Purpose: High resolution investigation of spectral lines of space sources requires low intrinsic noise of the radio telescope receiving system. It is provided with both input cryogenic amplifiers and low phase noise of local oscillators. To make spectral studies, it is neces ary to be able to tune the frequencies of local oscillators with a small frequency step. The paper presents the results of developing the frequency synthesizers, which simultaneously provide both a very high frequency resolution and low level of phase noise. The results of measurements of natural noise of the RT-32 radio telescope radio receiving systems are given also. Design/methodology/approach: The RT-32 receiving systems are constructed as heterodyne receivers with two stages of frequency conversion. Tuning of receiving systems with a frequency step of 10 or 20 MHz is provided by local oscillators of the first frequency conversion stage, and precise tuning is provided due to the ultra-high resolution (0.0001 MHz) of DDS-based (direct digital synthesizer) local oscillators of the second frequency conversion stage. Findings: It is shown that the application of direct digital synthesizers is possible only with the low values of frequency multiplication factors, as well as under the conditions of careful filtering of all reference signals. The parameters of the local oscillators were measured with the N9951A spectrum analyzer (Keysight Technologies) with the high resolution and wide dynamic range. To measure the radio telescope receiving system noise characteristics, a special matched loads with the possibility of cooling down to the liquid nitrogen temperature were made. The noise temperature measurements were made in different cross sections of the RT-32 receiving system. Comparison of such measurements in different configurations makes it possible to provide a preliminary estimation of the RT-32 self noise in the C- and K-bands. Conclusions: The results of measurements of self noise of radio receiving systems and phase noise of local oscillators of the RT-32 radio telescope show that within the C-band the radio telescope is capable to perform high-sensitive studies in both a wide frequency band and a narrow frequency band with the high spectral resolution. Within the K-band, the natural noise is comparable (≈60÷80 K) with the external noise that also allows studying the radiation of maser radio sources.  Key words: antenna, self noise, local oscillator, receiving system, radio telescope, RT-32, spectral lines  Manuscript submitted 15.07.2020  Radio phys. radio astron. 2020, 25(3): 1 75-192 REFERENCES 1. ULYANOV, O. M., REZNICHENKO, O. M., ZAKHARENKO, V. V., ANTYUFEYEV, A. V., KOROLEV, A. M., PATOKA, O. M., PRISIAZHNII, V. I., POICHALO, A. V., VOITYUK, V. V., MAMAREV, V. N., OZHINSKII, V. V., VLASENKO, V. P., CHMIL, V. M., LEBED, V. I., PALAMAR, M. I., CHAIKOVSKII, A. V., PASTERNAK, YU. V., STREMBITSKII, M. A., NATAROV, M. P., STESHENKO, S. O., GLAMAZDYN, V. V., SHUBNY, A. S., KIRILENKO, A. A., KULIK, D. Y., KONOVALENKO, A. A., LYTVYNENKO, L. M. and YATSKIV, Y. S., 2019. Creating the RT-32 Radio Telescope on the Basic of MARK-4B Antenna System. 1. Modernization Project and First Results.  Radio Phys. Radio Astron.  vol. 24, no. 2, pp. 87–116. DOI:  https://doi.org/10.15407/rpra24.02.087 2. ANTYUFEYEV, A. V., KOROLEV, A. M., PATOKA, O. M., SHULGA, V. M., ULYANOV, O. M., REZNICHENKO, O. M., ZAKHARENKO, V. V., PRISIAZHNII, V. I., POICHALO, A. V., VOITYUK ,V. V., MAMAREV, V. N., OZHINSKII, V. V., VLASENKO, V. P., CHMIL, V. M., LEBED, V. I., PALAMAR, M. I., CHAIKOVSKII, A. V., PASTERNAK, YU. V., STREMBITSKII, M. A., NATAROV, M. P., STESHENKO, S. O., GLAMAZDYN, V. V., SHUBNY, A. S., KIRILENKO, A. A., KULIK, D. Y. and PYLYPENKO, A. M., 2019. Creating the RT-32 Radio Telescope on the Basic of MARK-4B Antenna System. 1. Estimation of the Possibility for Making Spectral Observations of Radio Astronomical Objects.  Radio Phys. Radio Astron . vol. 24, no. 3, pp. 163–183. DOI:  https://doi.org/10.15407/rpra24.03.163 3. WOODBURN, L., NATUSCH, T., WESTON, S., THOMASSON, P., GODWIN, M., GRANET, C. and GULYAEV, S., 2015. Conversion of a New Zealand 30-metre telecommunications antenna into a radio telescope.  Publ. Astron. Soc. Aust . vol. 32, id. e017. DOI:  https://doi.org/10.1017/pasa.2015.13 4. YONEKURA, Y., SAITO, Y., SUGIYAMA, K., SOON, K. L., MOMOSE, M., YOKOSAWA, M., OGAWA, H., KIMURA, K., ABE, Y., NISHIMURA, A., HASEGAWA, Y., FUJISAWA, K., OHYAMA, T., KONO, Y., MIYAMOTO, Y., SAWADA-SATOH, S., KOBAYASHI, H., KAWAGUCHI, N., HONMA, M., SHIBATA, K. M., SATO, K., UENO, Y., JIKE, T., TAMURA, Y., HIROTA, T., MIYAZAKI, A., NIINUMA, K., SORAI, K., TAKABA, H., HACHISUKA, K., KONDO, T., SEKIDO, M., MURATA, Y., NAKAI, N. and OMODAKA, T., 2016. The Hitachi and Takahagi 32 m radio telescopes: Upgrade of the antennas from satellite communication to radio astronomy.  