Astroclimatic studies of the sites for forthcoming radio astronomical observatories (original) (raw)
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Spectral characteristics and variability of radio sources near the north celestial pole
Astronomy Reports, 2009
We present the results of our observations of compact extragalactic radio sources near the north celestial pole (+75 • ≤ δ ≤ +88 • ) obtained on the RATAN-600 radio telescope. Our sample consists of 51 radio sources with spectra that are either flat or inverted (growing toward shorter wavelengths) and with flux densities at 1.4 GHz S ν ≥ 200 mJy. We observed the sources at 1-21.7 GHz. Multi-frequency instantaneous spectra are presented for 1999-2007. We observed 33 of our sample source daily for 30 days in August 2007. As a result, we revealed 15 objects exhibiting rapid variations on time scales of a day. The multi-frequency instantaneous spectra of these sources indicate that radio flux variations on one-day timescales are characteristic of objects of various spectral types. More than half the sources exhibiting rapid variations demonstrate a growth in the variability amplitude with increasing frequency. For some of the objects, the variability amplitude is virtually independent of frequency.
arXiv (Cornell University), 2023
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Journal of the Franklin Institute, 1967
The research objectives of the Radio Astronomy Group may be broadly described as follows. 1. Studies of continuum emission of extraterrestrial radio sources. The antenna facilities of the Haystack Microwave Research Facility, Lincoln Laboratory, M.I.T., have been used at 2-cm and 3.75-cm wavelengths to study temporal variations in the radio flux from quasi-stellar radio sources, l to map the brightness distribution in both the polarized and unpolarized components of the radiation from the strong radio 2 sources, and to determine the absolute flux from the radio sources Cassiopeia A and Taurus A. 3 This work continues and is being extended to other sources. The National Radio Astronomy Observatory interferometer, Green Bank, West Virginia, has been used for determining the brightness distribution of many galatic and extragalatic radio sources at 234 Mc/sec. Studies of Venus and Jupiter at wavelengths near the watervapor and ammonia resonances have been carried out on the 28-ft radio telescope of Lincoln Laboratory.4 A radiometer operating at 4-mm wavelength has been installed and tested on the 29-ft radio telescope at the Prospect Park Field Station of Air Force Cambridge Research Laboratories, and planetary observations are planned for the near future. 2. Studies of the radio spectrum of the interstellar medium. The spectral lines of OH have been the subject of extensive observations with the antennas of the Haystack Microwave Research and Millstone Radar Facility, Lincoln Laboratory, M.I.T., and the 140-ft radio telescope of the National Radio Astronomy Observatory, Green Bank, West Virginia. The studies during the past year have led to (a) the detection of circularly polarized OH emission, 5 (b) the detection of the isotopic species 018H,6 and the establishment of an upper limit to the angular size of the OH emitting regions of 15 seconds of arc.7 Interferometric observations are being extended by using the Millstone and Agassiz (Harvard) radio telescopes as an interferometer to determine the angular size of the emission regions. Searches for other spectral lines are concentrating on the CH radical, with a line expected near 3300 Mc/sec. 3. Study of microwave emission and absorption by the terrestrial atmosphere and
Validation of the COSMIC radio occultation data over Gadanki (13.48° N, 79.2° E): a tropical region.
… -3/COSMIC Workshop …, 2009
Con stel la tion Ob serv ing Sys tem for Me te o rol ogy Ion o sphere and Cli mate (COS MIC), con sist ing of six Low Earth Or bit (LEO) Global Po si tion Sys tem (GPS) re ceiv ers, on board the Formosat Sat el lite 3 (FORMOSAT-3) is pro vid ing dense ob ser va tions of den sity, refractivity, tem per a ture and wa ter va por pro files of the neu tral at mo sphere since mid dle of July 2006. Spe cial ra dio sonde (Väisälä) cam paign was con ducted at Gadanki (13.48°N, 79.18°E), a trop i cal site in In dia, dur ing July 2006 to March 2007 to val i date these me te o ro log i cal pa ram e ters. Co-lo cated Nd: YAG Ray leigh lidar was also op er ated dur ing the over pass of COS MIC and is uti lized to val i date the tem per a tures in the height range of 30 to 40 km. A to tal of 142 over passes oc curred dur ing the above men tioned pe riod within 300 km dis tance from Gadanki out of which 41 over passes oc curred within a time dif fer ence of ±4 hours of ra dio sonde launch. In ad di tion, 18 over passes oc curred within the time dif fer ence of ±4 hours of lidar op er a tion. A de tailed com par i son has been made with all these over passes for the refractivity, tem per a ture and wa ter va por ob tained from COS MIC. The wa ter va por com par i son has shown gen er ally a good agree ment with a mean dif fer ence of 5 - 10% be low 6 - 7 km. Al though there is a colder bias be tween COS MIC and ra dio sonde, a very good com par i son in tem per a ture is also found be tween 10 and 27 km with a mean dif fer ence of less than 1 K (RMS dif fer ence is only 0.64 K). There ex ists a large dif fer ence in tem per a ture of about 8 K be tween 30 and 40 km (be tween COS MIC and lidar). Pos si ble rea sons for these large dif fer ences are given. There was one event that oc curred just over Gadanki for which a de tailed com par i son has been made with spe cial em pha sis on wa ter va por re triev als. Sen si tiv ity test is also done on the frac tional dif fer ence in N for the event that occurred on 24 July 2006 between COSMIC (1D-var) and radiosonde and found that pressure plays a key role than temperature in determining the refractivity.
Optical Characteristics of the Astrometric Radio Sources
2009
A new list of physical characteristics of 3914 astrometric radio sources, including all the 717 ICRF-Ext.2 sources, observed during IVS and NRAO VCS sessions have been compiled. The source list was taken from the Goddard VLBI astrometric catalog astro 2007c with addition of two ICRF-Ext.2 sources. At this stage the source characteristics were mainly taken from the NASA/IPAC Extragalactic Database (NED). Our list includes source type, redshift and visual magnitude (if available). In case of doubt detailed comment is provided. 667 sources from our list are included into the IERS list. Comparison of two lists has shown a significant difference in characteristics for about half of common sources. A list of frequently observed sources without known physical characteristics for urgent observations with large optical telescopes has been compiled.
The Karl G. Jansky Very Large Array Sky Survey (VLASS). Science Case and Survey Design
Publications of the Astronomical Society of the Pacific, 2020
The Very Large Array Sky Survey (VLASS) is a synoptic, all-sky radio sky survey with a unique combination of high angular resolution (≈2. 5), sensitivity (a 1σ goal of 70 µJy/beam in the coadded data), full linear Stokes polarimetry, time domain coverage, and wide bandwidth (2-4 GHz). The first observations began in September 2017, and observing for the survey will finish in 2024. VLASS will use approximately 5500 hours of time on the Karl G. Jansky Very Large Array (VLA) to cover the whole sky visible to the VLA (Declination > −40 •), a total of 33 885 deg 2. The data will be taken in three epochs to allow the discovery of variable and transient radio sources. The survey is designed to engage radio astronomy experts, multi-wavelength astronomers, and citizen scientists alike. By utilizing an "on the fly" interferometry mode, the observing overheads are much reduced compared to a conventional pointed survey. In this paper, we present the science case and observational strategy for the survey, and also results from early survey observations.