464 research outputs found
Country of qualification is linked to doctors’ General Medical Council performance assessment rate, but is it linked to their clinical competence?
The lexical access of multiple words during a single fixation:overlapping access processes?
Since it has become increasingly difficult to tease apart the predictions of serial and parallel models of eye movement control during reading, we return to theunderlying theoretical question of whether parallel lexical processing of two words is, at the very least, psychologically plausible. Two horizontally aligned letter strings were presented simultaneously on a screen, the task being to decide whether they were physically identical or not. Even with presentation durations short enough to prohibit serial inspection of each word the results show clear lexical effects: high frequency word pairs were responded to faster and with fewer errors than low frequency words. Effects of lexicality, orthography and scanning direction were also found. The results suggest that two words can be processed at a lexical level in an overlapping fashion
High temperature condensate clouds in super-hot Jupiter atmospheres
Deciphering the role of clouds is central to our understanding of exoplanet
atmospheres, as they have a direct impact on the temperature and pressure
structure, and observational properties of the planet. Super-hot Jupiters
occupy a temperature regime similar to low mass M-dwarfs, where minimal cloud
condensation is expected. However, observations of exoplanets such as WASP-12b
(Teq ~ 2500 K) result in a transmission spectrum indicative of a cloudy
atmosphere. We re-examine the temperature and pressure space occupied by these
super-hot Jupiter atmospheres, to explore the role of the initial Al- and
Ti-bearing condensates as the main source of cloud material. Due to the high
temperatures a majority of the more common refractory material is not depleted
into deeper layers and would remain in the vapor phase. The lack of depletion
into deeper layers means that these materials with relatively low cloud masses
can become significant absorbers in the upper atmosphere. We provide
condensation curves for the initial Al- and Ti-bearing condensates that may be
used to provide quantitative estimates of the effect of metallicity on cloud
masses, as planets with metal-rich hosts potentially form more opaque clouds
because more mass is available for condensation. Increased metallicity also
pushes the point of condensation to hotter, deeper layers in the planetary
atmosphere further increasing the density of the cloud. We suggest that planets
around metal-rich hosts are more likely to have thick refractory clouds, and
discuss the implication on the observed spectra of WASP-12b.Comment: Accepted for publication in MNRAS, 10 pages, 1 table, 5 figure
HST hot-Jupiter transmission spectral survey: Haze in the atmosphere of WASP-6b
We report Hubble Space Telescope (HST) optical to near-infrared transmission
spectroscopy of the hot Jupiter WASP-6b, measured with the Space Telescope
Imaging Spectrograph (STIS) and Spitzer's InfraRed Array Camera (IRAC). The
resulting spectrum covers the range m. We find evidence for
modest stellar activity of WASP-6b and take it into account in the transmission
spectrum. The overall main characteristic of the spectrum is an increasing
radius as a function of decreasing wavelength corresponding to a change of
from 0.33 to m. The spectrum suggests
an effective extinction cross-section with a power law of index consistent with
Rayleigh scattering, with temperatures of K at the planetary
terminator. We compare the transmission spectrum with hot-Jupiter atmospheric
models including condensate-free and aerosol-dominated models incorporating Mie
theory. While none of the clear-atmosphere models is found to be in good
agreement with the data, we find that the complete spectrum can be described by
models that include significant opacity from aerosols including Fe-poor
MgSiO, MgSiO, KCl and NaS dust condensates. WASP-6b is the
second planet after HD189733b which has equilibrium temperatures near
K and shows prominent atmospheric scattering in the optical.Comment: 18 pages, 15 figures, 7 table
HST/WFC3 transmission spectroscopy of the cold rocky planet TRAPPIST-1h
TRAPPIST-1 is a nearby ultra-cool dwarf star transited by seven rocky
planets. We observed three transits of its outermost planet, TRAPPIST-1h, using
the G141 grism of the Wide Field Camera 3 instrument aboard the Hubble Space
Telescope to place constraints on its potentially cold atmosphere. In order to
deal with the effect of stellar contamination, we model TRAPPIST-1 active
regions as portions of a cooler and a hotter photosphere, and generate
multi-temperature models that we compare to the out-of-transit spectrum of the
star. Using the inferred spot parameters, we produce corrected transmission
spectra for planet h under five transit configurations and compare these data
to planetary atmospheric transmission models using the forward model CHIMERA.
Our analysis reveals that TRAPPIST-1h is unlikely to host an aerosol-free
H/He-dominated atmosphere. While the current data precision limits the
constraints we can put on the planetary atmosphere, we find that the likeliest
scenario is that of a flat, featureless transmission spectrum in the WFC3/G141
bandpass due to a high mean molecular weight atmosphere (>1000x solar), no
atmosphere, or an opaque aerosol layer, all in absence of stellar
contamination. This work outlines the limitations of modeling active
photospheric regions with theoretical stellar spectra, and those brought by our
lack of knowledge of the photospheric structure of ultracool dwarf stars.
