New High-Amplitude SX Phœnicis (δ Scuti?) Star in the Direction of the Galactic Anti-Center: 2MASS 06451725 + 4122158

Abstract

ABSTRACTThe results of extensive time-series photometry of a new variable star, 2MASS 06451725 + 4122158, are presented. The B, V observations (over 4000 individual measurements) were made over 23 nights between 2006 and 2007. To investigate the star’s physical characteristics additional Strömgren photometric observations (uvbyHβ) were made on another four nights in 2007 and 2009. Thirteen frequencies were found from a multifrequency analysis of the V and B photometry. All but two of the frequencies, 19.99716 cycles day-1 (corresponding to the pulsation period of 0.0500071 day) and 25.84662 cycles day-1 (0.0386898 day), have been identified as combination frequencies. The ratio of the two frequencies, f1/f3 = 0.77369, and their pulsation constants, Q(f1) = 0.034 and Q(f3) = 0.026, are well matched with theoretical values of the fundamental and the first-overtone radial modes. But the phase shift of f3 was estimated to be a negative value, in contrast to that of f1 to be positive, suggesting that f3 may be a nonradial mode. The period versus amplitude diagram shows that the star has pulsational properties similar to those of high-amplitude SX Phœnicis stars. We obtained its photometric properties from the Strömgren indices: a metal abundance of [Fe/H] = -0.6 dex, an absolute magnitude of MV = 2.7 mag, a distance of ∼1.6 kpc in the direction of the Galactic anticenter from the Sun, and a vertical distance from the Galactic plane of ∼0.45 kpc. The tangential velocity of 78 km sec-1, which was estimated from the proper motion and the distance, gives us a hint that the star may have high-space motion. Considering these observational properties, we suggest that this new variable is a field SX Phœnicis-type star, although its metallicity value seems not to be low enough for matching the metallicity versus period relation. Future spectroscopic studies would be required to obtain the metallicity more accurately.