68 research outputs found
Reflection Positivity and Monotonicity
We prove general reflection positivity results for both scalar fields and
Dirac fields on a Riemannian manifold, and comment on applications to quantum
field theory. As another application, we prove the inequality
between Dirichlet and Neumann covariance operators on a manifold with a
reflection.Comment: 11 page
The Monitor project: Rotation of low-mass stars in the open cluster M34
We report on the results of a V and i-band time-series photometric survey of
M34 (NGC 1039) using the Wide Field Camera (WFC) on the Isaac Newton Telescope
(INT), achieving better than 1% precision per data point for 13 <~ i <~ 17.
Candidate cluster members were selected from a V vs V-I colour-magnitude
diagram over 14 < V < 24 (0.12 <~ M/Msun <~ 1.0), finding 714 candidates, of
which we expect ~ 400 to be real cluster members (taking into account
contamination from the field). The mass function was computed, and found to be
consistent with a log-normal distribution in dN/dlogM. Searching for periodic
variable objects in the candidate members gave 105 detections over the mass
range 0.25 < M/Msun < 1.0. The distribution of rotation periods for 0.4 <
M/Msun < 1.0 was found to peak at ~ 7 days, with a tail of fast rotators down
to periods of ~ 0.8 days. For 0.25 < M/Msun < 0.4 we found a peak at short
periods, with a lack of slow rotators (eg. P >~ 5 days, consistent with the
work of other authors (eg. Scholz & Eisloffel 2004) at very low masses. Our
results are interpreted in the context of previous work, finding that we
reproduce the same general features in the rotational period distributions. A
number of rapid rotators were found with velocities ~ a factor of two lower
than in the Pleiades, consistent with models of angular momentum evolution
assuming solid body rotation without needing to invoke core-envelope
decoupling.Comment: 22 pages, 19 figures, 5 tables, MNRAS accepte
Near-infrared Thermal Emission from WASP-12b: detections of the secondary eclipse in Ks, H & J
We present Ks, H & J-band photometry of the very highly irradiated hot
Jupiter WASP-12b using the Wide-field Infrared Camera on the
Canada-France-Hawaii telescope. Our photometry brackets the secondary eclipse
of WASP-12b in the Ks and H-bands, and in J-band starts in mid-eclipse and
continues until well after the end of the eclipse. We detect its thermal
emission in all three near-infrared bands. Our secondary eclipse depths are
0.309 +/- 0.013% in Ks-band (24-sigma), 0.176 +/- 0.020% in H-band (9-sigma)
and 0.131 +/- 0.028% in J-band (4-sigma). All three secondary eclipses are
best-fit with a consistent phase that is compatible with a circular orbit. By
combining our secondary eclipse times with others published in the literature,
as well as the radial velocity and transit timing data for this system, we show
that there is no evidence that WASP-12b is precessing at a detectable rate, and
show that its orbital eccentricity is likely zero. Our thermal emission
measurements also allow us to constrain the characteristics of the planet's
atmosphere; our Ks-band eclipse depth argues in favour of inefficient day to
nightside redistribution of heat and a low Bond albedo for this very highly
irradiated hot Jupiter. The J and H-band brightness temperatures are slightly
cooler than the Ks-band brightness temperature, and thus hint at the
possibility of a modest temperature inversion deep in the atmosphere of
WASP-12b; the high pressure, deep atmospheric layers probed by our J and H-band
observations are likely more homogenized than the higher altitude layer.
