We have derived new very accurate abundances of the Fe-group elements Sc through Zn (Z = 21−30) i... more We have derived new very accurate abundances of the Fe-group elements Sc through Zn (Z = 21−30) in the bright main-sequence turnoff star HD 84937, based on high-resolution spectra covering the visible and ultraviolet spectral regions. New or recent laboratory transition data for 14 species of seven elements have been used. Abundances from more than 600 lines of non-Fe species have been combined with about 550 Fe lines in HD 84937 to yield abundance ratios of high precision. The abundances have been determined from both neutral and ionized transitions, which generally are in agreement with each other. We find no substantial departures from standard LTE Saha ionization balance in this [Fe/H] = −2.32 star. Noteworthy among the abundances are: [Co/Fe] = +0.14 and [Cu/Fe] = −0.83, in agreement with past studies abundance trends in this and other low metallicity stars; and [Sc,Ti,V/Fe] = +0.31, which has not been noted previously. A detailed examination of scandium, titanium, and vanadium abundances in large-sample spectroscopic surveys reveals that they are positively
Proceedings of 11th Symposium on Nuclei in the Cosmos — PoS(NIC XI)
We report on new abundance determinations for the neutron-capture elements Cd I (Z=48), Lu II (Z ... more We report on new abundance determinations for the neutron-capture elements Cd I (Z=48), Lu II (Z = 71) and Os II (Z = 76) in the r-process enriched star BD + 17 3248. These abundances are derived from an ultraviolet spectrum obtained with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. These are the first detections of these elements in metal-poor r-process enriched halo stars. In addition to the HST observations we have obtained new abundance measurements of the elements Mo I, Ru I and Rh I, based upon High Resolution Echelle Spectrograph observations with Keck. Combining these and previous observations, we have now * Speaker. † Funding for this project has been generously provided by NSF.
Proceedings of 11th Symposium on Nuclei in the Cosmos — PoS(NIC XI)
In this review we summarize the current state of some aspects of observational studies of low met... more In this review we summarize the current state of some aspects of observational studies of low metallicity stars that have been enriched with products of rapid-neutron-capture (r-process) nucleosynthesis events. Attention will be drawn to the element domains where there is little star-tostar variation in relative abundances (such as the rare earths), and those with substantial variations (the lightest neutron-capture elements and the very heavy radioactive elements Th and U). We highlight some new work bearing on our understanding of the limits of abundance distributions that can be produced in the r-process. Finally, comments will be made on the metallicity at which significant contributions from the s-process can be seen in Galactic halo stars.
New branching fraction (BF) measurements based primarily on data from a cross-dispersed echelle s... more New branching fraction (BF) measurements based primarily on data from a cross-dispersed echelle spectrometer are reported for 84 lines of Co II. The BFs 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 z 5 D 0 level is used based on LIF measurements for lifetimes of the four other levels in the z 5 D term. Twelve of the eighty-four 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 the 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-squares fits to Fourier transform spectra line profiles are reported. These laboratory data are applied to re-determine the Co abundance in the metal-poor halo star HD 84937. BFs and transition probabilities for 19 lines are reported for the first time.
We derive a new abundance for vanadium in the bright, mildly metal-poor red giant Arcturus. This ... more 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±0.01 (σ=0.04) from 55 lines. There are no significant abundance trends with wavelength, line strength, or lower excitation energy.
This brief review highlights some current issues in Galactic stellar nucleosynthesis, and some re... more This brief review highlights some current issues in Galactic stellar nucleosynthesis, and some recent laboratory studies by the Wisconsin atomic physics group that have direct application to stellar spectroscopy, in order to advance our understanding of the chemical evolution of our Galaxy. The relevant publication history of the lab studies are summarized, and investigations into the abundances of neutron-capture and iron-peak elements in low metallicity stars are described. Finally, new initatives in near-infrared spectroscopy are briefly explored.
