arXiv subjects

S. Cheng

Publications and source records attributed to S. Cheng.

21 records · Page 2Linked to original sources

arXiv2007

Oscillator Strengths for Ultraviolet Transitions in P II

We report lifetimes, branching fractions, and the resulting oscillator strengths for transitions within the P II multiplet (3s^23p^2 ^3P - 3s^23p4s ^3P^o) at 1154 A. These beam-foil measurements represent the most comprehensive and precise set currently available experimentally. Comparison with earlier experimental and theoretical results is very good. Since Morton's most recent compilation is based on the earlier body of results, phosphorus abundances for interstellar material in our Galaxy and beyond derived from lambda 1154 do not require any revision.

astro-ph↗

arXiv2004

Statistical and Dynamic Models of Charge Balance Functions

Charge balance functions, which identify balancing particle-antiparticle pairs on a statistical basis, have been shown to be sensitive to whether hadronization is delayed by several fm/c in relativistic heavy ion collisions. Results from two classes of models are presented here, microscopic hadronic models and thermal models. The microscopic models give results which are contrary to recently published pi+pi- balance functions from the STAR collaboration, whereas the thermal model roughly reproduce the experimental results. This suggests that charge conservation is local at breakup, which is in line with expectations for a delayed hadronization. Predictions are also presented for balance functions binned as a function of Q_inv.

nucl-th↗

arXiv2001

Oscillator Strengths for B-X, C-X, and E-X Transitions in Carbon Monoxide

Band oscillator strengths for electronic transitions in CO were obtained at the Synchrotron Radiation Center of the University of Wisconsin-Madison. Our focus was on transitions that are observed in interstellar spectra with the Far Ultraviolet Spectroscopic Explorer; these transitions are also important in studies of selective isotope photodissociation where fractionation among isotopomers can occur. Absorption from the ground state (X ^1Sigma^+ v'' = 0) to A ^1Pi (v'= 5), B ^1Sigma^+ (v' = 0, 1), C ^1Sigma^+ (v' = 0, 1), and E ^1Pi (v' = 0) was measured. Fits to the A - X (5, 0) band, whose oscillator strength is well known, yielded the necessary column density and excitation temperature. These parameters were used in a least-squares fit of the observed profiles for the transitions of interest to extract their band oscillator strengths. Our oscillator strengths are in excellent agreement with results from recent experiments using a variety of techniques. This agreement provides the basis for a self-consistent set of f-values at far ultraviolet wavelengths for studies of interstellar (and stellar) CO.

astro-ph↗