16 research outputs found
Self-consistent method to extract non-linearities from pulsating stars light curves I. Combination frequencies
Combination frequencies are not solutions of the perturbed stellar structure
equations. In dense power spectra from a light curve of a given multi-periodic
pulsating star, they can compromise the mode identification in an asteroseismic
analysis, hence they must be treated as spurious frequencies and conveniently
removed. In this paper, a method based on fitting the set of frequencies that
best describe a general non-linear model, like the Volterra series, is
presented. The method allows to extract these frequencies from the power
spectrum, so helping to improve the frequency analysis enabling hidden
frequencies to emerge from the initially considered as noise. Moreover, the
method yields frequencies with uncertainties several orders of magnitude
smaller than the Rayleigh dispersion, usually taken as the present error in a
standard frequency analysis. Furthermore, it is compatible with the classical
counting cycles method, the so-called O-C method, which is valid only for
mono-periodic stars. The method opens the possibility to characterise the
non-linear behaviour of a given pulsating star by studying in detail the
complex generalised transfer functions.Comment: 10 pages, 4 figures. Submitted to MNRA
Impact of gaps in the asteroseismic characterization of pulsating stars. I. On the efficiency of pre-whitening
It is known that the observed distribution of frequencies in CoRoT and Kepler
{\delta} Scuti stars has no parallelism with any theoretical model.
Pre-whitening is a widespread technique in the analysis of time series with
gaps from pulsating stars located in the classical instability strip such as
{\delta} Scuti stars. However, some studies have pointed out that this
technique might introduce biases in the results of the frequency analysis. This
work aims at studying the biases that can result from pre-whitening in
asteroseismology. The results will depend on the intrinsic range and
distribution of frequencies of the stars. The periodic nature of the gaps in
CoRoT observations, just in the range of the pulsational frequency content of
the {\delta} Scuti stars, is shown to be crucial to determine their oscillation
frequencies, the first step to perform asteroseismolgy of these objects. Hence,
here we focus on the impact of pre-whitening on the asteroseismic
characterization of {\delta} Scuti stars. We select a sample of 15 {\delta}
Scuti stars observed by the CoRoT satellite, for which ultra-high quality
photometric data have been obtained by its seismic channel. In order to study
the impact on the asteroseismic characterization of {\delta} Scuti stars we
perform the pre-whitening procedure on three datasets: gapped data, linearly
interpolated data, and ARMA interpolated data. The different results obtained
show that at least in some cases pre-whitening is not an efficient procedure
for the deconvolution of the spectral window. therefore, in order to reduce the
effect of the spectral window to the minimum it is necessary to interpolate
with an algorithm that is aimed to preserve the original frequency content, and
not only to perform a pre-whitening of the data.Comment: 27 pages, 47 figures Tables and typos fixe
Rotation and pulsation in Ap stars: first light results from TESS sectors 1 and 2
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 micromag, 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.We thank the referee for very detailed and useful comments to the original manuscript. This work was supported by FCT - Fundação para a Ciência e a Tecnologia through national funds and by FEDER through COMPETE2020 - Programa Operacional Competitividade e Internacionalização
by these grants: UID/FIS/04434/2019, PTDC/FIS-AST/30389/2017 & POCI-01- 0145-FEDER-030389. MC is supported in the form of work contract funded by national funds through FCT. Funding for the Stellar Astrophysics Centre is provided by The Danish National Research Foundation (Grant agreement no.: DNRF106). DLH and DWK acknowledge financial support from the Science and Technology Facilities Council (STFC) via grant ST/M000877/1. