A List of Bright Interferometric Calibrators measured at the ESO VLTI

In a previous publication (Richichi & Percheron 2005) we described a program of observations of candidate calibrator stars at the ESO Very Large Telescope Interferometer (VLTI), and presented the main results from a statistical point of view. In the present paper, we concentrate on establishing a new homogeneous group of bright interferometric calibrators, based entirely on publicly available K-band VLTI observations carried out with the VINCI instrument up to July 2004. For this, we have defined a number of selection criteria for the quality and volume of the observations, and we have accordingly selected a list of 17 primary and 47 secondary calibrators. We have developed an approach to a robust global fit for the angular diameters using the whole volume of quality-controlled data, largely independent of a priori assumptions. Our results have been compared with direct measurements, and indirect estimates based on spectrophotometric methods, and general agreement is found within the combined uncertainties. The stars in our list cover the range K=-2.9 to +3.0 mag in brightness, and 1.3 to 20.5 milliarcseconds in uniform-disk diameter. The relative accuracy of the angular diameter values is on average 0.4% and 2% for the primary and secondary calibrators respectively. Our calibrators are well suited for interferometric observations in the near-infrared on baselines between ~20m and ~200m, and their accuracy is superior, at least for the primary calibrators, to other similar catalogues. Therefore, the present list of calibrators has the potential to lead to significantly improved interferometric scientific results

Vitamin A status of populations in three West african countries

Les résultats des enquêtes de consommation alimentaire et d'épidémiologie (clinique et biochimique) entreprises dans trois régions sub-sahéliennes ont mis en évidence l'existence de xérophtalmie au Burkina Faso, une déficience transitoire en vitamine A durant la saison humide au sud du Mali sans signes cliniques graves et un bon état en vitamine A en Casamanc

Mass Measurements and the Bound--Electron g Factor

The accurate determination of atomic masses and the high-precision measurement of the bound-electron g factor are prerequisites for the determination of the electron mass, which is one of the fundamental constants of nature. In the 2002 CODATA adjustment [P. J. Mohr and B. N. Taylor, Rev. Mod. Phys. 77, 1 (2005)], the values of the electron mass and the electron-proton mass ratio are mainly based on g factor measurements in combination with atomic mass measurements. In this paper, we briefly discuss the prospects for obtaining other fundamental information from bound-electron g factor measurements, we present some details of a recent investigation of two-loop binding corrections to the g factor, and we also investigate the radiative corrections in the limit of highly excited Rydberg S states with a long lifetime, where the g factor might be explored using a double resonance experiment.Comment: 13 pages, LaTeX; dedicated to Prof. H.-J. Kluge on the occasion of his 65th birthday, to appear in Int. J. Mass. Spectrometr

Atomic hydrogen in AGB circumstellar environments. A case study: X Her

We report the detection of the HI line at 21 cm from the circumstellar shell around the AGB star X Her using the position-switching technique with the Nancay Radio Telescope. At the star position the line shows 2 components: (i) a broad one (FWHM ~ 13 km/s) centered at -72.2 km/s, and (ii) a narrow one (FWHM \~ 4 km/s) centered at ~ -70.6 km/s. Our map shows that the source associated to the broad component is asymmetric with material flowing preferentially towards the North-East. This source extends to ~ 10 arcmin. (~ 0.4 pc) from the star in that direction. On the other hand, the narrow component is detected only at the star position and indicates material flowing away from the observer. The total mass of atomic hydrogen is ~ 6.5 10^{-3} solar mass which, within a factor 2, agrees with the estimate obtained from IRAS data at 60 microns.Comment: accepted for publication in MNRA

Spatially resolved H2 emission from the disk around T Tau N

We report the detection of quiescent H2 emission in a spatially resolved ring-like structure within 100 AU of T Tau N. We present evidence to show that the emission most likely arises from shocks in the atmosphere of a nearly face-on disk around T Tau N. Using high spatial resolution 3D spectroscopic K-band data, we trace the spatial distribution of several H2 NIR rovibrational lines in the vicinity of T Tau N. We detect weak H2 emission from the v=1-0 S(0), S(1), Q(1) lines and the v=2-1 S(1) line in a ring-like structure around T Tau N between 0.1'' (~15 AU) and 0.7'' (~100AU) from the star. The v=1-0 S(0) and v=2-1 S(1) lines are detected only in the outer parts of the ring structure. Closer to the star, the strong continuum limits our sensitivity to these lines. The total flux of the v=1-0 S(1) line is 1.8 *10^{-14} ergs s^{-1}cm^{-2}, similar to previous measurements of H2 in circumstellar disks. The velocity of the H2 emitting gas around T Tau N is consistent with the rest velocity of the star, and the H2 does not seem to be part of a collimated outflow. Both shocks impinging on the surface of a disk and irradiation of a disk by UV-photons and X-rays from the central star are plausible candidates for the H2 excitation mechanism. However, irradiation should not create a large degree of excitation at radii larger than 20 AU. Most likely the H2 emission arises in the atmosphere of a flared disk with radius 85-100 AU and mass 0.005-0.5Msun, where the gas is excited by shocks created when a wide-angle wind impinges on the disk. The H2 emission could also originate from shock excitation in the cavity walls of an envelope, but this requires an unusually high velocity of the wide-angle wind from T Tau N.Comment: Accepted by A&

Leptonic Probes of the Standard Model

Precise measurements of the lepton properties provide stringent tests of the Standard Model structure and accurate determinations of its parameters. We overview the present status of a few selected topics: lepton universality, QCD tests and the determination of alpha_s and m_s from hadronic tau decays, the anomalous lepton magnetic moments and neutrino oscillations.Comment: Invited talk at the Seventh International Workshop on Tau Lepton Physics (TAU02), Santa Cruz, Ca, USA, Sept 2002, 12 pages, LaTeX, 9 eps figure

