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1.
C. Codella R. Bachiller M. Benedettini P. Caselli 《Monthly notices of the Royal Astronomical Society》2003,341(2):707-716
The Cepheus A star-forming region has been investigated through a multiline H2 S and SO2 survey at millimetre wavelengths. Large-scale maps and high-resolution line profiles reveal the occurrence of several outflows. Cep A East is associated with multiple mass-loss processes: in particular, we detect a 0.6-pc jet-like structure which shows for the first time that the Cep A East young stellar objects are driving a collimated outflow moving towards the south.
The observed outflows show different clumps associated with definitely different H2 S/SO2 integrated emission ratios, indicating that the gas chemistry in Cepheus A has been altered by the passage of shocks. H2 S appears to be more abundant than SO2 in high-velocity clumps, in agreement with chemical models. However, we also find quite small H2 S linewidths, suggestive of regions where the evaporated H2 S molecules had enough time to slow down but not to freeze out on to dust grains. Finally, comparison between the line profiles indicates that the excitation conditions increase with the velocity, as expected for a propagation of collimated bow shocks. 相似文献
The observed outflows show different clumps associated with definitely different H
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A. J. L. Fernandes 《Monthly notices of the Royal Astronomical Society》2000,315(4):657-668
Long-slit spectra of the molecular outflow Herbig–Haro (HH) 46/47 have been taken in the J and K near-infrared bands. The observed H2 line emission confirms the existence of a bright and extended redshifted counter-jet outflow south-west of HH 46. In contrast with the optical appearance of this object, we show that this outflow seems to be composed of two different emission regions characterized by distinct heliocentric velocities. This implies an acceleration of the counter-jet.
The observed [Fe ii ] emission suggests an average extinction of 7–9 visual magnitudes for the region associated with the counter-jet.
Through position–velocity diagrams, we show the existence of different morphologies for the H2 and [Fe ii ] emission regions in the northern part of the HH 46/47 outflow. We have detected for the first time high-velocity (−250 km s−1 ) [Fe ii ] emission in the region bridging HH 46 to HH 47A. The two strong peaks detected can be identified with the optical positions B8 and HH 47B.
The H2 excitation diagrams for the counter-jet shock suggest an excitation temperature for the gas of T ex ≈2600 K . The lack of emission from the higher energy H2 lines, such as the 4–3 S(3) transition, suggests a thermal excitation scenario for the origin of the observed emission. Comparison of the H2 line ratios with various shock models yielded useful constraints about the geometry and type of these shocks. Planar shocks can be ruled out whereas curved or bow shocks (both J- and C-type) can be parametrized to fit our data. 相似文献
The observed [Fe ii ] emission suggests an average extinction of 7–9 visual magnitudes for the region associated with the counter-jet.
Through position–velocity diagrams, we show the existence of different morphologies for the H
The H
5.
K. J. Brooks † M. G. Burton J. M. Rathborne M. C. B. Ashley J. W. V. Storey 《Monthly notices of the Royal Astronomical Society》2000,319(1):95-102
To better understand the environment surrounding CO emission clumps in the Keyhole Nebula, we have made images of the region in H2 1–0 S(1) (2.122-μm) emission and polycyclic aromatic hydrocarbon (PAH) emission at 3.29 μm. Our results show that the H2 and PAH emission regions are morphologically similar, existing as several clumps, all of which correspond to CO emission clumps and dark optical features. The emission confirms the existence of photodissociation regions (PDRs) on the surface of the clumps. By comparing the velocity range of the CO emission with the optical appearance of the H2 and PAH emission, we present a model of the Keyhole Nebula whereby the most negative velocity clumps are in front of the ionization region, the clumps at intermediate velocities are in it and those which have the least negative velocities are at the far side. It may be that these clumps, which appear to have been swept up from molecular gas by the stellar winds from η Car, are now being overrun by the ionization region and forming PDRs on their surfaces. These clumps comprise the last remnants of the ambient molecular cloud around η Car. 相似文献
6.
J. M. C. Rawlings S. D. Taylor D. A. Williams 《Monthly notices of the Royal Astronomical Society》2000,313(3):461-468
Anomalous molecular line profile shapes are the strongest indicators of the presence of the infall of gas that is associated with star formation. Such profiles are seen for well-known tracers, such as HCO+ , CS and H2 CO. In certain cases, optically thick emission lines with appropriate excitation criteria may possess the asymmetric double-peaked profiles that are characteristic of infall. However, recent interpretations of the HCO+ infall profile observed towards the protostellar infall candidate B335 have revealed a significant discrepancy between the inferred overall column density of the molecule and that which is predicted by standard dark cloud chemical modelling.
