30,457 research outputs found
SOAP 2.0: A tool to estimate the photometric and radial velocity variations induced by stellar spots and plages
This paper presents SOAP 2.0, a new version of the SOAP code that estimates
in a simple way the photometric and radial velocity variations induced by
active regions. The inhibition of the convective blueshift inside active
regions is considered, as well as the limb brightening effect of plages, a
quadratic limb darkening law, and a realistic spot and plage contrast ratio.
SOAP 2.0 shows that the activity-induced variation of plages is dominated by
the inhibition of the convective blueshift effect. For spots, this effect
becomes significant only for slow rotators. In addition, in the case of a major
active region dominating the activity-induced signal, the ratio between the
full width at half maximum (FWHM) and the RV peak-to-peak amplitudes of the
cross correlation function can be used to infer the type of active region
responsible for the signal for stars with \vsini\kms. A ratio smaller
than three implies a spot, while a larger ratio implies a plage. Using the
observation of HD189733, we show that SOAP 2.0 manages to reproduce the
activity variation as well as previous simulations when a spot is dominating
the activity-induced variation. In addition, SOAP 2.0 also reproduces the
activity variation induced by a plage on the slowly rotating star Cen
B, which is not possible using previous simulations. Following these results,
SOAP 2.0 can be used to estimate the signal induced by spots and plages, but
also to correct for it when a major active region is dominating the RV
variation.Comment: 28 pages, 15 figures, accepted for publication in ApJ after minor
revisions (taken into account in this version
A rotating cylinder in an asymptotically locally anti-de Sitter background
A family of exact solutions is presented which represents a rigidly rotating
cylinder of dust in a background with a negative cosmological constant. The
interior of the infinite cylinder is described by the Godel solution. An exact
solution for the exterior solution is found which depends both on the rotation
of the interior and on its radius. For values of these parameters less than a
certain limit, the exterior solution is shown to be locally isomorphic to the
Linet-Tian solution. For values larger than another limit, it is shown that the
exterior solution extends into a region which contains closed timelike curves.
At large distances from the source, the space-time is shown to be asymptotic
locally to anti-de Sitter space.Comment: To appear in Classical and Quantum Gravit
SOAP-T: A tool to study the light-curve and radial velocity of a system with a transiting planet and a rotating spotted star
We present an improved version of SOAP (Boisse et al. 2012) named "SOAP-T",
which can generate the radial velocity variations and light-curves for systems
consisting of a rotating spotted star with a transiting planet. This tool can
be used to study the anomalies inside transit light-curves and the
Rossiter-McLaughlin effect, to better constrain the orbital configuration and
properties of planetary systems and active zones of their host stars. Tests of
the code are presented to illustrate its performance and to validate its
capability when compared with analytical models and real data. Finally, we
apply SOAP-T to the active star, HAT-P-11, observed by the NASA Kepler space
telescope and use this system to discuss the capability of this tool in
analyzing light-curves for the cases where the transiting planet overlaps with
the star's spots.Comment: 9 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
Improvements on analytic modelling of stellar spots
In this work we present the solution of the stellar spot problem using the
Kelvin-Stokes theorem. Our result is applicable for any given location and
dimension of the spots on the stellar surface. We present explicitely the
result up to the second degree in the limb darkening law. This technique can be
used to calculate very efficiently mutual photometric effects produced by
eclipsing bodies occulting stellar spots and to construct complex spot shapes.Comment: Resubmitted to MNRAS after accounting for minor comments of second
review, 9 pages, 5 figures, software available at
http://eduscisoft.com/KSINT
On the long-term correlation between the flux in the Ca II H & K and Halpha lines for FGK stars
The re-emission in the cores of the Ca II H & K and H lines, are well
known proxies of stellar activity. However, these activity indices probe
different activity phenomena, the first being more sensitive to plage
variation, while the other one being more sensitive to filaments. In this paper
we study the long-term correlation between and , two indices based on the Ca II H & K and H lines
respectively, for a sample of 271 FGK stars using measurements obtained over a
9 year time span. Because stellar activity is one of the main obstacles
to the detection of low-mass and long-period planets, understanding further
this activity index correlation can give us some hints about the optimal target
to focus on, and ways to correct for these activity effects. We found a great
variety of long-term correlations between and . Around 20% of our sample has strong positive correlation between
the indices while about 3% show strong negative correlation. These fractions
are compatible with those found for the case of early-M dwarfs. Stars
exhibiting a positive correlation have a tendency to be more active when
compared to the median of the sample, while stars showing a negative
correlation are more present among higher metallicity stars. There is also a
tendency for the positively correlated stars to be more present among the
coolest stars, a result which is probably due to the activity level effect on
the correlation. Activity level and metallicity seem therefore to be playing a
role on the correlation between and . Possible
explanations based on the influence of filaments for the diversity in the
correlations between these indices are discussed in this paper.Comment: 18 pages, 13 figures, 4 tables, accepted for publication in Astronomy
and Astrophysic
In vitro germination of zygotic embryos excised from cryopreserved endocarps of queen palm (Syagrus romanzoffiana (Cham.) Glassman).
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Viability assessment of Genipa americana L. (Rubiaceae) embryonic axes after cryopreservation using In Vitro culture.
Light elements in stars with exoplanets
It is well known that stars orbited by giant planets have higher abundances
of heavy elements when compared with average field dwarfs. A number of studies
have also addressed the possibility that light element abundances are different
in these stars. In this paper we will review the present status of these
studies. The most significant trends will be discussed.Comment: 10 pages, 6 figures. Submitted to the proceedings of IAU symposium
268: Light elements in the universe
Chemical abundances of stars with brown-dwarf companions
It is well-known that stars with giant planets are on average more metal-rich
than stars without giant planets, whereas stars with detected low-mass planets
do not need to be metal-rich. With the aim of studying the weak boundary that
separates giant planets and brown dwarfs (BDs) and their formation mechanism,
we analyze the spectra of a sample of stars with already confirmed BD
companions both by radial velocity and astrometry. We employ standard and
automatic tools to perform an EW-based analysis and to derive chemical
abundances from CORALIE spectra of stars with BD companions. We compare these
abundances with those of stars without detected planets and with low-mass and
giant-mass planets. We find that stars with BDs do not have metallicities and
chemical abundances similar to those of giant-planet hosts but they resemble
the composition of stars with low-mass planets. The distribution of mean
abundances of -elements and iron peak elements of stars with BDs
exhibit a peak at about solar abundance whereas for stars with low-mass and
high-mass planets the [X/H] and [X/H] peak abundances
remain at ~dex and ~dex, respectively. We display these
element abundances for stars with low-mass and high-mass planets, and BDs
versus the minimum mass, , of the most-massive substellar companion
in each system, and we find a maximum in -element as well as Fe-peak
abundances at jupiter masses. We discuss the
implication of these results in the context of the formation scenario of BDs in
comparison with that of giant planets.Comment: Accepted for publication in Astronomy & Astrophysic
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