Space Pole Publications Server
http://publi2-as.oma.be
Space Pole Publications Server latest documentsenSun, 25 Sep 2022 04:36:49 GMTInvenio 1.2.1sarah@oma.be3604125http://publi2-as.oma.be/img/site_logo_rss.pngSpace Pole Publications Server
http://publi2-as.oma.be
Search Search this site:p
http://publi2-as.oma.be/search
The Complicated Case of δ Scuti Pulsations and Rotation in KIC 6951642; a long-orbit Single-lined Spectroscopic Binary Star
http://publi2-as.oma.be/record/5616
More than four years of HERMES observations have confirmed KIC 6951642 is a very long orbit (P ≈ 1770 d) single-lined spectroscopic binary (F0-type) with a fast-rotating companion (vsin i = 123±3 km/s). The Fourier spectrum of its four-year photometric observations includes plenty of significant frequencies (594) in low- and high-frequency regions. The high-frequency modes appear with various time-delay patterns. We detected several rotationally split 𝛿 Scuti pulsations centered at 13.96 per day (and an average frequency spacing of Δ𝑓= 0.723±0.006 per day) for KIC 6951642. The detailed study of all significant low frequencies, ranging from 0.72 to 3.60 per day, revealed that the two most dominant frequencies (with the same amplitude or larger than that of the p-modes) are a combination of the lowest-frequency modes (𝑓3 = 𝑓< 0.17 per day), i.e. 𝑓orhrm + 𝑚𝑓orhrm (𝑚 = 12,14). We suggest the lowest-frequency modes are very large harmonics (orders of 10) of orbital frequency (≈0.0006 per day). We verified the other most dominant low-frequencies as harmonics of rota3on frequency 0.721 per day and its combinations. Finally, we reject the probability of hybrid pulsations in the fast-rotating companion of KIC 6951642, and propose that it is a 𝛿 Scuti pulsator with a candidate rotation frequency of 0.721 per day.Samadi-Ghadim, A.Tue, 25 Jan 2022 11:41:06 GMThttp://publi2-as.oma.be/record/56162021Orbital solutions derived from radial velocities and time delays for four Kepler systems with A/F-type (candidate) hybrid pulsators
http://publi2-as.oma.be/record/5287
The presence of A/F-type Kepler hybrid stars extending across the entire δ Sct-γ Dor instability strips and beyond remains largely unexplained. In order to better understand these particular stars, we performed a multi-epoch spectroscopic study of 49 candidate A/F-type hybrid stars and one cool(er) hybrid object detected by the Kepler mission. We determined a lower limit of 27% for the multiplicity fraction. For six spectroscopic systems, we also reported long-term variations of the time delays. For four systems, the time delay variations are fully coherent with those of the radial velocities and can be attributed to orbital motion. We aim to improve the orbital solutions for those systems with long orbital periods (order of 4-6 years) among the Kepler hybrid stars. The orbits are computed based on a simultaneous modelling of the RVs obtained with high-resolution spectrographs and the photometric time delays derived from time-dependent frequency analyses of the Kepler light curves. We refined the orbital solutions of four spectroscopic systems with A/F-type Kepler hybrid component stars: KIC4480321, KIC5219533, KIC8975515 and KIC9775454. Simultaneous modelling of both data types analysed together enabled us to improve the orbital solutions, obtain more robust and accurate information on the mass ratio, and identify the component with the short-period δ Sct-type pulsations. In several cases, we were also able to derive new constraints for the minimum component masses. From a search for regular frequency patterns in the high-frequency regime of the Fourier transforms of each system, we found no evidence of tidal splitting among the triple systems with close (inner) companions. However, some systems exhibit frequency spacings which can be explained by the mechanism of rotational splitting.Lampens, P.Tue, 09 Feb 2021 13:57:12 GMThttp://publi2-as.oma.be/record/52872021KIC 8975515: A fast-rotating (gamma Dor - delta Sct) hybrid star with Rossby modes and a slower delta Sct companion in a long-period orbit