Improved energy levels and hyperfine structure constants for a selected set of Ho ii levels were ... more Improved energy levels and hyperfine structure constants for a selected set of Ho ii levels were measured from spectra recorded using the 1 m Fourier transform spectrometer (FTS) at the US National Solar Observatory. Branching fractions for the strong blue-UV lines from these levels were also measured from the FTS data and combined with earlier radiative lifetimes from time-resolved laser-induced fluorescence measurements to determine accurate absolute transition probabilities for 22 lines of Ho ii. These new laboratory measurements, along with a recently reported partition function for ionized Ho, were used to improve Ho abundance determinations in the Sun and three metal-poor Galactic halo giant stars. The derived solar photospheric holmium abundance, log 10 ðHoÞ ¼ þ0:51 AE 0:10, is consistent with its meteoritic value, log 10 ðHoÞ ¼ þ0:49 AE 0:02. In each of the metal-poor, neutron-capture-rich program stars, the holmium abundance relative to those of other rare earth elements agrees well with solar system rapid-neutron-capture abundance values.
An experimental and theoretical investigation of the 594.5-nm optogalvanic effect in the Ne posit... more An experimental and theoretical investigation of the 594.5-nm optogalvanic effect in the Ne positive column is described. The effect is a decrease in discharge conductance due to laser-induced depletion of metastable atoms. Absolute measurements of the effect per unit of absorbed laser power are reported for a wide range of discharge conditions. Postive-column discharges with radiuspressure products of 0.1-1.0 cm Torr and with sustaining direct currents of 1-16 mA are studied. The effect is modeled in this regime by applying perturbation theory to key rate equations that describe the discharge. The model predictions are in agreement with the experimental measurements. Absolute densities of atoms excited to the 2p 3s levels are also reported. The regime studied covers the transition from a discharge sustained primarily by single-step electron-impact ionization to a discharge sustained primarily by two-step ionization via the 2p 3s metastable levels. The global power balance of the discharge is dominated by wall losses of atoms excited to the 2p'3s levels at all pressures and currents studied.
We describe radiative-decay-induced four-level crossover signals in Doppler-broadening-free satur... more We describe radiative-decay-induced four-level crossover signals in Doppler-broadening-free saturation spectroscopy. A four-level crossover signal occurs when atoms in a segment of the velocity distribution absorb light from the saturating beam, radiatively decay in part to a different lower level, and cause enhanced absorption from the probe beam on a transition that shares neither a common upper nor a common lower level with the transition of the first. absorption. We interpret a signal in a saturation spectrum published by Hansch, Shahin, and Schawlow as a four-level crossover signal induced by radiative decay.
We report a total collisional quenching rate of (6.4+0.3) p 10 " cm' sec ' at 292'K (or a thermal... more We report a total collisional quenching rate of (6.4+0.3) p 10 " cm' sec ' at 292'K (or a thermally 'averaged cross section of 0.36 &(10 ' cm) for He 3 S atoms colliding with ground-state He atoms. This rate is determined by using a pulsed dye laser to populate the 3'S level in a He aftergow and then observing the decay of the 3'S~2'P fluorescence. We see no evidence for three-body collisional quenching of 3'S atoms at pressures up to 300 Torr.
Journal of Physics B: Atomic, Molecular and Optical Physics
version of an article including any changes made following the peer review process but excluding ... more version of an article including any changes made following the peer review process but excluding any editing, typesetting or other changes made by IOP Publishing and/or its licensors. During the embargo period (the 12 month period from publication of the Version of Record of this article), the Accepted Manuscript: *Please see CC BY-NC-ND 3.0 licence for full terms.
New experimental absolute atomic transition probabilities are reported for 203 lines of V ii. Bra... more New experimental absolute atomic transition probabilities are reported for 203 lines of V ii. Branching fractions are measured from spectra recorded using a Fourier transform spectrometer and an echelle spectrometer. The branching fractions are normalized with radiative lifetime measurements to determine the new transition probabilities. Generally good agreement is found between this work and previously reported V ii transition probabilities. Two spectrometers, independent radiometric calibration methods, and independent data analysis routines enable a reduction in systematic uncertainties, in particular those due to optical depth errors. In addition, new hyperfine structure constants are measured for selected levels by least squares fitting line profiles in the FTS spectra. The new V ii data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to determine new, more accurate V abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. Very good agreement is found between our new solar photospheric V abundance, log ε(V) = 3.95 from 15 V ii lines, and the solar-system meteoritic value. In HD 84937, we derive [V/H] = −2.08 from 68 lines, leading to a value of [V/Fe] = 0.24.
