516 research outputs found
Composition of Ices in Low-Mass Extrasolar Planets
We study the formation conditions of icy planetesimals in protoplanetary
disks in order to determine the composition of ices in small and cold
extrasolar planets. Assuming that ices are formed from hydrates, clathrates,
and pure condensates, we calculate their mass fractions with respect to the
total quantity of ices included in planetesimals, for a grid of disk models. We
find that the composition of ices weakly depends on the adopted disk
thermodynamic conditions, and is rather influenced by the initial composition
of the gas phase. The use of a plausible range of molecular abundance ratios
and the variation of the relative elemental carbon over oxygen ratio in the gas
phase of protoplanetary disks, allow us to apply our model to a wide range of
planetary systems. Our results can thus be used to constrain the icy/volatile
phase composition of cold planets evidenced by microlensing surveys,
hypothetical ocean-planets and carbon planets, which could be detected by Corot
or Kepler.Comment: Accepted for publication in The Astrophysical Journa
A transcriptional switch controls sex determination in <i>Plasmodium falciparum</i>
Sexual reproduction and meiotic sex are deeply rooted in the eukaryotic tree of life, but mechanisms determining sex or mating types are extremely varied and are only well characterized in a few model organisms(1). In malaria parasites, sexual reproduction coincides with transmission to the vector host. Sex determination is non-genetic, with each haploid parasite capable of producing either a male or a female gametocyte in the human host(2). The hierarchy of events and molecular mechanisms that trigger sex determination and maintenance of sexual identity are yet to be elucidated. Here we show that the male development 1 (md1) gene is both necessary and sufficient for male fate determination in the human malaria parasite Plasmodium falciparum. We show that Md1 has a dual function stemming from two separate domains: in sex determination through its N terminus and in male development from its conserved C-terminal LOTUS/OST-HTH domain. We further identify a bistable switch at the md1 locus, which is coupled with sex determination and ensures that the male-determining gene is not expressed in the female lineage. We describe one of only a few known non-genetic mechanisms of sex determination in a eukaryote and highlight Md1 as a potential target for interventions that block malaria transmission
ExELS: an exoplanet legacy science proposal for the ESA Euclid mission. II. Hot exoplanets and sub-stellar systems
The Exoplanet Euclid Legacy Survey (ExELS) proposes to determine the
frequency of cold exoplanets down to Earth mass from host separations of ~1 AU
out to the free-floating regime by detecting microlensing events in Galactic
Bulge. We show that ExELS can also detect large numbers of hot, transiting
exoplanets in the same population. The combined microlensing+transit survey
would allow the first self-consistent estimate of the relative frequencies of
hot and cold sub-stellar companions, reducing biases in comparing "near-field"
radial velocity and transiting exoplanets with "far-field" microlensing
exoplanets. The age of the Bulge and its spread in metallicity further allows
ExELS to better constrain both the variation of companion frequency with
metallicity and statistically explore the strength of star-planet tides.
We conservatively estimate that ExELS will detect ~4100 sub-stellar objects,
with sensitivity typically reaching down to Neptune-mass planets. Of these,
~600 will be detectable in both Euclid's VIS (optical) channel and NISP H-band
imager, with ~90% of detections being hot Jupiters. Likely scenarios predict a
range of 2900-7000 for VIS and 400-1600 for H-band. Twice as many can be
expected in VIS if the cadence can be increased to match the 20-minute H-band
cadence. The separation of planets from brown dwarfs via Doppler boosting or
ellipsoidal variability will be possible in a handful of cases. Radial velocity
confirmation should be possible in some cases, using 30-metre-class telescopes.
We expect secondary eclipses, and reflection and emission from planets to be
detectable in up to ~100 systems in both VIS and NISP-H. Transits of ~500
planetary-radius companions will be characterised with two-colour photometry
and ~40 with four-colour photometry (VIS,YJH), and the albedo of (and emission
from) a large sample of hot Jupiters in the H-band can be explored
statistically.Comment: 18 pages, 16 figures, accepted MNRA
ExELS: an exoplanet legacy science proposal for the ESA Euclid mission. II. Hot exoplanets and sub-stellar systems
The Exoplanet Euclid Legacy Survey (ExELS) proposes to determine the
frequency of cold exoplanets down to Earth mass from host separations of ~1 AU
out to the free-floating regime by detecting microlensing events in Galactic
Bulge. We show that ExELS can also detect large numbers of hot, transiting
exoplanets in the same population. The combined microlensing+transit survey
would allow the first self-consistent estimate of the relative frequencies of
hot and cold sub-stellar companions, reducing biases in comparing "near-field"
radial velocity and transiting exoplanets with "far-field" microlensing
exoplanets. The age of the Bulge and its spread in metallicity further allows
ExELS to better constrain both the variation of companion frequency with
metallicity and statistically explore the strength of star-planet tides.
