اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدHerschel observations of the Herbig-Haro objects HH52-54
104
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We are aiming at the observational estimation of the relative contribution to the cooling by CO and H2O, as this provides decisive information for the understanding of the oxygen chemistry behind interstellar shock waves. Methods. The high sensitivity of HIFI, in combination with its high spectral resolution capability, allows us to trace the H2O outflow wings at unprecedented signal-to-noise. From the observation of spectrally resolved H2O and CO lines in the HH52-54 system, both from space and from ground, we arrive at the spatial and velocity distribution of the molecular outflow gas. Solving the statistical equilibrium and non-LTE radiative transfer equations provides us with estimates of the physical parameters of this gas, including the cooling rate ratios of the species. The radiative transfer is based on an ALI code, where we use the fact that variable shock strengths, distributed along the front, are naturally implied by a curved surface. Based on observations of CO and H2O spectral lines, we conclude that the emission is confined to the HH54 region. The quantitative analysis of our observations favours a ratio of the CO-to-H2O-cooling-rate >> 1. From the best-fit model to the CO emission, we arrive at an H2O abundance close to 1e-5. The line profiles exhibit two components, one of which is triangular and another, which is a superposed, additional feature. This additional feature likely originates from a region smaller than the beam where the ortho-water abundance is smaller than in the quiescent gas. Comparison with recent shock models indicate that a planar shock can not easily explain the observed line strengths and triangular line profiles.We conclude that the geometry can play an important role. Although abundances support a scenario where J-type shocks are present, higher cooling rate ratios than predicted by these type of shocks are derived.
قيم البحث
اقرأ أيضاً
Herbig-Haro objects are regions of shocked gas and dust which are produced when collimated outflows from a protostar interact with the surrounding dense gas. They have many similarities to supernova remnants which are interacting with molecular cloud
s. 1720-MHz OH masers have been identified towards a number of interacting supernova remnants. Observations and models indicate that these masers are shock excited and are produced behind C-type shocks. If conditions behind the shock fronts of Herbig-Haro objects are similarly able to support 1720-MHz OH masers they could be a useful diagnostic tool for star formation. We therefore searched for 1720-MHz OH maser emission towards a sample of 97 Herbig-Haro objects using the Green Bank radio telescope. We detected 1720-MHz OH lines in emission in 17 of them, but neither their spectral signature nor follow-up observations with the Very Large Array showed any conclusive evidence of maser emission. We conclude that the emission detected from our single-dish observations must be extended and most likely originates from thermal or quasi-thermal excitation processes. We also investigated the properties of Herbig-Haro shocks more closely and conclude that despite the overall similarities to supernova remnants, the conditions required for maser emission, in particular, a sufficient velocity-coherent column density, are not likely to occur in Herbig-Haro objects.
We present results of the narrow-band Halpha and [SII] imaging survey of Mon R1 association, performed with the 1 m Schmidt telescope of the Byurakan Observatory. Our observations covered one degree field near the center of the association. As a resu
lt of this study twenty new Herbig-Haro knots were discovered, some of which form collimated outflows. Among the most extended ones are HH 1203 and HH 1196, which have a length near one parsec or even more. In the course of search for the probable sources of HH objects several new nebulous stars were found. A list of all nebulous stellar objects in the Mon R1 area under study is presented, with the detailed description of most interesting objects. The near infrared data from the GLIMPSE360 and WISE surveys allowed to find several more objects, related to Mon R1, some of them with optical counterparts, as well as to outline at least three probable H_2 collimated flows from the deeply embedded pre-main-sequence objects. The probable members of Mon R1 were selected by their distances, their bolometric luminosities and extinctions were estimated. Among the outflow sources three embedded objects with luminosities greater than 10 L(sun) were found. The mean distance to Mon R1 complex is estimated as 715 pc.
We analyze the physical conditions, chemical composition and other properties of the photoionized Herbig-Haro object HH~204 through Very Large Telescope (VLT) echelle spectroscopy and Hubble Space Telescope (textit{HST}) imaging. We kinematically iso
late the high-velocity emission of HH~204 from the emission of the background nebula and study the sub-arcsecond distribution of physical conditions and ionic abundances across the HH object. We find that low and intermediate-ionization emission arises exclusively from gas at photoionization equilibrium temperatures, whereas the weak high-ionization emission from HH~204 shows a significant contribution from higher temperature shock-excited gas. We derive separately the ionic abundances of HH~204, the emission of the Orion Nebula and the fainter Diffuse Blue Layer.In HH~204, the O$^{+}$ abundance determined from Collisional Excited Lines (CELs) matches the one based on Recombination Lines (RLs), while the O$^{2+}$ abundance is very low, so that the oxygen abundance discrepancy is zero. The ionic abundances of Ni and Fe in HH~204 have similar ionization and depletion patterns, with total abundances that are a factor of 3.5 higher than in the rest of the Orion Nebula due to dust destruction in the bowshock. We show that a failure to resolve the kinematic components in our spectra would lead to significant error in the determination of chemical abundances (for instance, 40% underestimate of O), mainly due to incorrect estimation of the electron density.
Herbig-Haro objects (HHOs) are caused by outflows from young objects. Since the outflow relies on mass accretion from a circumstellar disk, it indicates ongoing growth. Recent results of infrared observations yielded evidence for disks around brown d
warfs. This suggests that at least a certain fraction of brown dwarfs forms like stars. Thus, young sub-stellar objects might cause HHOs as well. We present selected results of a general survey for HHOs based on DSS-II plates and CCD images taken with the Tautenburg Schmidt telescope. Numerous young objects could be identified due to their association with newly detected HHOs. In some cases the luminosity is consistent with very low-mass stars or close to sub-stellar values. This holds for L1415-IRS and a few infrared sources embedded in other dark clouds (e.g., GF9, BHR111). The question on the minimum mass for outflow activity is addressed.
We present the analysis of physical conditions, chemical composition and kinematic properties of two bow shocks -HH529 II and HH529 III- of the fully photoionized Herbig-Haro object HH 529 in the Orion Nebula. The data were obtained with the Ultravio
let and Visual Echelle Spectrograph at the 8.2m Very Large Telescope and 20 years of Hubble Space Telescope imaging. We separate the emission of the high-velocity components of HH529 II and III from the nebular one, determining $n_{rm e}$ and $T_{rm e}$ in all components through multiple diagnostics, including some based on recombination lines (RLs). We derive ionic abundances of several ions, based on collisionally excited lines (CELs) and RLs. We find a good agreement between the predictions of the temperature fluctuation paradigm ($t^2$) and the abundance discrepancy factor (ADF) in the main emission of the Orion Nebula. However, $t^2$ can not account for the higher ADF found in HH 529 II and III. We estimate a 6% of Fe in the gas-phase of the Orion Nebula, while this value increases to 14% in HH 529 II and between 10% and 25% in HH 529 III. We find that such increase is probably due to the destruction of dust grains in the bow shocks. We find an overabundance of C, O, Ne, S, Cl and Ar of about 0.1 dex in HH 529 II-III that might be related to the inclusion of H-deficient material from the source of the HH 529 flow. We determine the proper motions of HH 529 finding multiple discrete features. We estimate a flow angle with respect to the sky plane of $58pm 4^{circ}$ for HH 529.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
