Bounds on the fine structure constant variability from Fe ii absorption lines in QSO spectra
Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy
2 Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
3 Ioffe Physico-Technical Institute, St. Petersburg, Russia
Corresponding author: firstname.lastname@example.org
The Single Ion Differential α Measurement (SIDAM) method for measuring Δα/α and its figures of merit are illustrated together with the results produced by means of Fe ii absorption lines of QSO intervening systems. The method provides Δα/α = -0.12 ±1.79 ppm (parts-per-million) at zabs = 1.15 towards HE 0515-4414 and Δα/α = 5.66±2.67 ppm at zabs = 1.84 towards Q 1101-264, which are so far the most accurate measurements for single systems. SIDAM analysis for 3 systems from the Chand et al.  sample provides inconsistent results which we interpret as due to calibration errors of the Chand et al. data at the level ≈10 ppm. In one system evidence for photo-ionization Doppler shift between Mg ii and Fe ii lines is found. This evidence has important bearings on the Many Multiplet method where the signal for Δα/αvariability is carried mainly by systems involving Mg ii absorbers. Some correlations are also found in the Murphy et al.  sample which suggest larger errors than previously reported. Thus, we consider unlikely that both the Chand et al. and Murphy et al. datasets could provide an estimate of Δα/α with an accuracy at the level of 1 ppm. A new spectrograph like the ESPRESSO project will be crucial to make progress in the astronomical determination of Δα/α.
© EDP Sciences, Springer-Verlag, 2008