1,721,266 research outputs found
Constraints on Be star geometry form combined photometric, IR excess, and optical polarimetry data
No full textConstraints on Be star geometry form combined photometric, IR excess, and optical polarimetry data
No full textEstimating stellar-oscillation-related parameters and their uncertainties with the moment method
No full textThe moment method is a well-known astronomical mode identification technique in asteroseismology which uses a time series of the first three moments of a spectral line to estimate the discrete oscillation mode parameters "l" and "m". The method, in contrast with many other mode identification techniques, also provides estimates of other important continuous parameters such as the inclination angle "&agr;" and the rotational velocity "v" e. We developed a statistical formalism for the moment method based on so-called generalized estimating equations. This formalism allows an estimation of the uncertainty of the continuous parameters, taking into account that the different moments of a line profile are correlated and that the uncertainty of the observed moments also depends on the model parameters. Furthermore, we set up a procedure to take into account the mode uncertainty, i.e. the fact that often several modes ("l", "m") can adequately describe the data. We also introduce a new lack-of-fit function which works at least as well as a previous discriminant function, and which in addition allows us to identify the sign of the azimuthal order "m". We applied our method to star HD181558 by using several numerical methods, from which we learned that numerically solving the estimating equations is an intensive task. We report on the numerical results, from which we gain insight in the statistical uncertainties of the physical parameters that are involved in the moment method. Copyright 2005 Royal Statistical Society.
Astrophysical properties of 15062 Gaia DR3 gravity-mode pulsators: pulsation amplitudes, rotation, and spectral line broadening
Full text linkGravito-inertial asteroseismology saw its birth thanks to high-precision
CoRoT and Kepler space photometric light curves. So far, it gave rise to the
internal rotation frequency of a few hundred intermediate-mass stars, yet only
several tens of these have been weighed, sized, and age-dated with high
precision from asteroseismic modelling. We aim to increase the sample of
optimal targets for future gravito-inertial asteroseismology by assessing the
properties of 15062 newly found Gaia DR3 gravity-mode pulsators. We also wish
to investigate if there is any connection between their fundamental parameters
and dominant mode on the one hand, and their spectral line broadening measured
by Gaia on the other hand. After re-classifying about 22% of the F-type
gravity-mode pulsators as B-type according to their effective temperature, we
construct histograms of the fundamental parameters and mode properties of the
15062 new Gaia DR3 pulsators. We compare these histograms with those of 63
Kepler bona fide class members. We fit errors-in-variables regression models to
couple the effective temperature, luminosity, gravity, and oscillation
properties to the two Gaia DR3 parameters capturing spectral line broadening
for a fraction of the pulsators. We find that the selected 15062 gravity-mode
pulsators have properties fully in line with those of their well-known Kepler
analogues, revealing that Gaia has a role to play in asteroseismology. The
dominant g-mode frequency is a significant predictor of the spectral line
broadening for the class members having this quantity measured. We show that
the Gaia vbroad parameter captures the joint effect of time-independent
intrinsic and rotational line broadening and time-dependent tangential
pulsational broadening. Gaia was not desiged to detect non-radial oscillations,
yet its homogeneous data treatment allow us to identify many new gravity-mode
pulsators.Comment: 17 pages, 10 figures, 10 tables. Manuscript accepted for publication
in Astronomy & Astrophysics. Two datafiles will be made available via CDS;
they can already be requested from the main autho
Estimating stellar parameters from spectra - 1. Goodness-of-fit parameters and lack-of-fit test
Full text linkEstimating stellar parameters from spectrophotometric data is a key tool in the study of stellar structure and stellar evolution. Although many methods have been proposed to estimate stellar parameters from ultraviolet (UV), optical and infrared (IR) data using low, medium or high-resolution observational data of the target(s), only a few address the problem of the uncertainties in the stellar parameters. This information is critical for a meaningful comparison of the derived parameters with results obtained from other data and/or methods. Here we present a frequentist method to estimate these uncertainties. We demonstrate that the combined use of both a local and a global goodness-of-fit parameter alters the uncertainty intervals as determined from the use of only one of these deviation estimating parameters. This technique using both goodness-of-fit parameters is applied to the infrared 2.38-4.08 mum ISO-SWS data (Infrared Space Observatory - Short Wavelength Spectrometer) of alpha Boo yielding an effective temperature range from 4160 K to 4300 K, a logarithm of the gravity range from 1.35 to 1.65 dex and a metallicity from -0.30 to 0.00 dex. However, using a lack-of-fit test, it is shown that even the "best" theoretical models are still not capable of capturing all the structure in the data, and this is due to our incomplete knowledge and modelling of the full physical stellar structure or due to problems in the data reduction process.status: Publishe
Asteroseismic versus Gaia distances: A first comparison
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162622.pdf (Publisher’s version ) (Closed access
Asteroseismologie van OB sterren met de CoRoT ruimte missie.
