Wide-field Astronomy Research Articles

White Dwarfs in the Era of the LSST and Its Synergies with Space-based Missions

Abstract With the imminent start of the Legacy Survey for Space and Time (LSST) at the Vera C. Rubin Observatory and several new space telescopes expected to begin operations later in this decade, both time-domain and wide-field astronomy are on the threshold of a new era. In this paper, we use a new multicomponent model for the distribution of white dwarfs (WDs) in our Galaxy to simulate the WD populations in four upcoming wide-field surveys (i.e., LSST, Euclid, the Roman Space Telescope, and the Cosmological Advanced Survey Telescope for Optical and uv Research) and use the resulting samples to explore some representative WD science cases. Our results confirm that LSST will provide a wealth of information for Galactic WDs, detecting more than 150 million WDs at the final depth of its stacked 10 yr survey. Within this sample, nearly 300,000 objects will have 5σ parallax measurements, and nearly 7 million will have 5σ proper-motion measurements, allowing the detection of the turnoff in the halo WD luminosity function and the discovery of more than 200,000 ZZ Ceti stars. The wide wavelength coverage that will be possible by combining LSST data with observations from Euclid and/or the Roman Space Telescope will also discover WDs with debris disks, highlighting the advantages of combining data between the ground- and space-based missions.

Canadian participation in wide-field astronomy

Canadian astronomers and facilities have had a significant impact in wide-field astronomy. With community planning exercises underway this looks set to continue, with new capabilities and international collaborations in the near future.

The VLT Survey Telescope ATLAS

The VLT Survey Telescope (VST) ATLAS is an optical ugriz survey aiming to cover ~4700deg^2 of the Southern sky to similar depths as the Sloan Digital Sky Survey (SDSS). From reduced images and object catalogues provided by the Cambridge Astronomical Surveys Unit we first find that the median seeing ranges from 0.8 arcsec FWHM in i to 1.0 arcsec in u, significantly better than the 1.2-1.5 arcsec seeing for SDSS. The 5 sigma magnitude limit for stellar sources is r_AB=22.7 and in all bands these limits are at least as faint as SDSS. SDSS and ATLAS are more equivalent for galaxy photometry except in the z band where ATLAS has significantly higher throughput. We have improved the original ESO magnitude zeropoints by comparing m<16 star magnitudes with APASS in gri, also extrapolating into u and z, resulting in zeropoints accurate to ~+-0.02 mag. We finally compare star and galaxy number counts in a 250deg^2 area with SDSS and other count data and find good agreement. ATLAS data products can be retrieved from the ESO Science Archive, while support for survey science analyses is provided by the OmegaCAM Science Archive (OSA), operated by the Wide-Field Astronomy Unit in Edinburgh.

Adaptive optics (AO) and ground-layer AO for Dome C: numerical simulation results

We present the latest results of our on-going closed-loop “end-to-end” numerical adaptive optics (AO) simulations concerning both a standard-AO and a three-star ground-layer AO system for a near-infrared 2-m class telescope at Dome C, Antarctica. We demonstrate that Dome C is an ideal site for wide-field AO-aided astronomy, define in details the AO system(s) optimized for the median turbulence profile considered, and finally show that a ~0.3 Strehl ratio and 200-mas-wide stable point-spread function is reached in band J on at least a 15'-diameter field.

A Golden Decade for Stellar Populations?

AbstractPeople working on stellar populations can look forward to an exciting decade ahead. Investigations of stellar populations lie at the heart of the science cases being used to justify the development of upcoming telescopes and emerging instrumentation technologies. Examples abound, but I will focus on three case studies: (1) Wide field astronomy with upcoming ground-based and space-based survey facilities; (2) Adaptive optics, which has the potential to revolutionize our understanding of stellar populations in both nearby and distant galaxies; (3) The James Webb Space Telescope, which may well extend the reach of stellar population work to encompass the full range of the star-forming history of the Universe. However, most of these developments will require extensive advance preparation in order to be used effectively. The time to start that preparation is now (if not yesterday). Three areas which need urgent development are highlighted in these proceedings: (1) We need a wide-field high-resolution spectroscopic capability to augment wide-area imaging surveys; (2) We need a set of AO-friendly extragalactic deep fields in order to exploit upcoming AO-fed instrumentation; and (3) Existing tools for population synthesis modeling need to be extended in order to incorporate the effects of dust. Because the physics of dust creation and destruction is so complicated and uncertain, the latter capability sounds almost impossibly hard to develop, but in this talk I will argue that some simple approaches already exist that allow dust to be injected rather naturally into population synthesis models. I will show a concrete example where incorporation of dust into spectral synthesis models allows one to detect and characterize rate of formation of circumstellar disks at high redshifts.

