CH3OH Lines Research Articles

COMPACT MOLECULAR OUTFLOW FROM NGC 2264 CMM3: A CANDIDATE FOR VERY YOUNG HIGH-MASS PROTOSTAR

We have conducted a high-resolution observation of the molecular outflow with the CO (J = 2-1) and CH3OH (JK = 5 K -4 K , K = 0, 3) lines toward a high-mass protostar candidate, NGC 2264 CMM3, using the Submillimeter Array. A compact north-south bipolar outflow of 10'' in size associated with CMM3 is found in both CO and CH3OH emission. The outflow dynamical age is estimated to be as young as 140-2000 yr. Together with the non-detection of any 24 ?m source with the Spitzer Space Telescope, the result suggests that CMM3 likely harbors a young massive star at its very early evolutionary stage. The CH3OH outflow lobes are slightly offset outside those of the CO outflow, which indicates that the interaction between the outflow and the dense ambient gas causes a shock around the CO peak position, and the CH3OH molecule evaporated from the grain mantles is swept away from the shock front. The interaction is particularly strong in the southern (red) lobe, as indicated by the detection of the high excitation line of CH3OH (K = 3). The outflow seems to affect the chemical composition of CMM3 significantly.

CARBON-CHAIN AND ORGANIC MOLECULES AROUND VERY LOW LUMINOSITY PROTOSTELLAR OBJECTS OF L1521F-IRS AND IRAM 04191+1522

We have observed dense gas around the Very Low-Luminosity Ob jects (VeLLOs) L1521F-IRS and IRAM 04191+1522 in carbon-chain and organic molecular lines with the Nobeyama 45 m telescope. Towards L1521F-IRS, carbon-chain lines of CH3CCH (50-40), C4H (17/2-15/2), and C3H2 (212-101) are 1.5 - 3.5 times stronger than those towards IRAM 04191+1522, and the abundances of the carbon-chain molecules towards L1521F-IRS are 2 to 5 times higher than those towards IRAM 04191+1522. Mapping observations of these carbon-chain molecular lines show that in L1521F the peak positions of these carbon-chain molecular lines are different from each other and there is no emission peak towards the VeLLO position, while in IRAM 04191+1522 these carbon-chain lines are as weak as the detection limits except for the C3H2 line. The observed chemical differentiation between L1521F and IRAM 04191+1522 suggests that the evolutionary stage of L1521F-IRS is younger than that of IRAM 04191+1522, consistent with the extent of the associated outflows seen in the 13CO (1-0) line. The non-detection of the organic molecular lines of CH3OH (6-2-7-1 E) and CH3CN (60-50) implies that the warm (~ 100 K) molecular-desorbing region heated by the central protostar is smaller than ~ 100 AU towards L1521F-IRS and IRAM 04191+1522, suggesting the young age of these VeLLOs. We propose that the chemical status of surrounding dense gas can be used to trace the evolutionary stages of VeLLOs.

Spectral survey of the star-forming region W51 e1/e2 at 3 mm

A spectral survey of the W51 e1/e2 star-forming region at 84-115 GHz has yielded detections of 105 molecules and their isotopic species, from simple diatomic or triatomic molecules, such as CO, CS, HCN, up to complex organic compounds, such as CH3OCH3, CH3COCH3, and C2H5OOCH. Ninety-three lines that are absent from the Lovas list of molecular lines observed from space were detected, and approximately half of these were identified. A significant number of the detectedmolecules are typical for hot cores. These include the neutral molecules CH3OCHO, C2H5OH, CH3COCH3 etc., which are currently believed to exist in the gas phase only in hot cores and shock-heated gas. In addition, vibrationally excited SiO, C4H, HCN, l-C3H, HCCCN, CH3CN, CH3OH, H2O, and SO2 lines with upper-level temperatures of several hundred Kelvin were found. Such lines can arise only in hot gas with temperatures of the order of 100 K or higher. Apart from neutral molecules, various molecular ions were also detected. Some of these (N2H+, HCO+, HCS+) usually exist in molecular clouds with high visual extinctions A (V) . At the same time, the CF+ ion should be observed in photon-dominated regions with A (V) values of about unity or lower. An interesting result is the tentative detection of two molecules that have thus far been observed only in the atmospheres of late-type giant stars-MgCN and NaCN. This suggests that the conditions in the hottest W51 regions (probably, in the vicinities of protostars) are close to those in the atmospheres of giant stars. It would be desirable to search for other lines of these molecules to verify these tentative detections. Analysis of the radial velocities of the detected molecules suggests that the contribution from the e2 core dominates the emission of some O-bearing molecules (CH3OCHO, CH3CH2OH), while the contribution of the e1 core dominates the emission of some N-bearing molecules (e.g., CH3CH2CN). Thus, the molecular composition of the e2 core may be closer to the composition of the "Compact Ridge" in OMC-1, while the composition of the e1 core is closer to that for the "Hot Core" in the same cloud.

