We report photoelectric UBV data for 268 metal-poor candidates chosen from the northern HK objective-prism/interference-filter survey of Beers and colleagues. Over 40 % of the stars have been observed on more than one night, and most have at least several sets of photometric measurements. Reddening estimates, preliminary spectroscopic measurements of abundance, and type classifications are reported.

Context. The solar spectrum is a primary reference for the study of physical processes in stars and their variation during activity cycles. High resolution spectra of the Sun are easily obtained from spatially selected regions of the solar disk, while those taken over the integrated disk are more problematic. However, a proxy can be obtained by using solar light reflected by small bodies of the solar system. Aims. In November 2010 an experiment with a prototype of a laser frequency comb (LFC) calibration system was performed with the HARPS spectrograph of the 3.6m ESO telescope at La Silla during which high signal-to-noise spectra of the Moon were obtained. We exploit those Echelle spectra to study a portion of the optical integrated solar spectrum and in particular to determine the solar photospheric line positions. Methods. The DAOSPEC program is used to measure solar line positions through Gaussian fitting in an automatic way. The solar spectra are calibrated both with an LFC and a Th-Ar. Results. We first apply the LFC solar spectrum to characterize the CCDs of the HARPS spectrograph. The comparison of the LFC and Th-Ar calibrated spectra reveals S-type distortions on each order along the whole spectral range with an amplitude of ±40 m s −1 . This confirms the pattern found in the first LFC experiment on a single order and extends the detection of the distortions to the whole analyzed region revealing that the precise shape varies with wavelength. A new data reduction is implemented to deal with CCD pixel inequalities to obtain a wavelength corrected solar spectrum. By using this spectrum we provide a new LFC calibrated solar atlas with 400 line positions in the range of 476-530, and 175 lines in the 534-585 nm range corresponding to the LFC bandwidth. The new LFC atlas is consistent on average with that based on FTS solar spectra, but it improves the accuracy of individual lines by a significant factor reaching a mean value of ≈10 m s −1 . Conclusions. The LFC-based solar line wavelengths are essentially free of major instrumental effects and provide a reference for absolute solar line positions at the date of Nov. 2010, i.e. an epoch of low solar activity. We suggest that future LFC observations could be used to trace small radial velocity changes of the whole solar photospheric spectrum in connection with the solar cycle and for direct comparison with the predicted line positions of 3D radiative hydrodynamical models of the solar photosphere. The LFC calibrated solar atlas can be also used to verify the accuracy of ground or space spectrographs by means of the solar spectrum.

Context. High resolution observations of the asteroids Iris and Juno have been performed by means of the UV-Visual Echelle Spectrograph (UVES) at the European Southern Observatory (ESO) Very Large Telescope (VLT) to obtain the effective accuracy of the spectrograph's radial velocity. The knowledge of this quantity has important bearings on studies searching for a variability in the fine structure constant carried out with this instrument. Aims. Asteroids provide a precise radial velocity reference at the level of 1 m s −1 , which allows for instrumental calibration and the recognition of small instrumental drifts and calibration systematics. In particular, radial velocity drifts due to nonuniform slit illumination and slit optical misalignment in the two UVES spectrograph arms can be investigated. Methods. We compare the position of the solar spectrum reflected by the asteroids with the solar wavelength positions and with that of asteroid and twilight observations at other epochs to asses the UVES instrumental accuracy. Results. We observe radial velocities offsets in the range of ≈10−50 m s −1 , likely due to a nonuniform slit illumination. However, no radial velocity patterns with wavelengths are detected and the two UVES arms provide consistent radial velocities. These results suggest that the detected ∆α/α variability by Levshakov et al. (2007) deduced from a drift of −180 ± 85 m s −1 at z abs = 1.84, between two sets of Fe ii 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 us to make a real time quality check of the spectrograph and should be followed for very accurate measurements.

Context. Present knowledge of the solar spectrum is limited because it is very difficult to observe the integrated solar spectrum at high resolution. The reflected solar light from asteroids has been shown to provide a relatively straightforward integrated and unmodified solar spectrum. Aims. We exploit this methodology to improve our knowledge of solar photospheric line positions both in terms of line number and precision with respect to the available solar line atlas. Methods. We used the DAOSPEC program to measure solar line positions automatically in high signal-to-noise spectra of Ceres obtained with HARPS at the 3.6 m ESO telescope. The line positions were then verified with the solar HARPS spectra of Ganymede and daylight as well as with a new FTS solar spectra. Results. A new atlas with 2334 lines in the range 4000−6859 Å is provided. The new atlas is consistent with that based on FTS solar spectra but the new line list improves the precision of individual lines by at least a factor 3−5. Conclusions. The new atlas provides a benchmark for 3D models of the solar photosphere and can be used to trace possible line drifts related to solar activity or to calibrate space and ground spectrographs.

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