-
K. Zwintz,
L. Fossati,
D. B. Guenther,
T. Ryabchikova,
A. Baglin,
N. Themessl,
T. G. Barnes,
J. M. Matthews, M. Auvergne,
D. Bohlender,
S. Chaintreuil,
R. Kuschnig,
A. F. J. Moffat,
J. F. Rowe,
S. M. Rucinski,
D. Sasselov,
W. W. Weiss
[show abstract]
[hide abstract]
ABSTRACT: We concentrate on an asteroseismological study of HD 261711, a rather hot
delta Scuti type pulsating member of the young open cluster NGC 2264 located at
the blue border of the instability region. HD 261711 was discovered to be a
pre-main sequence delta Scuti star using the time series photometry obtained by
the MOST satellite in 2006. High-precision, time-series photometry of HD 261711
was obtained by the MOST and CoRoT satellites in 4 separate new observing runs
that are put into context with the star's fundamental atmospheric parameters
obtained from spectroscopy. With the new MOST data set from 2011/12 and the two
CoRoT light curves from 2008 and 2011/12, the delta Scuti variability was
confirmed and regular groups of frequencies were discovered. The two pulsation
frequencies identified in the data from the first MOST observing run in 2006
are confirmed and 23 new delta Scuti-type frequencies were discovered using the
CoRoT data. Weighted average frequencies for each group are related to l=0 and
l=1 p-modes. Evidence for amplitude modulation of the frequencies in two groups
is seen. The effective temperature was derived to be 8600$\pm$200 K, log g is
4.1$\pm$0.2, and the projected rotational velocity is 53$\pm$1km/s. Using our
Teff value and the radius of 1.8$\pm$0.5 Rsun derived from SED fitting, we get
a log L/Lsun of 1.20$\pm$0.14 which agrees well to the seismologically
determined values of 1.65 Rsun and, hence, a log L/Lsun of 1.13. The radial
velocity of 14$\pm$2 km/s we derived for HD 261711, confirms the star's
membership to NGC 2264. Our asteroseismic models suggest that HD 261711 is a
delta Scuti-type star close to the zero-age main sequence (ZAMS) with a mass of
1.8 to 1.9Msun. HD 261711 is either a young ZAMS star or a late PMS star just
before the onset of hydrogen-core burning.
02/2013;
-
[show abstract]
[hide abstract]
ABSTRACT: With the space-borne missions CoRoT and Kepler, a large amount of
asteroseismic data is now available. So-called global oscillation parameters
are inferred to characterize the large sets of stars, to perform ensemble
asteroseismology, and to derive scaling relations. The mean large separation is
such a key parameter. It is therefore crucial to measure it with the highest
accuracy. As the conditions of measurement of the large separation do not
coincide with its theoretical definition, we revisit the asymptotic expressions
used for analysing the observed oscillation spectra. Then, we examine the
consequence of the difference between the observed and asymptotic values of the
mean large separation. The analysis is focused on radial modes. We use series
of radial-mode frequencies to compare the asymptotic and observational values
of the large separation. We propose a simple formulation to correct the
observed value of the large separation and then derive its asymptotic
counterpart. We prove that, apart from glitches due to stellar structure
discontinuities, the asymptotic expansion is valid from main-sequence stars to
red giants. Our model shows that the asymptotic offset is close to 1/4, as in
the theoretical development. High-quality solar-like oscillation spectra
derived from precise photometric measurements are definitely better described
with the second-order asymptotic expansion. The second-order term is
responsible for the curvature observed in the \'echelle diagrams used for
analysing the oscillation spectra and this curvature is responsible for the
difference between the observed and asymptotic values of the large separation.
Taking it into account yields a revision of the scaling relations providing
more accurate asteroseismic estimates of the stellar mass and radius.
