arXiv subjects

D. L. King

Publications and source records attributed to D. L. King.

9 recordsLinked to original sources

arXiv2017

Laboratory and telescope demonstration of the TP3-WFS for the adaptive optics segment of AOLI

AOLI (Adaptive Optics Lucky Imager) is a state-of-art instrument that combines adaptive optics (AO) and lucky imaging (LI) with the objective of obtaining diffraction limited images in visible wavelength at mid- and big-size ground-based telescopes. The key innovation of AOLI is the development and use of the new TP3-WFS (Two Pupil Plane Positions Wavefront Sensor). The TP3-WFS, working in visible band, represents an advance over classical wavefront sensors such as the Shack-Hartmann WFS (SH-WFS) because it can theoretically use fainter natural reference stars, which would ultimately provide better sky coverages to AO instruments using this newer sensor. This paper describes the software, algorithms and procedures that enabled AOLI to become the first astronomical instrument performing real-time adaptive optics corrections in a telescope with this new type of WFS, including the first control-related results at the William Herschel Telescope (WHT).

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arXiv2016

High spatial resolution optical imaging of the multiple T Tauri system LkHα 262/LkHα 263

We report high spatial resolution i' band imaging of the multiple T Tauri system LkH$α$ 262/LkH$α$ 263 obtained during the first commissioning period of the Adaptive Optics Lucky Imager (AOLI) at the 4.2 m William Herschel Telescope, using its Lucky Imaging mode. AOLI images have provided photometry for each of the two components LkH$α$ 263 A and B (0.41 arcsec separation) and marginal evidence for an unresolved binary or a disc in LkH$α$ 262. The AOLI data combined with previously available and newly obtained optical and infrared imaging show that the three components of LkH$α$ 263 are co-moving, that there is orbital motion in the AB pair, and, remarkably, that LkH$α$ 262-263 is a common proper motion system with less than 1 mas/yr relative motion. We argue that this is a likely five-component gravitationally bounded system. According to BT-settl models the mass of each of the five components is close to 0.4 M$_{\odot}$ and the age is in the range 1-2 Myr. The presence of discs in some of the components offers an interesting opportunity to investigate the formation and evolution of discs in the early stages of multiple very low-mass systems. In particular, we provide tentative evidence that the disc in 263C could be coplanar with the orbit of 263AB.

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arXiv2015

Adaptive Optics and Lucky Imager (AOLI): presentation and first light

In this paper we present the Adaptive Optics Lucky Imager (AOLI), a state-of-the-art instrument which makes use of two well proved techniques for extremely high spatial resolution with ground-based telescopes: Lucky Imaging (LI) and Adaptive Optics (AO). AOLI comprises an AO system, including a low order non-linear curvature wavefront sensor together with a 241 actuators deformable mirror, a science array of four 1024x1024 EMCCDs, allowing a 120x120 down to 36x36 arcseconds field of view, a calibration subsystem and a powerful LI software. Thanks to the revolutionary WFS, AOLI shall have the capability of using faint reference stars ({\it I\/} $\sim$ 16.5-17.5), enabling it to be used over a much wider part of the sky than with common Shack-Hartmann AO systems. This instrument saw first light in September 2013 at William Herschel Telescope. Although the instrument was not complete, these commissioning demonstrated its feasibility, obtaining a FWHM for the best PSF of 0.151$\pm$0.005 arcsec and a plate scale of 55.0$\pm$0.3 mas/pixel. Those observations served us to prove some characteristics of the interesting multiple T Tauri system LkH$α$ 262-263, finding it to be gravitationally bounded. This interesting multiple system mixes the presence of proto-planetary discs, one proved to be double, and the first-time optically resolved pair LkH$α$ 263AB (0.42 arcsec separation).

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arXiv1996

Circumstellar H-alpha from SN 1994D and future Type Ia supernovae: an observational test of progenitor models

Searching for the presence of circumstellar material is currently the only direct way to discriminate between the different types of possible progenitor systems for Type Ia supernovae. We have therefore looked for narrow H-alpha in a high-resolution spectrum of the normal Type Ia supernova 1994D taken 10 days before maximum and only 6.5 days after explosion. We derive an upper limit of 2.0E-16 erg cm^{-2} s^{-1} for an unresolved emission line at the local H II region velocity. To estimate the limit this puts on wind density, we have made time-dependent photoionization calculations. Assuming spherical symmetry we find an upper limit of the mass loss rate which is roughly 1.5E-5 solar masses per year for a wind speed of 10 km s^{-1}. This limit can exclude only the highest-mass-loss-rate symbiotic systems as progenitors. We discuss the effect of asymmetry and assess the relative merits of early optical, radio and X-ray limits in constraining mass loss from Type Ia progenitors. We find that X-ray observations can probably provide the most useful limits on the progenitor mass loss, while high-resolution optical spectroscopy offers our only chance of actually identifying circumstellar hydrogen.

