Discovery of interstellar methane - Observations of gaseous and solid CH4 absorption toward young stars in molecular clouds

Lacy, J. H.; Carr, John S.; Evans, Neal J.; Baas, F.; Achtermann, J. M.; Arens, J. F.

doi:10.1086/170304

Cited by 177 publications

(124 citation statements)

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“…Lacy et al 1991;Boogert et al 2004). Öberg et al (2008) detected a 7.7 μm absorption feature, which is attributed to CH 4 , towards 25 sources out of 52 lowmass YSOs.…”

Section: Ch Band At 35 μMmentioning

confidence: 99%

AKARI observations of ice absorption bands towards edge-on young stellar objects

Aikawa

Kamuro

Sakon

et al. 2012

A&A

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Context. Circumstellar disks and envelopes of low-mass young stellar objects (YSOs) contain significant amounts of ice. Such icy material will evolve to become volatile components of planetary systems, such as comets in our solar system. Aims. To investigate the composition and evolution of circumstellar ice around low-mass young stellar objects (YSOs), we observed ice absorption bands in the near infrared (NIR) towards eight YSOs ranging from class 0 to class II, among which seven are associated with edge-on disks. Methods. We performed slit-less spectroscopic observations using the grism mode of the InfraRed Camera (IRC) on board AKARI, which enables us to obtain full NIR spectra from 2.5 μm to 5 μm, including the CO 2 band and the blue wing of the H 2 O band, which are inaccessible from the ground. We developed procedures to carefully process the spectra of targets with nebulosity. The spectra were fitted with polynomial baselines to derive the absorption spectra. The molecular absorption bands were then fitted with the laboratory database of ice absorption bands, considering the instrumental line profile and the spectral resolution of the grism dispersion element. Results. Towards the class 0-I sources (L1527, IRC-L1041-2, and IRAS 04302), absorption bands of H 2 O, CO 2 , CO, and XCN are clearly detected. Column density ratios of CO 2 ice and CO ice relative to H 2 O ice are 21−28% and 13−46%, respectively. If XCN is OCN − , its column density is as high as 2−6% relative to H 2 O ice. The HDO ice feature at 4.1 μm is tentatively detected towards the class 0-I sources and HV Tau. Non-detections of the CH-stretching mode features around 3.5 μm provide upper limits to the CH 3 OH abundance of 26% (L1527) and 42% (IRAS 04302) relative to H 2 O. We tentatively detect OCS ice absorption towards IRC-L1041-2. Towards class 0-I sources, the detected features should mostly originate in the cold envelope, while CO gas and OCN − could originate in the region close to the protostar, where there are warm temperatures and UV radiation. We detect H 2 O ice band towards ASR41 and 2MASSJ 1628137-243139, which are edge-on class II disks. We also detect H 2 O ice and CO 2 ice towards HV Tau, HK Tau, and UY Aur, and tentatively detect CO gas features towards HK Tau and UY Aur.

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“…Lacy et al 1991;Boogert et al 2004). Öberg et al (2008) detected a 7.7 μm absorption feature, which is attributed to CH 4 , towards 25 sources out of 52 lowmass YSOs.…”

Section: Ch Band At 35 μMmentioning

confidence: 99%

AKARI observations of ice absorption bands towards edge-on young stellar objects

Aikawa

Kamuro

Sakon

et al. 2012

A&A

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“…It has been found on the surface of several icy bodies in the Solar System Owen et al 1993;Brown et al 2005;Licandro et al 2006), such as the icy clouds of Jovian planets (Lindal et al 1987;Smith et al 1989), and of Saturn's moon Titan (McKay et al 1997;Griffith et al 1998;Brown et al 2002), and on the surface of Pluto and of Neptune's satellite Triton (Lanzerotti et al 1987). Methane ices have also been found throughout the interstellar medium (Lacy et al 1991;Boogert et al 1996;Gibb et al 2004;Öberg et al 2008). These CH 4 containing icy surfaces are exposed to a flux of energetic ions and photons that induce chemical alterations in the bulk (radiolysis and photolysis) and promote erosion at the surface (sputtering).…”

