653 research outputs found
The Development of Superconducting Magnets for Use in Particle Accelerators: From the Tevatron to the LHC
Superconducting magnets have played a key role in advancing the energy reach of proton synchrotrons and enabling them to play a major role in defining the Standard Model. The problems encountered and solved at the Tevatron are described and used as an introduction to the many challenges posed by the use of this technology. The LHC is being prepared to answer the many questions beyond the Standard Model and in itself is at the cutting edge of technology. A description of its magnets and their properties is given to illustrate the advances that have been made in the use of superconducting magnets over the past 30 years
An infrared jet in Centaurus A (NGC 5128): Evidence for interaction between the active nucleus and the interstellar medium
In the present study, higher resolution near infrared images of the visually-obscured central region of Centaurus A were obtained in order to investigate the effects of the active nucleus on the surrounding galaxy. Researchers present J(1.25 microns), H(1.65 microns), and K(2.2 microns) images of the central 40 seconds of the galaxy, taken with the Univ. of Texas InSb array camera on the Anglo Australian 3.9 meter telescope. These images reveal a jet extending approx. 10 arcseconds to the northeast of the nucleus at the same position angle as the x ray and radio jets. The infrared jet is most prominent at the shortest wavelength (1.25 microns), where its brightness surpasses that of the nucleus. The blue appearance of the infrared jet is remarkable considering the heavy obscuration that is evident at visual wavelengths. The amount of reddening in the vicinity of the jet is determined from the measured colors of the stellar core of the galaxy, and this value is used to generate an extinction-corrected energy distribution. In contrast to previously studied optical and infrared jets in active nuclei, the short-wavelength prominence of the Cen A jet indicates that it cannot be attributed to synchrotron emission from a beam of relativistic electrons. The remaining viable mechanisms involve an interaction between the interstellar medium and the active nucleus: the infrared radiation from the jet may be due to emission from interstellar gas that has been entrained and heated by the flow of relativistic particles from the nucleus; alternatively, luminous blue stars may have been created by compression of interstellar material by the relativistic plasma. To investigate these proposed mechanisms, near-infrared spectroscopic studies of Cen A are in progress to look for collisionally excited molecular hydrogen emission lines and recombination lines from ionized gas
Near and mid-infrared colours of star-forming galaxies in ELAIS fields
We present J and K-band near-infrared photometry of a sample of mid-infrared
sources detected by the Infrared Space Observatory (ISO) as part of the
European Large Area ISO-Survey (ELAIS) and study their classification and
star-forming properties. We have used the Preliminary ELAIS Catalogue for the
6.7 micron (LW2) and 15 micron (LW3) fluxes. All of the high-reliability LW2
sources and 80 per cent of the LW3 sources are identified in the near-IR survey
reaching K = 17.5 mag. The near- to mid-IR flux ratios can effectively be used
to separate stars from galaxies in mid-IR surveys. The stars detected in our
survey region are used to derive a new accurate calibration for the ELAIS
ISOCAM data in both the LW2 and LW3 filters. We show that near to mid-IR
colour-colour diagrams can be used to further classify galaxies, as well as
study star-formation. The ISOCAM ELAIS survey is found to mostly detect
strongly star-forming late-type galaxies, possibly starburst powered galaxies,
and it also picks out obscured AGN. The ELAIS galaxies yield an average mid-IR
flux ratio LW2/LW3 = 0.67 +/- 0.27. We discuss this [6.7/15] ratio as a star
formation tracer using ISO and IRAS data of a local comparison sample. We find
that the [K/15] ratio is also agood indicator of activity level in galaxies and
conclude that the drop in the [6.7/15] ratio seen in strongly star-forming
galaxies is a result of both an increase of 15 mic emission and an apparent
depletion of 6.7 mic emission. Near-IR data together with the mid-IR give the
possibility to estimate the relative amount of interstellar matter in the
galaxies.Comment: 18 pages, 15 figures; accepted for publication in MNRA
Trends in early childhood obesity in a large, urban school district in the Southwest from 2007 to 2014.
