136 research outputs found
The timescale for giant planet formation : constraints from the rotational evolution of exoplanet host stars
The timescale over which planets may form in the circumstellar disks of young
stars is one of the main issues of current planetary formation models. We
present here new constraints on planet formation timescales derived from the
rotational evolution of exoplanet host stars.Comment: SF2A 2008, Journees de l'Astrophysique Francaise, Paris : France
(2008
The rotational evolution of young low mass stars
10 pagesInternational audienceStar-disk interaction is thought to drive the angular momentum evolution of young stars. In this review, I present the latest results obtained on the rotational properties of low mass and very low mass pre-main sequence stars. I discuss the evidence for extremely efficient angular momentum removal over the first few Myr of pre-main sequence evolution and describe recent results that support an accretion-driven braking mechanism. Angular momentum evolution models are presented and their implication for accretion disk lifetimes discussed
Modeling of CoRoT and Spitzer lightcurves in NGC 2264 caused by an optically thick warp
Aims: We present an analysis of simultaneously observed CoRoT and Spitzer
lightcurves for systems in the stellar forming region NGC 2264: Mon-660,
Mon-811, Mon-1140 and Mon-1308. These objects share in common a high
resemblance between the optical and infrared lightcurves, such that the
mechanism responsible to produce them is the same. The aim of this paper is to
explain both lightcurves simultaneously with only one mechanism. Methods: We
have modeled the infrared emission as coming from a warp composed of an
optically thick wall and an optically thick asymmetric disk beyond this
location. We have modeled the optical emission mainly by partial stellar
occultation by the warp. Results: The magnitude amplitude of the CoRoT and
Spitzer observations for all the objects can be described with the emission
coming from the system components. The difference between them is the value of
the disk flux compared with the wall flux and the azimuthal variations of the
former. This result points out the importance of the hydrodynamical interaction
between the stellar magnetic field and the disk. Conclusions: CoRoT and Spitzer
lightcurves for the stellar systems Mon-660, Mon-811, Mon-1140 and Mon-1308 can
be simultaneously explained using the emission coming from an asymmetric disk
and emission with stellar occultation by an optically thick wall.Comment: 17 pages, 10 figure
The dipper light curve of V715 Per: is there dust in the magnetosphere?
The dipper optical light curves in young stellar objects are commonly
interpreted as partial or total occultation of the stellar radiation by dust
surrounding the star.
In this work, we analyze the amplitude of the optical light curve of V715
Per, located in the young star forming region IC 348. Observations gathered
over the years suggest that the light curve can be explained by dust extinction
events.
In our model, the dust is distributed inside the magnetosphere according to
the strength of the stellar magnetic field. The dust distribution is modulated
by the vertical component of the field, whose axis is misaligned with respect
to the rotational axis. We include a model for the evaporation of the dust
reaching the magnetosphere in order to consistently calculate its distribution.
For V715 Per, there is dust in the optically thick warp at the disk
truncation radius. We suggest that the optical light curve is explained by
extinction caused by dust reaching inside the magnetosphere. The dust
distribution is optically thin and due to the high temperature and low density,
it cannot survive for a long time. However because the grains rapidly move
towards the stellar surface and the sublimation is not instantaneous, there is
a layer of dust covering the magnetosphere responsible for the extinction.
Dust surviving the harsh conditions of the magnetospheric accretion flow may
be responsible for some of the dipper light curves.Comment: Accepted for publication in Astronomy & Astrophysics 20 pages, 7
figure
Rotation in NGC 2264: a study based on CoRoT photometric observations
Rotation is one of the key stellar parameters which undergo substantial
evolution during the stellar lifetime, in particular during the early stages.
Stellar rotational periods can be determined on the basis of the periodic
modulation of starlight produced by non-uniformities on the surface of the
stars, due to manifestation of stellar activity. We present the results of an
extensive search for rotational periods among NGC 2264 cluster members, based
on photometric monitoring using the CoRoT satellite, with a particular
attention to the distribution of classical and weak-line T-Tauri stars. NGC
2264 is one of the nearest and best studied star forming region in the solar
neighbourhood, with an estimated age of 3 Myr, and is the object of a recent
simultaneous multiband campaign including a new CoRoT observation with the aim
to assess the physical origin of the observed variability. We find that the
rotational distributions of classical and weak-line T-Tauri star are different,
suggesting a difference in the rotational properties of accreting and
non-accreting stars.Comment: 15 pages, 10 figure
The XMM-Newton Optical Monitor Survey of the Taurus Molecular Cloud
The Optical Monitor (OM) on-board XMM-Newton obtained optical/ultraviolet
data for the XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST),
simultaneously with the X-ray detectors. With the XEST OM data, we aim to study
the optical and ultraviolet properties of TMC members, and to do correlative
studies between the X-ray and OM light curves. In particular, we aim to
determine whether accretion plays a significant role in the optical/ultraviolet
and X-ray emissions. The Neupert effect in stellar flares is also investigated.
Coordinates, average count rates and magnitudes were extracted from OM images,
together with light curves with low time resolution (a few kiloseconds). For a
few sources, OM FAST mode data were also available, and we extracted OM light
curves with high time resolution. The OM data were correlated with Two Micron
All Sky Survey (2MASS) data and with the XEST catalogue in the X-rays. The XEST
OM catalogue contains 2,148 entries of which 1,893 have 2MASS counterparts.
However, only 98 entries have X-ray counterparts, of which 51 of them are known
TMC members and 12 additional are TMC candidates. The OM data indicate that
accreting stars are statistically brighter in the U band than non-accreting
stars after correction for extinction, and have U-band excesses, most likely
due to accretion. The OM emission of accreting stars is variable, probably due
to accretion spots, but it does not correlate with the X-ray light curve,
suggesting that accretion does not contribute significantly to the X-ray
emission of most accreting stars. In some cases, flares were detected in both
X-ray and OM light curves and followed a Neupert effect pattern, in which the
optical/ultraviolet emission precedes the X-ray emission of a flare, whereas
the X-ray flux is proportional to the integral of the optical flux.Comment: Accepted by A&A, to appear in a special section/issue dedicated to
the XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST). Version
with higher resolution figures available at this
http://www.issibern.ch/teams/Taurus/papers.htm
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