Publ. Astron. Soc. Jpn . vol. 68, is. 5, id. 74. DOI:  https://doi.org/10.1093/pasj/psw045 5. BELLOCHE, A., MESHCHERYAKOV, A. A., GARROD, R. T., ILYUSHIN, V. V., ALEKSEEV, E. A., MOTIYENKO, R. A., MARGULES, L., MULLER, H. S. P. and MENTEN, K. M., 2017. Rotational spectroscopy, tentative interstellar detection, and chemical modeling of N-methylformamid.  Astron. Astrophys . vol. 601, id. A49. DOI:  https://doi.org/10.1051/0004-6361/201629724 6. PENG, H., WU, Z., ZHANG, B., CHEN, Y., ZHENG, X., JIANG, D., SHEN, Z., CHEN, X. and SOTNIKOVA, YU. V., 2020. Radio properties of the OH megamaser galaxy IRAS 02524+2046.  Astron. Astrophys .vol. 638, id. A78. DOI:  https://doi.org/10.1051/0004-6361/202037559 7. GENTILE, K. and CUSHING, R. 1999. A Technical Tutorial on Digital Signal Synthesis, 1999 [online]. Analog Devices Inc. [viewed 25 July 2020]. Available from:  https://www.analog.com/en/education/education-library/technical-tutorial-dds.html 8. ZAKHARENKO, V., KONOVALENKO, A., ZARKA, P., ULYANOV, O., SIDORCHUK, M., STEPKIN, S., KOLIADIN, V., KALINICHENKO, N., STANISLAVSKY, A., DOROVSKYY, V., SHEPELEV, V., BUBNOV, I., YERIN, S., MELNIK, V., KOVAL, A., SHEVCHUK, N., VASYLIEVA, I., MYLOSTNA, K., SHEVTSOVA, A., SKORYK, A., KRAVTSOV, I., VOLVACH, Y., PLAKHOV, M., VASILENKO, N., VASYLKIVSKYI, Y., VAVRIV, D., VINOGRADOV, V., KOZHIN, R., KRAVTSOV, A., BULAKH, E., KUZIN, A., VASILYEV, A., RYABOV, V., REZNICHENKO, A., BORTSOV, V., LISACHENKO, V., KVASOV, G., MUKHA, D., LITVINENKO, G., BRAZHENKO, A., VASHCHISHIN, R., PYLAEV, O., KOSHOVYY, V., LOZINSKY, A., IVANTYSHYN, O., RUCKER, H. O., PANCHENKO, M., FISCHER, G., LECACHEUX, A., DENIS, L., COFFRE, A. and GRIEs-MEIER, J.-M., 2016. Digital Receiversfor Low-Frequency Radio Telescopes UTR-2, URAN, GURT. J. Astron. Instrum. vol. 5, is. 4, id. 1641010. DOI:  https://doi.org/10.1142/S2251171716410105 9. TEXAS INSTRUMENTS INC., 2019. LMX2595 20-GHz Wideband PLLATINUM™ RF Synthesizer With Phase Synchronization and JESD204B Support. Data Sheet [online]. [viewed 30 July 2020]. Available from:  https://www.ti.com/lit/gpn/lmx2595 10. ANALOG DEVICES INC., 2020. HMC814LC3B, SMT GaAs MMIC x2 Active frequency multiplier, 13 - 24.6 GHz output. HMC814LC3B Data Sheet [online]. [viewed 30 July 2020]. Available from:  https://www.analog.com/media/en/technical-documentation/data-sheets/hmc814.pdf 11. ANALOG DEVICES INC., 2019. Low Power 250 MSPS 10-Bit DAC 1.8 V CMOS Direct Digital Synthesizer. AD9913 Data Sheet [online]. [viewed 30 July 2020]. Available from:  https://www.analog.com/media/en/technicaldocumentation/data-sheets/AD9913.pdf 12. ANALOG DEVICES INC., 2016. 3.5 GSPS Direct Digital Synthesizer with 12-Bit DAC. AD9914 Data Sheet [online]. [viewed 30 July 2020]. Available from:  https://www.analog.com/media/en/technical-documentation/data-sheets/AD9914.pdf 13. CUSHING, R., 2000. Single-Sideband Upconversion of Quadrature DDS Signals to the 800-to-2500-MHz Band. Analog Dialogue [online]. vol. 34, no. 3 [viewed 25 July 2020]. Available from: URL:  https://www.analog.com/media/en/analog-dialogue/volume-34/number-1/articles/single-sideband-upconversion-of-quadrature-dds-signals.pdf 14. ALEKSEEV, E. A. and ZAKHARENKO, V. V., 2007. Direct Digital Synthesizer at the Microwave Spectroscopy.  Radio Phys. Radio Astron . vol. 12, no. 2, pp. 205–213. (in Russian). 15. ALEKSEEV, E. A., MOTIYENKO, R. A. and MARGULES, L., 2011. Millimeter- and Submillimeter-Wave Spectrometers on the Basis of Direct Digital Synthesizers.  Radio Phys. Radio Astron . vol. 16, no. 3, pp. 313–327. (in Russian). DOI:  https://doi.org/10.1615/RadioPhysicsRadioAstronomy.v3.i1.100 16. ALEKSEEV, E. A., ILYUSHIN, V. V. and MESCHERYAKOV, A. A., 2014. High-Precision Microwave Spectrometer with Sub-Doppler Spectral Resolution.  Radio Phys. Radio Astron . vol. 19, no. 4, pp. 364–374. (in Russian). DOI:  https://doi.org/10.15407/rpra19.04.364 17. ANALOG DEVICES INC., 2006. DC-to-2.5 GHz High IP3 Active Mixer. AD8343 Data Sheet [online]. [viewed 30 July 2020]. Available from:  https://www.analog.com/media/en/technical-documentation/data-sheets/AD8343.pdf 18. ANALOG DEVICES INC., 2017. Wideband Synthesizer with Integrated VCO. ADF4351 Data Sheet [online]. [viewed 30 July 2020]. Available from:  https://www.analog.com/media/en/technical-documentation/data-sheets/ADF4351.pdf 19. ANALOG DEVICES INC., 2016. MicroConverter® Multichannel 24-/16-Bit ADCs with Embedded 62 kB Flash and Single-Cycle MCU. ADuC845/ADuC847/ADuC848 Data Sheet [online]. [viewed 30 July 2020]. Available from:  https://www.analog.com/media/en/technical-documentation/data-sheets/ADUC845_847_848.pdf 20. BLEIDERS, M., BEZRUKOVS, V. and ORBIDANS, A., 2017. Performance Evaluation of Irbene RT-16 Radio Telescope Receiving System.  Latv. J. Phys. Tech. Sci.  vol. 54, is. 6, pp. 42–53. DOI:  https://doi.org/10.1515/lpts-2017-0040

