Dependence of Gas-Phase Abundances in the Interstellar Medium on Column Density

2000 ◽  
Vol 544 (2) ◽  
pp. L107-L110 ◽  
Author(s):  
B. P. Wakker ◽  
J. S. Mathis
Keyword(s):  
Interstellar Medium ◽  
Gas Phase ◽  
Column Density

scholarly journals The ALMA-PILS survey: First detection of nitrous acid (HONO) in the interstellar medium

2019 ◽  
Vol 623 ◽  
pp. L13 ◽  
Author(s):  
A. Coutens ◽  
N. F. W. Ligterink ◽  
J.-C. Loison ◽  
V. Wakelam ◽  
H. Calcutt ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Gas Phase ◽  
Nitrous Acid ◽  
Column Density ◽  
Local Thermodynamic Equilibrium ◽  
Excitation Temperature ◽  
Complex Species ◽  
Low Mass ◽  
Chemical Code ◽  
Thermodynamic Equilibrium Model

Nitrogen oxides are thought to play a significant role as a nitrogen reservoir and to potentially participate in the formation of more complex species. Until now, only NO, N2O, and HNO have been detected in the interstellar medium. We report the first interstellar detection of nitrous acid (HONO). Twelve lines were identified towards component B of the low-mass protostellar binary IRAS 16293–2422 with the Atacama Large Millimeter/submillimeter Array, at the position where NO and N2O have previously been seen. A local thermodynamic equilibrium model was used to derive the column density (∼9 × 1014 cm−2 in a 0 .″5 beam) and excitation temperature (∼100 K) of this molecule. HNO, NO2, NO+, and HNO3 were also searched for in the data, but not detected. We simulated the HONO formation using an updated version of the chemical code Nautilus and compared the results with the observations. The chemical model is able to reproduce satisfactorily the HONO, N2O, and NO2 abundances, but not the NO, HNO, and NH2OH abundances. This could be due to some thermal desorption mechanisms being destructive and therefore limiting the amount of HNO and NH2OH present in the gas phase. Other options are UV photodestruction of these species in ices or missing reactions potentially relevant at protostellar temperatures.

scholarly journals Abundances in the Gaseous Galactic Halo

1998 ◽  
Vol 11 (1) ◽  
pp. 86-89
Author(s):  
Ulysses J. Sofia
Keyword(s):  
Interstellar Medium ◽  
Gas Phase ◽  
High Velocity ◽  
Galactic Halo ◽  
Solar Neighborhood ◽  
Local Interstellar Medium ◽  
The Galaxy ◽  
Metal Abundances ◽  
High Velocity Clouds

Abstract The well measured gas-phase abundances in the low halo suggest that this region of the Galaxy has total (gas plus dust) metal abundances which are close to those in the solar neighborhood. The gas-phase abundances in the halo are generally higher than those seen in the disk, however, this affect is likely due to the destruction of dust in the halo clouds. Observations of high velocity clouds (HVCs) in the halo suggest that these clouds have metal abundances which are substantially lower than those measured for the local interstellar medium. These determinations, however, are often of lower quality than those for the low halo because of uncertainties in the hydrogen abundances along the sightlines, in the incorporation of elements into dust, and in the partial ionization of the clouds.

The HRS GTO program to study the neutral hydrogen column density and D/H ratio in the local interstellar medium

1986 ◽  
Vol 6 (2) ◽  
pp. 91-94
Author(s):  
J.L. Linsky, ◽  
W.B. Landsman ◽  
B.D. Savage ◽  
S.R. Heap ◽  
A.M. Smith ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Column Density ◽  
Neutral Hydrogen ◽  
Local Interstellar Medium ◽  
Hydrogen Column Density

scholarly journals SOME INSIGHTS INTO FORMAMIDE FORMATION THROUGH GAS-PHASE REACTIONS IN THE INTERSTELLAR MEDIUM

2013 ◽  
Vol 780 (2) ◽  
pp. 181 ◽  
Author(s):  
Pilar Redondo ◽  
Carmen Barrientos ◽  
Antonio Largo
Keyword(s):  
Interstellar Medium ◽  
Gas Phase ◽  
Gas Phase Reactions

scholarly journals Dark dust and single-cloud sightlines in the ISM

2020 ◽  
Vol 641 ◽  
pp. A35
Author(s):  
R. Siebenmorgen ◽  
J. Krełowski ◽  
J. Smoker ◽  
G. Galazutdinov ◽  
S. Bagnulo
Keyword(s):  
Interstellar Medium ◽  
Spectral Type ◽  
Column Density ◽  
Resolving Power ◽  
High Resolution Spectroscopy ◽  
Luminosity Distance ◽  
Ob Stars ◽  
Dust Extinction ◽  
Heating Source ◽  
Dust Component

