Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userStructure and Physical Conditions in the Huygens Region of the Orion Nebula
100
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
HST images, MUSE maps of emission-lines, and an atlas of high velocity resolution emission-line spectra have been used to establish for the firrst time correlations of the electron temperature, electron density, radial velocity, turbulence, and orientation within the main ionization front of the nebula. From the study of the combined properties of multiple features, it is established that variations in the radial velocity are primarily caused by the photo-evaporating ionization front being viewed at different angles. There is a progressive increase of the electron temperature and density with decreasing distance from the dominant ionizing star Theta1 Ori C. The product of these characteristics (NexTe) is the most relevant parameter in modeling a blister-type nebula like the Huygens Region, where this quantity should vary with the surface brightness in Halpha. Several lines of evidence indicate that small-scale structure and turbulence exists down to the level of our resolution of a few arcseconds. Although photo-evaporative ow must contribute at some level to the well-known non-thermal broadening of the emission lines, comparison of quantitative predictions with the observed optical line widths indicate that it is not the major additive broad- ening component. Derivation of Te values for H+ from radio+optical and optical-only ionized hydro- gen emission showed that this temperature is close to that derived from [Nii] and that the transition from the well-known at extinction curve that applies in the Huygens Region to a more normal steep extinction curve occurs immediately outside of the Bright Bar feature of the nebula.
rate research
Read More
Based on imaging and spectroscopic data, we develop a 3-D model for the Huygens Region of the Orion Nebula. Theta1OriC , the hottest star in the Trapezium, is surrounded by a wind-blown Central Bubble that opens SW into the Extended Orion Nebula. Outside of this feature lies a layer of ionized gas at about 0.4 pc from Theta1OriC. Both of these features are moving rapidly away from Theta1OriC with an expansion age for the Central Bubble of only 15,000 yrs.
We present results of long-slit spectroscopy in several positions of the Orion nebula. Our goal is to study the spatial distribution of a large number of nebular quantities, including line fluxes, physical conditions and ionic abundances at a spatial resolution of about 1. We find that protoplanetary disks (proplyds) show prominent spikes of T([N II]) probably produced by collisional deexcitation due to the high electron densities found in these objects. Herbig-Haro objects show also relatively high T([N II]) but probably produced by local heating due to shocks. We also find that the spatial distribution of pure recombination O II and [O III] lines is fairly similar, in contrast to that observed in planetary nebulae. The abundance discrepancy factor (ADF) of O^{++} remains rather constant along the slit positions, except in some particular small areas of the nebula where this quantity reaches somewhat higher values, in particular at the location of the most conspicuous Herbig-Haro objects: HH 202, HH 203, and HH 204. There is also an apparent slight increase of the ADF in the inner 40 around theta^1 Ori C. We find a negative radial gradient of T([O III]) and T([N II]) in the nebula based on the projected distance from theta^1 Ori C. We explore the behavior of the ADF of O^{++} with respect to other nebular quantities, finding that it seems to increase very slightly with the electron temperature. Finally, we estimate the value of the mean-square electron temperature fluctuation, the so-called t^2 parameter. Our results indicate that the hypothetical thermal inhomogeneities --if they exist-- should be smaller than our spatial resolution element.
The spatial morphology and dynamical status of a young, still-forming stellar cluster provide valuable clues on the conditions during the star formation event and the processes that regulated it. We analyze the Orion Nebula Cluster (ONC), utilizing the latest censuses of its stellar content and membership estimates over a large wavelength range. We determine the center of mass of the ONC, and study the radial dependence of angular substructure. The core appears rounder and smoother than the outskirts, consistent with a higher degree of dynamical processing. At larger distances the departure from circular symmetry is mostly driven by the elongation of the system, with very little additional substructure, indicating a somewhat evolved spatial morphology or an expanding halo. We determine the mass density profile of the cluster, which is well fitted by a power law that is slightly steeper than a singular isothermal sphere. Together with the ISM density, estimated from average stellar extinction, the mass content of the ONC is insufficient by a factor $sim 1.8$ to reproduce the observed velocity dispersion from virialized motions, in agreement with previous assessments that the ONC is moderately supervirial. This may indicate recent gas dispersal. Based on the latest estimates for the age spread in the system and our density profiles, we find that, at the half-mass radius, 90% of the stellar population formed within $sim 5$-$8$ free-fall times ($t_{rm ff}$). This implies a star formation efficiency per $t_{rm ff}$ of $epsilon_{rm ff}sim 0.04$-$0.07$, i.e., relatively slow and inefficient star formation rates during star cluster formation.
We investigate the physical conditions of the CO gas near the young star cluster, Trumpler 14 of the Carina Nebula. The observations presented in this work are taken with the Fourier Transform Spectrometer (FTS) of the Spectral and Photometric Imaging REceiver (SPIRE) onboard the Herschel Space Observatory. Our field of view covers the edge of a cavity carved by Trumpler 14 about $1,mathrm{Myr}$ ago and marks the transition from HII regions to photo-dissociation regions. With the state-of-the-art Meudon PDR code, we successfully derive the physical conditions, which include the thermal pressure ($P$) and the scaling factor of radiation fields ($G_{mathrm{UV}}$), from the observed CO spectral line energy distributions~(SLEDs) in the observed region. The derived $G_{mathrm{UV}}$ values generally show an excellent agreement with the UV radiation fields created by nearby OB-stars and thus confirm that the main excitation source of the observed CO emission are the UV-photons provided by the massive stars. The derived thermal pressure is between $0.5-3,times,10^{8},mathrm{K,cm^{-3}}$ with the highest values found along the ionization front in Car I-E region facing Trumpler 14, hinting that the cloud structure is similar to the recent observations of the Orion Bar. Comparing the derived thermal pressure with the radiation fields, we report the first observationally-derived and spatially-resolved $P sim 2times10^4,G_{mathrm{UV}}$ relationship. As direct comparisons of the modeling results to the observed $^{13}mathrm{CO}$, [OI] $63,mathrm{mu m}$, and [CII] $158,mathrm{mu m}$ intensities are not straightforward, we urge the readers to be cautious when constraining the physical conditions of PDRs with combinations of $^{12}mathrm{CO}$, $^{13}mathrm{CO}$, [CI], [OI] $63,mathrm{mu m}$, and [CII] $158,mathrm{mu m}$ observations.
We have used existing optical emission and absorption lines, [C II] emission lines, and H I absorption lines to create a new model for a Central Column of material near the Trapezium region of the Orion Nebula. This was necessary because recent high spectral resolution spectra of optical emission lines and imaging spectra in the [C II] 158 micron line have shown that there are new velocity systems associated with the foreground Veil and the material lying between Theta 1 Ori C and the Main Ionization Front of the nebula. When a family of models generated with the spectral synthesis code Cloudy were compared with the surface brightness of the emission lines and strengths of the Veil absorption lines seen in the Trapezium stars, distances from Theta 1 Ori C, were derived, with the closest, highest ionization layer being 1.3 pc. The line of sight distance of this layer is comparable with the size of the inner Huygens Region in the plane of the sky. These layers are all blueshifted with respect to the Orion Nebula Cluster of stars, probably because of the pressure of a hot central bubble created by Theta 1 Ori Cs stellar wind. We find velocity components that are ascribed to both sides of this bubble. Our analysis shows that the foreground [C II] 158 micron emission is part of a previously identified layer that forms a portion of a recently discovered expanding shell of material covering most of the larger Extended Orion Nebula.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
