Mechanical Luminosity Research Articles

Aperture Synthesis 13CO (J = 1-0) Observations of the Molecular Gas around DG Tauri: Evidence for a Dispersing Gas Disk

view Abstract Citations (37) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Aperture Synthesis 13CO (J = 1-0) Observations of the Molecular Gas around DG Tauri: Evidence for a Dispersing Gas Disk Kitamura, Yoshimi ; Kawabe, Ryohei ; Saito, Masao Abstract We made aperture synthesis 13CO (J = 1-0) observations of the molecular gas around a young star DG Tau, using the Nobeyama Millimeter Array. We have detected the gas in the velocity range υLSR = 4.3-7.3 km s-1, and have revealed the velocity structure of the gas with velocity resolution 0.43 km s - 1 The molecular gas around DG Tau is found to have a disklike structure, with the major axis perpendicular to the blueshifted optical jet ejected from the star. The radius, mass, and inclination angle of the disk are estimated to be ∼2800 AU, 0.03 Msun, and 40°, respectively. It is noted that an expanding motion is distinct in the disk. The expanding velocity is about 1.5 km s-1, which is larger than both the Kepler and free-fall velocities around DG Tau. Since the mechanical luminosity of the expanding motion is estimated to be 6 × 10-4 Lsun, much smaller than the stellar luminosity of ∼1 Lsun, the expansion is possibly driven by the stellar wind from the central star. The disk model for the expanding gas around DG Tau is quite consistent with the structures of the reflection nebula and the blueshifted optical jet that were observed around the star. It would be reasonable to make the interpretation that the outer part of the large gas disk around the star, or the disk-shaped remnant of the envelope surrounding the star, -is now being dispersed owing to the stellar wind during the evolution of a large protostellar disk into a compact protoplanetary one, because DG Tau has a flat spectral energy distribution and is considered to be evolving from a protostar to a T Tauri star. Publication: The Astrophysical Journal Pub Date: January 1996 DOI: 10.1086/176728 Bibcode: 1996ApJ...457..277K Keywords: ISM: JETS AND OUTFLOWS; STARS: MASS LOSS; STARS: PRE-MAIN-SEQUENCE; STARS: CIRCUMSTELLAR MATTER; ISM: MOLECULES; STARS: INDIVIDUAL CONSTELLATION NAME: DG TAURI full text sources ADS | data products SIMBAD (5)

Wolf-Rayet Bubbles. I. Analytic Solutions

view Abstract Citations (99) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Wolf-Rayet Bubbles. I. Analytic Solutions Garcia-Segura, Guillermo ; Mac Low, Mordecai-Mark Abstract Stellar wind bubble dynamics are sensitive to the stellar wind velocity and mass-loss history. Observations of ring nebulae can thus strongly constrain theories of stellar winds and massive stellar evolution. Furthermore, ring nebulae are often observed around Wolf-Rayet stars likely to soon become supernovae, so their influence on the circumstellar medium is vital to understanding young supernova remnants such as Cas A. To interpret the observations, the connection between the input wind and the observed gas distribution must be described. This is our goal in this series of papers. In this paper, we present analytic solutions for the dynamics of bubbles expanding into media with power-law density distributions such as r-2. We apply the solutions to Wolf-Rayet bubbles expanding into red supergiant winds. A semianalytic method is used to model aspherical bubbles resulting from nonspherical red supergiant winds. Applying this method, we find, for the case of steady winds, that bubbles expand at nearly constant velocity in each direction, keeping their shapes. We can then make the approximation that the bubbles have constant-eccentricity ellipsoidal shapes to derive a fully analytic dynamical model. From this we derive solutions for the diffuse X-ray luminosities from steady winds, using the assumption of classical conductive evaporation. Useful relationships between observables are also given. The solutions are compared to observations of the Wolf-Rayet ring nebula NGC 6888. We find that with either the assumption of energy conservation or momentum conservation, the dynamics of this nebula cannot be explained if the reported wind kinetic energy of the central star WR 136 is used. The nebular kinematics require an order of magnitude less effective mechanical luminosity from WR 136, demanding a lower mass-loss rate, a lower wind velocity, or both. Publication: The Astrophysical Journal Pub Date: December 1995 DOI: 10.1086/176563 Bibcode: 1995ApJ...455..145G Keywords: ISM: BUBBLES; ISM: INDIVIDUAL NGC NUMBER: NGC 6888; ISM: STRUCTURE; STARS: MASS LOSS; STARS: WOLF-RAYET full text sources ADS | data products SIMBAD (4) Related Materials (1) Part 2: 1995ApJ...455..160G

