373 research outputs found
Detection of oxygen and carbon in the hydrodynamically escaping atmosphere of the extrasolar planet HD209458b
Four transits of the planet orbiting the star HD209458 were observed with the
STIS spectrograph on board HST. The wavelength domain (1180-1710A) includes HI
as well as CI, CII, CIV, NV, OI, SI, SiII, SiIII and SiIV lines. During the
transits, absorptions are detected in HI, OI and CII (5+/-2%, 13+/-4.5% and
7.5+/-3.5%, respectively). No absorptions are detected for other lines. The 5%
mean absorption over the whole HI Lyman alpha line is consistent with the
previous detection at higher resolution (Vidal-Madjar et al. 2003). The
absorption depths in OI and CII show that oxygen and carbon are present in the
extended upper atmosphere of HD209458b. These species must be carried out up to
the Roche lobe and beyond, most likely in a state of hydrodynamic escape.Comment: 6 pages, 4 figures, 1 table, submitted to ApJ Letters, revised
version with slightly revisited absorption depth estimate
Historical Contingencies Modulate the Adaptability of Rice Yellow Mottle Virus
The rymv1-2 and rymv1-3 alleles of the RYMV1 resistance to Rice yellow mottle virus (RYMV), coded by an eIF(iso)4G1 gene, occur in a few cultivars of the Asiatic (Oryza sativa) and African (O. glaberrima) rice species, respectively. The most salient feature of the resistance breaking (RB) process is the converse genetic barrier to rymv1-2 and rymv1-3 resistance breakdown. This specificity is modulated by the amino acid (glutamic acid vs. threonine) at codon 49 of the Viral Protein genome-linked (VPg), a position which is adjacent to the virulence codons 48 and 52. Isolates with a glutamic acid (E) do not overcome rymv1-3 whereas those with a threonine (T) rarely overcome rymv1-2. We found that isolates with T49 had a strong selective advantage over isolates with E49 in O. glaberrima susceptible cultivars. This explains the fixation of the mutation T49 during RYMV evolution and accounts for the diversifying selection estimated at codon 49. Better adapted to O. glaberrima, isolates with T49 are also more prone than isolates with E49 to fix rymv1-3 RB mutations at codon 52 in resistant O. glaberrima cultivars. However, subsequent genetic constraints impaired the ability of isolates with T49 to fix rymv1-2 RB mutations at codons 48 and 52 in resistant O. sativa cultivars. The origin and role of the amino acid at codon 49 of the VPg exemplifies the importance of historical contingencies in the ability of RYMV to overcome RYMV1 resistance
The Impact of Phase Equilibrium Cloud Models on GCM Simulations of GJ~1214b
We investigate the impact of clouds on the atmosphere of GJ~1214b using the
radiatively-coupled, phase-equilibrium cloud model {\sc EddySed} coupled to the
{\sc Unified Model} general circulation model. We find that, consistent with
previous investigations, high metallicity ( solar) and clouds with
large vertical extents (a sedimentation factor of ) are
required to best match the observations, although metallicities even higher
than those investigated here may be required to improve agreement further. We
additionally find that in our case which best matches the observations
(), the velocity structures change relative to the clear
sky case with the formation of a superrotating jet being suppressed, although
further investigation is required to understand the cause of the suppression.
