Wide-field Optical Cameras Research Articles

The SVOM mission

The Sino-French space mission SVOM is mainly designed to detect, localize and follow-up Gamma-Ray Bursts and other high-energy transients. The satellite, to be launched mid 2023, embarks two wide-field gamma-ray instruments and two narrow-field telescopes operating at X-ray and optical wavelengths. It is complemented by a dedicated ground segment encompassing a set of wide-field optical cameras and two 1-m class follow-up telescopes. In this contribution, we describe the main characteristics of the mission and discuss its scientific rationale and some original GRB studies that it will enable.

Precision characterization of the TESS CCD detectors: Quantum efficiency, charge blooming and undershoot effects

NASA's Kepler mission revolutionized the exoplanet field by showing how abundant planets around stars are. The Transiting Exoplanet Survey Satellite (TESS) is the next logical step in searching for planets around nearby bright stars that can be followed up using spectroscopy to measure the planetary masses and atmospheric conditions. TESS was launched successfully in April 2018 as an Astrophysics Explorer mission, and is expected to discover a thousand or more planets that are smaller in size than Neptune. TESS employs four identical wide-field optical CCD cameras with a band-pass of 600 nm–1050 nm to perform differential time-series photometry by monitoring at least 200,000 main sequence stars. The detectors are designed for enhanced sensitivity to the redder wavelengths because it is easier to detect small planets around small red stars. The upper limit of the band-pass cutoff at 1050 nm is driven by the quantum-efficiency curve of the detectors. Exoplanet detection using planetary transits requires very high precision photometry because the occultation causes a dip in the brightness in the order of a few hundred parts per million (ppm). The detector noise should therefore be significantly low. This requires very accurate characterization and minimization of the noise sources. An optical test bench with significantly high photometric stability has been developed to perform precise noise measurements for TESS. In this paper, results from precision characterization techniques developed for the TESS CCD detectors are presented. In particular, the characterization of the absolute quantum efficiency (QE), gain, charge saturation and blooming, undershoot effects, and straps of the CCD detectors are presented.

Project “Universat-SOCRAT” of Multiple Small Satellites for Monitoring of Natural and Technogenic Space Hazards

Abstract The new space project of M. V. Lomonosov Moscow State University on elaboration of multiple satellites for real time monitoring in the near-Earth space of radiation environment, natural (asteroids, meteoroids) and artificial (space debris) potentially dangerous objects, electromagnetic transients, such as cosmic gamma ray bursts, terrestrial gamma ray flashes, optical and ultraviolet bursts in the Earth atmosphere is presented. It is intended to install on the satellites the following instruments for space monitoring of dangerous objects and hazards: spectrometers of electrons and protons, complex of instruments for study of transient electromagnetic phenomena including gamma ray spectrometer, detectors of ultraviolet and optical emission and wide-field optical cameras. Successful implementation of the project for the first time in the world allows realization of a space system prototype for monitoring and preventing of space hazards for both ongoing and planned space missions, and also for aircraft flying in the upper atmosphere. There are also discussed results of experiments on-board Lomonosov in view of good experience of wide field camera use for monitor observations in space. These results formed the base of scientific program for the new project Universat- SOCRAT.

Observation of Cosmic Gamma Ray Bursts in the Experiments Onboard Lomonosov and Vernov Satellites

The study of cosmic gamma ray bursts (GRBs) is one of the main goals of the Lomonosov space mission. The main advantage of this mission is simultaneous multiwavelength observations of GRBs covering the optical, X-ray and gamma-ray ranges. The mission payload includes the GRB monitor BDRG, wide-field optical cameras SHOK, and the UFFO instrument. Data are recorded mainly by the event trigger provided by the BDRG instrument, which measures the spectral and temporal properties of the burst in the energy range 10–3000 keV. The BDRG instrument also provides estimation of the source coordinates by comparing the readings of three differently directed detectors with an accuracy of several degrees. Wide-field SHOK optical cameras have a field of view of ~20° × 40°. They fix a set of images with a frequency of about five frames per second prior to the trigger and another set immediately after the trigger. The UFFO instrument includes the UBAT telescope with a coded mask for measurements in hard X-ray and soft gamma-ray ranges and an optical telescope with a slewing mirror (SMT) that can be directed on the GRB source for a time ~1 s for measuring GRB prompt emission in the early stages. In response to an BDRG trigger signal, the real-time data on a detected GRB are transmitted to the Earth via Globalstar network to the Gamma-ray Coordinates Network (GCN) and ground-based observatories. During observations on the Lomonosov satellite, 20 gamma-ray bursts were detected and catalogued. Several gamma-ray bursts were also detected in the Vernov satellite experiment. An example of such an event is given.

