Non-thermal desorption of complex organic molecules

Dartois, E.; Chabot, M.; Bacmann, A.; Boduch, P.; Domaracka, A.; Rothard, H.

doi:10.1051/0004-6361/201936934

Cited by 16 publications

(12 citation statements)

References 54 publications

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“…Both methanol in the gas phase and the proper IR radiation are two of the major requirements for maser excitation. While cosmic ray sputtering of dust grain mantles can also release methanol to the gas phase (Dartois et al 2020), thermal desorption due to grain heating will be the dominant process near the MYSO. It requires temperatures of at least 94 K (Luna et al 2018) while the maximum desorption rate is reached at about 120-125 K (Collings et al 2004).…”

Section: Methanol Maser Relocationmentioning

confidence: 99%

Infrared observations of the flaring maser source G358.93−0.03

Stecklum

Wolf

Linz

et al. 2021

A&A

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Context. Class II methanol masers are signposts of massive young stellar objects (MYSOs). Recent evidence shows that flares of these masers are driven by MYSO accretion bursts. Thus, maser monitoring can be used to identify such bursts which are hard to discover otherwise. Infrared observations reveal burst-induced changes in the spectral energy distribution (first and foremost a luminosity increase), which provide valuable information on a very intense phase of high-mass star formation. Aims. In mid-January 2019, flaring of the 6.7 GHz CH3OH maser (hereafter maser) of the MYSO G358.93-0.03 (hereafter G358) was reported. The international maser community initiated an extensive observational campaign which revealed extraordinary maser activity and yielded the detection of numerous new masering transitions. Interferometric imaging with the Atacama Large Millimeter/submillimeter Array and the Submillimeter Array resolved the maser emitting core of the star forming region and proved the association of the masers with the brightest continuum source (MM1), which hosts a hot molecular core. These observations, however, failed to detect a significant rise in the (sub)millimeter dust continuum emission. Therefore, we performed near-infrared (NIR) and far-infrared (FIR) observations to prove or disprove whether the CH3OH flare was driven by an accretion burst. Methods. NIR imaging with the Gamma-Ray Burst Optical/Near-infrared Detector has been acquired and integral-field spectroscopy with the Field-Imaging Far-Infrared Line Spectrometer (FIFI-LS) aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) was carried out on two occasions to detect possible counterparts to the (sub)millimeter sources and compare their photometry to archival measurements. The comparison of pre-burst and burst spectral energy distributions is of crucial importance to judge whether a substantial luminosity increase, caused by an accretion burst, is present and if it triggered the maser flare. Radiative transfer modeling of the spectral energy distribution (SED) of the dust continuum emission at multiple epochs provides valuable information on the bursting MYSO. Results. The FIR fluxes of MM1 measured with FIFI-LS exceed those from Herschel significantly, which clearly confirms the presence of an accretion burst. The second epoch data, taken about 16 months later, still show increased fluxes. Our radiative transfer modeling yielded major burst parameters and suggests that the MYSO features a circumstellar disk which might be transient. From the pre-burst, burst, and post-burst SEDs, conclusions on heating and cooling time-scales could be drawn. Circumstances of the burst-induced maser relocation have been explored. Conclusions. The verification of the accretion burst from G358 is another confirmation that Class II methanol maser flares represent an alert for such events. Thus, monitoring of these masers greatly enhances the chances of identifying MYSOs during periods of intense growth. The few events known to date already indicate that there is a broad range in burst strength and duration as well as environmental characteristics. The G358 event is the shortest and least luminous accretion burst known to date. According to models, bursts of this kind occur most often.

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Section: Methanol Maser Relocationmentioning

confidence: 99%

Infrared observations of the flaring maser source G358.93−0.03

Stecklum

Wolf

Linz

et al. 2021

A&A

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“…A sputtering yield of methanol close to that of the main water-ice matrix (Dartois et al 2018), which is ∼10 4 sputtered molecule per incident ion, was estimated for each studied ice. When it was embedded in a CO 2 ice, Dartois et al (2020) found that this sputtering yield is about six times higher. Experimental studies of UV photodesorption in the 7-10.5 eV range were first conducted for pure methanol ice at 20 K by Öberg et al (2009).…”

Section: Introductionmentioning

confidence: 99%

Complex organic molecules in protoplanetary disks: X-ray photodesorption from methanol-containing ices