Section: Introductionmentioning

confidence: 99%

Cosmic ray impact on astrophysical ices: laboratory studies on heavy ion irradiation of methane

Barros

Bordalo

Duarte

et al. 2011

A&A

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Laboratory data of CH 4 ice radiolysis promoted by fast heavy ions are obtained by infrared spectroscopy (FTIR). CH 4 molecules are condensed on a CsI substrate at 15 K, and the ice layer is bombarded by 220 MeV 16 O 7+ ion beam. The ice thickness is thin enough to be traversed by projectiles at constant velocity close to the equilibrium charge state. The induced CH 4 dissociation gives rise to the formation of molecular species CH 3 , C 2 H 2 , C 2 H 4 , C 2 H 6 , and C 3 H 8 . Their formation and dissociation cross sections are determined. C 2 H 6 represent the most abundant daughter molecules. The carbon budget analysis of CH 4 and its radiolysis products shows that the column density of carbon atoms contained in the methane destroyed during ion irradiation is 30−50% greater than the sum for the column densities of the newly formed species. As an astrophysical implication, the current results allow estimation of chemical reaction rates in ices covering interstellar grains.

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“…Indeed, methane is known to be ubiquitous throughout the interstellar medium, where it has been detected in both the gas phase and solid state (Lacy et al 1991). A recent survey of 23 infrared sources, mostly young stellar objects and field stars, carried out by Gibb et al (2004) using the Infrared Space Observatory (ISO) detected methane in interstellar ices via its 4 deformation mode at 7.676 m (1303 cm À1 ).…”

Section: Introductionmentioning

confidence: 99%

Laboratory Studies on the Irradiation of Methane in Interstellar, Cometary, and Solar System Ices

Bennett

Jamieson

Osamura

et al. 2006

ApJ

157

168

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Pure methane ices (CH 4 ) were irradiated at 10 K with energetic electrons to mimic the energy transfer processes that occur in the track of the trajectories of MeV cosmic-ray particles. The experiments were monitored via an FTIR spectrometer (solid state) and a quadrupole mass spectrometer (gas phase). Combined with electronic structure calculations, this paper focuses on the identification of CH x (x ¼ 1Y4) and C 2 H x (x ¼ 2Y6) species and also investigates their formation pathways quantitatively. The primary reaction step is determined to be the cleavage of a carbonhydrogen bond of the methane molecule to form a methyl radical (CH 3 ) plus a hydrogen atom. Hydrogen atoms recombined to form molecular hydrogen, the sole species detected in the gas phase during the irradiation exposure. In the matrix two neighboring methyl radicals can recombine to form an internally excited ethane molecule (C 2 H 6 ), which either can be stabilized by the surrounding matrix or was found to decompose unimolecularly to the ethyl radical (C 2 H 5 ) plus atomic hydrogen and then to the ethylene molecule (C 2 H 4 ) plus molecular hydrogen. The initially synthesized ethane, ethyl, and ethylene molecules can be radiolyzed subsequently by the impinging electrons to yield the vinyl radical (C 2 H 3 ) and acetylene (C 2 H 2 ) as degradation products. Upon warming the ice sample after the irradiation, the new species are released into the gas phase, simulating the sublimation processes interstellar ices undergo during the hot core phase or comets approaching perihelion. Our investigations also aid the understanding of the synthesis of hydrocarbons likely to be formed in the aerosol particles and organic haze layers of hydrocarbon-rich atmospheres of planets and their moons such as Titan.

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Discovery of interstellar methane - Observations of gaseous and solid CH4 absorption toward young stars in molecular clouds

Cited by 177 publications

References 0 publications

AKARI observations of ice absorption bands towards edge-on young stellar objects

AKARI observations of ice absorption bands towards edge-on young stellar objects

Cosmic ray impact on astrophysical ices: laboratory studies on heavy ion irradiation of methane

Laboratory Studies on the Irradiation of Methane in Interstellar, Cometary, and Solar System Ices

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