| 1. |
- Nummelin, Albert, 1968
(författare)
-
Complex Molecules in Star-Forming Regions
- 1998
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Results from spectral-line observations of molecular gas in star-forming regions, performed with the Swedish-ESO Submillimetre Telescope (SEST), are presented. The purpose of this work has been to provide better estimates of the chemical composition as a function of the physical conditions in the sources. The main investigation in this Thesis is a spectral line survey covering the 218.3--263.5 GHz band. Three positions towards the Galactic Centre molecular cloud Sgr B2 were observed. Two of them, Sgr B2(N) and Sgr B2(M), are dense cores where signs of advanced stages of star-formation are present, while the third position, Sgr B2(NW), sample gas in the surrounding cloud. More than 2500 emission lines originating from 42 molecular species were detected. A modified rotation diagram method, which accounts for the line optical depths, was applied in order to determine the rotational temperatures and molecular column densities. For a number of the species, most notably SO and SO2, the size of the emission regions could be estimated by virtue of their well-constrained optical depths. Most species are considerably more excited in the Sgr B2(N) and Sgr B2(M) cores than in Sgr B2(NW), as demonstrated by the detection of, e.g., 114 transitions of C2H3CN in its .ny.11 and .ny.15 vibrational states in Sgr B2(N). The beam-averaged column densities indicate, with a few exceptions, relatively small abundance variations among the three observed positions. However, in those cases where the source size is known, the abundances are considerably higher in Sgr B2(N) and Sgr B2(M), which emphasises the impact of source structure on the abundance estimates. The cores of Sgr B2 have the chemical characteristics of both the Compact Ridge and Hot Core sources in the Orion Molecular Cloud. The high abundance of SO2 in Sgr B2(M) is similar to that in the Orion outflow. By combining data from Haystack Observatory, our SEST survey, and a lower-frequency survey of the same positions carried out at Nobeyama Radio Observatory a rare cyclic molecule, ethylene oxide (c-C2H4O), could be identified in Sgr B2(N) for the first time in the interstellar medium. To verify the identification, a search towards a number of southern molecular clouds was subsequently made. Ethylene oxide and its isomer acetaldehyde (CH3CHO) were detected in four additional sources, NGC 6334F, G327.3-0.6, G31.41+0.31, and G34.3+0.2, all of which are hot cloud cores similar to Sgr B2(N). The abundances of CH3CHO were found to exceed those of c-C2H4O by a factor of 2.6 to 8.5, and the abundances of both species are orders of magnitudes larger than what is predicted by present models of gas-phase chemistry.
|
|
| 2. |
|
|
| 3. |
- Olofsson, Henrik, 1972, et al.
(författare)
-
A spectral line survey of Orion KL in the bands 486-492 and 541-577 GHz with the Odin satellite. I. The observational data
- 2007
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 476:number 2, December III, s. 791-806
-
Tidskriftsartikel (refereegranskat)abstract
- Aims.Spectral line surveys are useful since they allow identification of new molecules and new lines in uniformly calibrated data sets. The subsequent multi-transition analysis will provide improved knowledge of molecular abundances, cloud temperatures and densities, and may also reveal previously unsuspected blends of molecular lines, which otherwise may lead to erroneous conclusions. Nonetheless, large portions of the sub-millimetre spectral regime remain unexplored due to severe absorptions by H2O and O2 in the terrestrial atmosphere. The purpose of the measurements presented here is to cover wavelength regions at and around 0.55 mm - regions largely unobservable from the ground.Methods.Using the Odin astronomy/aeronomy satellite, we performed the first spectral survey of the Orion KL molecular cloud core in the bands 486-492 and 541-576 GHz with rather uniform sensitivity (22-25 mK baseline noise). Odin's 1.1 m size telescope, equipped with four cryo-cooled tuneable mixers connected to broad band spectrometers, was used in a satellite position-switching mode. Two mixers simultaneously observed different 1.1 GHz bands using frequency steps of 0.5 GHz (25 h each). An on-source integration time of 20 h was achieved for most bands. The entire campaign consumed ~1100 orbits, each containing one hour of serviceable astro-observation.Results.We identified 280 spectral lines from 38 known interstellar molecules (including isotopologues) having intensities in the range 80 to 0.05 K. An additional 64 weak lines remain unidentified. Apart from the ground state rotational 11,0-10,1 transitions of ortho-H2O, H218O and H217O, the high energy 62,4-71,7 line of para-H2O (Eu=867$\,$K) and the HDO(20,2-11,1) line have been observed, as well as the 10-01 lines from NH3 and its rare isotopologue 15NH3. We suggest assignments for some unidentified features, notably the new interstellar molecules ND and SH-. Severe blends have been detected in the line wings of the H218O, H217O and 13CO lines changing the true linewidths of the outflow emission.