/pdf/the-rt-32-radio-telescope-construction-based-on-the-mark-4b-2dc10gelzc.pdf

The rt-32 radio telescope construction based on the mark-4b antenna system. 3. local oscillators and self-noise of the receiving system

Based on the two-epoch European Very Long Baseline Interferometry (VLBI) Network (EVN) archive data from OH line observations of IIZw 096, we conﬁrm that the high-resolution OH emission in this source mainly comes from two spots (OH1 and OH2) of component (comp) D1 of this merging system. We found no signiﬁcant variations in the OH 1667MHz line emission, including ﬂux densities and peak positions. The OH 1665MHz line emission is detected at about the 6 σ level in the OH1 region by combining two epochs of EVN observations. By using archival data from the Very Long Baseline Array (VLBA), Very Large Array (VLA), and Atacama Large Millimeter Array (ALMA) observations, we investigated the properties of the environment of this component through H I , CO(3-2), and HCO + (4-3) lines and the multi-band radio continuum emission. We found that the comp D1 shows the brightest CO, HCO + line emission, as well as multi-band radio continuum emission. The environment around D1 shows no clear velocity structure associated with circular motions, making it di ﬀ erent from most other OH megamasers (OHMs) in the literature, which might have been caused by an e ﬀ ect during the merger stage. Meanwhile, we found that the CO emission shows three velocity structures around D1, including the central broad full width at half maximum (FWHM) region, the double-peak region where the CO line proﬁle shows two separated peaks, and the region of the high-velocity clouds where the CO line peaks at a high velocity ( ∼ 11000kms − 1 ). Similarly, H I observations in absorption also show high-velocity clouds around the D1 region, which might be due to inﬂows caused by the merging of two or more galaxy components. Based on the high-resolution K -band VLA and L -band VLBA observations of the radio continuum emission, we derived the brightness temperature in the range 10 5 K–10 6 K, which is consistent with other starburst dominant OHM sources in the literature. The multi-band VLA observations show that the radio continuum emission of comp D might also have contributions from free-free emission in addition to synchrotron emission. As a consequence, these results support a starburst origin for the OHMs, without the presence of an active galactic nucleus (AGN).

