The first evidence for multiple pulsation axes: a new roAp star in the Kepler field, KIC 10195926

Abstract

We have discovered a new rapidly oscillating Ap star among the Kepler Mission target stars, KIC 10195926. This star shows two pulsation modes with periods that are amongst the longest known for roAp stars at 17.1 min and 18.1 min, indicating that the star is near the terminal age main sequence. The principal pulsation mode is an oblique dipole mode that shows a rotationally split frequency septuplet that provides information on the geometry of the mode. The secondary mode also appears to be a dipole mode with a rotationally split triplet, but we are able to show within the improved oblique pulsator model that these two modes cannot have the same axis of pulsation. This is the first time for any pulsating star that evidence has been found for separate pulsation axes for different modes. The two modes are separated in frequency by 55 microHz, which we model as the large separation. The star is an alpha^2 CVn spotted magnetic variable that shows a complex rotational light variation with a period of Prot = 5.68459 d. For the first time for any spotted magnetic star of the upper main sequence, we find clear evidence of light variation with a period of twice the rotation period; i.e. a subharmonic frequency of ${\nu }_{\mathrm{rot}}/2$. We propose that this and other subharmonics are the first observed manifestation of torsional modes in an roAp star. From high resolution spectra we determine Teff = 7400 K, log g = 3.6 and v sin i = 21 km/s. We have found a magnetic pulsation model with fundamental parameters close to these values that reproduces the rotational variations of the two obliquely pulsating modes with different pulsation axes. The star shows overabundances of the rare earth elements, but these are not as extreme as most other roAp stars. The spectrum is variable with rotation, indicating surface abundance patches.

17 pages; 16 figures; MNRAS

References in corpus (5)

• ADIPLS -- the Aarhus adiabatic oscillation package
• Pulsation tomography of rapidly oscillating Ap stars. Resolving the third dimension in peculiar pulsating stellar atmospheres
• Improved pulsating models of magnetic Ap stars I: exploring different magnetic field configurations
• Discovery of very low amplitude 9-minute multiperiodic pulsations in the magnetic Ap star HD 75445
• New light on the driving mechanism in roAp stars. Part I. Effects of metallicity

Cited by in corpus (28)

• Revised Stellar Properties of Kepler Targets for the Quarter 1-16 Transit Detection Run
• Probing the interior physics of stars through asteroseismology
• Kepler Mission Stellar and Instrument Noise Properties
• Super-Nyquist asteroseismology with the Kepler Space Telescope
• Interaction Between Convection and Pulsation
• High frequency A-type pulsators discovered using SuperWASP
• Rotation and pulsation in Ap stars: first light results from TESS sectors 1 and 2
• Theoretical light curves of dipole oscillations in roAp stars
• Testing excitation models of rapidly oscillating Ap stars with interferometry
• Discovery of the longest-period rapidly oscillating Ap star HD177765
• Tidally Excited Oscillations in Heartbeat Binary Stars: Pulsation Phases and Mode Identification
• The Nainital-Cape Survey-IV
• TESS Cycle 1 observations of roAp stars with 2-min cadence data
• KIC 7582608: A new Kepler roAp star with frequency variability
• HD 24355 observed by the Kepler K2 mission: A rapidly oscillating Ap star pulsating in a distorted quadrupole mode
• Suppressed phase variations in a high amplitude rapidly oscillating Ap star pulsating in a distorted quadrupole mode
• Destroying Aliases from the Ground and Space: Super-Nyquist ZZ Cetis in K2 Long Cadence Data
• Statistical analysis of roAp, He-weak and He-rich stars
• Six new rapidly oscillating Ap stars in the Kepler long-cadence data using super-Nyquist asteroseismology
• Short time-scale frequency and amplitude variations in the pulsations of an roAp star: HD 217522
• Whole Earth Telescope discovery of a strongly distorted quadrupole pulsation in the largest amplitude rapidly oscillating Ap star
• The roAp stars observed by the Kepler Space Telescope
• Asteroseismology of Pulsating Stars
• Pulsation models for the roAp star HD 134214
• Large amplitude change in spot-induced rotational modulation of the Kepler Ap star KIC 2569073
• Flare Activity and Magnetic Feature Analysis of the Flare Stars II: Sub-Giant Branch
• The search for roAp stars: null results and new candidates from Stroemgren-Crawford photometry
• Numerical simulations of line-profile variation beyond a single-surface approximation for oscillations in roAp stars