1No.72

Feb. 2021

ISSN 0917-2211

Variable Star Bulletin
Multisite photometry of Algol-type binary system RZ Cas
Shin-ya Narusawa
Center for Astronomy, University of Hyogo, Sayo-cho, Hyogo, 679-5313, Japannarusawa@nhao.jp
Hidehiko Akazawa
Akazawa Funao Observatory, Kurashiki, Okayama, Japan
Kikuichi Arai
Arai North-River Observatory, Saitama, Japan
Mitugu Fujii
Fujii Bisei Observatory, Kurashiki, Okayama, Japan
Fredy Doncel Invernizzi
Observatorio Astronomico Prof. Alexis Troche, Facultad Politécnica, Universidad Nacional de Asunción,ParaguayMasayuki Ioroi
Nishi-Harima Astronomical Observatory Association, Sayo, Hyogo, Japan

Yoshiharu Ito
Seiwa Gakuen High School, Sendai, Miyagi, JapanKoichi Morikawa
Morikawa Yakage Observatory, Yagage, Okayama, JapanandNobuo Ohkura
Ohkura Senoh Observatory, Senoh, Okayama, Japan
Received 2021 Feb. 02

1Introduction

RZ Cas (HD 17138) is an Algol-type system whose primary and secondary components are A3 V and K0 IV
respectively. As this binary is bright (mv = 6.18 mag at light maxima) with a short orbital period (P = 1.195day), many reports of photometric observations of time of mid-minima have been published. Although theprimary minimum of this system is due to a partial eclipse, flat bottoms which resemble a total eclipse havefrequently been observed (Arganbright et al. 1988, Hegedüs et al. 1989, Nakamura et al. 1991a and Narusawa
et al. 1994 etc.). Several models were proposed, but the cause of the flat bottom was left unknown (Narusawa etal. 1994).

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We have performed cooperative photometry of RZ Cas not only during the primary eclipse, but also during
the out of eclipse phase from September 1997 to January 1998, and have found a δ Sct type, nonradial pulsation
with a frequency of 64.20 cycles day−1 (22.4 min), whose maximum amplitude is 0.02 mag (Ohshima et al. 2001;
hereafter O01). This has led us to understand that the flat bottom is synthesized with the light variation of thepartial eclipse and those of the oscillations as described in section 3.
RZ Cas is also famous for irregular and sudden orbital-period changes(SPCs). Many investigations of periodchanges of this system have been reported (e.g., Hegedüs et al. 1992, Narusawa et al. 1994, Mkrtichian et al.,2018 and Lehmann et al. 2020). In order to obtain more information, we have continued photometric studies ofthis system.

2Observations

The cooperative observations with PMT photometers and CCD cameras were conducted over 70 nights throughout October 1998 to November 2016 at seven sites in Japan. The instruments of each observation are listed inTable 1. The color filters similar to the standard Johnson-Kron-Cousins system were used at all places.

3Results

We obtained 19 primary and 6 secondary minima during observations over 70 nights. The results of photometricobservations at minima are reported here. The key information are summarized in Table 2.

3.1

Shape of light curve at mid-primary minima

We begin by discussing the shape of the light curve at mid-primary minima. O01 categorized the shapes into
three types; the “F-type” with a flat bottom; the “V-type” with a V-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 O01, when the light maximumof the δ Sct pulsation coincides with the center of eclipse, the F-type is observed. When the light minimum ofpulsation coincides with the mid-primary eclipse, the V-type light curve is observed. The intermediate case is theS-type. In addition to O01 ’s classification, we define the “P-type”, a partial-eclipsed curve. This type appears
when the amplitude of pulsation is small. Shapes at primary minima derived from our observations are listed inthe fifth column of Table 2. Apparent F-type and Sb-type curves were observed and they are shown in Figure 1.
As shown in the sixth column of Table 2, several of the light curves have asymmetric shapes probably showing
the effect of gas stream.

3.2

Orbital period

The estimated moments of minima are listed in the first column of Table 2. The E and O − C values werecalculated utilizing the following ephemeris provided by GCVS 5.1 1 .
Min I = HJD 2456529.766 + 1.19525031 E.