12/2012;
-
H. Lammer,
R. Dvorak,
M. Deleuil,
P. Barge,
H. J. Deeg,
C. Moutou,
A. Erikson,
Sz. Csizmadia,
B. Tingley,
H. Bruntt, [......],
D. Rouan,
B. Samuel,
J. Schneider,
A. Shporer,
B. Stecklum,
M. Steller,
R. Street,
S. Udry,
J. Weingrill,
G. Wuchterl
Solar System Research 05/2012; 45(4):374-375. · 0.68 Impact Factor
-
M Ollivier,
M Gillon,
A Santerne,
G Wuchterl,
M Havel,
H Bruntt,
P Bordé,
T Pasternacki,
M Endl,
D Gandolfi, [......],
M Pätzold,
D Queloz,
H Rauer,
D Rouan,
B Samuel,
J Schneider,
M Tadeu dos Santos,
L Tal-Or,
B Tingley,
J Weingrill
åp. 05/2012; 541:A149.
-
P. Degroote,
C. Aerts,
E. Michel,
M. Briquet,
P. I. Pápics,
P. Amado,
P. Mathias,
E. Poretti,
M. Rainer,
R. Lombaert,
M. Hillen,
T. Morel, M. Auvergne,
A. Baglin,
F. Baudin,
C. Catala,
R. Samadi
[show abstract]
[hide abstract]
ABSTRACT: B-type stars are promising targets for asteroseismic modelling, since their
frequency spectrum is relatively simple.
We deduce and summarise observational constraints for the hybrid pulsator,
HD50230, earlier reported to have deviations from a uniform period spacing of
its gravity modes. The combination of spectra and a high-quality light curve
measured by the CoRoT satellite allow a combined approach to fix the position
of HD50230 in the HR diagram.
To describe the observed pulsations, classical Fourier analysis was combined
with short-time Fourier transformations and frequency spacing analysis
techniques. Visual spectra were used to constrain the projected rotation rate
of the star and the fundamental parameters of the target. In a first
approximation, the combined information was used to interpret multiplets and
spacings to infer the true surface rotation rate and a rough estimate of the
inclination angle.
We identify HD50230 as a spectroscopic binary and characterise the two
components. We detect the simultaneous presence of high-order g modes and
low-order p and g-modes in the CoRoT light curve, but were unable to link them
to line profile variations in the spectroscopic time series. We extract the
relevant information from the frequency spectrum, which can be used for seismic
modelling, and explore possible interpretations of the pressure mode spectrum.
04/2012;
-
F. Carrier,
T. Morel,
A. Miglio,
J. Montalbán, M. Auvergne,
A. Baglin,
F. Baudin,
C. Barban,
C. Catala,
F. D’Antona, [......],
A. P. Hatzes,
S. Hekker,
T. Kallinger,
E. Michel,
A. Noels,
E. Poretti,
M. Rainer,
R. Samadi,
P. Ventura,
W. W. Weiss
[show abstract]
[hide abstract]
ABSTRACT: HR 7349 is a bright [V=5.8] red giant observed by CoRoT in the seismofield of the first long run. The outstanding CoRoT light curve allowed the
detection of several solar-like oscillation modes (both radial and non-radial). On top of these seismic constraints, our observational
knowledge on HR 7349 benefits as well from a precise parallax and detailed spectroscopic constraints. We present all the observational
constraints that are available for the theoretical modelling of this most promising target.
