Search

Based on a medium-band photometric survey at the 1-m Schmidt telescope of the Byurakan Astrophysical Observatory, we have produced a complete sample of quasars to 22.5 mag in the HS47.5-22 field with an area of 2.38 deg . We have classified the objects and produced the sample of quasars using broadband photometric data and the morphological classification from DECaLS (Dey et al. 2019), infrared photometry from WISE (Meisner et al. 2018), spectroscopy from SDSS (Pâris et al. 2018), ROSAT X-ray data (Molthagen et al. 1997), FIRST radio data (Becker et al. 1995), and data on the proper motions of objects from the Gaia survey (Brown et al. 2018). The sample contains 682 quasars for which we have determined the medium-band photometric redshifts, calculated the absolute magnitudes, and investigated the quasar space density distribution and luminosity function. As a result, we have obtained evidence for the absence of a significant reduction in the space density of quasars up to . [ABSTRACT FROM AUTHOR]

Optical surveys for space debris in high-altitude orbits have been conducted since more than ten years. Originally these efforts concentrated mainly on the geostationary region (GEO). Corresponding observation strategies, processing techniques and cataloguing approaches have been developed and successfully applied. The ESA GEO surveys, e.g., resulted in the detection of a significant population of small-size debris and later in the discovery of high area-to-mass ratio objects in GEO-like orbits. Comparably less experience (both, in terms of practical observation and strategy definition) is available for eccentric orbits that (at least partly) are in the MEO region, in particular for the Molniya-type orbits. Different survey and follow-up strategies for searching space debris objects in highly-eccentric MEO orbits, and to acquire orbits which are sufficiently accurate to catalog such objects and to maintain their orbits over longer time spans were developed. Simulations were performed to compare the performance of different survey and cataloguing strategies. Eventually, optical observations were conducted in the framework of an ESA study using ESA’s Space Debris Telescope (ESASDT) the 1-m Zeiss telescope located at the Optical Ground Station (OGS) at the Teide Observatory at Tenerife, Spain. Thirteen nights of surveys of Molniya-type orbits were performed between January and August 2013. Eventually 255 surveys were performed during these thirteen nights corresponding to about 47 h of observations. In total 30 uncorrelated faint objects were discovered. On average one uncorrelated object was found every 100 min of observations. Some of these objects show a considerable brightness variation and have a high area-to-mass ratio as determined in the orbit estimation process. [ABSTRACT FROM AUTHOR]

In this work we present updated forecasts on parameterised modifications of gravity that can capture deviations of the behaviour of cosmological density perturbations beyond Λ CDM. For these forecasts we adopt the SKA Observatory (SKAO) as a benchmark for future cosmological surveys at radio frequencies, combining a continuum survey for weak lensing and angular galaxy clustering with an Hi galaxy survey for spectroscopic galaxy clustering that can detect baryon acoustic oscillations and redshift space distortions. Moreover, we also add 21 cm Hi intensity mapping, which provides invaluable information at higher redshifts, and can complement tomographic resolution, thus allowing us to probe redshift-dependent deviations of modified gravity models. For some of these cases, we combine the probes with other optical surveys, such as the Dark Energy Spectroscopic Instrument (DESI) and the Vera C. Rubin Observatory (VRO). We show that such synergies are powerful tools to remove systematic effects and degeneracies in the non-linear and small-scale modelling of the observables. Overall, we find that the combination of all SKAO radio probes will have the ability to constrain the present value of the functions parameterising deviations from Λ CDM (μ and Σ) with a precision of 2.7% and 1.8% respectively, competitive with the constraints expected from optical surveys and with constraints we have on gravitational interactions in the standard model. Exploring the radio-optical synergies, we find that the combination of VRO with SKAO can yield extremely tight constraints on μ and Σ (0.9% and 0.7% respectively), which are further improved when the cross-correlation between intensity mapping and DESI galaxies is included. [ABSTRACT FROM AUTHOR]

