88 research outputs found
MADYS: the Manifold Age Determination for Young Stars
The unrivalled astrometric and photometric capabilities of the Gaia mission
have given new impetus to the study of young stars: both from an environmental
perspective, as members of comoving star-forming regions, and from an
individual perspective, as targets amenable to planet-hunting direct-imaging
observations. In view of the large availability of theoretical evolutionary
models, both fields would benefit from a unified framework that allows a
straightforward comparison of physical parameters obtained by different stellar
and substellar models. To this aim, we developed the Manifold Age Determination
for Young Stars (MADYS), a flexible Python tool for the age and mass
determination of young stellar and substellar objects. In this first release,
MADYS automatically retrieves and crossmatches photometry from several
catalogs, estimates interstellar extinction, and derives age and mass estimates
for individual objects through isochronal fitting. Harmonizing the
heterogeneity of publicly available isochrone grids, the tool allows one to
choose amongst 17 models, many of which with customizable astrophysical
parameters, for a total of isochrone grids. Several dedicated
plotting functions are provided to allow for an intuitive visual perception of
the numerical output. After extensive testing, we have made the tool publicly
available. Here, we demonstrate the capabilities of MADYS, summarizing
previously published results as well providing several new examples.Comment: 11 pages, 5 figures, 4 tables. Accepted for publication in A&
SPOTS: The Search for Planets Orbiting Two Stars: II. First constraints on the frequency of sub-stellar companions on wide circumbinary orbits
A large number of direct imaging surveys for exoplanets have been performed
in recent years, yielding the first directly imaged planets and providing
constraints on the prevalence and distribution of wide planetary systems.
However, like most of the radial velocity ones, these surveys generally focus
on single stars, hence binaries and higher-order multiples have not been
studied to the same level of scrutiny. This motivated the SPOTS (Search for
Planets Orbiting Two Stars) survey, which is an ongoing direct imaging study of
a large sample of close binaries, started with VLT/NACO and now continuing with
VLT/SPHERE. To complement this survey, we have identified the close binary
targets in 24 published direct imaging surveys. Here we present our statistical
analysis of this combined body of data. We analysed a sample of 117 tight
binary systems, using a combined Monte Carlo and Bayesian approach to derive
the expected values of the frequency of companions, for different values of the
companion's semi-major axis. Our analysis suggest that the frequency of
sub-stellar companions in wide orbit is moderately low (13% with a
best value of 6% at 95% confidence level) and not significantly different
between single stars and tight binaries. One implication of this result is that
the very high frequency of circumbinary planets in wide orbits around
post-common envelope binaries, implied by eclipse timing (up to 90% according
to Zorotovic & Schreiber 2013), can not be uniquely due to planets formed
before the common-envelope phase (first generation planets), supporting instead
the second generation planet formation or a non-Keplerian origin of the timing
variations.Comment: 21 pages, 3 figure
Science with EPICS, the E-ELT planet finder
EPICS is the proposed planet finder for the European Extremely Large Telescope. EPICS is a high contrast imager based on a high performing extreme adaptive optics system, a diffraction suppression module, and two scientific instruments: an Integral Field Spectrograph (IFS) for the near infrared (0.95-1.65 μm), and a differential polarization imager (E-POL). Both these instruments should allow imaging and characterization of planets shining in reflected light, possibly down to Earth-size. A few high interesting science cases are presente
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The SPHERE view of multiple star formation
While a large fraction of the stars are in multiple systems, our understanding of the processes leading to the formation of these systems is still inadequate. Given the large theoretical uncertainties, observation plays a basic role. Here we discuss the contribution of high contrast imaging, and more specifically of the SPHERE instrument at the ESO Very Large Telescope, in this area. SPHERE nicely complements other instruments such as Gaia or ALMA—in detecting and characterizing systems near the peak of the binary distribution with separation and allows to capture snapshots of binary formation within disks that are invaluable for the understanding of disk fragmentation
How do Most Planets Form? -- Constraints on Disk Instability from Direct Imaging
Core accretion and disk instability have traditionally been regarded as the
two competing possible paths of planet formation. In recent years, evidence
have accumulated in favor of core accretion as the dominant mode, at least for
close-in planets. However, it might be hypothesized that a significant
population of wide planets formed by disk instabilities could exist at large
separations, forming an invisible majority. In previous work, we addressed this
issue through a direct imaging survey of B2--A0-type stars, and concluded that
<30% of such stars form and retain planets and brown dwarfs through disk
instability, leaving core accretion as the likely dominant mechanism. In this
paper, we extend this analysis to FGKM-type stars by applying a similar
analysis to the Gemini Deep Planet Survey (GDPS) sample. The results strengthen
the conclusion that substellar companions formed and retained around their
parent stars by disk instabilities are rare. Specifically, we find that the
frequency of such companions is <8% for FGKM-type stars under our most
conservative assumptions, for an outer disk radius of 300 AU, at 99%
confidence. Furthermore, we find that the frequency is always <10% at 99%
confidence independently of outer disk radius, for any radius from 5 to 500 AU.
We also simulate migration at a wide range of rates, and find that the
conclusions hold even if the companions move substantially after formation.
Hence, core accretion remains the likely dominant formation mechanism for the
total planet population, for every type of star from M-type through B-type.Comment: 10 pages, 4 figures, accepted for publication in Ap
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