49 research outputs found
Exocomets in the circumstellar gas disk of HD 172555
The source HD172555 is a young A7V star surrounded by a debris disk with a
gaseous component. Here, we present the detection of variable absorption
features detected simultaneously in the Ca II K and H doublet lines (at 3,933
and 3,968 Angstrom). We identified the presence of these absorption signatures
at four different epochs in the 129 HARPS high-resolution spectra gathered
between 2004 and 2011. These transient absorption features are most likely due
to Falling Evaporating Bodies (FEBs, or exocomets) that produce absorbing gas
observed transiting in front of the central star. We also detect a stable Ca II
absorption component at the star's radial velocity. With no corresponding
detection in the Na I line, the resulting very low upper limit for the NaI/CaII
ratio suggests that this absorption is due to circumstellar gas.Comment: Accepted for publication in Astronomy&Astrophysics Letter
Temperature-Pressure Profile of the hot Jupiter HD 189733b from HST Sodium Observations: Detection of Upper Atmospheric Heating
We present transmission spectra of the hot Jupiter HD 189733b taken with the
Space Telescope Imaging Spectrograph aboard HST. The spectra cover the
wavelength range 5808-6380 Ang with a resolving power of R=5000. We detect
absorption from the NaI doublet within the exoplanet's atmosphere at the 9
sigma confidence level within a 5 Ang band (absorption depth 0.09 +/- 0.01%)
and use the data to measure the doublet's spectral absorption profile. We
detect only the narrow cores of the doublet. The narrowness of the feature
could be due to an obscuring high-altitude haze of an unknown composition or a
significantly sub-solar NaI abundance hiding the line wings beneath a H2
Rayleigh signature. We compare the spectral absorption profile over 5.5 scale
heights with model spectral absorption profiles and constrain the temperature
at different atmospheric regions, allowing us to construct a vertical
temperature profile. We identify two temperature regimes; a 1280 +/- 240 K
region derived from the NaI doublet line wings corresponding to altitudes below
~ 500 km, and a 2800 +/- 400 K region derived from the NaI doublet line cores
corresponding to altitudes from ~ 500-4000 km. The zero altitude is defined by
the white-light radius of Rp/Rstar=0.15628 +/- 0.00009. The temperature rises
with altitude, which is likely evidence of a thermosphere. The absolute
pressure scale depends on the species responsible for the Rayleigh signature
and its abundance. We discuss a plausible scenario for this species, a
high-altitude silicate haze, and the atmospheric temperature-pressure profile
that results. In this case, the high altitude temperature rise for HD 189733b
occurs at pressures of 10^-5 to 10^-8 bar
A Spitzer Search for Water in the Transiting Exoplanet HD189733b
We present Spitzer Space Telescope observations of the extrasolar planet
HD189733b primary transit, obtained simultaneously at 3.6 and 5.8 microns with
the Infrared Array Camera. The system parameters, including planetary radius,
stellar radius, and impact parameter are derived from fits to the transit light
curves at both wavelengths. We measure two consistent planet-to-star radius
ratios, (Rp/Rs)[3.6m] = 0.1560 +/- 0.0008(stat) +/- 0.0002(syst) and
(Rp/Rs)[5.8m] = 0.1541 +/- 0.0009(stat) +/- 0.0009(syst), which include
both the random and systematic errors in the transit baseline. Although planet
radii are determined at 1%-accuracy, if all uncertainties are taken into
account the resulting error bars are still too large to allow for the detection
of atmospheric constituants like water vapour. This illustrates the need to
observe multiple transits with the longest possible out-of-transit baseline, in
order to achieve the precision required by transmission spectroscopy of giant
extrasolar planets.Comment: Accepted in The Astrophysical Journal Letter
A Spitzer Search for Water in the Transiting Exoplanet HD189733b
We present Spitzer Space Telescope observations of the extrasolar planet
HD189733b primary transit, obtained simultaneously at 3.6 and 5.8 microns with
the Infrared Array Camera. The system parameters, including planetary radius,
stellar radius, and impact parameter are derived from fits to the transit light
curves at both wavelengths. We measure two consistent planet-to-star radius
ratios, (Rp/Rs)[3.6m] = 0.1560 +/- 0.0008(stat) +/- 0.0002(syst) and
(Rp/Rs)[5.8m] = 0.1541 +/- 0.0009(stat) +/- 0.0009(syst), which include
both the random and systematic errors in the transit baseline. Although planet
radii are determined at 1%-accuracy, if all uncertainties are taken into
account the resulting error bars are still too large to allow for the detection
of atmospheric constituants like water vapour. This illustrates the need to
observe multiple transits with the longest possible out-of-transit baseline, in
order to achieve the precision required by transmission spectroscopy of giant
extrasolar planets.Comment: Accepted in The Astrophysical Journal Letter
The Earth as an extrasolar transiting planet - II: HARPS and UVES detection of water vapor, biogenic O, and O
The atmospheric composition of transiting exoplanets can be characterized
during transit by spectroscopy. For the transit of an Earth twin, models
predict that biogenic and should be detectable, as well as water
vapour, a molecule linked to habitability as we know it on Earth. The aim is to
measure the Earth radius versus wavelength - or the atmosphere
thickness - at the highest spectral resolution available to fully
characterize the signature of Earth seen as a transiting exoplanet. We present
observations of the Moon eclipse of 21-12-2010. Seen from the Moon, the Earth
eclipses the Sun and opens access to the Earth atmosphere transmission
spectrum. We used HARPS and UVES spectrographs to take penumbra and umbra
high-resolution spectra from 3100 to 10400 Ang. A change of the quantity of
water vapour above the telescope compromised the quality of the UVES data. We
corrected for this effect in the data processing. We analyzed the data by 3
different methods. The 1st method is based on the analysis of pairs of penumbra
spectra. The 2nd makes use of a single penumbra spectrum, and the 3rd of all
penumbra and umbra spectra. Profiles are obtained with the three
methods for both instruments. The 1st method gives the best result, in
agreement with a model. The second method seems to be more sensitive to the
Doppler shift of solar spectral lines with respect to the telluric lines. The
3rd method makes use of umbra spectra which bias the result, but it can be
corrected for this a posteriori from results with the first method. The 3
methods clearly show the spectral signature of the Rayleigh scattering in the
Earth atmosphere and the bands of HO, O, and O. Sodium is detected.