This paper presents a model for the source of the HCO+ emission excess. Observations have shown that, in low-mass star-forming regions, the collapse process is invariably accompanied by the presence of collimated outflows; we therefore propose the presence of an interface region around the outflow in which the chemistry is enriched by the action of jets. This hypothesis suggests that the line profiles of HCO+ , as well as other molecular species, may require a more complex interpretation than can be provided by simple, chemically quiescent, spherically symmetric infall models.
The enhancement of HCO+ depends primarily on the presence of a shock-generated radiation field in the interface. Plausible estimates of the radiation intensity imply molecular abundances that are consistent with those observed. Further, high-resolution observations of an infall-outflow source show HCO+ emission morphology that is consistent with that predicted by this model. 相似文献
This paper presents a model for the source of the HCO
The enhancement of HCO
7.
G. A. Galazutdinov J. Kreowski F. A. Musaev P. Ehrenfreund B. H. Foing 《Monthly notices of the Royal Astronomical Society》2000,317(4):750-758
The identity of the carriers of the diffuse interstellar bands (DIBs) is one of the most fascinating puzzles of modern spectroscopy. Over the last few years the number of known DIBs has grown substantially. In this paper we discuss the two recently discovered near-infrared weak interstellar features which have already been proposed as fingerprints of the buckminsterfullerene We present and discuss measurements of the two related DIBs within a larger sample of reddened targets, observed with different spectrometers, telescopes and site conditions. We provide additional arguments in favour of the interstellar origin of the two bands. We find evidence around the 9577-Å DIB of far-wing structures, which may affect broad-band measurements. We estimate corrections and errors for telluric and stellar blends, and show that the cores of the two DIBs are well correlated with a ratio near unity within 20 per cent. Finally, we discuss their relation to the laboratory spectra of and the search for two expected weaker transitions. 相似文献
8.
Christopher J. Davis Michael D. Smith Jochen Eislöffel John K. Davies 《Monthly notices of the Royal Astronomical Society》1999,308(2):539-550
We present a comprehensive near-infrared study of two molecular bow shocks in two protostellar outflows, HH 99 in R Coronae Australis and VLA 1623A (HH 313) in Rho Ophiuchi. New, high-resolution, narrow-band images reveal the well-defined bow shock morphologies of both sources. These are compared with two-dimensional MHD modelling of molecular bows from which we infer flow inclination angles, shock speeds and the magnetic field in the pre-shock gas in each system. With combined echelle spectroscopy and low-resolution K -band spectra we further examine the kinematics and excitation of each source. Bow shock models are used to interpret excitation (CDR) diagrams and estimate the extinction and, in the case of VLA 1623, the ortho–para ratio associated with the observed H2 population. For the first time, morphology, excitation and kinematics are fitted with a single bow shock model.
Specifically, we find that HH 99 is best fitted by a C-type bow shock model (although a J-type cap is probably responsible for the [Fe ii ] emission). The bow is flowing away from the observer (at an angle to the line of sight of ∼45°) at a speed of roughly 100 km s−1 . VLA 1623A is interpreted in terms of a C-type bow moving towards the observer (at an angle to the line of sight of ∼75°) at a speed of ∼80 km s−1 . The magnetic field associated with HH 99 is thought to be orientated parallel to the flow axis; in VLA 1623A the field is probably oblique to the flow axis, since this source is clearly asymmetric in our H2 images. 相似文献
Specifically, we find that HH 99 is best fitted by a C-type bow shock model (although a J-type cap is probably responsible for the [Fe ii ] emission). The bow is flowing away from the observer (at an angle to the line of sight of ∼45°) at a speed of roughly 100 km s
9.
K. P. Johns D. M. Cragg P. D. Godfrey & A. M. Sobolev 《Monthly notices of the Royal Astronomical Society》1998,300(4):999-1005
We investigate the possibility of interstellar masers in transitions of the methanol isotopomers CH3 OD, 13 CH3 OH and CH3 18 OH, and of CH3 SH. The model used, in which masers are pumped through the first and second torsionally excited states by IR radiation, has accounted successfully for the Class II masers in main species methanol, 12 CH3 16 OH. Several potential maser candidates are identified for CH3 OD, their detectability depending on the enrichment of this species in star-forming regions. In 13 CH3 OH and CH3 18 OH the best maser candidates are direct counterparts of the well-known 6.7- and 12.2-GHz methanol masers, but the lower interstellar abundance of these substituted species means that the expected brightness is greatly reduced. The maser candidates in CH3 SH are also weak. By comparing these species we find that the large b -component of the dipole moment in methanol plays a significant role in its propensity to form masers, as does the strong torsion–rotation interaction due to the light hydroxyl frame. Thus the exceptional brightness of interstellar methanol masers is due to a favourable combination of molecular properties as well as high interstellar abundance. 相似文献
10.
