158 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
Nitrogen and Oxygen Abundance Variations in the Outer Ejecta of Eta Carinae: Evidence for Recent Chemical Enrichment
We present optical spectra of the ionized `Outer Ejecta' of Eta Carinae that
reveal differences in chemical composition at various positions. In particular,
young condensations just outside the dusty Homunculus Nebula show strong
nitrogen lines and little or no oxygen -- but farther away, nitrogen lines
weaken and oxygen lines become stronger. The observed variations in the
apparent N/O ratio may signify either that the various blobs were ejected with
different abundances, or more likely, that the more distant condensations are
interacting with normal-composition material. The second hypothesis is
supported by various other clues involving kinematics and X-ray emission, and
would suggest that Eta Car is enveloped in a ``cocoon'' deposited by previous
stellar-wind mass loss. In particular, all emission features where we detect
strong oxygen lines are coincident with or outside the soft X-ray shell. In
either case, the observed abundance variations suggest that Eta Car's ejection
of nitrogen-rich material is a recent phenomenon -- taking place in just the
last few thousand years. Thus, Eta Carinae may be at a critical stage of
evolution when ashes of the CNO cycle have just appeared at its surface.
Finally, these spectra reveal some extremely fast nitrogen-rich material, with
Doppler velocities up to 3200 km/s, and actual space velocities that may be
much higher. This is the fastest material yet seen in Eta Car's nebula, but
with unknown projection angles its age is uncertain.Comment: 18 pages, 5 figures, 2 tables. Accepted by ApJ, April 20 200
Rapid GRB Follow-up with the 2-m Robotic Liverpool Telescope
We present the capabilities of the 2-m robotic Liverpool Telescope (LT),
owned and operated by Liverpool John Moores University and situated at ORM, La
Palma. Robotic control and scheduling of the LT make it especially powerful for
observations in time domain astrophysics including: (i) rapid response to
Targets of Opportunity: Gamma Ray Bursts, novae, supernovae, comets; (ii)
monitoring of variable objects on timescales from seconds to years, and (iii)
observations simultaneous or coordinated with other facilities, both
ground-based and from space. Following a GRB alert from the Gamma Ray
Observatories HETE-2, INTEGRAL and Swift we implement a special over-ride mode
which enables observations to commence in about a minute after the alert,
including optical and near infrared imaging and spectroscopy. In particular,
the combination of aperture, site, instrumentation and rapid response (aided by
its rapid slew and fully-opening enclosure) makes the LT excellently suited to
help solving the mystery of the origin of optically dark GRBs, for the
investigation of short bursts (which currently do not have any confirmed
optical counterparts) and for early optical spectroscopy of the GRB phenomenon
in general. We briefly describe the LT's key position in the RoboNet-1.0
network of robotic telescopes.Comment: 6 pages, 2 figures, to appear in the proceedings of Interacting
Binaries: Accretion, Evolution and Outcomes, 4-10 July 2004, Cefalu, Sicily,
Italy, eds. Antonelli et a
Determination of the Physical Conditions of the Knots in the Helix Nebula from Optical and Infrared Observations
[Abridged] We use new HST and archived images to clarify the nature of the
knots in the Helix Nebula. We employ published far infrared spectrophotometry
and existing 2.12 micron images to establish that the population distribution
of the lowest ro-vibrational states of H2 is close to the distribution of a gas
in LTE at 988 +- 119 K. We derive a total flux from the nebula in H2 lines and
compare this with the power available from the central star for producing this
radiation. We establish that neither soft X-rays nor FUV radiation has enough
energy to power the H2 radiation, only the stellar EUV radiation shortward of
912 Angstrom does. Advection of material from the cold regions of the knots
produces an extensive zone where both atomic and molecular hydrogen are found,
allowing the H2 to directly be heated by Lyman continuum radiation, thus
providing a mechanism that can explain the excitation temperature and surface
brightness of the cusps and tails. New images of the knot 378-801 reveal that
the 2.12 micron cusp and tail lie immediately inside the ionized atomic gas
zone. This firmly establishes that the "tail" structure is an ionization
bounded radiation shadow behind the optically thick core of the knot. A unique
new image in the HeII 4686 Angstrom line fails to show any emission from knots
that might have been found in the He++ core of the nebula. We also re-examined
high signal-to-noise ratio ground-based telescope images of this same inner
region and found no evidence of structures that could be related to knots.Comment: Astronomical Journal, in press. Some figures are shown at reduced
resolution. A full resolution version is available at
http://www.ifront.org/wiki/Helix_Nebula_2007_Pape
Probing the Complex and Variable X-ray Absorption of Markarian 6 with XMM-Newton
We report on an X-ray observation of the Seyfert 1.5 galaxy Mrk 6 obtained
with the EPIC instruments onboard XMM-Newton. Archival BeppoSAX PDS data from
18-120 keV were also used to constrain the underlying hard power-law continuum.
