The envelope of the power spectra of over a thousand \delta Scuti stars. The Tˉeff\bar{T}_{eff}-νmax\nu_{max} scaling relation

CoRoT and Kepler high-precision photometric data allowed the detection and characterization of the oscillation parameters in stars other than the Sun. Moreover, thanks to the scaling relations, it is possible to estimate masses and radii for thousands of solar-type oscillating stars. Recently, a \Delta\nu - \rho relation has been found for \delta Scuti stars. Now, analyzing several hundreds of this kind of stars observed with CoRoT and Kepler, we present an empiric relation between their frequency at maximum power of their oscillation spectra and their effective temperature. Such a relation can be explained with the help of the \kappa-mechanism and the observed dispersion of the residuals is compatible with they being caused by the gravity-darkening effect

Evidence of amplitude modulation due to Resonant Mode Coupling in the delta Scuti star KIC5892969

A study of the star KIC5892969 observed by the Kepler satellite is presented. Its three highest amplitude modes present a strong amplitude modulation. The aim of this work is to investigate amplitude variations in this star and their possible cause. Using the 4 years-long observations available, we obtained the frequency content of the full light curve. Then, we studied the amplitude and phase variations with time using shorter time stamps. The results obtained are compared with the predicted ones for resonant mode coupling of an unstable mode with lower frequency stable modes. Our conclusion is that resonant mode coupling is consistent as an amplitude limitation mechanism in several modes of KIC5892969 and we discuss to which extent it might play an important role for other delta Scuti stars

Evidence of chaotic modes in the analysis of four delta Scuti stars

Since CoRoT observations unveiled the very low amplitude modes that form a flat plateau in the power spectrum structure of delta Scuti stars, the nature of this phenomenon, including the possibility of spurious signals due to the light curve analysis, has been a matter of long-standing scientific debate. We contribute to this debate by finding the structural parameters of a sample of four delta Scuti stars, CID 546, CID 3619, CID 8669, and KIC 5892969, and looking for a possible relation between these stars' structural parameters and their power spectrum structure. For the purposes of characterization, we developed a method of studying and analysing the power spectrum with high precision and have applied it to both CoRoT and Kepler light curves. We obtain the best estimates to date of these stars' structural parameters. Moreover, we observe that the power spectrum structure depends on the inclination, oblateness, and convective efficiency of each star. Our results suggest that the power spectrum structure is real and is possibly formed by 2-period island modes and chaotic modes

Dating young open clusters using delta Scuti stars. Results for Trumpler 10 and Praesepe

Aims. The main goal of this work is to date young open clusters using $\delta$ Sct stars. Seismic indices such as the large separation and the frequency at maximum power can help to constrain the models to better characterise the stars. We propose a reliable method to identify some radial modes, which gives us greater confidence in the constrained models. Methods. We extract the frequency content of a sample of $\delta$ Sct stars belonging to the same open cluster. We estimate the low-order large separation by means of different techniques and the frequency at maximum power for each member of the sample. We use a grid of models built with the typical parameters of $\delta$ Sct stars, including mass, metallicity and rotation as independent variables, and determine the oscillation modes. We select the observed frequencies whose ratios match those of the models. Once we find a range of radial modes matching the observed frequencies, mainly the fundamental mode, we add it to the other seismic parameters to derive the stellar age. Assuming star groups have similar chemistry and age, we estimate their mean age by computing a weighted probability density function fit to the age distribution of the seismically constrained models. Results. We estimate the age of Trumpler 10 to be $30_{-20}{+30}$ Myr, and that of Praesepe to be $580 \pm 230$ Myr. In this latter case, we find two apparent populations of $\delta$ Sct stars in the same cluster, one at $510 \pm 140$ Myr and another at $890 \pm 140$ Myr. This may be due to two different formation events, different rotational velocities of the members in our sample of stars (as rapid rotation may modify the observed large separation), or to membership of unresolved binary systems.Comment: 20 pages, 25 figure, uses the open-source code MultiModes (see https://github.com/davidpamos/MultiModes). It will be published in A&

