Near-infrared imaging in H2 of molecular (CO) outflows from young stars

We have imaged several known molecular (CO) outflows in H₂ v=1-0 S(1) and wide-band K in order to identify the molecular shocks associated with the acceleration of ambient gas by outflows from young stars. We detected H₂ line emission in all the flows we observed: L 1157, VLA 1623, NGC 6334I, NGC 2264G, L 1641N and Haro 4-255. A comparison of the H₂ data with CO outflow maps strongly suggests that prompt entrainment near the head of a collimated jet probably is the dominant mechanism for producing the CO outflows in these sources.     

The physical conditions in the BHR71 outflows

Highly-collimated outflows are believed to be the earliest stage in outflow evolution, so their study is essential for understanding the processes driving outflows. The BHR71 Bok globule is known to harbour such a highly-collimated outflow, which is powered by a protostar belonging to a protobinary system. Using the APEX telescope on Chajnantor, we mapped the BHR71 highly-collimated outflow in CO(3-2), and observed several bright points of the outflow in the molecular transitions CO(4-3), CO(7-6), ¹³CO(3-2), C¹⁸O(3-2), CH₃OH(7-6) and H₂CO(4-3). We use an LVG code to characterise the temperature enhancements in these regions. These observations are particularly interesting for investigating the interaction of collimated outflows with the ambient molecular cloud. In our CO(3-2) map, the second outflow driven by IRS2, which is the second source of the binary system, is completely revealed and shown to be bipolar. We also measure temperature enhancements in the lobes. The CO and methanol LVG modelling points to temperatures between 30 and 50 K in the two lobes. The methanol emission in the southern lobe bright knot is barely resolved with the APEX single-dish. ALMA will thus be a central tool to study the shock chemistry in these regions.     

The H2O maser toward IRAS 06308+0402

We present the monitoring results for the H₂O maser toward the infrared source IRAS 06308+0402 associated with a dense cold molecular cloud. The observations were carried out with the 22-m radio telescope at the Pushchino Radio Astronomy Observatory (Russia) during 1992–2003. The H₂O maser was discovered in May 1992 (Pashchenko 1992) during a survey of IRAS sources associated with dense cold clouds with bipolar molecular outflows. The H₂O spectrum contains many emission features, suggesting the fragmentation of the envelope around a young star. The star has a low peculiar velocity relative to the CO molecular cloud (～2.2 km s^?1). We found a cyclic variability of the total maser flux with a period from 1.8 to 3.1 yr.     

Near-infrared imaging of H2 in molecular outflows from young stars

In an attempt to identify the molecular shocks associated with the entrainment of ambient gas by collimated stellar winds from young stars, we have imaged a number of known molecular outflows in H₂ v=1-0 S(1) and wide-band K. In each flow, the observed H₂ features are closely associated with peaks in the CO outflow maps. We therefore suggest that the H₂ results from shocks associated with the acceleration or entrainment of ambient, molecular gas. This molecular material may be accelerated either in a bow shock at the head of the flow, or along the length of the flow through a turbulent mixing layer.     

Submillimeter/millimeter observations of the high-mass star forming region IRAS 22506+5944

The mapping observations of CO J = 2-1, CO J = 3-2, 13 CO J = 2-1 and 13 CO J = 3-2 lines in the direction of IRAS 22506+5944 have been made. The results show that the cores in the J = 2-1 transition lines have a similar morphology to those in the J = 3-2 transition lines. Bipolar molecular outflows are verified. The prior IRAS 22506+5944 observations indicated that two IRAS sources and three H 2 O masers were located close to the peak position of the core. One of the IRAS sources may be the driving source ...     

