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

I. D. Litovchenko  A. V. Alakoz  I. E. Val’tts  G. M. Larionov 《Astronomy Reports》2011,55(12):1086-1095

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.  相似文献   

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

I. D. Litovchenko  O. S. Bayandina  A. V. Alakoz  I. E. Val’tss  G. M. Larionov  D. V. Mukha  A. S. Nabatov  A. A. Konovalenko  V. V. Zakharenko  E. V. Alekseev  V. S. Nikolaenko  V. F. Kulishenko  S. A. Odintsov 《Astronomy Reports》2012,56(7):536-552

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.  相似文献   

Observations of Extended Green Objects in the 1.35-cm H<Subscript>2</Subscript>O Line on the 22-m Pushchino Radio Telescope     

G. M. Rudnitskii  E. E. Lekht  O. S. Bayandina  I. E. Val’tts  E. R. Khan 《Astronomy Reports》2016,60(1):129-144

Observations of H₂O maser sources at 1.35 cm associated with extended regions of 4.5-µm emission (indicated as “green” on Spitzer survey maps—so-called Extended Green Objects, EGOs) are reported. EGOs are considered as characteristic signposts of regions of formation of massive stars, which host high-velocity outflows, as well as methanol, water, and hydroxyl masers. The observations were carried out in January–May 2015 on the 22-meter radio telescope of the Pushchino Radio Astronomy Observatory. The sample studied includes 24 EGOs north of declination -29° taken from the Spitzer GLIMPSE survey, together with one of the brightest Class I methanol masers G6.05-1.45 (M8E) and the Class I methanol maser in an IRDC G359.94+0.17. H₂O maser emission was detected toward 11 of the EGOs: G11.94-0.62, G14.33-0.64, G16.59-0.06, G23.01-0.41, G24.943+0.074, G28.83-0.25, G34.3+0.2, G34.403+0.233, G35.20-0.74, G45.47+0.07, and G49.267-0.337. These including the well known H₂O maser in the W44 region, G34.3+0.2. H₂O emission from G28.83-0.25 was detected for the first time, at 77.6 km/s, with a flux density of 19 Jy in January and 16 Jy in February 2015. The source was probably caught at an early stage of the propagation of a shock wave. The Class I methanol masers G359.94+0.17 and G6.05-1.45 (M8E) and 13 of the EGOs were not detected in the H₂O line, with 3s upper limits of ~6-7 Jy. Spectra and maser-emission parameters are given for the detected H₂Omasers, for some of which strong variability of the H₂O maser emission was observed. The detected H₂Omasers, together with the Class I methanol masers and extended 4.5-µm emission, are associated with a very early stage in the development of young stellar objects in the regions of the EGOs. However, this sample of EGOs is not uniform. The presence of 44-GHz Class I methanol masers together with EGOs cannot be considered the only sign of early stages of star formation.  相似文献   

High resolution OH observations of Extended Green Objects     

Bayandina  O. S.  Val&#;tts  I. E.  Kurtz  S. E. 《Astronomy Reports》2015,59(11):998-1014

Themaser pumping schemes proposed for the various OH lines may not be as clear-cut as they once seemed. The main OH lines, at 1665 and 1667 MHz, are thought to be radiatively pumped, with the radiation typically coming from nearby ultracompact HII regions. Recently, a new class of main-line maser has been posited, collisionally pumped by shocks due to molecular outflows. The W3(OH)/W3(OH)-TW system is the archetype: traditional OH masers are excited by theW3(OH) ultracompact HII region, while collisionally pumped OH masers arise in the younger object W3(OH)-TW, which is driving an outflow. The 1720 MHz OH satellite line maser, typically found in SNR–cloud interaction regions, is thought to be collisionally pumped, as are class I methanol masers found in star formation regions. Thus it is plausible that these two masers arise in similar (shocked gas) circumstances. In this study we observe all four OH transitions in the direction of Extended Green Objects (EGOs) that trace shocked gas (possibly from outflows) in high-mass star formation regions. Previous studies have found a high incidence of class I methanol maser emission in these objects, suggesting that OH(1720) masers might also be abundant in this sample. Observations of 20 northern EGOs (δ > −17°) were carried out with the Jansky Very Large Array of all four ground state OH transitions, the HI line, and the 20 centimeter continuum. Positive detection of OH lines was obtained for 10 EGOs: OH lines at 1665 and 1667 MHz were detected toward 45% of the sample. The stellar OH line at 1612 MHz was detected toward 15% of the sample. The 1720 MHz emission line was detected in only one EGO source, G45.47+0.07, which is also presents the strongest main-line OH emission of our sample. We measure the projected separations between OH masers and GLIMPSE point sources associated with EGOs (median value 0.04 pc), betweenOH and class II methanol masers (median value 0.03 pc), and between OH and class I methanol masers (median value 0.14 pc), thus confirming previous findings that class I methanol masers are located further from exciting sources than areOH and class II methanol masers. Bearing in mind the theoretical incompatibility of class I and class II methanol maser pumping schemes, and the obtained separations between class I methanol masers and other masers in the EGOs, we conclude that class I methanol masers do not co-exist with GLIMPSE point sources, OH and class II methanol masers in one and the same core. Rather, we suggest that the class I masers arise in distinct but neighboring cores, about 1 pc distant, and in a different evolutionary state.

