THE SPECTRUM OF THORIUM FROM 250 nm TO 5500 nm: RITZ WAVELENGTHS AND OPTIMIZED ENERGY LEVELS

Redman, Stephen L.; Nave, Gillian; Sansonetti, Craig J.

doi:10.1088/0067-0049/211/1/4

Cited by 53 publications

(49 citation statements)

References 35 publications

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“…(∼10 m/s) (Redman et al 2014). On the other hand, the positions of weak lines on the detector exhibit typical measurement errors of 0.1 pixels or about 100 m/s.…”

Section: Mapping Wavelengths To Detector Coordinatesmentioning

confidence: 98%

“…When the thorium relaxes into a lower energy state, a photon carries away the energy difference and contributes to an emission line. The laboratory wavelengths of thorium lines can be measured or calculated, as done by Palmer & Engleman (1983), Lovis & Pepe (2007), Kerber et al (2008), and Redman et al (2014). The drawback of HCLs is the limited number of reference lines, the wide dynamic range spanned by the lines, and the irregular line distribution.…”

Section: Introductionmentioning

confidence: 99%

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Calibrating echelle spectrographs with Fabry-Pérot etalons

Bauer

Zechmeister

Reiners

2015

A&A

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Context. Over the past decades hollow-cathode lamps have been calibration standards for spectroscopic measurements. Advancing to cm/s radial velocity precisions with the next generation of instruments requires more suitable calibration sources with more lines and fewer dynamic range problems. Fabry-Pérot interferometers provide a regular and dense grid of lines and homogeneous amplitudes, which makes them good candidates for next-generation calibrators. Aims. We investigate the usefulness of Fabry-Pérot etalons in wavelength calibration, present an algorithm to incorporate the etalon spectrum in the wavelength solution, and examine potential problems. Methods. The quasi-periodic pattern of Fabry-Pérot lines was used along with a hollow-cathode lamp to anchor the numerous spectral features on an absolute scale. We tested our method with the HARPS spectrograph and compared our wavelength solution to the one derived from a laser frequency comb. Results. The combined hollow-cathode lamp/etalon calibration overcomes large distortion (50 m/s) in the wavelength solution of the HARPS data reduction software. The direct comparison to the laser frequency comb shows differences of only 10 m/s at most. Conclusions. Combining hollow-cathode lamps with Fabry-Pérot interferometers can lead to substantial improvements in the wavelength calibration of echelle spectrographs. Etalons can provide economical alternatives to the laser frequency comb, especially for smaller projects.

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“…(∼10 m/s) (Redman et al 2014). On the other hand, the positions of weak lines on the detector exhibit typical measurement errors of 0.1 pixels or about 100 m/s.…”

Section: Mapping Wavelengths To Detector Coordinatesmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Calibrating echelle spectrographs with Fabry-Pérot etalons

Bauer

Zechmeister

Reiners

2015

A&A

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“…Interestingly, for high precision redshift applications such as needed for tests of fine structure constant variation, knowledge of rest frame wavelengths has been a limiting factor -both the wavelengths of the calibration lamps (Lovis & Pepe 2007;Redman et al 2014), and the wavelengths of the spectral lines in the quasars being studied (Murphy & Berengut 2014).…”

Section: Rest Frame Wavelength Precisionmentioning

confidence: 99%

Can redshift errors bias measurements of the Hubble Constant?

Davis

Hinton

Howlett

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Redshifts have been so easy to measure for so long that we tend to neglect the fact that they too have uncertainties and are susceptible to systematic error. As we strive to measure cosmological parameters to better than 1% it is worth reviewing the accuracy of our redshift measurements. Surprisingly small systematic redshift errors, as low as 10 −4 , can have a significant impact on the cosmological parameters we infer, such as H 0 . Here we investigate an extensive (but not exhaustive) list of ways in which redshift estimation can go systematically astray. We review common theoretical errors, such as adding redshifts instead of multiplying by (1 + z); using v = cz; and using only cosmological redshift in the estimates of luminosity and angular-diameter distances. We consider potential observational errors, such as rest wavelength precision, air to vacuum conversion, and spectrograph wavelength calibration. Finally, we explore physical effects, such as peculiar velocity corrections, galaxy internal velocities, gravitational redshifts, and overcorrecting within a bulk flow. We conclude that it would be quite easy for small systematic redshift errors to have infiltrated our data and be impacting our cosmological results. While it is unlikely that these errors are large enough to resolve the current H 0 tension, it remains possible, and redshift accuracy may become a limiting factor in near future experiments. With the enormous efforts going into calibrating the vertical axis of our plots (standard candles, rulers, clocks, and sirens) we argue that it is now worth paying a little more attention to the horizontal axis (redshifts).

