Faust

We present observations of methanol lines in a sample of Class 0 low mass protostars. Using a 1-D radiative transfer model, we derive the abundances in the envelopes. In two sources of the sample, the observations can only be reproduced by the model if the methanol abundance is enhanced by about two order of magnitude in the inner hot region of the envelope. Two other sources show similar jumps, although at a lower confidence level. The observations for the other three sources are well reproduced with a constant abundance, but the presence of a jump cannot be ruled out. The observed methanol abundances in the warm gas around low mass protostars are orders of magnitude higher than gas phase chemistry models predict. Hence, in agreement with other evidence, this suggests that the high methanol abundance reflects recent evaporation of ices due to the heating by the newly formed star. The observed abundance ratios of CH 3 OH, H 2 CO and CO are in good agreement with grain surface chemistry models. However, the absolute abundances are more difficult to reproduce and may indicate the presence of multiple ice components in these regions.

We present a sensitive search for methanol line emission in evolved stars at 1 cm, aiming to detect, for the first time, methanol masers in this type of objects. Our sample comprised post-AGB stars and young planetary nebulae (PNe), whose mass-loss processes and circumstellar structures resemble those of young stellar objects (YSOs), where methanol masers are detected. Class I masers were searched for in 73 objects, whereas Class II ones were searched in 16. No detection was obtained. The non-detection of Class I methanol masers indicated that methanol production in dust grains and/or the enhancement of its gas-phase abundance in the shocked regions of evolved objects are not as efficient as in YSOs. We suggest that relatively more evolved PNe might have a better probability of harboring Class II masers.

Proceedings of the International Astronomical Union, 2012

Astronomy & Astrophysics, 2002

We present the results of a search for methanol maser and thermal lines in 11 transitions in the range 85-112 GHz toward 23 star-forming regions exhibiting class I and class II methanol masers. The selected frequencies are 85.5, 86.6, 94.5, 95.1, 96.7 (quartet line series), 107.0, 108.8 and 111.2 GHz. Five masers were confirmed at 107.0 GHz while new masers were found at 85.5, 86.6 and 108.8 GHz. Many detected emission lines have a quasi-thermal origin. The detection rates of methanol emission are high at 95.1 GHz (87%) and 96.7 GHz (96%), satisfactory at 107.0 and 108.9 GHz (∼50%) while the detection rates at 85.5, 94.5 and 111.3 GHz are low (∼20%). Most reported 95.1 GHz emission is masing.

Astronomy & Astrophysics, 2011

Context. The current theory of methanol deuteration on interstellar grains predicts that the abundance ratio of the singly deuterated isotopologues [CH 2 DOH]/[CH 3 OD] should always be ∼3. In warm regions where grain mantles have sublimated, gaseous methanol is detectable via its rotational transitions. In previous observational studies, the gas-phase [CH 2 DOH]/[CH 3 OD] ratio was measured and found to be significantly larger than 3 in low-mass protostars and close to 1 in the Orion IRc2 massive hot core. Aims. We present new measurements of the gas-phase [CH 2 DOH]/[CH 3 OD] ratio in two additional high-mass protostars, as well as in two intermediate-mass protostars, to either confirm or exclude the dependence of this ratio on the mass of the protostar. Methods. The observations were carried out using the IRAM-30 m telescope. Several rotational lines of each isotopologue were detected toward the intermediate-mass protostars, while only CH 3 OD lines were detected in the massive hot cores. The ratio [CH 2 DOH]/[CH 3 OD] (or its upper limit) was computed from both the averaged column densities and directly from line flux ratios.

Astronomy and Astrophysics, 2005

We present a multiwavelength study of five methanol maser sites which are not directly associated with a strong (>100 mJy) radio continuum source: G 31. 28+0.06, G 59.78+0.06, G 173.49+2.42 (S231, S233IR), G 188.95+0.89 (S252,. These radio-quiet methanol maser sites are often interpreted as precursors of ultracompact H  regions or massive protostar sites. In this work, the environment of methanol masers is probed from mid-IR to millimetre wavelengths at angular resolutions of 8 -34 . Spectral energy distribution (SED) diagrams for each site are presented, together with mass and luminosity estimates. Each radio-quiet maser site is always associated with a massive (>50 M ), deeply embedded (A v > 40 mag) and very luminous (>10 4 L ) molecular clump, with L total ∝ M 0.75 gas . These physical properties characterise massive star-forming clumps in earlier evolutionary phases than H  regions. In addition, colder gas clumps seen only at mm-wavelengths are also found near the methanol maser sites. These colder clumps may represent an even earlier phase of massive star formation. These results suggest an evolutionary sequence for massive star formation from a cold clump, seen only at mm wavelengths, evolving to a hot molecular core with a two-component SED with peaks at far-IR and mid-IR wavelengths, to an (ultra-compact) H  region. Alternatively, the cold clumps might be clusters of low-mass YSOs, in formation near the massive star-forming clusters. Finally, the values of the dust grain emissivity index (β) range between 1.6 and 1.9.