(1)

RZ Cas is a well-known system that shows SPCs as described in section 1. The O − C values listed in
the fourth column of Table 2 are plotted on the O − C diagram (after HJD 2429875 until the present time) inFigure 2 together with data (based on photoelectric and CCD observations) from the (B-R)-Generator für die
Lichtenknecker-Database of the BAV 2 and O-C gateway of Brno Regional Network of Observers (B.R.N.O.) ofthe Czech Astronomical Society 3 4 . Photoelectric data of primary minima that was published in Nakamura etal. (1991b) and photoelectric and CCD data that was published in O01 is also used. However, since this data is
1 http://www.sai.msu.su/gcvs/gcvs/gcvs5/gcvs5.txt
2 Obtained from http://www.bav-astro.de/LkDB/index.php?lang=en
3 Obtained from http://var2.astro.cz/ocgate/index.php?lang=en
4 Although both minima HJD 2452202.947 and HJD 2452228.048 are stated to be obtained by CCD observations in O-C gateway,
they are actually results of visual observations (Nagai 2002). Therefore we do not use these data for this study.

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Table 1: Observational sites observers, and instruments
Sitea
Funao

ARSO
Bisei
SendaiYakageNHAO
Senoh

Observer
Akazawa (1998-2000)
Akazawa (2015)
Akazawa (2016)
Arai
Fujii (except 2011/2012)
Fujii
Ito
Ito (last three nights)
Morikawa
Narusawa, Ioroi, Invernizzi
OhkuraTelescopeb
28 cm SC
8 cm refractor
20 cm SC
28 cm SC
7.5 cm refractor
7.5 cm refractor
5.5 cm(Camera lens)
6 cm refractor
25 cm SC
60 cm Cassegrain
35 cm SC

Camera/Detector c
PMT R647p PC
ST-9XE
ST-402 ME
PMT R647p VF
ST-7ST-10XME
ST-9
ST-9ST-7
PMT R647p PC
PMT R647p PC

FilterB, VRcVVRc, Ic
Rc
Rc
Rc
Ic
B, V
B, V

a: NHAO: Nishi-Harima Astronomical Observatory, ARSO: Arai River-Side Observatoryb: SC: Schmidt Cassegrain Telescope
c: PC: Photon-counting system, VF: V/F Conversion system

not registered in either the (B-R)-Generator nor the O-C gateway, we present them here in Table 3 and Table
4.
The Figure 3 shows the O − C values including our data during the period of HJD 2447500 (1988) toHJD 2454500 (2008) and it shows that the orbital period during the period ∼ HJD 2448500 (1991) to ∼HJD 2453000 (2003) was constant. This is an exceptionally long steady period for RZ Cas.
We are grateful to Tibor Hegedüs, Osamu Ohshima, Yuske Taguchi and Noritaka Tokimasa for their generous
contributions.

Reference:
Arganbright, D. V., Osborn, W., & Hall. D. S. 1988, Inf. Bull. Var. Stars, 3224
Hegedüs, T. 1989, Inf. Bull. Var. Stars, 3381
Hegedüs, T., Szatmáry, K., & Vinkó, J. 1992, Astrophy. Space Sci, 187, 57
Lehmann, H., Dervişoğlu, A., Mkrtichian, D. E., Petermann, F., Tkachenko, A., & Tsymbal, V. 2020, AA, 644,A121
Mkrtichian, D. E., et al. 2018, MNRAS, 475, 4745
Nagai, K. 2002, VSOLJ Variable Star Bulletin, 39, 5Nakamura, Y., Narusawa, S., & Kamada, M. 1991a, Inf. Bull. Var. Stars, 3641
Nakamura, Y., Kamada, M., Adachi, N., Narusawa, S., & Kontoh, N. 1991b, Science Report of Fukushima
University, 48, 25
Narusawa, S., Nakamura, Y., & Yamasaki, A. 1994, AJ, 107, 1141
Ohshima, O., Narusawa, S., Akazawa, H., Arai, K., Fujii, M., Kawabata, T., Morikawa, K., Ohkura, N. &Takeuti, M. 2001, AJ, 122, 418 (O01)

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Table 2: Estimated times and shapes of the observed minima
Min(HJD 2450000+)
1090.16541(8)1090.1643(1)1131.99788(4)1137.9744(1)1143.94801(7)1143.94933(6)1169.0502(1)1169.05150(7)1179.2057(1)1183.9947(2)1186.98036(4)1195.9479(1)1469.06145(7)1482.2022(1)1482.20622(6)1495.9525(2)1512.08831(7)1794.16848(5)2137.20653(5)2271.07789(3)5913.01557(3)7276.2028(3)7279.1960(1)7283.97567(5)7387.96376(8)7396.9245(1)7425.0159(1)7426.2121(1)7696.33959(7)

