Bipolar CO Outflow Research Articles

Multiwavelength investigation of extended green object G19.88-0.53: revealing a protocluster

ABSTRACT A multiwavelength analysis of star formation associated with the extended green object, G19.88-0.53 is presented in this paper. With multiple detected radio and millimetre components, G19.88-0.53 unveils as harbouring a protocluster rather than a single massive young stellar object. We detect an ionized thermal jet using the upgraded Giant Meterwave Radio Telescope, India, which is found to be associated with a massive, dense and hot ALMA 2.7 mm core driving a bipolar CO outflow. Near-infrared spectroscopy with UKIRT–UIST shows the presence of multiple shock-excited H2 lines concurrent with the nature of this region. Detailed investigation of the gas kinematics using ALMA data reveals G19.88-0.53 as an active protocluster with high-mass star-forming components spanning a wide evolutionary spectrum from hot cores in accretion phase to cores driving multiple outflows to possible UCH ii regions.

A study on subarcsecond scales of the ammonia and continuum emission toward the G16.59−0.05 high-mass star-forming region

We wish to investigate the structure, velocity field, and stellar content of the G16.59-0.05 high-mass star-forming region, where previous studies have established the presence of two almost perpendicular (NE-SW and SE-NW), massive outflows, and a rotating disk traced by methanol maser emission. We performed Very Large Array observations of the radio continuum and ammonia line emission, complemented by COMICS/Subaru and Hi-GAL/Herschel images in the mid- and far-infrared (IR). Our centimeter continuum maps reveal a collimated radio jet that is oriented E-W and centered on the methanol maser disk, placed at the SE border of a compact molecular core. The spectral index of the jet is negative, indicating non-thermal emission over most of the jet, except the peak close to the maser disk, where thermal free-free emission is observed. We find that the ammonia emission presents a bipolar structure consistent (on a smaller scale) in direction and velocity with that of the NE-SW bipolar outflow detected in previous CO observations. After analyzing our previous N2H+(1-0) observations again, we conclude that two scenarios are possible. In one case both the radio jet and the ammonia emission would trace the root of the large-scale CO bipolar outflow. The different orientation of the jet and the ammonia flow could be explained by precession and/or a non-isotropic density distribution around the star. In the other case, the N2H+(1-0) and ammonia bipolarity is interpreted as two overlapping clumps moving with different velocities along the line of sight. The ammonia gas also seems to undergo rotation consistent with the maser disk. Our IR images complemented by archival data allow us to derive a bolometric luminosity of about 10^4 L_sun and to conclude that most of the luminosity is due to the young stellar object associated with the maser disk.

Three intermediate-mass young stellar objects with different properties emerging from the same natal cloud in IRAS 00117+6412

We observed with the VLA, PdBI, and SMA the centimeter and millimeter continuum, N2H+(1-0), and CO(2-1) emission associated with a dusty cloud harboring a nascent cluster with intermediate-mass protostars. At centimeter wavelengths we found a strong source, tracing a UCHII region, at the eastern edge of the dusty cloud, with a shell-like structure, and with the near-infrared counterpart falling in the center of the shell. This is presumably the most massive source of the forming cluster. About 15'' to the west of the UCHII region and well embedded in the dusty cloud, we detected a strong millimeter source, MM1, associated with centimeter and near-infrared emission. MM1 seems to be driving a prominent high-velocity CO bipolar outflow, and is embedded in a ridge of dense gas traced by N2H+. We estimated that MM1 is an intermediate-mass source in the Class 0/I phase. About 15'' to the south of MM1, and still more deeply embedded in the dusty cloud, we detected a compact millimeter source, MM2, with neither centimeter nor near-infrared emission, but with water maser emission. MM2 is associated with a clump of N2H+, whose kinematics reveal a clear velocity gradient and additionally we found signposts of infall motions. MM2, being deeply embedded within the dusty cloud, with an associated water maser but no hints of CO outflow emission, is an intriguing object, presumably of intermediate mass. In conclusion, the UCHII region is found at the border of a dusty cloud which is currently undergoing active star formation. Two intermediate-mass protostars in the dusty cloud seem to have formed after the UCHII region and have different properties related to the outflow phenomenon.