Spectral imaging of the Sagittarius B2 region in multiple 7-mm molecular lines

We have undertaken a spectral-line imaging survey of a 6 × 6 arcmin2 area around Sagittarius (Sgr) B2 near the centre of the Galaxy, in the range from 30 to 50 GHz, using the Mopra telescope. The spatial resolution varies from 1.0 to 1.4 arcmin and the spectral resolution varies from 1.6 to 2.7 km s−1 over the frequency range. We present velocity-integrated emission images for 47 lines: 38 molecular lines and nine radio recombination lines. There are significant differences between the distributions of different molecules, in part due to spatial differences in chemical abundance across the complex. For example, HNCO and HOCO+ are found preferentially in the north cloud, and CH2NH near Sgr B2 (N). Some of the differences between lines are due to excitation differences, as shown by the 36.17- and 44.07-GHz lines of CH3OH, which have maser emission, compared to the 48.37-GHz line of CH3OH. Other major differences in integrated molecular line distribution are due to absorption of the 7-mm free–free continuum emission (spatially traced by the radio recombination line emission) by cool intervening molecular material, causing a central dip in the molecular line distributions. These line distribution similarities and differences have been statistically described by Principal Component Analysis and interpreted in terms of simple Sgr B2 physical components of the cooler, lower density envelope, and dense, hot cores Sgr B2 (N), (M) and (S).

Tracing early evolutionary stages of high-mass star formation with molecular lines

Despite its major role in the evolution of the interstellar medium, the formation of high-mass stars (M > 10 Msol) is still poorly understood. Two types of massive star cluster precursors, the so-called Massive Dense Cores (MDCs), have been observed, which differ in their mid-infrared brightness. The origin of this difference is not established and could be the result of evolution, density, geometry differences, or a combination of these. We compare several molecular tracers of physical conditions (hot cores, shocks) observed in a sample of mid-IR weak emitting MDCs with previous results obtained in a sample of exclusively mid-IR bright MDCs. The aim is to understand the differences between these two types of object. We present single-dish observations of HDO, H2O-18, SO2 and CH3OH lines at lambda = 1.3 - 3.5 mm. We study line profiles and estimate abundances of these molecules, and use a partial correlation method to search for trends in the results. The detection rates of thermal emission lines are found to be very similar between mid-IR quiet and bright objects. The abundances of H2O, HDO (1E-13 to 1E-9 in the cold outer envelopes), SO2 and CH3OH differ from source to source but independently of their mid-IR flux. In contrast, the methanol class I maser emission, a tracer of outflow shocks, is found to be strongly anti-correlated with the 12 micron source brightnesses. The enhancement of the methanol maser emission in mid-IR quiet MDCs may indicate a more embedded nature. Since total masses are similar between the two samples, we suggest that the matter distribution is spherical around mid-IR quiet sources but flattened around mid-IR bright ones. In contrast, water emission is associated with objects containing a hot molecular core, irrespective of their mid-IR brightness. These results indicate that the mid-IR brightness of MDCs is an indicator of their evolutionary stage.