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. LFM acknowledges support from the UNAM by the way of DGAPA project PAPIIT IN100918. The research leading to these results has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement N 670519: MAMSIE) and from the Fonds Wetenschappelijk Onderzoek - Vlaanderen (FWO) under the grant agreement G0H5416N (ERC Opvangproject). MS acknowledges the financial support of Postdoc@MUNI project CZ.02.2.69/0.0/0.0/16 027/0008360. EN acknowledges the Polish National Science Center grants no.2014/13/B/ST9/00902. JCS acknowledges funding support from Spanish public funds for research under projects ESP2017-87676-2-2 and ESP2015- 65712-C5-5-R, and from project RYC-2012-09913 under the ‘Ramón y Cajal’ program of the Spanish Ministry of Science and Education. AGH acknowledges funding support from Spanish public funds for research under projects ESP2017-87676-2-2 and ESP2015-65712-C5-5-R of the Spanish Ministry of Science and Education. A´ S, ZsB, and RSz acknowledge the financial support of the GINOP-2.3.2-15-2016- 00003, K-115709, K-113117, K-119517 and PD-123910 grants of the Hungarian National Research, Development and Innovation Office (NKFIH), and the Lendület Program of the Hungarian Academy of Sciences, project No. LP2018-7/2018. GH has been supported by the Polish NCN grant 2015/18/A/ST9/00578. MLM acknowledges funding support from Spanish public funds for research under project ESP2015- 65712-C5-3-R. JPG acknowledges funding support from Spanish public funds for research under project ESP2017-87676-C5-5-R. MLM and JPG also acknowledges funding support from the State Agency for Research of the Spanish MCIU through the ”Center of Excellence Severo Ochoa” award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709). IS acknowledges funding support of NSF under projects DN 08-1/2016 and DN 18/13-12.12.2017. P. Kołaczek-Szymański acknowledges support from the NCN grant no. 2016/21/B/ST9/01126. This paper includes data collected by the TESS mission. Funding for the TESS mission is provided by the NASA Explorer Program
The PL diagram for Sct stars: back in business as distance estimators
In this work, we focus on the period-luminosity relation (PLR) of
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 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 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 Sct, thus shedding some light on their
elusive mode selection mechanism.Comment: 10 pages, 5 figures, 1 table, IAU conference proceedin
Toward a New Paradigm in the Analysis of Asteroseismic Lightcurves
This paper aims at being a provocative guide to the future of asteroseismology from the
perspective of the analysis of time series, where the fundamentals of harmonic analysis
are subjected to stress tests. In this context, we give an annotated summary of our
research over the last decades on harmonic analysis of A-F stars. We discuss and explore
the consequences of our findings, which may extend to any kind of pulsators. As well, we
analyse the impact of this reconsideration on future asteroseismic studies, which would
entail a paradigm shift. This includes a discussion on the presence of fractal behavior in
δ Sct stars, and how this can be used to develop a stopping criterion of the pre-whitening
process, as an alternative to SNR (or significance) criterion. Drilling a scientific paradigm
has its natural resilience, hence the path described here is being arduous, although fruitful
at the same time.SF, JP-G, JR, ML-M, and RG acknowledges financial support
from the State Agency for Research of the Spanish MCIU
through the Center of Excellence Severo Ochoa award for
the Instituto de Astrofísica de Andalucía (SEV-2017-0709) and
Spanish public funds for research under projects ESP2015-65712-
C5-5-R. JS and AG acknowledge funding support from Spanish
public funds for research under projects ESP2017-87676-C5-2-
R. JS also acknowledges funding support from project RYC2012-09913 under the Ramón y Cajal program of the Spanish
MINECO. AG acknowledges support from Universidad de
Granada under project E-FQM-041-UGR18 from the Programa
Operativo FEDER 2014–2020 programme by Junta de Andalucía
regional Government
<em>TESS</em> Cycle 2 observations of roAp stars with 2-min cadence data
\ua9 The Author(s) 2023.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 multiepoch 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
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
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
Rotation and pulsation in Ap stars: first light results from TESS sectors 1 and 2
We present the first results from the Transiting Exoplanet Survey Satellite (TESS) on the ro- tational 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 pulsa-
tions 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 ro-
tation 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
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