Basalgète

Dupuy

Féraud

et al. 2021

A&A

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Context. Astrophysical observations show complex organic molecules (COMs) in the gas phase of protoplanetary disks. X-rays emitted from the central young stellar object that irradiate interstellar ices in the disk, followed by the ejection of molecules in the gas phase, are a possible route to explain the abundances observed in the cold regions. This process, known as X-ray photodesorption, needs to be quantified for methanol-containing ices. This Paper I focuses on the case of X-ray photodesorption from pure methanol ices. Aims. We aim at experimentally measuring X-ray photodesorption yields (in molecule desorbed per incident photon, displayed as molecule/photon for more simplicity) of methanol and its photo-products from pure CH3OH ices, and to shed light on the mechanisms responsible for the desorption process. Methods. We irradiated methanol ices at 15 K with X-rays in the 525–570 eV range from the SEXTANTS beam line of the SOLEIL synchrotron facility. The release of species in the gas phase was monitored by quadrupole mass spectrometry, and photodesorption yields were derived. Results. Under our experimental conditions, the CH3OH X-ray photodesorption yield from pure methanol ice is ~10−2 molecule/photon at 564 eV. Photo-products such as CH4, H2CO, H2O, CO2, and CO also desorb at increasing efficiency. X-ray photodesorption of larger COMs, which can be attributed to either ethanol, dimethyl ether, and/or formic acid, is also detected. The physical mechanisms at play are discussed and must likely involve the thermalization of Auger electrons in the ice, thus indicating that its composition plays an important role. Finally, we provide desorption yields applicable to protoplanetary disk environments for astrochemical models. Conclusions. The X-rays are shown to be a potential candidate to explain gas-phase abundances of methanol in disks. However, more relevant desorption yields derived from experiments on mixed ices are mandatory to properly support the role played by X-rays in nonthermal desorption of methanol (see Paper II).

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“…The bombardment of icy mantles by energetic particles such as cosmic rays could already affect the ice structure (e.g. Leger et al 1985;Dartois et al 2020;Ivlev et al 2015) in the pre-stellar phase, while protostellar activity (thermal heating and shocks) may also provide other mechanisms to mix a previously layered icy mantle onto dust grains.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic measurements of CH₃OH in layered and mixed interstellar ice analogues

Müller

Giuliano

Goto

et al. 2021

A&A

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Context. The molecular composition of interstellar ice mantles is defined by gas-grain processes in molecular clouds, with the main components being H2O, CO, and CO2. Methanol (CH3OH) ice is detected towards the denser pre-stellar cores and star-forming regions, where large amounts of CO molecules freeze out and get hydrogenated on top of the icy grains. The thermal heating from nearby protostars can further change the ice structure and composition. Despite the several observations of icy features carried out towards molecular clouds and along the line of site of protostars, it is not yet clear if interstellar ices are mixed or if they have a layered structure. Aims. We aim to examine the effect of mixed and layered ice growth in dust grain mantle analogues, with specific focus on the position and shape of methanol infrared bands, so dedicated future observations could shed light on the structure of interstellar ices in different environments. Methods. Mixed and layered ice samples were deposited on a cold substrate kept at a temperature of 10 K using a closed-cycle cryostat placed in a vacuum chamber. The spectroscopic features were analysed by Fourier transform infrared spectroscopy. Different proportions of the most abundant four molecular species in ice mantles, namely H2O, CO, CO2, and CH3OH, were investigated, with a special attention placed on the analysis of the CH3OH bands. Results. We measure changes in the position and shape of the CH and CO stretching bands of CH3OH depending on the mixed or layered nature of the ice sample. Spectroscopic features of methanol are also found to change due to heating. Conclusions. A layered ice structure best reproduces the CH3OH band position recently observed towards a pre-stellar core and in star-forming regions. Based on our experimental results, we conclude that observations of CH3OH ice features in space can provide information about the structure of interstellar ices, and we expect the James Webb Space Telescope to put stringent constraints on the layered or mixed nature of ices in different interstellar environments, from molecular clouds to pre-stellar cores to protostars and protoplanetary discs.

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Non-thermal desorption of complex organic molecules

Cited by 16 publications

References 54 publications

Infrared observations of the flaring maser source G358.93−0.03

Infrared observations of the flaring maser source G358.93−0.03

Complex organic molecules in protoplanetary disks: X-ray photodesorption from methanol-containing ices

Spectroscopic measurements of CH₃OH in layered and mixed interstellar ice analogues

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Non-thermal desorption of complex organic molecules

Cited by 16 publications

References 54 publications

Infrared observations of the flaring maser source G358.93−0.03

Infrared observations of the flaring maser source G358.93−0.03

Complex organic molecules in protoplanetary disks: X-ray photodesorption from methanol-containing ices

Spectroscopic measurements of CH3OH in layered and mixed interstellar ice analogues

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Spectroscopic measurements of CH₃OH in layered and mixed interstellar ice analogues