VLT/UVES shows no cosmological variability of alpha

The cosmological variability of alpha is probed from individual observations of pairs of FeII lines. This procedure allows a better control of the systematics and avoids the influence of the spectral shifts due to ionization inhomogeneities in the absorbers and/or non-zero offsets between different exposures. Applied to the FeII lines of the metal absorption systems at zabs = 1.839 in Q1101--264 and at zabs = 1.15 in HE0515--4414 observed by means of UVES at the ESO-VLT, it provides da/a = 0.4 (+/- 1.5 stat)x10^{-6}. The result is shifted with respect to the Keck/HIRES mean da/a = -5.7(+/- 1.1 stat})x10^{-6} (Murphy et al. 2004) at a high confidence level (95%). Full details of this work are given in Levshakov et al (2005)Comment: 3 pages, 1 postscript figur

UVES radial velocity accuracy from asteroid observations. Implications for the fine structure constant variability

High resolution observations of the asteroids Iris and Juno have been performed by means of the UVES spectrograph at the ESO VLT to obtain the effective accurac y of the spectrograph's radial velocity. The knowledge of this quantity has impo rtant bearings on studies searching for a variability of the fine structure cons tant carried on with this instrument. Asteroids provide a precise radial velocit y reference at the level of 1 m/s which allows instrumental calibration and the recognition of small instrumental drifts and calibration systematics. In particu lar, radial velocity drifts due to non uniform slit illumination and slit optica l misalignment in the two UVES spectrograph arms can be investigated. The positi on of the solar spectrum reflected by the asteroids are compared with the solar wavelength positions or with that of asteroid observations at other epochs or wi th the twilight to asses UVES instrumental accuracy . Radial velocities offsets in the range 10--50 m/s are generally observed likely due to a non uniform slit illumination. However, no radial velocity patterns with wavelength are detected and the two UVES arms provide consistent radial velocities. These results suggest that the detected alpha variability by Levshakov et al. (2007) deduced from a drift of -180 (+/- 85) m/s at z =1.84, between two sets of FeII lines falling in the two UVES arms may be real or induced by other kinds of systematics than those investigated here. The proposed technique allows real time quality check of the spectrograph and should be followed for very accurate measurements.Comment: Accepted A&

Implementation and modeling of a femtosecond laser-activated streak camera

8 June 2017) A laser-activated streak camera was built to measure the duration of femtosecond electron pulses. The streak velocity of the device is 1.89 mrad/ps, which corresponds to a sensitivity of 34.9 fs/pixels. The streak camera also measures changes in the relative time of arrival between the laser and electron pulses with a resolution of 70 fs RMS. A full circuit analysis of the structure is presented to describe the streaking field and the general behavior of the device. We have developed a general mathematical model to analyze the streaked images. The model provides an accurate method to extract the pulse duration based on the changes of the electron beam profile when the streaking field is applied

The UVES Large Program for testing fundamental physics - III. Constraints on the fine-structure constant from 3 telescopes

Large statistical samples of quasar spectra have previously indicated possible cosmological variations in the fine-structure constant, $\alpha$. A smaller sample of higher signal-to-noise ratio spectra, with dedicated calibration, would allow a detailed test of this evidence. Towards that end, we observed equatorial quasar HS 1549$+$1919 with three telescopes: the Very Large Telescope, Keck and, for the first time in such analyses, Subaru. By directly comparing these spectra to each other, and by `supercalibrating' them using asteroid and iodine-cell tests, we detected and removed long-range distortions of the quasar spectra's wavelength scales which would have caused significant systematic errors in our $\alpha$ measurements. For each telescope we measure the relative deviation in $\alpha$ from the current laboratory value, $\Delta\alpha/\alpha$, in 3 absorption systems at redshifts $z_{\mathrm{abs}}=1.143$, 1.342, and 1.802. The nine measurements of $\Delta\alpha/\alpha$ are all consistent with zero at the 2-$\sigma$ level, with 1-$\sigma$ statistical (systematic) uncertainties 5.6--24 (1.8--7.0) parts per million (ppm). They are also consistent with each other at the 1-$\sigma$ level, allowing us to form a combined value for each telescope and, finally, a single value for this line of sight: $\Delta\alpha/\alpha=-5.4 \pm 3.3_{\mathrm{stat}} \pm 1.5_{\mathrm{sys}}$ ppm, consistent with both zero and previous, large samples. We also average all Large Programme results measuring $\Delta\alpha/\alpha=-0.6 \pm 1.9_{\mathrm{stat}} \pm 0.9_{\mathrm{sys}}$ ppm. Our results demonstrate the robustness and reliability at the 3 ppm level afforded by supercalibration techniques and direct comparison of spectra from different telescopes.Comment: 24 pages, 11 figures, 9 table

Further Evidence for Chemical Fractionation from Ultraviolet Observations of Carbon Monoxide

Ultraviolet absorption from interstellar 12CO and 13CO was detected toward rho Oph A and chi Oph. The measurements were obtained at medium resolution with the Goddard High Resolution Spectrograph on the Hubble Space Telescope. Column density ratios, N(12CO)/N(13CO), of 125 \pm 23 and 117 \pm 35 were derived for the sight lines toward rho Oph A and chi Oph, respectively. A value of 1100 \pm 600 for the ratio N(12C16O)/N(12C18O) toward rho Oph A was also obtained. Absorption from vibrationally excited H_2 (v" = 3) was clearly seen toward this star as well. The ratios are larger than the isotopic ratios for carbon and oxygen appropriate for ambient interstellar material. Since for both carbon and oxygen the more abundant isotopomer is enhanced, selective isotopic photodissociation plays the key role in the fractionation process for these directions. The enhancement arises because the more abundant isotopomer has lines that are more optically thick, resulting in more self shielding from dissociating radiation. A simple argument involving the amount of self shielding [from N(12CO)] and the strength of the ultraviolet radiation field premeating the gas (from the amount of vibrationally excited H_2) shows that selective isotopic photodissociation controls the fractionation seen in these two sight lines, as well as the sight line to zeta Oph.Comment: 40 pages, 8 figures, to appear in 10 July 2003 issue of Ap