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Methanol radio emission at millimeter wavelengths: New masers at 1.3 and 2.8 millimeters     

V. I. Slysh  S. V. Kalenskii  I. E. Val’tts 《Astronomy Reports》2002,46(1):49-56

The results of a search for maser emission in the methanol lines 8_?1-7₀ E at 229.8 GHz, 3_?2-4_?1 E at 230.0 GHz, 0₀-1_?1 E at 108.9 GHz, and in the J ₁-J ₀ E series near 165 GHz in star-forming regions are reported. At least two masers and two candidates have been detected at 229.8 GHz. Thus, methanol masers have been detected in the 1-mm band for the first time. At 108.9 GHz, masers have been detected toward G345.01+1.79 and possibly toward M8E as well. Thermal emission was found toward 28 objects. The 229.8-GHz sources are class I masers, whereas the 108.9-GHz sources are class II masers. An analysis using a large velocity-gradient method shows that the 229.8-GHz masers can appear at densities of about 3×10⁴ cm^?3. The ratios of the flux densities in different class I lines toward DR 21(OH) and DR 21 West can be approximated in models with gas kinetic temperatures of about 50 K. Detection of the 108.9 GHz masers toward G345.01+1.79 and M8E may provide information about the geometry of these objects.  相似文献   

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

V. I. Slysh  S. V. Kalenskii 《Astronomy Reports》2009,53(6):519-527

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.  相似文献   

Magnetic fields in methanol maser condensations based on data for related regions. Seven sources: Observational parameters     

O. S. Bayandina  A. V. Alakoz  I. E. Val’tts 《Astronomy Reports》2013,57(12):889-903

Results of polarization observations of gas-dust condensations obtained on the Nançay radio telescope in the 1665 and 1667 MHz OH lines in all four Stokes parameters are reported. Seven OH maser sources associated with methanol masers were selected for this study. The goal was to estimate the magnetic fields in methanol condensations from the Zeeman splitting of OH maser lines associated with the methanol masers. The Gaussian parameters of features in the OH spectra are presented, and their polarization parameters are estimated: the degree of circular polarization m _C , flux density in linear polarization p, and degree of linear polarization m _L . The magnetic field intensity B has been estimated from the Zeeman splitting of the OH lines and approximation of the Stokes parameter V from the derivative of Stokes parameter I. B varies from ≤0.5 to 1.4 mG for different sources. The association of OH masers with methanol emission has been analyzed; the magnetic fields of OH masers in interstellar condensations associated with Class I methanol masers can be determined more reliably than the fields in interstellar condensations with OH masers associated with Class II methanol emission, and have higher values. The sizes of the studied regions suggest they may be bound structures such as Bok globules, small IRDC clouds, or protoplanetary disks.  相似文献   

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

S. V. Kalenskii  S. Kurtz  V. I. Slysh  P. Hofner  C. M. Walmsley  L. E. B. Johansson  P. Bergman 《Astronomy Reports》2010,54(10):932-939

