Ulf Litzén

Experimental f-Value and Isotopic Structure for the Ni I Line Blended with [O I] at 6300 Å

We have measured the oscillator strength of the Ni I line at 6300.34A, which is known to be blended with the forbidden line [O I]lambda6300 used for the determination of the oxygen abundance in coolstars. We also give wavelengths of the two isotopic line components of 58 Ni and 60 Ni derived from the asymmetriclaboratory line profile. These two line components of Ni I have to beconsidered when calculating a line profile of the 6300 A featureobserved in stellar and solar spectra. We also discuss the labeling ofthe energy levels involved in the Ni I line since level mixing makes thetheoretical predictions uncertain.

The Spectrum and Term System of Singly Ionized Titanium, Ti II

The TiII spectrum has been recorded in the region 1100-11 000 A. 1240 lines have been classified as transitions between 204 levels of the configurations (3d + 4s)3, 3d2 nl (nl = 5, 6s; 4, 5p; 4, 5d; 4f) and 3d4s4p. Parametric studies including configuration interaction have been carried out for a number of configurations. The ionization energy has been determined to 109 494 ± 20 cm-1.

Uncertainty of oscillator strengths derived from lifetimes and branching fractions

Abstract A widely used method for determination of transition probabilities and oscillator strengths is based on measurements of branching fractions and radiative lifetimes. In the present work the different sources of uncertainty in branching fraction measurements using Fourier transform spectroscopy and lifetime measurements using laser induced fluorescence are discussed. A detailed description is presented of how the uncertainties should be combined to provide a well-defined uncertainty of the derived quantity. Finally, an example shows how the individual uncertainties can be presented in an “uncertainty budget”.

Spectrum and term system of neutral nickel, Ni I

Spectra of nickel, emitted from hollow cathode discharges, have been recorded in the region 1700-55 000 A (58 800-1800 cm−1). Fourier transform spectrometers were used above 1800 A, yielding very high accuracy and resolution. The number of classified Ni I lines has increased from 1071 to 1996. 289 of the lines have been resolved in 2-4 isotope components. The term system derived from the observations comprises 286 energy levels. The term structure and the coupling conditions have been studied by means of ab initio and parametric theory.

The 2p53s, 3p and 3d Configurations in Neon-Like Ti XIII and Fe XVII

Spectra emitted from laser-produced plasmas of scandium, titanium, vanadium and chromium have been recorded in the region 270-600 A, and lines belonging to the 3s-3p and 3p-3d transition arrays in neonlike ions have been identified. The 2p53s, 3p and 3d energy levels have been derived from the observations for Ti XIII and from solar flare lines for Fe XVII. Hartree-Fock calculations and parametric fits have yielded scaling factors for ab initio energy integrals that make it possible to predicts 3s-3p and 3p-3d wavelengths. Observed and predicted wavelengths for the strongest lines in Sc XII, V XIV, Cr XV and Ni XIX are presented.

Revised and extended analysis of transitions and energy levels in the n=3 complex of Mg-like Ca IX-Ge XXI

Spectra emitted from laser-produced plasmas of Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga and Ge have been recorded in the region 170-800 A. In magnesium-like Ca IX-Mn XIV transitions establishing all the levels of 3s2, 3s3p, 3s3d, 3p2 and 3p3d have been identified, and new and improved level values have been derived. In Fe XV-Zn XIX additions have been made to recent analyses. In Ga XX and Ge XXI some strong lines in the 3-3 transition array have been identified. Ab initio and parametric calculations support the identifications and provide eigenvector components. Numerous observed transitions connect the singlet and triplet systems, and the wavelength of the resonance intercombination line 3s2 1S0–3s3p 3P1 has been derived from the energy levels for Ca IX-Zn XIX.

