We have analyzed high spatial, moderate spectral resolution observations of Eta Carinae (η Car) obtained with the Space Telescope Imaging Spectrograph (STIS) from 1998.0 to 2004.3. The data were obtained at discrete times covering an entire 2024 day spectroscopic cycle, with focus on the Xray/ionization low-state which began in 2003 June. The spectra show prominent P-Cygni lines in H I, Fe II and He I which are complicated by blends and contamination by nebular emission and absorption along the line-of-sight toward the observer. All lines show phase and species dependent variations in emission and absorption. For most of the cycle the He I emission is blueshifted relative to the H I and Fe II P-Cygni emission lines, which are approximately centered at system velocity. The blueshifted He I absorption varies in intensity and velocity throughout the 2024 day period. We construct radial velocity curves for the absorption component of the He I and H I lines. The He I absorption shows significant radial velocity variations throughout the cycle, with a rapid change of over 200 km s −1 near the 2003.5 event. The H I velocity curve is similar to that of the He I absorption, though offset in phase and reduced in amplitude. We interpret the complex line profile variations in He I, H I and Fe II to be a consequence of the dynamic interaction of the dense wind of η Car A with the less dense, faster wind plus the radiation field of a hot companion star, η Car B. The companion's wind carves out a cavity in η Car A's wind, which allows UV flux from η Car B to penetrate and photoionize an extended region of η Car A's wind. During most of the orbit, η Car B and the He + recombination zone are on the near side of η Car A, producing blueshifted He I emission. He I absorption is formed in the part of the He + zone that intersects the line-of-sight toward η Car. We use the variations seen in He I and the other P-Cygni lines to constrain the geometry of the orbit and the character of η Car B.

The first measurement of a one-dimensional relaxation law is reported. The photocurrent decay of the polydiacetylene PDA-1OH has been measured in the time range (1-2 x lo4) s. The measurements can be extremely well described by an exp(-btlb) law, characteristic of deep trapping in a one-dimensional system. Comparing experiment and theory we are able to estimate trap concentrations and effective jump rates.

Abstract.Optical region spectra for a number of upper main sequence chemically peculiar (CP) stars have been observed to study singly and doubly ionized praseodymium and neodymium lines. In order to improve existing atomic data of these elements, laboratory measurements have been carried out with the Lund VUV Fourier Transform Spectrometer (FTS). From these measurements wavelengths and hyperfine structure (hfs) have been studied for selected Pr ii, Pr iii and Nd iii lines of astrophysical interest. Radiative lifetimes for some excited states of Pr ii have been determined with the aid of laser spectroscopy at the Lund Laser Center (LLC) and have been combined with branching fractions measured in the laboratory to calculate gf values for some of the stronger optical lines of Pr ii. With the aid of the derived gf values and laboratory measurements of the hfs, a praseodymium abundance was derived from selected Pr ii lines in the spectrum of the Am star 32 Aqr. This abundance was used to derive astrophysical gf values for selected Pr iii lines in 32 Aqr, and these gf values were used to get a praseodymium abundance for the HgMn star HR 7775. The praseodymium abundance in HR 7775 was then utilized to derive astrophysical gf values for all observable Pr iii lines in this star. The neodymium abundance, derived from unblended lines of Nd ii in HR 7775, has been utilized to establish astrophysical gf values for observed Nd iii lines in the optical region of this star. Selected Pr iii and Nd iii lines have been identified and studied in a number of HgMn stars and three hot Am stars. The praseodymium and neodymium abundance change rapidly from an approximate 1-1.2 dex enhancement for the hot Am stars to 1.5-3 dex enhancement for the cool HgMn stars, indicating a well-defined boundary between the hot Am and HgMn stars in the vicinity of 10 500 K. The enhancement of praseodymium and neodymium in Am and HgMn stars may be explained by diffusive processes active in the stellar atmosphere, while the observed discontinuity might be explained by a thin hydrogen convection zone thought to be present for the Am stars, but absent in the HgMn stars. The absence of a convection zone would cause the diffused elements to gather higher in the atmosphere of HgMn stars compared to Am stars, and explain the observed increase in abundance.

Abstract. The radioactive decay of 238 U and 232 Th has recently been used to determine ages for some of the oldest stars in the Universe. This has highlighted the need for accurate observational constraints on production models for the heaviest r-process elements which might serve as stable references, notably osmium and iridium. In order to provide a firmer basis for the observed abundances, we have performed laser-induced fluorescence measurements and Fourier Transform Spectroscopy to determine new radiative lifetimes and branching fractions for selected levels in Os I and Ir I. From these data, we determine new absolute oscillator strengths and improved wavelengths for 18 Os I and 4 Ir I lines. A reanalysis of VLT spectra of CS 31082-001 and new results for other stars with Os and Ir detections show that (i): the lines in the UV and λ 4260 Å yield reliable Os abundances, while those at λλ 4135, 4420 Å are heavily affected by blending; (ii): the Os and Ir abundances are identical in all the stars; (iii): the heavy-element abundances in very metal-poor stars conform closely to the scaled solar r-process pattern throughout the range 56 ≤ Z ≤ 77; and (iv): neither Os or Ir nor any lighter species are suitable as reference elements for the radioactive decay of Th and U.