Structure of the class I methanol masers OMC-2 and NGC 2264

Results of interferometric observations of the class I methanol masers OMC-2 and NGC 2264 in the 7₀-6₁ A ⁺ and 8₀-7₁ A ⁺ lines at 44 and 95 GHz, respectively, are presented. The maser spots are distributed along the arcs bent toward infrared sources, which are young stellar objects. The distributions of the maser spots at 44 and 95 GHz are virtually identical, and the fluxes from the brightest spots are similar. The measured sizes of the maser spots at 44 GHz are, on average, about 50 AU. The brightness temperature of the strongest components at 44 GHz is 1.7 × 10⁷ K and 3.9 × 10⁷ K for OMC-2 and NGC 2264, respectively. A simple model for the excitation of Class I methanol masers is proposed; it yields an estimate of the limiting brightness temperature of the emission. The model is based solely on the properties of the methanol molecule without invoking the physical parameters of the medium. Using it, we showed that the emission opening angles for NGC 2264 and OMC-2 do not exceed 3° and 4.5°, respectively. The depth of the masing region is about 1000 AU. The emission directivity is naturally realized in the model of of maser consisting of a thermalized core and a thin inverted envelope, probably, with an enhanced methanol abundance. The maser emission has the greatest intensity in the direction tangential to the envelope. The size of the masing envelope estimated from the measured depth and spot extens is ～2 × 10⁴ AU, or 0.15 pc. This size is close to the sizes of the dense molecular cores surrounding the young stellar objects IRS 4 in OMC-2 and IRS 1 in NGC 2264.     

The detection of class I methanol masers towards regions of low-mass star formation

Six young bipolar outflows in regions of low-intermediate-mass star formation were observed in the 7₀-6₁ A ⁺, 8₀-7₁ A ⁺, and 5₋₁-4₀ E methanol lines at 44, 95, and 84 GHz, respectively. Narrow features were detected towards NGC 1333-IRS4A, HH 25MMS, and L1157-B1. The flux densities of the detected lines are not higher than 11 Jy, which is much lower than the flux densities of strong maser lines in regions of high-mass star formation. Analysis shows that the narrow features are most likely masers. Published in Russian in Astronomicheskiĭ Zhurnal, 2006, Vol. 83, No. 4, pp. 327–336. This text was submitted by the authors in English.     

Class I methanol masers in low-mass star-forming regions

Results of observations of Class I methanol masers in regions of low-mass star formation (MMIL) are summarized and analyzed. Four masers were detected at 44, 84, and 95 GHz towards “chemically active” bipolar outflows in the low-mass star-forming regions NGC1333 I4A, NGC 1333 I2A, HH 25, and L1157. Another maser was found at 36 GHz towards a similar outflow in NGC 2023. Thus, all the detected MMILs are associated with chemically active outflows. The brightness temperatures of the strongest 44-GHz maser spots in NGC 1333 I4A, HH 25, and L1157 exceed 2000 K, whereas the brightness temperature in NGC 1333 I2A is only 176 K, although a rotational-diagram analysis shows that this last source is also amaser. The flux densities of the newly detectedmasers are no higher than 18 Jy, and are much lower than those of strong masers in regions of high-mass star formation (MMIH). The MMIL luminosities match the maser luminosity-protostar luminosity relation established earlier for MMIHs. No MMIL variability was detected in 2004–2011. The radial velocities of the newly detected masers are close to the systemic velocities of the associated regions, except for NGC 2023, where the maser radial velocity is lower than the systemic velocity by approximately 3.5 km/s. Thus, the main MMILproperties are similar to those of MMIHs. MMILs are likely to be an extension of the MMIH population toward lower luminosities of both the masers and the associated young stellar objects. The results of VLA observations of MMILs can be explained using a turbulent-cloud model, which predicts that compact maser spots can arise in extended sources because the coherence lengths along some directions randomly appear to be longer than the mean coherence length in a turbulent velocity field. However, one must assume that the column density of methanol towardM1, the strongest maser in L1157, is appreciably higher than the mean column density of the clump B0a where the maser arises. The shape of the maser lines in L1157, forming double profiles with a red asymmetry, may indicate that the masers arise in collapsing clumps. However, although this model may be correct for L1157, it is specific to this source, since none of the other masers observed exhibited a double profile.     