Physical properties of the outflow sources in taurus

We have searched for CO outflows in eight embedded IRAS sources located in the Taurus molecular cloud using the 45m telescope of Nobeyama Radio Observatory. We have detected CO wing emission in four of these sources. CO outflow associated with TMC1A (04365+2535) is strong and spatially compact (radius 0.04 pc). The dynamical timescale of 2.5 × 10³ yr suggests this outflow is the youngest one in Taurus.We have combined our data with previously published survey data and have analyzed the physical properties of the outflow sources. We found that 12 out of 16 embedded sources ( 75 %) have CO outflows associated with them; this indicates that almost all stars experience a phase of molecular outflow in their embedded stage. The IRAS color of the outflow sources suggests that the outflows appear in considerably early phase of the evolution of YSOs, that is, as early as YSOs became observable with IRAS and that visible outflow sources are in a transient phase of evolution between embedded sources and visible T Tauri stars without outflow. Visible outflow sources are systematically more luminous than visible no-outflow sources, while embedded outflow sources have comparable luminosities with visible no-outflow sources. Such luminosity function suggests that the YSOs with outflow undergo mass accretion and increase their stellar mass as they progress from embedded sources to visible outflow sources. Typical mass accretion rate derived from the bolometric luminosity is 2 ×10^–6 M _yr ^–1. The timescale for mass accretion to acquire typical stellar mass, 0.5 – 0.8M , is 2.5 – 4 × 10⁵ yr.     

Exploring morphological correlations among H2CO, 12CO, MSX and continuum mappings

There are relatively few H₂CO mappings of large-area giant molecular cloud (GMCs). H₂CO absorption lines are good tracers for low-temperature molecular clouds towards star formation regions. Thus, the aim of the study was to identify H₂CO distributions in ambient molecular clouds. We investigated morphologic relations among 6-cm continuum brightness temperature (CBT) data and H₂CO (1₁₁−1₁₀; Nanshan 25-m radio telescope), ¹²CO (1–0; 1.2-m CfA telescope) and midcourse space experiment (MSX) data, and considered the impact of background components on foreground clouds. We report simultaneous 6-cm H₂CO absorption lines and H110α radio recombination line observations and give several large-area mappings at 4.8 GHz toward W49 (50′×50′), W3 (70′×90′), DR21/W75 (60′×90′) and NGC2024/NGC2023 (50′×100′) GMCs. By superimposing H₂CO and ¹²CO contours onto the MSX color map, we can compare correlations. The resolution for H₂CO, ¹²CO and MSX data was ∼10′, ∼8′ and ∼18.3″, respectively. Comparison of H₂CO and ¹²CO contours, 8.28-μm MSX colorscale and CBT data revealed great morphological correlation in the large area, although there are some discrepancies between ¹²CO and H₂CO peaks in small areas. The NGC2024/NGC2023 GMC is a large area of HII regions with a high CBT, but a H₂CO cloud to the north is possible against the cosmic microwave background. A statistical diagram shows that 85.21% of H₂CO absorption lines are distributed in the intensity range from −1.0 to 0 Jy and the ΔV range from 1.206 to 5 km s⁻¹.     

A burst of outflows from the Serpens cloud core: wide-field submillimetre continuum, CO J=2–1 and optical observations

Wide-field mapping of Serpens in submillimetre continuum emission and CO J =2–1 line emission is here complemented by optical imaging in [S  ii ] λλ 6716, 6731 line emission. Analysis of the 450- and 850-μm continuum data shows at least 10 separate sources, along with fainter diffuse background emission and filaments extending to the south and east of the core. These filaments describe 'cavity-like' structures that may have been shaped by the numerous outflows in the region. The dust opacity index, β , derived for the identifiable compact sources is of the order of 1.0±0.2, with dust temperatures in excess of 20 K. This value of β is somewhat lower than for typical class I YSOs; we suggest that the Serpens sources may be 'warm', late class 0 or early class I objects.
With the combined CO and optical data we also examine, on large scales, the outflows driven by the embedded sources in Serpens. In addition to a number of new Herbig–Haro flows (here denoted HH 455–460), a number of high-velocity CO lobes are observed; these extend radially outwards from the cluster of submillimetre sources in the core. A close association between the optical and molecular flows is also identified. The data suggest that many of the submillimetre sources power outflows. Collectively, the outflows traced in CO support the widely recognized correlation between source bolometric luminosity and outflow power, and imply a dynamical age for the whole protostellar cluster of ∼3×10⁴ yr. Notably, this is roughly equal to the proposed duration of the 'class 0' stage in protostellar evolution.     