We report the discovery of high-velocity dense gas from a bipolar outflow source near NGC 2068 in the L1630 giant molecular cloud. CO and HCO+ J =3→2 line wings have a bipolar distribution in the vicinity of LBS 17-H with the flow orientated roughly east–west and perpendicular to the elongation of the submillimetre dust continuum emission. The flow is compact (total extent ∼0.2 pc) and contains of the order of 0.1 M⊙ of swept-up gas. The high-velocity HCO+ emission is distributed over a somewhat smaller area <0.1 pc in extent.
A map of C18 O J =2→1 emission traces the LBS 17 core and follows the ambient HCO+ emission reasonably well, with the exception of the direction towards LBS 17-H where there is a significant anticorrelation between the C18 O and HCO+ . A comparison of beam-matched C18 O and dust-derived H2 column densities suggests that CO is depleted by up to a factor of ∼50 at this position if the temperature is as low as 9 K, although the difference is substantially reduced if the temperature is as high as 20 K. Chemical models of collapsing clouds can account for this discrepancy in terms of different rates of depletion on to dust grains for CO and HCO+ .
LBS 17-H has a previously known water maser coincident with it but there are no known near-infrared, IRAS or radio continuum sources associated with this object, leading to the conclusion that it is probably very young. A greybody fit to the continuum data gives a luminosity of only 1.7 L⊙ and a submillimetre-to-bolometric luminosity ratio of 0.1, comfortably satisfying the criteria for classification as a class 0 protostar candidate. 相似文献
A map of C
LBS 17-H has a previously known water maser coincident with it but there are no known near-infrared, IRAS or radio continuum sources associated with this object, leading to the conclusion that it is probably very young. A greybody fit to the continuum data gives a luminosity of only 1.7 L
11.
E. Herbst R. Terzieva D. Talbi 《Monthly notices of the Royal Astronomical Society》2000,311(4):869-876
The attempt to understand the temperature dependence of the HNC/HCN abundance ratio in interstellar clouds has been long standing and indecisive. In this paper we report quantum chemical and dynamical studies of two neutral–neutral reactions thought to be important in the formation of HNC and HCN, respectively – C+NH2 →HNC+H, and N+CH2 →HCN+H. We find that although these reactions do lead initially to the products suggested by astronomers, there is so much excess energy available in both reactions that the HCN and HNC products are able to undergo efficient isomerization reactions after production. The isomerization leads to near equal production rates of the two isomers, with HNC slightly favoured if there is sufficient rotational excitation. This result has been incorporated into our latest chemical model network of dense interstellar clouds. 相似文献
12.
C. J. Davis P. Scholz P. Lucas M. D. Smith A. Adamson 《Monthly notices of the Royal Astronomical Society》2008,387(3):954-968
We discuss wide-field near-infrared (near-IR) imaging of the NGC 1333, L1448, L1455 and B1 star-forming regions in Perseus. The observations have been extracted from a much larger narrow-band imaging survey of the Taurus–Auriga–Perseus complex. These H2 2.122-μm observations are complemented by broad-band K imaging, mid-IR imaging and photometry from the Spitzer Space Telescope , and published submillimetre CO J = 3–2 maps of high-velocity molecular outflows. We detect and label 85 H2 features and associate these with 26 molecular outflows. Three are parsec-scale flows, with a mean flow lobe length exceeding 11.5 arcmin. 37 (44 per cent) of the detected H2 features are associated with a known Herbig–Haro object, while 72 (46 per cent) of catalogued HH objects are detected in H2 emission. Embedded Spitzer sources are identified for all but two of the 26 molecular outflows. These candidate outflow sources all have high near-to-mid-IR spectral indices (mean value of α∼ 1.4 ) as well as red IRAC 3.6–4.5 μm and IRAC/MIPS 4.5–24.0 μm colours: 80 per cent have [3.6]–[4.5] > 1.0 and [4.5]–[24] > 1.5. These criteria – high α and red [4.5]–[24] and [3.6]–[4.5] colours – are powerful discriminants when searching for molecular outflow sources. However, we find no correlation between α and flow length or opening angle, and the outflows appear randomly orientated in each region. The more massive clouds are associated with a greater number of outflows, which suggests that the star formation efficiency is roughly the same in each region. 相似文献
13.