Goddard High-Resolution Spectrograph Observations of the B III Resonance Doublet in Early B Stars: Abundances and Isotope Ratios

Boron abundances and isotope ratios in two early B stars have been measured by using the Hubble Space Telescopes Goddard High-Resolution Spectrograph (GHRS) in order to observe the B III resonance doublet near 2066 A. We also report new experimental and theoretical results for the wavelengths, isotope shift, and hyperfine structure of these boron lines. In HD 886 (γ Pegasi; B2 IV), and HD 35299 (B1 V) the abundance of boron is about a factor of 2 lower than that inferred from solar system meteorites. The 11B/10B isotope ratio in HD 886 is determined to be 4.7, and for HD 35299 a value of 3.7 is found. These values are consistent with the solar system isotope ratio. In a third star, HD 3360 (ζ Cassiopeiae; B2 IV), our GHRS observations show that the boron abundance is a factor of 40 below the solar system abundance. Our results for HD 886 and HD 35299 appear to be consistent with little dispersion in the initial boron-to-oxygen ratio among Population I stars and a universal 11B/10B isotope ratio. However, the abundance measured for HD 3360 shows that either some stars suffer significant boron depletion while still in the core-hydrogen burning phase of their evolution, or there is indeed a very wide variation in initial Population I boron abundances. A much-improved understanding of boron astration in early B stars will be required before this question can be resolved.

The presence of Nd and Pr in HgMn stars

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 hyperne structure (hfs) have been studied for selected Pr ii ,P riii 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 identied 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-dened 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 diusive 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 diused elements to gather higher in the atmosphere of HgMn stars compared to Am stars, and explain the observed increase in abundance.

An Optical Region Elemental Abundance Analysis of the HgMn Type Star HR 7775

Optical region spectra of the chemically peculiar HgMn type star HR 7775 have been analyzed for the determination of elemental abundances and spectral line identification as a complementary study to the analysis of Hubble Space Telescope Goddard High Resolution Spectrograph spectra. The spectra were obtained with the SOFIN echelle spectrograph on the Nordic Optical Telescope at nominal resolving powers of R = 25,000, 80,000, and 170,000 and signal-to-noise ratios typically in excess of 100 : 1. The overall nature of the elemental abundance distribution is similar to other cool, HgMn stars; somewhat enhanced abundances for the iron-group elements, with progressively stronger enhancements for heavier elements. Of particular note are the presence of lines from the rare-earth spectra Nd III and Pr III, and the heavy elements Pt, Au, Hg, Tl, and Bi. The isotopic mixture for several lines of mercury and platinum has been investigated. For mercury a possible difference is found between the mixtures as derived from lines of Hg I and Hg II. Three lines of Pt II display the same mixture, which is different from that found from lower excitation lines at ultraviolet wavelengths. We present new laboratory Fourier Transform spectrometer measurements for isotopic and hyperfine structure components of Hg I λ4046 and 4358 and Hg II λ3984 A.

Atomic Data for the Re II UV 1 Multiplet and the Rhenium Abundance in the HgMn-type Star χ Lupi*

We report new laboratory spectroscopic analyses that have been conducted to acquire wavelength and oscillator strength data for lines of the Re II UV 1 multiplet. Wavelengths were determined to a sub-milliangstrom accuracy for the hyperfine and isotopic structure components from laboratory spectra obtained with the Lund VUV Fourier Transform Spectrometer. An absolute atomic transition probability is reported for Re II 2275.253 A, obtained from its upper level lifetime and an experimentally determined branching fraction. The radiative lifetime of the z 7Po2 level was found to be 4.47 ± 0.22 ns by the method of laser-induced fluorescence. With the new atomic data, synthetic spectra were generated to fit a Hubble Space Telescope Goddard High Resolution Spectrograph echelle mode spectrum of the chemically peculiar HgMn-type star χ Lupi. The weakness of the λ2275.253 A feature only allowed for the determination of an upper limit to the rhenium abundance, which was found to be consistent with the meteoritic value. Thus, in χ Lupi, rhenium appears to be several orders of magnitude less abundant than the apparent surficial abundances of the slightly heavier elements Pt, Au, Hg, and Tl.