|
|
| 4. |
- Persson, Carina, 1964, et al.
(författare)
-
A spectral line survey of Orion KL in the bands 486-492 and 541-577 GHz with the Odin satellite. II. Data analysis
- 2007
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 476:2, December III, s. 807-827
-
Tidskriftsartikel (refereegranskat)abstract
- Aims.We investigate the physical and chemical conditions in a typical star forming region, including an unbiased search for new molecules in a spectral region previously unobserved.Methods.Due to its proximity, the Orion KL region offers a unique laboratory of molecular astrophysics in a chemically rich, massive star forming region. Several ground-based spectral line surveys have been made, but due to the absorption by water and oxygen, the terrestrial atmosphere is completely opaque at frequencies around 487 and 557 GHz. To cover these frequencies we used the Odin satellite to perform a spectral line survey in the frequency ranges 486-492 GHz and 541-577 GHz, filling the gaps between previous spectral scans. Odin's high main beam efficiency, $\eta_{{\rm mb}}$ = 0.9, and observations performed outside the atmosphere make our intensity scale very well determined.Results.We observed 280 spectral lines from 38 molecules including isotopologues, and, in addition, 64 unidentified lines. A few U-lines have interesting frequency coincidences such as ND and the anion SH-. The beam-averaged emission is dominated by CO, H2O, SO2, SO, 13CO and CH3OH. Species with the largest number of lines are CH3OH, (CH3)2O, SO2, 13CH3OH, CH3CN and NO. Six water lines are detected including the ground state rotational transition 11,0-10,1 of o-H2O, its isotopologues o-H218O and o-H217O, the Hot Core tracing p-H2O transition 62,4-71,7, and the 20, 2-11,1 transition of HDO. Other lines of special interest are the 10-0$_$ transition of NH3 and its isotopologue 15NH3. Isotopologue abundance ratios of D/H, 12C/13C, 32S/34S, 34S/33S, and 18O/17O are estimated. The temperatures, column densities and abundances in the various subregions are estimated, and we find very high gas-phase abundances of H2O, NH3, SO2, SO, NO, and CH3OH. A comparison with the ice inventory of ISO sheds new light on the origin of the abundant gas-phase molecules.
|
|
| 5. |
- Wirström, Eva, 1977, et al.
(författare)
-
A search for pre-biotic molecules in hot cores
- 2007
-
Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 473, s. 177-180
-
Tidskriftsartikel (refereegranskat)abstract
- Aims. Our aim is to better understand the complex chemistry of organic molecules in the interstellar medium, leading to the formation of pre-biotic molecules such as amino acids.Methods. We have performed a search for the pre-biotic molecules amino acetonitrile (H2N CH2 CN) and vinyl acetylene (C2H3 CCH) towards four northern hot core sources using the Onsala 20 m telescope.Results. We have determined upper limits to the column density of amino acetonitrile (1-4*10^13 cm^-2) and vinyl acetylene (2-7*10^14 cm^-2) in the observed sources. In addition, from the absence of other lines within the observed frequency band, we have further constrained the column density of oxiranecarbonitrile (c-C3H3 NO) and amino-ethanol (NH2 CH2 CH2 OH) in these sources.
|
|
