RATAN-600 radio telescope in the 24th solar-activity cycle. III. System of data acquisition and control of the solar spectral facility

We report the development of a multichannel data acquisition and control system for the Spectral and Polarization High-Resolution Solar Research System, installed at the RATAN-600 radio telescope. This facility provides high-speed registration of signals from 240 channels and controls the preparation for observations and the process of automatic observations. The hardware is made in the form factor of 3U Evromekhanika modules. The measurement facility is controlled by the software based on the QT cross-platform library (the open source version), which can be run both on Linux and Windows operating systems. The data are written to a magnetic carrier and then transferred to the computer network of the Special Astrophysical Observatory for archiving, and can be accessed by external users.     

Small-scale galactic emission fluctuation observations with RATAN-600 radio telescope

We present the estimates of Galactic synchrotron and free-free emission power at intermediate and small scales (500 < l < 1000, 20′ < θ < 40′), based on the RATAN-600 radio telescope observations (SAO RAS). The observations were conducted in the frequency range of 2.3–11.2 GHz using the transit scan mode, in the declination range of 40.7° s δ < 42.3°. The power spectrum estimates of synchrotron and free-free components were obtained. They can be further used in the data processing stage of the high-resolution cosmological experiments like Planck.     

C-Band Radiometer for Continuum Observations at RATAN-600 Radio Telescope

We describe the development of the tools and methods of 4.7-GHz band observations on RATAN-600 radio telescope and present a new design solution—a radiometric unit, and the development of an uncooled tuned receiver based on this unit and meant for operating in the “total power” radiometer mode.We discuss the design of the radio unit and the specificities of the radiometer design.We demonstrate the possibility of conducting observations in the total power radiometer mode at the theoretical sensitivity on time scales up to 10 seconds. The sensitivity of such a radiometer remains higher than that of a Dicke radiometer on time scales up to 100 seconds.     

On the comparison of radio-astronomical measurements of the height structure of magnetic field with results of model approximations

The results of microwave observations of the polarized emission of active regionsmade with the RATAN-600 radio telescope are used to develop the method for determining the structure of the magnetic field of these regions at coronal heights. About 1000-G-strong magnetic fields are observed in the solar atmosphere at rather high altitudes (from 10 to 25 Mm). This result is confirmed fairly well by the ultraviolet observations of magnetic loops, it is consistent with earlier radio-astronomical observations of the magnetic field at the height of the transition region, and it corresponds as well, if interpreted in terms of the dipole magnetic field model, to the vertical gradients of the photospheric magnetic field.     

RATAN-600 radio telescope in the 24th solar activity cycle. IV. Information system for RATAN-600 solar observations

The development of observational equipment and software for processing and efficient representation of spectral and polarization solar microwave observations on the RATAN-600 contributes to obtaining new information about the parameters of plasma at the chromospheric and coronal levels. Current status of information system for RATAN-600 solar observations is described, which is devoted to automatically capturing, storing, transmitting and processing the data and near-real-time publishing them on the Internet. The user web interface for interactive search, visualization, and on-line analysis of the data is available at .     

Transition region above sunspots inferred from microwave observations

We report the results of spectral-polarization observations of the active region NOAA 10848 made with the RATAN-600 radio telescope. High spectral resolution (1%) of observations allowed obtaining detailed temperature height profiles for the sources located above the sunspots in the transition region from the chromosphere to the corona. The resulting vertical profiles indicate that the transition region above the sunspots may extend over a considerable height interval and be characterized by a gradual increase of temperature—a pattern that is inconsistent with model atmospheres having a sharp temperature increase in the transition region.     

Magnetic fields of sunspots based on combined optical and radio observations

In the present paper we present the results of measurement of magnetic fields in some sunspots at different heights in the solar atmosphere, based on simultaneous optical and radio measurements. The optical measurements were made by traditional photographic spectral observations of Zeeman splitting in a number of spectral lines originating at different heights in the solar photosphere and chromosphere. Radio observations of the spectra and polarization of the sunspot - associated sources were made in the wavelength range of 2–4 cm using large reflector-type radio telescope RATAN-600. The magnetic field penetrating the hot regions of the solar atmosphere were found from the shortest wavelength of generation of thermal cyclotron emission (presumably in the third harmonic of electron gyrofrequency). For all the eight cases under consideration we have found that magnetic field first drops with height, increases from the photosphere to lower chromosphere, and then decreases again as we proceed to higher chromosphere and chromosphere-corona transition region. Radio measurements were found to be well correlated with optical measurements of magnetic fields for the same sunspot. An alternative interpretation implies that different lines used for magnetic field measurements refer to different locations on the solar surface. If this is the case, then the inversion in vertical gradients of magnetic fields may not exist above the sunspots. Possible sources of systematic and random errors are also discussed.     

