2,379 research outputs found
The orbital motion, absolute mass, and high-altitude winds of exoplanet HD209458b
For extrasolar planets discovered using the radial velocity method, the
spectral characterization of the host star leads to a mass-estimate of the star
and subsequently of the orbiting planet. In contrast, if also the orbital
velocity of the planet would be known, the masses of both star and planet could
be determined directly using Newton's law of gravity, just as in the case of
stellar double-line eclipsing binaries. Here we report on the detection of the
orbital velocity of extrasolar planet HD209458b. High dispersion ground-based
spectroscopy during a transit of this planet reveals absorption lines from
carbon monoxide produced in the planet atmosphere, which shift significantly in
wavelength due to the change in the radial component of the planet orbital
velocity. These observations result in a mass determination of the star and
planet of 1.00+-0.22 Msun and 0.64+-0.09 Mjup respectively. A ~2 km/sec
blueshift of the carbon monoxide signal with respect to the systemic velocity
of the host star suggests the presence of a strong wind flowing from the
irradiated dayside to the non-irradiated nightside of the planet within the
0.01-0.1 mbar atmospheric pressure range probed by these observations. The
strength of the carbon monoxide signal suggests a CO mixing ratio of 1-3x10-3
in this planet's upper atmosphere.Comment: 11 Pages main article and 6 pages suppl. information: A final, edited
version appears in the 24 May 2010 issue of Natur
Carbon monoxide and water vapor in the atmosphere of the non-transiting exoplanet HD 179949 b
(Abridged) In recent years, ground-based high-resolution spectroscopy has
become a powerful tool for investigating exoplanet atmospheres. It allows the
robust identification of molecular species, and it can be applied to both
transiting and non-transiting planets. Radial-velocity measurements of the star
HD 179949 indicate the presence of a giant planet companion in a close-in
orbit. Here we present the analysis of spectra of the system at 2.3 micron,
obtained at a resolution of R~100,000, during three nights of observations with
CRIRES at the VLT. We targeted the system while the exoplanet was near superior
conjunction, aiming to detect the planet's thermal spectrum and the radial
component of its orbital velocity. We detect molecular absorption from carbon
monoxide and water vapor with a combined S/N of 6.3, at a projected planet
orbital velocity of K_P = (142.8 +- 3.4) km/s, which translates into a planet
mass of M_P = (0.98 +- 0.04) Jupiter masses, and an orbital inclination of i =
(67.7 +- 4.3) degrees, using the known stellar radial velocity and stellar
mass. The detection of absorption features rather than emission means that,
despite being highly irradiated, HD 179949 b does not have an atmospheric
temperature inversion in the probed range of pressures and temperatures. Since
the host star is active (R_HK > -4.9), this is in line with the hypothesis that
stellar activity damps the onset of thermal inversion layers owing to UV flux
photo-dissociating high-altitude, optical absorbers. Finally, our analysis
favors an oxygen-rich atmosphere for HD 179949 b, although a carbon-rich planet
cannot be statistically ruled out based on these data alone.Comment: 10 pages, 9 figures. Accepted for publication in Astronomy and
Astrophysic
Exoplanet atmospheres with GIANO. I. Water in the transmission spectrum of HD 189733b
High-resolution spectroscopy (R 20,000) at near-infrared wavelengths
can be used to investigate the composition, structure, and circulation patterns
of exoplanet atmospheres. However, up to now it has been the exclusive dominion
of the biggest telescope facilities on the ground, due to the large amount of
photons necessary to measure a signal in high-dispersion spectra. Here we show
that spectrographs with a novel design - in particular a large spectral range -
can open exoplanet characterisation to smaller telescope facilities too. We aim
to demonstrate the concept on a series of spectra of the exoplanet HD 189733 b
taken at the Telescopio Nazionale Galileo with the near-infrared spectrograph
GIANO during two transits of the planet. In contrast to absorption in the
Earth's atmosphere (telluric absorption), the planet transmission spectrum
shifts in radial velocity during transit due to the changing orbital motion of
the planet. This allows us to remove the telluric spectrum while preserving the
signal of the exoplanet. The latter is then extracted by cross-correlating the
residual spectra with template models of the planet atmosphere computed through
line-by-line radiative transfer calculations, and containing molecular
absorption lines from water and methane. By combining the signal of many
thousands of planet molecular lines, we confirm the presence of water vapour in
the atmosphere of HD 189733 b at the 5.5- level. This signal was
measured only in the first of the two observing nights. By injecting and
retrieving artificial signals, we show that the non-detection on the second
night is likely due to an inferior quality of the data. The measured strength
of the planet transmission spectrum is fully consistent with past CRIRES
observations at the VLT, excluding a strong variability in the depth of
molecular absorption lines.Comment: 10 pages, 8 figures. Accepted for publication in Astronomy &
Astrophysics. v2 includes language editin
The GROUSE project III: Ks-band observations of the thermal emission from WASP-33b
In recent years, day-side emission from about a dozen hot Jupiters has been
detected through ground-based secondary eclipse observations in the
near-infrared. These near-infrared observations are vital for determining the
energy budgets of hot Jupiters, since they probe the planet's spectral energy
