The optical spectra of atomic/ionic mixing layers in outflows from young stars
نویسندگان
چکیده
It has been previously suggested on kinematical grounds that at least part of the emission from Herbig-Haro (HH) objects might be produced in turbulent mixing layers associated with high velocity outflows. In order to explore this possibility, we compute 1D models of the temperature and ionization cross sections of mixing layers between a high velocity flow and a stationary environment (both the jet beam and the environment being atomic). The mixing layer models are very simple from the dynamical point of view (being based on a “turbulent viscosity” approach), but include a detailed treatment of the relevant atomic/ionic processes and radiative cooling for the 8 most important elements (H, He, C, N, O, Ne, S, Fe). In this way, we produce a grid of 1D models with three free parameters: the velocity of the jet, the local width of the mixing layer h, and the environment pressure Penv . These models are to some extent comparable to a family of plane-parallel, steady shock models computed for different pre-shock velocities and densities. We find that the temperature cross-section changes from parabolic to flat-topped as the layer width increases, as predicted by earlier analytical results. The ionization fraction does not show this behavior and is always strongly out of coronal equilibrium, because of turbulent diffusion of neutral gas from the jet and external medium into the layer. Above a minimum jet velocity, we find that the predicted temperature and optical spectra of the mixing-layer depend mostly on the combination hPenv/(αv j ) ≡ Σ [where α (' 0.007) is the adopted turbulent viscosity parameter and vj the velocity of the jet]. This contrasts with shock models, where line ratios are strongly dependent upon the shock velocity. The [O I]6300/Hα ratio predicted by mixing-layer models appears too high by a factor of two compared with the line ratios of lowexcitation HH objects. However, it may be compatible with line ratios in the intermediate velocity component of T Tauri jets, which have been suggested to trace jet mixing layers.
منابع مشابه
Effect of the temperature profile of the accretion disk on the structure of jets and outflows around protostars
Magnetic fields play an important role in creating, driving, and in the evolution of outflows and jets from protostars and accretion disks. On the other hand, the temperature profile of the accretion disks may also affect the structure of the magnetic field and outflows. In this paper, we use the self-similar method in cylindrical coordinates to investigate the effect of the temperature profile...
متن کاملPulsating red giant and supergiant stars in the Local Group dwarf galaxy Andromeda I
We have conducted an optical long-term monitoring survey of the majority of dwarf galaxies in the Local Group, with the Isaac Newton Telescope (INT), to identify the long period variable (LPV) stars. LPV stars vary on timescales of months to years, and reach the largest amplitudes of their brightness variations at optical wavelengths, due to the changing temperature. They trace stellar populati...
متن کاملChemical Evolution of the Circumstellar Envelopes of Carbon-rich Post-agb Objects
We have observed with the 30-m IRAM telescope, the CSO telescope and the ISO satellite (Infrared Space Observatory) the rotational lines of CO at millimeter, submillimeter and far infrared wavelengths in the direction of C-rich stellar objects at different stages of evolution : CRL 2688 (a very young Proto-Planetary Nebula), CRL 618 (a Proto-Planetary Nebula), and NGC 7027 (a young Planetary Ne...
متن کاملHighly Collimated Jets and Wide-angle Outflows in Hh 46/47: New Evidence from Spitzer Infrared Images
We present new details of the structure and morphology of the jets and outflows in HH 46/47 as seen in Spitzer infrared images from IRAC and MIPS, reprocessed using the “HiRes” deconvolution technique. HiRes improves the visualization of spatial morphology by enhancing resolution (to subarcsecond levels in IRAC bands) and removing the contaminating side lobes from bright sources. In addition to...
متن کاملEffects of particles size distribution and occupied area of CdS photosensitizer on photovoltaic performance
Cadmium sulfide (CdS) photosensitizers were successfully formed on the mesoporous titania films using the successive ionic layer adsorption and reaction (SILAR) method in five cycles, and the effects of particles size distribution and their occupied surface area on the morphology, topography, optical property, and photovoltaic performance were investigated. Scanning electron microscope (SEM) im...
متن کامل