New emission branching fraction measurements for 836 lines of the first spectrum of vanadium (V i... more New emission branching fraction measurements for 836 lines of the first spectrum of vanadium (V i) are determined from hollow cathode lamp spectra recorded with the National Solar Observatory 1 m Fourier transform spectrometer (FTS) and a high-resolution echelle spectrometer. The branching fractions are combined with recently published radiative lifetimes from laser-induced fluorescence measurements to determine accurate absolute atomic transition probabilities for the 836 lines. The FTS data are also used to extract new hyperfine structure A coefficients for 26 levels of neutral vanadium. These new laboratory data are applied to determine the V abundance in the Sun and metal-poor star HD 84937, yielding log ε(V) = 3.956 ± 0.004 (σ = 0.037) based on 93 V i lines and log ε(V) = 1.89 ± 0.03 (σ = 0.07) based on nine V i lines, respectively, using the Holweger-Müller 1D model. These new V i abundance values for the Sun and HD 84937 agree well with our earlier determinations based upon V ii.
High sensitivity absorption spectroscopy involves the use of modem diode and CCD (charge coupled ... more High sensitivity absorption spectroscopy involves the use of modem diode and CCD (charge coupled device) detector arrays to observe fractional absorptions of ultraviolet (UV) and vacuum ultraviolet (VUV) radiation as small as 0.00001. Stable arc lamps provide a continuum in some experiments, but experiments at very high spectral resolution or at VUV wavelengths require the greater spectral radiance of a synchrotron. Absolute densities of excited atoms, atomic ions, and molecular radicals are measured in both processing and lighting plasmas. Basic spectroscopic data needed for the analysis of astrophysical observations from the Hubble Space Telescope are measured using absorption ofFe+ in a hollow cathode discharge.
We have derived new very accurate abundances of the Fe-group elements Sc through Zn (Z = 21−30) i... more We have derived new very accurate abundances of the Fe-group elements Sc through Zn (Z = 21−30) in the bright main-sequence turnoff star HD 84937, based on high-resolution spectra covering the visible and ultraviolet spectral regions. New or recent laboratory transition data for 14 species of seven elements have been used. Abundances from more than 600 lines of non-Fe species have been combined with about 550 Fe lines in HD 84937 to yield abundance ratios of high precision. The abundances have been determined from both neutral and ionized transitions, which generally are in agreement with each other. We find no substantial departures from standard LTE Saha ionization balance in this [Fe/H] = −2.32 star. Noteworthy among the abundances are: [Co/Fe] = +0.14 and [Cu/Fe] = −0.83, in agreement with past studies abundance trends in this and other low metallicity stars; and [Sc,Ti,V/Fe] = +0.31, which has not been noted previously. A detailed examination of scandium, titanium, and vanadium abundances in large-sample spectroscopic surveys reveals that they are positively
Proceedings of 11th Symposium on Nuclei in the Cosmos — PoS(NIC XI)
We report on new abundance determinations for the neutron-capture elements Cd I (Z=48), Lu II (Z ... more We report on new abundance determinations for the neutron-capture elements Cd I (Z=48), Lu II (Z = 71) and Os II (Z = 76) in the r-process enriched star BD + 17 3248. These abundances are derived from an ultraviolet spectrum obtained with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. These are the first detections of these elements in metal-poor r-process enriched halo stars. In addition to the HST observations we have obtained new abundance measurements of the elements Mo I, Ru I and Rh I, based upon High Resolution Echelle Spectrograph observations with Keck. Combining these and previous observations, we have now * Speaker. † Funding for this project has been generously provided by NSF.