Observations of Near-Earth Optical Transients with the Lomonosov Space Observatory

The results of observations with the MASTER-SHOK robotic wide-field optical cameras onboard the Lomonosov Space Observatory carried out in 2016 are presented. In all, the automated transient detection system transmitted 22 181 images of moving objects with signal-to-noise ratios greater than 5 to the Earth. Approximately 84% of these images are identified with well-known artificial Earth satellites (including repeated images of the same satellite) and fragments of such satellites (space debris), according to databases of known satellites. The remaining 16% of the images are relate to uncatalogued objects. This first experience in optical space-based monitoring of near-Earth space demonstrates the high efficiency and great potential of using large-aperture cameras in space, based on the software and technology of the MASTER robotic optical complexes (the Mobile Astronomical System of TElescope-Robots (MASTER) global network of robotic telescopes of Lomonosov Moscow State University).

The Space-Based Photometry Revolution

AbstractThe Transiting Exoplanet Survey Satellite (TESS) is a NASA Astrophysics Explorer-class mission that will perform an all-sky survey to search for planets transiting nearby bright stars. The primary goal is to search for planets smaller than Neptune that are amenable to follow-up spectroscopic observations that will yield planet masses, thereby providing prime targets for future atmospheric characterization studies. In its two-year prime mission, TESS will monitor more than 200,000 stars with four wide-field optical CCD cameras that will tile more than 90% of the sky. TESS will also obtain full-frame images (FFIs) of the entire field of view with a cadence of 30 minutes to facilitate additional science. These FFIs will provide photometry for more than 30 million objects brighter than magnitude I =16 during the two-year prime mission. The TESS legacy will be a catalogue of the nearest and brightest main-sequence stars hosting transiting exoplanets. The TESS Mission will also have a robust Guest Investigator (GI) Programme that will be managed by the TESS Science Support Center at NASA Goddard Space Flight Center. Under the GI programme, the astrophysics community may propose new 2-minute cadence targets and investigations using the 30-minute cadence FFI data. TESS GI calls for proposals will occur once per year, and about 20,000 targets will be available for each GI programme cycle.TESS was launched in April 2018, and will observe from a unique elliptical high-Earth orbit that will provide an unobstructed view of its field to obtain continuous light-curves.

The mass index and mass of the Geminid meteoroid stream as determined with radar, optical and lunar impact data

The Geminid meteor shower was observed in 2015 using the Western Meteor Physics Group's Canadian Meteor Orbit Radar (CMOR), Marshall Space Flight Center's (MSFC) eight wide-field optical cameras, and telescopes of MSFC's lunar impact monitoring program. These observations allowed Geminid fluxes to be calculated in three unique mass-ranges, from 1.8×10−4g to 30g. From these fluxes, a mass index of 1.68±0.04 was measured. The quantities derived here, along with a profile of the Geminid meteor shower activity in 2015 from CMOR, were used to find a total Geminid mass of 3.5×107g the Earth encountered in 2015, along with a minimum total mass for the Geminid meteoroid stream of 1.6×1016g. Attempts have been made in the past to measure the mass of meteoroid streams using ZHR profiles, but this new and improved treatment uses empirically derived fluxes and measured mass indices for the 2015 encounter with the meteoroid stream. These results are compared to meteoroid stream mass estimate measured for the Perseids of 3.3×1017g. Instead of three flux values, a single flux value and an assumed mass index of 1.78 was used in Perseid analysis.

Transiting Exoplanet Survey Satellite

The Transiting Exoplanet Survey Satellite (TESS) will search for planets transiting bright and nearby stars. TESS has been selected by NASA for launch in 2017 as an Astrophysics Explorer mission. The spacecraft will be placed into a highly elliptical 13.7-day orbit around the Earth. During its two-year mission, TESS will employ four wide-field optical CCD cameras to monitor at least 200,000 main-sequence dwarf stars with I = 4-13 for temporary drops in brightness caused by planetary transits. Each star will be observed for an interval ranging from one month to one year, depending mainly on the star's ecliptic latitude. The longest observing intervals will be for stars near the ecliptic poles, which are the optimal locations for follow-up observations with the James Webb Space Telescope. Brightness measurements of preselected target stars will be recorded every 2 min, and full frame images will be recorded every 30 min. TESS stars will be 10-100 times brighter than those surveyed by the pioneering Kepler mission. This will make TESS planets easier to characterize with follow-up observations. TESS is expected to find more than a thousand planets smaller than Neptune, including dozens that are comparable in size to the Earth. Public data releases will occur every four months, inviting immediate community-wide efforts to study the new planets. The TESS legacy will be a catalog of the nearest and brightest stars hosting transiting planets, which will endure as highly favorable targets for detailed investigations.