The results from our spectral analyses generally favor a double
partial-covering model, although other spectral models such as absorption by a
mixture of partially ionized and neutral gas cannot be firmly ruled out. Our
best-fitting model consists of a power law with a photon index of 1.81+/-0.20
and partial covering with large column densities up to 10^{23} cm**-2. We also
detect a narrow emission line consistent with Fe Kalpha fluorescence at
6.45+/-0.04 keV with an equivalent width of ~93+/-25 eV. Joint analyses of
XMM-Newton, ASCA, and BeppoSAX data further provide evidence for both spectral
variability (a factor of ~2 change in absorbing column) and
absorption-corrected flux variations (by ~60%) during the ~4 year period probed
by the observations.Comment: 7 pages, 2 figures. accepted for publication in the Astronomical
Journa
Interphase chromosome positioning in in vitro porcine cells and ex vivo porcine tissues
Copyright @ 2012 The Authors. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and 85 reproduction in any medium, provided the original author and source are credited. The article was made available through the Brunel University Open Access Publishing Fund.BACKGROUND: In interphase nuclei of a wide range of species chromosomes are organised into their own specific locations termed territories. These chromosome territories are non-randomly positioned in nuclei which is believed to be related to a spatial aspect of regulatory control over gene expression. In this study we have adopted the pig as a model in which to study interphase chromosome positioning and follows on from other studies from our group of using pig cells and tissues to study interphase genome re-positioning during differentiation. The pig is an important model organism both economically and as a closely related species to study human disease models. This is why great efforts have been made to accomplish the full genome sequence in the last decade. RESULTS: This study has positioned most of the porcine chromosomes in in vitro cultured adult and embryonic fibroblasts, early passage stromal derived mesenchymal stem cells and lymphocytes. The study is further expanded to position four chromosomes in ex vivo tissue derived from pig kidney, lung and brain. CONCLUSIONS: It was concluded that porcine chromosomes are also non-randomly positioned within interphase nuclei with few major differences in chromosome position in interphase nuclei between different cell and tissue types. There were also no differences between preferred nuclear location of chromosomes in in vitro cultured cells as compared to cells in tissue sections. Using a number of analyses to ascertain by what criteria porcine chromosomes were positioned in interphase nuclei; we found a correlation with DNA content.This study is partly supported by Sygen International PLC
Differential spatial repositioning of activated genes in Biomphalaria glabrata snails infected with Schistosoma mansoni
Copyright @ 2014 Arican-Goktas et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.This article has been made available through the Brunel Open Access Publishing Fund.Schistosomiasis is an infectious disease infecting mammals as the definitive host and fresh water snails as the intermediate host. Understanding the molecular and biochemical relationship between the causative schistosome parasite and its hosts will be key to understanding and ultimately treating and/or eradicating the disease. There is increasing evidence that pathogens that have co-evolved with their hosts can manipulate their hosts' behaviour at various levels to augment an infection. Bacteria, for example, can induce beneficial chromatin remodelling of the host genome. We have previously shown in vitro that Biomphalaria glabrata embryonic cells co-cultured with schistosome miracidia display genes changing their nuclear location and becoming up-regulated. This also happens in vivo in live intact snails, where early exposure to miracidia also elicits non-random repositioning of genes. We reveal differences in the nuclear repositioning between the response of parasite susceptible snails as compared to resistant snails and with normal or live, attenuated parasites. Interestingly, the stress response gene heat shock protein (Hsp) 70 is only repositioned and then up-regulated in susceptible snails with the normal parasite. This movement and change in gene expression seems to be controlled by the parasite. Other differences in the behaviour of genes support the view that some genes are responding to tissue damage, for example the ferritin genes move and are up-regulated whether the snails are either susceptible or resistant and upon exposure to either normal or attenuated parasite. This is the first time host genome reorganisation has been seen in a parasitic host and only the second time for any pathogen. We believe that the parasite elicits a spatio-epigenetic reorganisation of the host genome to induce favourable gene expression for itself and this might represent a fundamental mechanism present in the human host infected with schistosome cercariae as well as in other host-pathogen relationships.NIH and Sandler Borroughs Wellcome Travel Fellowshi