Unveiling the power spectra of δ\delta Scuti stars with TESS. The temperature, gravity, and frequency scaling relation

Thanks to high-precision photometric data legacy from space telescopes like CoRoT and Kepler, the scientific community could detect and characterize the power spectra of hundreds of thousands of stars. Using the scaling relations, it is possible to estimate masses and radii for solar-type pulsators. However, these stars are not the only kind of stellar objects that follow these rules: $\delta$ Scuti stars seem to be characterized with seismic indexes such as the large separation ($\Delta\nu$). Thanks to long-duration high-cadence TESS light curves, we analysed more than two thousand of this kind of classical pulsators. In that way, we propose the frequency at maximum power ($\nu_{\rm max}$) as a proper seismic index since it is directly related with the intrinsic temperature, mass and radius of the star. This parameter seems not to be affected by rotation, inclination, extinction or resonances, with the exception of the evolution of the stellar parameters. Furthermore, we can constrain rotation and inclination using the departure of temperature produced by the gravity-darkening effect. This is especially feasible for fast rotators as most of $\delta$ Scuti stars seem to be.Comment: 12 pages, 13 figures, accepted in Astronomy & Astrophysic

The PL diagram for δ\delta Sct stars: back in business as distance estimators

In this work, we focus on the period-luminosity relation (PLR) of $\delta$ Sct stars, in which mode excitation and selection mechanisms are still poorly constrained, and whose structure and oscillations are affected by rotation. We review the PLRs in the recent literature, and add a new inference from a large sample of $\delta$ Sct. We highlight the difficulty in identifying the fundamental mode and show that rotation-induced surface effects can impact the measured luminosities, explaining the broadening of the PLR. We derive a tight relation between the low-order large separation and the fundamental radial mode frequency (F0) that holds for rotating stars, thus paving the way towards mode identification. We show that the PLRs we obtain for different samples are compatible with each other and with the recent literature, and with most observed $\delta$ Sct stars when taking rotation effects into account. We also find that the highest-amplitude peak in the frequency spectrum corresponds to the fundamental mode in most $\delta$ Sct, thus shedding some light on their elusive mode selection mechanism.Comment: 10 pages, 5 figures, 1 table, IAU conference proceedin

CHEOPS & stars (& asteroseismology)

The characterization of exoplanets has been considerably improved during the last decade mainly through space missions (Kepler/K2, CoRoT) and also the characterization of their host stars by stellar seismology. Nowadays, TESS and CHEOPS are the only two important missions that will provide short-cadence high-precision photometric time-series for a large amount of targets. This project explored the asteroseismic potential of CHEOPS light-curves. For that purpose, we analysed the probability of detecting solar-like pulsations, and the accuracy we could obtain for estimates of the seismic indices for the expected targets, observing time and expected duty cycle of this mission. Our results suggested that we can determine the frequency at maximum power for evolved and/or massive F-G-K solar-like stars with an uncertainty better than 5%. Asteroseismology therefore enables us to decrease age, mass, radius and density uncertainties significantly in the characterization of exoplanet host stars

