624 research outputs found
petitRADTRANS: a Python radiative transfer package for exoplanet characterization and retrieval
We present the easy-to-use, publicly available, Python package petitRADTRANS,
built for the spectral characterization of exoplanet atmospheres. The code is
fast, accurate, and versatile; it can calculate both transmission and emission
spectra within a few seconds at low resolution ( = 1000;
correlated-k method) and high resolution (;
line-by-line method), using only a few lines of input instruction. The somewhat
slower correlated-k method is used at low resolution because it is more
accurate than methods such as opacity sampling. Clouds can be included and
treated using wavelength-dependent power law opacities, or by using optical
constants of real condensates, specifying either the cloud particle size, or
the atmospheric mixing and particle settling strength. Opacities of amorphous
or crystalline, spherical or irregularly-shaped cloud particles are available.
The line opacity database spans temperatures between 80 and 3000 K, allowing to
model fluxes of objects such as terrestrial planets, super-Earths, Neptunes, or
hot Jupiters, if their atmospheres are hydrogen-dominated. Higher temperature
points and species will be added in the future, allowing to also model the
class of ultra hot-Jupiters, with equilibrium temperatures K. Radiative transfer results were tested by cross-verifying the low- and
high-resolution implementation of petitRADTRANS, and benchmarked with the
petitCODE, which itself is also benchmarked to the ATMO and Exo-REM codes. We
successfully carried out test retrievals of synthetic JWST emission and
transmission spectra (for the hot Jupiter TrES-4b, which has a of
1800 K). The code is publicly available at
http://gitlab.com/mauricemolli/petitRADTRANS, and its documentation can be
found at https://petitradtrans.readthedocs.io.Comment: 17 pages, 7 figures, published in A&
Refined physical properties and g',r',i',z',J,H,K transmission spectrum of WASP-23b from the ground
Multi-band observations of planetary transits using the telescope defocus
technique may yield high-quality light curves suitable for refining the
physical properties of exoplanets even with small or medium size telescopes.
Such observations can be used to construct a broad-band transmission spectrum
of transiting planets and search for the presence of strong absorbers. We have
thoroughly characterised the orbital ephemeris and physical properties of the
transiting planet and host star in the WASP-23b system, constructed a
broad-band transmission spectrum of WASP-23b and performed a comparative
analysis with theoretical models of hot Jupiters. We observed a complete
transit of WASP-23b in seven bands simultaneously, using the GROND instrument
on the MPG/ESO 2.2m telescope at La Silla Observatory and telescope
defocussing. The optical data were taken in the Sloan g',r',i' and z' bands.
The resulting light curves are of high quality, with a root-mean-square scatter
of the residual as low as 330ppm in the z'-band, with a cadence of 90s.
Near-infrared data were obtained in the JHK bands. We performed MCMC analysis
of our photometry plus existing radial velocity data to refine measurements of
the ephemeris and physical properties of the WASP-23. We constructed a
broad-band transmission spectrum of WASP-23b and compared it with a theoretical
transmission spectrum of a Hot Jupiter. We measured the central transit time
with a precision about 8s. From this and earlier observations we obtain an
orbital period of P=2.9444300+/-0.0000011d. Our analysis also yielded a larger
radius and mass for the planet (Rp=1.067+0.045-0.038 RJup and,
Mp=0.917+0.040-0.039MJup). The transmission spectrum is marginally flat, given
the limited precision of the measurements for the planet radius and poor
spectral resolution of the data.Comment: 8 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
Diversity of yeasts involved in the fermentation of tchoukoutou, an opaque sorghum beer from Benin
Opaque sorghum beers are traditional alcoholic beverages in several African countries. Known as tchoukoutou in Benin, the beer is often obtained from an uncontrolled fermentation. It is consumed in an actively fermenting state and has a sour taste. The present study characterized and identified the yeasts involved in the fermentation process of this type of beer using the phenotypical approach. Of 12 beers from 4 different locations, the mean values of the pH, titratable acidity, dry matter content and refractive index were respectively 3.67, 0.70 (% as lactic acid) 18.08% and 7.00. Lactic acid bacteria and yeasts were the predominant microorganisms involved in the fermentation of tchoukoutou. Their counts were respectively 9.1 log cfu/ml and 9.1 logcfu/g. Enterobacteriaceae were not detectable in the beer. Based on the phenotypic characters and the assimilation profiles of 40 isolated yeasts, four genera with seven species of yeasts were identified. The yeast species predominant in the Benin opaque sorghum beer tchoukoutou was Saccharomyces cerevisa
Resolving HD 100546 disc in the mid-infrared: Small inner disc and asymmetry near the gap
A region of roughly half of the solar system scale around the star HD 100546
is largely cleared of gas and dust, in contrast to the bright outer disc.
