A new list of thorium and argon spectral lines in the visible

Aims. We present a new list of thorium and argon emission lines in the visible obtained by analyzing high-resolution (R=110,000) spectra of a ThAr hollow cathode lamp. The aim of this new line list is to allow significant improvements in the quality of wavelength calibration for medium- to high-resolution astronomical spectrographs. Methods. We use a series of ThAr lamp exposures obtained with the HARPS instrument (High Accuracy Radial-velocity Planet Searcher) to detect previously unknown lines, perform a systematic search for blended lines and correct individual wavelengths by determining the systematic offset of each line relative to the average wavelength solution. Results. We give updated wavelengths for more than 8400 lines over the spectral range 3785-6915 A. The typical internal uncertainty on the line positions is estimated to be ~10 m/s (3.3 parts in 10^8 or 0.18 mA), which is a factor of 2-10 better than the widely used Los Alamos Atlas of the Thorium Spectrum (Palmer & Engleman 1983). The absolute accuracy of the global wavelength scale is the same as in the Los Alamos Atlas. Using this new line list on HARPS ThAr spectra, we are able to obtain a global wavelength calibration which is precise at the 20 cm/s level (6.7 parts in 10^10 or 0.0037 mA). Conclusions. Several research fields in astronomy requiring high-precision wavelength calibration in the visible (e.g. radial velocity planet searches, variability of fundamental constants) should benefit from using the new line list.Comment: 7 pages, 6 figures, accepted for publication in A&

Evaluating the stability of atmospheric lines with HARPS

Context: In the search for extrasolar systems by radial velocity technique, a precise wavelength calibration is necessary for high-precision measurements. The choice of the calibrator is a particularly important question in the infra-red domain, where the precision and exploits still fall behind the achievements of the optical. Aims: We investigate the long-term stability of atmospheric lines as a precise wavelength reference and analyze their sensitivity to different atmospheric and observing conditions. Methods: We use HARPS archive data on three bright stars, Tau Ceti, Mu Arae and Epsilon Eri, spanning 6 years and containing high-cadence measurements over several nights. We cross-correlate this data with an O2 mask and evaluate both radial velocity and bisector variations down to a photon noise of 1 m/s. Results: We find that the telluric lines in the three data-sets are stable down to 10 m/s (r.m.s.) over the 6 years. We also show that the radial velocity variations can be accounted for by simple atmospheric models, yielding a final precision of 1-2 m/s. Conclusions: The long-term stability of atmospheric lines was measured as being of 10 m/s over six years, in spite of atmospheric phenomena. Atmospheric lines can be used as a wavelength reference for short-time-scales programs, yielding a precision of 5 m/s "out-of-the box". A higher precision, down to 2 m/s can be reached if the atmospheric phenomena are corrected for by the simple atmospheric model described, making it a very competitive method even on long time-scales.Comment: 7 pages, accepted for publication in A&

Refined architecture of the WASP-8 system: a cautionary tale for traditional Rossiter-McLaughlin analysis

Probing the trajectory of a transiting planet across the disk of its star through the analysis of its Rossiter-McLaughlin effect can be used to measure the differential rotation of the host star and the true obliquity of the system. Highly misaligned systems could be particularly conducive to these mesurements, which is why we reanalysed the HARPS transit spectra of WASP-8b using the 'Rossiter-McLaughlin effect reloaded' (reloaded RM) technique. This approach allows us to isolate the local stellar CCF emitted by the planet-occulted regions. As a result we identified a $\sim$35% variation in the local CCF contrast along the transit chord, which might trace a deepening of the stellar lines from the equator to the poles. Whatever its origin, such an effect cannot be detected when analyzing the RV centroids of the disk-integrated CCFs through a traditional velocimetric analysis of the RM effect. Consequently it injected a significant bias into the results obtained by Queloz et al. (2010) for the projected rotational velocity $v_{eq} \sin i_{\star}$ (1.59$\stackrel{+0.08}{_{-0.09}}$ km/s) and the sky-projected obliquity $\lambda$ (-123.0$\stackrel{+3.4}{_{-4.4}}^{\circ}$). Using our technique, we measured these values to be $v_{eq} \sin i_{\star}$ = 1.90$\pm$0.05 km/s and $\lambda$ = -143.0$\stackrel{+1.6}{_{-1.5}}^{\circ}$. We found no compelling evidence for differential rotation of the star, although there are hints that WASP-8 is pointing away from us with the stellar poles rotating about 25% slower than the equator. Measurements at higher accuracy during ingress/egress will be required to confirm this result. In contrast to the traditional analysis of the RM effect, the reloaded RM technique directly extracts the local stellar CCFs, allowing us to analyze their shape and to measure their RV centroids, unbiased by variations in their contrast or FWHM.Comment: Accepted for publication in A&A. 12 page

