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Recent studies of the star formation region BBW 36 and associated molecular clouds are presented. The 12CO (1-0) observations, carried out with the 15-m SEST (Swedish-ESO) telescope (Cerro La Silla, Chile), revealed the existence
of cloud a, connected with BBW 36 and of cloud b, having elongation in SE-NW direction. A red-shifted molecular outflow with
velocity ∼+5 km/s (with respect to cloud a), having a direction parallel to the line of sight, was also observed. VLA observations
showed the presence of a source VLA 2 at 3.6 cm with an elongation in the N-S direction. It is suggested that the VLA 2 source
coincides with a dust disc (surrounding the object BBW 36). The star 3, which is one of the YSOs in the star-forming region
BBW 36 and is connected with a bright comma-like nebula, can be the source of the molecular outflow. The star 3 has very high
IR colors and is associated with an IRAS point source IRAS 07280-1829, which has IR colors, typical for an IRAS point source,
connected with a water maser. On the 2MASS K image of BBW 36 we can see the existence of a bright nebula; a group of stars
is embedded in that nebula, and among these stars there are stars with dust discs (or envelopes). On the 2MASS K image several
spiral jets are also present, some of them with a condensation at the end.
Published in Astrofizika, Vol. 51, No. 3, pp. 469–477 (August 2008). 相似文献
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D. R. Flower J. Le Bourlot G. Pineau des Forêts E. Roueff 《Monthly notices of the Royal Astronomical Society》2000,314(4):753-758
The results of recent quantum mechanical calculations of cross-sections for rotational transitions within the vibrational ground state of HD are used to evaluate the rate of radiative energy loss from gas containing HD, in addition to H, He and H2 . The cooling function for HD (i.e. the rate of cooling per HD molecule) is evaluated in steady state on a grid of values of the relevant parameters of the gas, namely the gas density and temperature, the atomic to molecular hydrogen abundance ratio and the ortho:para-H2 density ratio. The corresponding cooling function for H2 , previously computed by Le Bourlot et al., is slightly revised to take account of transitions induced by collisions with ground-state ortho-H2 ( J =1). The cooling functions and the data required for their calculation are available from http://ccp7.dur.ac.uk/. We then make a study of the rate of cooling of the primordial gas through collisions with H2 and HD molecules. In this case, radiative transitions induced by the cosmic background radiation field and, in the case of H2 , collisional transitions induced by H+ ions should additionally be included. 相似文献
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Helen J. Fraser † Mark P. Collings Martin R. S. McCoustra David A. Williams 《Monthly notices of the Royal Astronomical Society》2001,327(4):1165-1172
Water (H2 O) ice is an important solid constituent of many astrophysical environments. To comprehend the role of such ices in the chemistry and evolution of dense molecular clouds and comets, it is necessary to understand the freeze-out, potential surface reactivity and desorption mechanisms of such molecular systems. Consequently, there is a real need from within the astronomical modelling community for accurate empirical molecular data pertaining to these processes. Here we give the first results of a laboratory programme to provide such data. Measurements of the thermal desorption of H2 O ice, under interstellar conditions, are presented. For ice deposited under conditions that realistically mimic those in a dense molecular cloud, the thermal desorption of thin films (≪50 molecular layers) is found to occur with zeroth-order kinetics characterized by a surface binding energy, E des , of 5773 ± 60 K, and a pre-exponential factor, A , of 1030 ± 2 molecules cm−2 s−1 . These results imply that, in the dense interstellar medium, thermal desorption of H2 O ice will occur at significantly higher temperatures than has previously been assumed. 相似文献
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Alexandre Faure Jonathan Tennyson 《Monthly notices of the Royal Astronomical Society》2001,325(1):443-448
Molecular R -matrix calculations are performed to give rotational excitation rates for electron collisions with linear molecular ions. Results are presented for CO+ , HCO+ , NO+ and H2 + up to electron temperatures of 10 000 K. De-excitation rates and critical electron densities are also given. It is shown that the widely used Coulomb–Born approximation is valid for Δ j =1 transitions when the molecular ion has a dipole greater than about 2D, but otherwise is not reliable for studying electron-impact rotational excitation. In particular, transitions with Δ j >1 are found to have appreciable rates and are found to be entirely dominated by short-range effects. 相似文献
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S. Maret A. Faure E. Scifoni L. Wiesenfeld 《Monthly notices of the Royal Astronomical Society》2009,399(1):425-431
Ammonia inversion lines are often used as probes of the physical conditions in the dense interstellar medium. The excitation temperature between the first two para-metastable (rotational) levels is an excellent probe of the gas kinetic temperature. However, the calibration of this ammonia thermometer depends on the accuracy of the collisional rates with H2 . Here, we present new collisional rates for ortho- and para-NH3 colliding with para-H2 ( J = 0) , and investigate the effects of these new rates on the excitation of ammonia. Scattering calculations employ a new, high-accuracy, potential energy surface computed at the coupled-cluster CCSD(T) level with a basis set extrapolation procedure. Rates are obtained for all transitions involving ammonia levels with J ≤ 3 and for kinetic temperatures in the range 5–100 K. We find that the calibration curve of the ammonia thermometer – which relates the observed excitation temperature between the first two para-metastable levels to the gas kinetic temperature – does not change significantly when these new rates are used. Thus, the calibration of ammonia thermometer appears to be robust. Effects of the new rates on the excitation temperature of inversion and rotation–inversion transitions are also found to be small. 相似文献
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Large molecules in the envelope surrounding IRC+10216 总被引：1，自引：0，他引：1
T. J. Millar E. Herbst R. P. A. Bettens 《Monthly notices of the Royal Astronomical Society》2000,316(1):195-203
A new chemical model of the circumstellar envelope surrounding the carbon-rich star IRC+10216 is developed that includes carbon-containing molecules with up to 23 carbon atoms. The model consists of 3851 reactions involving 407 gas-phase species. Sizeable abundances of a variety of large molecules including carbon clusters, unsaturated hydrocarbons and cyanopolyynes have been calculated. Negative molecular ions of chemical formulae and C n H n H radicals are looked at carefully and compared with interferometric observations. 相似文献
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T.J. Millar J.R. Flores A.J. Markwick 《Monthly notices of the Royal Astronomical Society》2001,327(4):1173-1177
We have updated the chemical model of IRC+10216 developed by Millar, Herbst & Bettens to include recent routes to the formation of sulphuretted hydrocarbons. The routes are based on a quantum chemical study of the S+C2 H system. In addition, we have altered the parent species for sulphur to reflect new observational results. We find that the model calculations give excellent agreement with the observed column densities, and discuss the significance of these reactions to the formation of species as yet unobserved and to dark interstellar clouds. 相似文献
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E. Landi Degl'Innocenti 《Astronomische Nachrichten》2003,324(4):393-396
This contribution is intended to give a brief review of some of the results concerning the Zeeman effect which have been recently published in the literature or which appear to be particularly relevant at the light of recent technological improvements in observations. The arguments emphasized are the Zeeman effect in molecular lines, the asymmetries observed in Stokes profiles from sunspots, and the interpretation of spectropolarimetric observations in the infrared. 相似文献
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