Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 462, Issue 1, Pages 876-892Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stw1711
Keywords
asteroseismology; techniques: photometric; stars: chemically peculiar; stars: individual: HD 24355; stars: magnetic field; stars: oscillations
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Funding
- STFC [ST/M000877/1]
- Polish National Science Center [2015/18/A/ST9/00578]
- Queen's University Belfast
- Universities of Keele
- St. Andrews and Leicester
- Open University
- Isaac Newton Group
- Instituto de Astrofisica Canarias
- South African Astronomical Observatory
- STFC
- Science and Technology Facilities Council [ST/M000877/1] Funding Source: researchfish
- STFC [ST/M000877/1] Funding Source: UKRI
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We present an analysis of the first Kepler K2 mission observations of a rapidly oscillating Ap (roAp) star, HD 24355 (V = 9.65). The star was discovered in SuperWASP broad-band photometry with a frequency of 224.31 d(-1) (2596.18 mu Hz; P = 6.4 min) and an amplitude of 1.51 mmag, with later spectroscopic analysis of low-resolution spectra showing HD 24355 to be an A5 Vp SrEu star. The high-precision K2 data allow us to identify 13 rotationally split sidelobes to the main pulsation frequency of HD 24355. This number of sidelobes combined with an unusual rotational phase variation show this star to be the most distorted quadrupole roAp pulsator yet observed. In modelling this star, we are able to reproduce well the amplitude modulation of the pulsation, and find a close match to the unusual phase variations. We show this star to have a pulsation frequency higher than the critical cut-off frequency. This is currently the only roAp star observed with the Kepler spacecraft in short cadence mode that has a photometric amplitude detectable from the ground, thus allowing comparison between the mmag amplitude ground-based targets and the mu mag spaced-based discoveries. No further pulsation modes are identified in the K2 data, showing this star to be a single-mode pulsator.
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