Detection of interstellar vibrationally excited HCN

Vibrationally excited HCN has been observed for the first time in the interstellar medium. The J = 3-2 rotational transitions of the l-doubled (0,1(1d,1c), 0) bending mode of HCN have been detected toward Orion-KL and IRC +10216. In Orion, the overall column density in the (0,1,0) mode, which exclusively samples the "hot core", is 1.7 x 10(16) cm-2 and can be understood in terms of the "doughnut" model for Orion. The ground-state HCN column density implied by the excited-state observations is 2.3 x 10(18) cm-2 in the hot core, at least one order of magnitude greater than the column densities derived for HCN in its spike and plateau/doughnut components. Radiative excitation by 14 micrometers flux from IRc2 accounts for the (0,1,0) population, provided the hot core is approximately 6-7 x 10(16) cm distant from IRc2, in agreement with the "cavity" model for KL. Toward IRC +10216 we have detected J = 3-2 transitions of both (0,1(1c),(1d), 0) and (0, 2(0), 0) excited states. The spectral profiles have been modeled to yield abundances and excitation conditions throughout the expanding envelope.     

Reversed far-infrared line emission from OH in Orion

The fundamental OH rotational transition at 2514 GHz (119.2 micrometers) has been observed in the Orion IRc2 region at a spectral resolution of 0.6 km s-1. The emission is spatially compact (< 25" FWHM) and centered near IRc2. A comparison of the observed profile with spectra of other species known to exist in the region suggests that the entire blueshifted side of the OH profile has been "self-absorbed," leaving only a redshifted emission component. In addition, there is pronounced absorption near 5 km s-1 VLSR indicative of the "hot core" source. The presence of the 119 micrometers absorption provides a straightforward explanation for the high ratio of 163/119 micrometers integrated line intensities which was previously considered anomalous.     

Large-Scale Mapping Observations of the C i (3P1-3P0) and CO (J = 3-2) Lines toward the Orion A Molecular Cloud

Large-scale mapping observations of the 3P1-3P0 fine-structure transition of atomic carbon (C i, 492 GHz) and the J=3-2 transition of CO (346 GHz) toward the Orion A molecular cloud have been carried out with the Mount Fuji submillimeter-wave telescope. The observations cover 9 deg2 and include the Orion Nebula M42 and the L1641 dark cloud complex. The C i emission extends over almost the entire region of the Orion A cloud and is surprisingly similar to that of 13CO (J=1-0). The CO (J=3-2) emission shows a more featureless and extended distribution than C i. The C i/CO (J=3-2) integrated intensity ratio shows a spatial gradient running from the north (0.10) to the south (1.2) of the Orion A cloud, which we interpret as a consequence of the temperature gradient. On the other hand, the C i/13CO (J=1-0) intensity ratio shows no systematic gradient. We have found a good correlation between the C i and 13CO (J=1-0) intensities over the Orion A cloud. This result is discussed on the basis of photodissociation region models.     

BIMA and JCMT Spectropolarimetric Observations of the CO J = 2 − 1 Line Towards Orion KL/IRc2

We present results of JCMT and BIMA CO J = 2 ? 1 polarization observations towards the Orion KL/IRc2 high mass star forming region. The linear polarization fraction of the JCMT CO J = 2 ? 1 spectra presents a clear decrease towards the center of the line, as expected, due to the increase of the optical depth. The position angle remains constant along the spectral line, except at the line center, where the highest optical depth and lower fractional polarization are measured. The combined BIMA and JCMT maps of the redshifted and blueshifted CO emission show a uniform polarization pattern that does not coincide with previous dust continuum observations at similar angular resolution. This suggests that the CO and dust are tracing different spatial components along the line of sight.     