Observations of molecular jets in Orion A

We report on the results of a wide field near infrared survey for protostellar jets identified via their emission in the 2.12μm line of shock heated molecular hydrogen, done over a 1.2 square degree area in Orion A. We derive an evolutionary sequence for protostellar jets, based on the observed lenghts and H₂ luminosities as well as the evolutionary stage and bolometric luminosity of their driving sources. Protostellar jets start from zero length, evolve quickly to parsec scale extents during the Class 0 phase, and shrink during the Class I and Class II phase. They are first very bright in H₂ emission, and fade later on. This is indicative of strongly time-variably mass accretion onto the driving protostar, with a peak early on, and a subsequent continous decay of accretion activity. Finally, we present evidence for a molecular CO jet from a Class 0 object, supporting the idea that a very efficient outflow phase at very early evolutionary stages should produce very dense, molecular jets.     

Bipolar molecular outflows

Summary Bipolar molecular outflows are a ubiquitous phenomenon in the process of star formation. We review the main observational properties of the outflows around young stellar objects, highlighting the recent wealth of information provided by the new generation of large radiotelescopes operating at millimeter wavelengths (in particular the IRAM 30-m, the NRO 45-m, and the JCMT 15-m dishes). The observations of outflows containing molecular, jet-like flows and bullets are discussed in detail, as they provide key information for understanding origin and evolution of the outflows. We also discuss a number of closely related issues: the evidence for dense shocked gas associated with the flows, the interaction of the outflows with the ambient dense cores, the evolutionary status of the sources driving the outflows, the properties of circumstellar disks, and theoretical models of the origin of the neutral winds. All these areas are important for developing a plausible scenario for the formation and evolution of the bipolar molecular outflows.This article was processed by the author using the Springer-Verlag T_EX AAR macro package 1991.     

H2 Diagnostics of Magnetic Molecular Shocks in Bipolar Outflows

The shock waves associated with molecular outflows may be of continuous (C) type or jump (J) type, depending on conditions in the preshock gas, notably the magnetic field strength and the degree of ionisation. Intermediate situations also exist, in which a J-discontinuity terminates or is embedded in a C-type flow. We show that proper allowance for the departure of the chemistry from equilibrium (particularly the dissociation/reformation of H₂) and for the inertia of charged dust grains, is crucial for an accurate treatment of the C to J transition. We illustrate the use of H₂ population diagrams and H₂ line profiles, in conjunction with our detailed shock model, to constrain conditions in shocks propagating in molecular outflows. We show that H₂ pure rotational lines yield evidence for C-type precursors in bipolar outflows from young stars, with transverse magnetic field strengths B (μG) ? 1–10 × $\sqrt {n_{H/{\text{cm}}^{ - 3} } } $ similar to those inferred from Zeeman splitting and from the dispersion of dust polarization vectors in dense clouds.     

L 43: the late stages of a molecular outflow

Our new 21-arcsec resolution CO J  = 2 → 1 map of the L 43 dark cloud shows a poorly collimated molecular outflow, with little evidence for wings at velocities 10 km s⁻¹. The outflow appears not to be currently driven by a jet: its structure can instead be modelled as a slowly expanding shell. The shell may be compressed either by a wide-angled wind catching up with an existing shell (as in the case of planetary nebulæ), or by the thermal pressure of a hot low-emissivity medium interior to the shell. The outflow is most probably in a late stage of evolution, and appears to be in the process of blowing away its molecular cloud. We also present a 45-arcsec resolution CO J  = 1 → 0 map of the whole molecular cloud, showing that the outflow structure is clearly visible even in the integrated intensity of this low excitation line, and suggesting that rapid mapping may prove useful as a way of finding regions of outflow activity. We also examine the immediate surroundings of the driving source with 450 μm imaging: this confirms that the outflow has already evacuated a bay in the vicinity of the young stellar object.     

