Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userInfrared Observation of Hot Cores
55
0
0.0
(
0
)
Added by
Bringfried Stecklum
Publication date
2001
fields
Physics
and research's language is
English
Authors
B. Stecklum
Ask ChatGPT about the research
No Arabic abstract
We report on mid-infrared imaging of hot cores performed with SpectroCam-10 and TIMMI2. The observations aimed at the detection of thermal emission presumably associated with the hot cores. Mid-infrared flux measurements are required to improve the luminosity and optical depth estimates for these sources. Results are presented for W3(H$_2$O), G9.62+0.19, G10.47+0.03, and the possible hot core candidate G232.620+0.996. They illustrate that the morphology of these sources cannot be described by simple geometries. Therefore, line-of-sight effects and considerable extinction even at mid-infrared wavelengths must not be neglected.
rate research
Read More
We present 1.4-mm BIMA observations with subarcsecond resolution of the bright dust and molecular line emission from hot cores associated with a sample of four ultracompact HII regions: G9.62+0.19, G10.47-0.03, G29.96-0.02, G31.41+0.31. Density power laws can reproduce the observed continuum emission but break down on scales smaller than 2000 AU. A total of 38 transitions from 18 species are detected, with G10.47 and G31.41 showing the greatest number of lines. In particular, these sources display emission from two collisionally-excited transitions of methanol lying more than 950 K above the ground state. Outflows traced by H2S emission provide evidence for embedded exciting sources and the observed morphology of molecular lines is consistent with internal heating of the cores.
The very high rates of second generation star formation detected and inferred in high redshift objects should be accompanied by intense millimetre-wave emission from hot core molecules. We calculate the molecular abundances likely to arise in hot cores associated with massive star formation at high redshift, using several independent models of metallicity in the early Universe. If the number of hot cores exceeds that in the Milky Way Galaxy by a factor of at least one thousand, then a wide range of molecules in high redshift hot cores should have detectable emission. It should be possible to distinguish between independent models for the production of metals and hence hot core molecules should be useful probes of star formation at high redshift.
We present a theoretical study of CS line profiles in archetypal hot cores. We provide estimates of line fluxes from the CS(1-0) to the CS(15-14) transitions and present the temporal variation of these fluxes. We find that textit{i)} the CS(1-0) transition is a better tracer of the Envelope of the hot core whereas the higher-J CS lines trace the ultra-compact core; textit{ii)} the peak temperature of the CS transitions is a good indicator of the temperature inside the hot core; textit{iii)} in the Envelope, the older the hot core the stronger the self-absorption of CS; textit{iv)} the fractional abundance of CS is highest in the innermost parts of the ultra-compact core, confirming the CS molecule as one of the best tracers of very dense gas.
[Abridged] Ethylene oxide and its isomer acetaldehyde are important complex organic molecules because of their potential role in the formation of amino acids. Despite the fact that acetaldehyde is ubiquitous in the interstellar medium, ethylene oxide has not yet been detected in cold sources. We aim to understand the chemistry of the formation and loss of ethylene oxide in hot and cold interstellar objects (i) by including in a revised gas-grain network some recent experimental results on grain surfaces and (ii) by comparison with the chemical behaviour of its isomer, acetaldehyde. We test the code for the case of a hot core. The model allows us to predict the gaseous and solid ethylene oxide abundances during a cooling-down phase prior to star formation and during the subsequent warm-up phase. We can therefore predict at what temperatures ethylene oxide forms on grain surfaces and at what temperature it starts to desorb into the gas phase. The model reproduces the observed gaseous abundances of ethylene oxide and acetaldehyde towards high-mass star-forming regions. In addition, our results show that ethylene oxide may be present in outer and cooler regions of hot cores where its isomer has already been detected. Despite their different chemical structures, the chemistry of ethylene oxide is coupled to that of acetaldehyde, suggesting that acetaldehyde may be used as a tracer for ethylene oxide towards cold cores.
We study the origin of large abundances of complex organic molecules in the Galactic center (GC). We carried out a systematic study of the complex organic molecules CH3OH, C2H5OH, (CH3)2O, HCOOCH3, HCOOH, CH3COOH, H2CO, and CS toward 40 GC molecular clouds. Using the LTE approximation, we derived the physical properties of GC molecular clouds and the abundances of the complex molecules.The CH3OH abundance between clouds varies by nearly two orders of magnitude from 2.4x10^{-8} to 1.1x10^{-6}. The abundance of the other complex organic molecules relative to that of CH3OH is basically independent of the CH3OH abundance, with variations of only a factor 4-8. The abundances of complex organic molecules in the GC are compared with those measured in hot cores and hot corinos, in which these complex molecules are also abundant. We find that both the abundance and the abundance ratios of the complex molecules relative to CH3OH in hot cores are similar to those found in the GC clouds. However, hot corinos show different abundance ratios than observed in hot cores and in GC clouds. The rather constant abundance of all the complex molecules relative to CH3OH suggests that all complex molecules are ejected from grain mantles by shocks. Frequent (similar 10^{5}years) shocks with velocities >6km/s are required to explain the high abundances in gas phase of complex organic molecules in the GC molecular clouds. The rather uniform abundance ratios in the GC clouds and in Galactic hot cores indicate a similar average composition of grain mantles in both kinds of regions. The Sickle and the Thermal Radio Arches, affected by UV radiation, show different relative abundances in the complex organic molecules due to the differentially photodissociation of these molecules.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