VLA observations of class I methanol masers in the region of low-mass star formation L1157

We present the results of VLA observations of a maser candidate in the low-mass star formation region L1157 in the 7₀-6₁ A ⁺ transition at 44 GHz. The line is emitted by a compact, undoubtedly maser source associated with clump B0a, which is seen in maps of L1157 in thermal lines of methanol and other molecules. A much weaker compact source is associated with clump B1a, which is brighter than B0a in thermal methanol lines. The newly detected masers may form in thin layers of turbulent post-shock gas. In this case, the maser emission may be beamed, so that only an observer located in or near the planes of the layers can observe strong masers. On the other hand, the maser lines are double with a “red” asymmetry, indicating that the masers may form in collapsing clumps. A detailed analysis of collapsing-cloud maser models and their applicability to the masers in L1157 will be developed in subsequent papers.     

OH 1720-MHz lines as tracers of bipolar outflows in the vicinity of Class I methanol masers

A sample of Class I methanol masers (MMI) has been surveyed at 1720 MHz to search for possible associations between MMI and 1720-MHz OH masers, which should be formed by the same collisional pumping mechanism. If the model for methanol masers is correct, the sample should contain a statistically significant number of 1720-MHz OH masers at the positions of MMI. The observations were conducted on the 70-meter radio telescope of the National Academy of Sciences of Ukraine (NASU). The results show that ??50% of 72 MMI are associated with OH emission at 1720 MHz. In many sources, strong absorption lines are also observed. In most cases, the OH (1720) lines are narrow (linewidths of <2 km/s) suggesting they may be maser lines. The OH column densities obtained from Gaussian fitting of these narrow OH lines are, on average, 1.5 × 10¹⁷ cm^?2. TheH² density in the emitting medium reaches 10⁷ cm^?3 if the region of the OH (1720) emission has been subject to interaction with a bipolar-outflow front. This is sufficient to excite MMI, and the presence of narrow, possibly masing OH (1720) lines at the MMI velocities indicates the likely presence of shocks from bipolar outflows in the vicinity of the maser condensations, supporting models in which these molecules are collisionally pumped.     

Search for class I methanol maser emission toward several supernova remnants

Observations at 44 GHz in the 7₀−6₁ A ⁺ methanol line have been carried out on the 20-m telescope of the Onsala Space Observatory (Sweden) in the directions of the poorly studied region G27.4–0.2 and of several supernova remnants, at the coordinates of the OH(1720) maser satellite emission, with the aim of searching for Class I methanol maser emission in these sources. The region G27.4–0.2 has beenmapped, and contains maser sources and two supernova remnants with similar coordinates and radial velocities, which may accelerate condensation of the ambient gas-dust medium. This may play a role in enhancing the probability of methanol formation and maser emission. This is the first detection of 44 GHz maser emission in this source, and this maser is among the 10% of the strongest Class I methanol masers, within the uncertainties in the integrated flux (of a total of 198 currently knownmasers). A 27′ × 27′ region around the maser has been mapped at 44 GHz in steps of 1′. The 44-GHz emission forms only within the previously known maser region. Further studies in water lines are needed to estimate the influence of shocks from supernovae. No 44-GHz Class I methanol maser emission was detected at the 3σ level at the coordinates of the OH(1720) satellite emission in six supernova remnants; i.e., the presence of OH(1720) emission is not a sufficient condition for the detection of Class I methanol masers.     