4.8 – 20 micron imaging of orion BN/KL: luminosity sources and the role of IRc2

Mid-infrared imaging photometry of the Orion BN/KL infrared cluster at eight wavelengths between 5 and 20µm using a 58 × 62 pixel imaging array camera has revealed new compact sources and the large-scale structure of the region in diffraction-limited (1 arcsec) detail. Several new objects have been detected within a few arcsec of IRc2, widely thought to be the principal luminosity source for the entire BN/KL complex. Detailed color temperature and emission opacity images are derived from the 7.8, 12.4 and 20.0µm observations, and the 9.8µm image is used to derive an image of “silicate” dust extinction for the region. The color temperature, opacity, and extinction images show that IRc2 may not be the single dominant luminosity source for the BN/KL region; substantial contributions to the luminosity could be made by IRc7, BN, KL, and five new compact 10µm sources detected within a few arcseconds of IRc2. We suggest that a luminous, early-type star near IRc2, which is associated with the compact radio source “I” and the Orion SiO maser, is the dominant luminosity source in the BN/KL region, hidden from view by cool dust material with at least Av ～ 60 mag of visible extinction.     

Heterodyne spectroscopy of the J = 22-21 CO line in Orion

We have observed the J = 22-21 line of 12CO at 2528 GHz (118.8 micrometers) in the IRc2 region of Orion. The spectra at 0.6 km s-1 resolution show both plateau emission with FWHM approximately 35 km s-1 and a narrower component with FWHM approximately 8 km s-1. Comparison with heterodyne data of similar quality on the J = 17-16 line indicates that the broad and narrow components both originate in gas with an excitation temperature Tex approximately 600 K. The emission is consistent with the predictions of shock models in which the wide component arises from the heated outflow gas and postshock molecular material, while the narrow component comes from ambient material near the leading edge of the shock front where temperatures are high but significant acceleration has not yet occurred.     

A line survey of Orion KL from 325 to 360 GHz

We present a high-sensitivity spectral line survey of the high-mass star-forming region Orion KL in the 325-360 GHz frequency band. The survey was conducted at the Caltech Submillimeter Observatory on Mauna Kea, Hawaii. The sensitivity achieved is typically 0.1-0.5 K and is limited mostly by the sideband separation method utilized. We find 717 resolvable features consisting of 1004 lines, among which 60 are unidentified. The identified lines are due to 34 species and various isotopomers. Most of the unidentified lines are weak, and many of them most likely due to isotopomers or vibrationally or torsionally excited states of known species with unknown line frequencies, but a few reach the 2-5 K level. No new species have been identified, but we were able to strengthen evidence for the identification of ethanol in Orion and found the first nitrogen sulfide line in this source. The molecule dominating the integrated line emission is S02, which emits twice the intensity of CO, followed by SO, which is only slightly stronger than CO. In contrast, the largest number of lines is emitted from heavy organic rotors like HCOOCH3, CH3CH2CN, and CH3OCH3, but their contribution to the total flux is unimportant. CH3OH is also very prominent, both in the number of lines and in integrated flux. An interesting detail of this survey is the first detection of vibrationally excited HCN in the v2 = 2 state, 2000 K above ground. Clearly this is a glimpse into the very inner part of the Orion hot core.     

1300 micron continuum and C18O line mapping of the giant molecular cloud cores in Orion, W49, and W51

We present observations of the 1300 micron continuum emission and the C18O spectral-line emission from three well-studied giant molecular cloud cores: Orion, W49, and W51. The observations were obtained at the Five College Radio Astronomy Observatory, and they provide a means to examine the consistency of these two methods to trace the column density structure of molecular clouds. We find a good general correlation between the 1300 micron continuum, which traces the column density of dust, and the C18O J = 2 --> 1 line emission, which traces the column density of molecular gas, when the effects of source temperature are taken into consideration. Moreover, nominal values for the gas and dust abundances and the dust properties reproduce the observed continuum-to-line ratios. Thus, no strong C18O abundance gradients within sources has been found, and it appears that either the C18O emission lines or the submillimeter dust emission may be used to derive the mass column density within molecular clouds accurately.     