The ALHAMBRA Survey: Bayesian photometric redshifts with 23 bands for 3 deg2

The Advance Large Homogeneous Area Medium-Band Redshift Astronomical (ALHAMBRA) survey has observed eight different regions of the sky, including sections of the Cosmic Evolution Survey (COSMOS), DEEP2, European Large-Area Infrared Space Observatory Survey (ELAIS), Great Observatories Origins Deep Survey North (GOODS-N), Sloan Digital Sky Survey (SDSS) and Groth fields using a new photometric system with 20 optical, contiguous ∼300-Å filters plus the JHKs bands. The filter system is designed to optimize the effective photometric redshift depth of the survey, while having enough wavelength resolution for the identification of faint emission lines. The observations, carried out with the Calar Alto 3.5-m telescope using the wide-field optical camera Large Area Imager for Calar Alto (LAICA) and the near-infrared (NIR) instrument Omega-2000, represent a total of ∼700 h of on-target science images. Here we present multicolour point-spread function (PSF) corrected photometry and photometric redshifts for ∼438 000 galaxies, detected in synthetic F814W images. The catalogues are complete down to a magnitude I ∼ 24.5 AB and cover an effective area of 2.79 deg2. Photometric zero-points were calibrated using stellar transformation equations and refined internally, using a new technique based on the highly robust photometric redshifts measured for emission-line galaxies. We calculate Bayesian photometric redshifts with the Bayesian Photometric Redshift (bpz)2.0 code, obtaining a precision of δz/(1 + zs) = 1 per cent for I < 22.5 and δz/(1 + zs) = 1.4 per cent for 22.5 < I < 24.5. The global n(z) distribution shows a mean redshift 〈z〉 = 0.56 for I < 22.5 AB and 〈z〉 = 0.86 for I < 24.5 AB. Given its depth and small cosmic variance, ALHAMBRA is a unique data set for galaxy evolution studies.

The BDRG and SHOK instruments for studying gamma-ray burst prompt emission onboard the Lomonosov spacecraft

One of the goals of the Lomonosov satellite designed by scientists of Moscow State University is to study the prompt emission of cosmic gamma-ray bursts. This paper describes the gamma-ray burst monitor in the gamma-ray range (the BDRG instrument) and the wide-field optical cameras (the SHOK instrument) for detecting both the gamma-ray burst prompt emission and its precursors.

BDRG and shok instruments for study of GRB prompt emission in michaylo lomonosov space mission

The study of GRB prompt emission (PE) is one of the main goals of the Lomonosov space mission, which is being prepared at Moscow State University. The GRB monitor (BDRG) and the wide-field optical cameras (SHOK) are intended for detection of GRB prompt emission as well as optical counterparts. The BDRG instrument consists of three identical NaI(Tl)/CsI(Tl) (13.0 × 2.0cm ) phoswich detectors, whose axes determine the Cartesian coordinate system. This allows to localize any GRB source on the sky by means of the count rate seen by each detector with an accuracy of ~2 deg. The SHOK instrument consists of two identical wide-field cameras (WFC) directed in such a way that the field of view (FOV) of each WFC overlaps by the corresponding BDRG FOV, which produces a trigger on the WFC in case of a GRB detection. With this setup, the GRB prompt light curve will be obtained in the visible without any delay with respect to gamma-rays, which is crucial for a GRB central engine understanding.

Giant Transiting Planets Observations with LAIWO

We present preliminary single field results on a search for transiting extrasolar planets with the LAIWO wide field optical CCD camera, attached to the 1-m telescope at the Wise Observatory. With a 3 min integration time, the system achieved a few mmag precision for the brightest stars in a field of view of one square degree. We detect several periodic variables and a few transit-like events. The promising candidates will be followed-up in the near future. The Giant Transiting Planets Observations (GITPO) program is a collaboration

High star formation activity in the central region of a distant cluster atz= 1.46

