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Search Results: 1 - 10 of 297590 matches for " P. T. P. Ho "
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Geometry of Deformed Boson Algebras
P. Crehan,T. G. Ho
Mathematics , 1995, DOI: 10.1142/S0129055X96000342
Abstract: Phase-space realisations of an infinite parameter family of quantum deformations of the boson algebra in which the $q$-- and the $qp$--deformed algebras arise as special cases are studied. Quantum and classical models for the corresponding deformed oscillators are provided. The deformation parameters are identified with coefficients of non-linear terms in the normal forms expansion of a family of classical Hamiltonian systems. These quantum deformations are trivial in the sense that they correspond to non-unitary transformations of the Weyl algebra. They are non-trivial in the sense that the deformed commutators consistently quantise a class of non-canonical classical Poisson structures.
The Dynamics of Molecular Material Within 15 pcs of the Galactic Center
A. L. Coil,P. T. P. Ho
Physics , 1999, DOI: 10.1086/308650
Abstract: We report the results of a 5-field mosaic of the central 15pc of the Galaxy in the (1,1) and (2,2) lines of NH3. Two narrow filaments or streamers are seen running parallel to the Galactic plane. The southern streamer appears to carry gas directly toward the nuclear region from the 20 km/s cloud. The eastern streamer, which we will denote the molecular ridge, appears to be the denser part of the 50 km/s cloud which lies immediately east of the Sgr A East complex and extends in the south towards the 20 km/s cloud. This ridge of gas carries the kinematical signatures of interactions with Sgr A East as well as a SNR which lies south of the Galactic center. The bulk motion of the gas, the enhanced line widths, and the heating of the molecular material all suggest an active evolutionary phase for the gas immediately adjacent to the nucleus.
NH3 in the Central 10 pc of the Galaxy. II. Determination of Opacity for Gas with Large Linewidths
Robeson S. McGary,Paul T. P. Ho
Physics , 2002, DOI: 10.1086/342233
Abstract: The 23 GHz emission lines from the NH3 rotation inversion transitions are widely used to investigate the kinematics and physical conditions in dense molecular clouds. The line profile is composed of hyperfine components which can be used to calculate the opacity of the gas (Ho & Townes 1983). If the intrinsic linewidth of the gas exceeds one half of the separation of these quadrupole hyperfine components (~5-10 km/s) these lines blend together and the observed linewidths greatly overestimate the intrinsic linewidths. If uncorrected, these artificially broad linewidths will lead to artificially high opacities. We have observed this effect in our NH3 data from the central 10 pc of the Galaxy where uncorrected NH3 (1,1) linewidths of ~30 km/s exaggerate the intrinsic linewidths by more than a factor of two (Genzel & Townes 1987). Models of the effect of blending on the line profile enable us to solve for the intrinsic linewidth and opacity of NH3 using the observed linewidth and intensity of two NH3 rotation inversion transitions. We present the result of the application of this method to our Galactic Center data. We successfully recover the intrinsic linewidth and opacity of the gas. Clouds close to the nucleus in projected distance as well as those that are being impacted by Sgr A East show the highest intrinsic linewidths. The cores of the ``southern streamer'' (Ho et al. 1991; Coil & Ho 1999, 2000) and the ``50 km/s'' giant molecular cloud have the highest opacities.
Hot Molecular Gas in the Galactic Center
Robeson McGary Herrnstein,Paul T. P. Ho
Physics , 2002,
Abstract: Using the new 23 GHz receivers at the Very Large Array (VLA), we have detected NH3(6,6) emission (nu=25.056025 GHz) from hot (>150 K) molecular clouds in the central 10 pc of the Galaxy. This is the first successful detection of NH3(6,6) with the VLA. The brightest emission comes from a region interior to the ``circumnuclear disk'' (CND), less than 1.5 pc in projected distance from Sgr A*. This region does not show molecular emission from lower energy transitions such as NH3(1,1) and (2,2), HCN(1-0) and HCO+(1-0). Line ratios of NH3(6,6) and (3,3) emission as well as NH3(6,6) line widths have peak values within 1.5 pc of Sgr A*, indicating that the gas is physically close to the nucleus. NH3(6,6) is also detected towards many features outside the CND observed in NH3(1,1), (2,2), and (3,3). These features tend to lie along ridges of gas associated with Sgr A East or the massive ``molecular ridge'' that connects the ``20 km/s'' and ``50 km/s'' giant molecular clouds (GMCs).