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arXiv1996

The Wolf-Rayet counterpart of Cygnus X-3

We present orbital-phase resolved I and K-band spectroscopy of Cygnus X-3. All spectra show emission lines characteristic of Wolf-Rayet stars of the WN subclass. On time scales longer than about one day, the line strengths show large changes, both in flux and in equivalent width. In addition, the line ratios change, corresponding to a variation in spectral subtype of WN6/7 to WN4/5. We confirm the finding that at times when the emission lines are weak, they shift in wavelength as a function of orbital phase, with maximum blueshift coinciding with infrared and X-ray minimum, and maximum redshift half an orbit later. Furthermore, we confirm the prediction -- made on the basis of previous observations -- that at times when the emission lines are strong, no clear wavelength shifts are observed. We describe a simplified, but detailed model for the system, in which the companion of the X-ray source is a Wolf-Rayet star whose wind is at times ionised by the X-ray source, except for the part in the star's shadow. With this model, the observed spectral variations can be reproduced with only a small number of free parameters. We discuss and verify the ramifications of this model, and find that, in general, the observed properties can be understood. We conclude that Cyg X-3 is a Wolf-Rayet/X-ray binary.

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arXiv1996

The chemical evolution of galaxies at high redshift

Observations of absorption lines in the spectra of distant QSOs offer a new approach for tracking the evolution of normal galaxies from early epochs to the present day. The damped Ly alpha systems are particularly suitable for measuring the properties of what are likely to be the progenitors of present-day luminous galaxies. We have recently concluded a long-term survey of 30 damped absorbers (including eight from the literature) aimed at measuring the metallicity and dust content of the universe from redshift z = 3.39 to 0.69. The major conclusions are that the epoch of chemical enrichment in galaxies may have begun at z = 2.5-3--corresponding to a look-back time of 14 Gyr--and that at z = 2 the typical metallicity was 1/15 of solar. There is clear evidence for the presence of interstellar dust at z = 2, although several high-redshift galaxies, particularly the most metal-poor, appear to be essentially dust-free. We discuss the nature of the damped Ly alpha galaxies in the light of these and other new results.

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arXiv1995

An Observational Limit on Circumstellar H-Alpha from Supernova 1994D

We searched for narrow H$α$ in a high-resolution spectrum of SN 1994D taken 10 days before maximum, and found none. We estimate the limit this places on the progenitor mass loss, and find that it is competitive with recent radio limits, and excludes the highest-mass-loss-rate symbiotic systems as possible progenitors of the normal Type Ia SN 1994D.

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arXiv1995

The Chemical Evolution of Damped Lyman Alpha Galaxies

Measurements of element abundances in damped Lyman alpha systems are providing new means to investigate the chemical evolution of galaxies, particularly at early times. We review progress in this area, concentrating on recent efforts to extend the range of existing surveys to both higher and lower redshifts.

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arXiv1994

NGC 4526 gas, High Velocity Clouds, and Galactic Halo gas: the Interstellar Medium towards SN 1994D

We present spectroscopic observations of supernova 1994D in NGC 4526, an S0$_3$ galaxy in the Virgo cluster 15 Mpc distant. The datasets consist of the interstellar Ca\II\ and Na\I\ lines towards the supernova at high spectral resolution (FWHM 6 \kms), \halpha\ and [N\,II] observations at lower resolution (FWHM 33 \kms) of the nucleus of NGC 4526 and the supernova, obtained with the WHT at La Palma, and 21 cm spectra obtained with the 100 m Effelsberg Radiotelescope in the field of NGC 4526. The velocity of the gas in NGC 4526 determined from our \halpha\ spectra is +625 \kms\ at the centre and +880 \kms\ at the supernova position. Our value of the systemic velocity is higher than the previous value of +450 \kms. In our high resolution spectra we detect Ca\II\ and Na\I\ absorption at +714 \kms\ which is produced in interstellar gas in NGC 4526. To our knowledge this is the first detection of interstellar absorption originating in a galaxy of early morphological type. We detect multi-component Ca\II\ and Na\I\ absorption lines in the range from +204 to +254 \kms\ which originate in a complex of High Velocity Clouds (HVCs) located at a distance $\ll$ 1 Mpc, in the surroundings of the Milky Way. The gas appears to have near solar abundances, low dust content, and a diluted UV radiation field. At $-$29 \kms, we find weak Ca\II\ absorption and weak H\I\ emission. This component may originate in gas infalling onto the Galactic disk. Finally, close to rest velocity, we find both warm and cold gas located beyond 65 pc, probably associated with high latitude gas at the border of Loop I. The total reddening of the supernova, estimated using the standard Milky Way gas-to-dust ratio, is $E$(B$-$V) $\simeq$ 0.05.

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