OUTFLOW-CORE INTERACTION IN BARNARD 1

In order to study how outflows from protostars influence the physical and chemical conditions of the parent molecular cloud, we have observed Barnard 1 (B1) main core, which harbors four Class 0 and three Class I sources, in the CO (J=1-0), CH3OH (J_K=2_K-1_K), and the SiO (J=1-0) lines using the Nobeyama 45 m telescope. We have identified three CO outflows in this region; one is an elongated (~ 0.3 pc) bipolar outflow from a Class 0 protostar B1-c in the submillimeter clump SMM 2, another is a rather compact (~ 0.1 pc) outflow from a Class I protostar B1 IRS in the clump SMM 6, and the other is an extended outflow from a Class I protostar in SMM 11. In the western lobe of the SMM 2 outflow, both the SiO and CH3OH lines show broad redshifted wings with the terminal velocities of 25 km/s and 13 km/s, respectively. It is likely that the shocks caused by the interaction between the outflow and ambient gas enhance the abundance of SiO and CH3OH in the gas phase. The total energy input rate by the outflows (1.1x10^{-3} Lsun) is smaller than the energy loss rate (8.5x10^{-3} Lsun$) through the turbulence decay in B1 main core, which suggests that the outflows can not sustain the turbulence in this region. Since the outflows are energetic enough to compensate the dissipating turbulence energy in the neighboring, more evolved star forming region NGC 1333, we suggest that the turbulence energy balance depends on the evolutionary state of the star formation in molecular clouds.

H$_{\mathsf 2}$CO and CH$_{\mathsf 3}$OH maps of the Orion Bar photodissociation region

A previous analysis of methanol and formaldehyde towards the Orion Bar concluded that the two molecular species may trace different physical components, methanol the clumpy material, and formaldehyde the interclump medium. To verify this hypothesis, we performed multi-line mapping observations of the two molecules to study their spatial distributions. The observations were performed with the IRAM-30m telescope at 218 and 241 GHz, with an angular resolution of ~11''. Additional data for H2CO from the Plateau de Bure array are also discussed. The data were analysed using an LVG approach. Both molecules are detected in our single-dish data. Our data show that CH3OH peaks towards the clumps of the Bar, but its intensity decreases below the detection threshold in the interclump material. When averaging over a large region of the interclump medium, the strongest CH3OH line is detected with a peak intensity of ~0.06K. Formaldehyde also peaks on the clumps, but it is also detected in the interclump gas. We verified that the weak intensity of CH3OH in the interclump medium is not caused by the different excitation conditions of the interclump material, but reflects a decrease in the column density of methanol. The abundance of CH3OH relative to H2CO decreases by at least one order of magnitude from the dense clumps to the interclump medium.

FOUR HIGHLY LUMINOUS MASSIVE STAR-FORMING REGIONS IN THE NORMA SPIRAL ARM. I. MOLECULAR GAS AND DUST OBSERVATIONS

We report molecular line and dust continuum observations, made with the SEST telescope, towards four young high-mass star forming regions associated with highly luminous (L> 6x10^5 Lsun) IRAS sources (15290-5546, 15502-5302, 15567-5236 and 16060-5146). Molecular emission was mapped in lines of CS (J=2-1, 3-2 and 5-4), SiO (J=2-1 and 3-2), CH3OH (Jk=3k-2k and 2k-1k), and C34S (J=3-2). In addition, single spectra at the peak position were taken in the CO, 13CO and C18O (J=1-0) lines. We find that the luminous star forming regions are associated with molecular gas and dust structures with radii of typically 0.5 pc, masses of ~5x10^3 Msun, column densities of ~5x10^{23} cm^{-2}, molecular hydrogen densities of typically ~2x10^5 cm^{-3} and dust temperatures of ~40 K. The 1.2 mm dust continuum observations further indicate that the cores are centrally condensed, having radial density profiles with power-law indices in the range 1.6-1.9. We find that under these conditions dynamical friction by the gas plays an important role in the migration of high-mass stars towards the central core region, providing an explanation for the observed stellar mass segregation within the cores.

