We have conducted a full spectral line survey of the 3-13 micron region of two massive protostars, AFGL 2591 and AFGL 2136, for the first time at high spectral resolution. Utilising SOFIA/EXES... Show moreWe have conducted a full spectral line survey of the 3-13 micron region of two massive protostars, AFGL 2591 and AFGL 2136, for the first time at high spectral resolution. Utilising SOFIA/EXES observations, combined with ground based observations from TEXES and iSHELL, many transitions of HCN, C2H2, NH3, CS, CO and H2O are observed, with all species observed to be in absorption. High temperatures (600 K) and abundances (1-10e-6 w.r.t H) of each species are derived. In this thesis, I will present the new insights into the physical conditions and chemical composition of the disks that these absorption lines probe. In particular, hundreds of ro-vibrational transitions of H2O are detected with EXES towards each object, and are linked to a disk wind in AFGL 2591. Column density variations of HCN and C2H2 in bands that probe the same lower level, across different wavelengths, are also discussed, supporting the location of this gas in the circumstellar disk of these protostars. Finally emission lines of HCN are discussed towards MonR2 IRS 3 and are consistent with an origin in a circumstellar disk, or also possibly an expanding shell of gas, supported by P-Cygni profiles of CO lines. Show less
Context. As material from an infalling protostellar envelope hits the forming disk, an accretion shock may develop which could (partially) alter the envelope material entering the disk.... Show moreContext. As material from an infalling protostellar envelope hits the forming disk, an accretion shock may develop which could (partially) alter the envelope material entering the disk. Observations with the Atacama Large Millimeter/submillimeter Array (ALMA) indicate that emission originating from warm SO and SO2 might be good tracers of such accretion shocks.Aims. The goal of this work is to test under what shock conditions the abundances of gas-phase SO and SO2 increase in an accretion shock at the disk-envelope interface.Methods. Detailed shock models including gas dynamics were computed using the Paris-Durham shock code for nonmagnetized J-type accretion shocks in typical inner envelope conditions. The effect of the preshock density, shock velocity, and strength of the ultraviolet (UV) radiation field on the abundance of warm SO and SO2 is explored. Compared with outflows, these shocks involve higher densities (similar to 10(7) cm(-3)), lower shock velocities (similar to few km s(-1)), and large dust grains (similar to 0.2 mu m) and thus probe a different parameter space.Results. Warm gas-phase chemistry is efficient in forming SO under most J-type shock conditions considered. In lower-velocity (similar to 3 km s(-1)) shocks, the abundance of SO is increased through subsequent reactions starting from thermally desorbed CH4 toward H2CO and finally SO. In higher velocity (greater than or similar to 4 km s(-1)) shocks, both SO and SO2 are formed through reactions of OH and atomic S. The strength of the UV radiation field is crucial for SO and in particular SO2 formation through the photodissociation of H2O. Thermal desorption of SO and SO2 ice is only relevant in high-velocity (greater than or similar to 5 km s(-1)) shocks at high densities (greater than or similar to 10(7) cm(-3)). Both the composition in the gas phase, in particular the abundances of atomic S and O, and in ices such as H2S, CH4, SO, and SO2 play a key role in the abundances of SO and SO2 that are reached in the shock.Conclusions. Warm emission from SO and SO2 is a possible tracer of accretion shocks at the disk-envelope interface as long as a local UV field is present. Observations with ALMA at high-angular resolution could provide further constraints given that other key species for the gas-phase formation of SO and SO2, such as H2S and H2CO, are also covered. Moreover, the James Webb Space Telescope will give access to other possible slow, dense shock tracers such as H-2, H2O, and [SI} 25 mu m. Show less
Rivière Marichalar, P.; Fuente, A.; Le Gal, R.; Arabhavi, A.M.; Cazaux, S.M.; Navarro Almaida, D.; ... ; Montesinos, B. 2021
The formation of complex organic molecules that consist of more than four atoms in space is one of the main questions in the field of astrochemistry and star formation. Although the exact formation... Show moreThe formation of complex organic molecules that consist of more than four atoms in space is one of the main questions in the field of astrochemistry and star formation. Although the exact formation mechanisms are not yet known, they are expected to form in thin ice layers on the surfaces of small interstellar dust grains through successive addition of H, C, N or O atoms to CO (carbon monoxide). In this thesis the formation of these molecules is studied in two different ways: simulation of interstellar ices analogues in the laboratory and observations of the same molecules after evaporation toward star forming regions. The laboratory experiments are high and ultra high vacuum setups in which ices of e.g. CO, CO2, HCOOH and CH3CHO are frozen out on an inert surface. The spectroscopy and the thermal behavior of pure and layered ices have been studied. Furthermore, the ices have been bombarded with H-atoms to test reactions schemes relevant for astronomical environments. In the second part of this thesis the same molecules have been observed with the single dish submillimeter telescopes the __James Clerk Maxwell Telescope__ at Hawaii and the Institut de Radioastronomie Millim_trique in Spain toward a sample star forming regions as well as with interferometer the SubMillimeter Array at Hawaii toward two sources. The relative abundances of molecules in different star forming regions measured with the single dish telescopes as well as the spatial extent of the emission detected with the interferometer has been used to determine the chemical relations between complex organics that have also been studied in the laboratory. Show less