Further characterization of the planetary atmosphere of TRAPPIST-1h would
require higher precision measurements over wider wavelengths, which will be
possible with the James Webb Space Telescope
HST hot Jupiter transmission spectral survey: evidence for aerosols and lack of TiO in the atmosphere of WASP-12b
We present HST optical transmission spectra of the transiting hot Jupiter
WASP-12b, taken with the STIS instrument. From the transmission spectra, we are
able to decisively rule out prominent absorption by TiO in the exoplanet's
atmosphere. Strong pressure-broadened Na and K absorption signatures are also
excluded, as are significant metal-hydride features. We compare our combined
broadband spectrum to a wide variety of existing aerosol-free atmospheric
models, though none are satisfactory fits. However, we do find that the full
transmission spectrum can be described by models which include significant
opacity from aerosols: including Rayleigh scattering, Mie scattering, tholin
haze, and settling dust profiles. The transmission spectrum follows an
effective extinction cross section with a power-law of index alpha, with the
slope of the transmission spectrum constraining the quantity alphaT =
-3528+/-660 K, where T is the atmospheric temperature. Rayleigh scattering
(alpha=-4) is among the best fitting models, though requires low terminator
temperatures near 900 K. Sub-micron size aerosol particles can provide equally
good fits to the entire transmission spectrum for a wide range of temperatures,
and we explore corundum as a plausible dust aerosol. The presence of
atmospheric aerosols also helps to explain the modestly bright albedo implied
by Spitzer observations, as well as the near black body nature of the emission
spectrum. Ti-bearing condensates on the cooler night-side is the most natural
explanation for the overall lack of TiO signatures in WASP-12b, indicating the
day/night cold-trap is an important effect for very hot Jupiters. These finding
indicate that aerosols can play a significant atmospheric role for the entire
wide range of hot-Jupiter atmospheres, potentially affecting their overall
spectrum and energy balance.(abridged)Comment: 19 pages, 14 figures, 5 tables. Accepted for publication in MNRA
Detection of H2O and evidence for TiO/VO in an ultra hot exoplanet atmosphere
This is the author accepted manuscript. The final version is available from American Astronomical Society via the DOI in this recordWe present a primary transit observation for the ultra hot (Teq 2400 K) gas giant expolanetWASP-121b, made using the Hubble Space Telescope Wide Field Camera 3 in spectroscopic mode across the 1.12{1.64 m wavelength range. The 1.4 m water absorption band is detected at high con dence (5:4 ) in the planetary atmosphere. We also reanalyze ground-based photometric lightcurves taken in the B, r0, and z0 lters. Signi cantly deeper transits are measured in these optical bandpasses relative to the near-infrared wavelengths. We conclude that scattering by high-altitude haze alone is unlikely to account for this di erence, and instead interpret it as evidence for titanium oxide and vanadium oxide absorption. Enhanced opacity is also inferred across the 1:12{1:3 m wavelength range, possibly due to iron hydride absorption. If con rmed, WASP-121b will be the rst exoplanet with titanium oxide, vanadium oxide, and iron hydride detected in transmission. The latter are important species in M/L dwarfs, and their presence is likely to have a signi cant e ect on the overall physics and chemistry of the atmosphere, including the production of a strong thermal inversionThe research leading to these results has received funding from the European Research Council under the European Union Seventh Framework Program (FP7/2007-2013) ERC grant agreement no. 336792
A combined transmission spectrum of the Earth-sized exoplanets TRAPPIST-1 b and c
Three Earth-sized exoplanets were recently discovered close to the habitable
zone of the nearby ultracool dwarf star TRAPPIST-1. The nature of these planets
has yet to be determined, since their masses remain unmeasured and no
observational constraint is available for the planetary population surrounding
ultracool dwarfs, of which the TRAPPIST-1 planets are the first transiting
example. Theoretical predictions span the entire atmospheric range from
depleted to extended hydrogen-dominated atmospheres. Here, we report a
space-based measurement of the combined transmission spectrum of the two inner
planets made possible by a favorable alignment resulting in their simultaneous
transits on 04 May 2016. The lack of features in the combined spectrum rules
out cloud-free hydrogen-dominated atmospheres for each planet at 10-
levels; TRAPPIST-1 b and c are hence unlikely to harbor an extended gas
envelope as they lie in a region of parameter space where high-altitude
cloud/haze formation is not expected to be significant for hydrogen-dominated
atmospheres. Many denser atmospheres remain consistent with the featureless
transmission spectrum---from a cloud-free water vapour atmosphere to a
Venus-like atmosphere.Comment: Early release to inform further the upcoming review of HST's Cycle 24
proposal
Assessment of the Falkland Islands population of Argentine hake Merluccius hubbsi.
Spanish vessels fish for the Argentine hake, Merluccius hubbsi both in Falkland Islands Conservation Zones and in high seas waters along the shelf edge to the north of the islands. Data are collected by the Falkland Islands Fisheries Department, Instituto Español de Oceanografía and Asociación Nacional de Armadores de Buques Congeladores de Pesca de Merluza. Data from these three sources were combined, with the aim of producing assessments of M. hubbsi. There was no relationship between abundance indices for Falkland Islands waters and high seas areas, suggesting little interaction between the populations in the two areas. Virtual population analysis suggested that the spawning stock biomass in Falklands waters declined from approximately 60,000 t in 1987 to about 15,000 t in the early 1990s but has since made a partial recovery to approximately 20,000 t. However, low recruitment levels are, apparently, impeding the recovery of the population. The abundance trend contrasts with a continued decline suggested by assessments of the population in Argentine waters, implying some independence of the adult populations in the two areas. Nonetheless, it is likely that recruitment to the population is affected by processes not explained by the available data
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