All posts by Filipe Pereira

Dynamical investigation of modulated Kepler RR Lyrae stars

Authors. Plachy, E.; Benkő, J. M.; Kolláth, Z.; Szabó, R.; Molnár, L.

Journal.  EPJ Web of Conferences

Abstract. We performed a non-linear dynamical analysis on the Blazhko modulation for the first time. Our results suggest that the detection of chaotic nature behind the phenomenon is limited by the instrumental effects and the data processing problems of the Kepler pipeline concerning high-amplitude variable stars.


Tipsy pulsation of classical Cepheids – lessons from space photometry

Authors. L. Szabados, N. R. Evans, R. Szabó, A. Derekas, A. Cameron and the MOST team

Journal.  EPJ Web of Conferences

Abstract. Space photometric data of the Kepler Cepheid, V1154 Cygni, and those of SZ Tauri (MOST photometry) indicate that classical Cepheids are not strictly regular pulsators. Cycle-to-cycle period changes and variations in the shape of the light curve are revealed from the continuous photometry covering 6 cycles of SZ Tau pulsation and several hundred pulsation cycles of V1154 Cyg. To make the situation more interesting/complicated, the MOST light curve of RT Aurigae (a Cepheid pulsating in the fundamental mode) shows stellar oscillations in a highly repetitive manner.


Empirical solar/stellar cycle simulations

Authors. Angela R. G. Santos, Margarida S. Cunha, Pedro P. Avelino

Journal. EPJ Web of Conferences

Abstract. As a result of the magnetic cycle, the properties of the solar oscillations vary periodically. With the recent discovery of manifestations of activity cycles in the seismic data of other stars, the understanding of the different contributions to such variations becomes even more important. With this in mind, we built an empirical parameterised model able to reproduce the properties of the sunspot cycle. The resulting simulations can be used to estimate the magnetic-induced frequency shifts.


The HERMES Solar Atlas and the spectroscopic analysis of the seismic solar analogue KIC3241581

Authors. Beck, P. G.; Allende Prieto, C.; Van Reeth, T.; Tkachenko, A.; Raskin, G.; van Winckel, H.; do Nascimento, J.-D., Jr.; Salabert, D.; Corsaro, E.; Garcia, R. A.

Journal. Astronomy and Astrophysics

Abstract. Solar-analog stars provide an excellent opportunity to study the Sun’s evolution, i.e. the changes with time in stellar structure, activity, or rotation for solar-like stars. The unparalleled photometric data from the NASA space telescope Kepler allows us to study and characterise solar-like stars through asteroseismology. We aim to spectroscopically investigate the fundamental parameter and chromospheric activity of solar analogues and twins, based on observations obtained with the HERMES spectrograph and combine them with asteroseismology. Therefore, we need to build a solar atlas for the spectrograph, to provide accurate calibrations of the spectroscopically determined abundances of solar and late type stars observed with this instrument and thus perform differential spectral comparisons. We acquire high-resolution and high signal-to-noise spectroscopy to construct three solar reference spectra by observing the reflected light of Vesta and Victoria asteroids and Europa (100<S/N<450) with the \Hermes spectrograph. We then observe the Kepler solar analog KIC3241581 (S/N~170). We constructed three solar spectrum atlases from 385 to 900 nm obtained with the Hermes spectrograph from observations of two bright asteroids and Europa. A comparison between our solar spectra atlas to the Kurucz and HARPS solar spectrum shows an excellent agreement. KIC3241581 was found to be a long-periodic binary system. The fundamental parameter for the stellar primary component are Teff=5689+/-11K, logg=4.385+/-0.005, [Fe/H]=+0.22+/-0.01, being in agreement with the published global seismic values confirming its status of solar analogue. KIC 3241581 is a metal rich solar analogue with a solar-like activity level in a binary system of unknown period. The chromospheric activity level is compatible to the solar magnetic activity.

Links.  A&A, NASA ADSarXiv

Patterns, an efficient way to analyse the p-mode content in rapidly rotating stars

Authors. A. García Hernández, F. Lignières, L. Balona, D. R. Reese, M. J. P. F. G. Monteiro, J. C. Suárez and J. Ballot

Journal.  EPJ Web of Conferences

Abstract. High precision photometric observations from space has led to the detection of hundreds of frequencies in the light curves of δ Scuti pulsators. In this work, we analyzed a sample of Kepler δ Sct stars to search for frequency patterns in the p-mode regime. To avoid g-modes, we looked at the mode density histogram (MDH). We then used the Fourier transform technique (FT), histograms of frequency differences (HFD) and Echelle diagrams (ED) to find periodicities in the frequency content. We compared the results with those expected for SCF rotating models [4] with the aim of identifying large separations and rotational splittings.