406 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.
Estimating stellar parameters from spectra - 1. Goodness-of-fit parameters and lack-of-fit test
No full textEstimating 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
Probability distributions of initial rotation velocities and core-boundary mixing efficiencies of γ Doradus stars
No full text<p>MESA setup for models of rotating gamma Doradus stars, as described in Mombarg, Aerts & Molenberghs (2024, A&A). The text file contains a shear profile computed the ESTER code (see Mombarg et al. 2022, ApJ, 925, 154) that is used for the computation of rotational mixing. </p>
Backtracking the evolution of subdwarf B stars with asteroseismology
No full textContains fulltext :
75138.pdf (Publisher’s version ) (Open Access)Radboud Universiteit Nijmegen, 06 oktober 2009Promotor : Aerts, C.C. Co-promotor : Nelemans, G.A.121 p
Astrophysical properties of 15062 Gaia DR3 gravity-mode pulsators: pulsation amplitudes, rotation, and spectral line broadening
No full textGravito-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
Asteroseismic versus Gaia distances: A first comparison
No full textContains fulltext :
162622.pdf (Publisher’s version ) (Closed access
Physical Parameters of the Overcontact Binary AH Cnc in the Old Open Cluster M 67
No full textContains fulltext :
35571.pdf (Publisher’s version ) (Closed access)We present a photometric study of the overcontact binary AH Cnc. The CCD observations were done with the Russian-Turkish 1.5 m telescope and the light-curve was solved with the Wilson-Devinney code. The physical parameters of the components have been deduced as M1 = 1.22 Msun, M2 = 0.20 Msun, R1 = 1.37 Rsun, R2 = 0.66 Rsun, L1 = 2.65 Lsun and L2 = 0.63 Lsun from the obtained orbital parameters and the distance modules of M 67. AH Cnc has been compared with similar systems in the Hertzsprung-Russell diagram.Astrophysics of Variable Star
Blazhko Effect and Magnetic Field in RR Lyrae
No full textThe recent detection of a frequency splitting around the pulsation frequency and its harmonics points towards the magnetic model to explain the Blazhko effect. Here we show that it is urgent to confirm with modern observational techniques the existence of the magnetic field in RR Lyrae.sponsorship: RP :AERTS,C. : Katholieke Universiteit Leuven; Instituut voor Sterrenkunde, Celestijnenlaan 200B; B-3001 Leuven; Belgiumstatus: Publishe
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