/pdf/radio-properties-of-the-oh-megamaser-galaxy-iizw-096-2asdbl83.pdf

Radio properties of the OH megamaser galaxy IIZw 096

We present the study of arcsecond scale radio continuum and OH line emission of a sample of known OH megamaser galaxies with z ≥ 0.15 using archival Very Large Array (VLA) data. And also the results of our pilot Five hundred meter aperture spherical radio telescope (FAST) observations of 12 of these OHM galaxies. The arcsecond-scale resolution images show that the OH emission is distributed in one compact structure and spatially associated with radio continuum emission. Furthermore, nearly all the ﬁtted components are likely smaller than the beam size ( ∼ 1.4"), which indicates that the broad OH line proﬁles of these sources originated from one masing region or that more components are distributed in sub-arcsec scales. The radio parameters, including brightness temperature, spectral index, and q-index, show no signiﬁcant di ﬀ erences with the low-redshift OHM galaxies, which have signiﬁcantly lower OH line luminosities. Because these parameters are indicators of the central power sources (AGN, starburst, or both), our results indicate that the presence of radio AGN in the nuclei may not be essential for the formation of OH emission. Over 1 / 3 of OHMs in this sample (6 / 17) show possible variable features likely caused by interstellar scintillation due to small angular sizes. We might underestimate this value because these sources are associated with this sample’s highest OH line ﬂux densities. Those with low OH line ﬂux densities might need higher sensitivity observations to study the variabilities. These results support the compact nature of OH maser emission and a starburst origin for the OHMs in our selected sample.

Radio continuum and OH line emission of high-z OH megamaser galaxies

We present Very Long Baseline Array observations of radio continuum and OH line emission toward the OH megamaser (OHM) galaxy IRAS 01298$-$0744. We recover over 82 of the OH line emission seen in single-dish observations, including multiple strong OH line components and the broad shallow line profile spanning over 1000 The OH emission spatially has four compact components, as well as diffuse emission, and the 3 sigma signals are distributed in a rectangular region with size of sim 40times 30 mas. The spatial--velocity structure is complex and is consistent with that from HCN and HCO$^+$ lines in the literature, indicating that the nuclear region of this source is likely still in the merging process characterized by intense nuclear activities. The multiple strong OH peaks are blue-shifted compared to dense millimetre-wave molecular gas tracers, but similar to optical Na I absorption. This suggests that the compact masers might be in an outflow driven by an active galactic nucleus or starburst. We have detected compact radio continuum emissions adjacent to the maser positions with a brightness temperature of around $3 10^6$ K, similar to other OHM galaxies with very-long-baseline interferometry observations in the literature, which is consistent with a starburst origin.

Continuum and spectral-line observations of the OH megamaser galaxy IRAS 01298-0744

We present results from VLBI observations of continuum and OH line emission in IRAS 02524+2046 as well as arcsecond-scale radio properties of this galaxy using VLA archive data. We found that there is no significant detection of radio continuum emission from VLBI observations. The arcsecond-scale radio images of this source show no clear extended emission. The total radio flux density at L and C bands are approximately 2.9 mJy and 1.0 mJy, respectively, which indicates a steep radio spectral index between the two bands. A steep spectral index, low brightness temperature, and high q -ratio (i.e., the far-infrared to the radio flux density), which are three critical indicators in the classification of radio activity in the nuclei of galaxies, are all consistent with the classification of this source as a starburst galaxy from its optical spectrum. The high-resolution line profile reveals that we detected both the 1665 MHz and 1667 MHz OH maser lines, which show two and three clear components, respectively. The channel maps show that the maser emission are distributed in a region of ∼210 pc × 90 pc. The detected maser components in different regions indicate similar double spectral features, which might be evidence that this galaxy is at a stage of major merger as seen from the optical morphology.

/pdf/radio-properties-of-the-oh-megamaser-galaxy-iras-02524-2046-39y6h5cxp1.pdf

Radio properties of the OH megamaser galaxy IRAS 02524+2046

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Radio properties of the OH megamaser galaxy IRAS 02524+2046