Spectroscopic study of ‘CO’ and its isotopic mm/submillimeter lines from dark cloud Lynds 183

We have made spectral line analysis of CO and its isotopic lines from dark cloud Lynds 183 (L183). Our dataset incorporates ¹²CO(1-0), ¹³CO(1-0) and ¹³CO(2-1) lines using NRAO-12 m and ¹²CO(3-2), ¹³CO(3-2) lines using CSO-10 m telescopes, respectively. Observations suggest steep north-south (direction with respect to the offset position (0, 0)) temperature gradient in the cloud. These are likely to be caused by non-uniform, Inter Stellar Radiation Field (ISRF) illumination due to the shadow of nearby L134 cloud complex. As the emission of radiation depends on local properties like density and kinetic temperature, the present study attempts to deduce the irradiation contrast (and the resulting temperature difference) using 1D Monte Carlo radiative transfer code RATRAN. The model results accord with the observed data and shows a temperature difference of ∼7 K mainly within the cloud envelope. This results in a non-uniform intensity distribution of both CO and its species.     

Interstellar CO towards X Persei (HD 24534) – II. Two-component model

The observations made by the Goddard High Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope ( HST ) of molecular CO in absorbing gas towards X Persei are reported. The two-component statistical equilibrium model incorporating radiative excitation of CO by line emission at the same velocity that originates in nearby molecular clouds has been used to reproduce high-resolution GHRS spectra. Earlier analysis indicates that the cloud has a complex structure and at least a two-component model should be used to obtain accurate results. The spectra obtained from the International Ultraviolet Explorer ( IUE ) were used to complement GHRS data and constrain the space of possible solutions. The new oscillator strengths recommended by Eidelsberg et al. for A–X bands have been used. The results show that one of the components may be attributed to the Perseus OB2 molecular cloud, and the other component to an extension of the Taurus dark cloud. The total CO column density N (CO)=(1.0±0.2)×10¹⁶ cm⁻² has been determined. According to the results about 85 per cent of the observed CO belongs to an extension of the Taurus dark cloud. The CO radiation that originates in nearby molecular clouds may be the dominant excitation mechanism of the observed CO. The early results of ¹³CO line analysis indicate a ¹³CO/¹²CO ratio of about 40.     

Mass loss rates from protostars and Ol(63 μm) shock luminosities

The high-velocity ejection of material from protostars results in a wind shock which may be observable in Ol(63 μm) emission. It is shown that for a wide range of conditions, the Ol(63 μm) luminosity is proportional to the mass loss rate from the protostar. Application is made to shock Ol(63 μm) emission observed around IRc2 in the BN-KL region of Orion.     

A new evolutionary scenario of intermediate-mass star-formation revealed by multi-wavelength observations of OMC-2/3

We have performed millimeter- and submilli- meter-wave survey observations using the Nobeyama millimeter array (NMA) and the Atacama Submillimeter Telescope Experiment (ASTE) in one of the nearest intermediate-mass (IM) star-forming regions: Orion Molecular Cloud-2/3 (OMC-2/3). Using the high-resolution capabilities offered by the NMA (∼several arcsec), we observed dust continuum and H¹³CO⁺(1–0) emission in 12 pre- and proto-stellar candidates identified previously in single-dish millimeter observations. We unveiled the evolutionary changes with variations of the morphology and velocity structure of the dense envelopes traced by the H¹³CO⁺(1–0) emission. Furthermore, using the high-sensitivity capabilities offered by the ASTE, we searched for large-scale molecular outflows associated with these pre- and proto-stellar candidates observed with the NMA. As a result of the CO(3–2) observations, we detected six molecular outflows associated with the dense gas envelopes traced by H¹³CO⁺(1–0) and 3.3 mm continuum emission. The estimated CO outflow momentum increases with the evolutionary sequence from early to late type of the protostellar cores. We also found that the 24 μm flux increases as the dense gas evolutionary sequence. We propose that the enhancement of the 24 μm flux is caused by the growth of the cavity (i.e. the CO outflow destroys the envelope) as the evolutionary sequence. Our results show that the dissipation of the dense gas envelope plays an essential role in the evolution of the IM protostars. The extremely high-sensitivity and high-angular resolution offered by ALMA will reveal unprecedented details of the inner ∼50 AU of these protostars, which will provide us a break through in the classic scenario of IM star/disk formation.     

