1No.70

Feb. 2021

ISSN 0917-2211

Variable Star Bulletin
Reassess RZ Cas light curves at primary minima during 1995-1996
Shin-ya Narusawa
Center for Astronomy, University of Hyogo, Sayo-cho, Hyogo, 679-5313, Japannarusawa@nhao.jp
Kikuichi Arai
Arai North-River Observatory, Saitama, Japan
Mitugu Fujii
Fujii Bisei Observatory, Kurashiki, Okayama, Japan
Kazuo Nagai
VSOLJandTakeshi Yasuda
Himeji Science Museum, Himeji, Hyogo, Japan
Received 2021 Jan. 24

1Introduction

The Algol binary RZ Cas (HD 17138) has been well-known for its irregular and sudden period change(SPC)s.
Even though the primary minimum is due to partial occupation, occasionally flat bottoms which resemble a total
eclipse are observed at the mid-primary minimum (e.g., Narusawa et al. 1994).
In order to study the cause of flat bottoms and their relations to SPCs, we have carried out corporative
photometry of RZ Cas at five places in Japan from January 1995 to December 1996 (three seasons). Theobservations were conducted with photoelectric photometry at three observatories and CCD photometry at two.
At all the observatories, the V or R colour filters similar to the standard Johnson-Kron-Cousins system wereused.
The results have already been reported as Narusawa et al (1997, Paper I). Back then, we reported that six
partial eclipses were observed, however apparent flat bottoms did not appear in the primary minima during ourobservational period (see Table 2 of Paper I).
Ohshima et al. (1998, 2001) have found a δ Sct type nonradial pulsation (NRP) with a frequency of 64.20
cycles day−1 (22 min) whose maximum amplitude is 0.02 mag. This has led us to understand that the flat bottom
is synthesized with the light variation of the partial eclipse and those of the oscillations. Moreover, Ohshima
et al. (2001) categorized the shapes into four types; the “F-type” with a flat bottom; the “V-type” with aV-shaped curve; and the “S-type” with a slant increasing or decreasing smoothly. Furthermore, the subtypes“Sa” and “Sb” were classified which indicate an ascending slant and a descending one respectively. According
to the explanation by Ohshima (2001), when the light maximum of the δ Sct pulsation coincides with the centerof eclipse, the F-type is observed. When the light minimum of pulsation coincides with the mid-primary eclipse,
the V-type light curve is observed. The intermediate case is the S-type. In addition to Ohshima et al. (2001)’s
classifications, we defined a partial-eclipsed curve, the “P-type” which appears when the amplitude of pulsationis small.

2

Table 1: Shape of light curves at the primary minima
Obs. Date
1995/01/06
1995/01/25
1995/09/27
1995/10/03
1995/10/21
1995/10/27
1995/11/02
1995/11/09
1995/12/21
1995/12/27
1996/12/28

2

HJD
2400000+
49723
49723
49743
49988
49994
50012
50018
50023
50023
50031
50072
50078
50445

FilterShapeObserver

VV
VV
Rc
VVV
Rc
Rc
VV
V

P:
V
P
Sa
Sa-F
F: duration ∼ 20min(Sa-)F duration ∼ 10min
P:
-

Arai
OhmoriOhmori
Yasuda
Fujii
Nagai
Arai
Arai
Fujii
Fujii
Arai
Arai
Nagai

Reassessments and Results

We reassessed the shapes of Paper I’s light curves at primary minima, for δ Sct pulsations were not detected atthat time. The results are listed in Table1, and some of the light curves are shown in Figures 1-4. As shown in
Table 1, the F-, Sa-, and V-type light curve shapes appeared during the 1995/1996 seasons. Because only theP-types were observed in Paper I, we concluded that the amplitude of the δ Sct type pulsation was small during
this period. However, the observations from Narusawa & Nakamura (2020) also found Sa- and Sb- types on 1995
November 2 and 3, leading us to believe that the amplitude was not actually so small during this season.
Narusawa et al. (2006) performed Hα spectroscopic observations of RZ Cas on 1995 September 27 andOctober 3, and they discovered circumstellar matter in this system. Mkrtichian et al. (2018) proposed that thepresence of circumstellar matter causes a decrease in the pulsation amplitude. However, since all shapes of light
curves at the bottom of primary eclipse were observed in this season, the presence of circumstellar matter did
not cause the amplitude of δ Sct type NRP to decrease for RZ Cas.
We are grateful to O. Ohshima for the useful discussions. We would also like to acknowledge Y. Taguchi andlate S. Ohmori.

Reference:Mkrtichian, D. E., et al. 2018, MNRAS, 475, 4745
Narusawa, S., Arai, K., Nagai, K., Ohmori, S., Fujii, M., & Yasuda, T. 1997, IBVS, 4502 (Paper I)
Narusawa, S., Nakamura, Y., & Yamasaki, A. 1994, AJ, 107, 1141
Narusawa, S., & Nakamura, Y. 2020, VSB, 68
Narusawa, S., Ozaki, S., Okyudo, M., Takano, R., & Nakamura, Y. 2006, PASP, 118, 809
Ohshima, O., Narusawa, S., Akazawa, H., Fujii, M., Kawabata, T., & Ohkura, N. 1998, IBVS, 4581
Ohshima, O., Narusawa, S., Akazawa, H., Arai, K., Fujii, M., Kawabata, T., Morikawa, K., Ohkura, N. &Takeuti, M. 2001, AJ, 122, 418

3-0.2

ΔV-0.1
0.0
0.1
0.2
10.8

11.1

11.4
UT

11.7

12.0

Figure 1: The light curve on Jan. 6 1995 observed by Arai.

1.4
1.5
ΔV

1.6
1.7

1.8
1.9
11.1

11.4

11.7
UT

12.0

12.3

Figure 2: The typical Sa type light curve on Nov. 2 1995 observed by Arai.

-3.7

ΔRc-3.6-3.5-3.4-3.3-3.2

11.1

11.4

11.7
UT

12.0

12.3

Figure 3: The light curve on Nov. 2 1995 observed by Fujii.

4

1.4
1.5
ΔV

1.6
1.7

1.8
1.9
10.8

11.1

11.4
UT

11.7

12.0

Figure 4: The light curve on Dec. 27 1995 observed by Arai.

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