1,761 research outputs found
High-energy environment of super-Earth 55 Cnc e I: Far-UV chromospheric variability as a possible tracer of planet-induced coronal rain
The irradiation of close-in planets by their star influences their evolution
and might be responsible for a population of ultra-short period planets eroded
to their bare core. In orbit around a bright, nearby G-type star, the
super-Earth 55 Cnc e offers the possibility to address these issues through UV
transit observations. We used the Hubble Space Telescope to observe the transit
in the FUV over 3 epochs in Apr. 2016, Jan. 2017, and Feb. 2017. These
observations reveal significant short- and long-term variability in 55 Cnc
chromospheric emission lines. In the last 2 epochs, we detected a larger flux
in the C III, Si III, and Si IV lines after the planet passed the approaching
quadrature, followed by a flux decrease in the Si IV doublet. In the second
epoch these variations are contemporaneous with flux decreases in the Si II and
C II doublet. All epochs show flux decreases in the N V doublet as well, albeit
at different orbital phases. These flux decreases are consistent with
absorption from optically thin clouds of gas, are mostly localized at low and
redshifted radial velocities in the star rest frame, and occur preferentially
before and during the transit. These 3 points make it unlikely that the
variations are purely stellar, yet we show that the occulting material is also
unlikely to originate from the planet. We tentatively propose that the motion
of 55 Cnc e at the fringes of the stellar corona leads to the formation of a
cool coronal rain. The inhomogeneity and temporal evolution of the stellar
corona would be responsible for the differences between the visits. Additional
variations are detected in the C II doublet in the first epoch and in the O I
triplet in all epochs with a different behavior that points toward intrinsic
stellar variability. Further observations at FUV wavelengths are required to
disentangle between star-planet interactions and the activity of the starComment: 22 pages, 20 figures, accepted for publication in A&
Visual search in ecological and non-ecological displays: Evidence for a non-monotonic effect of complexity on performance
Copyright @ 2013 PLoSThis article has been made available through the Brunel Open Access Publishing Fund.Considerable research has been carried out on visual search, with single or multiple targets. However, most studies have used artificial stimuli with low ecological validity. In addition, little is known about the effects of target complexity and expertise in visual search. Here, we investigate visual search in three conditions of complexity (detecting a king, detecting a check, and detecting a checkmate) with chess players of two levels of expertise (novices and club players). Results show that the influence of target complexity depends on level of structure of the visual display. Different functional relationships were found between artificial (random chess positions) and ecologically valid (game positions) stimuli: With artificial, but not with ecologically valid stimuli, a âpop outâ effect was present when a target was visually more complex than distractors but could be captured by a memory chunk. This suggests that caution should be exercised when generalising from experiments using artificial stimuli with low ecological validity to real-life stimuli.This study is funded by Brunel University and the article is made available through the Brunel Open Access Publishing Fund
Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) I. Detection of hot neutral sodium at high altitudes on WASP-49b
High-resolution optical spectroscopy during the transit of HD 189733b, a
prototypical hot Jupiter, allowed the resolution of the Na I D sodium lines in
the planet, giving access to the extreme conditions of the planet upper
atmosphere. We have undertaken HEARTS, a spectroscopic survey of exoplanet
upper atmospheres, to perform a comparative study of hot gas giants and
determine how stellar irradiation affect them. Here, we report on the first
HEARTS observations of the hot Saturn-mass planet WASP-49b. We observed the
planet with the HARPS high-resolution spectrograph at ESO 3.6m telescope. We
collected 126 spectra of WASP-49, covering three transits of WASP-49b. We
analyzed and modeled the planet transit spectrum, while paying particular
attention to the treatment of potentially spurious signals of stellar origin.
We spectrally resolve the Na I D lines in the planet atmosphere and show that
these signatures are unlikely to arise from stellar contamination. The large
contrasts of (D) and (D) require the
presence of hot neutral sodium ( K) at high altitudes
(1.5 planet radius or 45,000 km). From estimating the cloudiness
index of WASP-49b, we determine its atmosphere to be cloud free at the
altitudes probed by the sodium lines. WASP-49b is close to the border of the
evaporation desert and exhibits an enhanced thermospheric signature with
respect to a farther-away planet such as HD 189733b.Comment: Accepted for publication in A&A. 14 page
Scale Invariance and Nonlinear Patterns of Human Activity
We investigate if known extrinsic and intrinsic factors fully account for the
complex features observed in recordings of human activity as measured from
forearm motion in subjects undergoing their regular daily routine. We
demonstrate that the apparently random forearm motion possesses previously
unrecognized dynamic patterns characterized by fractal and nonlinear dynamics.
