314 research outputs found
The Gaia Survey Contribution to EChO Target Selection and Characterization
The scientific output of the proposed EChO mission (in terms of spectroscopic
characterization of the atmospheres of transiting extrasolar planets) will be
maximized by a careful selection of targets and by a detailed characterization
of the main physical parameters (such as masses and radii) of both the planets
and their stellar hosts. To achieve this aim, the availability of high-quality
data from other space-borne and ground-based programs will play a crucial role.
Here we identify and discuss the elements of the Gaia catalogue that will be of
utmost relevance for the selection and characterization of transiting planet
systems to be observed by the proposed EChO mission.Comment: 6 pages, 2 figures. Accepted for publication in Experimental
Astronom
Biases in retrieving planetary signals in the presence of quasi-periodic stellar activity
Gaussian process regression is a widespread tool used to mitigate stellar
correlated noise in radial velocity time series. It is particularly useful to
search for and determine the properties of signals induced by small-size,
low-mass planets (, ). By using
extensive simulations based on a quasi-periodic representation of the stellar
activity component, we investigate the ability in retrieving the planetary
parameters in 16 different realistic scenarios. We analyse systems composed by
one planet and host stars having different levels of activity, focusing on the
challenging case represented by low-mass planets, with Doppler semi-amplitudes
in the range 1-3 . We consider many different configurations for the
quasi-periodic stellar activity component, as well as different combinations of
the observing epochs. We use commonly-employed analysis tools to search for and
characterize the planetary signals in the datasets. The goal of our
injection-recovery statistical analysis is twofold. First, we focus on the
problem of planet mass determination. Then, we analyse in a statistical way
periodograms obtained with three different algorithms, in order to explore some
of their general properties, as the completeness and reliability in retrieving
the injected planetary and stellar activity signals with low false alarm
probabilities. This work is intended to provide some understanding of the
biases introduced in the planet parameters inferred from the analysis of radial
velocity time series that contain correlated signals due to stellar activity.
It also aims to motivate the use and encourage the improvement of extensive
simulations for planning spectroscopic follow-up observations.Comment: 19 pages, 10 figures, accepted for publication in MNRA
TASTE IV. Refining ephemeris and orbital parameters for HAT-P-20b and WASP-1b
We present four new light curves of transiting exoplanets WASP-1b and
HAT-P-20b, observed within the TASTE (The Asiago Search for Transit timing
variations of Exoplanets) project. We re-analyzed light curves from the
literature in a homogeneous way, calculating a refined ephemeris and
orbital-physical parameters for both objects. WASP-1b does not show any
significant Transit Timing Variation signal at the 120 s-level. As for
HAT-P-20b, we detected a deviation from our re-estimated linear ephemeris that
could be ascribed to the presence of a perturber or, more probably, to a
previously unnoticed high level of stellar activity. The rotational period of
HAT-P-20 A we obtained from archival data (P_rot ~ 14.5 days), combined with
its optical variability and strong emission of CaII H&K lines, is consistent
with a young stellar age (< 1 Gyr) and support the hypothesis that stellar
activity may be responsible of the measured deviations of the transit times.Comment: 7 pages, 4 figures, 3 tables, accepted to Astronomische Nachrichte
A path towards understanding the rotation-activity relation of M dwarfs with K2 mission, X-ray and UV data
We study the relation between stellar rotation and magnetic activity fora sample of 134 bright, nearby M dwarfs observed in the Kepler Two-Wheel (K2) mission during campaigns C0-C4. The K2 light curves yield photometrically derived rotation periods for 97 stars (79 of which without previous period measurement), as well as various measures for activity related to cool spots and flares. We find a clear difference between fast and slow rotators with a dividing line at a period of ~10 d at which the activity level changes abruptly. All photometric diagnostics of activity (spot cycle amplitude, flare peak amplitude and residual variability after subtraction of spot and flare variations) display the same dichotomy, pointing to a quick transition between a high-activity mode for fast rotators and a low-activity mode for slow rotators. This unexplained behavior is reminiscent of a dynamo mode-change seen in numerical simulations that separates a dipolar from a multipolar regime. A substantial number of the fast rotators a revisual binaries. A tentative explanation is accelerated disc evolution in binaries leading to higher initial rotation rates on the main sequence and associated longer spin-down and activity lifetimes. We combine the K2 rotation periods with archival X-ray and UV data. X-ray, FUV and NUV detections are found for 26, 41, and 11 stars from our sample, respectively. Separating the fast from the slow rotators, we determine for the first time the X-ray saturation level separately for early- and for mid-M stars.Publisher PDFPeer reviewe
Rotation-activity relations and flares of M dwarfs with K2 long- and short-cadence data
Funding: UK STFC grant no. ST/R000824/1 (A.S.).Using light curves obtained by the K2 mission, we study the relation between stellar rotation and magnetic activity with special focus on stellar flares. Our sample comprises 56 bright and nearby M dwarfs observed by K2 during campaigns C0-C18 in long- and short-cadence mode. We derive rotation periods for 46 M dwarfs and measure photometric activity indicators such as amplitude of the rotational signal, standard deviation of the light curves, and the basic flare properties (flare rate, flare energy, flare duration, and flare amplitude). We found 1662 short-cadence flares, 363 of which have a long-cadence counterpart with flare energies of up to 5.6 × 1034 erg. The flare amplitude, duration, and frequency derived from the short-cadence light curves differ significantly from those derived from the long-cadence data. The analysis of the short-cadence light curves results in a flare rate that is 4.6 times higher than the long-cadence data. We confirm the abrupt change in activity level in the rotation-activity relation at a critical period of ~10 d when photometric activity diagnostics are used. This change is most drastic in the flare duration and frequency for short-cadence data. Our flare studies revealed that the highest flare rates are not found among the fastest rotators and that stars with the highest flare rates do not show the most energetic flares. We found that the superflare frequency (E ≥ 5 × 1034 erg) for the fast-rotating M stars is twice higher than for solar like stars in the same period range. By fitting the cumulative FFD, we derived a power-law index of α = 1.84 ± 0.14, consistent with previous M dwarf studies and the value found for the Sun.Publisher PDFPeer reviewe
A possibly inflated planet around the bright, young star DS Tuc A
The origin of the observed diversity of planetary system architectures is one
of the main topic of the exoplanetary research. The detection of a
statistically significant sample of planets around young stars allows us to
study the early stages of planet formation and evolution, but only a handful of
them is known so far. In this regard, a considerable contribution is expected
from the NASA TESS satellite, which is now performing a survey of
of the sky to search for short-period transiting planets In its first month of
operations, TESS found a planet candidate with an orbital period of 8.14 days
around a member of the Tuc-Hor young association ( 40 Myr), the G6V main
component of the binary system DS\,Tuc. If confirmed, it would be the first
transiting planet around a young star suitable for radial velocity and/or
atmospheric characterization. We aim to validate the planetary nature of this
companion and to measure its orbital and physical parameters. We obtain
accurate planet parameters by coupling an independent reprocessing of the TESS
light curve with improved stellar parameters and the dilution caused by the
binary companion; we analyse high precision archival radial velocities to
impose an upper limit of about 0.1 M on the planet mass; we finally
rule out the presence of external companions beyond 40 au with adaptive optics
images. We confirm the presence of a young, giant ( R) planet having a not negligible possibility to be inflated (theoretical
mass M) around DS\,Tuc~A. We discuss the feasibility
of mass determination, Rossiter-McLaughlin analysis and atmosphere
characterization, allowed by the brightness of the star.Comment: 12 pages, 11 figures. Accepted for publication in A&
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