37 research outputs found
Anisotropic winds from close-in extra-solar planets
We present two-dimensional hydrodynamic models of thermally driven winds from
highly irradiated, close-in extra-solar planets. We adopt a very simple
treatment of the radiative heating processes at the base of the wind, and
instead focus on the differences between the properties of outflows in
multidimensions in comparison to spherically symmetric models computed with the
same methods. For hot (T > 2 x 10^{4} K) or highly ionized gas, we find strong
(supersonic) polar flows are formed above the planet surface which produce weak
shocks and outflow on the night-side. In comparison to a spherically symmetric
wind with the same parameters, the sonic surface on the day-side is much closer
to the planet surface in multidimensions, and the total mass loss rate is
reduced by almost a factor of four. We also compute the steady-state structure
of interacting planetary and stellar winds. Both winds end in a termination
shock, with a parabolic contact discontinuity which is draped over the planet
separating the two shocked winds. The planetary wind termination shock and the
sonic surface in the wind are well separated, so that the mass loss rate from
the planet is essentially unaffected. However, the confinement of the planetary
wind to the small volume bounded by the contact discontinuity greatly enhances
the column density close to the planet, which might be important for the
interpretation of observations of absorption lines formed by gas surrounding
transiting planets.Comment: ApJ accepte
Molecular Hydrogen in the FUSE Translucent Lines of Sight: The Full Sample
We report total abundances and related parameters for the full sample of the
FUSE survey of molecular hydrogen in 38 translucent lines of sight. New results
are presented for the "second half" of the survey involving 15 lines of sight
to supplement data for the first 23 lines of sight already published. We assess
the correlations between molecular hydrogen and various extinction parameters
in the full sample, which covers a broader range of conditions than the initial
sample. In particular, we are now able to confirm that many, but not all, lines
of sight with shallow far-UV extinction curves and large values of the
total-to-selective extinction ratio, = / -- characteristic
of larger than average dust grains -- are associated with particularly low
hydrogen molecular fractions (). In the lines of sight with large
, there is in fact a wide range in molecular fractions, despite the
expectation that the larger grains should lead to less H formation.
However, we see specific evidence that the molecular fractions in this
sub-sample are inversely related to the estimated strength of the UV radiation
field and thus the latter factor is more important in this regime. We have
provided an update to previous values of the gas-to-dust ratio, (H)/, based on direct measurements of (H) and (H I).
Although our value is nearly identical to that found with Copernicus data, it
extends the relationship by a factor of 2 in reddening. Finally, as the new
lines of sight generally show low to moderate molecular fractions, we still
find little evidence for single monolithic "translucent clouds" with 1.Comment: 35 pages, 5 tables, 7 figures, accepted for publication in The
Astrophysical Journal Supplements Serie
The Lupus Transit Survey For Hot Jupiters: Results and Lessons
We present the results of a deep, wide-field transit survey targeting Hot
Jupiter planets in the Lupus region of the Galactic plane conducted over 53
nights concentrated in two epochs separated by a year. Using the Australian
National University 40-inch telescope at Siding Spring Observatory (SSO), the
survey covered a 0.66 sq. deg. region close to the Galactic Plane (b=11 deg.)
