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November 1997 - November 1999
Publications
Publications (80)
Context. Constraining the coplanarity status of very low mass (VLM) tight binary systems provides valuable information towards understanding the dominant mechanisms in star and planetary formation at the lower end of the initial mass function.
Aims. We sought to constrain the v sin i degeneracies of two nearby tight VLM binary systems, 2MASS J0746+...
We report $I$-band photometric observations of the radio-detected M9.5 dwarf BRI 0021-0214, obtained with the Galway Ultra Fast Imager (GUFI) on the 1.8m Vatican Advanced Technology Telescope VATT at Mt. Graham International Observatory, Arizona. In total, 19 hours of observations over a 73 day baseline were obtained. BRI 0021-0214 was shown to exh...
We report I-band photometric observations of the radio-detected M9.5 dwarf BRI 0021-0214, obtained with the Galway Ultra Fast Imager (GUFI) on the 1.8m Vatican Advanced Technology Telescope VATT at Mt. Graham International Observatory, Arizona. In total, 19 hours of observations over a 73 day baseline were obtained. BRI 0021-0214 was shown to exhib...
We report I-band photometric observations of the radio-detected M9.5 dwarf BRI 0021-0214, obtained with the Galway Ultra Fast Imager (GUFI) on the 1.8m Vatican Advanced Technology Telescope VATT at Mt. Graham International Observatory, Arizona. In total, 19 hours of observations over a 73 day baseline were obtained. BRI 0021-0214 was shown to exhib...
The Galway Ultra-Fast Imager (GUFI) located on the 1.8m Vatican Advanced Technology Telescope (VATT) was tasked to monitor tight brown dwarf binaries. However, due to the close separation between the components in these binaries, the GUFI photometer could not image each component of binary systems as a point source in our campaign. Therefore, we de...
Graphical Abstract for the article
"Using the Agile software development lifecycle to develop a standalone application for generating colour magnitude diagrams"
Virtual observatories allow the means by which an astronomer is able to discover, access, and process data seamlessly, regardless of its physical location. However, steep learning curves are often required to become proficient in the software employed to access, analyse and visualise this trove of data. It would be desirable, for both research and...
Aurorae are detected from all the magnetized planets in our Solar System, including Earth. They are powered by magnetospheric current systems that lead to the precipitation of energetic electrons into the high-latitude regions of the upper atmosphere. In the case of the gas-giant planets, these aurorae include highly polarized radio emission at kil...
A fraction of very low mass stars and brown dwarfs are known to be radio
active, in some cases producing periodic pulses. Extensive studies of two such
objects have also revealed optical periodic variability and the nature of this
variability remains unclear. Here we report on multi-epoch optical photometric
monitoring of six radio detected dwarfs,...
High performance computing has been used in various fields of astrophysical
research. But most of it is implemented on massively parallel systems
(supercomputers) or graphical processing unit clusters. With the advent of
multicore processors in the last decade, many serial software codes have been
re-implemented in parallel mode to utilize the full...
A sub-sampled deconvolution technique for crowded field photometry with the
HST WFPC2 instrument was proposed by Butler (2000) and applied to search for
optical counterparts to pulsars in globular clusters (Golden et al. 2001).
Simulations showed that the method, which takes account of the point-spread
function (PSF) spatial variation, can provide...
Studies of solar-type binaries have found coplanarity between the equatorial
and orbital planes of systems with $<$40 AU separation. By comparison, the
alignment of the equatorial and orbital axes in the substellar regime, and the
associated implications for formation theory, are relatively poorly
constrained. Here we present the discovery of the r...
A sub-sampled deconvolution technique for crowded field photometry with the HST WFPC2 instrument was proposed by Butler (2000) and applied to search for optical counterparts to pulsars in globular clusters (Golden et al. 2001). Simulations showed that the method, which takes account of the point-spread function (PSF) spatial variation, can provide...
A number of ultracool dwarfs have been unexpectedly detected as radio
sources in the last decade, four of which have been found to be
producing periodic pulses. More recently, two of these pulsing dwarfs
have also been found to be periodically variable in broadband optical
photometry. The detected periods match the periods of the radio pulses
which...
In the past ten years or so, radio observations of ultracool dwarfs have yielded the detection of both quiescent and time-variable radio emission in the late-M and L dwarf regime. Four of these dwarfs have been found to produce periodic pulses, determined to be associated with the dwarf's rotation. More recently, two of these radio pulsing dwarfs h...
Ultracool dwarf pulsars are a small group of very low-mass stars and brown dwarfs (collectively: ultracool dwarfs) which show highly coherent radio emission which is pulsed on the rotational period. The radio emission is providing a new framework within which to interpret the magnetic properties of ultracool, one in which the magnetic fields and ra...
