arXiv subjects

Paul Hickson

Publications and source records attributed to Paul Hickson.

50 records · Page 3Linked to original sources

arXiv2018

Gemini Infrared Multi-Object Spectrograph: Instrument Overview

The Gemini Infrared Multi-Object Spectrograph (GIRMOS) is a powerful new instrument being built to facility-class standards for the Gemini telescope. It takes advantage of the latest developments in adaptive optics and integral field spectrographs. GIRMOS will carry out simultaneous high-angular-resolution, spatially-resolved infrared ($1-2.4$ $μ$m) spectroscopy of four objects within a two-arcminute field-of-regard by taking advantage of multi-object adaptive optics. This capability does not currently exist anywhere in the world and therefore offers significant scientific gains over a very broad range of topics in astronomical research. For example, current programs for high redshift galaxies are pushing the limits of what is possible with infrared spectroscopy at $8-10$-meter class facilities by requiring up to several nights of observing time per target. Therefore, the observation of multiple objects simultaneously with adaptive optics is absolutely necessary to make effective use of telescope time and obtain statistically significant samples for high redshift science. With an expected commissioning date of 2023, GIRMOS's capabilities will also make it a key followup instrument for the James Webb Space Telescope when it is launched in 2021, as well as a true scientific and technical pathfinder for future Thirty Meter Telescope (TMT) multi-object spectroscopic instrumentation. In this paper, we will present an overview of this instrument's capabilities and overall architecture. We also highlight how this instrument lays the ground work for a future TMT early-light instrument.

astro-ph.IM↗

arXiv2018

Remote sensing of geomagnetic fields and atomic collisions in the mesosphere

Magnetic-field sensing has contributed to the formulation of the plate-tectonics theory, the discovery and mapping of underground structures on Earth, and the study of magnetism in other planets. Filling the gap between space-based and near-Earth observation, we demonstrate a novel method for remote measurement of the geomagnetic field at an altitude of 85-100 km. The method consists of optical pumping of atomic sodium in the upper mesosphere with an intensity-modulated laser beam, and simultaneous ground-based observation of the resultant magneto-optical resonance when driving the atomic-sodium spins at the Larmor precession frequency. The experiment was carried out at the Roque de Los Muchachos Observatory in La Palma (Canary Islands) where we validated this technique and remotely measured the Larmor precession frequency of sodium as 260.4(1) kHz, corresponding to a mesospheric magnetic field of 0.3720(1) G. We demonstrate a magnetometry accuracy level of 0.28 mG/$\sqrt{\text{Hz}}$ in good atmospheric conditions. In addition, these observations allow us to characterize various atomic-collision processes in the mesosphere. Remote detection of mesospheric magnetic fields has potential applications such as mapping of large-scale magnetic structures in the lithosphere and the study of electric-current fluctuations in the ionosphere.

physics.ao-ph↗

arXiv2011

Using Site Testing Data for Adaptive Optics Simulations

Astronomical Site testing data plays a vital role in the simulation, design, evaluation and operation of adaptive optics systems for large telescope. We present the example of TMT and its first light facilitiy adaptive optics system NFIRAOS, and illustrate the many simulations done based on site testing data.

astro-ph.IM↗

arXiv2008

A cryogenic liquid-mirror telescope on the moon to study the early universe

We have studied the feasibility and scientific potential of zenith observing liquid mirror telescopes having 20 to 100 m diameters located on the moon. They would carry out deep infrared surveys to study the distant universe and follow up discoveries made with the 6 m James Webb Space Telescope (JWST), with more detailed images and spectroscopic studies. They could detect objects 100 times fainter than JWST, observing the first, high-red shift stars in the early universe and their assembly into galaxies. We explored the scientific opportunities, key technologies and optimum location of such telescopes. We have demonstrated critical technologies. For example, the primary mirror would necessitate a high-reflectivity liquid that does not evaporate in the lunar vacuum and remains liquid at less than 100K: We have made a crucial demonstration by successfully coating an ionic liquid that has negligible vapor pressure. We also successfully experimented with a liquid mirror spinning on a superconducting bearing, as will be needed for the cryogenic, vacuum environment of the telescope. We have investigated issues related to lunar locations, concluding that locations within a few km of a pole are ideal for deep sky cover and long integration times. We have located ridges and crater rims within 0.5 degrees of the North Pole that are illuminated for at least some sun angles during lunar winter, providing power and temperature control. We also have identified potential problems, like lunar dust. Issues raised by our preliminary study demand additional in-depth analyses. These issues must be fully examined as part of a scientific debate we hope to start with the present article.