NGC 7538—IRS1致密HⅡ区研究

本文在分析研究NGC7538-IRS1致密HⅡ区H_2CO和OH脉泽辐射VLBI观测结果的基础上,指出该HⅡ区合理的模型是:HⅡ区表面为厚的尘埃层包围,尘埃层两极已被突破,并形成双极流;HⅡ区外面有一个环形转动气体-尘埃云,存在由环向HⅡ区表面的物质下落;包括环和HⅡ区在内的整个系统视向速度为-61km/s,该系统居于视向速度为-57km/s的更大分子云中。H_2CO和OH脉泽发生在HⅡ区两极附近离HⅡ区表面小于0.2R_(HⅡ)的区域内。利用上述模型,还讨论了H_2O脉泽及其他分子吸收线和发射线的发生区域。     

Potential protostars in cloud cores

We present H₂CO observations of young protostar candidates in the Serpens Cloud Core. We find evidence for dense molecular gas in the cores of these objects that is warmer than the surrounding dust. The strong emission and gas properties support the premise that many of these sources may be very young protostars.     

On a new cluster of H<Subscript>2</Subscript>O maser spots in the source ON2

We present the results of our observations of the H₂O maser emission toward the complex source ON2 associated with an active star-forming region. The observations were performed in a wide range of radial velocities, from ?75 to 90 km s^?1. We have detected an emission with flux densities of 9.2, 4, and 26 Jy at radial velocities of ?33.5, ?24.4, and ?18.8 km s^?1, respectively, at which no emission has been observed previously. The detected emission is most likely associated with a hitherto unknown cluster of maser spots located between the northern (N) and southern (S) components of the source ON2 (closer to the northern one). This cluster may be associated with one of the three CO molecular outflows in the ON2 region. We have also detected an emission at ?22 and ?14.5 km s^?1 in N and at 12.6 km s^?1 in S, which has extended significantly the velocity ranges of the maser emission in these sources and allowed their models to be improved.     

Global atmospheric monitoring with SCIAMACHY

SCIAMACHY (SCanning Imaging Absorption spectrometer for Atmospheric CHartographY) is a space based spectrometer designed to measure sunlight transmitted, reflected and scattered by the Earth atmosphere or surface. It is a contribution to the Envisat-1 satellite to be launched in late 1999.SCIAMACHY measurements will provide amounts and distribution of 0₃, BrO, OCl0, ClO, S0₂, H₂CO, N0₂, CO, CO₂, CH₄, H₂O, N₂0, pressure, temperature, aerosol, radiation, cloud cover and cloud top height from atmospheric measurements in nadir, limb and occultation geometry.By the combination of the near simultaneous limb and nadir observations SCIAMACHY is one of a limited number of instruments which is able to detect tropospheric column amounts of 0₃, N0₂, CO, CH₄, H₂O, N₂0, S0₂, H₂CO, and BrO down to the planetary boundary layer under cloud free conditions.     

The organic composition of Comet C/2000 WM1 (LINEAR) revealed through infrared spectroscopy

We investigated the parent volatile composition of the Oort cloud Comet C/2000 WM₁ (LINEAR) on 23-25 November 2001, using the Near Infrared Echelle Spectrograph on the Keck II telescope. Flux-calibrated spectra, absolute production rates, and mixing ratios are presented for H₂O, HCN, CH₄, C₂H₂, C₂H₆, H₂CO, CH₃OH and CO. Compared with “organics-normal” comets, WM₁ is moderately depleted in HCN, CH₄ and CH₃OH, and is even more depleted in C₂H₂ and CO. Its composition is thus intermediate to comets that are severely depleted in their organic volatile composition and those that exhibit “normal” organic volatile abundances. We argue that WM₁ may have formed closer to the young Sun than “organics-normal” comets, but at greater distance than the severely depleted comets, before its ejection to the Oort cloud. The mixing ratios of the above-listed organic volatiles agree day-by-day for 23-25 November 2001. Thus, there is no evidence of macroscopic heterogeneity in chemistry of this comet’s nucleus at the achieved measurement accuracy. As the first comet to show moderate organic depletion in parent volatiles, WM₁ represents an important addition to the emerging taxonomic classification based on chemical composition.     