KeywordsStars: oscillations-Stars: variables-Stars: interiors
Astrophysics and Space Science 04/2012; 328(1):83-86. · 1.69 Impact Factor
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L Mantegazza,
E Poretti,
E Michel,
M Rainer,
F Baudin,
A García Hernández,
T Semaan,
M Alvarez,
P J Amado,
R Garrido,
P Mathias,
A Moya,
J C Suárez, M Auvergne,
A Baglin,
C Catala,
R Samadi
[show abstract]
[hide abstract]
ABSTRACT: Aims. We present the results obtained with the CoRoT satellite for HD 50870, a δ Sct star which was observed for 114.4 d. The aim of these observations was to evaluate the results obtained for HD 50844, the first δ Sct star monitored with CoRoT, on a longer time baseline. Methods. The 307,570 CoRoT datapoints were analysed with different techniques. The photometric observations were complemented over 15 nights of high-resolution spectroscopy with HARPS on a baseline of 25 d. These spectra were analysed to study the line profile variations and to derive the stellar physical parameters. Some uvby photometric observations were also obtained to better characterize the pulsation modes. Results. HD 50870 proved to be a low-amplitude, long-period spectroscopic binary system seen almost pole-on (i ≃ 21 o). The brighter component, which also has the higher rotational velocity (v sin i = 37.5 km s −1), is a δ Sct-type variable with a full light amplitude variation of about 0.04 mag. There is a dominant axisymmetric mode (17.16 d −1). Moreover, there are two groups of frequencies (about 19) in the intervals 6-9 and 13-18 d −1 , with amplitudes ranging from a few mmag to 0.3 mmag. After the detection of about 250 terms (corresponding to an amplitude of about 0.045 mmag) a flat plateau appears in the power spectrum in the low-frequency region up to about 35 d −1 . We were able to detect this plateau only thanks to the short cadence sampling of the CoRoT measurements (32 s). The density distribution vs. frequency of the detected frequencies seems rule out the possibility that this plateau is the result of a process with a continuum power spectrum. The spacings of the strongest modes suggest a quasi-periodic pattern. We failed to find a satisfactory seismic model that simultaneously matches the frequency range, the position in the HR diagram, and the quasi-periodic pattern interpreted as a large separation. Nineteen modes were detected spectroscopically from the line profile variations and associated to the photometric ones. Tentative ℓ, m values have been attributed to the modes detected spectroscopically. Prograde as well as retrograde modes are present with ℓ values up to 9. There are no traces of variability induced by solar-like oscillations.
04/2012;
-
P. I. Pápics,
M. Briquet,
A. Baglin,
E. Poretti,
C. Aerts,
P. Degroote,
A. Tkatchenko,
T. Morel,
W. Zima,
E. Niemczura,
M. Rainer,
M. Hareter,
F. Baudin,
C. Catala,
E. Michel,
R. Samadi, M. Auvergne
[show abstract]
[hide abstract]
ABSTRACT: Context. OB stars are important building blocks of the Universe, but we have
only a limited sample of them well understood enough from an
asteroseismological point of view to provide feedback on the current
evolutionary models. Our study adds one special case to this sample, with more
observational constraints than for most of these stars.
Aims. Our goal is to analyse and interpret the pulsational behaviour of the
B3 IV star HD 43317 using the CoRoT light curve along with the ground-based
spectroscopy gathered by the Harps instrument. This way we continue our efforts
to map the Beta Cep and SPB instability strips.
Methods. We used different techniques to reveal the abundances and
fundamental stellar parameters from the newly-obtained high-resolution spectra.
We used various time-series analysis tools to explore the nature of variations
present in the light curve. We calculated the moments and used the
pixel-by-pixel method to look for line profile variations in the
high-resolution spectra.
Results. We find that HD 43317 is a single fast rotator (v_rot ~ 50% v_crit)
and hybrid SPB/Beta Cep-type pulsator with Solar metal abundances. We interpret
the variations in photometry and spectroscopy as a result of rotational
modulation connected to surface inhomogeneities, combined with the presence of
both g and p mode pulsations. We detect a series of ten consecutive frequencies
with an almost constant period spacing of 6339 s as well as a second shorter
sequence consisting of seven frequencies with a spacing of 6380 s. The dominant
frequencies fall in the regime of gravito-inertial modes.
