Structure and kinematics of the interstellar medium around WR 134 and WR 135

Based on our H _α interferometry and 21-cm and CO observations, we analyze the structure and kinematics of the interstellar medium around the stars WR 134 and WR 135. We conclude that the HI bubble found here previously is associated with WR 135, not with WR 134. High-velocity motions of ionized gas that can be interpreted as expansion of the gas swept up by the stellar wind with a velocity up to 50–80 km s^?1 are observed around both stars. The line-of-sight velocity field of the ionized hydrogen in the Cygnus arm is shown to agree with the large-scale line-of-sight velocity distribution of the CO emission.     

Statistics of high-velocity outflows in regions of massive star formation

Based on a SO and C¹⁸O survey of dense molecular-cloud cores in regions of massive star formation (selected by the presence of H₂O maser emission), we estimate the frequency of occurrence of high-velocity outflows in these regions and their parameters. The presence of extended SO-line wings (compared to C¹⁸O) is considered to be indicative of outflows. We estimate the outflow parameters (mass, momentum, and kinetic energy) from optically thin C¹⁸O lines, which increases the reliability of these estimates. According to this approach, high-velocity outflows were detected in ～40% of the observed objects, which is a lower limit on the frequency of their occurrence. There is a clear correlation between the outflow mass, momentum, and kinetic energy, on the one hand, and the bolometric luminosity of the associated infrared sources, on the other hand. The slope of the correlations is close to unity. Their comparison with similar correlations of the mass-loss rate, force, and mechanical luminosity with the bolometric luminosity shows that the spread in outflow dynamical age is small and that this age has no systematic correlation with the infrared luminosity. The mean outflow dynamical age that can be obtained from this comparison is ～7×10¹³ yr.     

Low density ionized gas in the inner galaxy — Interpretation of recombination line observations at 325 MHz

The recent survey of H 272α recombination line (324.99 MHz) in the direction of 34 Hn regions, 12 SNRs and 6 regions of continuum minimum (‘blank’ regions) in the galactic plane is used to derive the properties of diffuse ionized gas in the inner Galaxy. The intensity of radio recombination lines at high frequencies is dominated by spontaneous emission in high-density gas and that at low frequencies (325 MHz) by stimulated emission in low-density gas. We have used this property to obtain the electron density in the gas in the direction of blank regions and SNRs, by combining the H 272 α measurements (preceeding paper) with the published data at higher frequencies. Further, we have imposed constraints on the electron temperature and pathlength through this gas using the observed high-frequency continuum emission, average interstellar electron density and geometry of the line-emitting regions. The derived properties of the gas are (i) electron density 0.5–6 cm^-3, (ii) electron temperature 3000–8000 K and (iii) emission measures 500–3000 pc cm^-6 The corresponding pathlengths are 50–200 pc. As the derived sizes of the low-density regions are small compared to the pathlength through the Galaxy, the low-frequency recombination lines cannot be considered as coming from a widely distributed component of the interstellar medium. The Hn regions studied in the above survey cannot themselves produce the H 272α lines detected towards them because of pressure broadening, optical depth, and beam dilution. However, the agreement in velocity of these lines with those seen at higher frequencies suggests that the low-frequency recombination lines arise in low-density envelopes of the Hn regions. Assuming that the temperature of the envelopes are similar to those of the cores and invoking geometrical considerations we find that these envelopes should have electron densities in the range 1–10 cm^-3 and linear sizes of 30–300 pc in order to produce the observed H 272α lines.     

On a new cluster of H<Subscript>2</Subscript>O maser spots in the source ON2

We present the results of our observations of the H₂O maser emission toward the complex source ON2 associated with an active star-forming region. The observations were performed in a wide range of radial velocities, from ?75 to 90 km s^?1. We have detected an emission with flux densities of 9.2, 4, and 26 Jy at radial velocities of ?33.5, ?24.4, and ?18.8 km s^?1, respectively, at which no emission has been observed previously. The detected emission is most likely associated with a hitherto unknown cluster of maser spots located between the northern (N) and southern (S) components of the source ON2 (closer to the northern one). This cluster may be associated with one of the three CO molecular outflows in the ON2 region. We have also detected an emission at ?22 and ?14.5 km s^?1 in N and at 12.6 km s^?1 in S, which has extended significantly the velocity ranges of the maser emission in these sources and allowed their models to be improved.     