However, some material is observed in the immediate vicinity of the star. We
investigate how the dust is distributed within and outside the gap, and
constrain the disc geometry with mid-infrared interferometric observations
using VLTI/MIDI. With baseline lengths of 40m, our long baseline observations
are sensitive to the inner few AU from the star, and we combined them with
observations at shorter, 15m baselines, to probe emission beyond the gap at up
to 20AU from the star. We modelled the mid-infrared emission using radial
temperature profiles. Our model is composed of infinitesimal concentric annuli
emitting as black bodies, and it has distinct inner and outer disc components.
We derived an upper limit of 0.7AU for the radial size of the inner disc, from
our longest baseline data. This small dusty disc is separated from the edge of
the outer disc by a large, roughly 10AU wide gap. Our short baseline data place
a bright ring of emission at 11+-1AU, consistent with prior observations of the
transition region between the gap and the outer disc, known as the disc wall.
The inclination and position angle are constrained by our data to i=53+-8deg
and PA=145+-5deg. Compared to the rim and outer disc geometry this suggests
co-planarity. Brightness asymmetry is evident in both short and long baseline
data, and it is unequivocally discernible from any atmospheric or instrumental
effects. The origin of the asymmetry is consistent with the bright disc wall,
which we find to be 1-2AU wide. The gap is cleared of micron-sized dust, but we
cannot rule out the presence of larger particles and/or perturbing bodies.Comment: 12 pages, 9 figures, accepted for publication in A&
The structure of the protoplanetary disk surrounding three young intermediate mass stars. II. Spatially resolved dust and gas distribution
[Abridged] We present the first direct comparison of the distribution of the
gas, as traced by the [OI] 6300 AA emission, and the dust, as traced by the 10
micron emission, in the protoplanetary disk around three intermediate-mass
stars: HD 101412, HD 135344 B and HD 179218. N-band visibilities were obtained
with VLTI/MIDI. Simple geometrical models are used to compare the dust emission
to high-resolution optical spectra in the 6300 AA [OI] line of the same
targets. The disks around HD 101412 and HD 135344 B appear strongly flared in
the gas, but self-shadowed in the dust beyond ~ 2 AU. In both systems, the 10
micron emission is rather compact (< 2 AU) while the [OI] brightness profile
shows a double peaked structure. The inner peak is strongest and is consistent
with the location of the dust, the outer peak is fainter and is located at 5-10
AU. Spatially extended PAH emission is found in both disks. The disk around HD
179218 is flared in the dust. The 10 micron emission emerges from a double
ring-like structure with the first ring peaking at ~ 1 AU and the second at ~
20 AU. No dust emission is detected between ~ 3 -- 15 AU. The oxygen emission
seems also to come from a flared structure, however, the bulk of this emission
is produced between ~ 1 -- 10 AU. This could indicate a lack of gas in the
outer disk or could be due to chemical effects which reduce the abundance of OH
-- the parent molecule of the observed [OI] emission -- further away from the
star. The three systems, HD 179218, HD 135344 B and HD 101412, may form an
evolutionary sequence: the disk initially flared becomes flat under the
combined action of gas-dust decoupling, grain growth and dust settling.Comment: Accepted for publication in A&
A compact dusty disk around the Herbig Ae star HR 5999 resolved with VLTI / MIDI
This is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this record.Aims. We have used mid-infrared long-baseline interferometry to resolve the circumstellar material around the Herbig Ae star
HR 5999, providing the first direct measurement of its angular size, and to derive constraints on the spatial distribution of the dust.
Methods. MIDI at the VLTI was used to obtain a set of ten spectrally dispersed (8−13 µm) interferometric measurements of HR 5999
at different projected baseline lengths and position angles. To derive constraints on the geometrical distribution of the dust, we
compared our interferometric measurements to 2D, frequency-dependent radiation transfer simulations of circumstellar disks and
envelopes.
Results. The derived visibility values between ∼0.5 and ∼0.9 show that the mid-infrared emission from HR 5999 is clearly resolved.
The characteristic size of the emission region depends on the projected baseline length and position angle, and it ranges between
∼5−15 milliarcsec (Gauss FWHM), corresponding to remarkably small physical sizes of ∼1−3 AU. For disk models with radial
power-law density distributions, the relatively weak but very extended emission from outer disk regions (>∼3 AU) leads to model visibilities
that are significantly lower than the observed visibilities, making these models inconsistent with the MIDI data. Disk models
in which the density is truncated at outer radii of ∼2−3 AU, on the other hand, provide good agreement with the data.