Class I methanol maser emission in infrared clouds and the third version of the Astro Space Center MMI/SFR catalog

We have revised the Astro Space Center catalog of Class I methanol masers detected in star-forming regions (MMI/SFR), mainly at 44 GHz, and created a new electronic version of the catalog. Currently, the catalog contains 206 objects, selected from publications through 2011 inclusive. The data from the survey of Chen et al. (2011), performed specifically for objects EGO, which form a new specific catalog, are not included. The MMI/SFR objects were identified with emission and absorption objects in the near IR, detected during the MSX and Spitzer space missions. Seventy-one percent of Class I methanol masers that emit at 44 GHz and fall within the Galactic longitude range surveyed by Spitzer (GLIMPSE) are identified with Spitzer Dark Clouds (SDCs), and 42% with Extended Green Objects (EGOs). It is possible that Class I methanol masers arise in isolated, self-gravitating clumps, such as SDCs, at certain stages of their evolution. A sample of SDCs is proposed as a new target list for Class I methanol maser searches. A detailed statistical analysis was carried out, taking into account the characteristics of the regions of MMI/SFR formation presented in the catalog.     

The detection of new methanol masers in the 5−1–40 E line

Forty-eight objects were detected in the 5_?1–4₀ E methanol line at 84.5 GHz during a survey of Class I maser sources. Narrow maser features were found in 14 of these. Broad quasi-thermal lines were detected toward other sources. One of the objects with narrow features at 84.5 GHz, the young bipolar outflow L1157, was also observed in the 8₀–7₁ A ⁺ line at 95.2 GHz; a narrow line was detected at this frequency. Analysis showed that the broad lines are usually inverted. The quasi-thermal profiles imply that there are no more than a few line opacities. These results confirm the plausibility of models in which compact Class I masers appear in extended sources as a result of a preferential velocity field.     

Mapping of bipolar outflows and methanol masers in the CS(2-1)line

Eighteen regions (bipolar outflows and methanol masers) are mapped in the CS(2-1) line using the 20-m Onsala radio telescope. The coordinates of the CS emission peaks are refined. The sizes and masses of dense regions are estimated for 13 maps. Measurement of the angular sizes of regions of emission indicates that all the sources were resolved by the Onsala radio telescope. The lower limit for the linear dimensions of the CS condensations studied is 0.2–2.1 pc. The hydrogen densities and masses of the CS condensations are estimated to be n(H₂)=(0.3–13.1)×10⁴ cm^?3 and (M ≈ 7–2800M _⊙). Methanol masers are associated with denser and more massive regions, whether or not the maser condensation is connected with a bipolar outflow.     

Search for class I methanol maser emission in various types of objects in the interstellar medium

Observations of various types of objects in the northern sky were obtained at 44 GHz in the 7₀-6₁ A ⁺ methanol line on the 20-m Onsala radio telescope (Sweden), in order to search for Class I methanol maser emission in the interstellar medium: regions of formation of high-mass stars, dust rings around HII regions, and protostellar candidates associated with powerful molecular outflows and Galactic HII regions. Seven new Class Imethanolmasers have been discovered toward regions of formation of highmass stars, and the existence of two previously observed masers confirmed. The following conclusions are drawn: (1) neither the association of a bipolar outflow manifest in the wings of CO lines with a highmass protostellar object (HMPO) nor the presence of thermal emission in lines of complex molecules are sufficient conditions for the detection of Class I methanol emission; no association with HMPOs radiating at 44 GHz was found for EGOs (a new class of object tracing bipolar outflows); (2) the existence of H₂O masers and Class II methanol masers in the region of aHMPOenhances the probability of detecting Class I methanol emission toward the HMPO; Class II methanol masers with stronger line fluxes are associated with Class I methanol masers.     

Spatial structure of the class I methanol maser DR21(OH) at 44 GHz in 2003

We present the results of VLA observations of the class I methanol maser DR21(OH) at 44 GHz. The observations, retrieved from the NRAO archive (USA), were carried out in 2003. The maser has 18 spatial components, 17 of them confined to two clusters and one isolated component. In general, this spatial structure is similar to the structure observed earlier by other authors; the detected differences are too small to enable us to derive proper motions of the components: no proper motions exceeding the uncertainties were detecting during the 8 years since 1995. Amaser flare was observed in one of the spectral features for the first time. This is the first brightening detected for a class I methanol maser.     