Massive star formation and feedback in W49A: the source of our Galaxy's most luminous water maser outflow

We present high spatial resolution mid-IR images of the ring of UCHII regions in W49A obtained at Gemini North, allowing us to identify the driving source of its powerful H2O maser outflow. These data also confirm our previous report that several radio sources in the ring are undetected in the mid-IR because they are embedded deep inside the cloud core. We locate the source of the water maser outflow at the position of the compact mid-IR peak of source G (source G:IRS1). This IR source is not coincident with any identified compact radio continuum source, but is coincident with a hot molecular core, so we propose that G:IRS1 is a hot core driving an outflow analogous to the wide-angle bipolar outflow in OMC-1. G:IRS1 is at the origin of a larger bipolar cavity and CO outflow. The water maser outflow is orthogonal to the bipolar CO cavity, so the masers probably reside near its waist in the cavity walls. Models of the IR emission require a massive protostar of 45Msun, 3e5Lsun, and an effective envelope accretion rate of 1e-3Msun/yr. Feedback from the central star could potentially drive the H2O maser outflow, but it has insufficient radiative momentum to have driven the large-scale CO outflow, requiring that this massive star had an active accretion disk over the past 10^4 yr. Combined with the spatialy resolved morphology in IR images, G:IRS1 in W49 provides compelling evidence for a massive protostar that formed by accreting from a disk, accompanied by a bipolar outflow.

Submillimeter Observations of the Isolated Massive Dense Clump IRAS 20126+4104

We used the CSO 10.4 meter telescope to image the 350 micron and 450 micron continuum and CO J=6-5 line emission of the IRAS 20126+4104 clump. The continuum and line observations show that the clump is isolated over a 4 pc region and has a radius of ~ 0.5 pc. Our analysis shows that the clump has a radial density profile propto r ^{-1.2} for r ~ 0.1 pc which suggests the inner region is infalling, while the infall wave has not yet reached the outer region. Assuming temperature gradient of r^{-0.35}, the power law indices become propto r ^{-0.9} for r ~ 0.1 pc. Based on a map of the flux ratio of 350micron/450micron, we identify three distinct regions: a bipolar feature that coincides with the large scale CO bipolar outflow; a cocoon-like region that encases the bipolar feature and has a warm surface; and a cold layer outside of the cocoon region. The complex patterns of the flux ratio map indicates that the clump is no longer uniform in terms of temperature as well as dust properties. The CO emission near the systemic velocity traces the dense clump and the outer layer of the clump shows narrow line widths ( ~ 0.03 pc disk associated with the (proto)star. This is one of four objects in high-mass and low-mass star forming regions for which a discrepancy between the rotation sense of the envelope and the core has been found, suggesting that such a complex kinematics may not be unusual in star forming regions.

Mapping the PAHs and H2 in ρ Oph A

AbstractWe present an ISOCAM-CVF map of the ρ Oph A region, covering 3′ × 3′. For each 6 arcsec2 pixel, we extract the spectrum from 5–15 μm. We determine the fluxes of the main PAH features by fitting Lorentzian profiles to the spectrum. The peaks of the various PAH components correspond well with the known positions of the PDRs in this vicinity. The spectrum in several pixels exhibits strong rotational lines of molecular hydrogen which can be used to derive the physical properties of the cloud. The H2 emission traces the hot gas of the bipolar CO outflow from VLA1623.

The hyperyoung H ii region in G24.78+0.08 A1

Context. G24.78+0.08 A1 is a 20 $M_\odot$ star surrounded by a hypercompact (HC) Hii region, driving a CO bipolar outflow, and located at the center of a massive rotating toroid undergoing infall towards the HC Hii region. Recent water maser observations suggest that the HC Hii region is expanding and accretion onto the star is halted. Aims. To confirm the expansion scenario proposed for the HC Hii region on the basis of recent H 2 O maser observations. Methods. We carried out continuum VLA observations at 1.3 cm and 7 mm with the A array plus Pie Town configuration to map the HC Hii region towards G24.78+0.08 A1. Results. The emission of the HC Hii region has been resolved and shows a ring-shape structure. The profiles of the emission obtained by taking slices at different angles passing through the barycenter of the HC Hii region confirm the shell structure of the emission. The ratio between the inner and the outer radius of the shell, $R_{\rm i}/R_{\rm o}$, derived by fitting the normalized brightness temperature profile passing through the peak of the 7 mm emission, is 0.9, which indicates that the shell is thin. The deconvolved outer radius estimated from the fit is 590 AU. These results imply that the HC Hii region in G24 A1 cannot be described in terms of a classical, homogeneous Hii region but is instead an ionized shell. This gives support to the model of an expanding wind-driven, ionized shell suggested by the kinematics and distribution of the H 2 O masers associated with the HC Hii region. According to this model, the HC Hii region is expanding on very short times scales, 21–66 yr.