These patterns are unaffected by changes in the average activity level, and
persist when the same subjects undergo time-isolation laboratory experiments
designed to account for the circadian phase and to control the known extrinsic
factors. We attribute these patterns to a novel intrinsic multi-scale dynamic
regulation of human activity.Comment: 4 pages, three figure
Meta-Analysis of the Relation of Body Mass Index to All-Cause and Cardiovascular Mortality and Hospitalization in Patients With Chronic Heart Failure
Clinical studies have indicated the existence of an "obesity paradox" in patients with chronic heart failure (HF), that is, reduced mortality in patients who have elevated body mass index (BMI) scores compared with normal-weight reference groups. The aim of this study was to investigate the relation of BMI with all-cause and cardiovascular (CV) mortality and hospitalization in patients with chronic HF though a systematic review and meta-analysis of published research. PubMed, the Cumulative Index to Nursing and Allied Health Literature, Cochrane Central, Scopus, web of science and Embase were searched for studies reporting rates of total mortality, cardiac mortality, and risk for hospitalization in patients with HF in various BMI categories
A spectral survey of an ultra-hot Jupiter: Detection of metals in the transmission spectrum of KELT-9 b
Context: KELT-9 b exemplifies a newly emerging class of short-period gaseous
exoplanets that tend to orbit hot, early type stars - termed ultra-hot
Jupiters. The severe stellar irradiation heats their atmospheres to
temperatures of K, similar to the photospheres of dwarf stars. Due
to the absence of aerosols and complex molecular chemistry at such
temperatures, these planets offer the potential of detailed chemical
characterisation through transit and day-side spectroscopy. Studies of their
chemical inventories may provide crucial constraints on their formation process
and evolution history.
Aims: To search the optical transmission spectrum of KELT-9 b for absorption
lines by metals using the cross-correlation technique.
Methods: We analyse 2 transits observed with the HARPS-N spectrograph. We use
an isothermal equilibrium chemistry model to predict the transmission spectrum
for each of the neutral and singly-ionized atoms with atomic numbers between 3
and 78. Of these, we identify the elements that are expected to have spectral
lines in the visible wavelength range and use those as cross-correlation
templates.
Results: We detect absorption of Na I, Cr II, Sc II and Y II, and confirm
previous detections of Mg I, Fe I, Fe II and Ti II. In addition, we find
evidence of Ca I, Cr I, Co I, and Sr II that will require further observations
to verify. The detected absorption lines are significantly deeper than model
predictions, suggesting that material is transported to higher altitudes where
the density is enhanced compared to a hydrostatic profile. There appears to be
no significant blue-shift of the absorption spectrum due to a net day-to-night
side wind. In particular, the strong Fe II feature is shifted by km~s, consistent with zero. Using the orbital velocity of the
planet we revise the steller and planetary masses and radii.Comment: Submitted to Astronomy and Astrophysics on January 18, 2019. Accepted
on May 3, 2019. 26 pages, 11 figure
Domain Swapping within PDZ2 Is Responsible for Dimerization of ZO Proteins
ZO-1 is a multidomain protein involved in cell-cell junctions and contains three PDZ domains, which are necessary for its function in vivo. PDZ domains play a central role in assembling diverse protein complexes through their ability to recognize short peptide motifs on other proteins. We determined the structure of the second of the three PDZ domains of ZO-1, which is known to promote dimerization as well as bind to C-terminal sequences on connexins. The dimer is stabilized by extensive symmetrical domain swapping of ÎČ-strands, which is unlike any other known mechanism of PDZ dimerization. The canonical peptide-binding groove remains intact in both subunits of the PDZ2 dimer and is created by elements contributed from both monomers. This unique structure reveals an additional example of how PDZ domains dimerize and has multiple implications for both peptide binding and oligomerization in vivo
- âŠ