The increase in cloud extent with results in a cooler planet
due to a higher albedo, causing the atmosphere to contract. This also results
in a reduced day-night contrast seen in the phase curves, although the
introduction of cloud still results in a reduction of the phase offset. We
additionally investigate the impact the the {\sc Unified Model}'s
pseudo-spherical irradiation scheme on the calculation of heating rates,
finding that the introduction of nightside shortwave heating results in slower
mid-latitude jets compared to the plane parallel irradiation scheme used in
previous works. We also consider the impact of a gamma distribution, as opposed
to a log-normal distribution, for the distribution of cloud particle radii and
find the impact to be relatively minor.Comment: Accepted to MNRA
Understanding stellar activity-induced radial velocity jitter using simultaneous K2 photometry and HARPS RV measurements
One of the best ways to improve our understanding of the stellar
activity-induced signal in radial velocity (RV) measurements is through
simultaneous high-precision photometric and RV observations. This is of prime
importance to mitigate the RV signal induced by stellar activity and therefore
unveil the presence of low-mass exoplanets. The K2 Campaign 7 and 8
field-of-views were located in the southern hemisphere, and provided a unique
opportunity to gather unprecedented simultaneous high precision photometric
observation with K2 and high-precision RV measurements with the HARPS
spectrograph to study the relationship between photometric variability and RV
jitter. We observed nine stars with different levels of activity; from quiet to
very active. We probe the presence of any meaningful relation between measured
RV jitter and the simultaneous photometric variation, and also other activity
indicators (e.g. BIS, FWHM, , and F8), by evaluating the strength
and significance of the correlation between RVs and each indicator. We found
that for the case of very active stars, strong and significant correlations
exist between almost all the observables and measured RVs; however, for lower
activity levels the correlations become random. Except for the F8 which its
strong correlation with RV jitter persists over a wide range of stellar
activity level, and thus our result suggests that F8 might be a powerful proxy
for activity induced RV jitter. Moreover, we examine the capability of two
state-of-the-art modeling techniques, namely the FF' method and SOAP2.0, in
accurately predicting the RV jitter amplitude using the simultaneous
photometric observation. We found that for the very active stars both
techniques can reasonably well predict the amplitude of the RV jitter, however,
at lower activity levels the FF' method underpredicts the RV jitter amplitude.Comment: 13 pages, 7 figures, 2 tables, accepted for publication in A&
The deuterium-to-oxygen ratio in the interstellar medium
Because the ionization balances for HI, OI, and DI are locked together by
charge exchange, D/O is an important tracer for the value of the D/H ratio and
for potential spatial variations in the ratio. As the DI and OI column
densities are of similar orders of magnitude for a given sight line,
comparisons of the two values will generally be less subject to systematic
errors than comparisons of DI and HI, which differ by about five orders of
magnitude. Moreover, D/O is additionally sensitive to astration, because as
stars destroy deuterium, they should produce oxygen. We report here the results
of a survey of D/O in the interstellar medium performed with FUSE. We also
compare these results with those for D/N. Together with a few results from
previous missions, the sample totals 24 lines of sight. The distances range
from a few pc to ~2000 pc and log N(DI) from ~13 to ~16 (cm-2). The D/O ratio
is constant in the local interstellar medium out to distances of ~150 pc and
N(DI) ~ 1x10^15 cm-2, i.e. within the Local Bubble. In this region of the
interstellar space, we find D/O = (3.84+/-0.16)x10^-2 (1 sigma in the mean).
The homogeneity of the local D/O measurements shows that the spatial variations
in the local D/H and O/H must be extremely small, if any. A comparison of the
Local Bubble mean value with the few D/O measurements available for low
metallicity quasar sight lines shows that the D/O ratio decreases with cosmic
evolution, as expected. Beyond the Local Bubble we detected significant spatial
variations in the value of D/O. This likely implies a variation in D/H, as O/H
is known to not vary significantly over the distances covered in this study.
Our dataset suggests a present-epoch deuterium abundance below 1x10^-5, i.e.
lower than the value usually assumed, around 1.5x10^-5.Comment: 17 pages, 9 figures, 4 tables, accepted for publication in the
Astrophysical Journa
FUSE Observations of the HD Molecule toward HD 73882
The Lyman and Werner band systems of deuterated molecular hydrogen (HD) occur
in the far UV range below 1200 A. The high sensitivity of the FUSE mission can
give access, at moderate resolution, to hot stars shining through translucent
clouds, in the hope of observing molecular cores in which deuterium is
essentially in the form of HD. Thus, the measurement of the HD/H2 ratio may
become a new powerful tool to evaluate the deuterium abundance, D/H, in the
interstellar medium. We report here on the detection of HD toward the high
extinction star HD 73882 [E(B-V)=0.72]. A preliminary analysis is presented.Comment: 4 pages + 4 .ps figures. This paper will appear in a special issue of
Astrophysical Journal Letters devoted to the first scientific results from
the FUSE missio
Searching for Star-Planet interactions within the magnetosphere of HD 189733
HD 189733 is a K2 dwarf, orbited by a giant planet at 8.8 stellar radii. In
order to study magnetospheric interactions between the star and the planet, we
explore the large-scale magnetic field and activity of the host star.
