1,158,644 research outputs found
QCD calculation of J/psi+gamma mass distributions
We compute the J/psi+gamma invariant-mass distributions from the QCD
subprocess g + g --> J/psi+gamma. At large masses, this subprocess is the
dominant mechanism for J/psi+gamma production, and data could provide a good
test of QCD. The mass distribution peaks at relatively small masses (3.4 - 4.0
GeV) and the subprocess could, therefore, represent a significant QCD
background to J/psi+gamma decay of heavier charmonia. We also analyze the J/psi
angular distribution in the J/psi+gamma rest frame.Comment: 7 pages LaTex, 4 figures available on request. CERN-TH.6974/93,
ANL-HEP-PR-93.6
New Young Stars and Brown Dwarfs in the Upper Scorpius Association
To improve the census of the Upper Sco association (~11 Myr, ~145 pc), we
have identified candidate members using parallaxes, proper motions, and
color-magnitude diagrams from several wide-field imaging surveys and have
obtained optical and infrared spectra of several hundred candidates to measure
their spectral types and assess their membership. We also have performed
spectroscopy on a smaller sample of previously known or suspected members to
refine their spectral types and evidence of membership. We have classified 530
targets as members of Upper Sco, 377 of which lack previous spectroscopy. Our
new compilation of all known members of the association contains 1631 objects.
Although the census of Upper Sco has expanded significantly over the last
decade, there remain hundreds of candidates that lack spectroscopy. The precise
parallaxes and proper motions from the second data release of Gaia should
extend down to substellar masses in Upper Sco, which will greatly facilitate
the identification of the undiscovered members.Comment: Astronomical Journal, in press; machine readable tables and fits
spectra available at http://personal.psu.edu/kll207/usco.ta
Computer program determines thermal environment and temperature history of lunar orbiting space vehicles
Program computes the thermal environment of a spacecraft in a lunar orbit. The quantities determined include the incident flux /solar and lunar emitted radiation/, total radiation absorbed by a surface, and the resulting surface temperature as a function of time and orbital position
A study of the mass loss rates of symbiotic star systems
The amount of mass loss in symbiotic systems is investigated, specifically
mass loss via the formation of jets in R Aquarii (R Aqr). The jets in R Aqr
have been observed in the X-ray by Chandra over a four year time period. The
jet changes on times scales of a year and new outflows have been observed.
Understanding the amount of mass and the frequency of ejection further
constrain the ability of the white dwarf in the system to accrete enough mass
to become a Type 1a supernova progenitor. The details of multi-wavelength
studies, such as speed, density and spatial extent of the jets will be
discussed in order to understand the mass balance in the binary system. We
examine other symbiotic systems to determine trends in mass loss in this class
of objects.Comment: To be published in the proceedings of "The Multicoloured Landscape of
Compact Objects and their Explosive Origins
New calibrations for abundance determinations in HII regions
Simple relations for deriving the oxygen abundance in HII regions with
intensities of the three strong emission lines R_2, R_3, and N_2 (R
calibration) or S_2, R_3, and N_2 (S calibration) in their spectra are
suggested. A sample of 313 reference HII regions of the counterpart method is
used as calibrating data points. Relations for the determination of nitrogen
abundances, the R calibration, are also constructed. We find that the oxygen
and nitrogen abundances in high-metallicity HII regions can be estimated using
the intensities of the two strong lines R_2 and N_2 (or S_2 and N_2 for oxygen)
only. The corresponding two-dimensional relations are provided. There are
considerable advantages of the suggested calibration relations as compared to
the existing ones. First, the oxygen and nitrogen abundances estimated through
the suggested calibrations agree with the Te-based abundances within ~0.1 dex
over the whole metallicity range, i.e., the relative accuracy of the
calibration-based abundances is 0.1 dex. Although we constructed distinct
relations for high- and low-metallicity objects, the separation between these
two can be simply obtained from the intensity of the N_2 line. Moreover, the
applicability ranges of the high- and low-metallicity relations overlap for
adjacent metallicities, i.e., the transition zone disappears. Second, the
oxygen abundances produced by the two suggested calibrations are in remarkable
agreement with each other. In fact, the R-based and S-based oxygen abundances
agree within ~0.05 dex in the majority of cases for more than three thousand
HII region spectra.Comment: 16 pages, 9 figues, accepted to MNRA
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