distribution near its peak. The aim of this work is to measure the Ks-band
secondary eclipse depth of WASP-33b, the first planet discovered to transit an
A-type star. This planet receives the highest level of irradiation of all
transiting planets discovered to date. Furthermore, its host-star shows
pulsations and is classified as a low-amplitude delta-Scuti. As part of our
GROUnd-based Secondary Eclipse (GROUSE) project we have obtained observations
of two separate secondary eclipses of WASP-33b in the Ks-band using the LIRIS
instrument on the William Herschel Telescope (WHT). The telescope was
significantly defocused to avoid saturation of the detector for this bright
star (K~7.5). To increase the stability and the cadence of the observations,
they were performed in staring mode. We collected a total of 5100 and 6900
frames for the first and the second night respectively, both with an average
cadence of 3.3 seconds. On the second night the eclipse is detected at the
12-sigma level, with a measured eclipse depth of 0.244+0.027-0.020 %. This
eclipse depth corresponds to a brightness temperature of 3270+115-160 K. The
measured brightness temperature on the second night is consistent with the
expected equilibrium temperature for a planet with a very low albedo and a
rapid re-radiation of the absorbed stellar light. For the other night the short
out-of-eclipse baseline prevents good corrections for the stellar pulsations
and systematic effects, which makes this dataset unreliable for eclipse depth
measurements. This demonstrates the need of getting a sufficient out-of-eclipse
baseline.Comment: 12 pages, 10 figures. Accepted for publication in Astronomy and
Astrophysic
Detection of carbon monoxide in the high-resolution day-side spectrum of the exoplanet HD 189733b
[Abridged] After many attempts over more than a decade, high-resolution
spectroscopy has recently delivered its first detections of molecular
absorption in exoplanet atmospheres, both in transmission and thermal emission
spectra. Targeting the combined signal from individual lines in molecular
bands, these measurements use variations in the planet radial velocity to
disentangle the planet signal from telluric and stellar contaminants. In this
paper we apply high resolution spectroscopy to probe molecular absorption in
the day-side spectrum of the bright transiting hot Jupiter HD 189733b. We
observed HD 189733b with the CRIRES high-resolution near-infrared spectograph
on the Very Large Telescope during three nights. We detect a 5-sigma absorption
signal from CO at a contrast level of ~4.5e-4 with respect to the stellar
continuum, revealing the planet orbital radial velocity at 154+4/-3 km s-1.
This allows us to solve for the planet and stellar mass in a similar way as for
stellar eclipsing binaries, resulting in Ms= 0.846+0.068/-0.049 Msun and Mp=
1.162+0.058/-0.039 MJup. No significant absorption is detected from H2O, CO2 or
CH4 and we determined upper limits on their line contrasts here. The detection
of CO in the day-side spectrum of HD 189733b can be made consistent with the
haze layer proposed to explain the optical to near-infrared transmission
spectrum if the layer is optically thin at the normal incidence angles probed
by our observations, or if the CO abundance is high enough for the CO
absorption to originate from above the haze. Our non-detection of CO2 at 2.0
micron is not inconsistent with the deep CO2 absorption from low resolution
NICMOS secondary eclipse data in the same wavelength range. If genuine, the
absorption would be so strong that it blanks out any planet light completely in
this wavelength range, leaving no high-resolution signal to be measured.Comment: A&A, accepted for publication. Fig.1 reduced in qualit
Detection of water absorption in the day side atmosphere of HD 189733 b using ground-based high-resolution spectroscopy at 3.2 microns
We report a 4.8 sigma detection of water absorption features in the day side
spectrum of the hot Jupiter HD 189733 b. We used high-resolution (R~100,000)
spectra taken at 3.2 microns with CRIRES on the VLT to trace the
radial-velocity shift of the water features in the planet's day side atmosphere
during 5 h of its 2.2 d orbit as it approached secondary eclipse. Despite
considerable telluric contamination in this wavelength regime, we detect the
signal within our uncertainties at the expected combination of systemic
velocity (Vsys=-3 +5-6 km/s) and planet orbital velocity (Kp=154 +14-10 km/s),
and determine a H2O line contrast ratio of (1.3+/-0.2)x10^-3 with respect to
the stellar continuum. We find no evidence of significant absorption or
emission from other carbon-bearing molecules, such as methane, although we do
note a marginal increase in the significance of our detection to 5.1 sigma with
the inclusion of carbon dioxide in our template spectrum. This result
demonstrates that ground-based, high-resolution spectroscopy is suited to
finding not just simple molecules like CO, but also to more complex molecules
like H2O even in highly telluric contaminated regions of the Earth's
transmission spectrum. It is a powerful tool that can be used for conducting an
immediate census of the carbon- and oxygen-bearing molecules in the atmospheres
of giant planets, and will potentially allow the formation and migration
history of these planets to be constrained by the measurement of their
atmospheric C/O ratios.Comment: 5 pages, 4 figures, accepted for publication in MNRAS Letter
Capability-based governance patterns over the product life-cycle: an agent-based model
