CO Line Wings Research Articles

Mid-J CO Line Observations of Protostellar Outflows in the Orion Molecular Clouds

Ten protostellar outflows in the Orion molecular clouds were mapped in the $^{12}$CO/$^{13}$CO ${J=6\rightarrow5}$ and $^{12}$CO ${J=7\rightarrow6}$ lines. The maps of these mid-$J$ CO lines have an angular resolution of about 10$''$ and a typical field size of about 100$''$. Physical parameters of the molecular outflows were derived, including mass transfer rates, kinetic luminosities, and outflow forces. The outflow sample was expanded by re-analyzing archival data of nearby low-luminosity protostars, to cover a wide range of bolometric luminosities. Outflow parameters derived from other transitions of CO were compared. The mid-$J$ ($J_{\rm up} \approx 6$) and low-$J$ ($J_{\rm up} \leq 3$) CO line wings trace essentially the same outflow component. By contrast, the high-$J$ (up to $J_{\rm up} \approx 50$) line-emission luminosity of CO shows little correlation with the kinetic luminosity from the ${J=6\rightarrow5}$ line, which suggests that they trace distinct components. The low/mid-$J$ CO line wings trace long-term outflow behaviors while the high-$J$ CO lines are sensitive to short-term activities. The correlations between the outflow parameters and protostellar properties are presented, which shows that the strengths of molecular outflows increase with bolometric luminosity and envelope mass.

ALMA Detections of the Youngest Protostars in Ophiuchus

Abstract We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of 1.1 mm dust continuum and CO 2–1 emission toward six dense cores within the Ophiuchus molecular cloud. We detect compact, subarcsecond continuum structures toward three targets, two of which (Oph A N6 and SM1) are located in the Ophiuchus A ridge. Two targets, SM1 and GSS 30, contain two compact sources within the ALMA primary beam. We argue that several of the compact structures are small (R ≲ 80 au) accretion disks around young protostars, based on their resolved, elongated structures, coincident radio and X-ray detections, or bipolar outflow detections. While CO line wings extend to ±10–20 km s−1 for the more evolved sources GSS 30 IRS3 and IRS1, CO emission toward other sources, where detected, only extends a few km s−1 from the cloud v LSR. The dust spectral index toward the compact objects suggests either that the disks are optically thick at 1.1 mm or that significant grain growth has already occurred. We identify, for the first time, a single compact continuum source (R ∼ 100 au) toward N6 embedded within a larger continuum structure. SM1N is extended in the continuum but is highly centrally concentrated, with a density profile that follows a r −1.3 power law within 200 au and additional structure suggested by the uv-data. Both N6 and SM1N show no clear bipolar outflows with velocities greater than a few km s−1 from the cloud velocity. These sources are candidates to be the youngest protostars or first hydrostatic cores in the Ophiuchus molecular cloud.

Search for class I methanol maser emission in various types of objects in the interstellar medium

Observations of various types of objects in the northern sky were obtained at 44 GHz in the 70-61A+ methanol line on the 20-m Onsala radio telescope (Sweden), in order to search for Class I methanol maser emission in the interstellar medium: regions of formation of high-mass stars, dust rings around HII regions, and protostellar candidates associated with powerful molecular outflows and Galactic HII regions. Seven new Class Imethanolmasers have been discovered toward regions of formation of highmass stars, and the existence of two previously observed masers confirmed. The following conclusions are drawn: (1) neither the association of a bipolar outflow manifest in the wings of CO lines with a highmass protostellar object (HMPO) nor the presence of thermal emission in lines of complex molecules are sufficient conditions for the detection of Class I methanol emission; no association with HMPOs radiating at 44 GHz was found for EGOs (a new class of object tracing bipolar outflows); (2) the existence of H2O masers and Class II methanol masers in the region of aHMPOenhances the probability of detecting Class I methanol emission toward the HMPO; Class II methanol masers with stronger line fluxes are associated with Class I methanol masers.

OUTFLOWS, ACCRETION, AND CLUSTERED PROTOSTELLAR CORES AROUND A FORMING O STAR

We present a Submillimeter Array study in the 1.3 mm waveband of the NGC 7538 IRS 1--3 massive star-forming region. The brightest core in the mm continuum map, MM1, harbors the IRS 1 young O star. The core has a gas temperature of about 245 K and shows spatially unresolved emission in complex organic molecules, all typical of a hot molecular core. Toward MM1, redshifted absorption is seen in molecular lines with different energies above the ground state. This absorption probes inward motion of the dense gas toward the central young O star, and the estimated mass accretion rate reaches 10^{-3} Msun/yr. Multiple outflows are seen in the CO and 13CO maps. The gas mass of 50 Msun and mass outflow rate of 2.5 by 10^{-3} Msun/yr measured in CO line wings are dominated by the MM1 outflow, which is most likely driven by a fast wide-angle wind. Apart from MM1, we discover eight new dusty cores, MM2--9, within a projected distance of 0.35 pc from MM1. These cores show no counterpart in infrared or radio continuum emission, while seven of them appear to be forming intermediate- to high-mass stars. This manifests a deeply embedded star-forming component of the parent cloud of IRS 1--3. Apparently we are observing a Trapezium system in formation, and the system is presumably surrounded by a cluster of lower mass stars.

