2,359 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
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
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&
Young stars in Epsilon Cha and their disks: disk evolution in sparse associations
(abridge) The nearby young stellar association Epsilon Cha association has an
estimated age of 3-5 Myr, making it an ideal laboratory to study the disk
dissipation process and provide empirical constraints on the timescale of
planet formation. We combine the available literature data with our Spitzer IRS
spectroscopy and VLT/VISIR imaging data. The very low mass stars USNO-B120144.7
and 2MASS J12005517 show globally depleted spectral energy distributions
pointing at strong dust settling. 2MASS J12014343 may have a disk with a very
specific inclination where the central star is effectively screened by the cold
outer parts of a flared disk but the 10 micron radiation of the warm inner disk
can still reach us. We find the disks in sparse stellar associations are
dissipated more slowly than those in denser (cluster) environments. We detect
C_{2}H_{2} rovibrational band around 13.7 micron on the IRS spectrum of
USNO-B120144.7. We find strong signatures of grain growth and crystallization
in all Epsilon Cha members with 10 micron features detected in their IRS
spectra. We combine the dust properties derived in the Epsilon Cha sample with
those found using identical or similar methods in the MBM 12, Coronet cluster,
Eta Cha associations, and in the cores to disks (c2d) legacy program. We find
that disks around low-mass young stars show a negative radial gradient in the
mass-averaged grain size and mass fraction of crystalline silicates. A positive
correlation exists between the mass-averaged grain sizes of amorphous silicates
and the accretion rates if the latter is above ~10^{-9} Msun/yr, possibly
indicating that those disks are sufficiently turbulent to prevent grains of
several microns in size to sink into the disk interior.Comment: 17 pages, 18 figures, 6 tables, language revised; accepted to A&
Dust in the wind: Crystalline silicates, corundum and periclase in PG 2112+059
We have determined the mineralogical composition of dust in the Broad
Absorption Line (BAL) quasar PG 2112+059 using mid-infrared spectroscopy
obtained with the Spitzer Space Telescope. From spectral fitting of the solid
state features, we find evidence for Mg-rich amorphous silicates with olivine
stoichiometry, as well as the first detection of corundum (Al_2O_3) and
periclase (MgO) in quasars. This mixed composition provides the first direct
evidence for a clumpy density structure of the grain forming region. The
silicates in total encompass 56.5% of the identified dust mass, while corundum
takes up 38 wt.%. Depending on the choice of continuum, a range of mass
fractions is observed for periclase ranging from 2.7% in the most conservative
case to 9% in a less constrained continuum. In addition, we identify a feature
at 11.2 micron as the crystalline silicate forsterite, with only a minor
contribution from polycyclic aromatic hydrocarbons. The 5% crystalline silicate
fraction requires high temperatures such as those found in the immediate quasar
environment in order to counteract rapid destruction from cosmic rays.Comment: 2 figure
ISO spectroscopy of circumstellar dust in 14 Herbig Ae/Be systems: towards an understanding of dust processing
We present Infrared Space Observatory (ISO) spectra of fourteen isolated
Herbig Ae/Be (HAEBE) stars, to study the characteristics of their circumstellar
dust. These spectra show large star-to-star differences, in the emission
features of both carbon-rich and oxygen-rich dust grains. The IR spectra were
combined with photometric data ranging from the UV through the optical into the
sub-mm region. We defined two key groups, based upon the spectral shape of the
infrared region. The derived results can be summarized as follows: (1) the
continuum of the IR to sub-mm region of all stars can be reconstructed by the
sum of a power-law and a cool component, which can be represented by a black
body. Possible locations for these components are an optically thick,
geometrically thin disc (power-law component) and an optically thin flared
region (black body); (2) all stars have a substantial amount of cold dust
around them, independent of the amount of mid-IR excess they show; (3) also the
near-IR excess is unrelated to the mid-IR excess, indicating different
composition/location of the emitting material; (4) remarkably, some sources
lack the silicate bands; (5) apart from amorphous silicates, we find evidence
for crystalline silicates in several stars, some of which are new detections;
(6) PAH bands are present in at least 50% of our sample, and their appearance
is slightly different from PAHs in the ISM; (7) PAH bands are, with one
exception, not present in sources which only show a power-law continuum in the
IR; their presence is unrelated to the presence of the silicate bands; (8) the
