CCD observations of four long-period eclipsing variables

P. V. Pakhomova¹, L. N. Berdnikov², A. Y. Kniazev^2,3,4, O. Y. Malkov¹, N. P. Ikonnikova², A. A. Belinskii², N. A. Maslennikova², M. A. Burlak², E. O. Mishin², N. I. Shatskii²

1. Institute of Astronomy, Russian Academy of Sciences, ul. Pyatnitskaya 48, Moscow, 119017, Russia

2. Sternberg Astronomical Institute, Moscow State University, Universitetskij pr. 13, Moscow 119992, Russia

3. South African Astronomical Observatory, P.O. Box 9, Observatory, Cape Town, 7935, South Africa

4. Southern African Large Telescope, P.O. Box 9, Observatory, Cape Town, 7935, South Africa

About 600 CCD magnitude measurements in the , filters were acquired in 2022 for four long-period eclipsing binaries: V698 Cyg, V788 Cyg, EU Gem, V733 Per. The light elements for all these systems were derived using the ASAS-SN database.

1. Introduction

Long-period eclipsing binaries are interesting objects for investigation. First, their light elements are difficult to derive. Second, wide binary systems differ in their evolution from shorter-period binaries and can give interesting insight into their origin and life story.

For our study, we selected four long-period eclipsing binaries (V698 Cyg, V788 Cyg, EU Gem, V733 Per). In the GCVS (Samus et al., 2017), they have periods from to .

V698 Cyg. This variable star was discovered by Hoffmeister (1929) as an Algol type star, with only one reliable minimum detected. Whitney (1952) presented the star's light elements with the period 97738, reproduced in the GCVS along with a rather wide photographic range, 122-149.

V788 Cyg. The variability discovery was announced by Geyer et al. (1955) who determined the photographic range 100-109. The GCVS light elements with are from Baldwin (1977).

EU Gem. The star was announced as an Algol variable by Hoffmeister (1949). Later, Hoffmeister claimed the star to be irregular, but Meinunger (1966) confirmed its Algol type with the period 522665. The photographic range in the GCVS is 137-149.

V733 Per. This possible Algol was discovered by Hoffmeister (1968) but confirmed only years later by Otero et al. (2005). They found the period 7753, reproduced in the GCVS, and reported a rather narrow visual variation range, 1189-1217 (1203 in the secondary minimum).

2. Observations and Results

We performed CCD observations of the four long-period eclipsing binaries (V698 Cyg, V788 Cyg, EU Gem, V733 Per) in August 2022 - November 2022 (the JD range 2459813 - 2459900) at the Caucasus Mountain Observatory (CMO, Russia) with the 60-cm telescope using an Andor iKon-L camera, 20482048 pixels, with a pixel size of 13.5 microns. The -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 Berdnikov et al. (2020). We obtained a total of about 600 magnitude measurements with photometric errors close to 002-003.

Fig. 1. Light curves for the four observed stars. Red color shows observations in the filter.

Fig. 2. CCD frame of EU Gem.

Observations are given in Table 1 (the complete table is presented in the html version of the paper as a text file; the table in the text is a short fragment showing its format and contents).

V698 Cyg       g        r
JD 24...
59826.25062  12.3530    -
59826.25081  12.3440    -
59826.25100  12.3350    -
59826.25124    -      11.6780
59826.25138    -      11.7020
59826.25151    -      11.6560
59826.28024  12.4023    -
59826.28043  12.4069    -
59826.28063  12.4024    -
59826.28086    -      11.7260
59826.28100    -      11.7410
59826.28113    -      11.6950

The orbital elements given in Table 2 are derived from ASAS-SN data (Kochanek et al. 2017). The coordinates, for the equinox and epoch 2000.0, are extracted from the Gaia DR3 data release. The light curves, constructed for our observations with the derived periods, are presented in Fig. 1.

The reviewer kindly pointed out to us that EU Gem, according to Gaia data, has a comparable-luminosity companion only 4″ away. Figure 2 shows a part of a CCD frame for EU Gem (size 3.5′×3.5′) obtained with the 60-cm CMO telescope in the filter. The comparable-brightness star, which is in 4.1″ from EU Gem, does not affect our brightness measurements of EU Gem because PSF photometry was performed.

Acknowledgments: The authors thank the anonymous reviewer for valuable comments and suggestions. This study was supported by the Interdisciplinary Research and Educational School of the Moscow State University "Fundamental and Applied Studies of the Cosmos". The work was performed using the equipment purchased through the funds of the Development Program of the Moscow State University.

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