Using data collected with the Special Astrophysical Observatory (SAO) 6 m telescope and the University College Galway (UCG) Transputer Instrument for Fast Image Deconvolution (TRIFFID) imaging photometer, we show that the radio, X-ray, and γ-ray pulsar PSR 0656+14 exhibits pulsed optical emission. We observed that the pulsed fraction was consistent...
We have performed photometry in B and V of the field of the triple system PSR B1620-26 in the globular cluster M4. Our images were taken with two two-dimensional imaging photon-counting detectors, which permitted deep exposures to be made without saturation. Photometry of the proposed optical counterpart of the second companion of PSR B1620-26 was...
We find periodic I-band variability in two ultracool dwarfs, TVLM 513-46546 and 2MASS J00361617+1821104, on either side of the M/L dwarf boundary. Both of these targets are short-period radio transients, with the detected I-band periods matching those found at radio wavelengths (P = 1.96 hr for TVLM 513-46546 and P = 3 hr for 2MASS J00361617+182110...
Low Light Level CCD (L3‐CCD) cameras have received much attention for high cadence astronomical imaging applications. Efforts to date have concentrated on exploiting them for two scenarios: post‐exposure image sharpening and “lucky imaging”, and rapid variability in astrophysically interesting sources. We demonstrate their marked superiority in a t...
A high cadence imaging
system, based on a Low Light Level CCD (L3CCD) camera, has been developed for photometric and polarimetric applications. The camera
system is an iXon DV‐887 from Andor Technology, which uses a CCD97 L3CCD detector from E2V technologies. This is a back illuminated device, giving it an extended blue response, and has an activ...
As light from celestial bodies traverses Earth's atmosphere, the wavefronts are distorted by atmospheric turbulence, thereby lowering the angular resolution of ground‐based imaging. Rapid time‐series imaging enables Post‐Exposure Image Sharpening (PEIS) techniques, which employ shift‐and‐add frame registration to remove the tip‐tilt component...
The GUFI (Galway Ultra Fast Imager) has been primarily developed for high throughput differential photometry, in order to study variability in challenging circumstances, such as near bright sources or within crowded fields. The instrument features a low light level charged coupled device (L3-CCD) that enhances detector speed and sensitivity but onl...
We find periodic I-band variability in two ultracool dwarfs, TVLM 513-46546 and 2MASS J00361617+1821104, on either side of the M/L dwarf boundary. Both of these targets are short-period radio transients, with the detected I-band periods matching those found at radio wavelengths (P=1.96 hr for TVLM 513-46546, and P=3 hr for 2MASS J00361617+1821104)....
High-cadence imaging is required in several astronomical scenarios. These include: studies of rapidly varying sources, achieving maximum signal-to-noise observations of bright objects, and high dynamic range scenarios, such as faint objects embedded in a crowded field of bright objects. Conventional CCDs have drawbacks in this regime, because many...
We present methods which comprise a highly realistic exposure time
calculator (ETC) for planning observations, and a simulator for the
creation of realistic astronomical images - both of which are designed
for any combination of location, telescope, filter and detector. The
unique principle is that we begin with the physical properties of the
stell...
In an investigative 16 hour L band observation using the MERLIN radio interferometric array, we have resolved both the pulsar PSR B1951+32 and structure within the flat spectral radio continuum region, believed to be the synchrotron nebula associated with the interaction of the pulsar and its `host' supernova remnant CTB 80. The extended structure...
Abundance variations of carbon and nitrogen in globular star clusters provide astronomers with a means to determine a cluster's evolutionary past. Moreover, these clusters are so ancient (~13 billion years) and so well preserved that they provide an ideal diagnostic for the overall chemical history of the Milky Way Galaxy.
Traditionally, spectrosc...
Abundance variations of carbon and nitrogen in globular star clusters provide astronomers with a means to determine a cluster's evolutionary past. Moreover, these clusters are so ancient (~13 billion years) and so well preserved that they provide an ideal diagnostic for the overall chemical history of the Milky Way Galaxy. Traditionally, spectrosco...
The iAstro network is a European action supported by the COST program, to foster coordination in the domain of computational and
information infrastructure for the astronomical data grid.
To take advantage of the recent upsurge in astrophysical research applications of grid technologies coupled with the increase in temporal and spatial coverage afforded to us by dedicated all-sky surveys and on-line data archives, we have developed an automated image reduction and analysis pipeline for a number of different astronomical instruments....
As the astronomical community continues to produce deeper and higher resolution data, it becomes increasingly important to provide tools to the scientist that help mining the data in order to provide only the scientifically interesting images. In the case of uncalibrated archives, this task is especially difficult as it is difficult to know whether...
