arXiv subjects

G. Nave

Publications and source records attributed to G. Nave.

9 recordsLinked to original sources

arXiv2024

Laboratory confirmation and improved Accuracy of 4f and 5d energy levels of Fe II previously identified from stellar spectra

Many energy levels of singly ionised iron (Fe II, $Z=26$) remain uncertain or experimentally unknown. Their identification and spectral line data are required in reliable astrophysical spectral analyses. In motivation for improving the atomic data of Fe II, we analysed emission spectra of a Fe-Ne plasma produced by a Penning discharge lamp recorded by high-resolution Fourier transform spectroscopy in the region 9000-27,000 cm$^{-1}$ (11,111-3704 {\AA}). Semi-empirical transition probability calculations and stellar spectra of Fe II were used to guide the analysis. In total, 24 energy levels of the 3d$^6$4f and 3d$^6$5d configurations of Fe II lying between 122,351-127,881 cm$^{-1}$ were confirmed in the laboratory for the first time, in agreement with their identities proposed by previous investigations involving only stellar spectra. Level energy and wavelength uncertainties of the 24 levels are improved by up to an order-of-magnitude compared to previously published values. These results will enable more reliable application of Fe II in astrophysical spectroscopic analyses and support further investigations of the spectrum and energy levels of Fe II.

physics.atom-ph↗

arXiv2022

Hyperfine Structure Constants of Sc I and Sc II with Fourier Transform Spectroscopy

We report new experimental hyperfine structure (HFS) constants of neutral and singly ionized scandium (Sc I and Sc II). We observed spectra of Sc-Ar and Sc-Ne hollow cathode discharges in the region 200-2500 nm (50,000-4000 cm$^{-1}$) using Fourier transform spectrometers. The measurements show significant HFS patterns in 1431 spectral lines fitted in our 12 spectra given in Table 1. These were fitted using the computer package Xgremlin to determine the magnetic dipole hyperfine interaction constant (A) for 185 levels in Sc i and 6 levels in Sc II, of which 80 Sc I levels had no previous measurements. The uncertainty in the HFS A constant is between 1 $\times$ 10$^{-4}$ and 5 $\times$ 10$^{-4}$ cm$^{-1}$.

physics.atom-ph↗

arXiv2019

Spectra of Ni V and Fe V in the Vacuum Ultraviolet

This work presents 97 remeasured Fe V wavelengths (1200 Å to 1600 Å) and 123 remeasured Ni V wavelengths (1200 Å to 1400 Å) with uncertainties of approximately 2mÅ. An additional 67 remeasured Fe V wavelengths and 72 remeasured Ni V wavelengths with uncertainties greater than 2mÅ are also reported. A systematic calibration error is also identified in the previous Ni V wavelengths and is corrected in this work. Furthermore, a new energy level optimization of Ni V is presented that includes level values as well as Ritz wavelengths. This work improves upon the available data used for observations of quadruply ionized nickel (Ni V) in white dwarf stars. This compilation is specifically targeted towards observations of the G191-B2B white dwarf spectrum that has been used to test for variations in the fine structure constant, $α$, in the presence of strong gravitational fields. The laboratory wavelengths for these ions were thought to be the cause of inconsistent conclusions regarding the variation limit of $α$ as observed through the white dwarf spectrum. These inconsistencies can now be addressed with the improved laboratory data presented here.

astro-ph.IM↗

arXiv2018

Transition probabilities of Co II, weak lines to the ground and low metastable levels

New branching fraction measurements based primarily on data from a cross dispersed echelle spectrometer are reported for 84 lines of Co II. The branching fractions for 82 lines are converted to absolute atomic transition probabilities using radiative lifetimes from laser induced fluorescence (LIF) measurements on 19 upper levels of the lines. A lifetime of 3.3(2) ns for the z5D0 level is used based on LIF measurements for lifetimes of the four other levels in the z5D term. Twelve of the 84 lines are weak transitions connecting to the ground and low metastable levels of Co+. Another 46 lines are strong transitions connecting to the ground and low metastable levels of Co+. For these lines log(gf) values were measured in earlier studies and, with a few exceptions, are confirmed in this study. Such lines, if unblended in stellar spectra, have the potential to yield Co abundance values unaffected by any breakdown of the Local Thermodynamic Equilibrium approximation in stellar photospheres because the ground and low metastable levels of Co+ are the primary population reservoirs of Co in photospheres of interest. Weak lines, if unblended, are useful in photospheres with high Co abundance and strong lines are useful in metal-poor photospheres. New hyperfine structure A constants for 28 levels of ionized Co from least square fits to Fourier transform spectra line profiles are reported. These laboratory data are applied to re-determine the Co abundance in metal-poor halo star HD 84937. Branching fractions and transition probabilities for 19 lines are reported for the first time.

