2,374 research outputs found
The mid-infrared spectrum of the transiting exoplanet HD 209458b
We report the spectroscopic detection of mid-infrared emission from the
transiting exoplanet HD 209458b. Using archive data taken with the Spitzer/IRS
instrument, we have determined the spectrum of HD 209458b between 7.46 and
15.25 microns. We have used two independent methods to determine the planet
spectrum, one differential in wavelength and one absolute, and find the results
are in good agreement. Over much of this spectral range, the planet spectrum is
consistent with featureless thermal emission. Between 7.5 and 8.5 microns, we
find evidence for an unidentified spectral feature. If this spectral modulation
is due to absorption, it implies that the dayside vertical temperature profile
of the planetary atmosphere is not entirely isothermal. Using the IRS data, we
have determined the broad-band eclipse depth to be 0.00315 +/- 0.000315,
implying significant redistribution of heat from the dayside to the nightside.
This work required development of improved methods for Spitzer/IRS data
calibration that increase the achievable absolute calibration precision and
dynamic range for observations of bright point sources.Comment: 35 pages, 12 figures, revised version accepted by the Astrophysical
Journa
The Onset of Planet Formation in Brown Dwarf Disks
The onset of planet formation in protoplanetary disks is marked by the growth
and crystallization of sub-micron-sized dust grains accompanied by dust
settling toward the disk mid-plane. Here we present infrared spectra of disks
around brown dwarfs and brown dwarf candidates. We show that all three
processes occur in such cool disks in a way similar or identical to that in
disks around low- and intermediate-mass stars. These results indicate that the
onset of planet formation extends to disks around brown dwarfs, suggesting that
planet formation is a robust process occurring in most young circumstellar
disks.Comment: Published in Science 2005, vol 310, 834; 3 pages in final format, 4
figures + 8 pages Supporting Online Material. For final typeset, see
http://www.sciencemag.org/cgi/content/abstract/310/5749/834?eto
Mobile travel services: A three-country study into the impact of local circumstances
In this paper we explore the difference in acceptance patterns of mobile services that are related to travelling in three countries: Finland, The Netherlands and New Zealand. The objective of this paper is to understand differences in the use of Mobile Travel Services in three countries that differ with regard to national travel patterns. This paper also contributes to the discussion of the relevance of the Technology Acceptance Model for mobile applications by focusing on the importance of context characteristics, such as the degree of mobility of the user, the social situation people are in, and their need for social interaction. Based on surveys in the three countries as executed in 2009, we use structural equation modelling to find differences in patterns. The paper concludes that context factors have an impact on the relation between the core concepts as used in TAM and DOI approach, and that t here is a clear need for closer research in the moderating effect of physical (e.g. mobile and fixed context) and social context, as well as the need for social interaction. Moreover it is clear that country specific characteristics play a role in the acceptance of mobile travel services. As we pointed out in many of our research projects before the acceptance and use of mobile services requires deep understanding from individual, context and technology related characteristics and their mutual interactions
High spatial resolution mid-infrared observations of the low-mass young star TW Hya
We want to improve knowledge of the structure of the inner few AU of the
circumstellar disk around the nearby T Tauri star TW Hya. Earlier studies have
suggested the existence of a large inner hole, possibly caused by interactions
with a growing protoplanet. We used interferometric observations in the N-band
obtained with the MIDI instrument on the Very Large Telescope Interferometer,
together with 10 micron spectra recorded by the infrared satellite Spitzer. The
fact that we were able to determine N-band correlated fluxes and visibilities
for this comparatively faint source shows that MIR interferometry can be
applied to a large number of low-mass young stellar objects.
The MIR spectra obtained with Spitzer reveal emission lines from HI (6-5), HI
(7-6), and [Ne II] and show that over 90% of the dust we see in this wavelength
regime is amorphous. According to the correlated flux measured with MIDI, most
of the crystalline material is in the inner, unresolved part of the disk, about
1 AU in radius. The visibilities exclude the existence of a very large (3-4 AU
radius) inner hole in the circumstellar disk of TW Hya, which was required in
earlier models. We propose instead a geometry of the inner disk where an inner
hole still exists, but at a much reduced radius, with the transition from zero
to full disk height between 0.5 and 0.8 AU, and with an optically thin
distribution of dust inside. Such a model can comply with SED and MIR
visibilities, as well as with visibility and extended emission observed in the
NIR at 2 micron. If a massive planet was the reason for this inner hole, as has
been speculated, its orbit would have to be closer to the star than 0.3 AU.
