Mathematics – Logic
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008coast.157...24k&link_type=abstract
Communications in Asteroseismology, Vol.157, p. 24-28
Mathematics
Logic
Scientific paper
The study of pulsating stars through photometric observations, specially time series pho- tometry, has grown from visual to single channel photometry, double and triple channel and finally CCD photometry. The continuous measurement of the pulsating star, simultaneously with accurate sky measurements and several comparison stars, has allowed a huge increase in the detectability of low amplitude pulsations, and the possible correction of thin cloud and atmospheric variability, which can occur at timescales of minutes, due to g-modes on the Earth atmosphere. It has also been crucial to be able to use comparisons brighter than the target star and less than a few arcminutes from the pulsating star, decreasing the noise introduced in the differential photometry due to noise in the comparisons. On 4m class tele- scopes, and prime focus on 2m class telescopes, we can routinely achieve 1 mmag precision up to 19th mag stars, allowing the study of distant stars and possibly different populations. To be able to measure multiple periods present in non-radially pulsating stars, it is necessary to observe the star for several beat periods, and multi-site campaigns, with networks such as the Delta Scuti Network and the Whole Earth Telescope, for example, have allowed such long observations, lasting of the order of two to five months. On the data analysis side, corrections of the observations times to the barycenter of the solar system became necessary to join long data sets, and Monte Carlo simulations of the time series allowed an efficient way to estimate the detection limits for time series with gaps and multiperiodic, where the noise distribution is not Poissonic. The discovery of many pulsation modes in nonradially pulsating stars, as Delta Scuti, roAp, the Sun and white dwarf stars, has allowed seismological studies measur- ing accurately several internal properties of these pulsating stars, as each mode of pulsation is an independent measurement of the stellar structure, and both g-modes and p-modes in general sample a large fraction of the star. It has become evident that most types of pulsators show amplitude variations on timescales of weeks to years, even when we can untangle the individual modes, i.e., correct by the beating of nearby modes. These changes are most likely on timescales comparable to the growth timescales of the different modes and should carry detailed information on the instability mechanism. White dwarf pulsators show the largest number of pulsation modes detected after the Sun. Their study has allowed a strong test on stellar evolution and high density physics, including their secular time change rate, placing these stars in levels comparable to large collider experiments.
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