Three New Double-Mode Variables, Pulsating in First and Second Overtone Modes

A. V. Khruslov
Russia, Tula

Received:   20.10.2009;   accepted:   5.11.2009
(E-mail for contact: khruslov@bk.ru)

Comments:


1. According to ASAS-3 data, ASAS 062735+0949.8, listed in the ASAS catalog of variable stars (Pojmanski 2002) as a first-overtone Cepheid (period 1.06806 d), is actually a double-mode Cepheid. The phased light curves plotted for the following elements: JD(max) = 2453761.65 + 1.06802 x E (the first overtone mode) and JD(max) = 2453761.54 + 0.85905 x E (the second overtone mode), are given in the Figure. The period ratio P2/P1 = 0.8043 is typical of beat Cepheids pulsating in the first and second overtone modes. To improve the periods, I have also analysed the NSVS observations of the variable (Wozniak et al. 2004; also see http://skydot.lanl.gov/nsvs). The second-overtone pulsations were not found in the NSVS data, apparently because of the small number of observations. J-H = 0.394 (2MASS).

2. According to ASAS-3 data, ASAS 064135+0756.6, listed in the ASAS catalog of variable stars (Pojmanski 2002) as a fundamental-mode or first-overtone Cepheid (period 1.28859 d), is actually a double-mode Cepheid. The phased light curves plotted for the following elements: JD(max) = 2453800.65 + 1.28861 x E (the first overtone mode) and JD(max) = 2453800.32 + 1.03153 x E (the second overtone mode), are given in the Figure. The period ratio P2/P1 = 0.8005 is typical of beat Cepheids, pulsating in the first and second overtone modes. To improve the periods I have also analysed the NSVS observations of the variable (Wozniak et al. 2004; also see http://skydot.lanl.gov/nsvs). The NSVS data completely confirm the double-mode variability and the periods. J-H = 0.448 (2MASS).

3. According to ASAS-3 data, ASAS 081132-2821.3, listed in the ASAS catalog of variable stars (Pojmanski 2002) as an RRC star or a first-overtone Cepheid (period 0.457228 d), is actually a double-mode RR Lyrae variable star. The phased light curves plotted for the following elements: JD(max) = 2453456.144 + 0.457231 x E (the first overtone mode) and JD(max) = 2453456.065 + 0.366105 x E (the second overtone mode), are given in the Figure. The period ratio P2/P1=0.8007 is typical of variables radially pulsating in the first and second overtone modes. J-H = 0.318 (2MASS).

Remarks:
I present a new investigation of three known pulsating variables. The variability of these stars was reported by Pojmanski (2002).

I re-analysed the ASAS-3 data using the period-search software developed by Dr. V.P. Goranskij for Windows environment. According to ASAS-3 data, the stars are double-mode variables, pulsating in the first and second overtone modes. Their period ratios, P2/P1, are typical of radially pulsating double-mode variables. Along with the light curves, I present power spectra of the three variable stars, for the raw data and after subtraction of the first-overtone oscillations. The structure of the power spectra shows that the secondary periods are real. The tabulated coordinates of the variables were drawn from the 2MASS catalog.

References:
Pojmanski, G., 2002, Acta Astronomica, 52, 397
Wozniak, P.R., Vestrand, W.T., Akerlof, C.W., et al., 2004, Astron. J., 127, 2436