15669111
A spectroscopic technique for measuring stellar properties of pre-main-sequence stars
We describe a technique for deriving effective temperatures, surface gravities, rotation velocities, and radial velocities from high-resolution near-IR spectra. The technique matches the observed near-IR spectra to spectra synthesized from model atmospheres. Our analysis is geared toward characterizing heavily reddened pre–main-sequence stars, but the technique also has potential applications in characterizing main-sequence and post–main-sequence stars when these lie behind thick clouds of interstellar dust. For the pre–main-sequence stars, we use the same matching process to measure the amount of excess near-IR emission (which may arise in the protostellar disks) in addition to the other stellar parameters. The information derived from high-resolution spectra comes from line shapes and the relative line strengths of closely spaced lines. The values for the stellar parameters we derive are therefore independent of those derived from low-resolution spectroscopy and photometry. The new method offers the promise of improved accuracy in placing young stellar objects on evolutionary model tracks. Tests with an artificial noisy spectrum with typical stellar parameters and a signal-to-noise ratio of 50 indicate a 1 σ error of 100 K in Teff, 2 km s-1 in v sin i, and 0.13 in continuum veiling for an input veiling of 1. If the flux ratio between the sum of the Na, Sc, and Si lines at 2.2 μm and the (2–0) 12CO band head at 2.3 μm is known to an accuracy of 10%, the errors in our best-fit value for log g will be Δ log g = 0.1–0.2. We discuss the possible systematic effects on our determination of the stellar parameters and evaluate the accuracy of the results derivable from high-resolution spectra. In the context of this evaluation, we quantitatively explore the degeneracy between temperature and gravity that has bedeviled efforts to type young stellar objects using low-resolution spectra. The analysis of high-resolution near-IR spectra of MK standards shows that the technique yields very accurate values for the effective temperature. The greatest uncertainty in comparing our results with optical spectral typing of MK standards is in the spectral type–to–effective temperature conversion for the standards themselves. Even including this uncertainty, the 1 σ difference between the optical and infrared temperatures for dwarfs at 3000–5800 K is only 140 K. In a companion paper, we present an analysis of heavily extincted young stellar objects in the ρ Ophiuchi molecular cloud.
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
15532404
Molecular cloud structure in the magellanic clouds: Effect of metallicity
The chemical structure of neutral clouds in low-metallicity environments is examined, with particular emphasis on the H to H2 and C+ to CO transitions. We observed near-IR H2 (1, 0) S(1), (2, 1) S(1), and (5, 3) O(3) lines and the 12CO J = 1 → 0 line from 30 Doradus and N159/N160 in the Large Magellanic Cloud and from DEM S 16, DEM S 37, and LI-SMC 36 in the Small Magellanic Cloud. We find that the H2 emission is UV-excited and that (weak) CO emission always exists (in our surveyed regions) toward positions where H2 and [C II] emission have been detected. Using a PDR code and a radiative transfer code, we simulate the emission of line radiation from spherical clouds and from large planar clouds. Because [C II] emission and H2 emission arise on the surface of the cloud and because the lines are optically thin, these lines are not affected by changes in the relative sizes of the neutral cloud and the CO-bearing core, while the optically thick CO emission can be strongly affected. The sizes of clouds are estimated by measuring the deviation of CO emission strength from that predicted by a planar cloud model of a given size. The average cloud column density, and therefore its size, increases as the metallicity decreases. Our result agrees with the photoionization-regulated star formation theory of McKee.
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
197497757
LATEST RESULTS FROM MINOS.
Among the goals of the MINOS experiment are the test of the {nu}{sub {mu}} {yields} {nu}{sub {tau}} oscillation and the search for sub-dominant {nu}{sub {mu}} {yields} {nu}{sub {tau}} oscillations. The former proceeds by a {nu}{sub {mu}} ''disappearance'' analysis while the latter would involve the ''appearance'' of {nu}{sub e} interactions in a predominantly {nu}{sub {mu}} beam. The disappearance of muon neutrinos is described by P({nu}{sub {mu}} {yields} {mu}{sub {mu}}) = 1 - sin{sup 2} 2{theta}{sub 23} sin{sup 2} (1.27 {Delta} m{sub 23}{sup 2} L/E) in the two-flavor approximation where {theta}{sub 23} is the angle between the second row and third column of the neutrino mixing matrix, {Delta}m{sub 23}{sup 2} = m{sub 2}{sup 2}-m{sub 3}{sup 2} (eV{sup 2}), L is the neutrino flight distance in km and E is the neutrino energy in GeV. A generic disappearance experiment compares a measured muon neutrino energy spectrum at a fixed baseline to the known energy spectrum of muon neutrino beam to extract the oscillation parameters sin{sup 2} 2{theta} which controls the overall magnitude of the disappearance and {Delta}m{sup 2} which controls the energy dependence.
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.
119540499
Low cost lead glass cherenkov detectors
Abstract We have compared the optical properties of lead glass bars of three different surface qualities. One was ground and polished in the conventional manner; the other two were in the unimproved state resulting from the extrusion or casting process. We find that the three bars exhibit similar optical characteristics. Use of such unpolished lead glass Cherenkov bars in electromagnetic shower detectors should result in considerable cost savings.
117194771
Measurement of B(Lambda+(c) ---> p K- pi+)
The /\c->pKpi yield has been measured in a sample of two-jet continuum events containing a both an anticharm tag (Dbar) as well as an antiproton (e+e- -> Dbar pbar X), with the antiproton in the hemisphere opposite the Dbar. Under the hypothesis that such selection criteria tag e+e- -> Dbar pbar (/\c) X events, the /\c->pkpi branching fraction can be determined by measuring the pkpi yield in the same hemisphere as the antiprotons in our Dbar pbar X sample. Combining our results from three independent types of anticharm tags, we obtain B(/\c->pKpi)=(5.0+/-0.5+/-1.2)%
118745241
Status of Neutrino Physics Experiments
Relevant results from neutrino physics experiments since FPCP2009 with an emphasis on oscillations and the ability to measure or limit the mixing angle {theta}{sub 13}.