918 research outputs found
RISE: a fast-readout imager for exoplanet transit timing
By the precise timing of the low amplitude (0.005 - 0.02 magnitude) transits
of exoplanets around their parent star it should be possible to infer the
presence of other planetary bodies in the system down to Earth-like masses. We
describe the design and construction of RISE, a fast-readout frame transfer
camera for the Liverpool Telescope designed to carry out this experiment. The
results of our commissioning tests are described as well as the data reduction
procedure necessary. We present light curves of two objects, showing that the
desired timing and photometric accuracy can be obtained providing that
autoguiding is used to keep the target on the same detector pixel for the
entire (typically 4 hour) observing run.Comment: Published in PROC SPIE, vol 7014, 70416
Progress on reducing acrylamide levels in potato crisps in Europe, 2002 to 2019
European Snacks Association (ESA) data on acrylamide in potato crisps from 2002 to 2019 (99704 observations) were analysed. Acrylamide levels have plateaued since 2011, although the lowest mean so far was attained in 2018 at 353 ± 2.7 ng g-1: a 54% reduction since 2002. The 85th, 90th and 95th quantiles did show evidence of continued downward progress, the 90th quantile being lower than the 750 ng g-1 European Benchmark Level from 2017 to 2019. A smaller dataset from the European Food Safety Authority (2124 observations) for 2011-2018, was also analysed. The yearly means were higher than those of the ESA data, but showed a fall in average acrylamide from 715 ± 40.5 ng g-1 in 2015 to 505 ±28.5 ng g-1 in 2018, as well as steep falls in the 85th, 90th and 95th quantiles. Nevertheless, even the 85th quantile remained above the 750 ng g-1 Benchmark Level. The ESA data showed a reduction in the proportion of samples with acrylamide exceeding 750 ng g-1, from over 40 % in 2002 to 7.75 % in 2019. Seasonality was evident, with highest acrylamide levels from November to May. Crisp type had little effect except that thicker types had a higher proportion of samples containing >750 ng g-1 acrylamide. Analysis of the region of origin in Europe of the final product revealed improvements in the east and north. Geographical factors combined with seasonality continued to be problematic but was also an aspect in which progress was most evident. The findings show that improvements have been made in reducing the number of samples with very high levels of acrylamide, but do not suggest that mean acrylamide levels could be reduced substantially below where they have been since 2011, or that levels could be kept consistently below the current Benchmark Level
The Automatic Real-Time GRB Pipeline of the 2-m Liverpool Telescope
The 2-m Liverpool Telescope (LT), owned by Liverpool John Moores University,
is located in La Palma (Canary Islands) and operates in fully robotic mode. In
2005, the LT began conducting an automatic GRB follow-up program. On receiving
an automatic GRB alert from a Gamma-Ray Observatory (Swift, INTEGRAL, HETE-II,
IPN) the LT initiates a special override mode that conducts follow-up
observations within 2-3 min of the GRB onset. This follow-up procedure begins
with an initial sequence of short (10-s) exposures acquired through an r' band
filter. These images are reduced, analyzed and interpreted automatically using
pipeline software developed by our team called "LT-TRAP" (Liverpool Telescope
Transient Rapid Analysis Pipeline); the automatic detection and successful
identification of an unknown and potentially fading optical transient triggers
a subsequent multi-color imaging sequence. In the case of a candidate brighter
than r'=15, either a polarimetric (from 2006) or a spectroscopic observation
(from 2007) will be triggered on the LT. If no candidate is identified, the
telescope continues to obtain z', r' and i' band imaging with increasingly
longer exposure times. Here we present a detailed description of the LT-TRAP
and briefly discuss the illustrative case of the afterglow of GRB 050502a,
whose automatic identification by the LT just 3 min after the GRB, led to the
acquisition of the first early-time (< 1 hr) multi-color light curve of a GRB
afterglow.Comment: PASP, accepted (8 pages, 3 figures
Deformation of a nearly hemispherical conducting drop due to an electric field: theory and experiment
We consider, both theoretically and experimentally, the deformation due to an electric field of a pinned nearly-hemispherical static sessile drop of an ionic fluid with a high conductivity resting on the lower substrate of a parallel plate capacitor. Using both numerical and asymptotic approaches we find solutions to the coupled electrostatic and augmented YoungâLaplace equations which agree very well with the experimental results. Our asymptotic solution for the drop interface extends previous work in two ways, namely to drops that have zero-field contact angles that are not exactly Ï/2 and to higher order in the applied electric field, and provides useful predictive equations for the changes in the height, contact angle and pressure as functions of the zero-field contact angle, drop radius, surface tension and applied electric field. The asymptotic solution requires some numerical computations, and so a surprisingly accurate approximate analytical asymptotic solution is also obtained
The circumburst environment of a FRED GRB: study of the prompt emission and X-ray/optical afterglow of GRB 051111
We report a multi-wavelength analysis of the prompt emission and early
afterglow of GRB051111 and discuss its properties in the context of current
fireball models. The detection of GRB051111 by the Burst Alert Telescope
on-board Swift triggered early BVRi' observations with the 2-m robotic Faulkes
Telescope North in Hawaii, as well as X-ray observations with the Swift X-Ray
Telescope. The prompt gamma-ray emission shows a classical FRED profile. The
optical afterglow light curves are fitted with a broken power law, with
alpha_1=0.35 to alpha_2=1.35 and a break time around 12 minutes after the GRB.