Detrending time series for astronomical variability surveys

We present a detrending algorithm for the removal of trends in time series. Trends in time series could be caused by various systematic and random noise sources such as cloud passages, changes of airmass, telescope vibration, CCD noise or defects of photometry. Those trends undermine the intrinsic signals of stars and should be removed. We determine the trends from subsets of stars that are highly correlated among themselves. These subsets are selected based on a hierarchical tree clustering algorithm. A bottom-up merging algorithm based on the departure from normal distribution in the correlation is developed to identify subsets, which we call clusters. After identification of clusters, we determine a trend per cluster by weighted sum of normalized light curves. We then use quadratic programming to detrend all individual light curves based on these determined trends. Experimental results with synthetic light curves containing artificial trends and events are presented. Results from other detrending methods are also compared. The developed algorithm can be applied to time series for trend removal in both narrow and wide field astronomy.

Wide Field Astronomy at Dome C: two IR Surveys Complementary to SNAP

Surveys provide a wealth of data to the astronomical community that are used well after their completion. In this paper, we propose a project that would take the maximum benefit of Dome C in Antarctica by performing two surveys, in the wavelength range from 1–5 µm, complementary to SNAP space surveys. The first one over 1000 sq. deg. (1 KdF) for 4 years and the second one over 15 sq. deg (SNAP-IR) for the next 4 years at the same time as SNAP 0.35–1.7 µm survey. By using a Ground-Layer Adaptive Optics system, we would be able to recover, at the ice level and over at least half a degree in radius, the ~300 mas angular resolution available above the 30-m high turbulent layer. Such a survey, combining a high angular resolution with high sensitivities in the NIR and MIR, should also play the role of a pre-survey for JWST and ALMA.

Active optics and modified-Rumsey wide-field telescopes: MINITRUST demonstrators with vase- and tulip-form mirrors

Wide-field astronomy requires the development of larger aperture telescopes. The optical properties of a three-mirror modified-Rumsey design provide significant advantages when compared to other telescope designs: (i) at any wavelength, the design has a flat field and is anastigmatic; (ii) the system is extremely compact, i.e., it is almost four times shorter than a Schmidt. Compared to the equally compact flat-field Ritchey-Chrétien with a doublet-lens corrector, as developed for the Sloan digital sky survey-and which requires the polishing of six optical surfaces-the proposed modified-Rumsey design requires only a two-surface polishing and provides a better imaging quality. All the mirrors are spheroids of the hyperboloid type. Starting from the classical Rumsey design, it is shown that the use of all eight available free parameters allows the simultaneous aspherization of the primary and tertiary mirrors by active optics methods from a single deformable substrate. The continuity conditions between the primary and the tertiary hyperbolizations are achieved by an intermediate narrow ring of constant thickness that is not optically used. After the polishing of a double vase form in a spherical shape, the primary-tertiary hyperbolizations are achieved by in situ stressing. The tulip-form secondary is hyperbolized by stress polishing. Other active optics alternatives are possible for a space telescope. The modified-Rumsey design is of interest for developing large space- and ground-based survey telescopes in UV, visible, or IR ranges, such as currently demonstrated with the construction of identical telescopes MINITRUST-1 and -2, f/5-2 degrees field of view. Double-pass optical tests show diffraction-limited images.

The AAO/UKST SuperCOSMOS Hα survey

The UK Schmidt Telescope (UKST) of the Anglo-Australian Observatory completed a narrow-band Hα plus [N ii] 6548, 6584-Å survey of the Southern Galactic Plane and Magellanic Clouds in late 2003. The survey, which was the last UKST wide-field photographic survey and the only one undertaken in a narrow-band, is now an online digital data product of the Wide-Field Astronomy Unit of the Royal Observatory Edinburgh (ROE). The survey utilized a high specification, monolithic Hα interference bandpass filter of exceptional quality. In conjunction with the fine-grained Tech-Pan film as a detector it has produced a survey with a powerful combination of area coverage (4000 square degrees), resolution (∼1 arcsec) and sensitivity (≤5 Rayleighs), reaching a depth for continuum point sources of R≃ 20.5. The main survey consists of 233 individual fields on a grid of centres separated by 4° at declinations below +2° and covers a swathe approximately 20° wide about the Southern Galactic Plane. The original survey films were scanned by the SuperCOSMOS measuring machine at the Royal Observatory, Edinburgh, to provide the online digital atlas called the SuperCOSMOS Hα Survey (SHS). We present the background of the survey, the key survey characteristics, details and examples of the data product, calibration process, comparison with other surveys and a brief description of its potential for scientific exploitation.