astro-ph↗

arXiv2002

Classification and redshift estimation by principal component analysis

We show that the first 10 eigencomponents of the Karhunen-Loève expansion or Principal Component Analysis (PCA) provide a robust classification scheme for the identification of stars, galaxies and quasi-stellar objects from multi-band photometry. To quantify the efficiency of the method, realistic simulations are performed which match the planned Large Zenith Telescope survey. This survey is expected to provide spectral energy distributions with a resolution $R\simeq40$ for $\sim10^6$ galaxies to $R\le23$ ($z\sim 1$), $\sim 10^4$ QSOs, and $\sim 10^5$ stars. We calculate that for a median signal-to-noise ratio of 6, 98% of stars, 100% of galaxies and 93% of QSOs are correctly classified. These values increase to 100% of stars, 100% of galaxies and 100% of QSOs at a median signal-to-noise ratio of 10. The 10-component PCA also allows measurement of redshifts with an accuracy of $σ_\mathrm{Res.}\la0.05$ for galaxies with $z\la0.7$, and to $σ_\mathrm{Res.}\la0.2$ for QSOs with $z\ga2$, at a median signal-to-noise ratio of 6. At a median signal-to-noise ratio 20, $σ_\mathrm{Res.}\la0.02$ for galaxies with $z\la1$ and for QSOs with $z\ga2.5$ (note that for a median $S/N$ ratio of 20, the bluest/reddest objects will have a signal-to-noise ratio of $\la 2$ in their reddest/bluest filters). This redshift accuracy is inherent to the $R\simeq40$ resolution provided by the set of medium-band filters used by the Large Zenith Telescope survey. It provides an accuracy improvement of nearly an order of magnitude over the photometric redshifts obtained from broad-band $BVRI$ photometry.

astro-ph↗

arXiv2001

The Large Zenith Telescope Survey: a deep survey using a 6-m liquid mirror telescope

The Large Zenith Telescope Survey whose construction is almost completed (first light expected in spring 2002) near Vancouver (Canada) is designed to observed a total strip of ~17' x 120 deg in 40 medium-band filters spanning 4000-10000 A. It will gather the spectrophotometric energy distributions of ca. \~10^6 galaxies to redshifts z~1, with redshift accuracy sigma_z=0.01 at s/n=10, sigma_z=0.04 at s/n=3, ca. 10^5 stars, and a large sample of QSOs, variable stars, and transient objects of the solar system. The survey is optimized for studying of the evolution of both the luminosity function and the clustering of galaxies to a redshift z~1. It will also provide a complete and homogeneous sample of stars at various galactic latitudes useful for studying galactic structure, and it will be a good instrument for the monitoring of variable objects.

astro-ph↗

arXiv2001

Eliminating the Coriols Effect in Liquid Mirrors

If uncorrected, the Coriolis force due to the rotation of the Earth causes significant aberration of images produced by large liquid-mirror telescopes. We show that this problem can be eliminated by a fixed compensating tilt of the liquid-mirror rotation axis. The required tilt angle, which is a function of latitude and mirror rotation rate, is of order 10 arcsec for current telescopes. This result removes the last fundamental obstacle to achieving diffraction-limited performance with large liquid mirrors.

astro-ph↗

arXiv2001

Wide-field tracking with zenth-pointing telescopes

Equipped with a suitable optical relay system, telescopes employing low-cost fixed primary mirrors could point and track while delivering high-quality images to a fixed location. Such an optical tracking system would enable liquid-mirror telescopes to access a large area of sky and employ infrared detectors and adaptive optics. Such telescopes could also form the elements of an array in which light is combined either incoherently or interferometrically. Tracking of an extended field requires correction of all aberrations including distortion, field curvature and tilt. A specific design is developed that allows a 10-metre liquid-mirror telescope to track objects for as long as 30 minutes and to point as far as 4 degrees from the zenith, delivering a distortion-free diffraction-limited image to a stationary detector, spectrograph, or interferometric beam combiner.