Type

Ea

II
II
II
I
I
II
II
I
II
I
I
I
II
I
I
I
I
I
II
I
I
I
II
I
I
I

-4551
-4551
-4516
-4511
-4506
-4506
-4485
-4485
-4476.5-4472.5-4470-4462.5
-4234
-4223
-4223
-4211.5
-4198
-3962
-3675
-3563
-516
+624.5+627+631+718+725.5+749+750+976

O − Ca(days)-0.01643-0.0175-0.01772-0.0175-0.02009-0.01877-0.0182-0.01686-0.0222-0.0143-0.01676-0.0136-0.01474-0.0217-0.01772-0.0168-0.01689-0.01579-0.01458-0.01126-0.00127+0.0030+0.0081+0.00672+0.00804+0.0044+0.0074+0.0084+0.00929

ShapebAsymmetry?

VP
F: (12 min)PP:
F (20 min)PV
Yes (tinny)
P:
Sb:
V:
V:
PSb
PPP

Yes (tinny)Yes (tinny)

P
P:
P:
PPYes
Yes:Observer / Sitec
OhkuraNHAO
Arai
OhkuraArai
OhkuraNHAO
OhkuraFujii
Fujii
Akazawa
Fujii
NHAO
NHAO
Akazawa
Fujii
NHAO
NHAO
Fujii
NHAO
Fujii
Akazawa
Akazawa
Akazawa
Ito
Ito
Ito
Ito
Akazawa

a: The E and O − C values are calculated from the ephemeris (1)b: P: partial, V: V-shape, F: flat bottom, Sb: smoothly brightening, Null: uncertain
c: NHAO: Nishi-Harima Astronomical Observatory (Main observer was S. Narusawa)

Table 3: Utilized times of minima obtained by Nakamura et al. (1991b)
Min I (HJD)(+2440000)
7507.9864
7809.1875
7856.9968
8174.9307
8201.2257
8211.9832
8219.1546

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Table 4: Utilized times of minima obtained by O01
Filter
Rc
Rc
V
B
Rc
V
B
B
Rc
V
B
Rc
V
B
V
B
V
B
V
B
V
B
U
I
I
V
B

0.6

0.6

0.7

0.7

0.8

0.8

0.9

0.9

ΔV

ΔV

Min I (HJD)(+2450000)
722.0242
728.001
747.1252
747.1247
747.1258
754.2947
754.2957
759.0770
759.0765
759.0764
759.0761
771.0289
771.0300
771.0284
777.0077
777.0065
777.0070
777.0071
808.0829
808.0828
808.0831
808.0832
808.0825
808.0833
814.0593
826.0125826.0123

1.0

1.0

1.1

1.1

1.2

1.2

0.92

0.93

0.94

0.95
0.96
HJD (2451143+)

0.97

0.14

0.15

0.16
0.17
HJD (2451794+)

0.18

0.19

Figure 1: Light curve at a primary minimum in V. Left panel: F-tye (observed by Ohkura). Right panel: Sb-tyep(observed at NHAO).

60.01O-C (day)

0.00
-0.01
-0.02
-0.03
-0.04
30000

4000050000

60000

HJD (2400000+)

Figure 2: O-C diagram of RZ Cas. The circles and squares display the data determined by the Min I and theMin II respectively. The open symbols are the data from this study, and the filled ones are those from thethe (B-R)-Generator für die Lichtenknecker-Database of the BAV and O-C gateway of Brno Regional Networkof Observers (B.R.N.O.) of the Czech Astronomical Society (based on photoelectric and CCD observations).
Nakamura et al. (1991b)’s and O01’s data is also used.

0.000

O-C (day)-0.008-0.016-0.024-0.032-0.040
48000

49000

50000

51000
52000
HJD (2400000+)

53000

54000

Figure 3: Same as Fig. 2, but the period being from HJD 2447500 (1988) to HJD 2454500 (2008).

7VSOLJ
c/o Keiichi Saijo National Science Museum, Ueno-Park, Tokyo Japan
Editor Seeichiro Kiyota
e-mail:skiyotax@gmail.com
Publishing Masahiko Momose