03/2012;
-
M. Deleuil,
A. S. Bonomo,
S. Ferraz-Mello,
A. Erikson,
F. Bouchy,
M. Havel,
S. Aigrain,
J.-M. Almenara,
R. Alonso, M. Auvergne, [......],
D. Queloz,
H. Rauer,
A. Rodríguez,
D. Rouan,
A. Santerne,
J. Schneider,
L. Tal-Or,
B. Tingley,
J. Weingrill,
G. Wuchterl
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery by the CoRoT space mission of a new giant
planet, CoRoT-20b. The planet has a mass of 4.24 ± 0.23
MJup and a radius of 0.84 ± 0.04 RJup. With
a mean density of 8.87 ± 1.10 g cm-3, it is among the
most compact planets known so far. Evolutionary models for the planet
suggest a mass of heavy elements of the order of 800 M⊕
if embedded in a central core, requiring a revision either of the planet
formation models or both planet evolution and structure models. We note
however that smaller amounts of heavy elements are expected by more
realistic models in which they are mixed throughout the envelope. The
planet orbits a G-type star with an orbital period of 9.24 days and an
eccentricity of 0.56.The star's projected rotational velocity is vsini =
4.5 ± 1.0 km s-1, corresponding to a spin period of
11.5 ± 3.1 days if its axis of rotation is perpendicular to the
orbital plane. In the framework of Darwinian theories and neglecting
stellar magnetic breaking, we calculate the tidal evolution of the
system and show that CoRoT-20b is presently one of the very few
Darwin-stable planets that is evolving toward a triple synchronous state
with equality of the orbital, planetary and stellar spin periods.
The CoRoT space mission, launched on December 27th 2006, has been
developed and is operated by CNES, with the contribution of Austria,
Belgium, Brazil, ESA (RSSD and Science Programme), Germany, and Spain.
Astronomy and Astrophysics 01/2012; 538:145. · 4.59 Impact Factor
-
E. W. Guenther,
R. F. Diaz,
J. -C. Gazzano,
T. Mazeh,
D. Rouan,
N. Gibson,
Sz. Csizmadia,
S. Aigrain,
R. Alonso,
J. M. Almenara, [......],
H. Parviainen,
D. Queloz,
H. Rauer,
B. Samuel,
A. Santerne,
J. Schneider,
L. Tal-Or,
B. Tingley,
J. Weingrill,
G. Wuchterl
[show abstract]
[hide abstract]
ABSTRACT: Observations of transiting extrasolar planets are of key importance to our
understanding of planets because their mass, radius, and mass density can be
determined. The CoRoT space mission allows us to achieve a very high
photometric accuracy. By combining CoRoT data with high-precision radial
velocity measurements, we derive precise planetary radii and masses. We report
the discovery of CoRoT-19b, a gas-giant planet transiting an old, inactive
F9V-type star with a period of four days. After excluding alternative physical
configurations mimicking a planetary transit signal, we determine the radius
and mass of the planet by combining CoRoT photometry with high-resolution
spectroscopy obtained with the echelle spectrographs SOPHIE, HARPS, FIES, and
SANDIFORD. To improve the precision of its ephemeris and the epoch, we observed
additional transits with the TRAPPIST and Euler telescopes. Using HARPS spectra
obtained during the transit, we then determine the projected angle between the
spin of the star and the orbit of the planet. We find that the host star of
CoRoT-19b is an inactive F9V-type star close to the end of its main-sequence
life. The host star has a mass M*=1.21+/-0.05 Msun and radius R*=1.65+/-0.04
Rsun. The planet has a mass of Mp=1.11+/-0.06 Mjup and radius of Rp=1.29+/-0.03
Rjup. The resulting bulk density is only rho=0.71+/-0.06 gcm-3, which is much
lower than that for Jupiter. The exoplanet CoRoT-19b is an example of a giant
planet of almost the same mass as Jupiter but a 30% larger radius.
åp. 12/2011; 537.