Although contemporaneous X-ray observations were not taken, a power law
connection between the gamma-ray tail of the FRED temporal profile and the late
XRT flux decay is feasible. Alternatively, if the X-ray afterglow tracks the
optical decay, this would represent one of the first GRBs for which the
canonical steep-shallow-normal decay typical of early X-ray afterglows has been
monitored optically. We present a detailed analysis of the intrinsic
extinction, elemental abundances and spectral energy distribution. From the
absorption measured in the low X-ray band we find possible evidence for an
overabundance of some alpha elements such as oxygen, [O/Zn]=0.7+/-0.3, or,
alternatively, for a significant presence of molecular gas. The IR-to-X-ray
Spectral Energy Distribution measured at 80 minutes after the burst is
consistent with the cooling break lying between the optical and X-ray bands.
Extensive modelling of the intrinsic extinction suggests dust with big grains
or grey extinction profiles. The early optical break is due either to an energy
injection episode or, less probably, to a stratified wind environment for the
circumburst medium.Comment: accepted to A&A on Nov. 10 (14 pages, 8 figures
Early GRB Optical and Infrared Afterglow Observations with the 2-m Robotic Liverpool Telescope
We present the first optical observations of a Gamma Ray Burst (GRB)
afterglow using the 2-m robotic Liverpool Telescope (LT), which is owned and
operated by Liverpool John Moores University and situated on La Palma. We
briefly discuss the capabilities of LT and its suitability for rapid follow-up
observations of early optical and infrared GRB light curves. In particular, the
combination of aperture, site, instrumentation and rapid response (robotic
over-ride mode aided by telescope's rapid slew and fully-opening enclosure)
makes the LT ideal for investigating the nature of short bursts, optically-dark
bursts, and GRB blast-wave physics in general. We briefly describe the LT's key
position in the RoboNet-1.0 network of robotic telescopes. We present the LT
observations of GRB041006 and use its gamma-ray properties to predict the time
of the break in optical light curve, a prediction consistent with the
observations.Comment: 4 pages, 1 figure, accepted for publication in Il nuovo cimento (4th
Workshop Gamma-Ray Bursts in the Afterglow Era, Rome, 18-22 October 2004
Carina's Pillars of Destruction: the view from ALMA
Forming high-mass stars have a significant effect on their natal environment.
Their feedback pathways, including winds, outflows, and ionising radiation,
shape the evolution of their surroundings which impacts the formation of the
next generation of stars. They create or reveal dense pillars of gas and dust
towards the edges of the cavities they clear. They are modelled in feedback
simulations, and the sizes and shapes of the pillars produced are consistent
with those observed. However, these models predict measurably different
kinematics which provides testable discriminants. Here we present the first
ALMA Compact Array (ACA) survey of 13 pillars in Carina, observed in CO,
CO and CO J=2-1, and the 230 GHz continuum. The pillars in this
survey were chosen to cover a wide range in properties relating to the amount
and direction of incident radiation, proximity to nearby irradiating clusters
and cloud rims, and whether they are detached from the cloud. With these data,
we are able to discriminate between models. We generally find pillar velocity
dispersions of 1 km s and that the outer few layers of molecular
emission in these pillars show no significant offsets from each other,
suggesting little bulk internal motions within the pillars. There are instances
where the pillars are offset in velocity from their parental cloud rim, and
some with no offset, hinting at a stochastic development of these motions.Comment: 24 Pages, 19 figures. Accepted to MNRA
Shockingly low water abundances in Herschel / PACS observations of low-mass protostars in Perseus
Protostars interact with their surroundings through jets and winds impacting
on the envelope and creating shocks, but the nature of these shocks is still
poorly understood. Our aim is to survey far-infrared molecular line emission
from a uniform and significant sample of deeply-embedded low-mass young stellar
objects in order to characterize shocks and the possible role of ultraviolet
radiation in the immediate protostellar environment. Herschel/PACS spectral
maps of 22 objects in the Perseus molecular cloud were obtained as part of the
`William Herschel Line Legacy' survey. Line emission from HO, CO,
and OH is tested against shock models from the literature.
Observed line ratios are remarkably similar and do not show variations with
source physical parameters. Observations show good agreement with the shock
models when line ratios of the same species are compared. Ratios of various
HO lines provide a particularly good diagnostic of pre-shock gas
densities, cm, in agreement with typical
densities obtained from observations of the post-shock gas. The corresponding
shock velocities, obtained from comparison with CO line ratios, are above 20
km\,s. However, the observations consistently show one-to-two orders of
magnitude lower HO-to-CO and HO-to-OH line ratios
than predicted by the existing shock models.
The overestimated model HO fluxes are most likely caused by an
overabundance of HO in the models since the excitation is
well-reproduced. Illumination of the shocked material by ultraviolet photons
produced either in the star-disk system or, more locally, in the shock, would
decrease the HO abundances and reconcile the models with
observations. Detections of hot HO and strong OH lines support
this scenario.Comment: 28 pages, 12 figures, accepted to Astronomy & Astrophysic
RINGO: a novel ring polarimeter for rapid GRB followup - art. no. 62695M
We describe the design and construction of a novel optical ring-polarimeter (RINGO) for the Liverpool Telescope. The instrument is designed for rapid (< 5 minutes) followup observations of Gamma Ray Bursts in order to measure the early time polarization and its evolution for the first time. Sensitivity calculations and data reduction procedures are described, and the results of on-sky commissioning presented. The instrument is now on the telescope and in routine use during GRB followup. © (2006) COPYRIGHT SPIE--The International Society for Optical Engineering
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