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.  相似文献   

Methanol maser groups and class I emission: Flux density distribution     

G. M. Larionov  I. E. Val’tts 《Astronomy Reports》2007,51(10):813-819

A search for a relationship between class I and class II methanol maser flux densities has been carried out. A large sample of mixed-type sources has been studied, with each source in the sample radiating as a class I and class II maser simultaneously. In methanol maser groups for which the positions of prominent spectral features at different radial velocities coincide at different frequencies, the fluxes are anticorrelated, and are related as log S _6.7+12.2 = (?1.68 ± 0.38) × log S ₄₄ + (4.01 ± 0.60). For group I, which includes sources with preferred pumping for masers emitting at 6.7 GHz, the relationship between the 6.7 GHz masers and 44 GHz masers is less steep than for group II, which contains sources with normal pumping of class II masers. This implies that class I methanol masers that correspond to group I are suppressed more strongly.  相似文献   

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

O. S. Bayandina  I. E. Val’tts  G. M. Larionov 《Astronomy Reports》2012,56(7):553-563

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.  相似文献   

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

S. V. Kalenskii  S. Kurtz  P. Bergman 《Astronomy Reports》2013,57(2):120-127

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.  相似文献   

Map of the 6.7 GHz class II methanol maser emission of the protoplanetary disk G23.01-0.41     

S. V. Polushkin  I. E. Val’tts 《Astronomy Reports》2011,55(5):445-455

We present images of the star-forming regionG23.01–0.41 at 6.7GHz in the Class II methanol maser transition 5₁–6₀ A ⁺, produced from archival observations on the European VLBI Network. Our map of the source and its maser spots contains 24 maser components. The data for each spot—absolute coordinates, coordinates relative to the calibration feature, peak flux and flux integrated over the spot, size, position angle, velocity along the line of sight, and line full width at half-maximum—are collected in tabular form. The spatial region occupied by the maser spots is approximated by a 200×130 milliarcsec ellipse in position angle PA = −0.40°, centered on the absolute coordinates α ₀ = 18^h34^m40.282^s, δ ₀ = −09°00′38.27″ (J2000). If the source is a protoplanetary disk, then, for the distance estimate derived from trigonometric parallax, its diameter is 1800 AU, and the mass of the central protostar is 23.5M _⊙.  相似文献   

Class I Methanol Emission Around DR 21 (OH)     

S. V. Polushkin  I. E. Val’tts 《Astronomy Reports》2010,54(6):496-508

Results of new observations of the vicinity of DR 21 (OH) conducted on the 20-m Onsala radio telescope are presented. The goal was to search for associations between molecular hydrogen emission tracing shock waves and class I methanol maser emission. Observations at 44 and 36 GHz have shown that an extensive region of faint methanol maser emission elongated North-South is probably present in the vicinity of DR 21(OH). The linear size of this structure may be a factor of ten larger than the central region in DR 21(OH) that emits at 44 GHz. Three maser emission peaks are clearly visible in the northern (DR 21N), central (DR 21(OH)), and southern (vicinity of DR 21 West) parts of this structure. Many other structures are also embedded in this region, including the protostellar disk ERO 3 previously detected at 6.7 GHz. Maser components of these objects are formed with velocities from -5 to-2 km/s, with a velocity gradient from -5 in the North to -2 km/s in the South. The spatial resolution of the map is not high enough to distinguish fine structures at 44 GHz associated with spots and jets emitting in molecular hydrogen.  相似文献   

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

S. V. Kalenskii  V. I. Slysh  I. E. Val’tts  A. Winnberg  L. E. Johansson 《Astronomy Reports》2001,45(1):26-33

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.  相似文献   

Methanol emission in distant protoplanetary disks     

I. E. Val'tts  S. Yu. Lyubchenko 《Astronomy Reports》2003,47(10):797-808

Thirty four-frequency line profiles of Class II methanol masers have been analyzed to investigate carefully the coincidences of various spectral features. Data at 6.7, 12.2, 107, and 156.6 GHz have been analyzed. Two clusters of Class II methanol maser lines at 6.7 and 12.2 GHz are observed in the spectra of many sources. These maser-line clusters are located on either side of the thermal methanol lines at 107 and 156.6 GHz. To avoid the effect of amplification in these thermal methanol lines, a similar analysis was performed for 80 sources having both maser emission at 6.7 GHz and thermal CS emission. The relative distributions of the methanol maser lines and the thermal CS line confirm on the basis of richer statistics that the maser lines are located in two clusters on either side of the thermal feature. It is proposed that the two maser-line clusters correspond to two edges of a Keplerian disk. The thermal methanol and CS emission is formed in dense molecular cores, whose centers are coincident with the disk centers.  相似文献   

