Vladimir S. Strelnitski

H2O Masers and Supersonic Turbulence

We use unpublished and published VLBI results to investigate the geometry and the statistical properties of the velocity field traced by H2O masers in five galactic regions of star formation: Sgr B2(M), W49N, W51(MAIN), W51N, and W3(OH). In all sources the angular distribution of the H2O hot spots demonstrates approximate self-similarity (fractality) over almost 4 orders of magnitude in scale, with the calculated fractal dimension d between � 0.2 and 1.0. In all sources, the lower order structure functions for the line-ofsight component of the velocity field are satisfactorily approximated by power laws, with the exponents near their classic Kolmogorov values for high Reynolds number incompressible turbulence. These two facts, as well as the observed significant excess of large deviations of the two-point velocity increments from their mean values, strongly suggest that the H2O masers in regions of star formation trace turbulence. We propose a new conceptual model of these masers in which maser hot spots originate at the sites of ultimate dissipation of highly supersonic turbulence produced in the ambient gas by the intensive gas outflow from a newly born star. Because of the high brightness and small angular sizes of masing hot spots and the possibility of measuring their positions and velocities with high precision, they become a unique probe of supersonic turbulence. Subject headings: ISM: jets and outflows — masers — turbulence

3 Year Monitoring of Millimeter-Wave Radio Recombination Lines from MWC 349

Observations of the H30? (231?GHz) and H35? (147?GHz) recombination lines from MWC 349?we assume from the MWC 349A star?from 1997 May through 2000 June show variations in the intensities and radial velocities of the strongly masing, double-peaked lines on scales of a few weeks to a few months. The data include a few observations of the H40? (99?GHz) line during this period. We examine intensities, widths, and radial velocities of the line components and intensities of the free-free continuum emission. We detect both positive and negative correlations between the variations of some of these parameters, as well as a lack of correlation. We consider these results in terms of a differentially rotating, inhomogeneous disk viewed edge-on, having a considerable radial component of gas motion and surrounding a central object with strong, variable UV emission.

Hydrogen Masers. II. MWC 349A

The conditions of masing and lasing in the hydrogen recombination lines (HLR) in the disk and outflow of MWC349 are studied. Comparison of the complete set of the observed aphal-lines, with simple models of optically thin spontaneous emission shows that observable HRL masing in this source is limited to the interval of the principal quantum numbers 10-36.

Red Light Curve of MWC 349 in the Years 1967-1981: Possible Periodicity

The results of a red photographic photometry of the variable masing star MWC 349 are presented for 14 years, 1967–1981. Fourteen plates from the Harvard Damon collection were selected for the photometry. The plates were measured with the Cuffey iris photometer of the Maria Mitchell Observatory and were calibrated with the aid of two standard stars, both brighter than MWC 349. The magnitude of MWC 349 was then determined by extrapolation, assuming that the star is on the linear part of the calibration curve. In spite of larger errors, our results are in good agreement with one photoelectric observation made during the period covered. The obtained red light curve is indicative of periodic light variations. A combined Fourier–least-squares analysis gives a probable period of T = 9.1 ± 0.3 yr. The deduced period and phase of variations are not incompatible with the subsequent photoelectric photometry of Bergner et al. Possible mechanisms responsible for the periodic light variations are briefly discussed.

Water Maser Emission from Comets

We used the Very Large Array in 1997 January, February, March, and April to observe comet Hale-Bopp in the 1.35 cm H2O line. No line was detected in any of the four observations, and upper limits to the H2O line emission are presented. These upper limits are typically around 60 mJy, which is much lower than the ~2.5 Jy flux density reported for this line in comet Bradfield (1974b) and jansky-level flux densities sporadically reported for a few other comets. This discrepancy is most likely due to a combination of questionable reliability of past reported detections and the possibility that masing in particular observational geometries is required for detection of the line. We concur with previous studies that indicated that this line could be detected only if it were masing. In the only masing scenario likely to yield a positive result, a line may be seen only if the masing region is observed along a jet against the radio continuum background of the nucleus. We estimate the probabilities of a detection in a random search for two typical positions of the origin of a jet on a rotating nucleus: (1) close to the pole and (2) close to the equator. Because the probabilities are very low (0.01) in either case, our negative result for comet Hale-Bopp (as well as previous negative results for other comets) cannot exclude the possibility of such masing jets. Carefully scheduled observations of future comets whose rotation and jet locations have been determined must be used to evaluate this possibility.

