Richard Blackwell-Whitehead

High‐resolution photoabsorption cross‐section measurements of SO2 at 160 K between 199 and 220 nm

Photoabsorption cross sections of sulfur dioxide over a range of temperatures are required to interpret observations and to support models of the atmospheres of Io and Venus. We report high-resolution (lambda/Delta lambda approximate to 450,000) photoabsorption cross-section measurements by Fourier transform spectrometry of SO2 at 160 K in the wavelength region 199 to 220 nm, which encompasses the strongest features in the prominent (C) over tilde (1) B-2 -(X) over tilde (1)A(1) system. Our results are compared with literature values obtained at lower resolutions and with 295 K cross sections recorded earlier with the same instrument.

Hyperfine Structure Measurements of Neutral Manganese with Fourier Transform Spectroscopy

We report experimental hyperfine structure constants of levels in the neutral manganese atom, measured using Fourier transform spectroscopy of hollow cathode discharges. In total, 208 spectral lines of astrophysical interest have been analyzed to obtain hyperfine structure constants for 106 levels in Mn i, of which 67 have no previous hyperfine structure measurements. The uncertainties in the magnetic dipole constants, A ,a re between 1; 10 � 4 and 5 ;10 � 4 cm � 1 . Hyperfine structure constants for an additional 18 levels compiled from the literature are also given. Subject headingg atomic data — line: profiles — methods: laboratory

High-resolution photoabsorption cross-section measurements of SO2 at 198 K from 213 to 325 nm

SO2 plays an important role in the atmospheric chemistry of the Earth, Venus, and Io. This paper presents photoabsorption cross sections of SO2 from 213 to 325 nm at 198 K, encompassing the (C) over tilde B-1(2) - (X) over tilde (1)A(1) and (B) over tilde B-1(1) - (X) over tilde (1)A(1) electronic bands. These measurements are part of a series of measurements over the 160 to 300 K temperature range between 190 and 325 nm. The cross sections have been measured at high resolution (lambda/Delta lambda approximate to 450,000) using Fourier transform spectrometry and are compared to other high-resolution measurements in the literature.

Atomic lines in infrared spectra for ultracool dwarfs

We provide a set of atomic lines which are suitable for the description of ultracool dwarf spectra from 10 000 to 25 000 A. This atomic linelist was made using both synthetic spectra calculations and existing atlases of infrared spectra of Arcturus and Sunspot umbra. We present plots which show the comparison of synthetic spectra and observed Arcturus and Sunspot umbral spectra for all atomic lines likely to be observable in high resolution infrared spectra.

The FERRUM Project: laboratory-measured transition probabilities for Cr II

Aims: We measure transition probabilities for Cr II transitions from the z ^4H_J, z ^2D_J, y ^4F_J, and y ^4G_J levels in the energy range 63000 to 68000 cm^{-1}. Methods:Radiative lifetimes were m ...Aims. We measure transition probabilities for Cr ii transitions from the z HJ , z DJ , y FJ , and y GJ levels in the energy range 63 000 to 68 000 cm−1. Methods. Radiative lifetimes were measured using time-resolved laser-induced fluorescence from a laser-produced plasma. In addition, branching fractions were determined from intensity-calibrated spectra recorded with a UV Fourier transform spectrometer. The branching fractions and radiative lifetimes were combined to yield accurate transition probabilities and oscillator strengths. Results. We present laboratory measured transition probabilities for 145 Cr ii lines and radiative lifetimes for 14 Cr ii levels. The laboratory-measured transition probabilities are compared to the values from semi-empirical calculations and laboratory measurements in the literature.

