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We explore the feasibility of using current generation, off-the-shelf, indium gallium arsenide (InGaAs) near-infrared (NIR) detectors for astronomical observations. Light-weight InGaAs cameras, developed for the night vision industry and operated at or near room temperature, enable cost-effective new paths for observing the NIR sky, particularly when paired with small telescopes. We have tested an InGaAs camera in the laboratory and on the sky using 12 and 18-inch telescopes. The camera is a small-format, 320x240 pixels of 40$mu$m pitch, Short Wave Infra-Red (SWIR) device from Sensors Unlimited. Although the device exhibits a room-temperature dark current of $5.7 times 10^4$ $e^-s^{-1}$ per pixel, we find observations of bright sources and low-positional-resolution observations of faint sources remain feasible. We can record unsaturated images of bright ($J=3.9$) sources due to the large pixel well-depth and resulting high dynamic range. When mounted on an 18-inch telescope, the sensor is capable of achieving milli-magnitude precision for sources brighter than $J=8$. Faint sources can be sky-background-limited with modest thermoelectric cooling. We can detect faint sources ($J=16.4$ at $10sigma$) in a one-minute exposure when mounted to an 18-inch telescope. From laboratory testing, we characterize the noise properties, sensitivity, and stability of the camera in a variety of different operational modes and at different operating temperatures. Through sky testing, we show that the (unfiltered) camera can enable precise and accurate photometry, operating like a filtered $J$-band detector, with small color corrections. In the course of our sky testing, we successfully measured sub-percent flux variations in an exoplanet transit. We have demonstrated an ability to detect transient sources in dense fields using image subtraction of existing reference catalogs.
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The Simons Observatory (SO) is an upcoming cosmic microwave background (CMB) experiment located on Cerro Toco, Chile, that will map the microwave sky in temperature and polarization in six frequency bands spanning 27 to 285 GHz. SO will consist of one 6-meter Large Aperture Telescope (LAT) fielding $sim$30,000 detectors and an array of three 0.42-meter Small Aperture Telescopes (SATs) fielding an additional 30,000 detectors. This synergy will allow for the extremely sensitive characterization of the CMB over angular scales ranging from an arcmin to tens of degrees, enabling a wide range of scientific output. Here we focus on the SATs targeting degree angular scales with successive dichroic instruments observing at Mid-Frequency (MF: 93/145 GHz), Ultra-High-Frequency (UHF: 225/285 GHz), and Low-Frequency (LF: 27/39 GHz). The three SATs will be able to map $sim$10% of the sky to a noise level of 2 $mu$K-arcmin when combining 93 and 145 GHz. The multiple frequency bands will allow the CMB to be separated from galactic foregrounds (primarily synchrotron and dust), with the primary science goal of characterizing the primordial tensor-to-scalar ratio, $r$, at a target level of $sigma left(rright) approx 0.003$.
The second data release of ESAs Gaia satellite (Gaia DR2) revolutionised astronomy by providing accurate distances, proper motions, apparent magnitudes, and in many cases temperatures and radial velocities for an unprecedented number of stars. These new results, which are freely available, need to be considered in virtually any stellar research project, as they provide crucial information on luminosity, position, motion, orbit, and colours of observed targets. Ground-based spectroscopic surveys, like RAVE, Gaia-ESO, Apogee, LAMOST, and GALAH, are adding more measurements of radial velocities and, most importantly, chemistry of stellar atmospheres, including abundances of individual elements. We briefly describe the new information trove, together with some warnings against blind-folded use. Even though it may seem that Gaia is already providing any information that could be collected by small telescopes, the opposite is true. In particular, we discuss a possible reach of a ground-based photometric survey using a custom filter set. We demonstrate that it can provide valuable information on chemistry of observed stars, which is not provided by Gaia or other sky surveys. A survey conducted with a small telescope has the potential to measure both the metallicity and alpha enhancement at a ~0.1 dex level for a large fraction of Gaia targets, a valuable goal for galactic archaeology.
In this white paper (WP), we highlight several examples of small and moderate aperture telescopes that are being used for education and/or research. We further discuss potential costs for establishing new, small observatories, as well as joining existing international consortia. The WP includes a brief overview of select observing sites, with a discussion on how small telescopes at exceptional observing locations can be competitive, under certain circumstances, with larger and more expensive facilities located at poorer sites. In addition to research, these facilities enable many different types of educational experiences for wide range of people, from high school students to undergraduates to graduate students to postdocs. Canada should remain committed to partnering with large, international observatories such as CFHT, Gemini, and TMT, but it should also negotiate international agreements and commit funding to expand the use of small and moderate research observatories at domestic and international sites through coordination with the NRC, the Tri-Council, and the Canadian Foundation for Innovation. Both capital and operational costs (with site rental costs allowed) need to be included in support possibilities. CASCA should establish and maintain a small to moderate telescope expression of interest database that would help to facilitate Canadian institutions in organizing consortia, particularly for smaller institutions. The astronomical community should work with the NRC to make existing facilities more accessible to the astronomical community for research. This could involve, for example, automating the Plaskett and/or providing travel funds for supporting classical observing modes. Finally, a small to moderate aperture facility in the Arctic would be a world-class observatory and should be advanced over the next decade.
(Abridged) Typically large telescope construction and operation costs scale up faster than their collecting area. This slows scientific progress, making it expensive and complicated to increase telescope size. A metric that represents the capability of an imaging survey telescopes, and that captures a wide range of science objectives, is the telescope grasp -- the amount of volume of space in which a standard candle is detectable per unit time. We provide an analytic expression for the grasp, and also show that in the background-dominated noise limit, the optimal exposure time is three times the dead time. We introduce a related metric we call the information-content grasp, which summarizes the variance of all sources observed by the telescope per unit time. For seeing-dominated sky surveys, in terms of grasp, etendue, or collecting-area optimization, recent technological advancements make it more cost effective to construct multiple small telescopes rather than a single large telescope with a similar grasp or etendue. Among these key advancements are the availability of large-format back-side illuminated CMOS detectors with <4 micron pixels, well suited to sample standard seeing conditions given typical focal lengths of small fast telescopes. We also discuss the possible use of multiple small telescopes for spectroscopy. We argue that if all the obstacles to implementing cost-effective wide-field imaging and multi-object spectrographs using multiple small telescopes are removed, then the motivation to build new single large-aperture (>1m) visible-light telescopes which are seeing-dominated, will be weakened. These ideas have led to the concept of the, currently under construction, Large-Array Survey Telescope (LAST).
Wide field small aperture telescopes (WFSATs) are mainly used to obtain scientific information of point--like and streak--like celestial objects. However, qualities of images obtained by WFSATs are seriously affected by the background noise and variable point spread functions. Developing high speed and high efficiency data processing method is of great importance for further scientific research. In recent years, deep neural networks have been proposed for detection and classification of celestial objects and have shown better performance than classical methods. In this paper, we further extend abilities of the deep neural network based astronomical target detection framework to make it suitable for photometry and astrometry. We add new branches into the deep neural network to obtain types, magnitudes and positions of different celestial objects at the same time. Tested with simulated data, we find that our neural network has better performance in photometry than classical methods. Because photometry and astrometry are regression algorithms, which would obtain high accuracy measurements instead of rough classification results, the accuracy of photometry and astrometry results would be affected by different observation conditions. To solve this problem, we further propose to use reference stars to train our deep neural network with transfer learning strategy when observation conditions change. The photometry framework proposed in this paper could be used as an end--to--end quick data processing framework for WFSATs, which can further increase response speed and scientific outputs of WFSATs.
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