Peremennye Zvezdy (Variable Stars) 35, No. 1, 2015 Received 29 January; accepted 11 February.

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New Double-Mode RR Lyrae Variables II

A. V. Khruslov

Institute of Astronomy, Russian Academy of Sciences, Moscow, Russia; e-mail: khruslov@bk.ru

1. Introduction

According to the International Variable Star Index (VSX, AAVSO), about 600 double-mode RR Lyrae variable stars are currently known in our Galaxy, usually pulsating in the fundamental and first overtone radial modes (most of them, outside globular clusters). During the recent years, automated data surveys resulted in a considerable progress in the identification of stars of this type. The author of the present paper, with his co-authors, earlier discovered 56 double-mode RR Lyrae variable stars, pulsating in the fundamental and first-overtone radial modes ( Khruslov 2007, 2010, 2011, 2012ab; Khruslov, Huemmerich, and Bernhard 2013; Antipin and Khruslov 2013; Huemmerich and Khruslov 2014; Khruslov 2014). In this article, I present the discovery of additional 56 double-mode RR Lyrae variable stars, pulsating in the first-overtone and fundamental modes.

2. Results

I studied 56 known RR Lyrae variable stars from the Catalina surveys periodic variable star catalog (Drake et al. 2014), analyzing all observations available for them in the Catalina Surveys (Drake et al. 2009) and SuperWASP (Butters et al. 2010) online public archives using the period-search software developed by Dr. V.P. Goranskij for Windows environment. The SuperWASP observations are available as FITS tables, which were converted into ASCII tables using the OMC2ASCII program as described by Sokolovsky (2007). In the Catalina surveys periodic variable star catalog, all these variables are designated as RRC stars. Our analysis of the available data demonstrates that the variables are double-mode RR Lyrae variables, pulsating in the first-overtone and fundamental modes.

Light curves, finding charts, and data (CSS, SSS, MLS, 1SWASP) are available online in the html version of this paper as a zip-archive. The light curves are given in the format displayed in Fig. 1. Top panels present data folded with the fundamental-mode and first-overtone periods. Bottom panels show the same curves after prewhitening the other oscillation (if the frequencies and were excluded, it is also noted). These light curves are given for all data series.

Along with the light curves, we present power spectra of the RR Lyrae variables, for the raw data and after subtraction of the first-overtone (or fundamental mode) oscillations, as shown in Fig. 2. The structure of the power spectra shows that the secondary periods are real.

The stars' period ratios, , are typical of radially pulsating double-mode RR Lyrae stars. The Petersen diagram for double-mode RR Lyrae variables from this paper is displayed in Fig. 3.

In five cases, the periods presented in the Catalina surveys periodic variable star catalog are wrong. For Nos. 18, 28, and 56, the catalog period is a one-day alias of the real first overtone period; for Nos. 12 and 29, the catalog period is a one-day alias of the real fundamental mode period.

Information on the studied stars is presented in Tables 1-4. Table 1 contains numbers from the GSC and USNO-B1.0 catalogs; equatorial coordinates (J2000); magnitude at maximum and minimum in the Catalina surveys photometric system; period previously known for the star, according to the Catalina surveys periodic variable star catalog. Asterisks mark the presence of additional information on the star, as explained in Comments. The tabulated coordinates of the variables were drawn from either the GSC2.3 (Lasker et al. 2008) or 2MASS (Skrutskie et al. 2006) catalogs.

Light elements of all oscillations: the first-overtone period , fundamental period , first-overtone and fundamental mode epoch of maxima, period ratio , periods of the frequencies () and () are collected in Table 2.

Table 3 presents semi-amplitudes of all the oscillations, separately for Catalina surveys data: semi-amplitudes of first-overtone () and fundamental mode () oscillations, for the () and () frequencies. Table 4 presents semi-amplitudes of all the oscillations, separately for SuperWASP data.

Comments:

7. The star has a faint close red companion USBO-B1.0 1211-0158002, , visible only in DSS images in the red and infrared bands.

13. In USNO-B1.0 catalog, two entries correspond to one star: USNO-B1.0 1265-0169434 and USNO-B1.0 1265-0169435; the coordinates in the first entry are more accurate.

35. The star has a faint close companion USNO-B1.0 0997-0233329, ; the measured amplitudes can be somewhat underestimated.

42. In DSS images, the star USNO-B1.0 0965-0243978 is noticeably elongated; possibly it is a close pair, , unresolved in the catalogs. The faint companion is located to the west. Combined brightness of the two stars was measured in the CSS data; the measured amplitudes can be somewhat underestimated.

50. CSS data are for brightness of two stars, GSC2.3 N09A000095 and GSC2.3 N09A009350, . This pair is unresolved in the CSS data and in the GSC catalog (GSC 2222-02434). Most likely, the brighter star of the pair, GSC 2.3 N09A000095, varies. This pair is unresolved in the 1SWASP; the measured amplitudes can be somewhat underestimated. From 1SWASP data, .

51. The star has a faint close companion GSC2.3 N0OD009449 (=USNO-B1.0 1016-0656704), ; the measured amplitudes can be somewhat underestimated.

52. From 1SWASP data, . In 1SWASP data, the measured amplitudes possible can be somewhat underestimated because of the neighbor, USNO-B1.0 1233-0612342, .

56. From 1SWASP data, . In 1SWASP data, the measured amplitudes can be somewhat underestimated because of the neighbor, GSC 2255-00823, .

Acknowledgments: Thanks are due to Dr. K.V. Sokolovsky for his advice concerning data retrieving. The author wishes to thank Dr. V.P. Goranskij for providing his software. This study was supported by the Russian Foundation for Basic Research (grant 13-02-00664) and by the Programme "Transitional and Explosive Processes in Astrophysics" of the Presidium of Russian Academy of Sciences.

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