The infrared emission bands. II. A spatial and spectral study of the Orion Bar

We have studied the spectral and spatial distribution across the Orion Bar of the 3-14 micrometers emission, including hydrogen Brackett alpha and 12.8 micrometers [Ne II] emission lines and several "dust" emission features. The data indicate that the "dust" consists of three components; (1) "classical" dust with a temperature of approximately 60 K accounting for emission longward of 20 micrometers, (2) amorphous carbon particles or polycyclic aromatic hydrocarbon (PAH) clusters (approximately 400 C atoms) which produce broad emission features in the 6-9 and 11-13 micrometers bands, and (3) free PAHs which emit in sharper bands (most strongly at 3.3, 6.2, 7.7, 8.6, and 11.3 micrometers). The 3.3 and 11.3 micrometers features, which are due to C-H modes, are well correlated spatially, while the 7.7 micrometers band, due to C=C modes, has a different distribution than the 3.3 and 11.3 micrometers bands. We conclude that the sharp emission bands arise in the photodissociation transition region between the H II region and the molecular cloud and are not present in the H II region. The broad continuum feature extending from 11-13 micrometers is strong in both regions. Previous broad-band observations of the 10 and 20 micrometers flux distributions, which show that the 10 micrometers radiation extends farther into the neutral gas to the south than the 20 micrometers radiation, suggest that some of the 10 micrometers flux is supplied via a nonthermal mechanism, such as fluorescence.     

A search for HCCN in molecular clouds

We have conducted a deep search for HCCN towards the dark cloud TMC-l and several GMC's via its N(J) = 1(2)-->0(1) transition. HCCN was not detected in any of these sources. Towards TMC-l, assuming optically thin emission, the total column density upper limit is NHCCN < or = 2 x 10(12) cm-2, which corresponds to a fractional abundance upper limit with respect to molecular hydrogen of fHCCN < or = 2 x 10(-10). We find the abundance ratio of HCN:HCCN:HCCCN in TMC-l to be l : <0.01 : 0.3, which suggests that carbon-chain growth by the addition of single carbon atoms may not be efficient under dark cloud conditions. The HCCN abundance limit also places constraints on the branching ratio for the products of the dissociative electron recombination H3C2N+ + e.     

高红移亚毫米星系中星际介质的物理状态

<正>随着亚毫米波望远镜的发展,利用这些新的探测设备,人们在亚毫米波段发现了一类高红移且富含尘埃的星系,将其称为亚毫米星系.这类星系的发现革新了我们对星系的演化以及极端条件下的恒星形成过程的认知.这些亚毫米星系是宇宙中最强的星暴星系,其中的恒星形成过程产生的能量接近爱丁顿极限.人们普遍认为这类星系正是近邻宇宙中那些大质量星系的前身天体.但是,很难解释其在高红移为何具有较高的数密度.它们其中非常少的一部分会被处于视线方向上的大质量星系通过引     