and monitored a total of 110,372 stars (15.0<V<22.0). Using difference imaging
photometry, 16,134 light curves with a photometric precision of sigma<0.025 mag
were obtained. These light curves were searched for transits, and four
candidates were detected that displayed low-amplitude variability consistent
with a transiting giant planet. Further investigations, including spectral
typing and radial velocity measurements for some candidates, revealed that of
the four, one is a true planetary companion (Lupus-TR-3), two are blended
systems (Lupus-TR-1 and 4), and one is a binary (Lupus-TR-2). The results of
this successful survey are instructive for optimizing the observational
strategy and follow-up procedure for deep searches for transiting planets,
including an upcoming survey using the SkyMapper telescope at SSO.Comment: 27 pages, 9 figures, 4 tables. Accepted for publication in A
The X-Ray Environment During the Epoch of Terrestrial Planet Formation: Chandra Observations of h Persei
We describe Chandra/ACIS-I observations of the massive ~ 13--14 Myr-old
cluster, h Persei, part of the famous Double Cluster (h and chi Persei) in
Perseus. Combining the list of Chandra-detected sources with new optical/IR
photometry and optical spectroscopy reveals ~ 165 X-ray bright stars with V <
23. Roughly 142 have optical magnitudes and colors consistent with cluster
membership. The observed distribution of Lx peaks at Lx ~ 10^30.3 ergs/s and
likely traces the bright edge of a far larger population of ~ 0.4--2 Msun X-ray
active stars. From a short list of X-ray active stars with IRAC 8 micron excess
from warm, terrestrial-zone dust, we derive a maximum X-ray flux incident on
forming terrestrial planets. Although there is no correlation between X-ray
activity and IRAC excess, the fractional X-ray luminosity correlates with
optical colors and spectral type. By comparing the distribution of Lx/L* vs.
spectral type and V-I in h Per with results for other 1--100 Myr-old clusters,
we show that stars slightly more massive than the Sun (> 1.5 Msun) fall out of
X-ray saturation by ~ 10--15 Myr. Changes in stellar structure for > 1.5 Msun
stars likely play an important role in this decline of X-ray emission.Comment: 34 pages, 7 Figures, 2 Tables; Accepted for publication in The
Astronomical Journa
Cabbage and fermented vegetables : From death rate heterogeneity in countries to candidates for mitigation strategies of severe COVID-19
Large differences in COVID-19 death rates exist between countries and between regions of the same country. Some very low death rate countries such as Eastern Asia, Central Europe, or the Balkans have a common feature of eating large quantities of fermented foods. Although biases exist when examining ecological studies, fermented vegetables or cabbage have been associated with low death rates in European countries. SARS-CoV-2 binds to its receptor, the angiotensin-converting enzyme 2 (ACE2). As a result of SARS-CoV-2 binding, ACE2 downregulation enhances the angiotensin II receptor type 1 (AT(1)R) axis associated with oxidative stress. This leads to insulin resistance as well as lung and endothelial damage, two severe outcomes of COVID-19. The nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is the most potent antioxidant in humans and can block in particular the AT(1)R axis. Cabbage contains precursors of sulforaphane, the most active natural activator of Nrf2. Fermented vegetables contain many lactobacilli, which are also potent Nrf2 activators. Three examples are: kimchi in Korea, westernized foods, and the slum paradox. It is proposed that fermented cabbage is a proof-of-concept of dietary manipulations that may enhance Nrf2-associated antioxidant effects, helpful in mitigating COVID-19 severity.Peer reviewe
Nrf2-interacting nutrients and COVID-19 : time for research to develop adaptation strategies
There are large between- and within-country variations in COVID-19 death rates. Some very low death rate settings such as Eastern Asia, Central Europe, the Balkans and Africa have a common feature of eating large quantities of fermented foods whose intake is associated with the activation of the Nrf2 (Nuclear factor (erythroid-derived 2)-like 2) anti-oxidant transcription factor. There are many Nrf2-interacting nutrients (berberine, curcumin, epigallocatechin gallate, genistein, quercetin, resveratrol, sulforaphane) that all act similarly to reduce insulin resistance, endothelial damage, lung injury and cytokine storm. They also act on the same mechanisms (mTOR: Mammalian target of rapamycin, PPAR gamma:Peroxisome proliferator-activated receptor, NF kappa B: Nuclear factor kappa B, ERK: Extracellular signal-regulated kinases and eIF2 alpha:Elongation initiation factor 2 alpha). They may as a result be important in mitigating the severity of COVID-19, acting through the endoplasmic reticulum stress or ACE-Angiotensin-II-AT(1)R axis (AT(1)R) pathway. Many Nrf2-interacting nutrients are also interacting with TRPA1 and/or TRPV1. Interestingly, geographical areas with very low COVID-19 mortality are those with the lowest prevalence of obesity (Sub-Saharan Africa and Asia). It is tempting to propose that Nrf2-interacting foods and nutrients can re-balance insulin resistance and have a significant effect on COVID-19 severity. It is therefore possible that the intake of these foods may restore an optimal natural balance for the Nrf2 pathway and may be of interest in the mitigation of COVID-19 severity