Hot Molecular Gas in the Central 10 Parsecs of the Galaxy
Robeson M. Herrnstein,Paul T. P. Ho
Physics , 2003, DOI: 10.1002/asna.200385049
Abstract: We present results from observations of NH_3(1,1), (2,2), (3,3), and (6,6) with the Very Large Array. The data sample the inner 10 pc (4') of the Galaxy and have a velocity coverage of -140 to +130 km/s. The velocity integrated NH_3(3,3) image shows that the Sgr A East supernova remnant is impacting the 50 km/s GMC in the northeast, the northern ridge in the north, and the western streamer in the west. These results imply that the Sgr A East has a large effect on the molecular environment near Sgr A* and may be pushing much of the molecular gas away from Sgr A*. The physical properties of the western streamer and its relation to Sgr A East are discussed in detail. We also summarize the detection of hot molecular gas less than 2 pc from Sgr A* in projected distance. This gas is seen only in NH_3(6,6) and has line widths of 75-85 km/s, indicating that it is physically close to the nucleus.
Infalling Gas Towards the Galactic Center
Alison L. Coil,Paul T. P. Ho
Physics , 1998, DOI: 10.1086/306875
Abstract: VLA maps of ammonia emission were made for the Galactic Center region. The NH3(1,1) and NH3(2,2) transitions were observed in three 2' x 2' fields covering Sgr A* and the region 3' immediately south of it. In the central 3 parsecs surrounding Sgr A* we find emission which appears to be associated with the circumnuclear disk (CND), both morphologically and kinematically. This central emission is connected to a long, narrow 2 pc x 10 pc streamer of clumpy molecular gas located towards the south, which appears to be carrying gas from the nearby 20 km/s giant molecular cloud (GMC) to the circumnuclear region. We find a velocity gradient along the streamer, with progressively higher velocities as the gas approaches Sgr A*. The streamer stops at the location of the CND, where the line width of the NH3 emission increases dramatically. This may be the kinematic signature of accretion onto the CND. The ratio of the NH3(2,2)/NH3(1,1) emission indicates that the gas is heated at the northern tip of the streamer, located inside the eastern edge of the CND. The morphology, kinematics and temperature gradients of the gas all indicate that the southern streamer is located at the Galactic Center and is interacting with the circumnuclear region.
Radio Continuum Sources Associated with AB AUR
Rodríguez, Luis F.;Zapata, Luis;Ho, Paul T. P.;
Revista mexicana de astronomía y astrofísica , 2007,
Abstract: we present high angular resolution, high-sensitivity very large array observations at 3.6 cm of the herbig ae star ab aur. this star is of interest since its circumstellar disk exhibits characteristics that have been attributed to the presence of an undetected low mass companion or giant gas planet. our image confirms the continuum emission known to exist in association with the star, and detects a faint protuberance that extends about 0".3 to its se. previous theoretical considerations and observational results are consistent with the presence of a companion to ab aur with the separation and position angle derived from our radio data. we also determine the proper motion of ab aur by comparing our new observations with data taken about 17 years ago and find values consistent with those found by hipparcos.