A Magellan-IMACS-IFU Search for Dynamical Drivers of Nuclear Activity. I. Reduction Pipeline and Galaxy Catalog
Using the Inamori Magellan Areal Camera and Spectrograph (IMACS)
integral-field unit (IFU) on the 6.5m Magellan telescope, we have designed the
first statistically significant investigation of the two-dimensional
distribution and kinematics of ionized gas and stars in the central kiloparsec
regions of a well-matched sample of Seyfert and inactive control galaxies
selected from the Sloan Digital Sky Survey. The goals of the project are to use
the fine spatial sampling (0.2 arcsec/pixel) and large wavelength coverage
(4000-7000A) of the IMACS-IFU to search for dynamical triggers of nuclear
activity in the central region where active galactic nucleus (AGN) activity and
dynamical timescales become comparable, to identify and assess the impact of
AGN-driven outflows on the host galaxy and to provide a definitive sample of
local galaxy kinematics for comparison with future three-dimensional kinematic
studies of high-redshift systems. In this paper, we provide the first detailed
description of the procedure to reduce and calibrate data from the IMACS-IFU in
`long mode' to obtain two-dimensional maps of the distribution and kinematics
of ionized gas and stars. The sample selection criteria are presented,
observing strategy described and resulting maps of the sample galaxies
presented along with a description of the observed properties of each galaxy
and the overall observed properties of the sample.Comment: 62 pages. 41 figures. 5 tables. Accepted for publication in ApJS.
High-resolution version available at:
http://www.astro.ljmu.ac.uk/~pbw/IMACS-IFU/IMACS-1-highRes.pd
ISO-SWS spectroscopy of NGC 1068
We present ISO-SWS spectroscopy of NGC 1068 for the wavelength range 2.4 to
45um, detecting a total of 36 emission lines. Most of the observed transitions
are fine structure and recombination lines originating in the narrow line
region. We compare the line profiles of optical lines and reddening-insensitive
infrared lines to constrain the dynamical structure and extinction properties
of the NLR. The considerable differences found are most likely explained by two
effects. (1) The spatial structure of the NLR is a combination of a highly
ionized outflow cone and lower excitation extended emission. (2) Parts of the
NLR, mainly in the receding part at velocities above systemic, are subject to
extinction that is significantly suppressing optical emission. Line asymmetries
and net blueshifts remain, however, even for infrared fine structure lines
suffering very little obscuration. This may be either due to an intrinsic
asymmetry of the NLR, or due to a very high column density obscuring component
which is hiding part of the NLR even from infrared view. Mid-infrared emission
of molecular hydrogen in NGC 1068 arises in a dense molecular medium at
temperatures of a few hundred Kelvin that is most likely closely related to the
warm and dense components seen in the near-infrared H2 transitions, and in
millimeter wave tracers of molecular gas. Any emission of the putative pc-scale
molecular torus is likely overwhelmed by this larger scale emission.Comment: aastex (V4), 9 eps figures. Accepted by Ap
A Radio Study of the Seyfert galaxy Markarian 6: Implications for Seyfert life-cycles
We have carried out an extensive radio study with the Very Large Array on the
Seyfert 1.5 galaxy Mrk 6 and imaged a spectacular radio structure in the
source. The radio emission occurs on three different spatial scales, from ~7.5
kpc bubbles to ~1.5 kpc bubbles lying nearly orthogonal to them and a ~1 kpc
radio jet lying orthogonal to the kpc-scale bubble. To explain the complex
morphology, we first consider a scenario in which the radio structures are the
result of superwinds ejected by a nuclear starburst. However, recent Spitzer
observations of Mrk 6 provide an upper limit to the star formation rate (SFR)
of ~5.5 M_sun/yr, an estimate much lower than the SFR of ~33 M_sun/yr derived
assuming that the bubbles are a result of starburst winds energized by
supernovae explosions. Thus, a starburst alone cannot meet the energy
requirements for the creation of the bubbles in Mrk 6. We show that a single
plasmon model is energetically infeasible, and we argue that a jet-driven
bubble model while energetically feasible does not produce the complex radio
morphologies. Finally, we consider a model in which the complex radio structure
is a result of an episodically-powered precessing jet that changes its
orientation. This model is the most attractive as it can naturally explain the
complex radio morphology, and is consistent with the energetics, the spectral
index and the polarization structure. Radio emission in this scenario is a
short-lived phenomenon in the lifetime of a Seyfert galaxy which results due to
an accretion event.Comment: Accepted for publication in Ap
- …