Experimental Ca I oscillator strengths for the 4p-5s triplet

Context. Transition lines of neutral calcium are observed in the spectra of stellar and substellar objects. In particular, the abundance of α-elements in metal-poor stars can place important constraints on the galactic chemical evolution. Such stellar abundance analyses rely heavily on accurate values for the oscillator strength of the observable transitions. Theoretical oscillator strengths are available for most neutral calcium lines visible in stellar spectra, but there are a limited number of experimental values in the literature. Aims. We present new and improved experimental oscillator strengths for the optical Ca i 4p-5s triplet (6102.7, 6122.2, 6162.2 A). In addition, we present experimental radiative lifetimes for seven energy levels in the triplet system of Ca i. Methods. The oscillator strengths were determined by combining radiative lifetimes with branching fractions. The radiative lifetimes were measured using laser-induced fluorescence, and the branching fractions were determined using intensity calibrated spectra measured with Fourier transform spectrometry. In addition, the spectra were used to determine accurate (dλ = 0.001 A, dσ = 0.002 cm −1 ) laboratory wavelengths for the 4p-5s transitions. Results. Oscillator strengths for the Ca i 4p-5s lines were determined with an absolute uncertainty of 9%, an uncertainty of ±0.04 dex in the log(gf ) values. The branching fractions were determined with a higher accuracy, resulting in relative uncertainties of 2-3%.

Laboratory measurements of oscillator strengths and their astrophysical applications

We present an overview of current needs for accurate laboratory atomic transition probabilities (log(gf)) for astrophysical applications, particularly for iron group element spectra in the IR, optical, UV, and VUV spectral regions. Examples are given of our recent measurements, undertaken using the combination of high-resolution Fourier transform spectrometry and time-resolved laser-induced fluorescence. Laboratory measured log(gf) values are particularly important for the determination of elemental abundances in astrophysical objects. Advances in astronomical instrumentation, particularly access to underexplored regions (IR, vacuum UV, VUV), require improved accuracy and completeness of the atomic database for meaningful analyses of astrophysical spectra. (Less)

Infrared Mn I laboratory oscillator strengths for the study of late type stars and ultracool dwarfs

Aims. The aim of our new laboratory measurements is to measure accurate absolute oscillator strengths for neutral manganese transitions in the infrared needed for the study of late-type stars and ultracool dwarfs. Methods. Branching fractions have been measured by high resolution Fourier transform spectroscopy and combined with radiative level lifetimes in the literature to yield oscillator strengths. Results. We present experimental oscillator strengths for 20 Mn I transitions in the wavelength range 3216 to 13 997 angstrom, 15 of which are in the infrared. The transitions at 12 899 angstrom and 12 975 angstrom are observed as strong features in the spectra of late-type stars and ultracool dwarfs. We have fitted our calculated spectra to the observed Mn I lines in spectra of late-type stars. Using the new experimentally measured Mn I log(gf) values together with existing data for Mn I hyperfine structure splitting factors we determined the manganese abundance to be log N(Mn) = -6.65 +/- 0.05 in the atmosphere of the Sun, log N(Mn) = 6.95 +/- 0.20 in the atmosphere of Arcturus, and log N(Mn) = -6.70 +/- 0.20 in the atmosphere of M 9.5 dwarf 2MASSW 0140026+270150. (Less)

The FERRUM project: transition probabilities for forbidden lines in [Fe II] and experimental metastable lifetimes

Context. Accurate transition probabilities for forbidden lines are important diagnostic parameters for low-density astrophysical plasmas. In this paper we present experimental atomic data for forbi ...

Experimentally Measured Radiative Lifetimes and Oscillator Strengths in Neutral Vanadium

We report a new study of the V i atom using a combination of time-resolved laser-induced fluorescence and Fourier transform spectroscopy that contains newly measured radiative lifetimes for 25 levels between 24,648 cm-1 and 37,518 cm-1 and oscillator strengths for 208 lines between 3040 and 20000 from 39 upper energy levels. Thirteen of these oscillator strengths have not been reported previously. This work was conducted independently of the recent studies of neutral vanadium lifetimes and oscillator strengths carried out by Den Hartog et al. and Lawler et al., and thus serves as a means to verify those measurements. Where our data overlap with their data, we generally find extremely good agreement in both level lifetimes and oscillator strengths. However, we also find evidence that Lawler et al. have systematically underestimated oscillator strengths for lines in the region of 9000 ± 100. We suggest a correction of 0.18 ± 0.03 dex for these values to bring them into agreement with our results and those of Whaling et al. We also report new measurements of hyperfine structure splitting factors for three odd levels of V i lying between 24,700 and 28,400 cm-1.