-
C Cavarroc,
C Moutou,
D Gandolfi,
B Tingley,
M Ollivier,
S Aigrain,
R Alonso,
Hannu Parviainen, M Auvergne,
A Baglin, [......],
C Lovis,
T Mazeh,
M Pätzold,
D Queloz,
H Rauer,
D Rouan,
B Samuel,
A Santerne,
J. Schneider,
G Wuchterl
[show abstract]
[hide abstract]
ABSTRACT: We report the detection of CoRoT-23b, a hot Jupiter transiting in front of
its host star with a period of 3.6314 \pm 0.0001 days. This planet was
discovered thanks to photometric data secured with the CoRoT satellite,
combined with spectroscopic radial velocity (RV) measurements. A photometric
search for possible background eclipsing binaries conducted at CFHT and OGS
concluded with a very low risk of false positives. The usual techniques of
combining RV and transit data simultaneously were used to derive stellar and
planetary parameters. The planet has a mass of Mp = 2.8 \pm 0.3 MJup, a radius
of Rpl = 1.05 \pm 0.13 RJup, a density of \approx 3 g cm-3. RV data also
clearly reveal a non zero eccentricity of e = 0.16 \pm 0.02. The planet orbits
a mature G0 main sequence star of V =15.5 mag, with a mass M\star = 1.14 \pm
0.08 M\odot, a radius R\star = 1. 61 \pm 0.18 R\odot and quasi-solar
abundances. The age of the system is evaluated to be 7 Gyr, not far from the
transition to subgiant, in agreement with the rather large stellar radius. The
two features of a significant eccentricity of the orbit and of a fairly high
density are fairly uncommon for a hot Jupiter. The high density is, however,
consistent with a model of contraction of a planet at this mass, given the age
of the system. On the other hand, at such an age, circularization is expected
to be completed. In fact, we show that for this planetary mass and orbital
distance, any initial eccentricity should not totally vanish after 7 Gyr, as
long as the tidal quality factor Qp is more than a few 105, a value that is the
lower bound of the usually expected range. Even if Corot-23b features a density
and an eccentricity that are atypical of a hot Jupiter, it is thus not an
enigmatic object.
Astronomy and Astrophysics. 12/2011; 537(2012):A54.
-
F. Baudin,
C. Barban,
M. J. Goupil,
R. Samadi,
Y. Lebreton,
H. Bruntt,
T. Morel,
L. Lefèvre,
E. Michel,
B. Mosser,
F. Carrier,
J. De Ridder,
A. Hatzes,
S. Hekker,
T. Kallinger, M. Auvergne,
A. Baglin,
C. Catala
[show abstract]
[hide abstract]
ABSTRACT: The G6 giant HR\,2582 (HD\,50890) was observed by CoRoT for approximately 55
days. Mode frequencies are extracted from the observed Fourier spectrum of the
light curve. Numerical stellar models are then computed to determine the
characteristics of the star (mass, age, etc...) from the comparison with
observational constraints. We provide evidence for the presence of solar-like
oscillations at low frequency, between 10 and 20\,$\mu$Hz, with a regular
spacing of $(1.7\pm0.1)\mu$Hz between consecutive radial orders. Only radial
modes are clearly visible. From the models compatible with the observational
constraints used here, We find that HR\,2582 (HD\,50890) is a massive star with
a mass in the range (3--\,5\,$M_{\odot}$), clearly above the red clump. It
oscillates with rather low radial order ($n$ = 5\,--\,12) modes. Its
evolutionary stage cannot be determined with precision: the star could be on
the ascending red giant branch (hydrogen shell burning) with an age of
approximately 155 Myr or in a later phase (helium burning). In order to obtain
a reasonable helium amount, the metallicity of the star must be quite subsolar.
Our best models are obtained with a mixing length significantly smaller than
that obtained for the Sun with the same physical description (except
overshoot). The amount of core overshoot during the main-sequence phase is
found to be mild, of the order of 0.1\,$H_{\rm p}$.
11/2011;
-
K. Uytterhoeven,
P. Mathias,
A. Baglin,
M. Rainer,
E. Poretti,
P. Amado,
E. Chapellier,
L. Mantegazza,
K. Pollard,
J. C. Suarez,
P. M. Kilmartin,
K. H. Sato,
R. A. Garcia, M. Auvergne,
E. Michel,
R. Samadi,
C. Catala,
F. Baudin
[show abstract]
[hide abstract]
ABSTRACT: We present the preliminary results of a frequency and line-profile analysis
of the CoRoT gamma Dor candidate HD171834. The data consist of 149 days of
CoRoT light curves and a ground-based dataset of more than 1400 high-resolution
spectra, obtained with six different instruments. Low-amplitude frequencies
between 0 and 5 c/d, dominated by a frequency near 0.96 c/d and several of its
harmonics, are detected. These findings suggest that HD171834 is not a mere
gamma Dor pulsator and that stellar activity plays an important role in its
variable behaviour.