Proceedings of 11th Symposium on Nuclei in the Cosmos — PoS(NIC XI)
In this review we summarize the current state of some aspects of observational studies of low met... more In this review we summarize the current state of some aspects of observational studies of low metallicity stars that have been enriched with products of rapid-neutron-capture (r-process) nucleosynthesis events. Attention will be drawn to the element domains where there is little star-tostar variation in relative abundances (such as the rare earths), and those with substantial variations (the lightest neutron-capture elements and the very heavy radioactive elements Th and U). We highlight some new work bearing on our understanding of the limits of abundance distributions that can be produced in the r-process. Finally, comments will be made on the metallicity at which significant contributions from the s-process can be seen in Galactic halo stars.
New branching fraction (BF) measurements based primarily on data from a cross-dispersed echelle s... more New branching fraction (BF) measurements based primarily on data from a cross-dispersed echelle spectrometer are reported for 84 lines of Co II. The BFs 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 z 5 D 0 level is used based on LIF measurements for lifetimes of the four other levels in the z 5 D term. Twelve of the eighty-four 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 the 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-squares fits to Fourier transform spectra line profiles are reported. These laboratory data are applied to re-determine the Co abundance in the metal-poor halo star HD 84937. BFs and transition probabilities for 19 lines are reported for the first time.
We derive a new abundance for vanadium in the bright, mildly metal-poor red giant Arcturus. This ... more 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±0.01 (σ=0.04) from 55 lines. There are no significant abundance trends with wavelength, line strength, or lower excitation energy.
This brief review highlights some current issues in Galactic stellar nucleosynthesis, and some re... more This brief review highlights some current issues in Galactic stellar nucleosynthesis, and some recent laboratory studies by the Wisconsin atomic physics group that have direct application to stellar spectroscopy, in order to advance our understanding of the chemical evolution of our Galaxy. The relevant publication history of the lab studies are summarized, and investigations into the abundances of neutron-capture and iron-peak elements in low metallicity stars are described. Finally, new initatives in near-infrared spectroscopy are briefly explored.
Improved energy levels and hyperfine structure constants for a selected set of Ho ii levels were ... more Improved energy levels and hyperfine structure constants for a selected set of Ho ii levels were measured from spectra recorded using the 1 m Fourier transform spectrometer (FTS) at the US National Solar Observatory. Branching fractions for the strong blue-UV lines from these levels were also measured from the FTS data and combined with earlier radiative lifetimes from time-resolved laser-induced fluorescence measurements to determine accurate absolute transition probabilities for 22 lines of Ho ii. These new laboratory measurements, along with a recently reported partition function for ionized Ho, were used to improve Ho abundance determinations in the Sun and three metal-poor Galactic halo giant stars. The derived solar photospheric holmium abundance, log 10 ðHoÞ ¼ þ0:51 AE 0:10, is consistent with its meteoritic value, log 10 ðHoÞ ¼ þ0:49 AE 0:02. In each of the metal-poor, neutron-capture-rich program stars, the holmium abundance relative to those of other rare earth elements agrees well with solar system rapid-neutron-capture abundance values.
An experimental and theoretical investigation of the 594.5-nm optogalvanic effect in the Ne posit... more An experimental and theoretical investigation of the 594.5-nm optogalvanic effect in the Ne positive column is described. The effect is a decrease in discharge conductance due to laser-induced depletion of metastable atoms. Absolute measurements of the effect per unit of absorbed laser power are reported for a wide range of discharge conditions. Postive-column discharges with radiuspressure products of 0.1-1.0 cm Torr and with sustaining direct currents of 1-16 mA are studied. The effect is modeled in this regime by applying perturbation theory to key rate equations that describe the discharge. The model predictions are in agreement with the experimental measurements. Absolute densities of atoms excited to the 2p 3s levels are also reported. The regime studied covers the transition from a discharge sustained primarily by single-step electron-impact ionization to a discharge sustained primarily by two-step ionization via the 2p 3s metastable levels. The global power balance of the discharge is dominated by wall losses of atoms excited to the 2p'3s levels at all pressures and currents studied.