We present an unbiased deep [OII] emission survey of a cluster XMMXCS J2215.9-1738 at z=1.46, the most distant cluster to date with a detection of extended X-ray emission. With wide-field optical and near-infrared cameras (Suprime-Cam and MOIRCS, respectively) on Subaru telescope, we performed deep imaging with a narrow-band filter NB912 (lambda_c=9139A, Delta_lambda=134A) as well as broad-band filters (B, z', J and Ks). From the photometric catalogues, we have identified 44 [OII] emitters in the cluster central region of 6'x6' down to a dust-free star formation rate of 2.6 Msun/yr (3 sigma). Interestingly, it is found that there are many [OII] emitters even in the central high density region. In fact, the fraction of [OII] emitters to the cluster members as well as their star formation rates and equivalent widths stay almost constant with decreasing cluster-centric distance up to the cluster core. Unlike clusters at lower redshifts (z<1) where star formation activity is mostly quenched in their central regions, this higher redshift 2215 cluster shows its high star formation activity even at its centre, suggesting that we are beginning to enter the formation epoch of some galaxies in the cluster core eventually. Moreover, we find a deficit of galaxies on the red sequence at magnitudes fainter than ~M*+0.5 on the colour-magnitude diagram. This break magnitude is brighter than that of lower redshift clusters, and it is likely that we are seeing the formation phase of more massive red galaxies in the cluster core at z~1. These results may indicate inside-out and down-sizing propagation of star formation activity in the course of cluster evolution.

Dark red debris from three short-period comets: 2P/Encke, 22P/Kopff, and 65P/Gunn

We present observations of the extended dust structures near the orbits of three short-period comets: 2P/Encke, 22P/Kopff, and 65P/Gunn. The dust trails were originally discovered by the Infrared Astronomical Satellite (IRAS). Our observations were made using wide-field optical CCD cameras on the University of Hawaii 2.24-m telescope, the Canada–France–Hawaii 3.6-m telescope, and the Kiso 1.05-m Schmidt telescope. We compared the observed images with models and found that the extended structures seen around 2P/Encke and 22P/Kopff before perihelion passage were most likely “dust trails,” whereas images taken after perihelion passage show a high contamination by recently released particles (i.e., particles in Neck-Line structures are visible). We could not confirm the existence of a dust trail from 65P/Gunn within the field of view of the camera used. The effective sizes of the particles responsible for the scattered light were estimated at 1–100 mm (2P/Encke), 1–10 mm (22P/Kopff), and 100 μm–1 mm (65P/Gunn), respectively, which is consistent with previous studies of dust trails made with infrared space telescopes and optical telescopes. We evaluated the mass loss rates of these comets, averaged over their orbits, as reaching 48 ± 20 kg s −1 (2P/Encke), 17 ± 3 kg s −1 (22P/Kopff), and 27 ± 9 kg s −1 (65P/Gunn). These values are consistent with previous work. Therefore, the total amount of material ejected from these three comets is 10 2 kg s −1 , which would contribute a considerable fraction of the 10 4 kg s −1 lost within 1 AU that needs to be replaced if the zodiacal cloud is to be maintained in a steady state. We also found that the particles in the dust structures are significantly redder than the Sun and the zodiacal light, and might be redder than the average short-period comet nuclei. Specifically, the reflectivity gradients of 2P/Encke, 22P/Kopff, and 65P/Gunn are 13 ± 7 (% 10 3 Å −1 ), 20 ± 5 (% 10 3 Å −1 ), and 15 ± 4 (% 10 3 Å −1 ), respectively. We examined the change in color with distance from the nucleus. No clear correlation was detected for 2P/Encke or 22P/Kopff to an accuracy of 3–11%, while the 65P/Gunn tail did show color variation, becoming redder with increasing distance from the nucleus. This dark red material, consisting of particles of sand–cobble size, has marginally escaped from the nuclei and will evolve into finer-grained interplanetary dust particles after subsequent collisions.

On the potential of extrasolar planet transit surveys

We analyse the respective benefits and drawbacks of ground-based and space-based transit surveys for extrasolar planets. Based on simple but realistic assumptions about the fraction of lower main sequence stars harboring telluric and giant planets within the outer limit of the habitable zone, we predict the harvests of fictitious surveys with three existing wide field optical and near-IR cameras: the CFHT-Megacam, SUBARU-Suprime and VISTA-IR. An additional promising instrument is considered, VISTA-Vis, currently under development. The results are compared with the harvests predicted under exactly the same assumptions, for the space missions COROT and KEPLER. We show that ground-based wide field surveys may discover more giant planets than space missions. However, space surveys seem to constitute the best strategy to search for telluric planets. In this respect, the KEPLER mission appears 50 times more efficient than any of the ground-based surveys considered here. KEPLER might even discover telluric planets in the habitable zone of their host star.