ISO-Cha I 192: A New Embedded Eruptive Variable in the Chamaeleon I Dark Cloud

We report the detection of an increase of about 2 mag in the 2.2 μm brightness of ISO-Cha I 192, a class I low-mass stellar object thought to be driving a bipolar CO outflow in the Chamaeleon I cloud. This substantial brightness change has taken place during less than 3 yr, from 1996 March to 1999 April. An elongated infrared reflection nebula of size ∼530 AU is seen originating from the star in the direction of the CO bipolar outflow. The historic infrared properties of this young stellar object are examined in order to substantiate the hypothesis that this object is an FU Ori- or EX Lup-type system. Combining our new ground-based near- and mid-infrared photometry with Spitzer IRAC and MIPS broadband fluxes supplemented by published recent spectrophotometry, the spectral energy distribution of this source was constructed. We explored the plausibility of a "standard" configuration of infalling envelope + disk + central source for this object by fitting a two-dimensional radiative transfer code that includes the contributions of each of these components.

Near-infrared polarimetric and spectrometric study of the massive star-forming region S87

We present JHK' imaging polarimetry for the massive star-forming region S87, and K-band spectrometry from 2.0 to 2.35 mum for several infrared sources in the region. The polarimetric patterns of S87E reveal a deeply embedded source (DES-S87) associated with reflection nebulosities. Exciting OH maser and 1.3 mm dust continuum emission, the DES-S87 is suggested to be the youngest star in S87 and the driving source of bipolar CO outflow in the region. A blue cavity is discovered in the [J-K'] color image, to the southwest of DES. Radial dependence of polarization degrees in the cavity could be fitted to the slab model of outflows at an inclination of similar to60degrees out of the plane of the sky (Minchin et al. 1991b). The nebular complex of S87E can be divided into three area. The North nebula, exhibiting a bipolar structure, may represent a bipolar outflow in the northwest-southeast direction. The southwest nebula traces the blueshifted CO outflow and corresponds to the cavity structure discovered in the [J-K'] color image. The nebular structure of S87E suggests a quadrupolar outflow driven by DES-S87. A well-defined centrosymmetric pattern is found in the nebula of S87W with high degrees of polarization, which indicates single scattering off small dust grains in the reflection nebula. The polarimetric vectors around NIRSA show a polarization disk feature oriented in the southeast-northwest direction. Strong Brgamma emission and H-2 emissions are found in the K-band spectra, indicating the presences of strong stellar wind, envelope/disk, shocked gas, and high-density PDRs in the circumstellar environment of S87E and S87W. According to the K-band spectrum, the mass of DES-S87E is estimated to be 20 M-circle dot.

Observations of H2O maser and continuum emission in AFGL 2591

We report results of radio continuum (1.3 and 3.6 cm) and H2O maser line observations, made with the Very Large Array (A configuration), toward the star-forming region AFGL 2591. We detected 85 maser spots toward this region, which are distributed in three main groups. Two of these groups spatially coincide with the radio continuum sources VLA 2 and VLA 3. The maser spots associated with VLA 3 are distributed along a shell-like structure of 0.01 and nearly perpendicular to the CO bipolar outflow. We propose that VLA 3 is the center of the observed molecular flow in this region. Finally, we confirm that AFGL 2591 region is a cluster of B type stars, each one with its own optically thin H II region.

Very Large Array Observations of High‐Velocity Hiin L1551

We report Very Large Array (VLA) observations of the 21 cm continuum and H I line emission of the neutral wind in the prototypical molecular outflow source L1551. The intermediate-velocity gas observed with the VLA has a velocity with respect to the ambient cloud in the range 10-50 km s-1. Although the blueshifted flow appears weaker than the red one, the maps are indicative of a bipolar morphology confined inside the large-scale CO bipolar lobes. This morphology strongly suggests that the atomic wind is driving the bipolar CO outflow. We fit to the H I line profiles, at four different positions along the redshifted flow axis, a model of a decelerating conical wind that entrains ambient cloud material in a mixing layer at the walls of the cone. This model has a velocity at the axis v0 = 200 km s-1, a mass-loss rate * 9 × 10-7 M☉ yr-1, and a momentum rate 2 × 10-4 M☉ yr-1 km s-1. This is sufficient to drive the observed molecular flow, provided an age ≥8 × 104 yr. We find that the continuum emission spectrum of IRS 5, on scales of 10'', is similar to those of H II regions. This can be explained if most of the emission comes from material ionized by UV radiation from shock fronts due to the interaction of the stellar wind against the ambient cloud. The momentum rate required to produce the extended centimeter emission agrees well with the wind obtained by fitting the line profiles. Finally, the location of a background extragalactic continuum source in the red lobe allows us to probe the physical conditions of the neutral wind. We find that the most probable H I spin temperature in the wind is in the range 25-50 K, in agreement with predictions of the thermal structure of such winds.