A catalog of star-forming regions in the galaxy

This Catalog of Star-Forming Regions in the Galaxy contains coordinates and fluxes of young objects in the radio and infrared, as well as data on the radial velocities of recombination and molecular lines, for more than three thousand star-forming regions. In addition to photometric and kinematic data, we present information on diffuse and reflecting nebulae, dark and molecular clouds, and other objects related to young stars. The catalog consists of two parts. The main catalog lists star-forming regions in order of Galactic longitude and is supplemented by analogous information for star-forming regions in complexes of dark clouds with large angular sizes that are closest to the Sun. The main catalog is located at http://www.strasbg.-u.fr/pub/cats. In our preliminary study of the catalog data using a formal classification of the star-forming regions, we subdivided these objects into several classes and characterized them as being populated primarily by massive or low-mass stars at early or late stages of the star-formation process. We also distinguish between relatively nearby and distant complexes.     

A study of class II methanol maser condensations in the star-forming region W48

The methanol-line spectra in two maser condensations at velocities ～41 and ～45 km/s in the star-forming region W48 have been studied. The intensity of the 2₀-3_?1 E (12.2 GHz) line is anticorrelated with that of the 5₁-6₀ A ⁺ (6.7 GHz) line: the intensity of the 5₁-6₀ A ⁺ (6.7 GHz) line is greater at ～41 km/s than at ～45 km/s, while the opposite is true of the 2₀-3_?1 E (12 GHz) line. The remaining class II methanol lines in this source demonstrate the same behavior as the 2₀-3_?1 E (12 GHz) line. This contradicts current concepts about the maser line intensities in various methanol transitions: according to model calculations, the intensities of all class II lines should vary in phase. This effect is confirmed for a large homogeneous sample of 67 sources. Possible explanations of the observed effect are proposed; one suggests the possible role of “transpumping” of the methanol-level populations in the maser condensations. The relationships between the variations of the 2₀-3_?1 E (12 GHz) and 5₁-6₀ A ⁺ (6.7 GHz) line intensities, which are present for all 67 sources considered, may indicate that the condensations are at different distances from the pumping source. The presence of condensations at various distances from the pumping source in all 67 sources can be understood if they are ice planets revolving in different orbits around massive stars or protostars.     

Polarization observations of circumstellar OH masers

Results of observations of circumstellar OH masers in lines with wavelengths near 18 cm are reported. The observations were carried out on the radio telescope of the Nan cay Radio Astronomy Observatory (France). In 2007–2009, 70 late-type stars were observed (including Mira and semi-regular variables). For 53 of these, emission was detected in at least one of three OH lines (1612, 1665, or 1667 MHz). Circular and linear polarization of the maser emission was measured, yielding all four Stokes parameters. Polarized emission features were detected in the OH line spectra of 41 stars. A summary of all the observations is given. The results obtained for T Lep, R LMi, and R Crt are discussed. Emission in the 1665 and 1667 MHz OH lines was detected in T Lep for the first time. Features probably due to Zeeman splitting were detected in the OH line profiles of all three stars. Estimates of the magnetic-field strengths in the maser sources were obtained (0.46–2.32 mG). Variability of the polarization characteristics of the maser emission of the stars on time intervals of several months was found.     

A new physically based stochastic event catalog for hail in Europe

Hailstorms represent one of the major sources of damage and insurance loss to residential, commercial, and agricultural assets in several parts of Central Europe. However, there is little knowledge of hail risk across Europe beyond local historical damage reports due to the relative rarity of severe hail events and the lack of uniform detection methods. Here we present a new stochastic catalog of hailstorms for Europe. It is based on satellite observations of overshooting cloud tops (OT) that indicate very strong convective updrafts and hail reports from the European Severe Weather Database (ESWD). Historic hail events are defined based on OT detections from satellite infrared brightness temperatures between 2004 and 2011 for the warm seasons (April–September). The satellite-based historical event properties are complemented by hailstone observations from ESWD to stochastically simulate more than 1 million individual events with an event footprint resolution of 10 km. The final hail event catalog presented in this paper is the first one with a spatial event distribution that is based on a single homogeneous observation source over Europe. Areas of high hail probability or hail risk are found over Central and Southern Europe, including mountainous regions such as the Alps or the Pyrenees. Another region of relatively high hail risk is present over central Eastern Europe.     

