Four New Double-Mode Cepheids, Pulsating in First and Second Overtone Modes

A. V. Khruslov
Russia, Tula

Received:   27.05.2009;   accepted:   17.06.2009
(E-mail for contact: khruslov@bk.ru)

Comments:


1. According to ASAS-3 data, GSC 4818-03792, listed in the ASAS catalog of variable stars (Pojmanski et al. 2002) as a fundamental-mode Cepheid (period 0.87965 d), is actually a double-mode Cepheid. The phased light curves plotted for the following elements: JD(max) = 2453674.10 + 0.87962 x E (the first overtone mode) and JD(max) = 2453674.01 + 0.70772 x E (the second overtone mode), are given in the Figure. The period ratio P2/P1=0.8046 is typical of beat Cepheids, pulsating in the first and second overtone modes. J-H = 0.393 (2MASS).

2. According to ASAS-3 data, TYC 7670 02632 1, listed in the ASAS catalog of variable stars (Pojmanski et al. 2002) as a fundamental-mode Cepheid (period 1.16666 d), is actually a double-mode Cepheid. The phased light curves plotted for the following elements: JD(max) = 2453426.16 + 1.16662 x E (the first overtone mode) and JD(max) = 2453426.48 + 0.939354 x E (the second overtone mode), are given in the Figure. The period ratio P2/P1=0.8052 is typical of beat Cepheids, pulsating in the first and second overtone modes. B-V = 1.113 (Tycho2), J-H = 0.451 (2MASS).

3. According to ASAS-3 data, GSC 9002-00686, listed in the ASAS catalog of variable stars (Pojmanski et al. 2002) as a fundamental-mode Cepheid (period 0.913165 d), is probably a double-mode Cepheid. The phased light curves plotted for the following elements: JD(max) = 2453693.41 + 0.91308 x E (the first overtone mode) and JD(max) = 2453693.12 + 0.734376 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. J-H = 0.374 (2MASS).

4. According to ASAS-3 data, TYC 0467 03223 1, listed in the ASAS catalog of variable stars (Pojmanski et al. 2002) as a fundamental-mode Cepheid (period 1.257787 d), is actually a double-mode Cepheid. The phased light curves plotted for the following elements: JD(max) = 2453729.16 + 1.25771 x E (the first overtone mode) and JD(max) = 2453729.40 + 1.01121 x E (the second overtone mode), are given in the Figure. The period ratio P2/P1=0.8040 is typical of beat Cepheids, pulsating in the first and second overtone modes. B-V = 1.387 (Tycho2), J-H = 0.409 (2MASS).

Remarks:
I present a new investigation of four known Cepheids. 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 variables are double-mode Delta Cephei stars, pulsating in the first and second overtone modes. Their period ratios, P2/P1, are typical of radially pulsating double-mode Cepheids. Along with the light curves, I present power spectra of the four Cepheids, 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 either from the Tycho-2 or 2MASS catalogs.

References:
Pojmanski G., 2002, Acta Astronomica, 52, 397