The FERRUM project: improved experimental oscillator strengths in Cr II

Nilsson, Hampus; Ljung, Gunilla; Lundberg, Hans; Nielsen, K. E.

doi:10.1051/0004-6361:20054152

Cited by 76 publications

(87 citation statements)

References 15 publications

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“…Oscillator strengths from Nilsson et al (2006) or VALD (Kupka et al 1999)/Kurucz (1994 taking only LSpermitted lines. Results were essentially the same.…”

Section: T Eff -Log (G) Degeneracy; Curves Of Growthmentioning

confidence: 99%

Abundances in the Herbig Ae star HD 101412

Cowley

Hubrig

González

et al. 2010

A&A

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Context. Recent attention has been directed to abundance variations among very young stars. Aims. We perform a detailed abundance study of the Herbig Ae star HD 101412, taking advantage of its unusually sharp spectral lines. Methods. High-resolution spectra are measured for accurate wavelengths and equivalent widths. Balmer-line fits and ionization equlibria give a relation between T eff , and log(g). Abundance anomalies and uncertain reddening preclude the use of spectral type or photometry to fix T eff . Excitation temperatures are used to break the degeneracy between T eff and log(g). Results. Strong lines are subject to an anomalous saturation that cannot be removed by assuming a low microturbulence. By restricting the analysis to weak (≤20 mÅ) lines, we find consistent results for neutral and ionized species, based on a model with T eff = 8300 K, and log(g) = 3.8. The photosphere is depleted in the most refractory elements, while volatiles are normal or, in the case of nitrogen, overabundant with respect to the sun. The anomalies are unlike those of Ap or Am stars. Conclusions. We suggest the anomalous saturation of strong lines arises from heating of the upper atmospheric layers by infalling material from a disk. The overall abundance pattern may be related to those found for the λ Boo stars, though the depletions of the refractory elements are milder, more like those of Vega. However, the intermediate volatile zinc is depleted, precluding a straightforward interpretation of the abundance pattern in terms of gas-grain separation.

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“…Oscillator strengths from Nilsson et al (2006) or VALD (Kupka et al 1999)/Kurucz (1994 taking only LSpermitted lines. Results were essentially the same.…”

Section: T Eff -Log (G) Degeneracy; Curves Of Growthmentioning

confidence: 99%

Abundances in the Herbig Ae star HD 101412

Cowley

Hubrig

González

et al. 2010

A&A

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“…Cr ii BFs from the data of Nilsson et al (2006). The calibration was performed with a software routine implemented in the program XGremlin (Nave et al 1997).…”

Section: Branching Fractionsmentioning

confidence: 99%

“…In addition, branching fraction (BF) measurements were combined with radiative lifetimes to yield transition probabilities (Bergeson & Lawler 1993;Spreger et al 1994;Gonzalez et al 1994;Nilsson et al 2006), and oscillator strengths were measured by Musielok & Wujec (1979), Goly & Weniger (1980) and Wujec & Weniger (1981) using a wall-stabilized arc. Semi-empirical oscillator strengths have been calculated by Kurucz (1988) using the Cowan code, by Luke (1988) using the R matrix method, and by Raasen & Uylings (1997) using the orthogonal operator method.…”

Section: Introductionmentioning

confidence: 99%

The FERRUM project: laboratory-measured transition probabilities for $\ion{Cr}{\fontsize{9pt}{11pt}\selectfont{II}}$

Gurell¹,

Nilsson

Engström

et al. 2010

A&A

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Aims. We measure transition probabilities for Cr ii transitions from the z 4 H J , z 2 D J , y 4 F J , and y 4 G J 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.

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“…Measurements using the beam-foil technique have been reported by Pinnington et al (1973) and Engman et al (1975). The TR-LIF method has also been used in a number of previous studies (Schade et al 1990;Bergeson & Lawler 1993;Pinnington et al 1993;Nilsson et al 2006;and Gurell et al 2010), where the Cr + ions were produced in a fast ion beam, in a hollow cathode, and in laser-produced plasmas. By combining the measured lifetimes with branching fractions (BFs), usually obtained from intensity calibrated Fourier transform spectra, transition probabilities have been derived.…”

Section: Introductionmentioning

confidence: 99%

“…By combining the measured lifetimes with branching fractions (BFs), usually obtained from intensity calibrated Fourier transform spectra, transition probabilities have been derived. For example, the most recent studies by Nilsson et al (2006) and Gurell et al (2010) report 119 and 145 transition probabilities, respectively, for lines from the 3d 4 4p configuration. See Gurell et al (2010) for additional references to investigations of the 4p states.…”

Section: Introductionmentioning

confidence: 99%

The FERRUM project: Experimental transition probabilities from highly excited even 5s levels in Cr ii

Engström

Lundberg

Nilsson

et al. 2014

A&A

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We report lifetime measurements of the five levels in the 3d 4 (a 5 D)5s e 6 D term in Cr  at an energy around 83 000 cm −1 , and log(g f ) values for 38 transitions from the investigated levels. The lifetimes are obtained using time-resolved, laser-induced fluorescence on ions from a laser-produced plasma. Since the levels have the same parity as the low-lying states directly populated in the plasma, we used a two-photon excitation scheme. This process is greatly facilitated by the presence of the 3d 4 (a 5 D)4p z 6 F levels at roughly half the energy difference. The f -values are obtained by combining the experimental lifetimes with branching fractions derived using relative intensities from a hollow cathode lamp recorded with a Fourier transform spectrometer.

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The FERRUM project: improved experimental oscillator strengths in Cr II

Cited by 76 publications

References 15 publications

Abundances in the Herbig Ae star HD 101412

Abundances in the Herbig Ae star HD 101412

The FERRUM project: laboratory-measured transition probabilities for $\ion{Cr}{\fontsize{9pt}{11pt}\selectfont{II}}$

The FERRUM project: Experimental transition probabilities from highly excited even 5s levels in Cr ii

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