G.A. Galazutdinov F.A. Musaev J. Kre&#;owski 《Monthly notices of the Royal Astronomical Society》2001,325(4):1332-1334
An upper limit of the column density of the C5 linear molecule in translucent interstellar clouds is estimated from high-resolution ( R =80 000) and very high signal-to-noise ratio (∼1000) echelle spectra. It is 1012 cm−2 per E ( B − V )=1 (two orders of magnitude lower than that of C2 ). 相似文献
14.
Cesare Cecchi-Pestellini Alexander Dalgarno 《Monthly notices of the Royal Astronomical Society》2000,313(1):L6-L8
A model is constructed of the material in front of the star Cygnus OB2 no. 12 in which dense cores are embedded in diffuse clumps of gas. The model reproduces the measured abundances of C2 and CO, and predicts a column density of 91010 cm2 for HCO+ . 相似文献
15.
The distribution of C2 S and NH3 in two Bok globules at different evolutionary stages: CB246 and CB34
Claudio Codella & Flavio Scappini 《Monthly notices of the Royal Astronomical Society》1998,298(4):1092-1096
Two Bok globules, L1253 (CB246) and CB34, have been mapped in the C2 S (21 –10 ) transition and in the NH3 (1, 1) and NH3 (2, 2) inversion transitions, respectively. By comparing the C2 S map of L1253 (CB246) with the NH3 map of the same globule from Lemme et al., a clumped onion structure results as a consequence of the chemical and dynamical evolution of the object. From the derived parameters it appears that both L1253 (CB246) and CB34 are close to virial equilibrium. 相似文献
16.
I. Bains T. Wong M. Cunningham P. Sparks D. Brisbin P. Calisse J. T. Dempsey G. Deragopian S. Ellingsen B. Fulton F. Herpin P. Jones Y. Kouba C. Kramer E. F. Ladd S. N. Longmore J. McEvoy M. Maller V. Minier B. Mookerjea C. Phillips C. R. Purcell A. Walsh M. A. Voronkov M. G. Burton 《Monthly notices of the Royal Astronomical Society》2006,367(4):1609-1628
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Maps are presented of 3 P 1 →3 P 0 [C i ] and J =2→1 C18 O line emission from the interstellar molecular cloud G35.2−0.74N. The maps are interpreted with reference to a previous model for the structure of the cloud in which opposing jets from a central object, embedded in a rotating interstellar disc, precess and drive a bipolar molecular outflow. The C18 O emission traces the rotating interstellar disc, but the [C i ] emission shows several features. An unresolved component is observed which probably results from dissociation of CO in the centre of the disc by UV radiation from the central source. Background [C i ] emission is also observed which shares the rotation of the disc on larger scales. The C i /CO ratio in these components is typically a few per cent. High-velocity [C i ] emission, where C i /CO is high (>0.1–0.4), is observed between the CO molecular outflow and the cavity exacavated by the jet. This material has probably been accelerated by the jet but dissociated by far-UV radiation propagating through the cavity. The C i /CO ratio falls as the shocked outflow later sweeps up CO. 相似文献
19.
Stephen P. Todd Suzanne K. Ramsay Howat 《Monthly notices of the Royal Astronomical Society》2006,367(1):238-246
The results of B -band CCD imaging linear polarimetry obtained for stars from the Hipparcos catalogue are used to re-examine the distribution of the local interstellar medium towards the IRAS 100-μm emission void in the Lupus dark clouds. The analysis of the obtained parallax–polarization diagram assigns to the dark cloud Lupus 1 a distance between 130 and 150 pc and assures the existence of a low column density region coincident with the observed infrared void. Moreover, there are clear indications of the existence of absorbing material at distances closer than 60–100 pc, which may be associated with the interface boundary between the Local Bubble and its neighbourhood Loop I superbubble. 相似文献
20.
A. S. B. Schultz M. G. Burton P. W. J. L. Brand 《Monthly notices of the Royal Astronomical Society》2005,358(4):1195-1214
We present a model for empirically reproducing line profiles of molecular hydrogen emission in bow shocks. The model takes into account bow velocity, dissociation limit, a cooling function, viewing angle, bow shape and a limited form of extinction. Our results show that both geometrical factors and shock physics can significantly affect the profile morphology. In a companion paper we will apply this model to Fabry–Perot observations of bow shocks in the Orion BN–KL outflow. 相似文献