QSO 0347-383 and the invariance of m_p/m_e in the course of cosmic time
  The variation of the dimensionless fundamental physical constant mu = m_p/m_e
(the proton to electron mass ratio) can be constrained via observation of Lyman
and Werner lines of molecular hydrogen in the spectra of damped Lyman alpha
systems (DLAs) in the line of sight to distant QSOs. Drawing on VLT-UVES high
resolution data sets of QSO 0347-383 and its DLA obtained in 2009 our analysis
yields dmu/mu = (4.3 +/- 7.2) * 10^-6 at z_abs =3.025. We apply corrections for
the observed offsets between discrete spectra and for the first time we find
indications for inter-order distortions. Current analyses tend to underestimate
the impact of systematic errors. Based on the scatter of the measured redshifts
and the corresponding low significance of the redshift-sensitivity correlation
we estimate the limit of accuracy of line position measurements to about 220
m/s, consisting of roughly 150 m/s due to the uncertainty of the absorption
line fit and about 150 m/s allocated to systematics related to instrumentation
and calibration.