No full textThe CoRoT space telescope monitors the brightness of the stars continuously and with unprecedented quality. For the first time, variability measurements of massive stars have been obtained with micromagnitude precision, allowing for detailed seismic studies of hot stars in the instability strips to uncover the internal structure.After describing a wide range of relevant observational techniques to fully exploit the acquired data, we present analyses and seismic interpretations of specific stars observed by the CoRoT space as part of the seismology program. To achieve a full exploration of the instability strips, we traverse the Hertzsprung-Russel diagram from the hot to the cool side, via an O-type binary system and a Beta Cep star, to a hybrid pulsator and a small sample of late B-type stars.The discovery of solar-like oscillations in massive stars opens up the possibility of finding a new set of seismic constraints on massive star models. Via the detection of gravity mode period spacings, we were able to describe the mixing processes around the convective core of a massive star. Finally, the late type stars showed unexpected variability, possibly attributed to rotational modulation, e.g., due to spots on the surface of these stars.status: Publishe
Simulaties en software algoritmes voor ruimtemissies: ontwerp van een sterrenkundige multi-missie instrumentsimulator
No full textI. Study of data reduction and analysis of ACS/HST in UV line and continuum data for low-mass accreting T Tauri stars.II. Definition and implementation of a global software simulation package to assess and evaluate the performances of various detectors (CCD, CMOS,...) for high-precision measurements of various types of stars, applicable to both space and ground-based instrumentation. Application of this tool to the science detectors of the ESA M3 selected mission PLATO.status: Publishe
Automatische classificatie van variabele sterren: Toepassing op de OGLE en CoRoT databases.
Full text linkThe rapid developments in astronomical instrumentation and data acquisit ion techniques during the last decades, have been creating increasingly large volumes of data. The use of automated space or ground-based telesc opes in combination with high resolution CCD (Charge Coupled Device) ima gers, allows to accurately survey the sky in a very fast and efficient w ay. It seems that many of the currently used data analysis techniques ca nnot keep up with the exponentially growing accumulation rate of new dat a. In fact, we risk that much of the potential science, present in the d ata, is left unexplored. The way to reduce this discrepancy is the use o f efficient automated data-mining techniques. Currently, big efforts are undertaken in this direction, but a lot still remains to be done and in vestigated. The use of automated techniques, even very sophisticated one s, does not make the humain brain obsolete, in the sense that the real s cience is still done by a scientist. Both the development of the techniq ues, and the interpretation of the results produced, requires domain kno wledge. The real benefit of automated methods is their ability to perfor m certain tasks much faster than a human can ever do. Some tasks can onl y be done with CPU power. An important, and commonly used data-mining technique, is the automated classification of `objects' into a number of pre-defined classes. This thesis describes the application of these so called `supervised cla ssification' techniques to the field of stellar variability, and in part icular, to light curves of variable stars. The methodology was developed in preparation of the CoRoT space mission (Convection, Rotation and pla netary Transits), launched successfully on 27 December 2006. The main sc ientific goals of this mission are asteroseismology and the search for e xoplanets. A large database of high quality light curves is produced as a by-product of the exoplanet search. We have applied our methods to the first four fields observed by CoRoT, in total about 40000 light curves. The development of the methods was done before any CoRoT data were avai lable. We used the OGLE database (Optical Gravitational Lensing Experime nt) to evaluate the performance of the classifiers, showing at the same time their flexibility: they can be applied to databases of light curves produced by completely different instruments and with a variety of diff erent characteristics, usually with only minor adaptations. This work contains the methodology developed and its application to the OGLE and CoRoT exoplanet databases.status: Publishe
Calibratie van de CoRoT satelliet. Correctie van de fotometrie voor richtingsschommelingen en variaties in de achtergrond.
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