Use of combined suspension laryngoscopy, flexible bronchoscopy and high frequency jet ventilation for Y-shaped airway stents delivery

La trachée et les bronches proximales sont de fins conduits subtils, ingénieusement structurés par une partie cartilagineuse antérieure résistante aux variations de pression et une partie membraneuse postérieure souple. Par leurs faibles volumes (espace mort) ils délivrent un grand pourcentage de l'air inspiré aux voies distales, puis au parenchyme pulmonaire, permettant les échanges de gaz. Cette belle harmonie respiratoire peut être rapidement mise à mal dès qu'un processus atteint ces voies respiratoires proximales, soit en les comprimant, processus sténosant, soit en affaiblissant leur structure, trachéo-bronchomalacie, soit en ouvrant leur paroi sur les structures médiastinales, fistule trachéo/broncho-médiastinales, pleurales ou autres. Le pronostic vital est alors rapidement engagé au vu de l'absolue nécessité du bon fonctionnement de ces fins conduits, une petite diminution du calibre de leurs fines lumières provoquant une baisse importante de leurs surfaces. Dans ces situations à haut potentiel de complication majeure les interventions endoscopiques pour restaurer l'intégrité de ces conduits sont alors fort risquées, et il est primordial de pouvoir les effectuer dans un cadre sécurisé au maximum. La réalisation de ces gestes par la technique décrite dans notre article « Use of combined suspension laryngoscopy, flexible bronchoscopy and high frequency jet ventilation forY-shaped airway stents delivery" permet la sécurité nécessaire à ces situations instable, en effet -la laryngoscopie en suspension expose les voies proximales en offrant un accès le plus large possible à l'arbre trachéobronchique ce qui permet l insertion de multiples instruments parfois volumineux, -la Jet ventilation assure une oxygénation et une ventilation adéquate par un fin cathéter placé soit dans le poumon sain, soit en distalité de la lésion -la bronchoscopie souple, passant au travers d'endroits exigus et courbes permet le déploiement sous vision direct, au millimètre près, de divers dispositifs. Cette association remplace avantageusement la technique traditionnelle qui insère les stents à l'aveugle, et en apnée, ce qui représente de haut risque de mauvais positionnement des stents avec des conséquences immédiates sur l'oxygénation et la ventilation souvent déjà bien altérées. Perspective et conclusion : cette technique est utile pour l'insertion des stents en Y, centraux, comme décrit dans notre article, et les indications peuvent être étendues aux stents distaux pour lesquels l'accès n'est parfois pas aisé avec le bronchoscope rigide, et pour d'autres interventions endoscopiques, laser, cryothérapie, radiofréquence ou l'insertion de nouveaux dispositifs

Atmospheric Stellar Parameters from Cross-Correlation Functions

The increasing number of spectra gathered by spectroscopic sky surveys and transiting exoplanet follow-up has pushed the community to develop automated tools for atmospheric stellar parameters determination. Here we present a novel approach that allows the measurement of temperature ($T_{\rm eff}$), metallicity ($[{\rm Fe}/{\rm H}]$) and gravity ($\log g$) within a few seconds and in a completely automated fashion. Rather than performing comparisons with spectral libraries, our technique is based on the determination of several cross-correlation functions (CCFs) obtained by including spectral features with different sensitivity to the photospheric parameters. We use literature stellar parameters of high signal-to-noise ($\textrm{SNR}$), high-resolution HARPS spectra of FGK Main Sequence stars to calibrate $T_{\rm eff}$, $[{\rm Fe}/{\rm H}]$ and $\log g$ as a function of CCFs parameters. Our technique is validated using low $\textrm{SNR}$ spectra obtained with the same instrument. For FGK stars we achieve a precision of $\sigma_{T_{\rm eff}} = 50$ K, $\sigma_{\log g} = 0.09~ \textrm{dex}$ and $\sigma_{\textrm{Fe}/\textrm{H}]} =0.035~ \textrm{dex}$ at $\textrm{SNR}=50$, while the precision for observation with $\textrm{SNR} \gtrsim 100$ and the overall accuracy are constrained by the literature values used to calibrate the CCFs. Our approach can be easily extended to other instruments with similar spectral range and resolution, or to other spectral range and stars other than FGK dwarfs if a large sample of reference stars is available for the calibration. Additionally, we provide the mathematical formulation to convert synthetic equivalent widths to CCF parameters as an alternative to direct calibration. We have made our tool publicly available.Comment: Accepted by MNRAS. 12 pages, 12 figures. The code to retrieve the atmospheric stellar parameters from HARPS and HARPS-N spectra is available "at this url, https://github.com/LucaMalavolta/CCFpams

