6 research outputs found
Stellar evolution through the ages: period variations in galactic RRab stars as derived from the GEOS database and TAROT telescopes
The theory of stellar evolution can be more closely tested if we have the
opportunity to measure new quantities. Nowadays, observations of galactic RR
Lyr stars are available on a time baseline exceeding 100 years. Therefore, we
can exploit the possibility of investigating period changes, continuing the
pioneering work started by V. P. Tsesevich in 1969. We collected the available
times of maximum brightness of the galactic RR Lyr stars in the GEOS RR Lyr
database. Moreover, we also started new observational projects, including
surveys with automated telescopes, to characterise the O-C diagrams better. The
database we built has proved to be a very powerful tool for tracing the period
variations through the ages. We analyzed 123 stars showing a clear O-C pattern
(constant, parabolic or erratic) by means of different least-squares methods.
Clear evidence of period increases or decreases at constant rates has been
found, suggesting evolutionary effects. The median values are beta=+0.14
day/Myr for the 27 stars showing a period increase and beta=-0.20 day/Myr for
the 21 stars showing a period decrease. The large number of RR Lyr stars
showing a period decrease (i.e., blueward evolution) is a new and intriguing
result. There is an excess of RR Lyr stars showing large, positive
values. Moreover, the observed beta values are slightly larger than those
predicted by theoretical models.Comment: 15 pages, 9 figures; to be published in Astronomy and Astrophysics;
full resolution version available at
http://dbrr.ast.obs-mip.fr/tarot/publis/publis.htm
The all-sky GEOS RR Lyr survey with the TAROT telescopes. Analysis of the Blazhko effect
We used the GEOS database to study the Blazhko effect of galactic RRab stars.
The database is continuously enriched by maxima supplied by amateur astronomers
and by a dedicated survey by means of the two TAROT robotic telescopes. The
same value of the Blazhko period is observed at different values of the
pulsation periods and different values of the Blazhko periods are observed at
the same value of the pulsation period. There are clues suggesting that the
Blazhko effect is changing from one cycle to the next. The secular changes in
the pulsation and Blazhko periods of Z CVn are anticorrelated. The diagrams of
magnitudes against phases of the maxima clearly show that the light curves of
Blazhko variables can be explained as modulated signals, both in amplitude and
in frequency. The closed curves describing the Blazhko cycles in such diagrams
have different shapes, reflecting the phase shifts between the epochs of the
brightest maximum and the maximum O-C. Our sample shows that both clockwise and
anticlockwise directions are possible for similar shapes. The improved
observational knowledge of the Blazhko effect, in addition to some
peculiarities of the light curves, have still to be explained by a satisfactory
physical mechanism.Comment: 13 pages, 12 figures, accepted for publication in Astronomical
Journa
Maxima of RR Lyr stars from AAVSO International Database
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