Hydrocarbons in Massive Star Forming Regions: C2H Observations

AbstractIn order to better understand the chemical conditions and evolutionary properties of massive star-forming regions, and to explore the physical and chemical behavior of simple hydrocarbon molecules, we have used telescopes such as CSO, JCMT, CARMA and SMA, to map the multi-transitions of C2H and HC3N. The column densities and abundances are compared with chemical models to gain some diagnostic of the environment of the regions.

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Nitrogen bearing species in massive star forming regions

Proceedings of the International Astronomical Union ◽

10.1017/s174392131900958x ◽

2019 ◽

Vol 15 (S350) ◽

pp. 71-74

Author(s):

Zainab Awad ◽

Osama M. Shalabiea

Keyword(s):

Spatial Distribution ◽

Surface Chemistry ◽

Massive Star ◽

Nitrogen Species ◽

Star Forming ◽

Star Forming Regions ◽

Chemical Models ◽

Temperature Regimes

AbstractRecent observations revealed that there is a difference in the spatial distribution of both nitrogen and oxygen bearing species towards massive star forming regions. These differences can be explained under different temperature regimes in hot cores. In this study, we attempt to model the chemistry of few nitrogen species; namely, vinyl cyanide (CH2CHCN), ethyl cyanide (CH3CH2CN), and formamide (NH2CHO), using gas-grain chemical models. A special attention is given to the role and efficiency of surface chemistry as it is suggested to play one of the main key roles in manufacturing these species.

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Physicochemical models: source-tailored or generic?

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2443 ◽

2020 ◽

Vol 498 (1) ◽

pp. 276-291

Author(s):

Beatrice M Kulterer ◽

Maria N Drozdovskaya ◽

Audrey Coutens ◽

Sébastien Manigand ◽

Gwendoline Stéphan

Keyword(s):

Chemical Model ◽

Star Forming ◽

Physical Conditions ◽

Generic Models ◽

Physicochemical Models ◽

Star Forming Regions ◽

Chemical Models ◽

Molecular Abundances ◽

Physical And Chemical ◽

The Impact

ABSTRACT Physicochemical models can be powerful tools to trace the chemical evolution of a protostellar system and allow to constrain its physical conditions at formation. The aim of this work is to assess whether source-tailored modelling is needed to explain the observed molecular abundances around young, low-mass protostars or if, and to what extent, generic models can improve our understanding of the chemistry in the earliest stages of star formation. The physical conditions and the abundances of simple, most abundant molecules based on three models are compared. After establishing the discrepancies between the calculated chemical output, the calculations are redone with the same chemical model for all three sets of physical input parameters. With the differences arising from the chemical models eliminated, the output is compared based on the influence of the physical model. Results suggest that the impact of the chemical model is small compared to the influence of the physical conditions, with considered time-scales having the most drastic effect. Source-tailored models may be simpler by design; however, likely do not sufficiently constrain the physical and chemical parameters within the global picture of star-forming regions. Generic models with more comprehensive physics may not provide the optimal match to observations of a particular protostellar system, but allow a source to be studied in perspective of other star-forming regions.

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Using H 3 + and H 2 D + as probes of star-forming regions

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2006.1879 ◽

2006 ◽

Vol 364 (1848) ◽

pp. 3101-3106 ◽

Cited By ~ 8

Author(s):

Floris F.S van der Tak

Keyword(s):

Cosmic Ray ◽

Ionization Rate ◽

High Mass ◽

Mass Star ◽

Future Prospects ◽

Star Forming ◽

Star Forming Regions ◽

Chemical Conditions ◽

Physical And Chemical ◽

Kinematic Properties

The and H 2 D + ions are important probes of the physical and chemical conditions in regions of the interstellar medium where new stars are forming. This paper reviews how observations of these species and of heavier ions such as HCO + and H 3 O + can be used to derive chemical and kinematic properties of nearby pre-stellar cores and the cosmic ray ionization rate towards more distant regions of high-mass star formation. Future prospects in the field are outlined at the end.

