1No.82

Oct. 2021

ISSN 0917-2211

Variable Star Bulletin
Algol-type system RZ Cas: Times of primary minima by diﬀerent methods
Shin-ya Narusawa
Center for Astronomy, University of Hyogo, Sayo-cho, Hyogo, 679-5313, Japannarusawa@nhao.jp
andKazuo Nagai
Variable Star Observers League in Japan
Received 2021 Oct. 02
RZ Cas is one of the famous Algol-type binary systems whose primary constituent is the δ Sct-type pulsator.
Ohshima et al. (2001) discovered that the observed light curve at the primary minimum was a synthesis of thelight variation of the partial eclipse and that of the short-period quasi-regular variation. They classiﬁed thelight curves at the primary minimum into three types: the “F-type” with a ﬂat-bottom (total eclipse-like); the“V-type” with a V-shaped curve; and the “S-type” with a slant increasing or deceasing smoothly. Moreover,the subtypes “Sa” and “Sb” were classiﬁed which indicate an ascending slant and a descending one respectively.
According to the explanation of Ohshima et al (2001), when the light maximum of pulsation coincides with thecenter of eclipse, the F-type is observed. When the light minimum of oscillation passes the mid-primary eclipse,
the V-type light curve is observed. The intermediate case is the S-type.
RZ Cas is also well-known for its irregular and sudden period change (SPC)s. How much inﬂuence on the(O-C) values of this system do diﬀerent methods of determining mid-eclipse times have? We determined themid-time for the same light curve utilizing six methods, Kwee & van Woerden (KW) method (Kwee & vanWoerden 1956) , AVE and Peranso spline1 , bisection, Parabolic Fit, Tracing Paper, and Fourier Fit. The latter
three methods were derived by Minima25c programs 2 . Ohshima et al. (2001)’s light curves were used in orderto check all eclipse shapes (V, F, Sa, and Sb). Because these shapes were observed in a short time (one season).
The results are shown in Table 1, and this points that diﬀerences between maximum and minimum values
are within one minute (7×10−4 days) in each shape. In other words, the diﬀerent methods have little inﬂuenceon the (O-C) values. As a conclusion, types of method have no relation with the SPC.
We are indebted to Osamu Ohshima for useful comments, and to Yusuke Taguchi for his kind help.
Reference:Kwee, K.K., & H van Woerden, H. 1956, Bulletin of the Astronomical Institutes of the Netherlands, 12, 464
Ohshima, O., Narusawa, S., Akazawa, H., Arai, K., Fujii, M., Kawabata, T., Morikawa, K., Ohkura, N., &Takeuti, M. 2001, AJ, 122, 418

1 https://www.cbabelgium.com/peranso/
2 https://www.variablestarssouth.org/minima25c/

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Table 1: Times of primary minima determined for all shapes by several methods.
ShapeFilterHJD

PV
F
Sa
Sb

V
B
V
B
V

2450000+
826
777
747
747
808

KW
(AVE)

KW
(Peranso)

ParabolicFit

Tracing
PaperFourie

Bisectiona∆ Tb.0127(1).0063(1).1249(1).12475(8).08299(9).01319(8).00625(7).12475(8).12480(6).08276(5).0126(5).006(1).12510(5).12480(4).0830(1).0126(1).0062(1).1251(1).1248(1).0832(1).0127(1).0062(1).1251(1).1249(1).08320(4)

.0125
.0065
.1252
.1247
.0829

(sec)
60
26
39
17
37

a: determined by Ohshima et al. (2001)
b: diﬀerence between maximum and minimum values

VSOLJ
c/o Keiichi Saijo National Science Museum, Ueno-Park, Tokyo Japan
Editor Seiichiro Kiyota
e-mail:skiyotax@gmail.com