Detection of Shocked Molecular Gas by Full-Extent Mapping of the Supernova Remnant W44

Molecular gas toward the supernova remnant (SNR) W44 (G34.7� 0.4) was extensively mapped in CO J ¼ 1 0 emission with the 17 0 beam of the Nobeyama 45 m radio telescope. We detected high-velocity (>25 km s � 1 ) CO line wings. They are confined to compact (� 1.5 pc) spots, and they are located adjacent to bright radio filaments or knots. The low 13 CO/ 12 CO intensity ratio of 0.03 and high HCO + / 12 CO intensity ratio of 0.3 suggest that the wing-emitting gas has a moderate 12 CO opacity of � 1 and a high density of n(H2 )>1 0 5 cm � 3 . This gas might be shocked molecular gas that has been accelerated and compressed by the expanding blast waves of W44. In addition, the high spatial resolution CO maps reveal several other features that may reveal the interaction between the SNR and the surrounding interstellar gas. The giant molecular cloud CO G34.8� 0.6 (vLSR ¼ 48 km s � 1 ) has a sharp edge coincident with the eastern radio continuum rim of W44, which may indicate that we observe the SNR/cloud interaction almost edge-on. The existence of the ‘‘edge’’ suggests that most of the molecular mass resides in smaller clumps that evaporate rapidly after the passage of the supernova blast wave. We also find spatially extended moderately broad emission (SEMBE) with a moderately large intensity of � 30 K km s � 1 in CO J ¼ 1 0 and a typical line width of � 10 km s � 1 (FWHM). Its extent coincides with the brighter region of the radio synchrotron emission. We discuss the SEMBE in terms of molecular clumps shocked and disturbed by the compressed shell of the SNR.

High‐Resolution 4.7 Micron Keck/NIRSPEC Spectra of Protostars. II. Detection of the13CO Isotope in Icy Grain Mantles

We explore the infrared M band (4.7 micron) spectrum of the class I protostar L1489 IRS in the Taurus Molecular Cloud. This is the highest resolution wide coverage spectrum at this wavelength of a low mass protostar observed to date (R =25,000; (Delta)v =12 km s(exp -1). A large number of narrow absorption lines of gas phase (12)CO, (13)CO, and C(sup 18)O are detected, as well as a prominent band of solid (12)CO. The gas phase (12)CO lines have red shifted absorption wings (up to 100 km s(exp -1)), which likely originate from warm disk material falling toward the central object. Both the isotopes and the extent of the (12)CO line wings are successfully fitted with a contracting disk model of this evolutionary transitional object. This shows that the inward motions seen in millimeter wave emission lines continue to within approx. 0.1 AU from the star. The amount of high velocity infalling gas is however overestimated by this model, suggesting that only part of the disk is infalling, e.g. a hot surface layer or hot gas in magnetic field tubes. The colder parts of the disk are traced by the prominent CO ice band. The band profile results from CO in 'polar' ices (CO mixed with H2O), and CO in 'apolar' ices. At the high spectral resolution, the 'apolar' component is, for the first time, resolved into two distinct components, likely due to pure CO and CO mixed with CO2, O2 and/or N2. The ices have probably experienced thermal processing in the upper disk layer traced by our pencil absorption beam: much of the volatile 'apolar' ices has evaporated, the depletion factor of CO onto grains is remarkably low (approx. 7%), and the CO2 traced in the CO band profile was possibly formed energetically. This study shows that high spectral resolution 4.7 micron observations provide important and unique information on the dynamics and structure of protostellar disks and the origin and evolution of ices in these disks.