Structure and kinematics of the interstellar medium around WR 142a: Searching for traces of the action of stellar wind

Based on our Hα interferometric observations and CO data, we analyze the structure and kinematics of the gas in an extended region of the Cygnus arm around the recently discovered star WR 142a. We have established that WR 142a and the ionized hydrogen in its immediate neighborhood are associated with the complex of molecular clouds observed in a region with l ～ 78°–80°30′, b ～ 2°–3°20′, and V _LSR ～ 4–16 km s^?1. Traces of the action of the stellar wind from WR 142a on the ambient gas have been found to the northeast of the star in a region devoid of dense absorbing foreground clouds. These include very weak thin gas and dust filaments as well as high-velocity components of the Hα profile, which can be interpreted as a possible expansion of the shell swept up by the wind with a velocity as high as 50–80 km s^?1. Giant regions of reduced CO emission dominated by high-velocity motions of ionized hydrogen have been detected. Stars of the Cyg OB2 association and the cluster NGC 6910 can be responsible for these motions.     

Oxygen airglow emission on Venus and Mars as seen by VIRTIS/VEX and OMEGA/MEX imaging spectrometers

Imaging spectrometers are highly effective instruments for investigation of planetary atmospheres. They present the advantage of coupling the compositional information to the spatial distribution, allowing simultaneous study of chemistry and dynamics in the atmospheres of Venus and Mars. In this work, we summarize recent results about the O₂(a¹Δ_g) night and day glows, respectively obtained by VIRTIS/Venus Express and OMEGA/Mars Express, the imaging spectrometers currently in orbit around Venus and Mars. The case of the O₂(a¹Δ_g - X³Σ_g⁻) IR emission at 1.27 μm on the night side of Venus and the day side of Mars is analyzed, pointing out dynamical aspects of these planets, like the detection of gravity waves in their atmospheres. The monitoring of seasonal and daily airglow variations provides hints about the photochemistry on these planets.     

The structure of Galactic gas at high latitudes: The southern polar cap

We analyze the angular structure of the 21-cm interstellar neutral hydrogen emission at six and seven declinations in the northern (published previously) and southern polar caps of the Galaxy (Galactic latitudes from ?40° to ?90°), respectively, with an extent of 90° in right ascension. The RATAN-600 radio telescope has a beam width averaged over these regions of 2.′0×30′. One-dimensional power spectra for the angular distribution of interstellar neutral hydrogen emission were computed in each 6.3-km s^?1-wide spectral channel by using the standard Fast Fourier Transform (FFT) code and were smoothed over 1^h in right ascension. The Galactic latitude dependence of the mean parameters for the sky distribution of H I line emission at high latitudes was found to correspond to the distribution of gas in the form of a flat layer only in the northern region, while in the southern cap, the gas distribution is much less regular. In addition, the mean H I radial velocities are negative everywhere (?3.7±3.0 km s^?1 in the north and ?6.0±2.4 km s^?1 in the south). The power spectra of the angular fluctuations in the range of angular periods from 10′ to 6° appear as power laws. However, the spectral indices change greatly over the sky: from ?3 to ?1.2; on average, as the Galactic latitude increases and the H I column density decreases, the fluctuation spectrum of the interstellar gas emission becomes flatter. In the northern polar region, this behavior is much more pronounced, which probably stems from the fact that the gas column density in the south is generally a factor of 2 or 3 higher than that in the north. Therefore, the spectra are, on average, also steeper in the south, but the dependence on Galactic latitude is weaker. Using simulations, we show that the observed power-law spectrum of the H I emission distribution can be obtained in terms of not only a turbulent, but also a cloud model of interstellar gas if we use our previous spectra of the diameters and masses of H I clouds.     

A new evolutionary scenario of intermediate-mass star-formation revealed by multi-wavelength observations of OMC-2/3

We have performed millimeter- and submilli- meter-wave survey observations using the Nobeyama millimeter array (NMA) and the Atacama Submillimeter Telescope Experiment (ASTE) in one of the nearest intermediate-mass (IM) star-forming regions: Orion Molecular Cloud-2/3 (OMC-2/3). Using the high-resolution capabilities offered by the NMA (∼several arcsec), we observed dust continuum and H¹³CO⁺(1–0) emission in 12 pre- and proto-stellar candidates identified previously in single-dish millimeter observations. We unveiled the evolutionary changes with variations of the morphology and velocity structure of the dense envelopes traced by the H¹³CO⁺(1–0) emission. Furthermore, using the high-sensitivity capabilities offered by the ASTE, we searched for large-scale molecular outflows associated with these pre- and proto-stellar candidates observed with the NMA. As a result of the CO(3–2) observations, we detected six molecular outflows associated with the dense gas envelopes traced by H¹³CO⁺(1–0) and 3.3 mm continuum emission. The estimated CO outflow momentum increases with the evolutionary sequence from early to late type of the protostellar cores. We also found that the 24 μm flux increases as the dense gas evolutionary sequence. We propose that the enhancement of the 24 μm flux is caused by the growth of the cavity (i.e. the CO outflow destroys the envelope) as the evolutionary sequence. Our results show that the dissipation of the dense gas envelope plays an essential role in the evolution of the IM protostars. The extremely high-sensitivity and high-angular resolution offered by ALMA will reveal unprecedented details of the inner ∼50 AU of these protostars, which will provide us a break through in the classic scenario of IM star/disk formation.     

