LCO observations of a super-critical distorted pulsation in the roAp star J0855 (TYC 2488-1241-1)

Monthly Notices of the Royal Astronomical Society

Cunha

2019

The driving mechanism for high-frequency oscillations in some chemically peculiar Ap stars, the rapidly oscillating Ap stars (roAp stars), is not understood. The Transiting Exoplanet Survey Satellite mission (TESS) data provide an ideal opportunity to extend the number of roAp stars that might provide further clues to address this problem. From an examination of over 18 000 stars in TESS sectors 1–7, we have discovered high-frequency pulsations in 14 A–F stars, of which only 3 are classified as Ap stars. In addition to these new discoveries, we discuss the frequencies in nine previously known roAp stars. In one of these stars, HD 60435, we confirm a previous finding that the pulsations have lifetimes of only a few days. In another known roAp star, HD 6532, the relative amplitudes of the rotationally modulated sidelobes, which are generally used to estimate the inclination of the magnetic axis relative to the rotational axis, are significantly different from those found in ground-based B-band photometric observations. We also discuss four δ Scuti stars that appear to have independent frequencies similar to those of roAp stars.

Section: Introductionmentioning

confidence: 99%

High frequencies in TESS A–F main-sequence stars

Balona

Monthly Notices of the Royal Astronomical Society

Cunha

2019

“…In non-magnetic stars there is a theoretical limit to pulsation mode frequencies, the acoustic cutoff frequency, where the wavelength of the pulsation becomes short compared to the scale of the surface reflective boundary. However, there are many roAp stars that pulsate above this limit (see figure 6 of Holdsworth et al 2018c). It was shown by Cunha et al (2013) Hubrig et al (2006).…”

Section: Introductionmentioning

confidence: 99%

HD 42659: the only known roAp star in a spectroscopic binary observed with B photometry, TESS, and SALT

Monthly Notices of the Royal Astronomical Society

Saio

Kurtz

2019

Self Cite

We present a multi-instrument analysis of the rapidly oscillating Ap (roAp) star HD 42659. We have obtained B photometric data for this star and use these data, in conjunction with TESS observations, to analyse the high-frequency pulsation in detail. We find a triplet which is split by the rotation frequency of the star (ν rot = 0.3756 d −1 ; P rot = 2.66 d) and present both distorted dipole and distorted quadrupole mode models. We show that the pulsation frequency, 150.9898 d −1 (P puls = 9.54 min) is greater than the acoustic cutoff frequency. We utilise 27 high-resolution (R ≃ 65 000), high signal-to-noise (∼ 120) spectra to provide new orbital parameters for this, the only known roAp star to be in a short period binary (P orb = 93.266 d). We find the system to be more eccentric than previously thought, with e = 0.317, and suggest the companion is a mid-F to early-K star. We find no significant trend in the average pulsation mode amplitude with time, as measured by TESS, implying that the companion does not have an affect on the pulsation in this roAp star. We suggest further photometric observations of this star, and further studies to find more roAp stars in close binaries to characterise how binarity may affect the detection of roAp pulsations.

“…A few problems have been identified by confronting the theoretical results with observations. Among these problems is the existence of some roAp stars which pulsate with frequencies higher than those predicted by the models (Cunha et al 2013;Holdsworth et al 2018); this is one of the most interesting challenges for the theory. Cunha et al (2013) have shown some evidence that these very high frequencies may be excited by an entirely different mechanism, associated with the turbulent pressure, but a thorough test of this possibility still needs to be performed.…”

Section: Introductionmentioning

confidence: 99%

Rotation and pulsation in Ap stars: first light results from TESS sectors 1 and 2

Cunha

Antoci

Monthly Notices of the Royal Astronomical Society

et al. 2019

We present the first results from the Transiting Exoplanet Survey Satellite (TESS) on the rotational and pulsational variability of magnetic chemically peculiar A-type stars. We analyse TESS 2-min cadence data from sectors 1 and 2 on a sample of 83 stars. Five new rapidly oscillating Ap (roAp) stars are announced. One of these pulsates with periods around 4.7 min, making it the shortest period roAp star known to date. Four out of the five new roAp stars are multiperiodic. Three of these, and the singly-periodic one show the presence of rotational mode splitting. Individual frequencies are provided in all cases. In addition, seven previously known roAp stars are analysed. Additional modes of oscillation are found in some stars, while in others we are able to distinguish the true pulsations from possible aliases present in the ground-based data. We find that the pulsation amplitude in the TESS filter is typically a factor 6 smaller than that in the B filter which is usually used for ground-based observations. For four roAp stars we set constraints on the inclination angle and magnetic obliquity, through the application of the oblique pulsator model. We also confirm the absence of roAp-type pulsations down to amplitude limits of 6 and 13 µmag, respectively, in two of the best characterised non-oscillating Ap (noAp) stars. We announce 27 new rotational variables along with their rotation periods, and provide different rotation periods for seven other stars. Finally, we discuss how these results challenge state-of-the-art pulsation models for roAp stars.