Development of ephemeris support in observations of distant radio sources and solar system objects at RATAN-600 radio telescope

New elements of the algorithmic and software bases of the ephemeris support for the RATAN-600 radio telescope observations of distant radio sources and objects of the Solar system are briefly described.     

A high-resolution study of Jupiter at a frequency of 30 GHz

We present the results of our study of Jupiter and its radiation belts with a resolution of 6 arcsec at a frequency of 30 GHz using the RATAN-600 radio telescope and a MARS matrix radiometer with a sensitivity of about 6 mK ^?1/2. We monitored the integrated emission from the Jovian disk with a signal-to-noise ratio of more than 1000 for 30 days and showed its radio emission to be highly stable (≈1%). Based on daily data for the one-dimensional radio brightness distribution over the disk, we mapped the longitudinal radio brightness distribution over 100 rotation periods of Jupiter around its axis. Neither hot nor cold spots with a temperature contrast of more than 1 K were detected; their contribution to the total radio flux from the Jovian disk was no more than 0.2%. The one-dimensional latitudinal (longitude-averaged) distribution obtained on VLA with a similar resolution is shown to be an order of magnitude less uniform than the one-dimensional longitudinal (latitude-averaged) distribution obtained on RATAN-600. We have studied the radiation belts at such high frequencies for the first time and estimated their intensities and variability levels under the effect of external factors. The variable component of the radiation belts was shown to have not exceeded 0.5% of the integrated spectrum of Jupiter over the entire period of its observations. We estimated the contribution of the Galilean satellites (“Galilean noise”) in low-resolution observations; the accuracy of allowing for this noise is determined by the accuracy of estimating the temperatures of the satellites at the observing frequency. The uncertainty in the total flux does not exceed 0.1%.     

Radio observations of small Hii regions with identified exciting stars

The radio maps of ten small Hii regions at λλ=2.8, 6 and 11 cm, obtained with the 100-m MPIR radiotelescope, are given. A comparison of the radio fluxes obtained with parameters of exciting stars is carried out. For four compact Hii regions — namely, S146, S152, S237 and S297 — we present the results of observations with the radiotelescope of the U.S.S.R. Academy of Sciences, RATAN-600. The paper also presents estimates of the physical conditions in nebulae, and conclusions are drawn about the possible stage of their evolution.     

A study of RATAN-600 observations of solar S-component sources

A sample of 36 S-component sources observed by the radio telescope RATAN-600 was compared with calculations of gyromagnetic emission and bremsstrahlung based on recent sunspot models. The diagnostic possibilities of the spectral distributions in the radio flux, the degree of polarization, and the source sizes for the estimation of magnetic scale heights and other source parameters were checked by different methods.Depending on the magnetic field structure, the observations show different types of polarization spectra. Most regular spectra and highest values of the degree of polarization were observed from sources above the leading part of the associated spot group. Magnetic scale heights were found to be intrinsically associated with the source size of the gyromagnetic emission.The flare production rate of active regions appears to be related to their S-component flux and magnetic scale heights.     

On the height scale of magnetic fields above sunspots derived from RATAN-600 observations

Model calculations of the S-component are compared with observations of the RATAN-600 telescope at five discrete microwave frequencies referring to active region McMath No. 15974 on May 1, 1979. The spectral variations of source diameter, flux density, and degree of polarization are used to derive the height scale of the magnetic field in accordance with a magnetic dipole distribution under the assumption of advanced temperature and electron density distributions according to most recent EUV observations.     

Perspectives of advance of RATAN-600 solar observations

The potential possibilities of RATAN-600 for solar studies are considered which are going on to be realized during the present maximum of solar activity. Different methods of an improvement of the characteristics of the antenna-receiver system are analyzed. These are: – realization of tracking the Sun during about 4 hours for a day and attaining temporal resolution up to some msec, – realization of radio-heliographic observations, – realization of a full spectral coverage of the radio telescope from 1,5 to 18 GHz with a frequency reslution up to 1–2 MHz, – combination of all possibilities mentioned above in an adaptable solar observing complex.     

A new spectrum analyzer for radio astronomical studies with the radio telescope RATAN-600

The spectral measuring facility with a new Fourier analyzer for use with the radio telescope RATAN-600 is described and its experimental data are reported.     