Mid Infrared Hydrogen Recombination Line Emission from the Maser Star MWC 349A

We have detected and spectrally resolved the mid-IR hydrogen recombination lines H6(alpha)(12.372 micrometers), H7(alpha)(19.062 micrometers), H7(beta)(l1.309 micrometers) and H8(gamma)(12.385 micrometers) from the star MWC349A. This object has strong hydrogen maser emission (reported in the millimeter and submillimeter hydrogen recombination lines from H36(alpha) to H21(alpha)) and laser emission (reported in the H15(alpha), H12(alpha) and H10(alpha) lines). The lasers/masers are thought to arise predominantly in a Keplerian disk around the star. The mid-IR lines do not show evident signs of lasing, and can be well modeled as arising from the strong stellar wind, with a component arising from a quasi-static atmosphere around the disk, similar to what is hypothesized for the near IR (less than or equal to 4 micrometers) recombination lines. Since populations inversions in the levels producing these mid-IR transitions are expected at densities up to approximately 10(exp 11)/cu cm, these results imply either that the disk does not contain high-density ionized gas over long enough path lengths to produce a gain approximately 1, and/or that any laser emission from such regions is small compared to the spontaneous background emission from the rest of the source as observed with a large beam. The results reinforce the interpretation of the far-IR lines as true lasers.

HIGH-n HYDROGEN RECOMBINATION LINES FROM THE FIRST GALAXIES

We investigate the prospects of blind and targeted searches in the radio domain (10 MHz to 1 THz) for high-n hydrogen recombination lines from the first generation of galaxies, at z 10. The expected optically thin spontaneous α-line luminosities are calculated as a function of the absolute AB magnitude of a galaxy at 1500 A. For a blind search, semi-empirical luminosity functions are used to calculate the number of galaxies whose expected flux densities exceed an assumed detectability threshold. Plots of the minimum sky area, within which at least one detectable galaxy is expected at a given observing frequency, in the fiducial instantaneous passband of 104 km s–1, allow us to assess the blind search time necessary for detection by a given facility. We show that the chances for detection are the highest in the millimeter and submillimeter domains, but finding spontaneous emission in a blind search, especially from redshifts z 1, is a challenge even with powerful facilities, such as the Actama Large Millimeter/Submillimeter Array and Square Kilometre Array. The probability of success is higher for a targeted search of lines with principal quantum number n ~ 10 in Lyman-break galaxies amplified by gravitational lensing. Detection of more than one hydrogen line in such a galaxy will allow for line identification and a precise determination of the galaxys redshift.

Uniqueness and evolutionary status of MWC 349A

MWC349A, which had remained an ordinary member of the MWC catalog for a few decades, is now known as: (1) the brightest stellar source of radio continuum; (2) the only known high-gain natural maser in hydrogen recombination lines; and (3) the only strictly proven natural high-gain laser (in IR hydrogen recombination lines). These phenomena seem to occur in the circumstellar disk seen almost edge-on. They help us understand the structure and kinematics of the disk. The evolutionary status of MWC 349A is still debated: a young HAeBe star with a pre-planetary disk or an old B[e] star or even a protoplanetary nebula? We discuss new observational data obtained at the Maria Mitchell Observatory and elsewhere which may cast light on this issue.

Short-term variations in Class I methanol masers?

Class I methanol masers are found near regions of high-mass star formation and are pumped by collisions. Some indication of long-term variability in these masers has previously been reported (Kurtz et al. 2004). Here we will present evidence for variations in the intensity of the Class I methanol masers at 44 GHz on much shorter timescales. We present preliminary results of the observation of the 44 GHz Class I methanol transition toward sources in the DR21 region that indicates variability on timescales of days to possibly hours.

Masers, Lasers and the Interstellar Medium

This paper discusses recent results obtained by myself and my colleagues in three domains of astrophysics: interstellar supersonic turbulence, circumstellar disks, and natural masers and lasers. S.A. Kaplan, S.B. Pikelner, and I.S. Shklovskii were among those who, 30-40 years ago, laid the foundation of these domains.H2O masers become an effective probe of supersonic turbulence associated with mass outflow from very young stars. They demonstrate a very low (≲1) fractal dimension of the spatial set on which turbulence dissipates its kinetic energy, and, thereby, a strong intermittency of the turbulence. They also indicate that supersonic turbulence, like incompressible turbulence, has an inner scale, on which the bulk of turbulent energy dissipates in low-Mach, random shocks. H2O masers themselves find thereby a new pumping source in these random shocks.Masers in hydrogen recombination lines, discovered 8 years ago, originate in a circumstellar disk surrounding a massive star MWC 349A. They give a possibility to investigate kinematics and structure of the disk. Far-infrared nydrogen recombination lines, recently detected in MWC349A from the Kuiper Airborn Observatory, proved to be amplified as well. They are the first known natural amplifiers of electromagnetic waves in the laser wavelength domain. Analysis of their radiation, along with the radiation in other recombination lines, gives a possible key to understanding the lack of optical lasers in the Universe.