Le Borgne J.F.,Toulouse 1 University Capitole |
Le Borgne J.F.,French National Center for Scientific Research |
Poretti E.,Toulouse 1 University Capitole |
Poretti E.,French National Center for Scientific Research |
And 24 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014
RR Lyr is one of the most studied variable stars. Its light curve has been regularly monitored since the discovery of its periodic variability in 1899. The analysis of all observed maxima allows us to identify two primary pulsation states, defined as pulsation over a long (P0 longer than 0.56684 d) and a short (P0 shorter than 0.56682 d) primary pulsation period. These states alternate with intervals of 13-16 yr, and are well defined after 1943. The 40.8-d periodical modulations of the amplitude and the period (i.e. the Blazhko effect) were noticed in 1916.We provide homogeneous determinations of the Blazhko period in the different primary pulsation states. The Blazhko period does not follow the variations of P0 and suddenly diminished from 40.8 d to around 39.0 d in 1975. The monitoring of these periodicities deserved, and still deserves, a continuous and intensive observational effort. For this purpose, we have built dedicated, transportable and autonomous small instruments, Very Tiny Telescopes (VTTs), to observe the times of maximum brightnessof RR Lyr. As immediate results, the VTTs recorded the last change of the P0 state in mid-2009 and extended the time coverage of the Kepler observations, thus recording a maximumO-C amplitude of the Blazhko effect at the end of 2008, followed by the historically smallest O-C amplitude in late 2013. This decrease is still ongoing and the VTTs are ready to monitor the expected increase in the next few years. © 2014 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society.
Scheirich P.,Academy of Sciences of the Czech Republic |
Durech J.,Charles University |
Pravec P.,Academy of Sciences of the Czech Republic |
Kozubal M.,Clay Center Observatory |
And 7 more authors.
Meteoritics and Planetary Science | Year: 2010
On October 6, 2008, a small F-class asteroid 2008 TC3 was discovered by Catalina Sky Survey telescope, and exploded 20-hr later in the Earth's atmosphere at 37-km altitude. We analyzed available photometric data taken from 6 October 21:10 to 7 October 01:46-UT, and created a numerical model of a shape and rotation state of the asteroid. The asteroid was in excited rotational state. We found two approximately mirror solutions of orientation of its angular momentum vector. Rotational and precession periods are 99.20 and 97.00-s (errors of the rotational period for the two solutions are 0.03 and 0.04-s; of the precession period are 0.05-s for both solutions). The volume of the convex model and the length of the longest axis of the dynamically equivalent, equal volume ellipsoid are and, where pV is surface geometric albedo. Assuming a mean albedo value for F taxonomic class, 0.049-±-0.010, the volume is (25-±-10)-m3 and the longest axis is (6.7-±-0.8)-m. This volume of the convex model is an upper limit on a real volume of the asteroid, which may be less by up to 20% due to concavities. © The Meteoritical Society, 2010.
Le Borgne J.-F.,Toulouse 1 University Capitole |
Le Borgne J.-F.,French National Center for Scientific Research |
Klotz A.,Toulouse 1 University Capitole |
Klotz A.,French National Center for Scientific Research |
And 13 more authors.
Astronomical Journal | Year: 2012
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 counterclockwise directions are possible for similar shapes. The improved observational knowledge of the Blazhko effect, in addition to some peculiarities of the light curves, has yet to be explained by a satisfactory physical mechanism. © © 2012. The American Astronomical Society. All rights reserved.