A Molecular Counterpart to the HH 1–2 Flow

We present high angular resolution (12''-24'') and high-sensitivity 12CO and 13CO J = 2-1 and J = 1-0 observations of the HH 1-2 outflow. The observations show the molecular counterpart, moving with a velocity of 30 km s-1, of the optical bipolar system driven by the VLA 1 embedded source. Along with the optical jet there are certain regions where the molecular gas reaches deprojected velocities of 100-200 km s-1 and that we interpret as the molecular jet. The bipolar CO outflow has a length of ~260'' with a curved morphology toward the north where it extends beyond the HH 1 object (120''). Two new molecular outflows have been detected, one arising from IRAS 05339-0647, which excites the HH 147 optical flow, and another powered by VLA 2, which drives the HH 144 optical outflow. The molecular outflow driven by the VLA 3 source is also clearly detected and spatially resolved from the VLA 1 main outflow.

A Jet–driven, Extreme High‐Velocity Outflow Powered by a Cold, Low‐Luminosity Protostar near NGC 2023

We have discovered an extreme high-velocity bipolar CO outflow in the vicinity of NGC 2023, with total outflow velocities of ~200 km s-1. At very high velocities this outflow is jetlike with an opening angle ≤4°, while it shows a separate outflow lobe at low velocities. The outflow is bipolar and exhibits a clear mirror symmetry, which suggests that the source powering the outflow is episodic or precessing. The dynamical timescales for the outflow are ≤3000 yr. We identify the source driving the CO jet with a deeply embedded low-luminosity submillimeter double source (separation ~23''), where the primary component lies on the symmetry axis of the outflow and has all the signatures of a protostellar object. Analysis of molecular data and (sub)millimeter photometry suggests that the driving source is cold and compact, with a luminosity of lesssim10 L☉ and a total mass of 1.8-4.6 M☉. It has no near-IR counterpart, it drives an extremely young outflow, and it emits a large fraction of its luminosity in the submillimeter regime. Both millimeter sources have low dust emissivity, β ~ 0.8-1.3, similar to what is found for other class 0 objects, while the surrounding molecular cloud core appears to have a β ~ 2.0, the canonical value for normal interstellar dust in the submillimeter regime.

Discovery of an Extremely Young Accreting Protostar in Taurus

We report the discovery of a new, very young accreting class 0 protostar in the southern part of the Taurus molecular cloud. This object, designated by IRAM 04191+1522, coincides with a cold (T~12 K) dust continuum condensation found at 1.3 mm with the IRAM 30 m telescope ~1' southwest of the class I infrared source IRAS 04191+1523. Although IRAM 04191+1522 was not seen by IRAS, it is associated with a weak 3.6 cm VLA radio continuum source, a highly collimated CO bipolar outflow, and 60-850 μm emission detected by ISOPHOT and SCUBA. Molecular line observations are consistent with the protostellar condensation currently undergoing gravitational collapse. The spectral energy distribution and low bolometric luminosity (Lbol~0.15 L☉) we derive suggest that the protostellar core at the center of IRAM 04191+1522 may still be dissociating molecular hydrogen. High-resolution snapshot 1.4 mm continuum observations with the IRAM interferometer fail to detect this protostar, implying it has not yet developed a large accretion disk.