Assuming no atmospheric perturbations, we show that the E-ELT is theoretically
able to detect the A-band in 8~h of integration for an Earth twin at
10pc.Comment: Final version accepted for publication in A&A - 21 pages, 27 figures.
Abstract above slightly shortened wrt the original. The ArXiv version has low
resolution figures, but a version with full resolution figures is available
here:
http://www.obs-hp.fr/~larnold/publi_to_download/eclipse2010_AA_v5_final.pd
Infrared Transmission Spectra for Extrasolar Giant Planets
Among the hot Jupiters that transit their parent stars known to date, the two
best candidates to be observed with transmission spectroscopy in the
mid-infrared (MIR) are HD189733b and HD209458b, due to their combined
characteristics of planetary density, orbital parameters and parent star
distance and brightness. Here we simulate transmission spectra of these two
planets during their primary eclipse in the MIR, and we present sensitivity
studies of the spectra to the changes of atmospheric thermal properties,
molecular abundances and C/O ratios. Our model predicts that the dominant
species absorbing in the MIR on hot Jupiters are water vapor and carbon
monoxide, and their relative abundances are determined by the C/O ratio. Since
the temperature profile plays a secondary role in the transmission spectra of
hot Jupiters compared to molecular abundances, future primary eclipse
observations in the MIR of those objects might give an insight on EGP
atmospheric chemistry. We find here that the absorption features caused by
water vapor and carbon monoxide in a cloud-free atmosphere, are deep enough to
be observable by the present and future generation of space-based
observatories, such as Spitzer Space Telescope and James Webb Space Telescope.
We discuss our results in light of the capabilities of these telescopes.Comment: 12 pages, 6 figures, ApJ accepte
Spatial Variability in the Ratio of Interstellar Atomic Deuterium to Hydrogen. II. Observations toward Gamma2 Velorum and Zeta Puppis by the Interstellar Medium Absorption Profile Spectrograph
To measure interstellar atomic deuterium abundances, we used the Interstellar
Medium Absorption Profile Spectrograph (IMAPS) to obtain spectra of gamma2 Vel
and zeta Pup over the wavelength interval 930-1150 A at a resolving power of
80,000. The interstellar D I features are resolved and cleanly separated from
interstellar H I in the Ly-delta and Ly-epsilon profiles of both sight lines,
and also in the Ly-gamma profile of zeta Pup. The D I profiles were modeled
using a velocity template derived from several N I lines in the IMAPS spectra
recorded at higher S/N. To find the best D I column density, we minimized
chi-squares for model D I profiles that included not only the N(D I) as a free
parameter, but also the effects of several potential sources of systematic
error which could also be varied. For both stars, H I column densities were
measured by analyzing Ly-alpha absorption profiles in a large number of IUE
high dispersion spectra. Ultimately we found that D/H = 2.18(+0.36,-0.31)e-5
for gamma2 Vel and 1.42(+0.25,-0.23)e-5 for zeta Pup, values that contrast
markedly with D/H derived in Paper I for delta Ori (the stated errors are 90%
confidence limits). Evidently, the atomic D/H ratio in the ISM, averaged over
path lengths of 250 to 500 pc, exhibits significant spatial variability.
Furthermore, variations in D/H do not appear to be anticorrelated with N/H.
Within the framework of standard Big Bang Nucleosynthesis, the large value of
D/H found toward gamma2 Vel is equivalent to a cosmic baryon density of Omega_B
h^2 = 0.023 (+-0.002), which we regard as an upper limit since there is no
correction for the destruction of deuterium in stars.Comment: 37 pages, 10 figures, to appear in the Astrophysical Journa