A contracting circumbinary molecular ring around Ori 139-409 with an inner cavity of about 140 au

We present sensitive and subarcsecond resolution (∼0.7 arcsec) CH3OH(7−2,6–6−2,5) line and 890-μm continuum observations, made with the Submillimeter Array (SMA), towards the hot molecular circumbinary ring associated with the young multiple star Ori 139–409. The CH3OH(7−2,6–6−2,5) emission from the ring is well resolved at this angular resolution, revealing an inner cavity with a size of about 140 au. A local thermodynamic equilibrium model of a Keplerian disc with an inner cavity of the same size confirms the presence of this cavity. Additionally, this model suggests that the circumbinary ring is contracting with a velocity of Vinf∼ 1.5 km s−1 towards the binary central compact circumstellar discs reported at a wavelength of 7 mm. The inner central cavity seems to be formed by the tidal effects of the young stars in the middle of the ring. The ring does not appear to be a stationary object. Furthermore, the infall velocity we determine is about a factor of 3 slower than the free-fall velocity corresponding to the dynamical mass. This would correspond to a mass accretion rate of about 10−5 M⊙ yr−1. We have found that the dust emission associated with Ori 139–409 appears to be arising from the circumstellar discs, with no strong contribution from the molecular gas ring. Furthermore, a simple comparison with other classical molecular dusty rings (e.g. GG Tau, UZ Tau and UY Aur) suggests that Ori 139–409 could be one of the youngest circumbinary rings reported to date. Finally, our results confirm that the circumbinary rings are actively funnelling fresh gas material to the central compact binary circumstellar discs (i.e. to the protostars in the very early phases of their evolution).

MOLECULES IN G1.6–0.025—“HOT” CHEMISTRY IN THE ABSENCE OF STAR FORMATION AT THE PERIPHERY OF THE GALACTIC CENTER REGION

We present molecular line mapping of the Giant Molecular Cloud G1.6-0.025, which is located at the high longitude end of the Central Molecular Zone of our Galaxy. We assess the degree of star formation activity in that region using several tracers and find very little. We made a large scale, medium (2') resolution map in the J = 2-1 transition of SiO for which we find clumpy emission over a ~0.8 x 0.3 degree-sized region stretching along the Galactic plane. Toward selected positions we also took spectra in the easy to excite J_k=2_k-1_k quartet of CH3OH and the CS 2-1 line. Throughout the cloud these \meth lines are, remarkably, several times stronger than, both, the CS and the SiO lines. The large widths of all the observed lines, similar to values generally found in the Galactic center, indicate a high degree of turbulence. Several high LSR velocity clumps that have 0-80 km/s higher velocities than the bulk of the molecular cloud appear at the same projected position as "normal" velocity material; this may indicate cloud-cloud collisions. Statistical equilibrium modeling of the CH3OH lines observed by us and others yield relatively high densities and moderate temperatures for a representative dual velocity position. We find 8 10^4 cm-3/30 K for material in the G1.6-0.025 cloud and a higher temperature (190 K), but a 50% lower density in a high velocity clump projected on the same location. Several scenarios are discussed in which shock chemistry might enhance the CH3OH and SiO abundances in G1.6-0.025 and elsewhere in the Central Molecular Zone.

Chemistry in disks

We study the molecular content and chemistry of a circumstellar disk surrounding the Herbig Ae star AB Aur at (sub-)millimeter wavelengths. Our aim is to reconstruct the chemical history and composition of the AB Aur disk and to compare it with disks around low-mass, cooler T Tauri stars. We observe the AB Aur disk with the IRAM Plateau de Bure Interferometer in the C- and D- configurations in rotational lines of CS, HCN, C2H, CH3OH, HCO+, and CO isotopes. Using an iterative minimization technique, observed columns densities and abundances are derived. These values are further compared with results of an advanced chemical model that is based on a steady-state flared disk structure with a vertical temperature gradient, and gas-grain chemical network with surface reactions. We firmly detect HCO+ in the 1--0 transition, tentatively detect HCN, and do not detect CS, C2H, and CH3OH. The observed HCO+ and 13CO column densities as well as the upper limits to the column densities of HCN, CS, C2H, and CH3OH are in good agreement with modeling results and those from previous studies. The AB Aur disk possesses more CO, but is less abundant in other molecular species compared to the DM Tau disk. This is primarily caused by intense UV irradiation from the central Herbig A0 star, which results in a hotter disk where CO freeze out does not occur and thus surface formation of complex CO-bearing molecules might be inhibited.