http://publi2-as.oma.be/record/5153
Aims: KIC 8975515 is a double-lined spectroscopic binary system with hybrid nature. Regular monitoring with the échelle spectrograph HERMES show that both components have matching atmospheric properties (T_eff ~ 7400 K), and that one of them is a fast rotator (v sin i = 162 versus 32 km s$^{-1}$). Our aim is to study the Kepler light curve in order to determine the frequencies of the pulsations, to search for regular spacing patterns in the Fourier spectrum, if any, and to discuss their origin in the context of binarity and fast rotation. Methods: In this paper, we study the properties of the stellar pulsations based on a careful analysis of the Fourier spectrum. This was done by performing repeated frequency-search analyses with successive prewhitenings of all the significant frequencies detected in the spectrum. Moreover, we searched for regular period spacing among the g modes as well as frequency splitting among the g and p modes in frequency. Results: In the low-frequency regime, one series of prograde g modes and four series of retrograde r modes, were detected. The r modes are well- distributed with respect to the harmonics of the rotational frequency of the fast-rotating star f_rot = 1.647 d$^{-1}$. The dominant g mode is f_2 = 2.37 d$^{-1}$. The strongest p mode is f_1 = 13.97 d$^{-1}$. We identified two multiplets of regularly split p modes with the mean values of 0.42 d$^{-1}$ and 1.65 d$^{-1}$. In addition, we also identified a few incidences of mode coupling (between f_1 and a g or r mode). Conclusions: We detected five series of retrograde r and prograde g modes as well as two multiplets of p modes with rotational frequency splitttings related to both components of KIC 8975515. We identified the fast-rotating component as a hybrid pulsator with r modes, and the slowly- rotating component as a delta Sct pulsator.Samadi-Ghadim, A. Thu, 21 Jan 2021 19:35:20 GMThttp://publi2-as.oma.be/record/51532020Hybrid Pulsations and Tidal Splitting detected in the Kepler Eclipsing and Spotted Binary System KIC 6048106
http://publi2-as.oma.be/record/3985
We present a new asteroseismic analysis of KIC 6048106, a Kepler Algol-type eclipsing binary star in a circularized orbit with Porb=1.559361±0.000036 d. Based on a physical model for the binary and its corresponding set of fundamental parameters (Teff=7033±187 K, M1=1.55±0.11 M⊙, R1=1.58±0.12 R⊙ and Teff=4522±103 K, M2=0.33±0.07 M⊙, R2=1.78±0.16 R⊙, respectively for the primary and the secondary component), we obtained the residual light curve after removal of the full binary model, including a 290-d activity cycle for the secondary component. In this work, we used the method of Fourier analysis of the residual light curve in combination with least squares optimization for the frequency analysis. We detected seven dominant, independent gravity (g) modes as well as 34 low-amplitude acoustic (p) modes. The g modes in the range of 1.96-2.85 d^(-1) have a mean spacing of ΔΠmean=1517.92±131.54 s. Though of much lower amplitude, additional significant frequencies were detected in the intervals 7.49-15.2 d^(-1) and 19-22.5 d^(-1) (i.e., in the p mode region), with corresponding dominant modes νmax1=11.745±0.001 d^(-1) and νmax2=20.960±0.002 d^(-1). From its position in the HR diagram, we conclude that the primary component is the source of the detected hybrid pulsations. Consequently, the pulsation constants, Q, of the high frequencies cover the range of 0.028-0.064 d. Furthermore, ν43 (19.037±0.002 d^(-1)) might correspond to the fundamental radial mode (Q=0.033±0.007 d). The other frequencies in the range of 19-22.5 d^(-1) could be radial or non-radial overtone modes. Moreover, the low-amplitude p modes show an equidistant splitting by forb, which we interpret as tidal splitting following theoretical predictions. Samadi Ghadim, A.Tue, 29 Jan 2019 12:24:41 GMThttp://publi2-as.oma.be/record/39852018