We conservatively estimate that ExELS will detect ~4100 sub-stellar objects,
with sensitivity typically reaching down to Neptune-mass planets. Of these,
~600 will be detectable in both Euclid's VIS (optical) channel and NISP H-band
imager, with ~90% of detections being hot Jupiters. Likely scenarios predict a
range of 2900-7000 for VIS and 400-1600 for H-band. Twice as many can be
expected in VIS if the cadence can be increased to match the 20-minute H-band
cadence. The separation of planets from brown dwarfs via Doppler boosting or
ellipsoidal variability will be possible in a handful of cases. Radial velocity
confirmation should be possible in some cases, using 30-metre-class telescopes.
We expect secondary eclipses, and reflection and emission from planets to be
detectable in up to ~100 systems in both VIS and NISP-H. Transits of ~500
planetary-radius companions will be characterised with two-colour photometry
and ~40 with four-colour photometry (VIS,YJH), and the albedo of (and emission
from) a large sample of hot Jupiters in the H-band can be explored
statistically.Comment: 18 pages, 16 figures, accepted MNRA
Phenotyping to dissect the biostimulant action of a protein hydrolysate in tomato plants under combined abiotic stress
Drought and heat stresses are the main constrains to agricultural crop production worldwide. Precise and efficient phenotyping is essential to understand the complexity of plant responses to abiotic stresses and to identify the best management strategies to increase plant tolerance. In the present study, two phenotyping platforms were used to investigate the effects of a protein hydrolysate-based biostimulant on the physiological response of two tomato genotypes (âE42â and âLA3120â) subjected to heat, drought, or combined stress. The free amino acids in the biostimulant, or other molecules, stimulated growth in treated plants subjected to combined stress, probably promoting endogenous phytohormonal biosynthesis. Moreover, biostimulant application increased the net photosynthetic rate and maximal efficiency of PSII photochemistry under drought, possibly related to the presence of glycine betaine and aspartic acid in the protein hydrolysate. Increased antioxidant content and a decreased accumulation of hydrogen peroxide, proline, and soluble sugars in treated plants under drought and combined stress further demonstrated that the biostimulant application mitigated the negative effects of abiotic stresses. Generally, the response to biostimulant in plants had a genotype-dependent effect, with âE42â showing a stronger response to protein hydrolysate application than âLA3120â. Altogether, in this study a fine and multilevel phenotyping revealed increased plant performances under water-limited conditions and elevated temperatures induced by a protein hydrolysate, thus highlighting the great potential biostimulants have in improving plant resilience to abiotic stresses
Limb-darkening measurements for a cool red giant in microlensing event OGLE 2004-BLG-482
Aims: We present a detailed analysis of OGLE 2004-BLG-482, a relatively
high-magnification single-lens microlensing event which exhibits clear
extended-source effects. These events are relatively rare, but they potentially
contain unique information on the stellar atmosphere properties of their source
star, as shown in this study. Methods: Our dense photometric coverage of the
overall light curve and a proper microlensing modelling allow us to derive
measurements of the OGLE 2004-BLG-482 source star's linear limb-darkening
coefficients in three bands, including standard Johnson-Cousins I and R, as
well as in a broad clear filter. In particular, we discuss in detail the
problems of multi-band and multi-site modelling on the expected precision of
our results. We also obtained high-resolution UVES spectra as part of a ToO
programme at ESO VLT from which we derive the source star's precise fundamental
parameters. Results: From the high-resolution UVES spectra, we find that OGLE
2004-BLG-482's source star is a red giant of MK type a bit later than M3, with
Teff = 3667 +/- 150 K, log g = 2.1 +/- 1.0 and an assumed solar metallicity.