Abstract: In the framework of its space debris research activities ESA established an optical survey program to study the space debris environment at high altitudes, in particular in the geostationary ring and in the geostationary transfer orbit region. The Astronomical Institute of the University of Bern (AIUB) performs these surveys on behalf of ESA using ESA’s 1-m telescope in Tenerife. Regular observations were started in 1999 and are continued during about 120–140 nights per year. Results from these surveys revealed a substantial amount of space debris at high altitudes in the size range from 0.1 to 1m. Several space debris populations with different dynamical properties were identified in the geostationary ring. During the searches for debris in the geostationary transfer orbit region a new population of objects in unexpected orbits, where no potential progenitors exist, was found. The orbital periods of these objects are clustered around one revolution per day; the eccentricities, however, are scattered between 0 and 0.6. By following-up some of these objects using the ESA telescope and AIUB’s 1-m telescope in Zimmerwald, Switzerland, it was possible to study the properties of this new population. One spectacular finding from monitoring the orbits over time spans of days to months is the fact that these objects must have extreme area-to-mass ratios, which are by several orders of magnitudes higher than for ‘normal-type’ debris. This in turn supports the hypothesis that the new population actually is debris generated in or near the geostationary ring and which is in orbits with periodically varying eccentricity and inclination due to perturbations by solar radiation pressure. In order to further study the nature of these debris, multi-color and temporal photometry (light curves) were acquired with the Zimmerwald telescope. The light curves show strong variations over short time intervals, including signals typical for specular reflections. Some objects exhibit distinct periodic variations with periods ranging from 10 to several 100s. All this is indicative for objects with complicated shapes and some highly reflective surfaces. [Copyright &y& Elsevier]

A number of optical instruments are involved in making systematic surveys of the geosynchronous Earth orbit (GEO) region. Because of the limited field of view of an optical instrument, it is impossible at any one time to observe objects in all orbit planes in the region. Therefore, the orbit distributions seen are biased relative to the true populations of orbits in space. Because the observations represent a statistical sample of the population, statistical variations must be accounted for. The full procedure to remove the biases is extremely difficult with the limited orbit data measured because objects in GEO can have a wide spectrum of possible orbits. The measurements themselves are often insufficient to distinguish whether the object is in an elliptical or circular orbit. However, by limiting the range of possible orbit types it is possible to simplify the problem and obtain reasonable orbit distribution estimates. These distributions can in turn be used to identify interesting groupings of objects that may be part of an unrecognized breakup event. This paper describes the methods used to remove observational biases, and presents estimates of orbit distributions of uncatalogued objects at GEO visible to the instruments. [Copyright &y& Elsevier]

Since more than 10 years there is evidence that small-size space debris is accumulating in the geosynchronous orbit (GEO), probably as the result of breakups. Two break-ups have been reported in GEO. The 1978 break-up of an EKRAN 2 satellite, SSN 10365, was identified in 1992, and in 1992 a Titan 3C Transtage, SSN 3432, break-up produced at least twenty observable pieces. Subsequently several nations performed optical surveys of the GEO region in the form of independent observation campaigns. Such surveys suffer from the fact that the field of view of optical telescopes is small compared with the total area covered by the GEO ring. As a consequence only a small volume of the orbital element-magnitude-space is covered by each individual survey. Results from these surveys are thus affected by observational biases and therefore difficult to compare. This paper describes the development of a common search strategy to overcome these limitations. The strategy optimizes the sampling for objects in orbits similar to the orbits of the known GEO population but does not exclude the detection of objects with other orbital planes. A properly designed common search strategy clearly eases the comparison of results from different groups and the extrapolation from the sparse (biased) samples to the entire GEO environment. [ABSTRACT FROM AUTHOR]

Optical surveys using astronomical telescopes are an efficient way to observe and catalogue space debris, especially for detecting debris in medium or geostationary Earth orbits. Nowadays, small aperture and wide field of view telescopes are widely used and play significant roles in optical space debris surveys. However, special challenges arise since space debris is moving relatively to the background stars and the optics suffer from defects. This affects the efficiency of traditional source extraction methods. Here, a dedicated image processing technique is developed to automatically detect and measure space debris from consecutive CCD images. In order to improve the detection efficiency and robustness, several innovative algorithms are introduced to eliminate noise and increase the object detection ability, and the whole pipeline is optimized to reduce the raw images in real time. A trial survey with a wide field of view and small aperture telescope is presented to test our technique. In our survey, two observing strategies are adopted according to the dynamical features of space objects in the high Earth orbital region, and large numbers of raw CCD images are obtained for both strategies; the efficiency of our reduction is investigated based on the reduction results. Our technique exhibits a correlation rate higher than 97%, and around 400 objects can be routinely observed and catalogued just utilizing one wide field of view telescope in one night. [ABSTRACT FROM AUTHOR]