The pressure of an equilibrium interstellar medium in galactic disks

Based on an axisymmetric galactic disk model, we estimate the equilibrium gas pressure P/k in the disk plane as a function of the galactocentric distance R for several galaxies (MW, M33, M51, M81, M100, M101, M106, and the SMC). For this purpose, we solve a self-consistent system of equations by taking into account the gas self-gravity and the presence of a dark pseudo-isothermal halo. We assume that the turbulent velocity dispersions of the atomic and molecular gases are fixed and that the velocity dispersion of the old stellar disk corresponds to its marginal stability (except for the Galaxy and the SMC). We also consider a model with a constant disk thickness. Of the listed galaxies, the SMC and M51 have the highest pressure at a given relative radius R/R ₂₅, while M81 and the Galaxy has the lowest pressure. The pressure dependence of the relative molecular gas fraction confirms the existence of a positive correlation between these quantities, but it is not so distinct as that obtained previously when the pressure was estimated very roughly. This dependence breaks down for the inner regions of M81 and M106, probably because the gas pressure has been underestimated in the bulge region. We discuss the possible effects of factors other than the pressure affecting the relative content of the molecular gas in the galaxies under consideration.     

Mapping of Io's thermal radiation by the Galileo photopolarimeter-radiometer (PPR) instrument

Between 1999 and 2002, the Galileo spacecraft made 6 close flybys of Io during which many observations of Io's thermal radiation were made with the photopolarimeter-radiometer (PPR). While the NIMS instrument could measure thermal emission from hot spots with T>200 K, PPR was the only Galileo instrument capable of mapping the lower temperatures of older, cooling lava flows, and the passive background. We tabulate all data taken by PPR of Io during these flybys and describe some scientific highlights revealed by the data. The data include almost complete coverage of Io at better than 250 km resolution, with extensive regional coverage at higher resolutions. We found a modest poleward drop in nighttime background temperatures and evidence of thermal inertia variations across the surface. Comparison of high spatial resolution temperature measurements with observed daytime SO₂ gas pressures on Io provides evidence for local cold trapping of SO₂ frost on scales smaller than the 60 km resolution of the PPR data. We also calculated the power output from several hot spots and estimated total global heat flow to be about 2.0-2.6 W m⁻². The low-latitude diurnal temperature variations for the regions between obvious hot spots are well matched by a laterally-inhomogeneous thermal model with less than 1 W m⁻² endogenic heat flow.     

Molecules as probes of star-forming regions (Review)

This paper is a brief review of molecular spectroscopy methods for the diagnostics of star-forming regions. Principal attention is paid to the determination of the kinetic temperature and gas density in dense clouds, the radiation field temperature, the magnetic field, and the spatial and velocity structure of regions of star formation.     

Interferometric observations of the H II region around ξ Per

A Fabry-Perot spectrometer was used to map the H II region around the O star ξ Per in the Hβ emission line. The angular size of the region is \(9_.^ \circ 1 \times 6_.^ \circ 0\). The region-boundary contour drawn at the double background level is centered on the star. The accuracy of our emission intensity measurements is 0.2 rayleigh. The proximity of the nebula NGC 1499 has virtually no effect on the measured emission measure toward the star. The star excitation parameter derived from observations corresponds to the spectral type O7.5 III and is U(Sp)=56.0±8.4 pc cm^?2; the mean electron density in the region is n_e=3.1±0.4 cm^?3.     