Presented at: Experimental Biology 2016; April 2-6, 2016; San Diego, CA.https://digitalrepository.unm.edu/prc-posters-presentations/1022/thumbnail.jp
Synchronous Optical and Radio Polarization Variability in the Blazar OJ287
We explore the variability and cross-frequency correlation of the flux
density and polarization of the blazar OJ287, using imaging at 43 GHz with the
Very Long Baseline Array, as well as optical and near-infrared polarimetry. The
polarization and flux density in both the optical waveband and the 43 GHz
compact core increased by a small amount in late 2005, and increased
significantly along with the near-IR polarization and flux density over the
course of 10 days in early 2006. Furthermore, the values of the electric vector
position angle (EVPA) at the three wavebands are similar. At 43 GHz, the EVPA
of the blazar core is perpendicular to the flow of the jet, while the EVPAs of
emerging superluminal knots are aligned parallel to the jet axis. The core
polarization is that expected if shear aligns the magnetic field at the
boundary between flows of disparate velocities within the jet. Using variations
in flux density, percentage polarization, and EVPA, we model the inner jet as a
spine-sheath system. The model jet contains a turbulent spine of half-width 1.2
degrees and maximum Lorentz factor of 16.5, a turbulent sheath with Lorentz
factor of 5, and a boundary region of sheared field between the spine and
sheath. Transverse shocks propagating along the fast, turbulent spine can
explain the superluminal knots. The observed flux density and polarization
variations are then compatible with changes in the direction of the inner jet
caused by a temporary change in the position of the core if the spine contains
wiggles owing to an instability. In addition, we can explain a stable offset of
optical and near-IR percentage polarization by a steepening of spectral index
with frequency, as supported by the data.Comment: 34 pages, 12 figures; To be published in Astrophysical Journal,
accepted 03/200
Infrared L Band Observations of the Trapezium Cluster: A Census of Circumstellar Disks and Candidate Protostars
We report the results of a sensitive near-infrared JHKL imaging survey of the
Trapezium cluster in Orion. We use the JHKL colors to obtain a census of
infrared excess stars in the cluster. Of (391) stars brighter than 12th
magnitude in the K and L bands, 80 +/- 7% are found to exhibit detectable
infrared excess on the J-H, K-L color-color diagram. Examination of a subsample
of 285 of these stars with published spectral types yields a slightly higher
infrared excess fraction of 85%. We find that 97% of the optical proplyds in
the cluster exhibit excess in the JHKL color-color diagram indicating that the
most likely origin of the observed infrared excesses is from circumstellar
disks. We interpret these results to indicate that the fraction of stars in the
cluster with circumstellar disks is between 80-85%. Moreover, we find that the
probability of finding an infrared excess/protoplanetary disk around a star is
independent of stellar mass over essentially the entire range of the stellar
mass function down to the hydrogen burning limit. We identify 78 stars in our
sample characterized by K-L colors suggestive of deeply embedded protostellar
objects. If even a modest fraction fraction (i.e., ~ 50%) of these objects are
protostars, then star formation could be continuing in the molecular ridge at a
rate comparable to that which produced the foreground Trapezium cluster.Comment: 33 pages plus 3 separate color figures. For higher resolution color
figures and a single file containing the entire paper, figures and tables see
http://cfa-www.harvard.edu/~gmuench/thesis/clusters/TRAP/traplband.html Used
AASTEX macros v 5.0. Paper will appear in December A
The Infrared Array Camera (IRAC) for the Spitzer Space Telescope
The Infrared Array Camera (IRAC) is one of three focal plane instruments in
the Spitzer Space Telescope. IRAC is a four-channel camera that obtains
simultaneous broad-band images at 3.6, 4.5, 5.8, and 8.0 microns. Two nearly
adjacent 5.2x5.2 arcmin fields of view in the focal plane are viewed by the
four channels in pairs (3.6 and 5.8 microns; 4.5 and 8 microns). All four
detector arrays in the camera are 256x256 pixels in size, with the two shorter
wavelength channels using InSb and the two longer wavelength channels using
Si:As IBC detectors. IRAC is a powerful survey instrument because of its high
sensitivity, large field of view, and four-color imaging. This paper summarizes
the in-flight scientific, technical, and operational performance of IRAC.Comment: 7 pages, 3 figures. Accepted for publication in the ApJS. A higher
resolution version is at http://cfa-www.harvard.edu/irac/publication
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