In recent literature, there is disagreement over the temporal pattern of vertical governance of firms over the product life-cycle. We use a novel neo-Schumpeterian agent-based simulation model to investigate emerging patterns of vertical governance for different levels of imitability and substitutability of capabilities. We find that, in the mature phase of the product life-cycle, firms generally prefer vertical specialization. However, in the early phase, imitability and substitutability, in interplay, determine the governance form preferred. High imitability frustrates appropriation and thereby discourages integration for synergistic advantages. However, firms need not vertically specialize: under low substitutability, incompatibilities reduce the advantages of specialization. When both substitutability and imitability are low, firms can appropriate the value of their inventions and there is no combinatorial advantage of specialization, so firms predominantly integrate. If substitutability is high and imitability is low, the combinatorial advantage of specialization balances with the synergistic advantage of integration
Capability-based governance patterns over the product life-cycle
We investigate patterns of vertical governance over the product life-cycle as function of the capability regime properties imitability and substitutability. We use a novel neo-Schumpeterian model to study emerging governance patterns. We find that, in the era of incremental change, firms prefer vertical specialization. In the era of ferment, no governance form dominates. Imitability and substitutability, in interplay, determine the governance form preferred. High imitability frustrates appropriation and thereby integration for synergistic advantages. However, firms need not vertically specialize: under low substitutability, incompatibilities reduce the advantages of specialization. When both substitutability and imitability are low, firms can appropriate the value of their inventions and there is no combinatorial advantage of specialization, so firms predominantly integrate. If substitutability is high and imitability is low, the combinatorial advantage of specialization balances with the synergistic advantage of integration
Evidence for the disintegration of KIC 12557548 b
Context. The Kepler object KIC 12557548 b is peculiar. It exhibits
transit-like features every 15.7 hours that vary in depth between 0.2% and
1.2%. Rappaport et al. (2012) explain the observations in terms of a
disintegrating, rocky planet that has a trailing cloud of dust created and
constantly replenished by thermal surface erosion. The variability of the
transit depth is then a consequence of changes in the cloud optical depth.
Aims. We aim to validate the disintegrating-planet scenario by modeling the
detailed shape of the observed light curve, and thereby constrain the cloud
particle properties to better understand the nature of this intriguing object.
Methods. We analysed the six publicly-available quarters of raw Kepler data,
phase-folded the light curve and fitted it to a model for the trailing dust
cloud. Constraints on the particle properties were investigated with a
light-scattering code. Results. The light curve exhibits clear signatures of
light scattering and absorption by dust, including a brightening in flux just
before ingress correlated with the transit depth and explained by forward
scattering, and an asymmetry in the transit light curve shape, which is easily
reproduced by an exponentially decaying distribution of optically thin dust,
with a typical grain size of 0.1 micron. Conclusions. Our quantitative analysis
supports the hypothesis that the transit signal of KIC 12557548 b is due to a
variable cloud of dust, most likely originating from a disintegrating object.Comment: 5 pages, 4 figures. Accepted for publication in Astronomy and
Astrophysic
Cognitive development and children's perceptions of fruit and vegetables; a qualitative study
<p>Abstract</p> <p>Background</p> <p>Most children do not meet the recommended guidelines for fruit and vegetable intake. Since preference is an important predictor of intake, more knowledge is needed about children's preferences and about how these preferences develop. As most research about preferences has ignored cognitive development, this study was designed to explore the relation between children's perceptions and preferences for fruit and vegetables and their cognitive development.</p> <p>Methods</p> <p>The study population consisted of eight 4–5-year-old children, eight 7–8-year-old children and twelve 11–12-year-old children, recruited via a primary school in Wageningen, The Netherlands. Qualitative in-depth information was obtained by duo-interviews and focus group discussions. A structured guide with questions and game tasks was applied to address different domains in a consistent way.</p> <p>Results</p> <p>The developmental progress at the abstraction level was seen in children's reasoning across all domains. Children's preferences expanded and increased in complexity as they moved to a higher age bracket. The most important determinants for liking and disliking shifted from appearance and texture attributes in 4–5-year-olds towards taste attributes in 11–12-year-olds. Children's knowledge of basic tastes increased. Their understanding of health improved as they grew older. The emergence of social norms and perspectives of others as the children grew older was also seen in relation to fruit and vegetables. Child-reported parental strategies to stimulate healthy eating appeared to vary with age in line with cognitive development.</p> <p>Conclusion</p> <p>Cognitive development is paralleled by changes in the importance given to the attributes that determine whether a child likes or dislikes fruits and vegetables; children's understanding of and reasoning about health; and parental use of strategies. These developmental differences should be incorporated in programs designed to increase long-term fruit and vegetable intake in children.</p
- …