The variable mass loss of the AGB star WX Psc as traced by the CO J=1-0 through 7-6 lines and the dust emission

Low and intermediate mass stars lose a significant fraction of their mass through a dust-driven wind during the Asymptotic Giant Branch (AGB) phase. Recent studies show that winds from late-type stars are far from being smooth. Mass-loss variations occur on different time scales, from years to tens of thousands of years. The variations appear to be particularly prominent towards the end of the AGB evolution. The occurrence, amplitude and time scale of these variations are still not well understood. The goal of our study is to gain insight into the structure of the circumstellar envelope (CSE) of WX Psc and map the possible variability of the late-AGB mass-loss phenomenon. We have performed an in-depth analysis of the extreme infrared AGB star WX Psc by modeling (1) the CO J=1-0 through 7-6 rotational line profiles and the full spectral energy distribution (SED) ranging from 0.7 to 1300 micron. We hence are able to trace a geometrically extended region of the CSE. Both mass-loss diagnostics bear evidence of the occurrence of mass-loss modulations during the last ~2000 yr. In particular, WX Psc went through a high mass-loss phase (Mdot~5e-5 Msun/yr) some 800 yr ago. This phase lasted about 600 yr and was followed by a long period of low mass loss (Mdot~5e-8 Msun/yr). The present day mass-loss rate is estimated to be ~6e-6 Msun/yr. The AGB star WX Psc has undergone strong mass-loss rate variability on a time scale of several hundred years during the last few thousand years. These variations are traced in the strength and profile of the CO rotational lines and in the SED. We have consistently simulated the behaviour of both tracers using radiative transfer codes that allow for non-constant mass-loss rates.Comment: 12 pages, accepted for publication in A&

Near Infrared Angular Diameters of a few AGB variables by Lunar Occultations

The uniform disk (UD) angular diameter measurements of two oxygen-rich Mira variables (AW Aur and BS Aur) and three semiregular (SRb) variables (GP Tau, RS Cap, RT Cap), in near Infrared K-band (2.2 micron) by lunar occultation observations are reported. UD angular diameters of the two Miras and one SRV are first time measurements. In addition a method of predicting angular diameters from (V-K) colour is discussed and applied to the five sources. The effect of mass-loss enhancing measured K-band diameters is examined for Miras using (K-[12]) colour excess as an index. In our sample the measured angular diameter of one of the Miras (BS Aur) is found enhanced by nearly 40% compared to its expected value, possibly due to mass loss effects leading to formation of a circumstellar shell.Comment: 8 pages, 5 figures, Accepted for publication in MNRA

Two-photon spectroscopy of the biphenyl chromophore. The electronic excited states of biphenyl and fluorene below 50000 cm-1

The two-photon excitation spectra of biphenyl and fluorene in dil. soln. were measured up to 50,000 cm-1. Both spectra exhibit a medium intense band system in the range 32,000-42,000 cm-1, and a strong band above 45,000 cm-1. The lowest frequency feature is assigned to a B3 symmetry transition in biphenyl and the corresponding B2 transition in fluorene. The polarization of the higher bands leads to the assignment of 2 A states at 38,000 and 47,000 cm-1. The origin of the electronically excited states of the biphenyl chromophore is discussed by simple composite mol. considerations as well as CNDO CI calcns. The latter give a semiquant. picture of transition energies and transition probabilities for 1- and 2-photon allowed excitations. A compilation of 1-photon spectra and calcns. from the literature is included in the anal. to provide a consistent picture of the electronically excited states of the biphenyl chromophore up to 50,000 cm-1

Deconvolving the pre-Himalayan Indian margin – tales of crustal growth and destruction

The metamorphic core of the Himalaya is composed of Indian cratonic rocks with two distinct crustal affinities that are defined by radiogenic isotopic geochemistry and detrital zircon age spectra. One is derived predominantly from the Paleoproterozoic and Archean rocks of the Indian cratonic interior and is either represented as metamorphosed sedimentary rocks of the Lesser Himalayan Sequence (LHS) or as slices of the distal cratonic margin. The other is the Greater Himalayan Sequence (GHS) whose provenance is less clear and has an enigmatic affinity. Here we present new detrital zircon Hf analyses from LHS and GHS samples spanning over 1000 kilometers along the orogen that respectively show a striking similarity in age spectra and Hf isotope ratios. Within the GHS, the zircon age populations at 2800–2500 Ma, 1800 Ma, 1000 Ma and 500 Ma can be ascribed to various Gondwanan source regions; however, a pervasive and dominant Tonian age population (∼860–800 Ma) with a variably enriched radiogenic Hf isotope signature (εHf = 10 to -20) has not been identified from Gondwana or peripheral accreted terranes. We suggest this detrital zircon age population was derived from a crustal province that was subsequently removed by tectonic erosion. Substantial geologic evidence exists from previous studies across the Himalaya supporting the Cambro-Ordovician Kurgiakh Orogeny. We propose the tectonic removal of Tonian lithosphere occurred prior to or during this Cambro-Ordovician episode of orogenesis in a similar scenario as is seen in the modern Andean and Indonesian orogenies, wherein tectonic processes have removed significant portions of the continental lithosphere in a relatively short amount of time. This model described herein of the pre-Himalayan northern margin of Greater India highlights the paucity of the geologic record associated with the growth of continental crust. Although the continental crust is the archive of Earth history, it is vital to recognize the ways in which preservation bias and destruction of continental crust informs geologic models