Pulsating subdwarf B stars observed with K2 during Campaign 7 and an examination of seismic group-properties

Abstract

We report the discovery of four new pulsating subdwarf B (sdBV) stars from Campaign 7 of the Kepler spacecraft's K2 mission. EPICs 215776487, 217280630, 218366972, and 218717602 are all gravity (g)-mode pulsators and we also detect two pressure (p)-mode pulsations in EPIC 218717602. We detect asymptotic l=1 sequences in all four stars, allowing us to identify nearly all of the g modes. We detect evenly-spaced frequency multiplets in EPIC 218717602, from which we determine a rotation period near seven days. Spectroscopic observations determine that EPIC 218366972, is in a 5.92d binary with most likely a white dwarf companion of canonical mass while the others have no detected companions. As we detect no multiplets in EPIC 218366972, it is added to the growing list of subsynchronously rotating stars. With 40 Kepler-detected sdBV stars and a growing number of TESS publications, we update an examination of the group properties to provide direction for models. We notice a correlation between effective temperature and period of maximum pulsation amplitude, at least for g-mode pulsations, and update the previously-observed effective temperature-rotation period relation.

20 pages, 12 figures, 1 large table at the end. Accepted for publication in MNRAS

References in corpus (14)

• The K2 Mission: Characterization and Early results
• Gravity-mode pulsations in subdwarf B stars: a critical test of stellar opacity
• The orbits of subdwarf-B + main-sequence binaries: III. The period - eccentricity distribution
• Asteroseismology revealing trapped modes in KIC 10553698A
• Discovery of a variable lead-rich hot subdwarf: UVO 0825+15
• KIC7668647: a 14 day beaming sdB+WD binary with a pulsating subdwarf
• Fe-bump instability: the excitation of pulsations in subdwarf B and other low-mass stars
• The discovery of differential radial rotation in the pulsating subdwarf B star KIC 3527751
• Evolutionary modelling of subdwarf B stars using MESA with the predictive mixing and convective premixing schemes
• KIC 1718290: A Helium-rich V1093-Her-like Pulsator on the Blue Horizontal Branch
• TESS first look at evolved compact pulsators : Discovery and asteroseismic probing of the g-mode hot B subdwarf pulsator EC 21494-7018
• The blue-edge problem of the V1093 Her instability strip revisited using evolutionary models with atomic diffusion
• Asteroseismic analysis of variable hot subdwarf stars observed with TESS I. The mean g-mode period spacings in hot subdwarf B stars
• Follow-up observations of pulsating subdwarf B stars: Multisite campaigns on PG 1618+563B and PG 0048+091

Cited by in corpus (5)

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• K2 photometry on oscillation mode variability: the new pulsating hot B subdwarf star EPIC 220422705
• Identifying and characterising the population of hot sub-luminous stars with multi-colour MeerLICHT data
• The theoretical pulsation spectra of hot B subdwarfs. Static and evolutionary STELUM models
• TIC 5724661: A Long-Period Binary with a Pulsating sdB Star and $\delta$ Scuti Variable