The Refractive Index of Air

Edlén, Bengt

doi:10.1088/0026-1394/2/2/002

Cited by 1,116 publications

(501 citation statements)

References 13 publications

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“…Of course, if such a spurious velocity shift were equally imparted to all transitions in a given spectrum, this would not result in a spurious shift in ∆α/α, because only velocity shifts between transitions should affect a measured value of ∆α/α. According to the Edlén (1966) formula for the refractive index of air, pressure, and temperature changes of 0.1 K and 1 mbar would cause differential velocity shifts of < ∼ 15 m s −1 across the wavelength range of the spectrum studied here, implying a negligible effect on ∆α/α.…”

Section: Wavelength Calibrationmentioning

confidence: 84%

“…While the CPL code redisperses the spectra on to a linear wavelength scale by default, we used only the original, un-redispersed flux and error array for each Echelle order in subsequent reduction steps. After wavelength calibration, the air wavelength scale of each quasar exposure was corrected from air to vacuum using the Edlén (1966) formula, and placed in the solar system's barycentric reference frame using the date and time of the mid-point of the exposure's integration.…”

Section: Data Reductionmentioning

confidence: 99%

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The UVES Large Program for testing fundamental physics I. Bounds on a change inαtowards quasar HE 2217−2818

Molaro

Centurión

Whitmore

et al. 2013

A&A

118

178

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Context. Absorption-line systems detected in quasar spectra can be used to compare the value of the fine-structure constant, α, measured today on Earth with its value in distant galaxies. In recent years, some evidence has emerged of small temporal and also spatial variations in α on cosmological scales. These variations may reach a fractional level of ≈10 ppm (parts per million). Aims. To test these claims we are conducting a Large Program of observations with the Very Large Telescope's Ultraviolet and Visual Echelle Spectrograph (UVES), and are obtaining high-resolution (R ≈ 60 000) and high signal-to-noise ratio (S /N ≈ 100) UVES spectra calibrated specifically for this purpose. Here we analyse the first complete quasar spectrum from this programme, that of HE 2217−2818. Methods. We applied the many multiplet method to measure α in five absorption systems towards this quasar: z abs = 0.7866, 0.9424, 1.5558, 1.6279 , and 1.6919. Results. The most precise result is obtained for the absorber at z abs = 1.6919 where 3 Fe  transitions and Al  λ1670 have high S/N and provide a wide range of sensitivities to α. The absorption profile is complex with several very narrow features, and it requires 32 velocity components to be fitted to the data. We also conducted a range of tests to estimate the systematic error budget. Our final result for the relative variation in α in this system is ∆α/α = +1.3 ± 2.4 stat ± 1.0 sys ppm. This is one of the tightest current bounds on α-variation from an individual absorber. A second, separate approach to the data reduction, calibration, and analysis of this system yielded a slightly different result of −3.8 ± 2.1 stat ppm, possibly suggesting a larger systematic error component than our tests indicated. This approach used an additional 3 Fe  transitions, parts of which were masked due to contamination by telluric features. Restricting this analysis to the Fe  transitions alone and using a modified absorption profile model gave a result that is consistent with the first approach, ∆α/α = +1.1 ± 2.6 stat ppm. The four other absorbers have simpler absorption profiles, with fewer and broader features, and offer transitions with a narrower range of sensitivities to α. They therefore provide looser bounds on ∆α/α at the > ∼ 10 ppm precision level. Conclusions. The absorbers towards quasar HE 2217−2818 reveal no evidence of any variation in α at the 3-ppm precision level (1σ confidence). If the recently reported 10-ppm dipolar variation in α across the sky is correct, the expectation at this sky position is (3.2−5.4) ± 1.7 ppm depending on dipole model used. Our constraint of ∆α/α = +1.3 ± 2.4 stat ± 1.0 sys ppm is not inconsistent with this expectation.

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Section: Wavelength Calibrationmentioning

confidence: 84%

Section: Data Reductionmentioning

confidence: 99%

The UVES Large Program for testing fundamental physics I. Bounds on a change inαtowards quasar HE 2217−2818

Molaro

Centurión

Whitmore

et al. 2013

A&A

118

178

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“…We applied the CPL wavelength solutions to each order and merged the orders by implementing a weighted mean in the overlapping regions. All the exposures were shifted to the heliocentricvacuum frame correcting for the motion of the observatory along the quasar line of sight obtained at the exposure mid-point and using the air-to-vacuum relation from Edlén (1966). Then we combined all exposures using a weighted mean at each pixel.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