Automated system for reduction of observational data on RATAN-600 radio telescope

We present the automated systemfor estimating the parameters of radio sources observed on all available continuum radiometers (two receiving facilities of secondary mirrors No. 1 and No. 2 with a total of 30 radiometers) developed at RATAN-600 radio telescope and put into normal operation. The system is also used for the monitoring of the parameters of the antenna and receiving systems of RATAN-600 radio telescope, which is carried out using current measurements of calibration radio sources.     

Study of the RATAN-600 power beam pattern and antenna effective area based on deep sky survey data

The power beam pattern and antenna effective area of the RATAN-600 radio telescope are analyzed based on source samples observed during the 7.6-cm sky surveys preformed in 1980, 1988, 1990, 1991, 1993, 1994, and 1999. The surveys were made with the Northern sector of the RATAN-600 at the same declination as the COLD experiment (δ ∼ 5°). Experimental power beam patterns derived from the survey data are compared with the computed patterns. The r.m.s. deviation of the experimental data from the corresponding computed values averaged over all years is (0.19 − 0.23) ± 0.02. The vertical pattern of the 1980 survey is offset by about 1t’ with respect to the central horizontal section. The patterns obtained from the data for other years are symmetric within the measurement errors. The mean antenna effective area averaged over all years except 1993 is 803 ± 88 m². The behavior of both the beam pattern and effective telescope surface areas was stable from 1980 through 1999     

Observations of the rapid variability of the two BL Lac type objects J2005+77 and J2022+76 with the RATAN-600

We report here the results of observations of two BL Lacertae-type objects, J2005+77 and J2022+76, using the RATAN-600 at frequencies 11.2, 7.7, and 4.8 GHz. We found variations of radio emission on timescales of one day and we are the first to discover a variability of this type for J2022+76.We compare our observations with long-term multifrequency radio observations of the same sources performed on RATAN-600 within the framework of other observational programs. We analyze the behaviour of variability of the two sources and provide arguments in favour of the preferred emission generation mechanisms for the objects studied.     

Results of astrometrical observations of the Sun and major planets at the mountain astronomical station of the Pulkovo Observatory

A series of daytime observations of the Sun and major planets are obtained at the mountain astronomical station of the Pulkovo Observatory using the Ertel-Struve meridian instruments. A series of declinations of Solar System bodies and major planets includes 4057 positions and that of right ascensions of Solar System bodies comprising 2057 positions. Based on the joint processing of observations of the Sun, Mercury, Venus, and Mars obtained with the Ertel-Struve vertical circle and large transit instrument, the orientation elements of the DE200/LE200 dynamic coordinate system, namely, a correction for the right ascensions of FK5 stars ΔA = +0.127″ ± 0.033″, a correction for declinations of FK5 stars ΔD = +0.056″ ± 0.011″, a correction for the ecliptic inclination Δɛ = −0.044″ ± 0.012″, and a correction for the average longitude of the Sun ΔL = −0.083″±0.035″, are determined with respect to the stellar coordinate system.     

The Gelfreikh–Lubyshev effect according to microwave observations of sunspots

We report the results of RATAN-600 radio telescope observations of the fine structure of the source of cyclotron microwave emission (SCMR) located in the solar corona above the main sunspot of NOAA11899 active region. Compared to earlier and mostly episodic observations of the SCMR, our regular observations with RATAN-600 radio telescope showed rather conclusively that the variation of the structure of the SCMR as a function of the angle of view in the present case is of geometric nature. The behavior of image variations generally agree with the computations performed by Gelfreikh and Lubyshev in terms of the simplest model of the solar atmosphere above the sunspot. The results of their computations are widely used for interpreting observations.     

Brightness temperature distribution in solar corona based on RATAN-600 observations of the maximum phase of the March 29, 2006 solar eclipse

We describe the technique and results of modelling the solar radio emission during the maximum phase of the solar eclipse of March 29, 2006 on the RATAN-600. The aim of modelling is to refine the brightness temperature of the solar corona at the distances up to two solar radii from the center of the optical disk of the Sun. We obtained the distribution of brightness temperature in the vicinity of the coronal hole above the solar North Pole at the wavelength of 13 cm. The results of modelling showed that brightness temperatures of the coronal hole at the distances greater than 1.02 R_C (here R_C is the radius of the optical disk of the Sun) is substantially lower than the expected average brightness temperature of a typical coronal hole, and that of the quiescent Sun (below 30000 K) at the wavelength of 13 cm. The classical Baumbach-Allen formula for electron density in a spherically symmetric corona agrees with the results of observations starting at distances of (1.4–1.5) R_C.