ATCA 3 mm observations of NGC 6334I and I(N): dense cores, outflows, and an UCH II region

Aims. We investigate the dense gas, the outflows, and the continuum emission from the massive twin cores NGC 6334I and I(N) at high spatial resolution. Methods. We imaged the region with the Australia Telescope Compact Array (ATCA) at 3.4 mm wavelength in continuum, as well as CH3CN(5K −4K ) and HCN(1−0) spectral line emission. Results. While the continuum emission in NGC 6334I mainly traces the UCHii region, toward NGC 6334I(N) we detect continuum emission from four of the previously identified dust continuum condensations that are of protostellar or pre-stellar nature. The CH3CN(5K −4K ) lines are detected in all K-components up to energies of 128 K aboveground toward two protostellar condensations in both regions. We find line width increasing with increasing K for all sources, which indicates a higher degree of internal motions of the hotter gas probed by these high K-transitions. Toward the main mm and CH3CN source in NGC 6334I, we identify a velocity gradient approximately perpendicular to the large-scale molecular outflow. This may be interpreted as a signature of an accretion disk, although other scenarios, e.g., an unresolved double source, could produce a similar signature. No comparable signature is found toward any of the other sources. HCN does not trace the dense gas well in this region but it is dominated by the molecular outflows. While the outflow in NGC 6334I exhibits a normal Hubble-law like velocity structure, the data are consistent with a precessing outflow close to the plane of the sky for NGC 6334I(N). Furthermore, we observe a wide (∼15.4 km s −1 ) HCN absorption line, much broader than the previously observed CH3OH and NH3 absorption lines. Several explanations for the difference are discussed. The fits-files of the 3.4 mm continuum images and of the HCN(1−0) and CH3CN(5K−4K ) data-cubes are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat? J/481/169

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

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.

Multiple Jets from the High‐Mass (Proto)stellar Cluster AFGL 5142

We present studies of the massive protocluster AFGL 5142 in the J ¼ 2Y1 transition of the CO isotopologues, SO, CH3OH, and CH3CN lines, as well as in the continuum at 225 GHz and 8.4 GHz. The 225 GHz continuum emission reveals at least five dust continuum peaks. The strongest peaks, MM-1 and MM-2, are associated with hot cores with temperatures of 90 � 20 and 250 � 40 K, respectively. With similar core mass, the higher temperature and CH3CN abundance in the MM-2 core suggest that it might be at a more evolved stage than the MM-1 core. A total of 22 lines fromninemoleculesaredetected.Thelinestrengthvariesremarkablyintheregion.StrongSOemissionisfoundboth in molecular outflows and cloud cores. CH3OH emission, onthe contrary, is much weaker in molecular outflows, and isdetectedtowardhotcoresMM-1andMM-2,butisabsentinthelessmassiveandperhapslessevolvedcoresMM-3, MM-4, and MM-5. The CO and SO emission reveals at least three molecular outflows originating from the center of thedustcore.Theoutflowsarewellcollimated,withterminalvelocitiesupto50kms � 1 fromthecloudvelocity.Since jetlike outflows and disk-mediated accretion process are physically connected, the well-collimated outflows indicate that even in this cluster environment, accretion is responsible for the formation of individual stars in the cluster. Subject headingg s: H ii regions — ISM: clouds — ISM: individual (AFGL 5142) — ISM: kinematics and dynamics — masers — stars: formation

Radio observations of comet 9P/Tempel 1 with the Australia Telescope facilities during the Deep Impact encounter

We present radio observations of comet 9P/Tempel 1 associated with the Deep Impact spacecraft collision of 2005 July 4. Weak 18-cm OH emission was detected with the Parkes 64-m telescope, in data averaged over July 4–6, at a level of 12 ± 3 mJy km s−1, corresponding to OH production rate 2.8 × 1028 molecules s−1 (Despois et al. inversion model, or 1.0 × 1028 s−1 for the Schleicher & A'Hearn model). We did not detect the HCN 1–0 line with the Mopra 22-m telescope over the period July 2–6. The 3σ limit of 0.06 K km s−1 for HCN on July 4 after the impact gives the limit to the HCN production rate of <1.8 × 1025 s−1. We did not detect the HCN 1–0 line, 6.7 GHz CH3OH line or 3.4-mm continuum with the Australia Telescope Compact Array (ATCA) on July 4, giving further limits on any small-scale structure due to an outburst. The 3σ limit on HCN emission of 2.5 K km s−1 from the ATCA around impact corresponds to limit < 4 × 1029 HCN molecules released by the impact.

