COMMISSION 27 OF THE I.A.U.
INFORMATION BULLETIN ON VARIABLE STARS
Number 1244
Konkoly Observatory
Budapest
1977 February 21
ON THE PERIOD OF THE ECLIPSING BINARY RW PERSEI
The aim of this note is to establish a numerical value of the
period change of the eclipsing binary RW Persei and to test its
significance. Hall (1969) collected all available times of minimum
till 1968 and mentioned a sudden period decrease around
1925. A period increase, suspected around 1960 (Baldwin, 1974),
has been confirmed by Hall & Stuhlinger (1974), but their observational
data were not sufficient for a refinement of Baldwin's
period (13.198940d). Bush (1976) recently published additional
times of minimum which enable us to get an idea of the behaviour
of the period of RW Persei during the last fifteen years.
The whole set of data can be divided in three time intervals
in which a linear regression of the times of minimum yields
periods which differ significantly (Table 1, Fig. 1). The number
of cycles elapsed at each minimum has been calculated from
Woodward's linear ephemeris
Min (JD hel.) = 2429217.587 + 13.198454d E
From table 1 we conclude that the amount of period decrease
around 1925 is 4.95*10^-4 +- 2.15*10^-4 days, while we find an
increase of 5.11*10^-4 +- 3.38*10^-4 days around 1960.
Table 1
Time interval Epoch of Period Mean error
Mid interval
1898-1924 -745 13.198938d +-0.000099d
1925-1955 + 55 13.198443d +-0.000116d
1955-1972 +794 13.198954d +-0.000222d
[FIGURE 1]
Fig. 1: The variation of the period of RW Persei
circle with dot: Woodward's value
dot : this note
[FIGURE 2]
Fig. 2: (O-C) residuals of Busch's times of minimum
x : values of Hall (1969)
circle with dot : value of Hall & Stuhlinger (1975)
A parabolic least squares fit of the (O-C)-values on the other
hand yields a linear decrease of the period of 0.66*10^-6 +-
0.09*10^-6 days/cycle in the interval -1200 < E < 0, while the
same procedure in the interval 0 < E < 800 gives an increase of
0.72*10^-6 +- 0.20*10^-6 days/cycle.
These values agree with the abovementioned results.
The time interval 1960-1972 cannot be divided in subintervals
in which a linear regression of the times of minimum reveals
significant different values of the period. The (O-C) residuals
in this interval, which are plotted in Fig. 2, fit the straight
line -0.25 + 0.00042 E. This indicates that the period was nearly
+-4 +-6
constant between 1960 and 1972. On the other hand the coefficient
of the quadratic term of the least squares parabola fitted to
Busch's residuals (indicated in Fig. 2) amounts -0.10*10^-5
days/cycle^2 +- 0.08*10^-5 days/cycle^2.
So we conclude that the results from Busch's data show a tendency
towards a decreasing period for the system. New times of minimum
are needed to confirm the hypothesis that the period of
RW Persei is decreasing again.
WALTER VAN HAMME
Aspirant van het Belgisch
National Fonds voor
Watenschappelijk Onderzoek
Observatorium R.U.G.
Krijgslaan 271 (S9)
B-9000 Gent
References :
Baldwin, B.W., 1974, I.B.V.S. No 910
Busch, H., 1976, I.B.V.S. No 1121
Hall, D.S., 1969, Mass Loss from Stars, p. 171-183 [BIBCODE 1969ASSL...13..171H ]
Hall, D.S. & Stuhlinger, T., 1975, I.B.V.S. No 972
Woodward, E.J., 1943, Harvard Bull. 917, p. 7