Most precise single redshift bound to $\mathsf{\Delta\alpha/\alpha}$

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.

Section: Discussionmentioning

confidence: 99%

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

Agafonova

Molaro

et al. 2011

A&A

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“…For atomic spectra, the estimate of Δα/α is given in linear approximation (|Δα/α| 1) by (e.g., Levshakov et al 2006):…”

Section: Introductionmentioning

confidence: 99%

Searching for spatial variations ofα²/μin the Milky Way

Molaro²,

Reimers

2010

A&A

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Aims. We probe the dependence of α 2 /μ on the ambient matter density by means of spectral observations in submm-and mm-wave bands. Methods. A procedure is suggested for exploring the value of F = α 2 /μ, where μ = m e /m p is the electron-to-proton mass ratio, and α = e 2 /( c) is the fine-structure constant. The fundamental physical constants, which are measured in different physical environments of high (terrestrial) and low (interstellar) densities of baryonic matter are supposed to vary in chameleon-like scalar field models, which predict that both masses and coupling constant may depend on the local matter density. The parameter ΔF/F = (F obs − F lab )/F lab can be estimated from the radial velocity offset, ΔV = V rot − V fs , between the low-laying rotational transitions in carbon monoxide 13 CO and the fine-structure transitions in atomic carbon [C i]. A model-dependent constraint on Δα/α can be obtained from ΔF/F using Δμ/μ independently measured from the ammonia method. Results. Currently available radio astronomical datasets provide an upper limit on |ΔV| < 110 m s −1 (1σ). When interpreted in terms of the spatial variation of F, this gives |ΔF/F| < 3.7 × 10 −7 . An order of magnitude improvement in this limit will allow us to independently test a non-zero value of Δμ/μ = (2.2 ± 0.4 stat ± 0.3 sys ) × 10 −8 , recently found with the ammonia method. Considering that the ammonia method restricts the spatial variation of μ at the level of |Δμ/μ| ≤ 3 × 10 −8 and assuming that ΔF/F is the same in the entire interstellar medium, one obtains that the spatial variation of α does not exceed the value |Δα/α| < 2 × 10 −7 . Since extragalactic gas clouds have similar densities to those in the interstellar medium, the bound on Δα/α is also expected to be less than 2 × 10 −7 at high redshift if no significant temporal dependence of α is present.

“…The comparison of ∆α/α = −0.07 ± 0.84 ppm at z 1 = 1.15 towards HE 0515-4414 [5] with the measured quantity ∆α/α = 5.36 ± 2.38 ppm at z 2 = 1.84 shows a tentative change of the value of ∆α/α between these two redshifts: (α z2 − α z1 )/α 0 = 5.43 ± 2.52 ppm.…”

Section: Resultsmentioning

confidence: 68%

“…In order to fulfill this requirement we developed a method called 'Single Ion Differential α Measurement, SIDAM' [2,3,4,5]. Based on the measurements of the relative line position of only one element Fe ii, it is free from many systematics which affect other methods, e.g., [6,7].…”

Section: Introductionmentioning

confidence: 99%

High-Precision Measurements of Δα/αfrom QSO Absorption Spectra

Precision Spectroscopy in Astrophysics

Molaro

López

et al.

Summary. Precise radial velocity measurements (δv/c ∼ 10 −7 ) of Fe ii lines in damped Lyα systems from very high quality VLT/UVES spectra of quasars HE 0515-4414 and Q 1101-264 are used to probe cosmological time dependence of the fine structure constant, α. It is found that between two redshifts z1 = 1.15 and z2 = 1.84 the value of ∆α/α changes at the level of a few ppm: (αz 2 − αz 1 )/α0 = 5.43 ± 2.52 ppm. Variations of α can be considered as one of the most reliable method to constrain the dark energy equation of state and improvements on the accuracy of the wavelength calibration of QSO spectra are of great importance.