Synthetic properties of starburst galaxies

We present the results of an extensive grid of evolutionary synthesis models for populations of massive stars. The parameter space has been chosen to correspond to conditions typically found in objects like giant H II regions, H II galaxies, blue compact dwarf galaxies, nuclear starbursts, and infrared luminous starburst galaxies. The models are based on the most up-to-date input physics for the theory of stellar atmospheres, stellar winds, and stellar evolution. A population of massive stars is not only important in terms of its output of radiation but also via its deposition of mechanical energy. The output of radiative and mechanical luminosity is compared at various starburst epochs. In a supernova dominated instantaneous starburst, the mechanical luminosity can be as large as almost 10% of the total radiative luminosity. This occurs when most massive O stars have disappeared, and the synthetic spectrum in the optical and near-ultraviolet is dominated by B and A stars. During this epoch, the output of ionizing radiation below 912 A becomes very small, as indicated by a very large Lyman discontinuity and a very small ratio of ionizing over mechanical luminosity. We discuss the relevance of these results for the interpretation of starburst galaxies, active galactic nuclei, and the energetics of the interstellar medium.

Multi-line transfer and line blanketing in a clumpy Wolf-Rayet wind

We present a Wolf-Rayet wind model including clumping, which is assumed to be due to full-scale supersonic compressible turbulence as suggested by Moffat & Robert (1994). It is shown that clumping leads to a larger transfer of radiative to mechanical luminosity, which corresponds to a momentum ratio of (Ṁv∞)/(L/c) = 12 for a typical WN5 star. We also show how clumping reduces the effects of line blanketing in spectral analyses.

Circumprotostellar environments. 2: Envelopes, activity, and evolution

We have obtained 800 and 1100 micron photometric observations of a complete, flux-limited, IRAS-selected sample of cold sources in Taurus, whose infrared and molecular properties indicate them to be low-mass protostars which are younger than T Tauri stars. The goal of this study is to understand the role of the circumstellar envelope and disk during low-mass star formation and to search for signs of evolution. We find a good correlation between the submillimeter flux density (as well as of envelope mass) with both the mechanical luminosity of the molecular outflow and with the far-infrared luminosity, presumably produced by accretion onto the protostar. This suggests that the mass of the disk/envelope may be linked to the rate of accretion onto the protostar and to the generation of outflows. However, in contrast to the results of Cabrit & Andre (1991) we see no evidence for a lower limit to the disk/envelope mass which can produce outflow. We also find a significant difference between the spectral energy distributions at submillimeter wavelengths of embedded protostars compared to optically visible T Tauri stars. The more evolved (T Tuari) objects tend to have shallower spectral indices than embedded sources, suggesting (1) an evolution of dust grains, and/or (2) a more compact envelope and optically thick disk in the older objects.

A multiwavelength study of IRAS 19550+3248: A protostar possibly formed by a cloud-cloud collision