Spatially Resolving Substructures within the Massive Envelope around an Intermediate-mass Protostar: MMS 6/OMC-3
Satoko Takahashi,Kazuya Saigo,Paul T. P. Ho,Kengo Tomida
Physics , 2012, DOI: 10.1088/0004-637X/752/1/10
Abstract: With the Submillimeter Array, the brightest (sub)millimeter continuum source in the OMC-2/3 region, MMS 6, has been observed in the 850 um continuum emission with approximately 10 times better angular resolution than previous studies (~0.3"; ~120 AU at Orion). The deconvolved size, the mass, and the column density of MMS 6-main are estimated to be 0.32"x0.29" (132 AUx120 AU), 0.29 Mo, and 2.1x10^{25} cm^{-2}, respectively. The estimated extremely high mean number density, 1.5x10^{10} cm^{-3}, suggests that MMS 6-main is likely optically thick at 850 um. We compare our observational data with three theoretical core models: prestellar core, protostellar core + disk-like structure, and first adiabatic core. These comparisons clearly show that the observational data cannot be modeled as a simple prestellar core with a gas temperature of 20 K. A self-luminous source is necessary to explain the observed flux density in the (sub)millimeter wavelengths. Our recent detection of a very compact and energetic outflow in the CO (3-2) and HCN (4-3) lines, supports the presence of a protostar. We suggest that MMS 6 is one of the first cases of an intermediate mass protostellar core at an extremely young stage. In addition to the MMS 6-main peak, we have also spatially resolved a number of spiky structures and sub-clumps, distributed over the central 1000 AU. The masses of these sub-clumps are estimated to be 0.066-0.073 Mo, which are on the order of brown dwarf masses. Higher angular resolution and higher sensitivity observations with ALMA and EVLA will reveal the origin and nature of these structures such as whether they are originated from fragmentations, spiral arms, or inhomogeneity within the disk-like structures/envelope.
NH3 in the Central 10 pc of the Galaxy I: General Morphology and Kinematic Connections Between the CND and GMCs
Robeson S. McGary,Alison L. Coil,Paul T. P. Ho
Physics , 2001, DOI: 10.1086/322390
Abstract: New VLA images of NH3 (1,1), (2,2), and (3,3) emission in the central 10 parsecs of the Galaxy trace filamentary streams of gas, several of which appear to feed the circumnuclear disk (CND). The NH3 images have a spatial resolution of 16.5''x14.5'' and have better spatial sampling than previous NH3 observations. The images show the ``southern streamer,'' ``50 km/s cloud,'' and new features including a ``western streamer'', 6 parsecs in length, and a ``northern ridge'' which connects to the CND. NH3(3,3) emission is very similar to 1.2 mm dust emission indicating that NH3 traces column density well. Ratios of the NH3(2,2) to (1,1) line intensities give an estimate of the temperature of the gas and indicate high temperatures close to the nucleus and CND. The new data cover a velocity range of 270 km/s, including all velocities observed in the CND, with a resolution of 9.8 km/s. Previous NH3 observations with higher resolution did not cover the entire range of velocities seen in the CND. The large-scale kinematics of the CND do not resemble a coherent ring or disk. We see evidence for a high velocity cloud within a projected distance of 50'' (2 pc) which is only seen in NH3(3,3) and is likely to be hot. Comparison to 6 cm continuum emission reveals that much of the NH3 emission traces the outer edges of Sgr A East and was probably pushed outward by this expanding shell. The connection between the northern ridge (which appears to be swept up by Sgr A East) and the CND indicates that Sgr A East and the CND are in close proximity to each other. Kinematic evidence for these connections is presented in this paper, while the full kinematic analysis of the central 10 pc will be presented in Paper II.
Radiative Transfer Modelling of the Accretion Flow onto a Star-Forming Core in W51
Lisa M. Young,Eric Keto,Paul T. P. Ho
Physics , 1998, DOI: 10.1086/306310
Abstract: We present an analysis of the temperature, density, and velocity of the molecular gas in the star-forming core around W51 e2. A previous paper (Ho and Young 1996) describes the kinematic evidence which implies that the core around e2 is contracting onto a young massive star. The current paper presents a technique for modelling the three-dimensional structure of the core by simulating spectral line images of the source and comparing those images to observed data. The primary conclusions of this work are that the molecular gas in e2 is radially contracting at about 5 km/s and that the temperature and density of the gas decrease outward over 0.15 pc scales. The simple model of the collapse of the singular isothermal sphere for low-mass star formation (Shu 1977) is an inadequate description of this high-mass molecular core; better models have temperature decreasing outward as r^-0.6, density as r^-2, and velocity increasing as r^+0.1. The core appears to be spherical rather than disk-like at the scale of these observations, 0.3 pc. In this paper we show how a series of models of gradually increasing complexity can be used to investigate the sensitivity of the model to its parameters. Major sources of uncertainty for this method and this dataset are the interdependence of temperature and density and the assumed NH3 abundance.
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