Whole-sky patrol with 7kx4k-CCD chips

Since the twenties of the last century Sonneberg Observatory runs in each clear night a photographic sky patrol with a system of small telescopes reaching 14m in the blue and 13m in the yellow-red. Currently much effort is made to take over this photographic sky patrol by a system of electronic detectors. Owing to the fact that wide-field systems need either large CCDs or arrays of CCDs in order to cover the whole field of view, the technical availability of large detectors was one of the central problems in the past. We now introduce the use of a PHILIPS 7k × 4k chip in wide-field astronomy for our whole-sky patrol. Although the chip has a quantum efficiency of only about 30%, its big size (12μm pixel size) of 48 × 84 mm offers, for the first time, the replacement of large photographic plates by a single CCD chip. We report our first experiences with this chip when using it with a fish-eye lens for whole-sky imaging. An integration of five minutes reaches down to approximately 9m and enables the investigation of different targets such as variable stars, meteors, GRB counterparts, a.s.o..

Whole-sky patrol with 7kx4k-CCD chips

Since the twenties of the last century Sonneberg Observatory runs in each clear night a photographic sky patrol with a system of small telescopes reaching 14m in the blue and 13m in the yellow-red. Currently much effort is made to take over this photographic sky patrol by a system of electronic detectors. Owing to the fact that wide-field systems need either large CCDs or arrays of CCDs in order to cover the whole field of view, the technical availability of large detectors was one of the central problems in the past. We now introduce the use of a PHILIPS 7k × 4k chip in wide-field astronomy for our whole-sky patrol. Although the chip has a quantum efficiency of only about 30%, its big size (12μm pixel size) of 48 × 84 mm offers, for the first time, the replacement of large photographic plates by a single CCD chip. We report our first experiences with this chip when using it with a fish-eye lens for whole-sky imaging. An integration of five minutes reaches down to approximately 9m and enables the investigation of different targets such as variable stars, meteors, GRB counterparts, a.s.o..

Digital stacking of photographic plates with SuperCOSMOS

Photographic Schmidt plates are among the most effective tools in wide-field astronomy. One of the principal difficulties of photographic plates when compared to modern detectors is lack of image depth. We present a technique for stacking plates digitized using the SuperCOSMOS microdensitometer, aimed at maximizing the signal-to-noise ratio in faint images. The efficacy of several image combination algorithms is tested by stacking plate frames in the presence of spurious images. We find that an ‘average sigma clipping’ type pixel rejection in conjunction with our weighting scheme is most effective in delivering a clean, high signal-to-noise ratio stack. The gain in limiting magnitude obtained from stacking is found to be consistent with that expected: ΔM∼1.5 for a stack of 16 good-quality plates.

Wide-field Astronomy with Tech Pan Film - A Positive Outlook for Schmidt Photography

AbstractThe introduction of film-based Kodak Technical Pan emulsion at the UKST has led to a new lease of life for deep, wide-field astrophotography. This is because the excellent imaging, resolution and low noise characteristics of Tech Pan typically yield a one magnitude depth gain over equivalent IIIa-F plates. Many new projects are underway to take advantage of the significant information gains. The cheap cost of film and ease of transportation gives direct economic benefits too. Tech Pan could also offer a medium term, competitive alternative to CCD mosaics for providing new, deep, wide-field surveys via stacking of several digitised exposures of the same field. A one magnitude gain could result from the stacking of just 6 Tech Pan films to yield an R ∼ 23.5–24. Even without digital co-addition the largest current CCDs cannot hope to match Tech Pan’s inherent ∼ 3 µm resolution and the 40 square degree area coverage of the UKST.

Photography in Wide-Field Astronomy

It is an honour for me to be able to present this review of photography in wide-field astronomy. Let me begin by assuring this distinguished audience that this talk is not some sort of sentimental tribute to a redundant technology. Although photography may be the oldest way of accurately recording images of stars and galaxies it is still the most powerful tool which we possess for surveying the sky on the world's large Schmidt telescopes. Indeed, if the full promise of Tech Pan film is realised (and there will be more on that subject from Dr. Parker later today), photography in its ‘old’ age may extend in its usefulness well into the next century. So, far from being on its last legs, photography is just reaching its maturity, though not without something of a mid-life crisis.

A Flair for Multi-Object Spectroscopy

Unique in the regime of wide-field astronomy is the multi-object spectroscopy system ‘FLAIR’ developed for the UK Schmidt Telescope (UKST). The current system can perform simultaneous observations of ∼ 90 objects across 40 sq. degrees of sky. FLAIR has given a whole new platform for performing astronomical observations with a Schmidt telescope in a non-photographic role. The system is simple to operate, highly stable, easy to interchange with standard photography and outclasses single-object spectroscopy systems on 2.0 m class telescopes for many types of observation. The system has continued to be developed to enhance its flexibility, robustness and versatility, culminating recently in the commissioning of new fibre feeds and formats. The facility to observe independent standard stars, and the capability of observing objects in two UKST fields in a single night has recently been demonstrated. FLAIR is a powerful, cost-effective addition to the instrumental repertoire of the Anglo-Australian Observatory in a way that was not even remotely envisaged when the UKST was built.