view Abstract Citations (11) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Multiwavelength Study of IRAS 19550+3248: A Protostar Possibly Formed by a Cloud-Cloud Collision Koo, Bon-Chul ; Lee, Youngung ; Fuller, G. A. ; Lee, Myung Gyoon ; Kwon, Suk-Minn ; Jung, Jae-Hoon Abstract We have carried out radio, near-infrared, and optical observations of the IRAS point source IRAS 19550+3248. (12)CO J = 1-0 line observations revealed a high-velocity (HV) molecular outflow centered on IRAS 19550+ 3248. The HV gas has a bipolar pattern with the blue and red peaks separated by 1 arcmin along the north-south direction. The mechanical luminosity of the HV molecular outflow is approximately 9 x 1031d2 ergs/s, and its dynamical age is approximately 5 x 104d2 yr, where d2 is the distance to the source normalized to 2 kpc. Inside the 95% confidence ellipse of IRAS position, we have detected a nebulous K band source. The nebulosity extends to 0.1d2 pc in the east-west direction. In R and I bands, the source appears to be composed of two extended weak peaks shifted toward the blueshifted CO lobe from the peak position K band. These near-infrared emission features are likely scattered stellar light. The infrared source has a steep spectral index between 2 and 25 microns (d log nuFnu/d log nu = -0.93), which indicates that it is a protostar deeply embedded in a dense molecular cloud core. The bolometric luminosity based on R, I, H, and K band photometry together with the IRAS data is 150d2 exp 2 Solar Luminosities. IRAS 19550+3248 islocated at the center of a small (4 arcmin x 7 arcmin) dense molecular clump. The clump is at the tip of a long (approximately 1 deg) filmentary molecular cloud. The molecular cloud is composed of clumps which are not confined by gravity and nor, probably, by external pressure. The characteristic timescale for dispersal is approximately 6 x 106 yr. We suggest cloud-cloud collision as a possible mechanism for the disruption of the cloud and for the formation of IRAS 19550+3248. Publication: The Astrophysical Journal Pub Date: July 1994 DOI: 10.1086/174314 Bibcode: 1994ApJ...429..233K Keywords: Molecular Clouds; Nebulae; Protostars; Star Formation; Carbon Monoxide; Collision Parameters; Extragalactic Radio Sources; Infrared Astronomy Satellite; Astrophysics; INFRARED: ISM: CONTINUUM; ISM: CLOUDS; ISM: INDIVIDUAL ALPHANUMERIC: IRAS 19550; 3248; ISM: MOLECULES; RADIO LINES: ISM; STARS: FORMATION full text sources ADS | data products SIMBAD (2)

Molecular Cloud Core and CS Outflow Associated with Haro 4-255 FIR

view Abstract Citations (8) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Molecular Cloud Core and CS Outflow Associated with Haro 4-255 FIR Tatematsu, Ken'ichi ; Umemoto, Tomofumi ; Murata, Yasuhiro ; Chen, Hua ; Hirano, Naomi ; Takaba, Hiroshi Abstract The region containing the two young stellar objects, Haro 4-255 and Haro 4-255 FIR, has been studied through single-dish and aperture-synthesis CS (1-0) observations. We have detected an intense CS outflow, whose FWZI velocity extent is about 9 km s-1, in the single-dish observations. The distribution of the blue CS lobe is appreciably different from that of the blue CO lobe, whereas the distribution of the red CS lobe is similar to that of the red CO lobe. The CS abundance in this outflow seems to be enhanced nearly by one order of magnitude, although that in the quiescent gas shows a more normal value. The mass of the CS outflow is appreciably larger than that of the CO outflow, while the mechanical luminosity of the CS outflow is smaller than that of the CO outflow. The aperture-synthesis data show no counterpart to the CS outflow but contain two emission features which correspond to two local intensity maxima seen in the single-dish map. One of these features extends from Haro 4-255 to Haro 4-255 FIR: it might represent a density maximum in the molecular cloud core. The blueshifted emission of the CS outflow is less prominent, probably because it is impeded by the densest portion of the core. Publication: The Astrophysical Journal Pub Date: December 1993 DOI: 10.1086/173525 Bibcode: 1993ApJ...419..746T Keywords: ISM: CLOUDS; ISM: INDIVIDUAL NAME: HARO 4-255 FIR; ISM: MOLECULES; ISM: JETS AND OUTFLOWS; STARS: PRE-MAIN-SEQUENCE full text sources ADS | data products SIMBAD (5)

Enrichment and heating of the intracluster medium through galactic winds

view Abstract Citations (112) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Enrichment and Heating of the Intracluster Medium through Galactic Winds David, L. P. ; Forman, W. ; Jones, C. Abstract In previous papers we presented the results of simulations concerning the dynamic and X-ray evolution of the interstellar medium in elliptical galaxies. We found that all model galaxies developed Type II supernova- driven winds at early epochs and that low-luminosity ellipticals (L_B_ <~ 10^9.5^) maintained galactic winds for most of their lifetime. Since the galaxy population of rich regular clusters is dominated by elliptical and S0 galaxies, we examine in this paper what effect these galactic winds have on the heavy element abundance and energetics of the intracluster medium. Substantial injection of highly enriched gas occurs within 3 x 10^8^ yr after galaxy formation through galactic winds. The resulting iron abundance of the intracluster medium through galactic winds varies considerably with the assumed stellar initial mass function, Type I supernova rate, and the primordial mass fraction of the cluster gas. The combined mechanical luminosity of the winds from the galaxies in a cluster can greatly exceed the present optical luminosity of a cluster. Any residual gas remaining in a cluster after the cessation of galaxy formation can be heated to temperatures exceeding that produced by gravitational heating alone. Assuming the distribution of galaxy luminosities in a cluster can be described by a Schechter luminosity function, our calculations show that the observed iron abundance, oxygen- to-iron mass ratio, and gas temperature in clusters can all be simultaneously reproduced only if the first generation of stars formed with a relatively flat initial mass function. Results from calculations using a Salpeter initial mass function do not agree with observations. Publication: The Astrophysical Journal Pub Date: October 1991 DOI: 10.1086/170560 Bibcode: 1991ApJ...380...39D Keywords: Cosmic Plasma; Elliptical Galaxies; Interacting Galaxies; Intergalactic Media; Luminosity; Galactic Clusters; Galactic Evolution; Astrophysics; ABUNDANCES; GALAXIES: INTERGALACTIC MEDIUM; LUMINOSITY FUNCTION full text sources ADS | data products SIMBAD (2)