We describe how instrument data-processing pipelines can be quickly and easily developed using the modularity, header-manipulation, and scripting features of the IRAF suite. Our illustration case is the design of a simple IRAF-based reduction and analysis pipeline for the BFOSC instrument on the 1.52m Cassini Telescope at Loiano, run by the Osserva...
Mining large quantities of uncalibrated archives, for specific sources can prove to be a hard task. Even an automated search engine able to use an archive metadata (instrument, a filter, exposure time...) is not completely sufficient. Indeed, without calibration it is difficult to know whether an interesting source can be seen on images without act...
We are developing an automated image reduction and analysis pipeline for WFI (Wide Field Imager, mounted on the 2.2-m MPG/ESO telescope at La Silla) and HST/WFPC2 images to complement Querator, the custom search-engine which accesses the astronomical image archives based at the ST-ECF/ESO centre in Garching, Germany. The image reduction and analysi...
I describe the design of a simple IRAF-based reduction and analysis
pipeline, developed for the BFOSC instrument on the 1.52m Cassini
Telescope at Loiano, run by the Osservatorio Astronomico di Bologna. The
original motivation for this was pedagological: to enable our NUIG
undergraduate students to quickly process their observations while still
'at...
We present the results of TRIFFID simultaneous V- and B-band observations of the cores of the globular clusters M15, M92 and NGC 6712. A variability search of their dense centres
was made feasible through performing post-exposure image sharpening on the images, increasing the image resolution by a factor
of ∼2. The isis implementation of the image...
A new modular high time resolution imaging camera system with sub-microsecond timing accuracy has been built in the Physics Dept. of NUI, Galway. The system was designed to be mounted on large telescopes for observing the temporal, spectral and polarisation characteristics of faint astronomical objects, such as optical pulsars. The camera system de...
The EGRET gamma-ray telescope has left a legacy of unidentified astronomical sources. Most likely, many of the galactic plane sources will be rotation-powered pulsars. Firm identification has been difficult, given the instrument's poor spatial resolution. The problem is exacerbated by the energy dependant Point Spread Function (PSF) and low numbers...
There is a family of difficult image-processing scenarios which involve
seeking out and quantifying minute changes within a sequence of
near-identical images. Traditionally these have been dealt with by
carefully registering the images in terms of position, orientiation and
intensity, and subtracting them from some template image. However, for
crit...
A two-week campaign of high-resolution imaging of the centre of M15 using the tip/tilt correcting TRIFFID-2 camera, followed by analysis with ISIS (image matching & subtraction software), has produced the most sensitive survey to date of variable stars in the central ~1x1 arcmin^2 - a total of 48 were detected -, and constrains the size of the dwar...
Stromgren indices v and b are combined with broad-band index I, and a new index p, the short wavelength half of the v band, to estimate CN 4215A molecular absorption in a sample of stars in M22. The results have been used to estimate carbon and nitrogen abundances and suggest groups of stars within this cluster, each with a characteristic nitrogen...
There remain several definitive gamma-ray pulsars that are as yet undetected in the optical regime. A classic case is the pulsar PSR B1951+32, associated with the complex CTB 80 SNR. Previous ground based high speed 2-d optical studies have ruled out candidates to m_V ~ 24. Hester (2000) has reported an analysis of archival HST/WFPC2 observations o...
It is shown that in very crowded fields, such as the cores of globular clusters, aperture photometry of subsampled-deconvolved HST/WFPC2 images gives statistically better results than any of the following DAOPHOT-II reductions of the original data: aperture photometry, profile-fitting photometry, and the hybrid method of aperture photometry on neig...
There remain several definitive gamma-ray pulsars that are as yet undetected in the optical regime. A classic case is the pulsar PSR B1951+32, associated with the complex CTB 80 SNR. Previous ground based high speed 2-d optical studies have ruled out candidates to V ~ 24. Hester (2000a) has reported an analysis of archival HST/WFPC2 observations of...
Using MERLIN we report the analysis of a recent 16 hr L band observation of the inner flat radio continuum of the CTB 80 remnant which successfully resolved both the pulsar PSR B1951+32 and fine structure within the `hot spot' previously identified at lower resolution radio &X-ray observations, towards which the pulsar is moving. This `hot spot' is...
There remain several definitive gamma-ray pulsars that are as yet undetected in the optical regime. A classic case is the pulsar PSR B1951+32, associated with the complex CTB 80 SNR. Previous ground based high speed 2-d optical studies have ruled out candidates to mV ~ 24. Hester (2000) has reported an analysis of archival HST/WFPC2 observations of...
We show that observations of pulsars with pulsed optical emission indicate that the peak flux scales according to the magnetic field strength at the light cylinder. The derived relationships indicate that the emission mechanism is common across all of the observed pulsars with periods ranging from 33 ms to 385 ms and ages of 1000-300,000 years. It...
