979)
has been revised to include the minima of this note, with the following
result:
Hel. JD (Min) = 2,441,595.3598 + 1.8125898d*E.
This ephemeris gives residuals less than +-0.0015d (except for one in
1978 of -0.0035d) for observations back to 1972. The above result
reflects a decrease by 1.68d x 10^-5, or 1.45 seconds, relative to the
period given in SAC 50.
The residuals for TW Cas have generally become more negative
since 1975, with primary eclipses now occurring about 15 minutes
early. The epoch in SAC 50, the minima of IBVS Nos. 1478 and 1631,
and those of this note yield the following linear ephemeris:
Hel. JD (Min) = 2,442,008.3856 + 1.4283216d*E.
The mean residual for the least-squares fit is 0.0026d. The new period
reflects a decrease of 6.4d x 10^-6 with respect to the SAC 50 value.
The residual for XX Cep given here continues the trend to later
eclipse occurrences evident in 1975 (Margrave et al., 1978).
Increasing the SAC 50 period to 2.3373158d reduces the residual of this
note to +0.0018d and may perhaps be used for more accurate prediction
over the next couple of years.
The situation of AT Peg presently appears to involve a continuous
period decrease at the rather large rate of 19.3 seconds per century,
with primary minima being predictable by the following revised
quadratic ephemeris:
Hel. JD (Min) = 2,440,407.4368 + 1.14611077d*E
- 7.0158 x 10^-9*E^2.
This ephemeris fits the observations from 1969 to the present with
a mean residual of 0.0026d. The epoch number for the last minimum
of AT Peg in Table 1 is E = 3254 for the quadratic ephemeris.
Continued timing of this system is necessary to determine the duration
of the present stage of continuous period decrease.
T. E. MARGRAVE
Blue Mountain Observatory
University of Montana
Missoula, Montana 59812
USA
References:
Doolittle, J.: Master's Thesis, Univ. of Montana, 1976.
Ebersberger, J., Pohl, E., and Kizilirmak, A.: IBVS No. 1449, 1978.
Herczeg, T. and Friboes-Conde, H.: Astr. and Ap., 30, 259, 1974. [BIBCODE 1974A&A....30..259H ]
Kizilirmak, A. and Pohl, E.: IBVS No. 937, 1974.
Kordylewski, K.: Supplemento ad Annuario Cracoviense No. 49, Krakow 1978.
Margrave, T. et al.: IBVS No. 1478, 1978.
Margrave, T.: IBVS No. 1631, 1979.
Pohl, E. and Kizilirmak, A.: IBVS No. 1163, 1976.
Rudnicki, K.: Supplemento ad Annuario Cracoviense No. 50, Krakow 1978. [BIBCODE 1978raok.book.....R ]