Shock-excited H[TINF]2[/TINF] Flows in OMC-2 and OMC-3

We report the discovery of nearly a dozen collimated outflows from young stellar objects embedded in the molecular filament that extends north of the Orion Nebula towards the H II region NGC 1977. The large number of nearly coeval outflows and embedded class 0 young stellar objects indicates that the OMC-2/3 region is one of the most active sites of ongoing low- to intermediate-mass star formation known. These outflows were identified in the 2.12 μm v = 1-0 S(1) H2 line during a survey of a 6' × 16' region containing the OMC-2 and OMC-3 cloud cores and over a dozen recently discovered class 0 protostars. We also observe filamentary emission that is likely to trace possible fluorescent H2 in photodissociation regions associated with M43 and NGC 1977. Neither the suspected outflows nor the fluorescent emission are seen at the continuum wavelength of 2.14 μm, which confirms their emission-line nature. Several of the new H2 flows are associated with recently discovered bipolar molecular outflows. However, the most prominent bipolar CO outflow from the region (the MMS 8 flow) has no clear H2 counterpart. Several H2 flows consist of chains of knots and compact bow shocks that likely trace highly collimated protostellar jets. Our discovery of more than 80 individual H2-emitting shocks demonstrate that outflows from young stars are churning this molecular cloud.

Dust Filaments and Star Formation in OMC-2 and OMC-3

We have mapped the 1300 μm dust emission of a 6' × 16' field in the OMC-2 and -3 region and detected an extended filamentary structure with at least 11 embedded condensations in OMC-2 and 10 in OMC-3. Six have been observed previously at 1300 μm, and two were also detected by IRAS. We observed eight of the new sources at six wave bands from 350 to 2000 μm and derived upper limits for their far-infrared (FIR) emission from the IRAS raw data. The millimeter/submillimeter emission originates from cold dust (Td ~ 20 K), and the individual components have gas masses of 5 M☉ < Mgas < 36 M☉. The ratio Lbol/Lsmm is below 70 for six sources associated with OMC-3, indicating that they are class 0-type objects. Condensations in the OMC-2 region have Lbol/Lsmm ≤ 360, suggesting an evolutionary effect from north to south. We report the discovery of a highly collimated bipolar CO outflow, most likely driven by the source OMC-3 MMS 8. The flow is over 5' (0.7 pc) long and less than 1' (0.15 pc) wide and is oriented nearly east-west. Less prominent outflows are associated with OMC-2 FIR 2/3 and OMC-3 MMS 6. The 1300 μm continuum emission is confined to a ridge less than 1' wide while the emission in J = 2-113CO, C18O, and CS is between 5' and 10' wide. The continuum emission is displaced toward the eastern side of the molecular ridge that contains it. Most 1300 μm sources lie in or close to line emission peaks. However, not all line emission peaks contain prominent 1300 μm continuum sources. The curved filamentary structure of the large-scale dust and molecular emission is likely the result of compression by the superbubble centered ~25-70 pc further north, plus the impact of energy from the younger 1c subgroup of the Orion OB association, which lies 10-50 pc in front of our mapped region, and by the very recent expansion of the NGC 1977 and M42 H II regions.

Discovery of a molecular hydrogen jet near IC 348

view Abstract Citations (162) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Discovery of a Molecular Hydrogen Jet near IC 348 McCaughrean, Mark J. ; Rayner, John T. ; Zinnecker, Hans Abstract We present near-infrared images of a newly discovered molecular hydrogen jet (HH 211) near the young stellar cluster IC 348 in the Perseus dark cloud complex. A wide-field true-color JHK' image locates HH 211 relative to the embedded source IC 348 IR, and a high-resolution image taken in the H2 upsilon = 1 - 0 S(1) line at 2.122 micrometers delineates the shock-excited gas. The jet is very young, with a dynamical age of less than 1000 yr. We suggest that the H2 emission arises in a turbulent sheath around the true jet, leading to an unusual symmetric limb-brightened appearance. This boundary layer is probably where ambient molecular material is being entrained to form a coincident bipolar CO outflow. We discuss possible models for the knots in HH 211, including internal working surfaces in an episodic outflow and crossing shocks in a recollimating jet. The exciting source of the jet and outflow was detected at lambda greater than or = 350 micrometers, and our observations imply that the exciting source is a young star deeply embedded in a dense NH3 core, perhaps an edge-on circumstellar disk. The HH 211 system of jet, molecular outflow, and embedded exciting source is the first discovered through near-infrared imaging. Publication: The Astrophysical Journal Pub Date: December 1994 DOI: 10.1086/187664 Bibcode: 1994ApJ...436L.189M Keywords: Hydrogen; Interstellar Gas; Jet Flow; Molecular Clouds; Molecular Flow; Star Clusters; Star Formation; Stellar Envelopes; Rosat Mission; Stellar Luminosity; Astrophysics; STARS: CIRCUMSTELLAR MATTER; INFRARED: ISM: CONTINUUM; INFRARED: ISM: LINES AND BANDS; ISM: JETS AND OUTFLOWS; ISM: MOLECULES; STARS: FORMATION full text sources ADS | data products SIMBAD (39)