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Methanol and glycolaldehyde production from formaldehyde in massive star-forming regions

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2244 ◽

2020 ◽

Vol 497 (4) ◽

pp. 4486-4494 ◽

Cited By ~ 1

Author(s):

Silvia G S Silva ◽

Rafael M Vichietti ◽

Roberto L A Haiduke ◽

Francisco B C Machado ◽

Rene F K Spada

Keyword(s):

Chemical Kinetic ◽

Time Interval ◽

Gas Phase Reactions ◽

Star Forming ◽

Star Forming Regions ◽

Electronic Structure Methods ◽

Chemical Conditions ◽

Kinetic Calculations ◽

High Level ◽

Physical And Chemical

ABSTRACT Based on typical physical and chemical conditions expected in massive and dense hot cores during the protostar collapse, the formation of glycolaldehyde (CH2OHCHO) and methanol (CH3OH) was investigated from H2 and CO and formaldehyde (H2CO) as an intermediate. Thermochemical properties and rate constants were obtained for gas-phase reactions using high-level electronic structure methods and chemical kinetic calculations, and the concentrations of the molecules were evolved along time. The chemical equilibrium was reached in minutes at 1500 K, a time interval much shorter than that required time for a protostar formation process. The results indicate that the formaldehyde and methanol abundances are always larger than those for glycolaldehyde, for example, at 2000 K and [H2]0 equals to 1023 molecule cm−3, the abundances of H2CO, CH3OH, and CH2OHCHO relative to H2 are equal to 3 × 10−6, 5 × 10−6, and 1 × 10−12, while for [H2]0 equals to 1020 molecule cm−3 these abundances are 3 × 10−9, 5 × 10−12, and 2 × 10−21, respectively. Considering that our results can be applied to explain the proximity of methanol and formaldehyde maser emissions, from the whole set of results, the CH3OH abundance relative to H2CO ranges from 10−3 to 102.

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The Circumstellar Environment of Embedded Massive Stars

Highlights of Astronomy ◽

10.1017/s1539299600013083 ◽

2002 ◽

Vol 12 ◽

pp. 143-145 ◽

Cited By ~ 1

Author(s):

Lee G. Mundy ◽

Friedrich Wyrowski ◽

Sarah Watt

Keyword(s):

Massive Star ◽

Massive Stars ◽

Low Mass Stars ◽

Submillimeter Wavelength ◽

Star Forming ◽

Star Forming Regions ◽

Low Mass ◽

Circumstellar Environments ◽

Near Future

Millimeter and submillimeter wavelength images of massive star-forming regions are uncovering the natal material distribution and revealing the complexities of their circumstellar environments on size scales from parsecs to 100’s of AU. Progress in these areas has been slower than for low-mass stars because massive stars are more distant, and because they are gregarious siblings with different evolutionary stages that can co-exist even within a core. Nevertheless, observational goals for the near future include the characterization of an early evolutionary sequence for massive stars, determination if the accretion process and formation sequence for massive stars is similar to that of low-mass stars, and understanding of the role of triggering events in massive star formation.

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Millimetre wavelength methanol masers survey towards massive star forming regions

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307013051 ◽

2007 ◽

Vol 3 (S242) ◽

pp. 234-235

Author(s):

T. Umemoto ◽

N. Mochizuki ◽

K. M. Shibata ◽

D.-G. Roh ◽

H.-S. Chung

Keyword(s):

Detection Rate ◽

Massive Star ◽

Molecular Line ◽

Maser Emission ◽

Star Forming ◽

Methanol Maser ◽

Physical Conditions ◽

Star Forming Regions ◽

Methanol Masers ◽

Maser Sources

AbstractWe present the results of a mm wavelength methanol maser survey towards massive star forming regions. We have carried out Class II methanol maser observations at 86.6 GHz, 86.9 GHz and 107.0 GHz, simultaneously, using the Nobeyama 45 m telescope. We selected 108 6.7 GHz methanol maser sources with declinations above −25 degrees and fluxes above 20 Jy. The detection limit of maser observations was ~3 Jy. Of the 93 sources surveyed so far, we detected methanol emission in 25 sources (27%) and “maser” emission in nine sources (10%), of which thre “maser” sources are new detections. The detection rate for maser emission is about half that of a survey of the southern sky (Caswell et al. 2000). There is a correlation between the maser flux of 107 GHz and 6.7 GHz/12 GHz emission, but no correlation with the “thermal” (non maser) emission. From results of other molecular line observations, we found that the sources with methanol emission show higher gas temperatures and twice the detection rate of SiO emission. This may suggest that dust evaporation and destruction by shock are responsible for the high abundance of methanol molecules, one of the required physical conditions for maser emission.

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