Far-Infrared CO Rotational Lines in the Orion Molecular Cloud

We present a high signal-to-noise grating spectrum between 43-196.9 μm of the Orion molecular cloud towards the massive star-forming region IRc2, obtained with the Long Wavelength Spectrometer (LWS) on board the Infrared Space Observatory (ISO). CO lines up to J=20-19 have been detected around Orion-IRc2, while in the central position higher quantum numbers have been found. Lines of the ¹³CO isotopic species have also been observed in several directions. In addition, high quality LWS-FP observations of some CO lines have been performed towards IRc2. The data analysis suggest that at least two regions of Orion-IRc2 contribute to the observed CO emission: the ridge, responsible of the spatial extension, and the plateau, dominating the line flux observed towards the center of the map. CO emission through the Orion molecular cloud has been studied in terms of temperature, column density and H₂ volume density, using and Large Velocity Gradient (LVG) model. We find that the flux ratio of the several CO lines can not be explained in terms of an homogeneous source, but a gradient in temperature and density must be involved. Besides the CO lines, several molecular and fine-structure atomic lines have been detected in all observed positions. A detailed discussion of other molecular species rather than CO (H2O, OH...) can be found in the contribution by Cernicharo et al (1998). This revised version was published online in July 2006 with corrections to the Cover Date.     

新外向流源S 146和IRAS 23545 6508

用紫金山天文台青海观测站１３７ｍ射电望远镜对Ｓ１４６和ＩＲＡＳ２３５４５＋６５０８进行了１２ＣＯ（Ｊ＝１－０）谱线的成图观测,结果表明两源附近存在ＣＯ高速外向流．分析了这两个外向流的形态,求出了其物理和动力学参数,同时结合ＩＲＡＳ资料,对中心源的演化阶段和环境气体的热特性作了分析．     

Spectroscopic Observations of Comet C/1996 B2 (Hyakutake) with the Caltech Submillimeter Observatory

The apparition of Comet C/1996 B2 (Hyakutake) offered an unexpected and rare opportunity to probe the inner atmosphere of a comet with high spatial resolution and to investigate with unprecedented sensitivity its chemical composition. We present observations of over 30 submillimeter transitions of HCN, H¹³CN, HNC, HNCO, CO, CH₃OH, and H₂CO in Comet Hyakutake carried out between 1996 March 18 and April 9 at the Caltech Submillimeter Observatory. Detections of the H¹³CN (4–3) and HNCO (16_0,16–15_0,15) transitions represent the first observations of these species in a comet. In addition, several other transitions, including HCN (8–7), CO (4–3), and CO (6–5) are detected for the first time in a comet as is the hyperfine structure of the HCN (4–3) line. The observed intensities of the HCN (4–3) hyperfine components indicate a line center optical depth of 0.9 ± 0.2 on March 22.5 UT. The HCN/HNC abundance ratio in Comet Hyakutake at a heliocentric distance of 1 AU is similar to that measured in the Orion extended ridge— a warm, quiescent molecular cloud. The HCN/H¹³CN abundance ratio implied by our observations is 34 ± 12, similar to that measured in giant molecular clouds in the galactic disk but significantly lower than the Solar System¹²C/¹³C ratio. The low HCN/H¹³CN abundance ratio may be in part due to contamination by an SO₂line blended with the H¹³CN (4–3) line. In addition, chemical models suggest that the HCN/H¹³CN ratio can be affected by fractionation during the collapse phase of the protosolar nebula; hence a low HCN/H¹³CN ratio observed in a comet is not inconsistent with the solar system¹²C/¹³C isotopic ratio. The abundance of HNCO relative to water derived from our observations is (7 ± 3) × 10⁻⁴. The HCN/HNCO abundance ratio is similar to that measured in the core of Sagittarius B2 molecular cloud. Although a photo-dissociative channel of HNCO leads to CO, the CO produced by HNCO is a negligible component of cometary atmospheres. Production rates of HCN, CO, H₂CO, and CH₃OH are presented. Inferred molecular abundances relative to water are typical of those measured in comets at 1 AU from the Sun. The exception is CO, for which we derive a large relative abundance of 30%. The evolution of the HCN production rate between March 20 and March 30 suggests that the increased activity of the comet was the cause of the fragmentation of the nucleus. The time evolution of the H₂CO emission suggests production of this species from dust grains.