Alternatively, we may be witnessing the end of the accretion phase and an early
phase of an inward-out dispersal of the circumstellar disk.Comment: 13 pages, 9 figures, accepted by A&
Mobile travel services: the effect of moderating context factors
This article has two objectives: (1) to draw an international comparison regarding the acceptance of mobile travel services in three countries with different profiles when it comes to travelling and mobile telecommunications, and (2) to extend relevant literature on mobile applications, more specifically travel services, by including context-related concepts, taking moderating factors like location, mobility of users, physical, and social context into account. Based on surveys that were carried out in 2009, structural equation modelling is used to identify differences in patterns in the use of mobile travel services and in the role of context-related variables. the conclusion of this article is that context-related factors, that is, mobility and (physical and social) context, have an impact on the relationship between the core concepts of technology Acceptance model (TAM) and Diffusion of Innovation (DoI) research. many studies on the acceptance and use of mobile services indicate that a deep understanding is needed of individual, context-related, and technological characteristics and the way they interact. this is also highly relevant to the travel industry, which wants to utilize the opportunities provided by mobile technology
Dynamic walking stability of the TUlip robot by means of the extrapolated center of mass
The TUlip robot was created to participate in the teensize league of Robocup. The TUlip robot is a bipedal robot intended for dynamic walking. It has six degrees of freedom for each leg: three for the hip, one for the knee and two for the ankle. This paper elaborates on the algorithm for the sideways control during gait. The algorithm uses the extrapolated center of mass (XcoM) to achieve limit cycle stability. The algorithm is tested in simulation using a linear inverted pendulum and, then, experimentally applied to the TUlip robot. The result is an adaptive behavior of the TUlip robot, promising for future application to legged robot stability
The absence of the 10 um silicate feature in the isolated Herbig Ae star HD 100453
We analyse the optical and IR spectra, as well as the spectral energy
distribution (UV to mm) of the candidate Herbig Ae star HD100453. This star is
particular, as it shows an energy distribution similar to that of other
isolated Herbig Ae/Be stars (HAEBEs), but unlike most of them, it does not have
a silicate emission feature at 10 um, as is shown in Meeus (2001). We confirm
the HAEBE nature of HD100453 through an analysis of its optical spectrum and
derived location in the H-R diagram. The IR spectrum of HD100453 is modelled by
an optically thin radiative transfer code, from which we derive constraints on
the composition, grain-size and temperature distribution of the circumstellar
dust. We show that it is both possible to explain the lack of the silicate
feature as (1) a grain-size effect - lack of small silicate grains, and (2) a
temperature effect - lack of small, hot silicates, as proposed by Dullemond
(2001), and discuss both possibilities.Comment: 9 pages, 7 figures; accepted by A&
Millennium Ecosystem Assessment Scenario drivers (1970-2050): Climate and hydrological alterations
This study was carried out to support and enhance a series of global studies assessing contemporary and future changes in nutrient export from watersheds (Global Nutrient Export from Watersheds (NEWS)). Because hydrography is one of the most important drivers in nutrient transport, it was essential to establish how climatic changes and direct human activities (primarily irrigation and reservoir operations) affect the hydrological cycle. Contemporary and future hydrography was established by applying a modified version of a global water balance and transport model (WBMplus) driven by present and future climate forcing, as described in the Millennium Ecosystem Assessment scenarios (1970-2050). WBMplus represents a major upgrade to previous WBM implementations by incorporating irrigational water uptake and reservoir operations in a single modeling framework. Contemporary simulations were carried out by using both observed climate forcings from the Climate Research Unit of East Anglia (CRU) data sets and from Global Circulation Model (GCM) simulations that are comparable to the future simulations from the same GCM forcings. Future trends in three key human activities (land use, irrigation, and reservoirs operation for hydropower) were taken from the Integrated Model to Assess the Global Environment (IMAGE). The reservoir operation required establishing a realistic distribution of future reservoirs since the IMAGE model provided only the hydropower potentials for the different future scenarios
Herschel observations of the circumstellar environment of the two Herbig Be stars R Mon and PDS27
We report and analyse FIR observations of two Herbig Be stars, R Mon and PDS
27, obtained with Herschel's instruments PACS and SPIRE. We construct SEDs and
derive the infrared excess. We extract line fluxes from the PACS and SPIRE
spectra and construct rotational diagrams in order to estimate the excitation
temperature of the gas. We derive CO, [OI] and [CI] luminosities to determine
physical conditions of the gas, as well as the dominant cooling mechanism. We
confirm that the Herbig Be stars are surrounded by remnants from their parental
clouds, with an IR excess that mainly originates in a disc. In R Mon we detect
[OI], [CI], [CII], CO (26 transitions), water and OH, while in PDS 27 we only
detect [CI] and CO (8 transitions). We attribute the absence of OH and water in
PDS 27 to UV photo-dissociation and photo-evaporation. From the rotational
diagrams, we find several components for CO: we derive 94990 K,
35820 K & 7712 K for R Mon, 9612 K & 314 K for PDS 27 and
258 K & 276 K for their respective compact neighbours. The forsterite
feature at 69m was not detected in either of the sources, probably due to
the lack of (warm) crystalline dust in a flat disc. We find that cooling by
molecules is dominant in the Herbig Be stars, while this is not the case in
Herbig Ae stars where cooling by [OI] dominates. Moreover, we show that in the
Herbig Be star R Mon, outflow shocks are the dominant gas heating mechanism,
while in Herbig Ae stars this is stellar. The outflow of R Mon contributes to
the observed line emission by heating the gas, both in the central spaxel/beam
covering the disc and the immediate surroundings, as well as in those
spaxels/beams covering the parabolic shell around it. PDS 27, a B2 star, has
dispersed a large part of its gas content and/or destroyed molecules; this is
likely given its intense UV field.Comment: Accepted for publication in Astronomy & Astrophysic
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