Peremennye Zvezdy (Variable Stars) 40, No. 13, 2020 Received 17 December; accepted 20 December.	Article in PDF
	DOI: 10.24411/2221-0474-2020-10015

Variability of GSC 08977-08895 and GSC 07418-01521

A. V. Khruslov^1,2

Sternberg Astronomical Institute, Moscow State University, Universitetsky pr. 13, 119992, Moscow,
Russia; e-mail: khruslov@bk.ru

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

1. Introduction

In this paper, I present a study of two variable stars, GSC 08977-08895 and GSC 07418-01521. Our search for double-mode and multi-mode periodicity among RR Lyrae and  Scuti variables in the ASAS-SN Catalog of Variable Stars¹ (Jayasinghe et al., 2019) resulted in detection of additional brightness variations of these two stars. GSC 08977-08895 is a Doubly Eclipsing System (type ELL+EA in the GCVS catalog classification, Samus et al., 2017), similar to the systems detected by the author (Khruslov, 2018) and earlier, by the OGLE team in the Galactic disk fields (Pietrukowicz et al., 2013) and in the Galactic bulge (Soszynski et al., 2016). GSC 07418-01521 is a rare case of a high-amplitude double-mode  Scuti variable, pulsating in the fundamental mode and the first overtone mode, with an eclipsing component (type HADS(B)+EA, or DSCT(B)+EA in the classification scheme of the GCVS). In both cases, the double periodicity cannot be explained with a blend of two variable sources. Both stars are single photometric objects, very well identified in the ASAS-SN data.

Our photometric study of both stars is based mainly on data of the All-Sky Automated Survey for Supernovae, ASAS-SN²(Shappe et al., 2014; Kochanek et al., 2017). Additionally, I used all observations available for these stars in the All Sky Automated Survey, ASAS-3³(Pojmanski, 2002), the Wide Angle Search for Planets, 1SWASP⁴ (Butters et al., 2010), and Siding Spring Survey from the Catalina Sky Surveys, SSS⁵(Drake et al., 2009) online public archives. The 1SWASP observations are available as FITS tables, which were converted into ASCII tables using the OMC2ASCII program as described by Sokolovsky (2007); we also used the SuperWASP FITS to ASCII lightcurve conversion service⁶.

I analyzed all the observations using Deeming's method (Deeming, 1975) and Lafler-Kinman method (Lafler & Kinman, 1965) implemented in the WinEfk code⁷ written by V.P. Goranskij.

The stars were identified in the USNO-B1.0 (Monet et al., 2003) and GSC (Morrison et al., 2001) catalogs. The coordinates of the variables were drawn from the Gaia DR2 catalog (Gaia Collaboration, Brown et al., 2018).

The photometric data used in my study are available online in the html version of this paper as a zip-archive . Symbols after star numbers in the names of data files correspond to the photometry source: "a" stands for ASAS-SN -band data; "a3", for ASAS-3 observations; "s", for Catalina SSS data; and"w" designates data from the 1SWASP survey. Figure 1 presents the finding charts.

2. GSC 08977-08895

The variability of GSC 08977-08895 = USNO-B1.0 0278-0392959, RA(J2000) =
11471156, Dec(J2000) = -620847 3, was announced in the GDS catalog (Hackstein et al., 2015). The variable was designated as GDS_J1147115-620847, its variability type and light elements were not given; the full amplitude was 026 and the median magnitude, 1250 in the Sloan band. Later, in The ASAS-SN Catalog of Variable Stars (Jayasinghe et al., 2019), the variable was classified as an RR Lyrae star (RRc type) with the light elements HJD(max) , mean magnitude 1256, and amplitude 019 in Johnson's band.

I detected two components of the star's variability using the ASAS-SN data. GSC 08977-08895 is a doubly eclipsing system, the primary component shows an ellipsoidal variability (or EW-type eclipsing variations), the secondary component exhibits Algol-type variability. The variation range in the ASAS-SN data is (). The light elements of the detected variations are:

Component 1 (ELL or EW type):

Component 2 (EA type):

To improve the light elements, we used ASAS-3 data.

For component 1, the depth of primary minimum is 014; the difference of minimum depths, . The classification as an ellipsoidal or eclipsing variable (opposed to RR Lyrae) is based on the fact that no asymmetry of the light curve is detected (for the twice shorter period, the asymmetry parameter is ). For component 2, the depth of primary minimum is 014; the difference of minimum depths, ; the eclipse duration is .

The color indices are: (2MASS; Skrutskie et al., 2006); (APASS⁸). The light curves of GSC 08977-08895 according to ASAS-SN data are displayed in Fig. 2.

3. GSC 07418-01521

The variability of GSC 07418-01521 = USNO-B1.0 0544-0769983, RA(J2000) =
19115902, Dec(J2000) = -353526 7, was announced in the ASAS-SN Catalog of Variable Stars (Jayasinghe et al., 2019). The variable was designated as ASASSN-V J191159.03-353526.5, type HADS with the following light elements: , mean magnitude 1389, and amplitude 021 in Johnson's band.

Using ASAS-SN data, I detected three variability components of the star. Later this conclusion was confirmed on the base of 1SWASP and SSS data. GSC 07418-01521 is an eclipsing binary system; one of its components is a double-mode high-amplitude  Scuti star, HADS(B). The range of variability in the ASAS-SN data is (). Additionally, I found the following variability ranges in other surveys: (, 1SWASP); (CV, SSS). In the 1SWASP data, the amplitude is underestimated due to blending of several stars. During our analysis of the SSS data, I removed probable erroneous observations, CV . The light elements of the detected variations are:

Component 1 (pulsating, fundamental mode, ):

Component 2 (pulsating, first overtone mode, ):

Component 3 (eclipsing, EA):

The period ratio of pulsation modes, , is typical of the high-amplitude double-mode  Scuti variables with the fundamental mode and the first-overtone mode. Asymmetry parameters of the phased light curve for the fundamental mode are according to all data; for the first-overtone mode, according to ASAS-SN data and according to 1SWASP and SSS data. For the eclipsing component, the eclipse duration is .

The power spectrum of GSC 07418-01521 according to ASAS-SN data is displayed in Fig. 3.

Information on variability amplitudes of all the components is presented in Table 1. For pulsating modes, I give semi-amplitudes of oscillation; for the eclipsing mode, I give the depths of munuma I and II (full amplitudes), according to ASAS-SN, 1SWASP and SSS data, respectively. In the 1SWASP data, the amplitude is underestimated.

The full amplitude of the sum of both pulsating oscillations is 021 (, ASAS-SN data). Because of the second component of the binary system, the amplitude is possibly underestimated. This confirms our classification of the system's pulsating component as a high-amplitude double-mode  Scuti star.

The color indices are: (2MASS); (APASS). GSC 07418-01521 is included in the GALEX catalogs of UV sources (Bianchi et al., 2011) with the magnitudes FUV = 21.60, NUV = 17.75.

The light curves of GSC 07418-01521 according to ASAS-SN, 1SWASP, and SSS data are displayed in Figs. 4, 5 and 6, respectively. When deriving the light elements and plotting the light curves (bottom panel), we also pre-whitened the two detected interaction frequencies, and (periods 00392575 and 03060463, respectively).

Acknowledgments: The author is grateful to Dr. V.P. Goranskij for providing light-curve analysis software.

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