High‐Resolution 4.7 Micron Keck/NIRSPEC Spectra of Protostars. I. Ices and Infalling Gas in the Disk of L1489 IRS

We explore the infrared M-band (4.7 μm) spectrum of the Class I protostar L1489 IRS in the Taurus molecular cloud. This is the highest-resolution wide-coverage spectrum at this wavelength of a low-mass protostar observed to date (R = 25,000; Δv = 12 km s^(-1)). A large number of narrow absorption lines of gas-phase ^(12)CO, ^(13)CO, and C^(18)O are detected, as well as a prominent band of solid ^(12)CO. The gas-phase ^(12)CO lines have redshifted absorption wings (up to 100 km s^(-1)), which likely originate from warm disk material falling toward the central object. Both the isotopes and the extent of the ^(12)CO line wings are successfully fitted with a contracting-disk model of this evolutionary transitional object. This shows that the inward motions seen in millimeter-wave emission lines continue to within ~0.1 AU of the star. The amount of high-velocity infalling gas is, however, overestimated by this model, suggesting that only part of the disk is infalling, e.g., a hot surface layer or hot gas in magnetic field tubes. The colder parts of the disk are traced by the prominent CO-ice band. The band profile results from CO in polar ices (CO mixed with H_2O) and CO in apolar ices. At high spectral resolution, the apolar component is, for the first time, resolved into two distinct components, likely due to pure CO and CO mixed with CO_2, O_2, and/or N_2. The ices have probably undergone thermal processing in the upper disk layer traced by our pencil absorption beam: much of the volatile apolar ices has evaporated, the depletion factor of CO onto grains is remarkably low (~7%), and the CO_2 traced in the CO-band profile was possibly formed energetically. This study shows that high spectral resolution 4.7 μm observations provide important and unique information on the dynamics and structure of protostellar disks and on the origin and evolution of ices in these disks.

Properties of the molecular cloud about S140 IRS 1 deduced from HCO(+) J = 3-2 observations

HCO(+) J = 3-2 emission from the molecular cloud centered on S140 IRS 1 has been observed with a spatial resolution of 20 arcsec. The innermost region of the cloud is characterized by strong HCO(+) J = 3-2 emission elongated in a north-south direction, having the same orientation as the bipolar outflow previously discovered from CO line wings. The HCO(+) J = 3-2 lines exhibit broad, asymmetric wings. The full width of the wings at the position of IRS 1 is 30 km/s. In a nine-point average spectrum, the wings have a total width of 60 km/s. The blue and red wing emissions show no spatial displacement, in contrast to CO line wings.

Collisions Between High Latitude Clouds: Theory Meets Observations

We report on fully three-dimensional hydrodynamic and radiative transfer simulations of collisions between high latitude clouds. Our model uses the smoothed particle hydrodynamics code described by Lattanzio and Henriksen (1988) to compute the velocity, temperature, and density fields in the impacted clouds and a recently developed radiative transfer code to compute 13 CO line radiation from the simulated source. By including the instrumental effects involved in a particular observations we can make detailed comparisons with the observations. The model shows that: 1) The previously unexplained energy source for the broad CO line wings reported by Blitz, Magnani, and Wandel (1988) derives from the collisions. 2) Collisions can induce rapid gravitational collapse and star formation in these clouds which are otherwise supported against gravitational contraction via their internal energy content. 3) The external pressure due to intercloud HI, firts proposed for these objects by Keto and Myers (1986), plays a significant role in the stability and evolution of the high latitude clouds.

Energetic activity in a star-forming molecular cloud core - A disk constrained bipolar outflow in NGC 2071

The discovery of an extended, high-velocity molecular outflow associated with the infrared sources in NGC 2071 is reported. High-velocity CO emission from this star-forming molecular cloud core can be traced over a region 4' in diameter and detected over a velocity range of 70 km s/sup -1/. The flow is bipolar; the blueshifted CO emission is displaced to the northeast, while the redshifted emission is displaced to the southwest. Observations in the 98 GHz transition of CS reveal a ridge of dense gas oriented orthogonal to the high-velocity flow axis. A systematic velocity gradient seen in the CS line core suggests that the ridge is a dense, rotating disk centered on the IR source. The disk may be responsible for collimating a spherically symmetric wind originating near the IR source into the bipolar flow observed in the high-velocity CO line wings. The high-velocity CO line wings are modeled as beam diluted emission from clumps or filaments with /sup 12/ CO optical depths close to unity and a small filling factor. The clumps may be either objects ejected from the vicinity of the central infrared source or shocked gas at the front where a higher velocity but invisible flow encounters ambientmore » cloud material.« less

High-velocity CO wings and CO self-reversals

The redshifted and blueshifted CO line wings are found to occur in two oppositely directed lobes in a number of molecular clouds associated with recent star formation. These CO lobes may have their origin in nonisotropic mass outflow from young protostellar objects embedded in the cloud. Away from the cloud's dense core, the velocity extent of the CO wings decreases with projected radial distance (R), following a R/sup -0.5/ law indicating deceleration of the stellar wind material as it encounters the surrounding molecular cloud. CO profiles with enhanced wings are found beyond the boundaries of the compact H II region-molecular cloud interface have line widths narrower than the /sup 13/CO lines and much narrower than the broad CO profiles. This suggests that carbon recombination line emission and the broad wings of CO lines arise in substantially different regimes in the cloud.