The precise characteristics of clouds and the nature of dust in the diffuse interstellar medium can only be extracted by inspecting the rare cases of single-cloud sightlines. In our nomenclature such objects are identified by interstellar lines, such as K I, that show at a resolving power of λ∕Δλ ~ 75 000 one dominating Doppler component that accounts for more than half of the observed column density. We searched for such sightlines using high-resolution spectroscopy towards reddened OB stars for which far-UV extinction curves are known. We compiled a sample of 186 spectra, 100 of which were obtained specifically for this project with UVES. In our sample we identified 65 single-cloud sightlines, about half of which were previously unknown. We used the CH/CH+ line ratio of our targets to establish whether the sightlines are dominated by warm or cold clouds. We found that CN is detected in all cold (CH/CH+ > 1) clouds, but is frequently absent in warm clouds. We inspected the WISE (3−22 μm) observed emission morphology around our sightlines and excluded a circumstellar nature for the observed dust extinction. We found that most sightlines are dominated by cold clouds that are located far away from the heating source. For 132 stars, we derived the spectral type and the associated spectral type-luminosity distance. We also applied the interstellar Ca II distance scale, and compared these two distance estimates with Gaia parallaxes. These distance estimates scatter by ~40%. By comparing spectral type-luminosity distances with those of Gaia, we detected a hidden dust component that amounts to a few mag of extinction for eight sightlines. This dark dust is populated by ≳ 1 μm large grains and predominately appears in the field of the cold interstellar medium.

Computational UV Spectra for Amorphous Solids of Small Molecules

2021 ◽  
Author(s):  
Austin Michael Wallace ◽  
Ryan C. Fortenberry
Keyword(s):  
Carbon Dioxide ◽  
Interstellar Medium ◽  
Small Molecules ◽  
Gas Phase ◽  
Amorphous Solids ◽  
Uv Spectra ◽  
Ammonia Water ◽  
Gas Phase Molecules ◽  
High Level

Ices in the interstellar medium largely exist as amorphous solids composed of small molecules including ammonia, water, and carbon dioxide. Describing gas-phase molecules can be readily accomplished with current high-level...

scholarly journals The Absorption Line Systems of the Supershell LMC2 in the Large Magellanic Cloud

1999 ◽  
Vol 190 ◽  
pp. 154-155
Author(s):  
Adeline Caulet
Keyword(s):  
Optical Absorption ◽  
Interstellar Medium ◽  
Gas Phase ◽  
Absorption Line ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Absorption Lines

The interstellar medium of LMC2, a well studied supershell in the Large Magellanic Cloud, has been probed in UV and optical absorption lines. The data allow to derive the kinematics, abundances and depletions of gas clouds in this supershell. The relative gas-phase abundances of observed elements with respect to sulphur are useful to determine the origins of the supershell absorption-line clouds.

Quantum chemical study on the formation of isopropyl cyanide and its linear isomer in the interstellar medium

2020 ◽  
pp. 1-11
Author(s):  
Keshav Kumar Singh ◽  
Poonam Tandon ◽  
Alka Misra ◽  
Shivani ◽  
Manisha Yadav ◽  
...  
Keyword(s):  
Amino Acids ◽  
Interstellar Medium ◽  
Gas Phase ◽  
Quantum Chemical ◽  
Density Functional ◽  
Quantum Chemical Study ◽  
Chemical Study ◽  
Dark Cloud ◽  
Water Ice ◽  
Hydrocarbon Radicals

Abstract The formation mechanism of linear and isopropyl cyanide (hereafter n-PrCN and i-PrCN, respectively) in the interstellar medium (ISM) has been proposed from the reaction between some previously detected small cyanides/cyanide radicals and hydrocarbons/hydrocarbon radicals. n-PrCN and i-PrCN are nitriles therefore, they can be precursors of amino acids via Strecker synthesis. The chemistry of i-PrCN is especially important since it is the first and only branched molecule in ISM, hence, it could be a precursor of branched amino acids such as leucine, isoleucine, etc. Therefore, both n-PrCN and i-PrCN have significant astrobiological importance. To study the formation of n-PrCN and i-PrCN in ISM, quantum chemical calculations have been performed using density functional theory at the MP2/6-311++G(2d,p)//M062X/6-311+G(2d,p) level. All the proposed reactions have been studied in the gas phase and the interstellar water ice. It is found that reactions of small cyanide with hydrocarbon radicals result in the formation of either large cyanide radicals or ethyl and vinyl cyanide, both of which are very important prebiotic interstellar species. They subsequently react with the radicals CH2 and CH3 to yield n-PrCN and i-PrCN. The proposed reactions are efficient in the hot cores of SgrB2 (N) (where both n-PrCN and i-PrCN were detected) due to either being barrierless or due to the presence of a permeable entrance barrier. However, the formation of n-PrCN and i-PrCN from the ethyl and vinyl cyanide always has an entrance barrier impermeable in the dark cloud; therefore, our proposed pathways are inefficient in the deep regions of molecular clouds. It is also observed that ethyl and vinyl cyanide serve as direct precursors to n-PrCN and i-PrCN and their abundance in ISM is directly related to the abundance of both isomers of propyl cyanide in ISM. In all the cases, reactions in the ice have smaller barriers compared to their gas-phase counterparts.

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