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“…The Atlas of the Thorium Spectrum obtained by Palmer & Engleman (1983) and more recently the thorium atlas made by Redman et al (2014) provide a complete list of accurate thorium and argon wavelengths that are used for wavelength calibration. The accurate Th wavelengths of the Atlas of the Thorium Spectrum were obtained with the McMath-Pierce 1 m Fourier Transform Spectrometer (FTS) of the National Solar Observatory at Kitt Peak.…”

Section: Introductionmentioning

confidence: 99%

“…The accurate Th wavelengths of the Atlas of the Thorium Spectrum were obtained with the McMath-Pierce 1 m Fourier Transform Spectrometer (FTS) of the National Solar Observatory at Kitt Peak. The more recent Redman et al (2014) combines the lines measured with the 2 m FTS at the National Institute of Standards and Technology (NIST) with several other studies. Redman et al (2014)'s list contains two sets of wavelengths: the Ritz wavelengths computed from globally optimized energy levels, and the measured wavelengths.…”

Section: Introductionmentioning

confidence: 99%

New wavelength calibration for echelle spectrographs using Fabry-Pérot etalons

Cersullo

Coffinet

Chazelas

et al. 2019

A&A

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Context. The study of Earth-mass extrasolar planets via the radial-velocity technique and the measurement of the potential cosmological variability of fundamental constants call for very-high-precision spectroscopy at the level of δλ/λ < 10 −9 . Only an accurate wavelength calibration of the spectrograph can guarantee that the aimed precision is achieved over a multi-exposure and multi-epoch data set. Wavelength accuracy is obtained by providing two fundamental ingredients: 1) an absolute and information-rich wavelength source and 2) the ability of the spectrograph and its data reduction of transferring the reference scale (wavelengths) to a measurement scale (detector pixels) in a repeatable manner. Aims. The goal of this work is to improve the wavelength calibration accuracy of the HARPS spectrograph by combining the absolute spectral reference provided by the emission lines of a thorium-argon hollow-cathode lamp (HCL) with the spectrally rich and precise spectral information of a Fabry-Pérot-based calibration source. Methods. On the basis of calibration frames acquired each night since the Fabry-Pérot etalon was installed on HARPS in 2011, we construct a combined wavelength solution which fits simultaneously the thorium emission lines and the Fabry-Pérot lines. The combined fit is anchored to the absolute thorium wavelengths, which provide the "zero-point" of the spectrograph, while the Fabry-Pérot lines are used to improve the (spectrally) local precision. The obtained wavelength solution is verified for auto-consistency and tested against a solution obtained using the HARPS Laser-Frequency Comb (LFC). Results. The combined thorium+Fabry-Pérot wavelength solution shows significantly better performances compared to the thoriumonly calibration. In both cases, the residuals of the LFC line positions to the fitted wavelength solution follow a Gaussian distribution with an rms value of about 14 m s −1 for the combined solution, and twice as large for the thorium-only solution (29 m s −1 ). Given these positive results, we have applied the new calibrations to scientific frames and tested the radial-velocity residual on three well-known stars: HD 10700, HD 20794 and HD 69830. In all three cases the RV scatter could be reduced compared to the measurements using the previous calibration.Conclusions. The richness of the Fabry-Pérot spectrum helps improving the wavelength calibration using thorium-argon lamps or extending the wavelength domain of LFCs with limited operational range. The presented techniques will therefore be used in the new HARPS and HARPS-N pipeline, and will be exported to the ESPRESSO spectrograph.

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THE SPECTRUM OF THORIUM FROM 250 nm TO 5500 nm: RITZ WAVELENGTHS AND OPTIMIZED ENERGY LEVELS

Cited by 53 publications

References 35 publications

Calibrating echelle spectrographs with Fabry-Pérot etalons

Calibrating echelle spectrographs with Fabry-Pérot etalons

Can redshift errors bias measurements of the Hubble Constant?

New wavelength calibration for echelle spectrographs using Fabry-Pérot etalons

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