High Spatial Resolution Observations of NH3and CH3OH toward the Massive Twin Cores NGC 6334I and NGC 6334I(N)

Molecular line observations of NH3 (J ; K) ¼ (1; 1) and (2, 2) and CH3OH at 24.93 GHz taken with the Australian Telescope Compact Array (ATCA) toward the massive twin cores NGC 6334I and NGC 6334I(N) reveal significant variations in the line emission between the two massive cores. The UC H ii region/hot core NGC 6334I exhibits strong thermal NH3 and CH3OH emission adjacent to the UC H ii region and coincident with two millimeter continuum peaks observed by T. R. Hunter et al. In contrast, we find neither compact NH3 nor thermal CH3OH line emission toward NGC 6334I(N). There the NH3 emission is distributed over a broad region (>10) without a clear peak, and we find Class I CH3OH maser emission with peak brightness temperatures up to 7000 K. The maser emission peaks appear to be spatially associated with the interfaces between the molecular outflows and the ambient dense gas. Peak NH3 (1, 1) line brightness temperatures 70 K in both regions indicate gas temperatures on the same order. NH3 emission is also detected toward the outflow in NGC 6334I, resulting in an estimated rotational temperature of Trot 19 K. Furthermore, we observe CH3OH and NH3 absorption toward the UC H ii region; the velocity structure is consistent with expanding molecular gas around the UC H ii region. Thermal and kinematic effects possibly imposed from the UC H ii region on the molecular core are also discussed.

H2CO and CH3OH abundances in the envelopes around low-mass protostars

This paper presents the third in a series of single-dish studies of molecular abundances in the envelopes around a large sample of 18 low-mass pre- and protostellar objects. It focuses on typical grain mantle products and organic molecules, including H2CO, CH3OH and CH3CN. With a few exceptions, all H2CO lines can be fit by constant abundances of throughout the envelopes if ortho- and para lines are considered independently. The current observational dataset does not require a large H2CO abundance enhancement in the inner warm regions, but this can also not be ruled out. Through comparison of the H2CO abundances of the entire sample, the H2CO ortho-para ratio is constrained to be consistent with thermalization on grains at temperatures of 10-15 K. The H2CO abundances can be related to the empirical chemical network established on the basis of our previously reported survey of other species and is found to be closely correlated with that of the nitrogen-bearing molecules. These correlations reflect the freeze-out of molecules at low temperatures and high densities, with the constant H2CO abundance being a measure of the size of the freeze-out zone. An improved fit to the data is obtained with a “drop” abundance structure in which the abundance is typically a few 10-10 when the temperature is lower than the evaporation temperature and the density high enough so that the timescale for depletion is less than the lifetime of the core. The location of the freeze-out zone is constrained from CO observations. Outside the freeze-out zone, the H2CO abundance is typically a few . The observations show that the CH3OH lines are significantly broader than the H2CO lines, indicating that they probe kinematically distinct regions. CH3OH is moreover only detected toward a handful of sources and CH3CN toward only one, NGC 1333-IRAS2. For NGC 1333-IRAS2, CH3OH and CH3CN abundance enhancements of two-three orders of magnitude at temperatures higher than 90 K are derived. In contrast, the NGC 1333-IRAS4A and IRAS4B CH3OH data are fitted with a constant abundance and an abundance enhancement at a lower temperature of 30 K, respectively. This is consistent with a scenario where CH3OH probes the action of compact outflows on the envelopes, which is further supported by comparison to high frequency, high excitation CS and HDO line profiles which uniquely probe warm, dense gas. The extent to which the outflow dominates the abundance enhancements compared with the passively heated inner envelope depends on the filling factors of the two components in the observing beam.

