18241960
Molecular Hydrogen Emission from the Inner 400 Parsecs of the Galaxy II. The UV-Excited H_2
We have observed near-IR H$_2$ line emission on large scales in the Galactic center. Paper I discussed our 400 pc long strip map and 50 pc map of the H_2 v=1-0 S(1) line. In this paper, we present observations of the higher vibrational lines, H_2 v=2-1 S(1) and v=3-2 S(3), at selected positions and conclude that strong far--UV radiations excites the H_2. We compare the H_2 v=1-0 S(1) emission to far-IR continuum emission and show that the ratio of these two quantities in the Galactic center equals the ratio seen in the starburst galaxies, M82 and NGC 253, and in ultraluminous infrared bright galaxies.
16861138
High Sensitivity, High Spectral Resolution, Mid-infrared Spectroscopy
We broadly discuss mid-infrared spectroscopy and detail our new high spectral resolution instrument, the Texas Echelon-cross-Echelle Spectrograph (TEXES).
16613665
NEAR-INFRARED MOLECULAR HYDROGEN EMISSION FROM THE CENTRAL REGIONS OF GALAXIES: REGULATED PHYSICAL CONDITIONS IN THE INTERSTELLAR MEDIUM
The central regions of many interacting and early-type spiral galaxies are actively forming stars. This process affects the physical and chemical properties of the local interstellar medium, as well as the evolution of the galaxies. We observed near-infrared H2 emission lines: v ¼ 1 0 S(1), 3–2 S(3), 1–0 S(0), and 2–1 S(1) from the central � 1 kpc regions of the archetypical starburst galaxies M82 and NGC 253 and the less dramatic but still vigorously star-forming galaxies NGC 6946 and IC 342. Like the far-infrared continuum luminosity, the nearinfrared H2 emission luminosity can directly trace the amount of star formation activity because the H2 emission lines arise from the interaction between hot and young stars and nearby neutral clouds. The observed H2 line ratios show that both thermal excitation and nonthermal excitation are responsible for the emission lines but that the great majority of the near-infrared H2 line emission in these galaxies arises from energy states excited by ultraviolet fluorescence. The derived physical conditions, e.g., far-ultraviolet radiation field and gas density, from [C ii ]a nd [O i] lines and far-infrared continuum observations when used as inputs to photodissociation models also explain the luminosity of the observed H2 1–0S(1) line. The ratio of the H2 1–0S(1) line to far-IR continuum luminosity is remarkably constant over a broad range of galaxy luminosities: LH2 =LFIR ’ 10 � 5 , in normal late-type galaxies (including the Galactic center), in nearby starburst galaxies, and in luminous IR galaxies (LIRGs: LFIR >10 11 L� ). Examining this constant ratio in the context of photodissociation region models, we conclude that it implies that the strength of the incident UV field on typical molecular clouds follows the gas density at the cloud surface. Subject headings: galaxies: individual(M82,NGC 253,NGC6946,IC 342) — galaxies: ISM — galaxies:spiral — galaxies: starburst — infrared: ISM — ISM: lines and bands
209907524
Photon - dominated regions in low UV fields : a study of the peripheral regions of L1204 /S140
122125252
The TEXES Survey For H-2 Emission From Protoplanetary Disks
119015950
Evidence for J- and H-Band Excess in Classical T Tauri Stars and the Implications for Disk Structure and Estimated Ages
We argue that classical T Tauri stars (CTTSs) possess significant nonphotospheric excess in the J and H bands (1.25 and 1.66 μm, respectively). We first show that normalizing the spectral energy distributions (SEDs) of CTTSs to the J band leads to a poor fit of the optical fluxes (which are systematically overestimated), while normalizing the SEDs to the IC band (0.8 μm) produces a better fit to the optical bands and in many cases reveals the presence of a considerable excess at J and H. Near-infrared spectroscopic veiling measurements from the literature support this result. We find that J- and H-band excesses correlate well with the K-band (2.2 μm) excess and that the J - K and H - K colors of the excess emission are consistent with that