Submillimetre and near-infrared observations of L1448: a curving Formula jet with multiple bow shocks

A high-resolution (0.6 arcsec pixel −1 ), narrow-band, H 2 v=1-0 S(1) image of the high-velocity CO outflow in L1448 reveals a remarkable jet-like structure. The coincidence of this H 2 jet with the CO bipolar outflow implies a close association between the two phenomena. The H 2 jet comprises a series of knots, and three bow-shaped features equally spaced along the jet length, which we associate with the sporadic nature of this outflow. K-band imaging of the source also shows a conical reflection nebula extending towards the H 2 jet structure, whilst maps in HCO + J=3-2 and CS J=5-4 show two peaks, one towards the source of the H 2 jet and CO outflow, and the other towards the infrared source IRS 3 situated to the north of this region

The outflow in the L1157 dark cloud - Evidence for shock heating of the interacting gas

view Abstract Citations (95) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Outflow in the L1157 Dark Cloud: Evidence for Shock Heating of the Interacting Gas Umemoto, T. ; Iwata, T. ; Fukui, Y. ; Mikami, H. ; Yamamoto, S. ; Kameya, O. ; Hirano, N. Abstract In the L1157 dark cloud, a well-collimated bipolar CO outflow associated with a cold IRAS source 20386 + 6751 was discovered. The gas temperature toward the blue lobe of the outflow rises to about 30 K from the temperature of the surrounding gas (not greater than 10 K); this high temperature region is very localized within the blue lobe. The HCO(+), HCN, and NH3 lines show blueshifted and broad-line profiles toward the blue CO lobe. Furthermore, their distributions are similar to that of the blue lobe. Analysis of the energy of the outflow and dense gas suggests that a strong shock caused by the outflow is responsible for the temperature enhancement. Such shock heating has rarely been observed in low-mass star-forming regions. These data show that the outflow has an influence on the thermal properties of the parent cloud at least locally through shock processes in its early evolutionary stage. Publication: The Astrophysical Journal Pub Date: June 1992 DOI: 10.1086/186431 Bibcode: 1992ApJ...392L..83U Keywords: Gas Flow; Infrared Astronomy Satellite; Interstellar Matter; Shock Wave Interaction; Star Formation; Stellar Composition; Ammonia; Carbon Monoxide; Formyl Ions; Hydrocyanic Acid; Shock Heating; Astrophysics; ISM: MOLECULES; ISM: INDIVIDUAL ALPHANUMERIC: L1157; ISM: JETS AND OUTFLOWS; STARS: FORMATION; SHOCK WAVES full text sources ADS | data products SIMBAD (2)

Aperture synthesis CS(2-1) observations of a young stellar object GL 490 - Accretion flow in gas disk

view Abstract Citations (14) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Aperture Synthesis CS(2--1) Observations of a Young Stellar Object GL 490: Accretion Flow in Gas Disk Nakamura, Akiko ; Kawabe, Ryohei ; Kitamura, Yoshimi ; Ishiguro, Masato ; Murata, Yasuhiro ; Ohashi, Nagayoshi Abstract Aperture synthesis CS(J = 2-1) observations of the disk structure of the dense molecular gas around the young stellar object GL 490 are performed with 4-arcsec resolution using the Nobeyama Millimeter Array. The gas is found to have a noncircular velocity of about (1-1.5) km/s/sin i (i = inclination angle of the disk) and a mass of about 10 solar masses inside an 8500 AU region of the disk. According to the disk orientation indicated from one-sided cone-shaped optical and IR nebulocities, and the bipolar CO outflow, the noncircular motion is interpreted as inflow. The accretion time scale of the gas is estimated to be about 30,000 yr and the mass accretion rate to be 0.0003 solar mass/yr. Publication: The Astrophysical Journal Pub Date: December 1991 DOI: 10.1086/186247 Bibcode: 1991ApJ...383L..81N Keywords: Accretion Disks; Infrared Sources (Astronomy); Interstellar Gas; Molecular Gases; Star Formation; Infrared Astronomy; Millimeter Waves; Radio Astronomy; Stellar Mass Accretion; Synthetic Apertures; Astrophysics; INTERSTELLAR: MOLECULES; INFRARED: SOURCES; STARS: FORMATION; STARS: INDIVIDUAL ALPHANUMERIC: GL 490 full text sources ADS | data products SIMBAD (1)