The Influence of Fluctuations of the Solar Emission Line Profileon the Doppler Shift of Interplanetary HLyα Lines Observed by the Hubble–Space–Telescope

In an earlier research the employment of a radiation transport model with angle-dependent partial frequency redistribution, self-absorption by interplanetary hydrogen, realistic solar H_Lyαemission profile, and a time dependent `hot' hydrogen model to analyze 5 interplanetary H_Lyα glow spectra obtained with theHubble–Space–Telescope–GHRS spectrometer, has not resulted in unequivocal determination of a set of thermodynamical parameters of the interstellar hydrogen The residual discrepancies between the model and the data concern the observations performed within an interval of 1 year close to the solar minimum from very similar lines of sight. In this paper we investigate by calculating interplanetary H_Lyα lines with the use of a one hydrogen distribution and several solar H_Lyα line profiles whether this residual may be caused by possible variations in time of the shape of the solar H_Lyα emission line profile which cause variable illuminations of the interplanetary gas. These variations of illuminations cause variations in Doppler shift of the resonant interplanetary H_Lyα line that can amount to ≃ 4 km s^-1in the line peak. Consequently we conclude that without adequate knowledge of the solar H_Lyα emission line profile during spectral observations of the interplanetary hydrogen gas it is impossible to obtain an agreement between models and observations better than by this value. This revised version was published online in July 2006 with corrections to the Cover Date.     

The environment of Hercules A

We have made VLA radio total intensity and polarisation observations in the A, B and C configurations at 1665, 1435, 1365 and 1295 MHz and in the B, C and D configurations at 8465 and 8415 MHz to study the environment of the powerful radio galaxy Hercules A. We have also made ROSAT PSPC and HRI X-ray observations to study the intracluster gas in the Hercules A cluster. We have mapped the Faraday rotation field with high resolution (1.′′42.5 h⁻¹₁₀₀ kpc for q₀=0), and combined this with the X-ray data on the gas distribution in order to map the magnetic field of the cluster. We have found that Hercules A exhibits a strong Laing-Garrington effect: the western side of the radio emission is more depolarised than the eastern side. The X-ray observations have revealed an extended X-ray emission elongated along the radio galaxy axis and a weak nuclear component. The Hercules A cluster is a cooling flow cluster, which appears isothermal at large radii. Comparing the Faraday dispersion profile with the X-ray estimated density profile, we found that the magnetic field is decreasing with radius and we have estimated a central value of 3B₀ (μG) 9. The estimated core electron density of n₀6.6×10³ m⁻³ reveals a dense environment in which Hercules A is situated.     

The Origin of the Diffuse Hα in Spirals

Using high-quality H_α images of five spiral galaxies, we have studied the luminosity and distribution of the emission from diffuse ionized gas (DIG). The estimated DIG luminosities account for 25–60%of the total H_α emission in each galaxy and analysis of the distribution has shown that the DIG is highly correlated geometrically with the most luminous HII regions of the galaxies. The power required to ionize the DIG is very high. The mean ionization rates per unit surface area of a galaxy disc are of the order of 10⁷ cm^-2 s^-1. Lyman continuum photons (Lyc) from OB asociations are the most probable sources of this ionization. Here we propose a specific model for these sources: we show that the Lyman photon flux that leaks out of the density-bounded HII regions of the galaxies is more than enough to ionize the measured DIG in the five galaxies analysed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evolution of the structure of the H<Subscript>2</Subscript>O supermaser outburst region in Orion KL

During the period 1979–1999, we investigated the hyperfine structure of the H₂O supermaser region located in the core of the molecular cloud OMC-1 in Orion KL. The angular resolution is 0.1 mas, which corresponds to 0.045 AU. The detected structure, which consists of a central object, an accretion disk, a bipolar outflow, and an envelope, corresponds to the initial formation stage of a low-mass star. The accretion disk is at the stage of separation into groups of concentric rings. The bipolar outflow is a neutral, highly collimated jet of accreted material that includes H₂O molecules and dust grains in the icy envelope. The injector is a bright compact source with a size <0.05 AU and a brightness temperature T_b≈10¹⁷ K. The velocity of the bipolar outflow is v≈10 km s^?1. The rotation velocity of the jet is v_rot≈1.5 km s^?1. The jet has the shape of a conical helix due to the precession of the rotation axis. Occasionally, dense blobs (comet-shaped bullets) are ejected. The envelope amplifies the radio emission from the structures in a ～0.5 km s^?1 maser window band with velocities v≈7.65 km s^?1 by more than two orders of magnitude.     