2020

Aims. The Seeds Of Life In Space IRAM/NOEMA large program aims at studying a set of crucial complex organic molecules in a sample of sources with a well-known physical structure that covers the various phases of solar-type star formation. One representative object of the transition from the prestellar core to the protostar phases has been observed toward the very low luminosity object (VeLLO) L1521F. This type of source is important to study to link prestellar cores and Class 0 sources and also to constrain the chemical evolution during the process of star formation. Methods. Two frequency windows (81.6-82.6 GHz and 96.65-97.65 GHz) were used to observe the emission from several complex organics toward the L1521F VeLLO. These setups cover transitions of ketene (H 2 CCO), propyne (CH 3 CCH), formamide (NH 2 CHO), methoxy (CH 3 O), methanol (CH 3 OH), dimethyl ether (CH 3 OCH 3), and methyl formate (HCOOCH 3). Results. Only two transitions of methanol (A + , E 2) have been detected in the narrow window centered at 96.7 GHz (with an upper limit on E 1) in a very compact emission blob (∼7 corresponding to ∼1000 au) toward the northeast of the L1521F protostar. The CS 2-1 transition is also detected within the WideX bandwidth. Consistently with what has been found in prestellar cores, the methanol emission appears ∼1000 au away from the dust peak. The location of the methanol blob coincides with one of the filaments that have previously been reported in the literature. The excitation temperature of the gas inferred from methanol is (10 ± 2) K, while the H 2 gas density (estimated from the detected CS 2-1 emission and previous CS 5-4 ALMA observations) is a factor >25 higher than the density in the surrounding environment (n(H 2) ≥ 10 7 cm −3). Conclusions. Based on its compactness, low excitation temperature, and high gas density, we suggest that the methanol emission detected with NOEMA is (i) either a cold and dense shock-induced blob that formed recently (≤ a few hundred years) by infalling gas or (ii) a cold and dense fragment that may just have been formed as a result of the intense gas dynamics within the L1521F VeLLO system.

Astronomy & Astrophysics, 2010

Observations of Serpens have been performed at the JCMT using Harp-B. Maps over a 4.5'x5.4' region were made in a frequency window around 338 GHz, covering the 7-6 transitions of methanol. Emission is extended over each source, following the column density of H2 but showing up also particularly strongly around outflows. The rotational temperature is low, 15-20 K, and does not vary with position within each source. The abundance is typically 10^-9 - 10^-8 with respect to H2 in the outer envelope, whereas "jumps" by factors of up to 10^2 -10^3 inside the region where the dust temperature exceeds 100 K are not excluded. A factor of up to ~ 10^3 enhancement is seen in outflow gas. In one object, SMM4, the ice abundance has been measured to be ~ 3x10^-5 with respect to H2 in the outer envelope, i.e., a factor of 10^3 larger than the gas-phase abundance. Comparison with C18O J=3-2 emission shows that strong CO depletion leads to a high gas-phase abundance of CH3OH not just for the Serpens sources, but for a larger sample of protostars. The observations illustrate the large-scale, low-level desorption of CH3OH from dust grains, extending out to and beyond 7500 AU from each source, a scenario which is consistent with non-thermal (photo-)desorption from the ice. The observations also illustrate the usefulness of CH3OH as a tracer of energetic input in the form of outflows, where methanol is sputtered from the grain surfaces. Finally, the observations provide further evidence of CH3OH formation through CO hydrogenation proceeding on grain surfaces in low-mass envelopes.

Astronomy & Astrophysics, 2011

Context. It has been established that the classical gas-phase production of interstellar methanol (CH 3 OH) cannot explain observed abundances. Instead it is now generally thought that the main formation path has to be by successive hydrogenation of solid CO on interstellar grain surfaces. Aims. While theoretical models and laboratory experiments show that methanol is efficiently formed from CO on cold grains, our aim is to test this scenario by astronomical observations of gas associated with young stellar objects (YSOs). Methods. We have observed the rotational transition quartets J = 2 K-1 K of 12 CH 3 OH and 13 CH 3 OH at 96.7 and 94.4 GHz, respectively, towards a sample of massive YSOs in different stages of evolution. In addition, the J = 1−0 transitions of 12 C 18 O and 13 C 18 O were observed towards some of these sources. We use the 12 C/ 13 C ratio to discriminate between gas-phase and grain surface origin: If methanol is formed from CO on grains, the ratios should be similar in CH 3 OH and CO. If not, the ratio should be higher in CH 3 OH due to 13 C fractionation in cold CO gas. We also estimate the abundance ratios between the nuclear spin types of methanol (E and A). If methanol is formed on grains, this ratio is likely to have been thermalized at the low physical temperature of the grain, and therefore show a relative overabundance of A-methanol. Results. We show that the 12 C/ 13 C isotopic ratio is very similar in gas-phase CH 3 OH and C 18 O, on the spatial scale of about 40 , towards four YSOs. For two of our sources we find an overabundance of A-methanol as compared to E-methanol, corresponding to nuclear spin temperatures of 10 and 16 K. For the remaining five sources, the methanol E/A ratio is less than unity. Conclusions. While the 12 C/ 13 C ratio test is consistent with methanol formation from hydrogenation of CO on grain surfaces, the result of the E/A ratio test is inconclusive.

Astronomy & Astrophysics, 2007

Aims. We characterize the molecular environment of candidate massive young stellar objects (MYSOs) signposted by methanol masers. Methods. Single pixel observations of 10 transitions of HCO + , CO and CS isotopomers were carried out, using the IRAM 30 m telescope. We studied a sample of 28 targets for which the 6.7 GHz maser emission positions are known with a sub-arcsecond accuracy. Results. The systemic velocity inferred from the optically thin lines agrees within ±3 km s −1 with the central velocity of the maser emission for most of the sources. About 64% of the sources show line wings in one or more transitions of CO, HCO + and CS species, indicating the presence of molecular outflows. Comparison of the widths of line wings and methanol maser emission suggests that the 6.7 GHz maser line traces the environment of MYSO of various kinematic regimes. Therefore, conditions conducive for the methanol maser can exist in the inner parts of molecular clouds or circumstellar discs as well as in the outer parts associated with molecular outflows. Calculations of the physical conditions based on the CO and HCO + lines and the CS line intensity ratios refine the input parameters for maser models. Specifically, a gas number density of <10 7 cm −3 is sufficient for strong maser emission and a high methanol fractional abundance (>5 × 10 −7) is required.