Based on CoRoT space data and on ground-based observations with ESO
Telescopes at the La Silla Observatory under the ESO Large Programmes ESO LP
178.D-0361 and ESO LP 182.D-0356 (FEROS/2.2m and HARPS/3.6m), and data
collected with FOCES/2.2m at the Centro Astronomico Hispano Aleman at Calar
Alto, SOPHIE/1.93m at Observatoire de Haute Provence, FIES/NOT at Observatorio
del Roque de los Muchachos, and HERCULES/1.0m at Mount John University
Observatory.
11/2011;
-
P. Degroote,
B. Acke,
R. Samadi,
C. Aerts,
D. W. Kurtz,
A. Noels,
A. Miglio,
J. Montalban,
S. Bloemen,
A. Baglin,
F. Baudin,
C. Catala,
E. Michel, M. Auvergne
[show abstract]
[hide abstract]
ABSTRACT: Context. There exist few variability studies of stars in the region in the
Hertzsprung-Russell diagram between the A and B-star pulsational instability
strips. With the aid of the high precision continuous measurements of the CoRoT
space satellite, low amplitudes are more easily detected, making a study of
this neglected region worthwhile. Aims. We collected a small sample of B stars
observed by CoRoT to determine the origin of the different types of variability
observed. Methods. We combine literature photometry and spectroscopy to measure
the fundamental parameters of the stars in the sample, and compare
asteroseismic modelling of the light curves with (differentially rotating)
spotted star models. Results. We found strong evidence for the existence of
spots and differential rotation in HD 174648, and formulated hypotheses for
their origin. We show that the distinction between pulsations and rotational
modulation is difficult to make solely based on the light curve, especially in
slowly rotating stars.
10/2011;
-
L. Carone,
D. Gandolfi,
J. Cabrera,
A. P. Hatzes,
H. J. Deeg,
Sz. Csizmadia,
M. Paetzold,
J. Weingrill,
S. Aigrain,
R. Alonso, [......],
D. Rouan,
A. Santerne,
B. Samuel,
J Schneider,
A. Shporer,
B. Stecklum,
L. Tal-Or,
B. Tingley,
S. Udry,
G. Wuchterl
[show abstract]
[hide abstract]
ABSTRACT: Context: CoRoT is a pioneering space mission whose primary goals are stellar
seismology and extrasolar planets search. Its surveys of large stellar fields
generate numerous planetary candidates whose lightcurves have transit-like
features. An extensive analytical and observational follow-up effort is
undertaken to classify these candidates. Aims: The list of planetary transit
candidates from the CoRoT LRa01 star field in the Monoceros constellation
towards the Galactic anti-center is presented. The CoRoT observations of LRa01
lasted from 24 October 2007 to 3 March 2008. Methods: 7470 chromatic and 3938
monochromatic lightcurves were acquired and analysed. Instrumental noise and
stellar variability were treated with several filtering tools by different
teams from the CoRoT community. Different transit search algorithms were
applied to the lightcurves. Results: Fifty-one stars were classified as
planetary transit candidates in LRa01. Thirty-seven (i.e., 73 % of all
candidates) are "good" planetary candidates based on photometric analysis only.
Thirty-two (i.e., 87 % of the "good" candidates) have been followed-up. At the
time of this writing twenty-two cases have been solved and five planets have
been discovered: three transiting hot-Jupiters (CoRoT-5b, CoRoT-12b, and
CoRoT-21b), the first terrestrial transiting planet (CoRoT-7b), and another
planet in the same system (CoRoT-7c, detected by radial velocity survey only).
Evidences of another non-transiting planet in the CoRoT-7 system, namely
CoRoT-7d, have been recently found.