Lastly, our best-fit Ks-band eclipse has a marginally longer duration than
would otherwise be expected; this may be tentative evidence for material being
tidally stripped from the planet - as was predicted for this system by Li &
collaborators, and for which observational confirmation was recently arguably
provided by Fossati & collaborators.Comment: AJ accepted. 12 pages, 11 figures, in EmulateApJ format. Version 2
removes two figures that were added by mistak
The Monitor project: the search for transits in the open cluster NGC 2362
We present the results of a systematic search for transiting planets in a ~5
Myr open cluster, NGC 2362. We observed ~1200 candidate cluster members, of
which ~475 are believed to be genuine cluster members, for a total of ~100
hours. We identify 15 light curves with reductions in flux that pass all our
detection criteria, and 6 of the candidates have occultation depths compatible
with a planetary companion. The variability in these six light curves would
require very large planets to reproduce the observed transit depth. If we
assume that none of our candidates are in fact planets then we can place upper
limits on the fraction of stars with hot Jupiters (HJs) in NGC 2362. We obtain
99% confidence upper limits of 0.22 and 0.70 on the fraction of stars with HJs
(f_p) for 1-3 and 3-10 day orbits, respectively, assuming all HJs have a
planetary radius of 1.5R_Jup. These upper limits represent observational
constraints on the number of stars with HJs at an age <~10 Myr, when the vast
majority of stars are thought to have lost their protoplanetary discs. Finally,
we extend our results to the entire Monitor Project, a survey searching young,
open clusters for planetary transits, and find that the survey as currently
designed should be capable of placing upper limits on f_p near the observed
values of f_p in the solar neighbourhood.Comment: 17 pages, 11 figures, accepted to MNRA
The Monitor project: JW 380 -- a 0.26, 0.15 Msol pre main sequence eclipsing binary in the Orion Nebula Cluster
We report the discovery of a low-mass (0.26 +/- 0.02, 0.15 +/- 0.01 Msol)
pre-main-sequence eclipsing binary with a 5.3 day orbital period. JW 380 was
detected as part of a high-cadence time-resolved photometric survey (the
Monitor project) using the 2.5m Isaac Newton Telescope and Wide Field Camera
for a survey of a single field in the Orion Nebula Cluster (ONC) region in V
and i bands. The star is assigned a 99 per cent membership probability from
proper motion measurements, and radial velocity observations indicate a
systemic velocity within 1 sigma of that of the ONC. Modelling of the combined
light and radial velocity curves of the system gave stellar radii of 1.19 +0.04
-0.18 Rsol and 0.90 +0.17 -0.03 Rsol for the primary and secondary, with a
significant third light contribution which is also visible as a third peak in
the cross-correlation functions used to derive radial velocities. The masses
and radii appear to be consistent with stellar models for 2-3 Myr age from
several authors, within the present observational errors. These observations
probe an important region of mass-radius parameter space, where there are
currently only a handful of known pre-main-sequence eclipsing binary systems
with precise measurements available in the literature.Comment: 11 pages, 9 figures, accepted for publication in MNRA
Can the Prechtl method for the qualitative assessment of general movements be used to predict neurodevelopmental outcome, at eighteen months to three years, of infants born preterm?
Background: Preterm infants are more at risk of atypical neurodevelopment and diagnosis of impairment often occurs later in life. The Prechtl method for the qualitative assessment of general movements has been found to predict neurodevelopmental outcome in full term infants. Despite this, it is not clear whether the Prechtl assessment is predictive of neurodevelopmental outcome when used for preterm infants. Objectives: To review the literature regarding the use of the Prechtl method for the qualitative assessment of general movements in predicting neurodevelopmental outcome, at eighteen months to three years, of infants born preterm. Methods: A systematic search of MEDLINE, CINAHL, Science Citation Index, PsycINFO, Science Direct, Scopus, Social Sciences Index, Education Source, ERIC, SPORTDiscus, SciELO and SocINDEX was conducted in November 2015. The methodological quality of the included studies was critically appraised using a modified version of the Downs and Black quality index. Results: Five articles met the inclusion criteria. The Prechtl method of assessment was found to be predictive of both neuromotor and cognitive impairments at eighteen months to three years. The writhing period was found to have higher sensitivity but lower specificity and correlation to neurodevelopmental outcomes compared to the fidgety period. Combining both periods of assessment led to higher predictive power. The assessment was also found to be more predictive of severe impairment as opposed to minor impairment. Conclusions: The results of this systematic review suggest that Prechtl method of assessment can be used to predict neurodevelopmental outcome in preterm infants