Future multidisciplinary problems in European Astrobiological research will require a large effort across a broad spectrum of work activities. These activities are likely to involve resources and personnel distributed amongst the various ESA member states. Current and evolving informatic technologies could, by means of centralising and distributing...
We have analysed archival HST/WFPC2 images in both the F555W & F814W bands of the core field of the globular cluster M 28 in an attempt to identify the optical counterpart of the magnetospherically active millisecond pulsar PSR B1821-24. Examination of the radio derived error circle yielded several potential candidates, down to a magnitude of V ~ 2...
We have further adapted our deconvolution-based HST/WFPC2 reduction techniques, which our simulations have shown to be very effective in crowded fields (Butler 2000), to take advantage of the extra resolution afforded by "dithered" observations. This appears to be the first attempt at non-linear restorations of data which had already been sub-sampl...
We have monitored Supernova 1987A in optical/near-infrared bands from a few weeks following its birth until the present time in order to search for a pulsar remnant. We have found an apparent pattern of emission near the frequency of 467.5 Hz - a 2.14 ms pulsar candidate, first detected in data taken on the remnant at the Las Campanas Observatory (...
We have monitored Supernova 1987A in optical/near-infrared bands using various high-speed photometers from a few weeks following its birth until early 1996 in order to search for a pulsar remnant. While we have found no clear evidence of any pulsar of constant intensity and stable timing, we have found emission with a complex period modulation near...
The conventional approach to performing crowded-field photometry,
whether with ground- or space-based telescopes, is to use either
PSF-fitting alone or some hybrid method of aperture photometry on
neighbor-subtracted images, which also requires a PSF-fitting step. I
show here that in very crowded fields, such as the cores of globular
clusters, aper...
A foreground galaxy between a Gamma-Ray Burst (GRB) source and the observer will produce the repetition of the observed transients by means of gravitational lensing effect. The detection of the first repetition will allow one to predict with good accuracy the time of the second repetition. A quantitative description of the phenomenon is given.
This thesis presents work performed at the Department of Physics,
University College Galway from 1992 to 1997. It is concerned with
ground- and space-based high-resolution optical imaging of globular
cluster cores, and the subsequent application of image-restoration and
crowded-field photometry techniques; thus we may gain an improved
understanding...
Discusses the possibility of detection and study of flares in all ranges of the electromagnetic spectrum which are related to gamma-ray bursts. This possibility can be provided by means of gravitational lensing of cosmological gamma-bursts in an intervening galaxy. It is noted that the photometric history of events related to gamma-bursts can be st...
We present optical data which suggests that G", the optical counterpart of the gamma -ray pulsar Geminga, possibly pulses in B with a period of 0.237 seconds. The similarity between the optical pulse shape and the gamma -ray light curve indicates that a large fraction of the optical emission is non-thermal in origin - contrary to recent suggestions...
The Galway/DIAS Image Sharpening Camera, TRIFFID, has been used to make observations in two colours of the centre of the post-core-collapse
globular cluster M15. We present here our analysis of the photometry in B over two seasons. We have combined the complementary qualities of the HST's high astrometric precision and TRIFFTD's extended coverage a...
There are several pieces of evidence that the sample of gamma-ray bursts (GRBs) is inhomogeneous and that these objects can be situated in the Galaxy as well as at cosmological distances. We consider single black holes (BHs) of 10-100 Msolar as parent objects for GRBs of both types. The origin of GRBs is connected to the release of energy generated...
Using time-resolved two-dimensional aperture photometry we have put upper limits on the pulsed emission from two proposed optical counterparts for PSR B1951+32. Our pulsed upper limits of m_{vpulsed}>23.3, m_{bpulsed}>24.4$, for the first candidate and m_{vpulsed}>23.6$, m_{bpulsed}>24.3 for the second, make it unlikely that either of these is, in...
We have combined the complementary qualities of HST’s high astrometric precision with TRIFFID’s extended coverage and photometric precision to perform crowded-field photometry in the innermost region of the post core-collapse globular cluster M15. Our technique virtually eliminates the problem of extreme crowding which has hitherto hampered searche...
IAUC 6502 available at Central Bureau for Astronomical Telegrams.
High-resolution imaging has been performed for a number of years using TRIFFID, the UCG/DIAS High Resolution Camera. Post-exposure image sharpening (PEIS) of TRIFFID data routinely produces resolution improvements up to the theoretical maximum factor of two. HST resolution remains superior but unlike TRIFFID it cannot be used for extended observati...
Using time-resolved two-dimensional photon counting techniques we have found an accurate position for the X-ray and optical pulsar PSR 0540-69. Our position using postexposure variable aperture photometry confirms the position suggested by Caraveo et al.
IAUC 5786 available at Central Bureau for Astronomical Telegrams. IAUC 5786 available at Central Bureau for Astronomical Telegrams.