We describe radiative-decay-induced four-level crossover signals in Doppler-broadening-free satur... more We describe radiative-decay-induced four-level crossover signals in Doppler-broadening-free saturation spectroscopy. A four-level crossover signal occurs when atoms in a segment of the velocity distribution absorb light from the saturating beam, radiatively decay in part to a different lower level, and cause enhanced absorption from the probe beam on a transition that shares neither a common upper nor a common lower level with the transition of the first. absorption. We interpret a signal in a saturation spectrum published by Hansch, Shahin, and Schawlow as a four-level crossover signal induced by radiative decay.
We report a total collisional quenching rate of (6.4+0.3) p 10 " cm' sec ' at 292'K (or a thermal... more We report a total collisional quenching rate of (6.4+0.3) p 10 " cm' sec ' at 292'K (or a thermally 'averaged cross section of 0.36 &(10 ' cm) for He 3 S atoms colliding with ground-state He atoms. This rate is determined by using a pulsed dye laser to populate the 3'S level in a He aftergow and then observing the decay of the 3'S~2'P fluorescence. We see no evidence for three-body collisional quenching of 3'S atoms at pressures up to 300 Torr.
Journal of Physics B: Atomic, Molecular and Optical Physics
version of an article including any changes made following the peer review process but excluding ... more version of an article including any changes made following the peer review process but excluding any editing, typesetting or other changes made by IOP Publishing and/or its licensors. During the embargo period (the 12 month period from publication of the Version of Record of this article), the Accepted Manuscript: *Please see CC BY-NC-ND 3.0 licence for full terms.
New experimental absolute atomic transition probabilities are reported for 203 lines of V ii. Bra... more New experimental absolute atomic transition probabilities are reported for 203 lines of V ii. Branching fractions are measured from spectra recorded using a Fourier transform spectrometer and an echelle spectrometer. The branching fractions are normalized with radiative lifetime measurements to determine the new transition probabilities. Generally good agreement is found between this work and previously reported V ii transition probabilities. Two spectrometers, independent radiometric calibration methods, and independent data analysis routines enable a reduction in systematic uncertainties, in particular those due to optical depth errors. In addition, new hyperfine structure constants are measured for selected levels by least squares fitting line profiles in the FTS spectra. The new V ii data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to determine new, more accurate V abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. Very good agreement is found between our new solar photospheric V abundance, log ε(V) = 3.95 from 15 V ii lines, and the solar-system meteoritic value. In HD 84937, we derive [V/H] = −2.08 from 68 lines, leading to a value of [V/Fe] = 0.24.
New emission branching fraction measurements for 836 lines of the first spectrum of vanadium (V i... more New emission branching fraction measurements for 836 lines of the first spectrum of vanadium (V i) are determined from hollow cathode lamp spectra recorded with the National Solar Observatory 1 m Fourier transform spectrometer (FTS) and a high-resolution echelle spectrometer. The branching fractions are combined with recently published radiative lifetimes from laser-induced fluorescence measurements to determine accurate absolute atomic transition probabilities for the 836 lines. The FTS data are also used to extract new hyperfine structure A coefficients for 26 levels of neutral vanadium. These new laboratory data are applied to determine the V abundance in the Sun and metal-poor star HD 84937, yielding log ε(V) = 3.956 ± 0.004 (σ = 0.037) based on 93 V i lines and log ε(V) = 1.89 ± 0.03 (σ = 0.07) based on nine V i lines, respectively, using the Holweger-Müller 1D model. These new V i abundance values for the Sun and HD 84937 agree well with our earlier determinations based upon V ii.
High sensitivity absorption spectroscopy involves the use of modem diode and CCD (charge coupled ... more High sensitivity absorption spectroscopy involves the use of modem diode and CCD (charge coupled device) detector arrays to observe fractional absorptions of ultraviolet (UV) and vacuum ultraviolet (VUV) radiation as small as 0.00001. Stable arc lamps provide a continuum in some experiments, but experiments at very high spectral resolution or at VUV wavelengths require the greater spectral radiance of a synchrotron. Absolute densities of excited atoms, atomic ions, and molecular radicals are measured in both processing and lighting plasmas. Basic spectroscopic data needed for the analysis of astrophysical observations from the Hubble Space Telescope are measured using absorption ofFe+ in a hollow cathode discharge.
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