Pulsational frequency and amplitude modulation in the δ Sct star KIC 7106205

Analysis of the Kepler δ Sct star KIC 7106205 showed amplitude modulation in a single pressure mode, whilst all other pressure and gravity modes remained stable in amplitude and phase over the 1470 d length of the data set. The Kepler data set was divided into a series with time bins of equal length for which consecutive Fourier transforms were calculated. An optimum fixed frequency, calculated from a least-squares fit of all data, allowed amplitude and phase of each pulsation mode for each time bin to be tracked. The single pressure mode at ν = 13.3942 d-1 changed significantly in amplitude, from 5.16 ± 0.03 to 0.53 ± 0.06 mmag, but also varied quasi-sinusoidally in phase, with a characteristic period similar to the length of the data set. All other p and g modes were stable in both amplitude and phase, which is clear evidence that the visible pulsation mode energy is not conserved within this star. Possible causes of the observed amplitude and phase modulation and the missing mode energy are discussed

Amplitude modulation and energy conservation of pulsation modes in delta Scuti stars

The pulsations in δ Sct stars are excited by a heat engine driving mechanism caused by in-creased opacity in their surface layers, and have pulsation periods of order a few hours. Space based observations in the last decade have revealed a diverse range of pulsational be-haviour in these stars, which is investigated using an ensemble of 983 δ Sct stars observed continuously for 4 yr by the Kepler Space Tele-scope. A statistical search for amplitude modu-lation of pulsation modes is carried out and it is shown that 61.3 per cent of the 983 δ Sct stars exhibit significant amplitude modulation in at least a single pulsation mode, and that this is uncorrelated with effective temperature and surface gravity. Hence, the majority of δ Sct stars exhibit amplitude modulation, with time-scales of years and longer demonstrated to be significant in these stars both observationally and theoretically. An archetypal example of amplitude modulation in a δ Sct star is KIC 7106205, which contains only a single pulsation mode that varies signifi-cantly in amplitude whilst all other pulsation modes stay constant in amplitude and phase throughout the 4-yr Kepler data set. Therefore, the visible pulsational energy budget in this star, and many others, is not conserved over 4 yr. Models of beating of close-frequency pulsation modes are used to identify δ Sct stars with fre-quencies that lie closer than 0.001 d−1, which are barely resolved using 4 yr of Kepler observa-tions, and maintain their independent identi-ties over 4 yr. Mode coupling models are used to quantify the strength of coupling and distin-guish between non-linearity in the form of combination frequencies and non-linearity in the form of resonant mode coupling for families of pulsation modes in several stars. The changes in stellar structure caused by stel-lar evolution are investigated for two high am-plitude δ Sct (HADS) stars in the Kepler data set, revealing a positive quadratic change in phase for the fundamental and first overtone radial modes in KIC 5950759. The observed phase modulation of the radial modes in this star is two orders of magnitude larger than predicted by stellar evolutionary models, yet is consistent with the prediction of increasing pe-riods of radial modes for stars on the main se-quence. The statistical analysis of 983 δ Sct stars, in-cluding the results from the search for ampli-tude modulation, is a valuable resource for on-going and future space missions such as K2, TESS and PLATO, because the high quality 4-yr Kepler data set will not be surpassed for some time. The observational studies of individual stars in this thesis provide strong evidence that non-linear processes are clearly at work in the majority of δ Sct stars, and provide valuable constraints for future asteroseismic modelling

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

We report the results of a 60-hr photometric campaign of a rapidly oscillating Ap star, J0855 (TYC 2488-1241-1). We have utilised the multi-site Las Cumbres Observatory’s (LCO) 0.4- m telescopes to obtain short cadence B−band observations of an roAp star previously lacking detailed study. Our observations confirm the rotation period presented in the discovery paper of this star (Prot = 3.0918 d), and reveal the star to be pulsating in a distorted mode. The B data show this star to be among the highest amplitude roAp stars, with a peak-to-peak amplitude of 24 mmag. Modelling of the pulsation frequency at 197.2714 d−1 (2283 µHz; P = 7.30 min) shows that this star belongs to the subgroup of super-critical pulsators, where the observed frequencies are above the theoretical acoustic cutoff frequency. From the modelling, we deduce that the star’s rotation axis is inclination angle of about 30◦ to the line-of-sight, with an angle of obliquity of the magnetic axis to the rotation axis of either 40◦ or 24◦ depending on whether the pulsation mode is dipole or quadrupole, respectively

