A frequency analysis of new observations of the rapidly oscillating AP star HD 137949 (33 Lib) - an apparent change of frequency and detection of the first harmonic

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A Stars, Astronomical Photometry, Harmonic Analysis, Magnetic Stars, Peculiar Stars, Stellar Oscillations, Amplitude Distribution Analysis, Light Curve

Scientific paper

Fifty hours of new high-speed photometric observations of the rapidly oscillating Ap star HD 137949 obtained mostly in 1987 with the 1.0- and 1.9-m telescopes of the SAAO are presented. These new observations have less noise than the previous observations made in 1981 with a 0.5-m telescope. The principal frequency in HD 137949 in the 1987 data is ν1 = 2014.781±0.001 μHz; in the 1981 data it is ν1 = 2014.821±0.003 μHz. This indicates that dln ν/dt=(-9.9±0.7) × 10-14 s-1 [dP/dt=(+4.9±0.3) × 10-11 s s-1], which is about two orders of magnitude larger than expected theoretically from evolution. There is however, possibly a second frequency at, or near, ν2 = 1975 μHz, the reality of which needs confirmation. This secondary frequency, and possibly other unresolved secondary frequencies, could perturb the measurement of ν1 and hence distort the measurement of dln v/dt so that it is unreliable. If ν2 is real, the separation ν1-ν2 ≍ 40 μHz gives an estimate of the luminosity of HD 137949. The first harmonic of ν1 at 2ν1 = 4029.559±0.009 μHz is clearly present in the data. This brings to five the number of rapidly oscillating Ap stars which have non-linear light variations.

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