Planetary nebula haloes - II. NGC 7662 and shock heating mechanisms in haloes

New spectra and images of the large halo around the ‘triple-shell’ planetary nebula NGC 7662 are presented. The halo’s electron temperature, |$T_\text e(\text O^{2+})= 17 500\enspace\text K$|⁠, is 4400 K higher than the value for the bright core, and apparent O/H and Ne/H ratios are almost a factor 2 lower in the halo. The ionized halo mass is |$\le0.19M_\odot$|⁠. Combined spectroscopic results for the haloes of NGC 6543, NGC 6826 and NGC 7662 are interpreted in terms of shocked filamentary regions, with the energy input coming from the hot, fast central star winds of these objects. For NGC 6543 only 3 per cent of the mechanical luminosity of the wind needs to be converted to provide the excess heating observed. It is shown that the halo emission is not due to a rapid drop in the central stars’ luminosity. A sketch of the evolution of these three haloes is given. Two mechanisms whereby energy from the fast wind can penetrate halo filaments are discussed: either high-velocity electrons and ions from a hot shocked wind enter and heat the gas, or else a slow shock compresses it and produces a heated region with |$T_\text e\sim25000\enspace\text K$|⁠. New shock models are presented for a slow shock wave exciting an externally photoionized, low-density gas. The observed emission may come from a mixture of hot and cool ionized gas, so that a nebular analysis with a single electron temperature produces incorrect, apparently-low O/H and Ne/H ratios.

The bipolar molecular outflow of V645 Cygni

A map is presented of the CO J = 3-2 line emission from the cloud associated with V645 Cygni. Line wings extending to 15 km/s on either side of the central velocity can be attributed to a bipolar outflow over a region 1 arcmin in angular extent. The redshifted and blueshifted emission peaks are separated by 20 arcsecs along an axis that is approximately perpendicular to the polarization vector of the visible light. The outflow is of relatively low velocity, low mass, and low mechanical luminosity.

Molecular outflows in the Monoceros OB1 molecular cloud

view Abstract Citations (94) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Molecular Outflows in the Monoceros OB1 Molecular Cloud Margulis, Michael ; Lada, Charles J. ; Snell, Ronald L. Abstract The authors present observations of J = 1-0 emission from CO in nine suspected molecular outflows in the Monoceros OB1 molecular cloud. These sources comprise a complete sample of outflow candidates in the surveyed region whose flow mechanical luminosities would be about equal to or greater than that of the well-known outflow in L1551. The authors conclude that five of the sources are definitely outflows and three of the remaining candidates are likely to be outflows. A catalog of the candidate sources is presented including maps, sample spectra, positions, sizes, collimation factors, velocity widths, and estimated masses, momenta, and mechanical luminosities. Publication: The Astrophysical Journal Pub Date: October 1988 DOI: 10.1086/166748 Bibcode: 1988ApJ...333..316M Keywords: Molecular Clouds; Molecular Flow; Sky Surveys (Astronomy); Solar Neighborhood; Stellar Evolution; Stellar Luminosity; Energy Dissipation; Molecular Gases; Morphology; Star Formation; Astrophysics; INTERSTELLAR: MOLECULES; NEBULAE: INDIVIDUAL NAME: MONOCEROS OB1 full text sources ADS | data products SIMBAD (12)