astro-ph.SR↗

arXiv2017

Vanadium Transitions in the Spectrum of Arcturus

We derive a new abundance for vanadium in the bright, mildly metal-poor red giant Arcturus. This star has an excellent high-resolution spectral atlas and well-understood atmospheric parameters, and it displays a rich set of neutral vanadium lines that are available for abundance extraction. We employ a newly recorded set of laboratory FTS spectra to investigate any potential discrepancies in previously reported V I log(gf) values near 900 nm. These new spectra support our earlier laboratory transition data and the calibration method utilized in that study. We then perform a synthetic spectrum analysis of weak V I features in Arcturus, deriving log ε(V) = 3.54 $\pm$ 0.01 (σ = 0.04) from 55 lines. There are no significant abundance trends with wavelength, line strength, or lower excitation energy.

astro-ph.SR↗

arXiv2014

Fe I Oscillator Strengths for the Gaia-ESO Survey

The Gaia-ESO Public Spectroscopic Survey (GES) is conducting a large-scale study of multi-element chemical abundances of some 100 000 stars in the Milky Way with the ultimate aim of quantifying the formation history and evolution of young, mature and ancient Galactic populations. However, in preparing for the analysis of GES spectra, it has been noted that atomic oscillator strengths of important Fe I lines required to correctly model stellar line intensities are missing from the atomic database. Here, we present new experimental oscillator strengths derived from branching fractions and level lifetimes, for 142 transitions of Fe I between 3526 Å and 10864 Å, of which at least 38 are urgently needed by GES. We also assess the impact of these new data on solar spectral synthesis and demonstrate that for 36 lines that appear unblended in the Sun, Fe abundance measurements yield a small line-by-line scatter (0.08 dex) with a mean abundance of 7.44 dex in good agreement with recent publications.

astro-ph.SR↗

arXiv2013

Infrared Laboratory Oscillator Strengths of Fe I in the H-Band

We report experimental oscillator strengths for 28 infrared Fe I transitions, for which no previous experimental values exist. These transitions were selected to address an urgent need for oscillator strengths of lines in the H-band (between 1.4 um and 1.7 um) required for the analysis of spectra obtained from the Sloan Digital Sky Survey (SDSS-III) Apache Point Galactic Evolution Experiment (APOGEE). Upper limits have been placed on the oscillator strengths of an additional 7 transitions, predicted to be significant by published semi-empirical calculations, but not observed to be so.

astro-ph.SR↗

arXiv2006

Experimental Ti I oscillator strengths and their application to cool star analysis

We report experimental oscillator strengths for 88 Ti I transitions covering the wavelength range 465 to 3892 nm, 67 of which had no previous experimental values. Radiative lifetimes for thirteen energy levels, including the low energy levels 3d2 (3F) 4s4p (3P) z5Dj, have been measured using time resolved laser induced fluorescence. Intensity calibrated Ti I spectra have been measured using Fourier transform spectroscopy to determine branching fractions for the decay channels of these levels. The branching fractions are combined with the radiative lifetimes to yield absolute transition probabilities and oscillator strengths. Our measurements include 50 transitions in the previously unobserved infrared region lambda > 1000 nm, a region of particular interest to the analysis of cool stars and brown dwarfs.

astro-ph↗

arXiv1994

Analysis of the 3d6 4s(6D)4f-5g Supermultiplet of Fe I in Laboratory and Solar Infrared Spectra

The combined laboratory and solar analysis of the highly-excited subconfigurations 4f and 5g of Fe I has allowed us to classify 87 lines of the 4f-5g supermultiplet in the spectral region 2545-2585 cm-1. The level structure of these JK-coupled configurations is predicted by semiempirical calculations and the quadrupolic approximation. Semiempirical gf-values have been calculated and are compared to gf values derived from the solar spectrum. The solar analysis has shown that these lines, which should be much less sensitive than lower excitation lines to departures from LTE and to temperature uncertainties, lead to a solar abundance of iron which is consistent with the meteoritic value (A_Fe = 7.51).

astro-ph↗