Assimilation of soil moisture inferred from infrared remote sensing in a hydrological model over the HAPEX-MOBILHY region
International audienceHydrological models are generally unable to simulate correctly water exchanges at the soilatmosphere interface and the time evolution of surface soil humidity. This drawback often leads to poor simulation of water flows after periods of low flows because of the wrong estimation of the surface soil water content. In this paper, we describe how remote sensing can be used to account for the vegetation in the estimation of the actual evapotranspiration, and to estimate soil moisture regularly throughout the year and use it to correct the model simulation. This work has been done on the Adour river basin, in the framework of the HAPEX-MOBILHY experiment. The results presented show the improvements that result from the use of remote sensing data in hydrological modelling: better simulation of the soil moisture and of water flows at the outlets, and more realistic calculation of evaporation
Taking into account vegetation effects to estimate soil moisture from C-band radar measurements
International audienceEstimation of surface soil moisture is one of the major potential applications of radar remote sensing. The European Remote Sensing Satellites (ERS1 and 2) are equipped with a synthetic aperture radar working at C-band (5 Ghz) using a rather low incidence angle (23°). For this fequency and angle, the effect of soil roughness and vegetation attenuation are not negligible. It is shown that, for wheat canopy, it is possible to apply an empirical relation for correcting for the effect of vegetation. The proposed algorithm is derived from a data set acquired over several years using an airborne radar. It uses a simple cloud model to describe the vegetation attenuation. This algorithm does not need very precise information on vegetation density and yields a final precision for the moisture content on the order of 0.05 cm3/cm3
Utilisation des signaux rétrodiffusés d'un radar pour la mesure de l'humidité du sol et la rugosité de sa surface
International audienceIn this article, the possible use of synthetic-aperture radar (SAR), for measuring the moisture content and surface roughness is analyzed. Data have been acquired on the Melarchez subwatershed during the Orgeval'89 campaign from March to December 1989. Radar backscattering measurements were provided by the French airborne scatterometer ERASME. Simultaneous ground measurements of soil moisture and roughness, leaf-area index, and water content of the canopy were conducted on 12 test fields. Using radar configurations close to that of the ERS-1 SAR, the results clearly indicate that radar cannot be easily converted into moisture estimates at the field scale over a variety of bare soils, essentially due to the effect of roughness on radar response. Nevertheless, mean soil-moisture values measured within bare soil fields over the whole subwatershed, show a decrease in soil-surface moisture from March to October. The same values are clearly obtained by averaged radar measurements over all bare-soil fields, indicating that ERS-1 could be used for monitoring the moisture state on a regional scale.Dans cet article, la possibilité d'utiliser un radar à ouverture synthétique (SAR) pour mesurer la teneur en humidité et la rugosité de surface est analysée. Des données ont été acquises concernant la ligne de partage souterraine de Melarchez pendant la campagne d'Orgeval de 89 de mars à décembre 1989. Des mesures de rétrodiffusion du radar ont été fournies par le scattéromètre aéroporté français ERASME. Des mesures au sol simultanées de l'humidité et de la rugosité du sol, l'indice feuille-surface et la teneur en eau de la canopée ont été conduites sur 12 champs d'essai. A l'aide de configurations radar proches de celle du ERS-1 SAR, les résultats montrent clairement que le radar ne peut pas facilement être converti en estimations de l'humidité à l'échelle du champ sur une variété de sols nus, essentiellement due à l'effet de la rugosité sur la réaction du radar. Néanmoins, les valeurs moyennes sol-humidité mesurées sur les champs sur toute la ligne de partage souterraine montrent une baisse de l'humidité sol-surface de mars à octobre. Les mêmes valeurs sont clairement obtenues par mesures moyennes du radar sur tous les champs nus, indiquant que ERS-1 pouvait être utilisé pour surveiller le degré d'humidité à une échelle régionale