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Astron. Astrophys. 354, 589-594 (2000)

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1. Introduction

High-amplitude [FORMULA] Scuti stars are short-period pulsators, oscillating in one or two radial modes with amplitudes of a few tenths of a magnitude, with possible non-radial low-amplitude variations superimposed. They are found in the classical Cepheid instability strip on or just above the Main Sequence, in the same region as the low-amplitude multiperiodic [FORMULA] Scuti stars. There are, however, certain characteristics that separate them from the low-amplitude pulsators: the amplitude of the light variations, and the fact that they are found in a very narrow strip in the HR-diagram (only 200-300 K wide), inside the [FORMULA] Scuti instability strip (McNamara 1997).

The [FORMULA] Scuti stars are very important objects for asteroseismic investigations, and the high-amplitude [FORMULA] Scuti stars can furthermore be used as distance indicators (McNamara 1997; Petersen & Hog 1998).

Several [FORMULA] Scuti stars have changing pulsation periods. Such changes are expected from stellar evolution, but many stars show period changes which currently cannot be described by stellar evolution theories, see Breger & Pamyatnykh (1998). These authors have collected data on period changes from a number of [FORMULA] Scuti stars, and find that the observed change-rates are larger than what is expected from theory. The changes are furthermore equally distributed between increasing and decreasing periods, while mainly increasing periods are expected.

V 1162 Ori is a high-amplitude [FORMULA] Scuti star discovered by Lampens (1985). It was later observed by Poretti et al. (1990), who found the star to be monoperiodic. They determined a period of 0.07868614 days and a V-amplitude of 0[FORMULA]22. Hintz et al. (1998) observed the star several years later, and found a much smaller amplitude (0[FORMULA]10), and a different period: 0.07869165 days, implying an increase of 0.5 seconds over 8.5 years. They also saw evidence of a possible second period, but were not able to determine it from their dataset. In this paper we present the results of new CCD time-series photometry of V 1162 Ori. We address the question of period- and amplitude changes in this star, and we search for a possible second period. We present new times of maximum and minimum light, and compare with previously obtained results. We show that the light of V 1162 Ori undergoes period- and amplitude changes on a short time scale.

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© European Southern Observatory (ESO) 2000

Online publication: February 9, 2000
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