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122Peremennye Zvezdy ( Variable ¡Stars) 40, No. 7, 2020 Received 1 October; accepted 15 October.
DOI: 10.24411/2221-0474-2020-10008
BVIcg'r' CCD observations of three classical Cepheids in NGC 7790
L.N. Berdnikov1, A.A. Belinskii1, E.N. Pastukhova2, M.A. Burlak1, N.P. Ikonnikova1, E.O. Mishin1, N.I. Shatskii1
1 Sternberg Astronomical Institute, Moscow State University, Universitetskij pr. 13, Moscow 119992, Russia
2 Institute of Astronomy, Russian Academy of Sciences, ul. Pyatnitskaya 48, Moscow, 119017, Russia
We present 2728 magnitude measurements in the B, V, Ic, g', and r' filters acquired for three classical Cepheids in the open cluster NGC 7790: CEa Cas, CEb Cas, and CF Cas. Reliable separate PSF-photometry of the components of CE Cas was obtained for the first time.
1 Introduction
NGC 7790 is the only galactic open cluster which hosts tree classical Cepheids: visual binary with components CEa Cas and CEb Cas at the angular distance 2.2 arcsec between them, and CF Cas.
There were several attempts to obtain light curves for the components of CE Cas using the aperture photometry method (Efremov and Kholopov, 1965; Smak, 1966; Sandage and Tammann, 1969; Opal et al., 1988), but they were burden with systematic errors because this method does not make it possible to avoid the influence of the other component. The same problem existed in radial velocity measurements as well (Gorynya et al., 1992).
Because these Cepheids are used in calibration of the period-luminosity relation's zero point, we decided to improve their light curves using the PSF-photometry method.
2 Observational data
We performed CCD observations of NGC 7790 in February-September, 2020 (the JD range 2458906 - 2459121) with the 60-cm telescope at the Caucasus Mountain Observatory (CMO, Russia) using an Andor iKon-L camera, 2048x2048 pixels, with a pixel size of 13.5 microns. The BV-band filters of the Kron-Cousins photometric system (Cousins, 1976) and gV-band filters of the ZTF survey system (Masci et al., 2019) were used. Information about the CMO and description of the observing data reduction technique can be found in our previous paper (Berdnikov et al., 2020). We obtained a total of 2150 magnitude measurements for the three Cepheids with photometric errors close to 0.01 mag.
We also used the 60-cm reflector of the Mount Maidanak Observatory (MMO, Uzbekistan) to acquire 208 CCD VIc-band (Cousins, 1976) frames using a CCD FLI camera, 1024x1024 pixels, with a pixel size of 15 microns during the time interval JD 2456183 -2456246. We extracted 578 magnitude measurements for three Cepheids; the photometric errors of these observations were close to 0.02 mag.
The light curves for CEa Cas, CEb Cas, and CF Cas, obtained in the CMO and MMO, are shown in Figs. 1-3 and Figs. 4-6, respectively. All observations are presented in Table 1 (CMO data) and in Table 2 (MMO data) in the html version of the paper.
From our observations, we constructed the B, g', V, r', and /c-band template light curves for CEa Cas and CEb Cas, shown respectively in Fig. 7 and Fig. 8; they are presented in the html version of the paper as Table 3, which lists the B, g , V, r , and Ic-band magnitudes for phases from 0 to 0.995 with a step of 0.005.
We plan to use our data to study the period behavior of these Cepheids.
Acknowledgments: This work was supported by the Russian Foundation for Basic Research (project nos. 18-02-00890 and 19-02-00611).
References:
Berdnikov, L.N., Belinskij, A.A., Shatskij, N.I., et al., 2020, Astron. Rep., 64, 310
Cousins, A.W.J., 1976, Mem. RAS, 81, 25
Efremov, Yu.N., Kholopov, P.N., 1965, Astron. Tsirk., Nr.326, 1
Gorynya, N.A., Irsmambetova, T.R., Rastorgouev, A.S., Samus, N.N., 1992, Sov. Astron. Lett., 18, 316
Masci, F.J., Laher, R.R., Rusholme, B., et al., 2019, Publ. Astron. Soc. Pacif., 131, 018003
Opal, C.B., Krist, J.E., Barnes, T.G., et al., 1988, Astron.J., 96, 1677 Sandage, A., Tammann, G.A., 1969, Astrophys. J., 157, 683 Smak, J., 1966, Acta Astron., 16, 11
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Figure 1. BVg'r'-band phased light curves of CEa Cas from observations obtained at the CMO.
Figure 2. BVg'r'-band phased light curves of CEb Cas from observations obtained at the CMO.
Figure 3. BVg'r'-band phased light curves of CF Cas from observations obtained at the CMO.
Figure 4. VIc-band phased light curves of CEa Cas from observations obtained at the MMO.
Figure 5. VIc-band phased light curves of CEb Cas from observations obtained at the MMO.
Figure 6. VIc-band phased light curves of CF Cas from observations obtained at the MMO.
Figure 7. B, g', V,'r', and Ic-band template light curves of CEa Cas.
Figure 8. B-, g'-, V-,' r'-, and Ic-band template light curves of CEb Cas.