Methanol and other molecular tracers of outflows and dense gas in the molecular cloud G345.01+1.79     

S. V. Salii  A. M. Sobolev 《Astronomy Reports》2006,50(12):965-982

The results of SEST millimeter observations of the molecular cloud G345.01+1.79 are presented. Spectra of CH₃OH, SO₂, SiO, HCO⁺, C¹⁸O, C³³S, C³⁴S, HCN, and DCN lines have been obtained. Mapping of the cloud in CH₃OH, SiO, and C³⁴S lines indicates that the maximum integrated intensity in the SiO and C³⁴S lines and in low-excitation CH₃OH transitions coincide with the northern group of methanol masers, while the corresponding maximum for high-excitation CH₃OH transitions coincides with the southern methanol-maser group. The physical parameters are estimated from the quasi-thermal CH₃OH lines under the large-velocity-gradient approximation, and their distribution on the sky derived. The density and temperature are higher toward the southern group of methanol masers than in the northern group. This may indicate that star formation is in an earlier stage of evolution in the northern than toward the southern group. A maser component can be distinguished in 14 (of 71) CH₃OH lines. We have detected for the first time weak, probably maser, emission in the CH₃OH lines at 148.11, 231.28, 165.05, 165.06, and 165.07 GHz. A blue wing is clearly visible in the CH₃OH, SiO, C¹⁸O, and SO₂ lines. The emission in this wing is probably associated with a compact source whose velocity is characteristic of the CH₃OH maser emission in the southern group of masers.  相似文献   

Methanol and H2O masers in a disk around GL 2789     

V. I. Slysh  M. A. Voronkov  I. E. Val’tts  V. Migenes 《Astronomy Reports》2002,46(12):969-980

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A statistical analysis of methanol maser groups     

I. E. Val’tts  S. Yu. Lyubchenko 《Astronomy Reports》2004,48(10):834-839

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.  相似文献   

Spectral scan of the star-forming region DR21(OH). Observations and LTE analysis     

S. V. Kalenskii  L. E. B. Johansson 《Astronomy Reports》2010,54(4):295-316

Seventy-eight molecules have been detected as a result of a spectral survey of the star-forming region DR21(OH) at 84–115 GHz. The abundances of most molecules are typical of those in the dense cores of molecular clouds. The rotational temperatures derived using the lines of most molecules fall in the range 9–56 K, which is also typical for dense cores. However, emission from high-lying levels of methanol and sulfur dioxide was detected; since the rotational temperatures for methanol and sulfur dioxide are 252 and 186 K, this indicates the presence of hot regions. Another fact indicating the existence of hot regions is the detection of CH₃OCHO, CH₃CH₂OH, and CH₃OCH₃, which have thus far been observed only in hot cores and shock-heated regions. An interesting result is the tentative detection of the J = 2 − 1, v = 1 SiO line, with the upper level energy of 1775 K. This is probably a maser line, similar to but weaker than the well-known SiO masers in the star-forming regions Orion-KL,W51(N), and Sgr B2(N).  相似文献   

A general catalog of class I methanol masers     

I. E. Val’tts  G. M. Larionov 《Astronomy Reports》2007,51(7):519-530

A catalog of class I methanol masers discovered so far in the Southern and Northern hemispheres is presented. The catalog contains 160 sources. A statistical analysis shows that, within 2’ of the telescope pointing (which corresponds approximately to the field of view of single antennas used in search surveys), 50% of class I methanol masers are associated with objects characteristic of active starforming regions: IRAS sources, ultracompact HII regions, and dense gas—dust clouds, as well as OH and H₂O interstellar masers. At the same time, bipolar outflows (which could play an active part in pumping the methanol masers) are associated with fewer than 25% of class I methanol masers. In 72% of cases, class I methanol masers are associated with class II methanol maser sources. These results suggest that methanol maser condensations are more appropriately classified by the transition type (that is, the pumping mechanism) than their association with other astronomical objects.  相似文献