Peremennye Zvezdy (Variable Stars) 42, No. 12, 2022 Received 1 December; accepted 16 December.	Article in PDF
	DOI: 10.24412/2221-0474-2022-42-106-110

Four High-amplitude  Scuti Stars from the ZTF Survey

A. M. Zubareva^{1, 2}, S. V. Antipin², N. P. Ikonnikova², A. A. Belinskii², A. V. Samokhvalov³

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

2. Sternberg Astronomical Institute, Lomonosov Moscow University, Universitetsky Ave., 13, 119234 Moscow, Russia

3. Surgut, Russia

1. Introduction

While preparing a paper on the discovery of a bimodal high-amplitude  Scuti star (HADS) that will be published elsewhere, we have checked whether the star is now contained in the VSX database¹. We found out that our object is listed in the VSX among a group of cases with the same common feature. Several dozens of variables from the ZTF catalog of periodic variable stars (Chen et al., 2020) have ambiguous classification (HADS: EW). In our attempt to find several multiperiodic HADS stars or at least to distinguish between two types of variability, HADS and W UMa (EW) with a twice longer period, we carried out CCD photometry of selected stars from this particular group of VSX-listed stars.

2. Observations and Analysis

We observed several targets in constellations Aquila, Cygnus, and Vulpecula, which are easily observable in July with the Zeiss-600 telescope of the Crimean Astronomical Station (P.K. Sternberg Astronomical Institute, M.V. Lomonosov Moscow State University). Additional data were collected at the Caucasus Mountain Observatory (CMO) of M.V. Lomonosov Moscow State University with two Ritchey-Chretién telescopes: the 60-cm RC600 telescope (Berdnikov et al., 2020) and the 25-cm Astrosib telescope ( cm). The detailed information about observing runs is given in Table 1².

We picked stars brighter than 17 in the filter that can be reliably measured with a good signal-to-noise ratio. The images were reduced in the standard manner comprising bias, dark and flat-field frames. To perform aperture photometry and magnitude calibration, we used VaST³ software (Sokolovsky and Lebedev, 2018). Information on magnitudes of field stars was extracted from the GAIA DR3 catalog (GAIA Collaboration et al., 2022) for calibration purposes. To derive periods, we applied WinEfk software⁴. The package allows us to implement calculations with the Deeming method (Deeming, 1975) that is very suitable for analysis of smooth sine-like light curves of variable stars, especially for pulsating variables.

3. Results

3.1. ZTF J195936.84+365219.3

The first observational set for ZTF J195936.84+365219.3 was carried out from July, 14 to July, 16, 2022 with the Zeiss-600 telescope, exposure times being 120 seconds. After analyzing the light curve of ZTF J195936.84+365219.3 more thoroughly, we found changes in the level of maximum brightness. To confirm or to discard possible bimodality of ZTF J195936.84+365219.3, we decided to continue observations of the star with the two CMO telescopes (see Table 1). In total, we collected 1023 individual measurements on 25 individual runs between July, 14 and December, 11, 2022. We derive the following light elements:

The phased light curve is presented in Fig. 1. The brightness in maximum is and in minimum, ; thus, the peak-to-peak amplitude is . After performing periodogram analysis of the combined photometry from three telescopes, we did not detect any signal implying a second periodicity.

3.2. Three Confirmed HADS Variables

The summary results concerning the three observed stars are presented in Table 2.

The corresponding phased light curves are presented in Figs. 2-4.

The rapid rise to maximum brightness and resulting asymmetry of the light curves, the amplitudes and the periods for all four objects in the section are typical of high-amplitude  Scuti stars.

4. Conclusions

Unfortunately, we did not succeed in our attempts to find multiperiodicities in the course of analyzing our CCD photometry of ZTF J190321.93-011900.0, ZTF J192734.17+233948.7, ZTF J195936.84+365219.3, and ZTF J204838.44+413414.7. However, these variables can be classified as assured high-amplitude  Scuti stars.

References:

Berdnikov, L. N., Belinskii, A. A., Shatskii, N. I., et al., 2020, Astron. Rep., 64, 310

Chen, X., Wang, S., Deng, L., et al., 2020, Astron. J. Suppl. Ser., 249, id. 18

Deeming, T. J., 1975, Astrophys. and Space Sci., 36, 137

Gaia Collaboration, Vallenari, A., Brown, A. G. A., Prusti, T., et al., 2022, Gaia Data Release 3: Summary of the content and survey properties, arXiv:2208.00211

Sokolovsky, K. V., Lebedev, A. A., 2018, Astron. and Computing, 22, 28

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