This is confirmed by an OGLE calibrated colour-magnitude diagram. We then
obtain from a detailed microlensing modelling of the light curve linear
limb-darkening coefficients that we compare to model-atmosphere predictions
available in the literature, and find a very good agreement for the I and R
bands. In addition, we perform a similar analysis using an alternative
description of limb darkening based on a principal component analysis of ATLAS
limb-darkening profiles, and also find a very good agreement between
measurements and model predictions.Comment: Accepted in A&
A systematic fitting scheme for caustic-crossing microlensing events
We outline a method for fitting binary-lens caustic-crossing microlensing
events based on the alternative model parameterisation proposed and detailed in
Cassan (2008). As an illustration of our methodology, we present an analysis of
OGLE-2007-BLG-472, a double-peaked Galactic microlensing event with a source
crossing the whole caustic structure in less than three days. In order to
identify all possible models we conduct an extensive search of the parameter
space, followed by a refinement of the parameters with a Markov Chain-Monte
Carlo algorithm. We find a number of low-chi2 regions in the parameter space,
which lead to several distinct competitive best models. We examine the
parameters for each of them, and estimate their physical properties. We find
that our fitting strategy locates several minima that are difficult to find
with other modelling strategies and is therefore a more appropriate method to
fit this type of events.Comment: 12 pages, 11 figure
Finite-source and finite-lens effects in astrometric microlensing
The aim of this paper is to study the astrometric trajectory of microlensing
events with an extended lens and/or source. We consider not only a dark lens
but also a luminous lens as well. We find that the discontinuous finite-lens
trajectories given by Takahashi (2003) will become continuous in the
finite-source regime. The point lens (source) approximation alone gives an
under (over)estimation of the astrometric signal when the size of the lens and
source are not negligible. While the finiteness of the source is revealed when
the lens transits the surface of the source, the finite-lens signal is most
prominent when the lens is very close to the source. Astrometric microlensing
towards the Galactic bulge, Small Magellanic Cloud and M31 are discussed, which
indicate that the finite-lens effect is beyond the detection limit of current
instruments. Nevertheless, it is possible to distinguish between self-lensing
and halo lensing through a (non-)detection of the astrometric ellipse. We also
consider the case where the lens is luminous itself, as has been observed where
a lensing event was followed up with the Hubble Space Telescope. We show that
the astrometric signal will be reduced in a luminous-lens scenario. The
physical properties of the event, such as the lens-source flux ratio, the size
of the lens and source nevertheless can be derived by fitting the astrometric
trajectory.Comment: 12 pages, 12 figures, 1 table, published in MNRA
RoboTAP: Target priorities for robotic microlensing observations
Context. The ability to automatically select scientifically-important transient events from an alert stream of many such events, and to conduct follow-up observations in response, will become increasingly important in astronomy. With wide-angle time domain surveys pushing to fainter limiting magnitudes, the capability to follow-up on transient alerts far exceeds our follow-up telescope resources, and effective target prioritization becomes essential. The RoboNet-II microlensing program is a pathfinder project, which has developed an automated target selection process (RoboTAP) for gravitational microlensing events, which are observed in real time using the Las Cumbres Observatory telescope network.
Aims. Follow-up telescopes typically have a much smaller field of view compared to surveys, therefore the most promising microlensing events must be automatically selected at any given time from an annual sample exceeding 2000 events. The main challenge is to select between events with a high planet detection sensitivity, with the aim of detecting many planets and characterizing planetary anomalies.
Methods. Our target selection algorithm is a hybrid system based on estimates of the planet detection zones around a microlens. It follows automatic anomaly alerts and respects the expected survey coverage of specific events.
Results. We introduce the RoboTAP algorithm, whose purpose is to select and prioritize microlensing events with high sensitivity to planetary companions. In this work, we determine the planet sensitivity of the RoboNet follow-up program and provide a working example of how a broker can be designed for a real-life transient science program conducting follow-up observations in response to alerts; we explore the issues that will confront similar programs being developed for the Large Synoptic Survey Telescope (LSST) and other time domain surveys
A frozen super-Earth orbiting a star at the bottom of the Main Sequence
We observed the microlensing event MOA-2007-BLG-192 at high angular
resolution in JHKs with the NACO adaptive optics system on the VLT while the
object was still amplified by a factor 1.23 and then at baseline 18 months
later. We analyzed and calibrated the NACO photometry in the standard 2MASS
system in order to accurately constrain the source and the lens star fluxes. We
detect light from the host star of MOA-2007-BLG-192Lb, which significantly
reduces the uncertainties in its char- acteristics as compared to earlier
analyses. We find that MOA-2007-BLG-192L is most likely a very low mass late
type M-dwarf (0.084 [+0.015] [-0.012] M\odot) at a distance of 660 [+100] [-70]
pc orbited by a 3.2 [+5.2] [-1.8] M\oplus super-Earth at 0.66 [+0.51] [-0.22]
AU. We then discuss the properties of this cold planetary system.Comment: published version A&A 540, A78 (2012) A&A, 10 pages, 7 Figure
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