dust in HAEBE stars shows strong evidence for coagulation; this dust processing
is unrelated to any of the central star properties (such as age, spectral type
and activity).Comment: 15 pages, accepted by A&
DIGIT survey of far-infrared lines from protoplanetary disks I
[abridged] We present far-infrared spectroscopic observations of PMS stars
taken with Herschel/PACS as part of the DIGIT key project. The sample includes
22 Herbig AeBe and 8 T Tauri sources. Multiple atomic fine structure and
molecular lines are detected at the source position: [OI], [CII], CO, OH, H_2O,
CH^+. The most common feature is the [OI] 63micron line detected in almost all
of the sources followed by OH. In contrast with CO, OH is detected toward both
Herbig AeBe groups (flared and non-flared sources). An isothermal LTE slab
model fit to the OH lines indicates column densities of 10^13 < N_OH < 10^16
cm^-2, emitting radii 15 < r < 100 AU and excitation temperatures 100 < T_ex <
400 K. The OH emission thus comes from a warm layer in the disk at intermediate
stellar distances. Warm H_2O emission is detected through multiple lines toward
the T Tauri systems AS 205, DG Tau, S CrA and RNO 90 and three Herbig AeBe
systems HD 104237, HD 142527, HD 163296 (through line stacking). Overall,
Herbig AeBe sources have higher OH/H_2O abundance ratios across the disk than
do T Tauri disks, from near- to far-infrared wavelengths. Far-infrared CH^+
emission is detected toward HD 100546 and HD 97048. The slab model suggests
moderate excitation (T_ex ~ 100 K) and compact (r ~ 60 AU) emission in the case
of HD 100546. The [CII] emission is spatially extended in all sources where the
line is detected. This suggests that not all [CII] emission is associated with
the disk and that there is a substantial contribution from diffuse material
around the young stars. The flux ratios of the atomic fine structure lines are
consistent with a disk origin for the oxygen lines for most of the sources.Comment: Accepted for publication in A&
Molecular Signatures in the Near Infrared Dayside Spectrum of HD 189733b
We have measured the dayside spectrum of HD 189733b between 1.5 and 2.5
microns using the NICMOS instrument on the Hubble Space Telescope. The emergent
spectrum contains significant modulation, which we attribute to the presence of
molecular bands seen in absorption. We find that water (H2O), carbon monoxide
(CO), and carbon dioxide (CO2) are needed to explain the observations, and we
are able to estimate the mixing ratios for these molecules. We also find
temperature decreases with altitude in the ~0.01 < P < ~1 bar region of the
dayside near-infrared photosphere and set an upper limit to the dayside
abundance of methane (CH4) at these pressures.Comment: 13 pages, 3 figures. accepted in Astrophysical Journal Letter
Nutrigenomics: a survey on continuing education needs of registered dietitians in Malaysia
Nutrigenomics or diet-gene interactions have become the focus of much nutritional research
in recent years. However, little is known about Malaysian dietitians’ involvement and education
needs regarding nutrigenomics. The aim of this survey was to assess the awareness and continuing
education needs for registered dietitians regarding nutrigenomics. A validated questionnaire
was developed to assess involvement, knowledge, chances, barriers and continuing education
needs on nutrigenomics among Malaysian dietitians. The questionnaire was distributed to all
(n=90) registered dietitians who attended the Malaysian Dietitians’ Association Scientific Conference
in year 2007 which resulted in a 46% response rate (n=41). The majority of the respondents (91.5%)
graduated from local universities between the years 1988 to 2007. All respondents used information
on dietary pattern, lifestyle and body mass index for composing dietary advice. For the same
purpose, a high percentage of respondents (91.4%) used family history but only two respondents (5.7%) experienced relying on genetic tests. Although 85.7% of respondents are aware of
nutrigenomics, only 22.3% understood its definition. More than 80% of dietitians are interested in
learning and increase their knowledge on human genetics, nutrigenomics and ways to communicate
this knowledge to the public. Three highest barriers to the application of nutrigenomics are lack
of patient education materials (91.5%), lack of background knowledge among dietitians (85.7%)
and lack of continuing education for dietitians (80%). The most preferred learning activity for
continuing education was seminars. This survey revealed great interest among dietitians to increase
and update their knowledge on nutrigenomics. There is a need to include genetics and nutrigenomics
knowledge in the continuing education programmes for dietitians in Malaysia. This may help
dietitians to make informed decision about the possible use of nutrigenomics in their practice
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