Stellar Associations and their Field East of LMC 4 in the Large Magellanic Cloud

We report about the stellar content and the luminosity and mass functions of three stellar associations and their field located on the north-east edge of the super-bubble LMC 4 in the Large Magellanic Cloud.Comment: To be appeared in the meeting Proceedings of ``Modes of Star Formation and the Origin of Field Populations'', Heidelberg, Germany, October 2000; to be published in the ASP Conference Series, edited by E. K. Grebel and W. Brandne

Chandra Detection of X-ray Absorption Associated with a Damped Lyman Alpha System

We have observed three quasars, PKS 1127-145, Q 1331+171 and Q0054+144, with the ACIS-S aboard the Chandra X-ray Observatory, in order to measure soft X-ray absorption associated with intervening 21-cm and damped Ly$\alpha$ absorbers. For PKS 1127-145, we detect absorption which, if associated with an intervening z_{abs}=0.312 absorber, implies a metallicity of 23% solar. If the absorption is not at z_{abs}=0.312, then the metallicity is still constrained to be less than 23% solar. The advantage of the X-ray measurement is that the derived metallicity is insensitive to ionization, inclusion of an atom in a molecule, or depletion onto grains. The X-ray absorption is mostly due to oxygen, and is consistent with the oxygen abundance of 30% solar derived from optical nebular emission lines in a foreground galaxy at the redshift of the absorber. For Q1331+171 and Q 0054+144, only upper limits were obtained, although the exposure times were intentionally short, since for these two objects we were interested primarily in measuring flux levels to plan for future observations. The imaging results are presented in a companion paper.Comment: 23 pages, 6 figures, accepted for publication in the Astrophysical Journa

A non-renormalization theorem for chiral primary 3-point functions

In this note we prove a non-renormalization theorem for the 3-point functions of 1/2 BPS primaries in the four-dimensional N = 4 SYM and chiral primaries in two dimensional N =(4,4) SCFTs. Our proof is rather elementary: it is based on Ward identities and the structure of the short multiplets of the superconformal algebra and it does not rely on superspace techniques. We also discuss some possible generalizations to less supersymmetric multiplets.Comment: 32 pages, added references, corrected typo

Monitoring the Variable Interstellar Absorption toward HD 219188 with HST/STIS

We discuss the results of continued spectroscopic monitoring of the variable intermediate-velocity (IV) absorption at v = -38 km/s toward HD 219188. After reaching maxima in mid-2000, the column densities of both Na I and Ca II in that IV component declined by factors >= 2 by the end of 2006. Comparisons between HST/STIS echelle spectra obtained in 2001, 2003, and 2004 and HST/GHRS echelle spectra obtained in 1994--1995 indicate the following: (1) The absorption from the dominant species S II, O I, Si II, and Fe II is roughly constant in all four sets of spectra -- suggesting that the total N(H) and the (mild) depletions have not changed significantly over a period of nearly ten years. (2) The column densities of the trace species C I (both ground and excited fine-structure states) and of the excited state C II* all increased by factors of 2--5 between 1995 and 2001 -- implying increases in the hydrogen density n_H (from about 20 cm^{-3} to about 45 cm^{-3}) and in the electron density n_e (by a factor >= 3) over that 6-year period. (3) The column densities of C I and C II* -- and the corresponding inferred n_H and n_e -- then decreased slightly between 2001 and 2004. (4) The changes in C I and C II* are very similar to those seen for Na I and Ca II. The relatively low total N(H) and the modest n_H suggest that the -38 km/s cloud toward HD 219188 is not a very dense knot or filament. Partial ionization of hydrogen appears to be responsible for the enhanced abundances of Na I, C I, Ca II, and C II*. In this case, the variations in those species appear to reflect differences in density and ionization [and not N(H)] over scales of tens of AU.Comment: 33 pages, 6 figures, aastex, accepted to Ap