Studies of sources from the WMAP catalog

Observations of a complete sample of sources from the WMAP catalog were obtained at 22.2 and 36.8 GHz on the RT-22 radio telescope of the Crimean Astrophysical Observatory. We have determined the distribution of the source spectral indices between these frequencies. The distributions of the spectral indices of the WMAP catalog (between 23 and 33 GHz) and in the RT-22 sample have the same shape and half-width, suggesting that the mean source parameters are constant in time. We have plotted the log N — log S dependence down to the flux levels of about 0.1 Jy using pilot data from the AT20 survey, where a cosmological “cutoff” in the source counts is already observed. The variability of individual sources in connection with flare activity is considered. The optical characteristics of the complete sample of WMAP sources are compared to those of identified AT20 survey sources.     

Variability of stars in the Pulkovo spectrophotometric catalog

We present the results of a statistical study of brightness variability for 693 stars of the Pulkovo spectrophotometric database in five spectral bands in the range λλ 320–1080 nm. Significant brightness variations were detected in at least one spectral band against the background of the random noise for one-third of the stars not earlier believed to be variable. A comparison of the distributions of these variations in amplitude and spectral band for the normal and variable stars shows that variability is inherent to most stars to some extent and is often wavelength dependent.     

A statistical analysis of methanol maser groups

An analysis of the flux densities of the 5₁-6₀ A ⁺ (6.7 GHz) and 2₀-3_?1 E (12.2 GHz) class II methanol maser lines in a large and homogeneous sample of maser sources has been carried out. For convenience, the maser lines were divided into three groups: group I contains spectral features for the lines most prominent in the 5₁-6₀ A ⁺ (6.7 GHz) transition, group II contains spectral features for the lines strongest in the 2₀-3_?1 E (12.2 GHz) transition, group III contains spectral features for which the velocities of the emission maxima of the two lines coincide. The same dependence was found for group II and group III: log S _6.7=(0.79±0.05)×log S _12.2+(0.79±0.05). The spectral features in group I do not obey this relation, and deviations from a linear dependence are considerably greater. It is suggested that methanol class II masers be divided into a subclass IIa, which has special conditions favoring 6.7 GHz masers, and a subclass IIb, which is comprised of the 12.2 GHz masers and those 6.7 GHz masers that necessarily accompany them under the same conditions.     

A catalog of galaxies in and around the cluster A1367. Spectral studies of several galaxies

We present a catalog of galaxies in and around the cluster A1367, together with the results of a spectroscopic study of eight faint galaxies projected onto the central part of the cluster. The observations were carried out with the Boller and Chivens spectrograph of the 2m telescope of the Guillermo Haro Observatory (Cananea, Mexico). Redshifts of eight galaxies were derived from both emission and absorption lines; the redshift for one of these, derived from Hα, SII, OIII, and Hβ emission lines, is z = 0.015. The spectrum of this galaxy displays no absorption lines at z = 0.026, testifying that it is located between the observer and A1367.     

Poisson distribution of the Iranian declustered earthquake catalog

Two main goals are considered in this paper: (1) modification and computation of the local coefficients of the space-time windows in the well-known declustering algorithm introduced by Gardner and Knopoff (1974) and (2) checking the independence of the Iranian mainshocks obtained from applying the new modified model. First, 21 of the well-documented earthquake sequences of Iran in the time period of 1972 to 2008 with the mainshock magnitude ranged from M _w = 5.4–7.1 were used to define the new local space-time windows of declustering. Generally, using these Iranian earthquake sequences led to introduce bigger space-time windows for the new model in comparison to the Gardner and Knopoff’s (1974) windows. In the next step, to control the independence of Iranian mainshocks, the events of the Iranian earthquake catalog in the time span of 1964–2010 with moment magnitude of M _w = 3.5–7.4 were used. In this respect, dependent events corresponding to the seven seismotectonic zones of Iran were removed using the new modified space-time windows. After declustering, the mainshock catalog was examined by the Kolmogorov–Smirnov goodness-of-fit test, and it was found to follow a Poisson distribution in all the studied seismotectonic zones of Iran. The same test on times between successive declustered events shows that the inter-event times of all catalogs follow an exponential distribution.