Astronomy and Astrophysics. 10/2011; 538(2012).
-
M. Deleuil,
A. S. Bonomo,
S. Ferraz-Mello,
A. Erikson,
F. Bouchy,
M Havel,
S. Aigrain,
J. M. Almenara,
R. Alonso, M. Auvergne, [......],
D. Queloz,
H. Rauer,
A. Rodríguez,
D. Rouan,
A. Santerne,
J Schneider,
L. Tal-Or,
B. Tingley,
J. Weingrill,
G. Wuchterl
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery by the CoRoT space mission of a new giant planet,
CoRoT-20b. The planet has a mass of 4.24 +/- 0.23 MJ and a radius of 0.84 +/-
0.04 RJ. With a mean density of 8.87 +/- 1.10 g/cm^3, it is among the most
compact planets known so far. Evolution models for the planet suggest a mass of
heavy elements of the order of 800 ME if embedded in a central core, requiring
a revision either of the planet formation models or of planet evolution and
structure models. We note however that smaller amounts of heavy elements are
expected from more realistic models in which they are mixed throughout the
envelope. The planet orbits a G-type star with an orbital period of 9.24 days
and an eccentricity of 0.56. The star's projected rotational velocity is vsini
= 4.5 +/- 1.0 km/s, corresponding to a spin period of 11.5 +/- 3.1 days if its
axis of rotation is perpendicular to the orbital plane. In the framework of
Darwinian theories and neglecting stellar magnetic breaking, we calculate the
tidal evolution of the system and show that CoRoT-20b is presently one of the
very few Darwin-stable planets that is evolving towards a triple synchronous
state with equality of the orbital, planetary and stellar spin periods.
09/2011;
-
R. Blomme,
M. Briquet,
P. Degroote,
L. Mahy,
C. Aerts,
J. Cuypers,
M. Godart,
E. Gosset,
M. Hareter,
J. Montalban, [......],
S. Simon-Diaz,
K. Smolders,
P. Ventura,
M. Vuckovic, M. Auvergne,
A. Baglin,
F. Baudin,
C. Catala,
E. Michel,
R. Samadi
[show abstract]
[hide abstract]
ABSTRACT: Six O-type stars were observed continuously by the CoRoT satellite during a
34.3-day run. The unprecedented quality of the data allows us to detect even
low-amplitude stellar pulsations in some of these stars (HD 46202 and the
binaries HD 46149 and Plaskett's star). These cover both opacity-driven modes
and solar-like stochastic oscillations, both of importance to the
asteroseismological modelling of O stars. Additional effects can be seen in the
CoRoT light curves, such as binarity and rotational modulation. Some of the
hottest O-type stars (HD 46223, HD 46150 and HD 46966) are dominated by the
presence of red-noise: we speculate that this is related to a sub-surface
convection zone.
09/2011;
-
L. Tal-Or,
A. Santerne,
T. Mazeh,
F. Bouchy,
C. Moutou,
R. Alonso,
D. Gandolfi,
S. Aigrain, M. Auvergne,
P. Barge, [......],
H. Lammer,
A. Leger,
A. Llebaria,
M. Ollivier,
M. Patzold,
D. Queloz,
H. Rauer,
D. Rouan,
Y. Tsodikovich,
G. Wuchterl
[show abstract]
[hide abstract]
ABSTRACT: This paper presents the case of CoRoT LRa02_E2_0121, which was initially
classified as a Neptune-size transiting-planet candidate on a relatively wide
orbit of 36.3 days. Follow-up observations were performed with UVES, Sandiford,
SOPHIE and HARPS. These observations revealed a faint companion in the spectra.
To find the true nature of the system we derived the radial velocities of the
faint companion using TODMOR - a two-dimensional correlation technique, applied
to the SOPHIE spectra. Modeling the lightcurve with EBAS we discovered a
secondary eclipse with a depth of ~0.07%, indicating a diluted eclipsing
binary. Combined MCMC modeling of the lightcurve and the radial velocities
suggested that CoRoT LRa02_E2_0121 is a hierarchical triple system with an
evolved G-type primary and an A-type:F-type grazing eclipsing binary. Such
triple systems are difficult to discover.