of a blackbody at the dust sublimation temperature (~1500-2000 K). We propose that this near-IR excess originates at a hot inner rim, analogous to those suggested to explain the "near-IR bump" in the SEDs of Herbig Ae/Be stars. To test our hypothesis, we use the model presented by Dullemond and coworkers to fit the photometry data between 0.5 and 24 μm of 10 CTTSs associated with the Chamaeleon II molecular cloud. We find that simple models that include luminosities calculated from IC-band magnitudes and an inner rim may account for the reported J- and H-band excesses. The models that best fit the data are those in which the inner radius of the disk is larger than expected for a rim in thermal equilibrium with the photospheric radiation field alone. In particular, we find that large inner rims are necessary to account for the mid-infrared fluxes (3.6-8.0 μm) obtained by the Spitzer Space Telescope (Spitzer). The large radius could be explained if, as proposed by D'Alessio and colleagues, the UV radiation from the accretion shock significantly affects the sizes of the inner holes in disks around CTTSs. Finally, we argue that deriving the stellar luminosities of CTTSs by making bolometric corrections to the J-band fluxes, which is the "standard" procedure for obtaining CTTS luminosities, systematically overestimates these luminosities. The overestimated luminosities translate into underestimated ages when the stars are placed in the H-R diagram. Thus, the results presented herein have important implications for the dissipation timescale of inner accretion disks.
56433327
A multiplicity-vertex detector for the PHENIX experiment at RHIC
Abstract A Multiplicity-Vertex Detector (MVD) has been designed, and is in construction for the PHENIX Experiment at the Relativistic Heavy Ion Collider (RHIC). The 35 000 channel silicon detector is a two-layer barrel comprised of 112 strip detectors, and two disk-shaped endcaps comprised of 24 wedge-shaped pad detectors. The support structure of the MVD is very low mass, only 0.4% of a radiation length in the central barrel. The detector front-end electronics are a custom CMOS chip set containing preamplifier, discriminator, analog memory unit, and analog-to-digital converter. The system has pipelined acquisition, performs in simultaneous read/write mode, and is clocked by the 10 MHz beam crossing rate at RHIC. These die, together with a pair of commercial FPGAs that are used for control logic, are packaged in a mutlichip-module (MCM). The MCM will be fabricated in the High-Density-Interconnect (HDI) process. The prototype MCM design layout is described.
118180492
Recent results on rare $b$ decays
Recent experimental results on charmless rare b decays are reviewed.
124863739
The PHENIX Multiplicity and Vertex Detector
Abstract We describe the design and expected performance of the PHENIX Multiplicity and Vertex Detector (MVD) sub-system of the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC).
42580412
Identification of High Transverse-Momentum Hadrons with a Ring-Imaging Cerenkov Counter
We have constructed and operated a large aperture ring-imaging Cerenkov counter in a high transverse-momentum experiment at Fermilab. We used multistep proportional chambers with a He/TEA photosensitive gas mixture to observe approximately 3.5 photons per relativistic particle. Hadron identification is obtained with good efficiency from threshold to 250 GeV/c.
123152124
Preliminary measurements of shadowing at very low XBj
The ratio of cross sections for inelastic muon scattering on xenon and deuterium nuclei was measured at very low XBj (0.00002<XBj<0.25) for 0.01<Q2<60 (GeV/c)2. The data were taken at Fermilab experiment E665 with an average muon beam energy of 490 GeV incident on 1.1 meter long deuterium and xenon targets. Two largely independent analysis techniques gave statistically consistent results and show a smooth decrease in the ratio of the xenon‐to‐deuterium per–nucleon cross sections from ∼1 to ∼0.7 as XBj decreases from ∼0.1 to ∼0.003. In the XBj range 0.00002 to 0.003, the ratio remains roughly constant at ∼0.7.