astro-ph↗

arXiv2000

The 2-point angular correlation function of 20,000 galaxies to V<23.5 and I<22

The UH8K wide field camera of the CFHT was used to image 0.68 deg^2 of sky. From these images, ~20,000 galaxies were detected to completeness magnitudes V<23.5 and I<22.5. The angular correlation function of these galaxies is well represented by the parameterization omega(theta) = A_W*theta^-delta. The slope delta=-0.8 shows no significant variation over the range of magnitude. The amplitude A_W decreases with increasing magnitude in a way that is most compatible with a Lambda-CDM model (Omega_0 = 0.2, Lambda=0.8) with a hierarchical clustering evolution parameter epsilon>0. We infer a best-fit spatial correlation length of r_00= 5.85+/-0.5 h^-1 Mpc at z=0. The peak redshift of the survey (I<22.5) is estimated to be z_peak~0.58, using the blue-evolving luminosity function from the CFRS and the flat Lambda cosmology, and r_0(z_peak)=3.5+/-0.5 h^-1 Mpc. We also detect a significant difference in clustering amplitude for the red and blue galaxies, quantitatively measured by correlation lengths of r_00=5.3+/-0.5 h^-1 Mpc and r_00=1.9+/-0.9 h^-1 Mpc respectively, at z=0.

astro-ph↗

arXiv2000

Topology of the Las Campanas Redshift Survey

The topology of the Las Campanas Redshift Survey is analyzed using Minkowski functional statistics, taking into account the selection effects of the survey. The results are compared with the predictions of some toy models of structure formation, including the Standard Cold Dark Matter Model and topological defect-based models. All of the toy models have a scale invariant primordial spectrum of perturbations, but quite different topologies. The statistics can discriminate between the predictions of the models with high significance. Amongst the four Minkowski functionals, the integrated mean curvature statistic appears to be the most powerful discriminant, followed by the genus statistic. None of the models considered gives an acceptable fit to the data.

astro-ph↗

arXiv1998

A Curvature-Compensated Corrector for Drift-Scan Observations

Images obtained by drift-scanning with a stationary telescope are affected by the declination-dependent curvature of star trails. The image displacement to curvature and drift rate variation increases with the angular field of view and can lead to significant loss of resolution with modern large-format CCD arrays. We show that these effects can be essentially eliminated by means of an optical corrector design in which individual lenses are tilted and decentered. A specific example is presented, of a four-element corrector designed for the Large-Zenith Telescope. The design reduces curvature errors to less than 0.074 arcsec over a 10 arcmin x 20 arcmin field of view centered at 49 degrees declination. By changing the positions and tilts of the lenses, the same design can also be used for any field centers between 0 degrees and 49 degrees.

astro-ph↗

arXiv1997

A Technique for Photometric Detection and Measurement of Unresolved Binary Systems

A technique is described for the detection and measurement of close binary systems whose images are unresolved. The method is based on analysis of the moment of inertia tensor of the image, from which the product of the binary flux ratio and square of the angular separation may be determined. Intrinsic asymmetries of the point-spread function are removed by comparison with the image of a reference star. Multiple exposures may be used to increase the signal-to-noise ratio without need of image alignment. An example is given of a simulated measurement of the dwarf carbon star system G77-61.

astro-ph↗

arXiv1997

Compact groups of galaxies

Compact groups of galaxies have posed a number of challenging questions. Intensive observational and theoretical studies are now providing answers to many of these, and at the same time, are revealing unexpected new clues about the nature and role of these systems. Most compact groups contain a high fraction of galaxies having morphological or kinematical peculiarities, nuclear radio and infrared emission, and starburst or active galactic nuclei (AGN) activity. They contain large quantities of diffuse gas and are dynamically dominated by dark matter. They most likely form as subsystems within looser associations and evolve by gravitational processes. Strong galaxy interactions result and merging is expected to lead to the ultimate demise of the group. Compact groups are surprisingly numerous, and may play a significant role in galaxy evolution.

astro-ph↗

arXiv1997

UBC-NASA Multi-Narrowband Survey. I. Description and Photometric Properties of the Survey

Observations, analysis techniques and photometric properties of a multi-narrowband survey of a 20 square-degree area of sky at +33 degrees declination are described. The survey is conducted with the 3-meter liquid-mirror telescope of the NASA Orbital Debris Observatory using intermediate-bandwidth filters. These filters have central wavelengths ranging from 455 to 948 nm, at intervals of 0.01 in log(wavelength) and give a spectral resolving power of 44. In two spring observing seasons we have completed observations in 16 bands. Our preliminary object catalog contains over 10^5 detections to a typical 50% completeness limit of m(AB) = 20.4. This paper describes the observational techniques, data analysis methods, and photometric properties of the survey. The survey is expected to provide object classifications, spectral energy distributions and multi-narrowband redshifts for over 10^4 galaxies and QSOs, for use in studies of galaxy and QSO distributions, evolution and large-scale structure. It will also provide photometry and spectral classifications for over 10^4 stars.

astro-ph↗