We collected spectra using the ESPaDOnS and the NARVAL spectropolarimeters,
installed at the 3.6-m Canada-France-Hawaii telescope and the 2-m Telescope
Bernard Lyot at Pic du Midi, during two monitoring campaigns (June 2007 and
July 2008).
HD 189733 has a mainly toroidal surface magnetic field, having a strength
that reaches up to 40 G. The star is differentially rotating, with latitudinal
angular velocity shear of domega = 0.146 +- 0.049 rad/d, corresponding to
equatorial and polar periods of 11.94 +- 0.16 d and 16.53 +- 2.43 d
respectively. The study of the stellar activity shows that it is modulated
mainly by the stellar rotation (rather than by the orbital period or the beat
period between the stellar rotation and the orbital periods). We report no
clear evidence of magnetospheric interactions between the star and the planet.
We also extrapolated the field in the stellar corona and calculated the
planetary radio emission expected for HD 189733b given the reconstructed field
topology. The radio flux we predict in the framework of this model is time
variable and potentially detectable with LOFAR
Rossiter-McLaughlin Effect Measurements for WASP-16, WASP-25 and WASP-31
We present new measurements of the Rossiter-McLaughlin (RM) effect for three
WASP planetary systems, WASP-16, WASP-25 and WASP-31, from a combined analysis
of their complete sets of photometric and spectroscopic data. We find a low
amplitude RM effect for WASP-16 (Teff = 5700 \pm 150K), suggesting that the
star is a slow rotator and thus of an advanced age, and obtain a projected
alignment angle of lambda = -4.2 degrees +11.0 -13.9. For WASP-25 (Teff =
5750\pm100K) we detect a projected spin-orbit angle of lambda = 14.6 degrees
\pm6.7. WASP-31 (Teff = 6300\pm100K) is found to be well-aligned, with a
projected spin-orbit angle of lambda = 2.8degrees \pm3.1. A circular orbit is
consistent with the data for all three systems, in agreement with their
respective discovery papers. We consider the results for these systems in the
context of the ensemble of RM measurements made to date. We find that whilst
WASP-16 fits the hypothesis of Winn et al. (2010) that 'cool' stars (Teff <
6250K) are preferentially aligned, WASP-31 has little impact on the proposed
trend. We bring the total distribution of the true spin-orbit alignment angle,
psi, up to date, noting that recent results have improved the agreement with
the theory of Fabrycky & Tremaine (2007) at mid-range angles. We also suggest a
new test for judging misalignment using the Bayesian Information Criterion,
according to which WASP-25 b's orbit should be considered to be aligned.Comment: 20 pages, 14 tables, 10 figures. Accepted to MNRA
The spin-orbit angles of the transiting exoplanets WASP-1b, WASP-24b, WASP-38b and HAT-P-8b from Rossiter-McLaughlin observations
We present observations of the Rossiter-McLaughlin effect for the transiting
exoplanet systems WASP-1, WASP-24, WASP-38 and HAT-P-8, and deduce the
orientations of the planetary orbits with respect to the host stars' rotation
axes. The planets WASP-24b, WASP-38b and HAT-P-8b appear to move in prograde
orbits and be well aligned, having sky-projected spin orbit angles consistent
with zero: {\lambda} = -4.7 \pm 4.0{\deg}, {\lambda} = 15 + 33{\deg}/-43{\deg}
and {\lambda} = -9.7 +9.0{\deg}/-7.7{\deg}, respectively. The host stars have
Teff < 6250 K and conform with the trend of cooler stars having low
obliquities. WASP-38b is a massive planet on a moderately long period,
eccentric orbit so may be expected to have a misaligned orbit given the high
obliquities measured in similar systems. However, we find no evidence for a
large spin-orbit angle. By contrast, WASP-1b joins the growing number of
misaligned systems and has an almost polar orbit, {\lambda} = -79
+4.5{\deg}/-4.3{\deg}. It is neither very massive, eccentric nor orbiting a hot
host star, and therefore does not share the properties of many other misaligned
systems.Comment: Submitted to MNRAS, 13 pages, 8 tables, 6 figures. Includes revised
parameter values for WASP-38 and HAT-P-
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