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Mode Identification in a Pulsating Subdwarf B Star EPIC 212707862 Observed with K2

Bachulski S., Baran A. S., Jeffery C. S., Østensen R. H., Reed M. D., Telting J. H., Kuutma T.

Acta Astronomica

2016

Vol. 66, No. 4

455--467

We present an analysis of K2 observations of EPIC 212707862, a pulsating subdwarf B star. We detected 13 significant frequencies from an 81 day run during Campaign 6. Our goal was to find features that could help us to identify pulsation modes. We could not identify any multiplets, which would also have enabled us to precisely derive a rotation period. Based on amplitude modulation we estimated that period to be around 80 days. We found two period-spacing sequences, and successfully identified modal degrees for 11 out of 13 detected frequencies. We assigned six of them to l=1, and another five to l=2. These results will facilitate future theoretical modeling. This star brings to 19 the number of pulsating subdwarf B stars observed with K2. Radial velocities obtained to date and the spectral energy distribution are consistent with EPIC 212707862 being a single hot subdwarf. Analysis of the spectrum gives atmospheric parameters: Teff=28 298±162 K, log g[cm/s2]=5.479±0.025 and log (n(He)/n(H))=-2.752±0.069.

A New Subdwarf-OB Pulsator J23341+4622

Pakštiene E., Qvam J. K. T., Østensen R. H., Telting J. H.

Acta Astronomica

2014

Vol. 64, No. 4

349--358

A new sdOB variable star, J23341+4622 (SDSS J233406.10+462249.3), was discovered during photometric observations with the Nordic Optical Telescope (La Palma). We found its main pulsation frequency at 7422(±9) μHz with an amplitude of 4.5(±0.5) mma. The star is possibly a complex pulsator, as we found another significant peak at 7759(±11) μHz with an amplitude of 2.0(±0.3) mma and a possible subharmonic of the main frequency at 3508 μHz with an amplitude of 2.3 mma.

Detection of Multiplets of Degree ℓ=3 and ℓ=4 in the Subdwarf-B Pulsator KIC 10139564

Baran A. S., Østensen R. H.

Acta Astronomica

2013

Vol. 63, No. 1

79--90

We present up-to-date results on the short-period sdB pulsator in the Kepler field, KIC 10139564, including 27 months of near continuous photometric data. With this extended dataset we significantly lower the detection threshold, which allows us to detect multiplet components that were missing in our previous analysis based on 15 months of data. We conclude that two regions in the amplitude spectrum of KIC 10139564 contain modes of degree ℓ=3 and ℓ=4, respectively. We also identify many combination frequencies, in both the sub- and super-Nyquist regions, as well as several pulsation modes which show strong frequency or amplitude variability.