CO-dark molecular gas at high redshift: very large H2 content and high pressure in a low-metallicity damped Lyman alpha system

Balashev

Noterdaeme

Rahmani

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present a detailed analysis of an H 2 -rich, extremely strong intervening damped Ly-α absorption system (DLA) at z abs = 2.786 towards the quasar J 0843+0221, observed with the Ultraviolet and Visual Echelle Spectrograph on the Very Large Telescope. The total column density of molecular (resp. atomic) hydrogen is log N(H 2 )=21.21 ± 0.02 (resp. log N(H i)=21.82 ± 0.11), making it to be the first case in quasar absorption line studies with H 2 column density as high as what is seen in 13 CO-selected clouds in the Milky-Way.We find that this system has one of the lowest metallicity detected among H 2 -bearing DLAs, with [Zn/H] = −1.52 +0.08 −0.10 . This can be the reason for the marked differences compared to systems with similar H 2 column densities in the local Universe: (i) the kinetic temperature, T ∼120 K, derived from the J = 0, 1 H 2 rotational levels is at least twice higher than expected; (ii) there is little dust extinction with A V < 0.1; (iii) no CO molecules are detected, putting a constraint on the X CO factor X CO > 2 × 10 23 cm −2 /(km/s K), in the very low metallicity gas. Low CO and high H 2 contents indicate that this system represents "CO-dark/faint" gas.We investigate the physical conditions in the H 2 -bearing gas using the fine-structure levels of C i, C ii, Si ii and the rotational levels of HD and H 2 . We find the number density to be about n ∼ 260 − 380 cm −3 , implying a high thermal pressure of 3 − 5 × 10 4 cm −3 K. We further identify a trend of increasing pressure with increasing total hydrogen column density. This independently supports the suggestion that extremely strong DLAs (with log N(H) ∼ 22) probe high-z galaxies at low impact parameters.

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“…The component of the observatory's barycentric velocity in the direction to the object was calculated using the date and time of the integration midpoint. The air wavelengths were transformed to vacuum by means of the dispersion formula by Edlén (1966). We note that the barycentric and vacuum corrections require a rebinning, which introduces a certain degree of correlations between the fluxes in the adjacent pixels.…”

Section: Observationsmentioning

confidence: 99%

First measurement of Mg isotope abundances at high redshifts and accurate estimate of Δα/α

Agafonova

Molaro

Levshakov

et al. 2011

A&A

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Aims. Abundances of the Mg isotopes 24 Mg, 25 Mg, and 26 Mg can be used to test models of chemical enrichment of interstellar/intergalactic gas clouds. Additionally, because the position of the Mg ii λλ2796, 2803 Å lines is often taken as a reference in computations of possible changes of the fine-structure constant α, it should be clarified to which extent these lines are affected by isotopic shifts. Methods. We use a high-resolution spectrum (pixel size ≈1.3 km s −1 ) of the quasar HE0001-2340 observed with the UVES/VLT to measure Mg isotope abundances in the intervening absorption-line systems at high redshifts. Line profiles are prepared taking into account possible shifts between the individual exposures. In the line-fitting procedure, the lines of each ion are treated independently. Because of the unique composition of the selected systems -the presence of several transitions of the same ion -we can test the local accuracy of the wavelength scale calibration, which is the main source of errors in the sub-pixel line position measurements. Results. In the system at z abs = 0.45, which is probably a fragment of the outflow caused by SN Ia explosion of highmetallicity white dwarf(s), we measured velocity shifts of Mg ii and In the systems at z abs = 1.58 and z abs = 1.65 enriched by AGB-stars we find only upper limits on the content of heavy Mg isotopes ( 25 Mg+ 26 Mg)/ 24 Mg < ∼ 0.7 and ( 25 Mg+ 26 Mg)/ 24 Mg < ∼ 2.6, respectively. At z abs = 1.58, we also put a strong constraint on a putative variation of α: Δα/α = (−1.5 ± 2.6) × 10 −6 , which is one of the most stringent limits obtained from optical spectra of QSOs. We reveal that the wavelength calibration in the range above 7500 Å is subject to systematic wavelength-dependent drifts.

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The Refractive Index of Air

Cited by 1,116 publications

References 13 publications

The UVES Large Program for testing fundamental physics I. Bounds on a change inαtowards quasar HE 2217−2818

The UVES Large Program for testing fundamental physics I. Bounds on a change inαtowards quasar HE 2217−2818

CO-dark molecular gas at high redshift: very large H2 content and high pressure in a low-metallicity damped Lyman alpha system

First measurement of Mg isotope abundances at high redshifts and accurate estimate of Δα/α

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