A model for the Cl (609 μm) emission of Orion

A model for the energy balance and chemical equilibrium of the gas in photodissociation regions at the edge of molecular clouds, which are illuminated by strong FUV fields (6 eV ≦ hv ≦ 13.6 eV), has been developed. This model is used to calculate the emergent intensities in the fine structure lines of OI (63 μm, 145 μm), CI (609 μm, 370 μm), and CII (158 μm) and in the low-lying rotational transitions of CO. The numerical results show that column densities in the range 2 × 10¹⁷ to 2 × 10¹⁸ cm² can be expected from the C⁺/C/CO transition region at the edge of molecular clouds. This difference with previous chemical calculations is partly due to a higher assumed carbon abundance, partly due to the charge exchange reactions of C⁺ with S and SiO, and partly due to carbon self-shielding which is taken into account. A detailed model is constructed for the Orion photodissociation region, which explains the observed OI (63 μm, 145 μm), CII (158 μm), CI (609 μm), and CO emission. In this model the CI (609 μm) emission originates in the warm (50°K) molecular gas behind Θ¹C Ori but near the surface of OMCI.     

分子云核与恒星形成区的良好探针－CH_3CN

本文作者通过对猎户座ＫＬ区的观测、分析与计算，阐明ＣＨ３ＣＮ分子转动谱线系作为分子云核与恒星形成区探针的可能性和优越性．并对观测该线系所需要的仪器条件进行了讨论．     

The Gas to Dust Ratio in Three Star Forming Regionstwo

Gas to Dust Ratio (GDR) indicates the mass ratio of interstellar gas to dust. It is widely adopted that the GDR in our Galaxy is 100～150. We choose three typical star forming regions to study the GDR: the Orion molecular cloud — a massive star forming region, the Taurus molecular cloud — a low-mass star forming region, and the Polaris molecular cloud — a region with no or very few star formation activities. The mass of gas only takes account of the neutral gas, i.e. only the atomic and molecular hydrogen, because the amount of ionized gas is very small in a molecular cloud. The column density of atomic hydrogen is taken from the high-resolution and high-sensitivity all-sky survey EBHIS (Effelsberg-Bonn HI Survey). The CO J = 1 →0 line is used to trace the molecular hydrogen, since the spectral lines of molecular hydrogen which can be detected are rare. The intensity of CO J = 1 →0 line is taken from the Planck all-sky survey. The mass of dust is traced by the interstellar extinction based on the 2MASS (Two Micron All Sky Survey) photometric database in the direction of anti-Galactic center. Adopting a constant conversion coefficient from the integrated intensity of the CO line to the column density of molecular hydrogen, X_CO = 2.0 × 10²⁰ cm^?2 · (K · km/s)^?1, the gas to dust ratio N(H)/A_V is calculated, which is 25, 38, and 55 (in units of 10²⁰ cm^?2 · mag^?1) for the Orion, Taurus, and Polaris molecular clouds, respectively. These values are significantly higher than the previously obtained average value of the Galaxy. Adopting the WD01 interstellar dust model (when the V-band selective extinction ratio is R_V = 3.1), the derived GDRs are 160, 243, and 354 for the Orion, Taurus, and Polaris molecular clouds, respectively, which are apparently higher than 100～150, the commonly accepted GDR of the diffuse interstellar medium. The high N(H)/A_V values in the star forming regions may be explained by the growth of dust in the molecular clouds because of either the particle collision or accretion, which can lead to the reduction of extinction efficiency per unit mass in the V band, rather than the increase of the GDR itself.     

Heterodyne spectroscopy of the J = 17-16 CO line in Orion

We have obtained high-resolution spectra of the 153 micrometers J = 17-16 CO line in the BN-KL region of Orion using a laser heterodyne spectrometer. The line shows broad wings (30 km s-1 FWHM at BN) characteristic of the plateau emission as well as a narrower component probably associated with the quiescent gas in the molecular ridge. From an analysis of the plateau emission together with that observed in lower J CO transitions, we derive an excitation temperature of 180 +/- 50 K and minimum column density of 1 x 10(18) cm-2 for CO in this component, which constitutes 80% of the total integrated intensity of the J = 17-16 line near BN. The peak intensity of the narrower component observed at 0.8 km s-1 resolution increases relative to that of the plateau component toward theta 1C and away from BN, while the width decreases from 10 to 4 km s-1 (FWHM).