Microwave and Soft X-ray Study of Solar Active Region Evolution

We have studied the properties and evolution of several active regions observed at multiple wavelengths over a period of about 10 days. We have used simultaneous microwave (1.5 and 17 GHz) and soft X-ray measurements made with the Very Large Array (VLA), the Nobeyama Radio Heliograph (NRH) and the Soft X-ray Telescope (SXT) on board the Yohkoh spacecraft, as well as photospheric magnetograms from KPNO. This is the first detailed comparison between observations at radio wavelengths differing by one order of magnitude. We have performed morphological and quantitative studies of active region properties by making inter-comparison between observations at different wavelengths and tracking the day-to-day variations. We have found good general agreement between the 1.5 and 17 GHz radio maps and the soft X-rays images. The 17 GHz emission is consistent with thermal bremsstrahlung (free-free) emission from electrons at coronal temperatures plus a small component coming from plasma at lower temperatures. We did not find any systematic limb darkening of the microwave emission from active regions. We discuss the difference between the observed microwave brightness temperature and the one expected from X-ray data and in terms of emission of a low temperature plasma at the transition region level. We found a coronal optical thickness of 10^-3 and 1 for radiation at 17 and 1.5 GHz, respectively. We have also estimated the typical coronal values of emission measure ( 5 × 10²⁸ cm^-5), electron temperature ( 4.5 × 10⁶6 K) and density ( 1.2 × 10⁹ cm₃). Assuming that the emission mechanism at 17 GHz is due to thermal free-free emission, we calculated the magnetic field in the source region using the observed degree of polarization. From the degree of polarization, we infer that the 17 GHz radiation is confined to the low-lying inner loop system of the active region. We also extrapolated the photospheric magnetic field distribution to the coronal level and found it to be in good agreement with the coronal magnetic field distribution obtained from microwave observations.     

Searches for the shell swept up by the stellar wind from Cyg OB2

We investigated the kinematics of ionized gas in an extended (20°×15°) region containing the X-ray Superbubble in Cygnus with the aim of finding the shell swept up by a strong wind from Cyg OB2. Hα observations were carried out with high angular and spectral resolutions using a Fabry-Perot interferometer attached to the 125-cm telescope at the Crimean Observatory of the Sternberg Astronomical Institute. We detected high-velocity gas motions, which could result from the expansion of the hypothetical shell at a velocity of 25–50 km s^?1. Given the number of OB stars increased by Knödlseder (2000) by an order of magnitude, Cyg OB2 is shown to possess a wind that is strong enough [L _w ? (1–2) × 10³⁹ erg s^?1] to produce a shell comparable in size to the X-ray Superbubble and to a giant system of optical filaments. Based on our measurements and on X-ray and infrared observations, we discuss possible observational manifestations of the shell swept up by the wind.     

Molecular emission in dense massive clumps from the star-forming regions S231–S235

The paper is concerned with the study of the star-forming regions S231–S235 in radio lines of molecules of the interstellar medium—carbon monoxide (CO), ammonia (NH₃), cyanoacetylene (HC₃N), in maser lines—methanol (CH₃OH) and water vapor (H₂O). The regions S231–S235 belong to the giant molecular cloudG174+2.5. The goal of this paper is to search for new sources of emission toward molecular clumps and to estimate their physical parameters from CO and NH₃ molecular lines. We obtained new detections ofNH₃ andHC₃Nlines in the sources WB89673 and WB89 668 which indicates the presence of high-density gas. From the CO line, we derived sizes, column densities, and masses of molecular clumps. From the NH₃ line, we derived gas kinetic temperatures and number densities in molecular clumps. We determined that kinetic temperatures and number densities of molecular gas are within the limits 16–30 K and 2.8–7.2 × 10³ cm^?3 respectively. The shock-tracing line of CH₃OH molecule at a frequency of 36.2 GHz was detected in WB89 673 for the first time.     

Observations of C2 Molecules in the Coma of Comets at Mitaka

In order to monitor the various phenomena of comets, we continuously made the near-nucleus imaging observations of comets at National Astronomical Observatory, Mitaka. Here we report on the results of the observations of two spectacular comets. One is the analysis of photometry of C₂ emission images in the coma of comet Hyakutake (C/1996 B2). By comparing the production rates of C₂ radicals with C₂H₂ molecules, we conclude that the most C₂ radicals were originated from C₂H₂, while some of them might be produced from other parents. The second item is the analysis of the morphology of C₂ emission images in the coma of comet Hale-Bopp(C/1995 O1). By applying a ring masking technique, we detected asymmetrical distribution of the C₂ molecules. The results of these two comets might suggest that a portion of C₂ radicals were formed by the disintegration of the small organic dust grains, like the so-called CHON particles. This revised version was published online in July 2006 with corrections to the Cover Date.