Study of HD 169392A observed by CoRoT and HARPS

International audienceContext. The results obtained by asteroseismology with data from space missions such as CoRoT and Kepler are providing new insights into stellar evolution. After five years of observations, CoRoT is continuing to provide high-quality data and we here present an analysis of the CoRoT observations of the double star HD 169392, complemented by ground-based spectroscopic observations.Aims. This work aims at characterising the fundamental parameters of the two stars, their chemical composition, the acoustic-mode global parameters including their individual frequencies, and their dynamics.Methods. We analysed HARPS observations of the two stars to derive their chemical compositions. Several methods were used and compared to determine the global properties of stars’ acoustic modes and their individual frequencies from the photometric data of CoRoT.Results. The new spectroscopic observations and archival astrometric values suggest that HD 169392 is a weakly bound wide binary system. We obtained spectroscopic parameters for both components which suggest that they originate from the same interstellar cloud. However, only the signature of oscillation modes of HD 169392 A was measured; the signal-to-noise ratio of the modes in HD 169392B is too low to allow any confident detection. For HD 169392 A we were able to extract parameters of modes for ℓ = 0, 1, 2, and 3. The analysis of splittings and inclination angle gives two possible solutions: one with with splittings and inclination angles of 0.4−1.0 μHz and 20 − 40°, the other with 0.2−0.5 μHz and 55−86°. Modelling this star using the Asteroseismic Modeling Portal (AMP) gives a mass of 1.15 ± 0.01 M⊙, a radius of 1.88 ± 0.02 R⊙, and an age of 4.33 ± 0.12 Gyr. The uncertainties come from estimated errors on the observables but do not include uncertainties on the surface layer correction or the physics of stellar models

TESS Cycle 2 observations of roAp stars with 2-min cadence data

We present the results of a systematic search of the Transiting Exoplanet Survey Satellite (TESS) 2-min cadence data for new rapidly oscillating Ap (roAp) stars observed during the Cycle 2 phase of its mission. We find seven new roAp stars previously unreported as such and present the analysis of a further 25 roAp stars that are already known. Three of the new stars show multiperiodic pulsations, while all new members are rotationally variable stars, leading to almost 70 per cent (22) of the roAp stars presented being $\alpha^2$ CVn-type variable stars. We show that targeted observations of known chemically peculiar stars are likely to overlook many new roAp stars, and demonstrate that multi-epoch observations are necessary to see pulsational behaviour changes. We find a lack of roAp stars close to the blue edge of the theoretical roAp instability strip, and reaffirm that mode instability is observed more frequently with precise, space-based observations. In addition to the Cycle 2 observations, we analyse TESS data for all known roAp stars. This amounts to 18 further roAp stars observed by TESS. Finally, we list six known roAp stars that TESS is yet to observe. We deduce that the incidence of roAp stars amongst the Ap star population is just 5.5 per cent, raising fundamental questions about the conditions required to excite pulsations in Ap stars. This work, coupled with our previous work on roAp stars in Cycle 1 observations, presents the most comprehensive, homogeneous study of the roAp stars in the TESS nominal mission, with a collection of 112 confirmed roAp stars in total.Comment: Accepted for publication in MNRAS. 32 Pages, 2 Tables, 77 Figure

TESS Cycle 2 observations of roAp stars with 2-min cadence data

We present the results of a systematic search of the Transiting Exoplanet Survey Satellite (TESS) 2-min cadence data for new rapidly oscillating Ap (roAp) stars observed during the Cycle 2 phase of its mission. We find seven new roAp stars previously unreported as such and present the analysis of a further 25 roAp stars that are already known. Three of the new stars show multiperiodic pulsations, while all new members are rotationally variable stars, leading to almost 70 per cent (22) of the roAp stars presented being α2 CVn-type variable stars. We show that targeted observations of known chemically peculiar stars are likely to overlook many new roAp stars, and demonstrate that multi-epoch observations are necessary to see pulsational behaviour changes. We find a lack of roAp stars close to the blue edge of the theoretical roAp instability strip, and reaffirm that mode instability is observed more frequently with precise, space-based observations. In addition to the Cycle 2 observations, we analyse TESS data for all known roAp stars. This amounts to 18 further roAp stars observed by TESS. Finally, we list six known roAp stars that TESS is yet to observe. We deduce that the incidence of roAp stars amongst the Ap star population is just 5.5 per cent, raising fundamental questions about the conditions required to excite pulsations in Ap stars. This work, coupled with our previous work on roAp stars in Cycle 1 observations, presents the most comprehensive, homogeneous study of the roAp stars in the TESS nominal mission, with a collection of 112 confirmed roAp stars in total