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Subject and Purpose. In Part 2 of the current paper, we seek to analyze the observational results of decameter carbon radio recombination lines (RRLs) detected near the frequency 26 MHz through the UTR-2 radio telescope towards the S140 emission nebula and the GSH 139-03-69 super shell. These lines have proven themselves as a highly effective tool for cold, rarefied interstellar medium (ISM) diagnostics. The aim is to determine an association of line-forming regions (CII regions) with other ISM components and study physical conditions (electron temperature Te and electron density Ne) in these regions. Methods and Methodology. By iterative comparison of detected and modeled integral intensities of decameter carbon RRLs, we determine physical state ranges where recorded experimental data best fit the model values for various combinations of Te,Ne, and path lengths s. Results.It has been found that the characteristics of the detected decameter carbon RRLs are consistent with the higher-frequency data for both the S140 line of sight and other Galactic plane directions, including the GSH 139-03-69 direction. Ranges of physical conditions where recorded data and model values are in the best agreement have been determined, being Te = 50÷ 100 K, Ne = 0.01 cm–3, and s= 10 pc — for the S140 nebula direction and its vicinity and, also, Te = 50÷ 100 K, Ne =0.01 cm–3, and s = 5÷ 7 pc — for the GSH 139-03-69 super shell direction. Conclusions. The obtained results indicate that the detected decameter carbon RRLs originate from CII regions associated with clouds of diffuse neutral hydrogen HI in the Galactic plane. The lines are seen against a background Galactic radio emission whose brightness temperature increases as frequency decreases.

Subject and Purpose. Since decameter carbon radio recombination lines (RRLs) were detected for the first time more than forty years ago, they have significantly extended our knowledge of the physics, kinematics and chemistry of the cold rarefied interstellar medium (ISM). A large number of these lines have been observed towards various Galactic radio sources. The present paper describes our studies of decameter carbon RRLs in such Galactic directions as the sight-lines to the S140 emission nebula and to the large volume of cold neutral hydrogen known as the GSH 139-03-69 super shell. Methods and Methodology. Observations within a 1-MHz frequency band centered at 26 MHz were performed using the UTR-2 radio telescope and a multi-channel digital correlator. The UTR-2 is still the world largest and the most sensitive low-frequency radio telescope. Results. We report the detection of decameter carbon RRL series C627α – C637α from the medium lying towards the S140 nebula. The extents of RRL forming regions have been estimated. It is suggested that RRLs in the S140 direction are formed in the local ISM lying along the line of sight. The RRL-forming region is probably associated with omnipresent diffuse neutral HI gas in the Galactic plane rather than with S140 nebula itself. Toward the GSH 139-03-69 super shell, decameter RRLs have been detected as well. Likewise, they apparently originate from the local medium lying along the sight-line. Yet, the spectrum contains a RRL component corresponding to the absorption of the cold gas of the GSH 139-03-69 itself in the ISM. Conclusions. The obtained results indicate great possibilities of decameter carbon RRLs not only for cold ISM probing but also for making a good auxiliary tool for studying large complexes of extremely cold hydrogen HI in the Galaxy.

Purpose: The analytical review of the main results of research in the new direction of the low-frequency radio astronomy, the interstellar medium radio spectroscopy at decameter waves, which had led to astrophysical discovery, recording of the radio recombination lines in absorption for highly excited states of interstellar carbon atoms (more than 600). Design/methodology/approach: The UTR-2 world-largest broadband radio telescope of decameter waves optimally connected with the digital correlation spectrum analyzers has been used. Continuous modernization of antenna system and devices allowed increasing the analysis band from 100 kHzto 24 MHz and a number of channels from 32 to 8192. The radio telescope and receiving equipment with appropriate software allowed to have a long efficient integration time enough for a large line series simultaneously with high resolution, noise immunity and relative sensitivity. Findings: A new type of interstellar spectral lines has been discovered and studied, the interstellar carbon radio recombination lines in absorption for the record high excited atoms with principal quantum numbers greater than 1000. The line parameters (intensity, shape, width, radial velocity) and their relation ship with the interstellar medium physical parameters have been determined. The temperature of line forming regions is about 100 K, the electron concentration up to 0.1 cm–3 and the size of a line forming region is about 10 pc. For the first time, radio recombination lines were observed in absorption. They have significant broadening and are amplified by the dielectronic-like recombination mechanism and are also the lowest frequency lines in atomic spectroscopy. Conclusions: The detected low-frequency carbon radio recombination lines and their observations have become a new highly effective tool for the cold partially ionized interstellar plasma diagnostics. Using them allows obtaining the information which is not available with the other astrophysical methods. For almost half a century of their research, a large amount of hardware-methodical and astrophysical results have been obtained including a record number of Galaxy objects, where there levant lines have been recorded. The domestic achievements have stimulated many theoretical and experimental studies in other countries, but the scientific achievements of Ukrainian scientists prove the best prospects for further development of this very important area of astronomical science.

Samuil Kaplan (1921-1978) was a productive and famous astrophysicist. He was affiliated with a number of scientific centers in different cities of the former Soviet Union. During the earliest 13 years of his career, namely in 1948-1961, he worked at the Lviv University in Ukraine. In the present paper, the Lviv period of his life and scientific activity is described on the basis of archival materials and his published studies. Kaplan arrived in Lviv in June 1948, the same month when he obtained the degree of the Candidate of Science. He was a head of the astrophysics sector at the Astronomical Observatory of the University, a professor of the department for theoretical physics, as well as the founder and head of a station for optical observations of artificial satellites of the Earth. He was active in the organization of an astronomical observatory outside the city. During the years in Lviv, Kaplan wrote more than 80 articles and 3 monographs in 9 areas. At that time, his focus was on the stability of circular orbits in the Schwarzschild field, on the white dwarf theory, on space gas dynamics, on cosmic plasma physics and turbulence, on the acceleration of cosmic rays, on the physics of interstellar medium, on the physics and evolution of stars, on cosmology and gravitation, and on the optical observations of the Earth's artificial satellites. Some of his findings are fundamental to the development of theory in those fields as well as of observational techniques. The paper presents a complete bibliography of Kaplan's works published during the Lviv period and reviews his respective scientific achievements in the light of the current state of research in those areas. [ABSTRACT FROM AUTHOR]