60 research outputs found
Spectral, Spatial, and Time properties of the hydrogen nebula around exoplanet HD209458b
All far ultraviolet observations of HD209458 tend to support a scenario in
which the inflated hydrogen atmosphere of its planetary companion strongly
absorbs the stellar \lya flux during transit. However, it was not clear how the
transit absorption depends on the selected wavelength range in the stellar line
profile, nor how the atomic hydrogen cloud was distributed spatially around
HD209458b. Here we report a sensitivity study of observed time and spectral
variations of the stellar flux. In particular, the sensitivity of the
absorption depth during transit to the assumed spectral range in the stellar
line profile is shown to be very weak, leading to a transit depth in the range
for all possible wavelength ranges, and thereby confirming
our initially-reported absorption rate. Taking the ratio of the line profile
during transit to the unperturbed line profile, we also show that the spectral
signature of the absorption by the exoplanetary hydrogen nebula is symmetric
and typical of a Lorentzian, optically thick medium. Our results question the
adequacy of models that require a huge absorption and/or a strong asymmetry
between the blue and red side of the absorption line during transit as no such
features could be detected in the HST FUV absorption profile. Finally, we show
that standard atmospheric models of HD209458b provide a good fit to the
observed absorption profile during transit. Other hybrid models assuming a
standard model with a thin layer of superthermal hydrogen on top remain
possible.Comment: 10 pages, 7 figures, accepted for publication in Astrophysical
Journa
The ERE of the "Red Rectangle" revisited
We present in this paper high signal-to-noise long-slit optical spectra of
the Extended Red Emission (ERE) in the "Red Rectangle" (RR) nebula. These
spectra, obtained at different positions in the nebula, reveal an extremely
complex emission pattern on top of the broad ERE continuum. It is well known
that three features converge at large distance from the central object, in
wavelength and profile to the diffuse interstellar bands (DIBs) at 5797, 5849.8
and 6614 ang., (e.g. Sarre et al., 1995). In this paper we give a detailed
inventory of all spectral subfeatures observed in the 5550--6850 ang. spectral
range. Thanks to our high S/N spectra, we propose 5 new features in the RR that
can be associated with DIBs. For the 5550--6200 ang. spectral range our slit
position was on top of the NE spike of the X shaped nebula. A detailed
description of the spatial profile-changes is given of the strongest features
revealing that even far out in the nebula at 24 arcsec from the central star,
there remains a small shift in wavelength of 1 respectively 2 ang between the
ERE subfeatures and the DIB wavelengths of 5797.11 and 5849.78 ang.Comment: 8 pages, 9 figures accepted by Astronomy and Astrophysic
Neutral interstellar hydrogen in the inner heliosphere under the influence of wavelength-dependent solar radiation pressure
With the plethora of detailed results from heliospheric missions and at the
advent of the first mission dedicated IBEX, we have entered the era of
precision heliospheric studies. Interpretation of these data require precision
modeling, with second-order effects quantitatively taken into account. We study
the influence of the non-flat shape of the solar Ly-alpha line on the
distribution of neutral interstellar H in the inner heliosphere. Based on
available data, we (i) construct a model of evolution for the solar Ly-alpha
line profile with solar activity, (ii) modify an existing test-particle code
used to calculate the distribution of neutral interstellar H in the inner
heliosphere so that it takes the dependence of radiation pressure on radial
velocity into account, and (iii) compare the results of the old and new
version. Discrepancies between the classical and Doppler models appear between
~5 and ~3 AU and increase towards the Sun from a few percent to a factor of 1.5
at 1 AU. The classical model overestimates the density everywhere except for a
~60-degr cone around the downwind direction, where a density deficit appears.
The magnitude of the discrepancies appreciably depends on the phase of the
solar cycle, but only weakly on the parameters of the gas at the termination
shock. For in situ measurements of neutral atoms performed at ~1 AU, the
Doppler correction will need to be taken into account, because the
modifications include both the magnitude and direction of the local flux by a
few km/s and degrees, respectively, which, when unaccounted for, would
introduce an error of a few km/s and degrees in determination of the magnitude
and direction of the bulk velocity vector at the termination shock.Comment: 10 pages, 13 figures, accepted by A&
Bipolar outflow on the Asymptotic Giant Branch - the case of IRC+10011
Near-IR imaging of the AGB star IRC+10011 (= CIT3) reveals the presence of a
bipolar structure within the central ~0.1 arcsec of a spherical dusty wind. We
show that the image asymmetries originate from ~1E-4 Msun of swept-up wind
material in an elongated cocoon whose expansion is driven by bipolar jets. We
perform detailed 2D radiative transfer calculations with the cocoon modeled as
two cones extending to ~1,100 AU within an opening angle of ~30deg, imbedded in
a wind with the standard r^{-2} density profile. The cocoon expansion started
<~200 years ago, while the total lifetime of the circumstellar shell is ~5,500
years. Similar bipolar expansion, at various stages of evolution, has been
recently observed in a number of other AGB stars, culminating in jet breakout
from the confining spherical wind. The bipolar outflow is triggered at a late
stage in the evolution of AGB winds, and IRC+10011 provides its earliest
example thus far. These new developments enable us to identify the first
instance of symmetry breaking in the evolution from AGB to planetary nebula.Comment: accepted for publication in MNRAS, high-resolution pdf version can be
found at http://www.leluya.org/downloads/Vinkovic_et_al_IRC+10011.pd
The Red Rectangle: Its Shaping Mechanism and its Source of Ultraviolet Photons
The proto-planetary Red Rectangle nebula is powered by HD 44179, a
spectroscopic binary (P = 318 d), in which a luminous post-AGB component is the
primary source of both luminosity and current mass loss. Here, we present the
results of a seven-year, eight-orbit spectroscopic monitoring program of HD
44179, designed to uncover new information about the source of the
Lyman/far-ultraviolet continuum in the system as well as the driving mechanism
for the bipolar outflow producing the current nebula. Our observations of the
H-alpha line profile around the orbital phase of superior conjunction reveal
the secondary component to be the origin of the fast (max. v~560^{-1}\sun_{max} \ge 17,0002 -
5\times10^{-5}\sun^{-1}\sun$, about 5% of the
luminosity of the entire system. (abridged)Comment: Accepted for publication in Ap
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