Mass Outflows Associated with Young Stellar Objects

The fundamental properties of optical and molecular outflows associated with young stellar objects are reviewed. Particular emphasis is placed on a discussion of new results concerning outflow energetics, collimating structures and the relationship between outflow properties and the magnetic field geometry characterizing their host molecular clouds. IRAS observations of YSO mass outflows reveal extended far-IR emission associated with high velocity molecular gas; in the case of L1551 IRS5, the luminosity of the extended emission is ∼10 times the mechanical luminosity inferred from observation of the molecular flow (and thus ≳0.1 the bolometric luminosity of the YSO driving the outflow). Circumstellar disks of size ∼100 au appear to be a common, if not certain outcome of the stellar birth process for stars of ∼1M⊙. In a few cases, it has been possible to resolve disk-like structures associated with YSO outflow sources. In such cases, the disk axes appear to lie along the direction of molecular outflows or stellar jets. The mass outflows (and by inference, the axes of circumstellar disks) show a remarkable tendency to align along the direction of the magnetic fields which thread their host molecular clouds. This suggests that the cloud magnetic field must play an important role in determining the flattening (and perhaps the rotation) of protostellar structures.

Shocked Molecular Hydrogen from Star Forming Regions

Near infrared (2 micron) emission lines from molecular hydrogen provide a powerful probe of the morphology and energetics of outflows associated with stellar birth. The H2 emission regions trace the location of shock waves formed when the high velocity outflow from young stars encounters dense quiescent gas. Since H2 is the dominant coolant of the hot post-shock molecular gas, the H2 lines provide a measure of the fraction of the total mechanical luminosity radiated away from the cloud.

Discovery of seven bipolar outflows by an unbiased survey

The discovery of seven CO outflows in an unbiased CO survey with the Nagoya 4 m millimeter telescope of the Orion southern giant molecular cloud and a few other dark clouds is reported. In the Orion southern cloud four regions of outflows have been found in addition to three regions previously detected, suggesting that the number of outflow sources may be increased by 50-90 percent through unbiased surveys. The total mechanical luminosity of the outflows in this cloud is about 2 solar luminosities. This luminosity can provide the kinetic energy of the cloud in about 5 Myr, a time scale which is nearly equal to that of turbulence dissipation, about 7 Myr, but is longer than the free-fall time of 1 Myr. Therefore, outflows can support the giant molecular cloud if turbulence dissipates in a time scale an order of magnitude longer than the free-fall time. 18 references.

The Effect of Mass-Loss On the Evolution of HII Regions in the L.M.C.

Empirical calibrations based on prior studies of Galactic OB Stars are used to determine the integrated stellar wind mechanical luminosity (Lw) and the integrated Lyman continuum photon luminosity (S*) for 10 OB clusters in the L.M.C. These values of Lw and S*, together with narrow band H-α surface photometry of an overlapping sample of 15 L.M.C. HII regions, are used to show that the large shell-like HII regions, in the L.M.C. are stellar wind bubbles 3 to 5 million years old. In order to reproduce the general properties of these HII shells, a thick cushion of shocked stellar wind gas must have been present on the inside of the shell for most of the life time of the nebula, and the shell itself must be ram pressure confined by the HI/molecular cloud out of which it formed.

The high-velocity molecular flows near young stellar objects

The results of a search for high-velocity molecular gas associated with star forming molecular clouds are reported. Faint, high-velocity (..delta..V> or approx. =30 km s/sup -1/) /sup 12/CO emission is freqently found near buried infrared sources when sufficiently deep (T/sub rms/ <100 mK) integrations are obtained. In most clouds, the high-velocity gas is observed over an extended area having a typical radius around 10/sup 18/ cm and exhibits bipolar structure with the redshifted emission formed in a different region from the corresponding blueshifted emission. The ratio of the flow major and minor diameters varies from about 6 to less than 2, with most sources in the range between 2 and 3, indicating that most flows are not highly collimated. In many sources, the red portion of the line wings is stronger and/or covers a larger angular region of the sky than the corresponding blue wing. The opacity of the /sup 12/CO line wings appears to be greater than unity. Correlations between the central source luminosity and both the flow mechanical luminosity and momentum flux are found. A correlation between the mass of a flow and its apparent size suggests that the flows may be located in molecular clouds with steeplymore » decreasing radial density gradients. The presence of high-velocity outflow in molecular clouds indicates an unanticipated phase of energetic mass loss associated with the birth and early evolution of stars. Even though the flows have large energies, momenta, and a high birthrate, they may not be capable of supporting molecular clouds against free-fall gravitational collapse.« less