EPIC 201585823, a rare triple-mode RR Lyrae star discovered in K2 mission data

We have discovered a new, rare triple-mode RR Lyr star, EPIC 201585823, in the Kepler K2 mission Campaign 1 data. This star pulsates primarily in the fundamental and first-overtone radial modes, and, in addition, a third non-radial mode. The ratio of the period of the non-radial mode to that of the first-overtone radial mode, 0.616 285, is remarkably similar to that seen in 11 other triple-mode RR Lyr stars, and in 260 RRc stars observed in the Galactic bulge. This systematic character promises new constraints on RR Lyr star models. We detected subharmonics of the non-radial mode frequency, which are a signature of period doubling of this oscillation; we note that this phenomenon is ubiquitous in RRc and RRd stars observed from space, and from ground with sufficient precision. The non-radial mode and subharmonic frequencies are not constant in frequency or in amplitude. The amplitude spectrum of EPIC 201585823 is dominated by many combination frequencies among the three interacting pulsation mode frequencies. Inspection of the phase relationships of the combination frequencies in a phasor plot explains the ‘upward’ shape of the light curve. We also found that raw data with custom masks encompassing all pixels with significant signal for the star, but without correction for pointing changes, is best for frequency analysis of this star, and, by implication, other RR Lyr stars observed by the K2 mission. We compare several pipeline reductions of the K2 mission data for this star

Acceptability of donor funding for clinical trials in the UK : a qualitative empirical ethics study using focus groups to elicit the views of research patient public involvement group members, research ethics committee chairs and clinical researchers

Objectives The Plutocratic Proposal is a novel method of funding early phase, clinical trials where a single donor funds the entire trial and in so doing secures a place on it. The aim of this study was to identify and explore concerns that may be raised by UK research ethics committees (RECs) when reviewing clinical trials funded in this way. Design Empirical ethics combining ethical analysis and qualitative data from three focus groups held online using Frith’s symbiotic approach. Data were analysed using inductive thematic approach informed by the study aims and ethical analysis. Participants 22 participants were recruited: 8 research patient public involvement group members, 7 REC chairs and 7 clinical researchers. All were based in the UK. Results With one exception, participants thought the Plutocratic Proposal may be ‘all things considered’ acceptable, providing their concerns were met, primary of which was upholding scientific integrity. Other concerns discussed related to the acceptability of the donor securing a place on the trail including: whether this was unfair distribution of benefits, disclosing the identity of the donor as the funder, protecting the donor from exploitation and funding a single study with multiple donors on the same terms. Some misgivings fell outside the usual REC purview: detrimental impact of donors of bad character, establishing the trustworthiness of matching agency and its processes and optimising research funding and resources. Despite their concerns, participants recognised that because the donor funds the whole trial, others would also potentially benefit from participating. Conclusions We identified concerns about the Plutocratic Proposal. UK RECs may be open to approving studies if these can be addressed. Existing governance processes will do some of this work, but additional REC guidance, particularly in relation to donors securing a place on the trial, may be necessary to help RECs navigate ethical concerns consistently

The ESO UVES/FEROS Large Programs of TESS OB pulsators. I. Global stellar parameters from high-resolution spectroscopy

Modern stellar structure and evolution theory experiences a lack of observational calibrations for the interior physics of intermediate- and high-mass stars. This leads to discrepancies between theoretical predictions and observed phenomena mostly related to angular momentum and element transport. Analyses of large samples of massive stars connecting state-of-the-art spectroscopy to asteroseismology may provide clues on how to improve our understanding of their interior structure. We aim to deliver a sample of O- and B-type stars at metallicity regimes of the Milky Way and the Large Magellanic Cloud (LMC) galaxies with accurate atmospheric parameters from high-resolution spectroscopy, along with a detailed investigation of line-profile broadening, for future asteroseismic studies. After describing the general aims of our two Large Programs, we develop dedicated methodology to fit spectral lines and deduce accurate global stellar parameters from high-resolution multi-epoch UVES and FEROS spectroscopy. We use the best available atmosphere models for three regimes covered by our global sample, given its breadth in terms of mass, effective temperature, and evolutionary stage. Aside from accurate atmospheric parameters and locations in the Hertzsprung-Russell diagram, we deliver detailed analyses of macroturbulent line broadening, including estimation of the radial and tangential components. We find that these two components are difficult to disentangle from spectra with signal-to-noise ratios below 250. Future asteroseismic modelling of the deep interior physics of the most promising stars in our sample will improve the existing dearth of such knowledge for large samples of OB stars, including those of low metallicity in the LMC.Comment: Accepted for publication in Astronomy & Astrophysic