51 research outputs found
CoRoT reveals a magnetic activity cycle in a Sun-like star
The 11-year activity cycle of the Sun is a consequence of a dynamo process
occurring beneath its surface. We analyzed photometric data obtained by the
CoRoT space mission, showing solar-like oscillations in the star HD49933, for
signatures of stellar magnetic activity. Asteroseismic measurements of global
changes in the oscillation frequencies and mode amplitudes reveal a modulation
of at least 120 days, with the minimum frequency shift corresponding to maximum
amplitude as in the Sun. These observations are evidence of a stellar magnetic
activity cycle taking place beneath the surface of HD49933 and provide
constraints for stellar dynamo models under conditions different from those of
the Sun.Comment: Brevia text and supporting online material, published in Scienc
Probing the Deep End of the Milky Way with New Oscillating Kepler Giants
The Kepler mission has been a success in both exoplanet search and stellar
physics studies. Red giants have actually been quite a highlight in the Kepler
scene. The Kepler long and almost continuous four-year observations allowed us
to detect oscillations in more than 15,000 red giants targeted by the mission.
However by looking at the power spectra of 45,000 stars classified as dwarfs
according to the Q1-16 Kepler star properties catalog, we detected red-giant
like oscillations in 850 stars. Even though this is a small addition to the
known red-giant sample, these misclassified stars represent a goldmine for
galactic archeology studies. Indeed they happen to be fainter (down to Kp~16)
and more distant (d>10kpc) than the known red giants, opening the possibility
to probe unknown regions of our Galaxy. The faintness of these red giants with
detected oscillations is very promising for detecting acoustic modes in red
giants observed with K2 and TESS. In this talk, I will present this new sample
of red giants with their revised stellar parameters derived from
asteroseismology. Then I will discuss about the distribution of their masses,
distances, and evolutionary states compared to the previously known sample of
red giants.Comment: 5 pages, 4 figures, Proceedings of the KASC9-TASC2 meetin
Investigating the properties of granulation in the red giants observed by Kepler
More than 1000 red giants have been observed by NASA/Kepler mission during a
nearly continuous period of ~ 13 months. The resulting high-frequency
resolution (< 0.03 muHz) allows us to study the granulation parameters of these
stars. The granulation pattern results from the convection motions leading to
upward flows of hot plasma and downward flows of cooler plasma. We fitted
Harvey-like functions to the power spectra, to retrieve the timescale and
amplitude of granulation. We show that there is an anti-correlation between
both of these parameters and the position of maximum power of acoustic modes,
while we also find a correlation with the radius, which agrees with the theory.
We finally compare our results with 3D models of the convection.Comment: 4 pages, 1 figure. To appear in the ASP proceedings of "The 61st
Fujihara seminar: Progress in solar/stellar physics with helio- and
asteroseismology", 13th-17th March 2011, Hakone, Japa
Seismic analysis of four solar-like stars observed during more than eight months by Kepler
Having started science operations in May 2009, the Kepler photometer has been
able to provide exquisite data of solar-like stars. Five out of the 42 stars
observed continuously during the survey phase show evidence of oscillations,
even though they are rather faint (magnitudes from 10.5 to 12). In this paper,
we present an overview of the results of the seismic analysis of 4 of these
stars observed during more than eight months.Comment: 5 pages, 1 figure. To appear in the ASP proceedings of "The 61st
Fujihara seminar: Progress in solar/stellar physics with helio- and
asteroseismology", 13th-17th March 2011, Hakone, Japa
Unveiling stellar magnetic activity using CoRoT seismic observations
International audienceIt is well known that in the Sun, the frequencies and amplitudes of acoustic modes vary throughout the solar cycle. Indeed, while the magnetic activity goes towards its maximum, the frequencies of the modes increase and their amplitudes decrease. We have analyzed data from the CoRoT mission on a few stars that exhibit solar-like oscillations. The study of HD49933 (observed during 60 days and 137 days spanning a total of 400 days) showed a modulation of the maximum amplitude per radial mode and the frequency shifts of the modes, showing magnetic activity in this rapidly rotating star. Moreover, both properties vary in an anticorrelated way and the data allowed us to establish a lower limit for the activity-cycle period of 120 days. Measurements in Ca H and K lines confirmed that this star is in the "active stars" category. We will also discuss the results obtained for other targets such as HD181420 and HD49835 for which we have investigated a similar behavior
Probing the Deep End of the Milky Way with New Oscillating Kepler Giants
The Kepler mission has been a success in both exoplanet search and stellar physics studies. Red giants have actually been quite a highlight in the Kepler scene. The Kepler long and almost continuous four-year observations allowed us to detect oscillations in more than 15,000 red giants targeted by the mission. However by looking at the power spectra of 45,000 stars classified as dwarfs according to the Q1–16 Kepler star properties catalog, we detected red-giant like oscillations in 850 stars. Even though this is a small addition to the known red–giant sample, these misclassified stars represent a goldmine for galactic archeology studies. Indeed they happen to be fainter (down to Kp~16) and more distant (d>10kPc) than the known red giants, opening the possibility to probe unknown regions of our Galaxy. The faintness of these red giants with detected oscillations is very promising for detecting acoustic modes in red giants observed with K2 and TESS. In this talk, I will present this new sample of red giants with their revised stellar parameters derived from asteroseismology. Then I will discuss about the distribution of their masses, distances, and evolutionary states compared to the previously known sample of red giants
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