The Kahler Structure of Supersymmetric Holographic RG Flows

We study the metrics on the families of moduli spaces arising from probing with a brane the ten and eleven dimensional supergravity solutions corresponding to renormalisation group flows of supersymmetric large n gauge theory. In comparing the geometry to the physics of the dual gauge theory, it is important to identify appropriate coordinates, and starting with the case of SU(n) gauge theories flowing from N=4 to N=1 via a mass term, we demonstrate that the metric is Kahler, and solve for the Kahler potential everywhere along the flow. We show that the asymptotic form of the Kahler potential, and hence the peculiar conical form of the metric, follows from special properties of the gauge theory. Furthermore, we find the analogous Kahler structure for the N=4 preserving Coulomb branch flows, and for an N=2 flow. In addition, we establish similar properties for two eleven dimensional flow geometries recently presented in the literature, one of which has a deformation of the conifold as its moduli space. In all of these cases, we notice that the Kahler potential appears to satisfy a simple universal differential equation. We prove that this equation arises for all purely Coulomb branch flows dual to both ten and eleven dimensional geometries, and conjecture that the equation holds much more generally.Comment: 26 pages. Late

A new wavelength calibration for echelle spectrographs using Fabry-Perot etalons

The study of Earth-mass extrasolar planets via the radial-velocity technique and the measurement of the potential cosmological variability of fundamental constants call for very-high-precision spectroscopy at the level of \updelta\lambda/\lambda<10^{-9}. Wavelength accuracy is obtained by providing two fundamental ingredients: 1) an absolute and information-rich wavelength source and 2) the ability of the spectrograph and its data reduction of transferring the reference scale (wavelengths) to a measurement scale (detector pixels) in a repeatable manner. The goal of this work is to improve the wavelength calibration accuracy of the HARPS spectrograph by combining the absolute spectral reference provided by the emission lines of a thorium-argon hollow-cathode lamp (HCL) with the spectrally rich and precise spectral information of a Fabry-P\'erot-based calibration source. On the basis of calibration frames acquired each night since the Fabry-P\'erot etalon was installed on HARPS in 2011, we construct a combined wavelength solution which fits simultaneously the thorium emission lines and the Fabry-P\'erot lines. The combined fit is anchored to the absolute thorium wavelengths, which provide the `zero-point' of the spectrograph, while the Fabry-P\'erot lines are used to improve the (spectrally) local precision. The obtained wavelength solution is verified for auto-consistency and tested against a solution obtained using the HARPS Laser-Frequency Comb (LFC). The combined thorium+Fabry-P\'erot wavelength solution shows significantly better performances compared to the thorium-only calibration. The presented techniques will therefore be used in the new HARPS and HARPS-N pipeline, and will be exported to the ESPRESSO spectrograph.Comment: 15 pages, 8 figure

Spectroscopic direct detection of reflected light from extra-solar planets

At optical wavelengths, an exoplanet's signature is essentially reflected light from the host star - several orders of magnitude fainter. Since it is superimposed on the star spectrum its detection has been a difficult observational challenge. However, the development of a new generation of instruments like ESPRESSO and next generation telescopes like the E-ELT put us in a privileged position to detect these planets' reflected light as we will have access to extremely high signal-to-noise ratio spectra. With this work, we propose an alternative approach for the direct detection of the reflected light of an exoplanet. We simulated observations with ESPRESSO@VLT and HIRES@E-ELT of several star+planet systems, encompassing 10h of the most favourable orbital phases. To the simulated spectra we applied the Cross Correlation Function to operate in a much higher signal-to-noise ratio domain than when compared with the spectra. The use of the Cross-Correlation Function permitted us to recover the simulated the planet signals at a level above 3 \sigma_{noise} significance on several prototypical (e.g., Neptune type planet with a 2 days orbit with the VLT at 4.4 \sigma_{noise} significance) and real planetary systems (e.g., 55 Cnc e with the E-ELT at 4.9 \sigma_{noise} significance). Even by using a more pessimistic approach to the noise level estimation, where systematics in the spectra increase the noise 2-3 times, the detection of the reflected light from large close-orbit planets is possible. We have also shown that this kind of study is currently within reach of current instruments and telescopes (e.g., 51 Peg b with the VLT at 5.2 \sigma_{noise} significance), although at the limit of their capabilities.Comment: Accepted for Publication on MNRAS: 2013 August 29; Online Article: http://mnras.oxfordjournals.org/content/early/2013/09/27/mnras.stt1642; 5 Figures, 11 page