A study of the Keplerian accretion disk and precessing outflow in the massive protostar IRAS 20126+4104

We report on interferometric observations at 3.2 and 1.3 mm of the massive young stellar object IRAS 20126+4104 obtained in the C 34 Sa nd CH 3OH lines and in the continuum emission. The C 34 S data confirm the existence of a Keplerian disk, as already suggested by various authors. However, the mass of the central object is ∼7 M� , significantly less than previous estimates. We believe that such a discrepancy is due to the fact that the rotation curve is affected not only by the star but also by the mass in the innermost regions of the disk itself: this leads to an overestimate of the stellar mass when low-density tracers are used to study the velocity field over regions larger than a few seconds of arc (i.e. a few 0.01 pc). On the basis of the line profiles we speculate that accretion onto the star might be still occurring through the disk. This seems consistent with current models of high-mass star formation which predict an accretion luminosity equal to that of IRAS 20126+4104 for a 7 Mprotostar. The CH3OH lines trace both the disk and the bipolar outflow previously detected in other molecules such as HCO + ,S iO, and H 2. New H2 images obtained at 2.2 µm confirm that the outflow axis is undergoing precession. We elaborate a simple model that suitably fits the data thus allowing derivation of a few basic parameters of the precession.

Methanol in W3(H2O) and Surrounding Regions

We present the results of an interferometric study of 38 millimeter-wave lines of CH3OH in the region around the water maser source W3(H2O) and a region extending about 30 to the south and west of the hydroxyl maser source W3(OH). The methanol emitting region around W3(H2O) has an extent of 2.0 x 1.2 (4400 x 2600 AU). The density is of order 1.e7 cm-3, sufficient to thermalize most of the methanol lines. The kinetic temperature is approximately 140 K and the methanol fractional abundance greater than 1.e-6, indicative of a high degree of grain mantle evaporation. The W3(H2O) source contains sub-structure, with peaks corresponding to the TW source and Wyrowski's B/C, separated by 2500 AU in projection. The kinematics are consistent with these being distinct protostellar cores in a wide binary orbit and a dynamical mass for the region of a few tens of Mo. The extended methanol emission to the southwest of W3(OH) is seen strongly only from the lowest excitation lines and from lines known elsewhere to be class I methanol masers, namely the 84.5 GHz 5(-1)-4(0)E and 95.2 GHz 8(0)-7(1)A+ lines. Within this region there are two compact clumps, which we denote as swA and swB, each about 15 (0.16 pc projected distance) away from W3(OH). Excitation analysis of these clumps indicates the presence of lines with inverted populations but only weak amplification. The sources swA and swB appear to have kinetic temperatures of order 50-100 K and densities of order 1.e5 - 1.e6 cm-3. The methanol fractional abundance for the warmer clump is of order 1.e-7, suggestive of partial grain mantle evaporation. The clumping occurs on mass scales of order 1 Mo.

Interaction between the Outflow and the Core in IRAM 04191+1522

We have carried out mapping observations of the molecular core associated with the young Class 0 protostar, IRAM 04191+1522, in the CH3OH (JK=2K-1K) and C34S (J=2-1) lines using the 45 m telescope at Nobeyama Radio Observatory. As well as an elongated envelope associated with the protostellar formation (size \~0.07 pc x 0.04 pc, mass ~ 2.3 Mo), two compact (~ 0.03 pc) condensations were found in the CH3OH line at the southern edge of the elongated envelope, where the blueshifted CO outflow emerging from the protostar is located. In contrast to the elongated envelope, those compact CH3OH condensations show much larger line width (up to 2.0 km s-1) with centroid velocities blueshifted by ~ 0.8 km s-1. The compact condensations have momenta (~ 0.06 Mo km s-1) comparable to that of the blueshifted molecular outflow. These results suggest that the compact condensations are probably formed in the course of interaction between the outflow and the ambient gas surrounding the protostar, and that such interaction may cause dissipation of a part of the ambient gas. No drastic, localized enhancement of the CH3OH abundance is, however, observed toward the compact condensations, implying that there seems to be no significant shock heating at the compact condensations. This may be because the CO outflow velocity (< 10 km s-1) is too low to cause effective heating to release CH3OH on dust grains into gas phase.