HD 54272, a classical λ Bootis star and γ Doradus pulsator

Abstract

We detect the second known λ Bootis star (HD 54272) which exhibits γ Doradus-type pul- sations. The star was formerly misidentified as a RR Lyrae variable. The λ Bootis stars are a small group (only 2 per cent) of late B to early F-type, Population I stars which show moderate to extreme (up to a factor 100) surface underabundances of most Fe-peak elements and solar abundances of lighter elements (C, N, O, and S). The photometric data from the Wide Angle Search for Planets (WASP) and All Sky Automated Survey (ASAS) projects were analysed. They have an overlapping time base of 1566 d and 2545 d, respectively. Six statistically sig-
nificant peaks were identified (f1 = 1.410 116 d−1, f2 = 1.283 986 d−1, f3 = 1.293 210 d−1, f4 = 1.536 662 d−1, f5 = 1.157 22 d−1 and f6 = 0.226 57 d−1). The spacing between f1 and f2, f1 and f4, f5 and f2 is almost identical. Since the daily aliasing is very strong, the interpretation of
frequency spectra is somewhat ambiguous. From spectroscopic data, we deduce a high rota- tional velocity (250 ± 25 km s−1) and a metal deficiency of about −0.8 to −1.1 dex compared to the Sun. A comparison with the similar star, HR 8799, results in analogous pulsational
characteristics but widely different astrophysical parameters. Since both are λ Bootis-type stars, the main mechanism of this phenomenon, selective accretion, may severely influence γ Doradus-type pulsations.