08/2011;
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G. Hebrard,
T. M. Evans,
R. Alonso,
M. Fridlund,
A. Ofir,
S. Aigrain,
T. Guillot,
J. M. Almenara, M. Auvergne,
A. Baglin, [......],
M. Ollivier,
H. Parviainen,
M. Patzold,
D. Queloz,
H. Rauer,
D. Rouan,
A. Santerne,
J Schneider,
B. Tingley,
G. Wuchterl
[show abstract]
[hide abstract]
ABSTRACT: We report the detection of CoRoT-18b, a massive hot jupiter transiting in
front of its host star with a period of 1.9000693 +/- 0.0000028 days. This
planet was discovered thanks to photometric data secured with the CoRoT
satellite combined with spectroscopic and photometric ground-based follow-up
observations. The planet has a mass M_p = 3.47 +/- 0.38 M_Jup, a radius R_p =
1.31 +/- 0.18 R_Jup, and a density rho_p = 2.2 +/- 0.8 g/cm3. It orbits a G9V
star with a mass M_* = 0.95 +/- 0.15 M_Sun, a radius R_* = 1.00 +/- 0.13 R_Sun,
and a rotation period P_rot = 5.4 +/- 0.4 days. The age of the system remains
uncertain, with stellar evolution models pointing either to a few tens Ma or
several Ga, while gyrochronology and lithium abundance point towards ages of a
few hundred Ma. This mismatch potentially points to a problem in our
understanding of the evolution of young stars, with possibly significant
implications for stellar physics and the interpretation of inferred sizes of
exoplanets around young stars. We detected the Rossiter-McLaughlin anomaly in
the CoRoT-18 system thanks to the spectroscopic observation of a transit. We
measured the obliquity psi = 20 +/- 20 degrees (sky-projected value: lambda =
-10 +/- 20 degrees), indicating that the planet orbits in the same way as the
star is rotating and that this prograde orbit is nearly aligned with the
stellar equator.
åp. 07/2011; 533.
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R. Blomme,
L. Mahy,
C. Catala,
J. Cuypers,
E. Gosset,
M. Godart,
J. Montalban,
P. Ventura,
G. Rauw,
T. Morel,
P. Degroote,
C. Aerts,
A. Noels,
E. Michel,
F. Baudin,
A. Baglin, M. Auvergne,
R. Samadi
[show abstract]
[hide abstract]
ABSTRACT: The detection of pulsational frequencies in stellar photometry is required as
input for asteroseismological modelling. The second short run (SRa02) of the
CoRoT mission has provided photometric data of unprecedented quality and
time-coverage for a number of O-type stars. We analyse the CoRoT data
corresponding to three hot O-type stars, describing the properties of their
light curves and we search for pulsational frequencies, which we then compare
to theoretical model predictions. We determine the amplitude spectrum of the
data, using the Lomb-Scargle and a multifrequency HMM-like technique.
Frequencies are extracted by prewhitening, and their significance is evaluated
under the assumption that the light curve is dominated by red noise. We search
for harmonics, linear combinations and regular spacings among these
frequencies. We use simulations with the same time sampling as the data as a
powerful tool to judge the significance of our results. From the theoretical
point of view, we use the MAD non-adiabatic pulsation code to determine the
expected frequencies of excited modes. A substantial number of frequencies is
listed, but none can be convincingly identified as being connected to
pulsations. The amplitude spectrum is dominated by red noise. Theoretical
modelling shows that all three O-type stars can have excited modes but the
relation between the theoretical frequencies and the observed spectrum is not
obvious. The dominant red noise component in the hot O-type stars studied here
clearly points to a different origin than the pulsations seen in cooler O
stars. The physical cause of this red noise is unclear, but we speculate on the
possibility of sub-surface convection, granulation, or stellar wind
inhomogeneities being responsible.
07/2011;