The thermal emission of the exoplanets WASP-1b and WASP-2b
We present a comparative study of the thermal emission of the transiting
exoplanets WASP-1b and WASP-2b using the Spitzer Space Telescope. The two
planets have very similar masses but suffer different levels of irradiation and
are predicted to fall either side of a sharp transition between planets with
and without hot stratospheres. WASP-1b is one of the most highly irradiated
planets studied to date. We measure planet/star contrast ratios in all four of
the IRAC bands for both planets (3.6-8.0um), and our results indicate the
presence of a strong temperature inversion in the atmosphere of WASP-1b,
particularly apparent at 8um, and no inversion in WASP-2b. In both cases the
measured eclipse depths favor models in which incident energy is not
redistributed efficiently from the day side to the night side of the planet. We
fit the Spitzer light curves simultaneously with the best available radial
velocity curves and transit photometry in order to provide updated measurements
of system parameters. We do not find significant eccentricity in the orbit of
either planet, suggesting that the inflated radius of WASP-1b is unlikely to be
the result of tidal heating. Finally, by plotting ratios of secondary eclipse
depths at 8um and 4.5um against irradiation for all available planets, we find
evidence for a sharp transition in the emission spectra of hot Jupiters at an
irradiation level of 2 x 10^9 erg/s/cm^2. We suggest this transition may be due
to the presence of TiO in the upper atmospheres of the most strongly irradiated
hot Jupiters.Comment: 10 pages, submitted to Ap
The Monitor project: Data processing and lightcurve production
We have begun a large-scale photometric survey of nearby open clusters and
star-forming regions, the Monitor project, aiming to measure time-series
photometry for >10,000 cluster members over >10 sq.deg of sky, to find low-mass
eclipsing binary and planet systems. We describe the software pipeline we have
developed for this project, showing that we can achieve peak RMS accuracy over
the entire data-set of better than 2 mmag using aperture photometry, with RMS <
1% over 4 mag, in data from 2 and 4m class telescopes with wide-field mosaic
cameras. We investigate the noise properties of our data, finding correlated
`red' noise at the 1 - 1.5 mmag level in bright stars, over transit-like
timescales of 2.5 hours. An important source of correlated noise in aperture
photometry is image blending, which produces variations correlated with the
seeing. We present a simple blend index based on fitting polynomials to these
variations, and find that subtracting the fit from the data provides a method
to reduce their amplitude, in lieu of using techniques such as point spread
function fitting photometry which tackle their cause. Finally, we use the
Sysrem algorithm to search for any further systematic effects.Comment: 14 pages, 15 figures, MNRAS accepte
The Roles of Tidal Evolution and Evaporative Mass Loss in the Origin of CoRoT-7 b
CoRoT-7 b is the first confirmed rocky exoplanet, but, with an orbital
semi-major axis of 0.0172 AU, its origins may be unlike any rocky planet in our
solar system. In this study, we consider the roles of tidal evolution and
evaporative mass loss in CoRoT-7 b's history, which together have modified the
planet's mass and orbit. If CoRoT-7 b has always been a rocky body, evaporation
may have driven off almost half its original mass, but the mass loss may depend
sensitively on the extent of tidal decay of its orbit. As tides caused CoRoT-7
b's orbit to decay, they brought the planet closer to its host star, thereby
enhancing the mass loss rate. Such a large mass loss also suggests the
possibility that CoRoT-7 b began as a gas giant planet and had its original
atmosphere completely evaporated. In this case, we find that CoRoT-7 b's
original mass probably didn't exceed 200 Earth masses (about 2/3 of a Jupiter
mass). Tides raised on the host star by the planet may have significantly
reduced the orbital semi-major axis, perhaps causing the planet to migrate
through mean-motion resonances with the other planet in the system, CoRoT-7 c.
The coupling between tidal evolution and mass loss may be important not only
for CoRoT-7 b but also for other close-in exoplanets, and future studies of
mass loss and orbital evolution may provide insight into the origin and fate of
close-in planets, both rocky and gaseous.Comment: Accepted for publication by MNRAS on 2010 May
- …