Conclusions. A satisfactory fit to the observed MIDI visibilities of HR 5999 is found with a model of a geometrically thin disk that is
truncated at 2.6 AU and seen under an inclination angle of 58◦ (i.e. closer to an edge-on view than to a face-on view). Neither models
of a geometrically thin disk seen nearly edge-on, nor models of spherical dust shells can achieve agreement between the observed
and predicted visibilities. The reason why the disk is so compact remains unclear; we speculate that it has been truncated by a close
binary companion
Community-dwelling and recently widowed older adults:Effects of spousal loss on psychological well-being, perceived quality of life, and health-care costs
This study is on the effects of spousal loss among older adults who continue to live independently after bereavement. Little longitudinal studies focus on this group, which is of special interest, since in many countries, care policy and system reform are aimed at increasing independent living among older adults. Using longitudinal data from a Dutch public data repository, we investigate the effects of spousal loss on psychological well-being, perceived quality of life, and (indication of) yearly health-care costs. Of the respondents who had a spouse and were living independently (N = 9,400) at baseline, the majority had not lost their spouse after 12 months (T12, n = 9,150), but 2.7% (n = 250) had lost their spouse and still lived independently. We compared both groups using multivariate regression (ordinary least squares) analyses. The results show that spousal loss significantly lowers scores on psychological well-being and perceived quality of life, but we found no effect on health-care costs
Physical properties of the WASP-44 planetary system from simultaneous multi-colour photometry
We present ground-based broad-band photometry of two transits in the WASP-44
planetary system obtained simultaneously through four optical (Sloan g', r',
i', z') and three near-infrared (NIR; J, H, K) filters. We achieved low
scatters of 1-2 mmag per observation in the optical bands with a cadence of 48
s, but the NIR-band light curves present much greater scatter. We also observed
another transit of WASP-44 b by using a Gunn-r filter and telescope
defocussing, with a scatter of 0.37 mmag per point and an observing cadence
around 135 s. We used these data to improve measurements of the time of
mid-transit and the physical properties of the system. In particular, we
improved the radius measurements of the star and planet by factors of 3 and 4,
respectively. We find that the radius of WASP-44 b is 1.002 R_Jup, which is
slightly smaller than previously thought and differs from that expected for a
core-free planet. In addition, with the help of a synthetic spectrum, we
investigated the theoretically-predicted variation of the planetary radius as a
function of wavelength, covering the range 370-2440 nm. We can rule out extreme
variations at optical wavelengths, but unfortunately our data are not precise
enough (especially in the NIR bands) to differentiate between the theoretical
spectrum and a radius which does not change with wavelength.Comment: 13 pages, 6 figures, to appear in Monthly Notices of the Royal
Astronomical Societ
Willingness to pay for market information received by mobile phone among smallholder pineapple farmers in Benin
Published online: 04 April 2016Access to up-to-date information on market prices and quality requirements remains a key issue for smallholder farmers’ access to high income markets. The aim of this chapter is to explore the problem of information asymmetry between farmers and buyers in the pineapple supply chain in Benin, and to assess strategies using mobile phones to overcome this problem. Data was collected from an exploratory case study in Ghana and a survey with 285 farmers in Benin. Results show that farmers face market information asymmetry leading to lower prices and income. In Ghana, market price alerts through mobile phones messaging allowed decreasing transaction costs for farmers. In Benin, farmers expressed a willingness to pay a premium of up to US$ 2.5 per month to get market price and quality information. Econometric analysis showed that decisive factors for the size of the premium include farm location, market channel, profit margin, contact with agricultural extension services, and technical support from buyers
The radial distribution of dust species in young brown dwarf disks
We present a study of the radial distribution of dust species in young brown
dwarf disks. Our work is based on a compositional analysis of the 10 and 20
micron silicate emission features for brown dwarfs in the Taurus-Auriga
star-forming region. A fundamental finding of our work is that brown dwarfs
exhibit stronger signs of dust processing in the cold component of the disk,
compared to the higher mass T Tauri stars in Taurus. For nearly all of our
targets, we find a flat disk structure, which is consistent with the stronger
signs of dust processing observed in these disks. For the case of one brown
dwarf, 2M04230607, we find the forsterite mass fraction to be a factor of ~3
higher in the outer disk compared to the inner disk region. Simple large-scale
radial mixing cannot account for this gradient in the dust chemical
composition, and some local crystalline formation mechanism may be effective in
this disk. The relatively high abundance of crystalline silicates in the outer
cold regions of brown dwarf disks provides an interesting analogy to comets. In
this context, we have discussed the applicability of the various mechanisms
that have been proposed for comets on the formation and the outward transport
of high-temperature material. We also present Chandra X-ray observations for
two Taurus brown dwarfs, 2M04414825 and CFHT-BD-Tau 9. We find 2M04414825,
which has a ~12% crystalline mass fraction, to be more than an order of
magnitude brighter in X-ray than CFHT-BD-Tau 9, which has a ~35% crystalline
mass fraction. Combining with previous X-ray data, we find the inner disk
crystalline mass fractions to be anti-correlated with the X-ray strength.Comment: Accepted in MNRA
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