Few-mode fibers and AO-assisted high resolution spectroscopy: coupling efficiency and modal noise mitigation

NIRPS (Near Infra-Red Planet Searcher) is an AO-assisted and fiber-fed spectrograph for high precision radial velocity measurements that will operate in the YJH-bands. While using an AO system in such instrument is generally considered to feed a single-mode fiber, NIRPS is following a different path by using a small multi-mode fiber (more specifically called "few-mode fiber"). This choice offers an excellent trade-off by allowing to design a compact cryogenic spectrograph, while maintaining a high coupling efficiency under bad seeing conditions and for faint stars. The main drawback resides in a much more important modal-noise, a problem that has to be tackled for allowing 1m/s precision radial velocity measurements. We study the impact of using an AO system to couple light into few-mode fibers. We focus on two aspects: the coupling efficiency into few-mode fibers and the question of modal noise and scrambling. We show first that NIRPS can reach coupling >= 50% up to magnitude I=12, and offer a gain of 1-2 magnitudes over a single-mode solution. We finally show that the best strategy to mitigate modal noise with the AO system is among the simplest: a continuous tip-tilt scanning of the fiber core.Comment: 10 pages, 5 figures. Proceeding of the AO4ELT5 conferenc

Stellar signal components seen in HARPS and HARPS-N solar radial velocities

Context. Radial velocity (RV) measurements induced by the presence of planets around late-type stars are contaminated by stellar signals that are of the order of a few meters per second in amplitude, even for the quietest stars. Those signals are induced by acoustic oscillations, convective granulation patterns, active regions co-rotating with the stellar surface, and magnetic activity cycles. Aims. This study investigates the properties of all coherent stellar signals seen on the Sun on timescales up to its sidereal rotational period. By combining HARPS and HARPS-N solar data spanning several years, we are able to clearly resolve signals on timescales from minutes to several months. Methods. We use a Markov Chain Monte Carlo (MCMC) mixture model to determine the quality of the solar data based on the expected airmass-magnitude extinction law. We then fit the velocity power spectrum of the cleaned and heliocentric RVs with all known variability sources, to recreate the RV contribution of each component. Results. After rejecting variations caused by poor weather conditions, we are able to improve the average intra-day root mean square (RMS) value by a factor of ~1.8. On sub-rotational timescales, we are able to fully recreate the observed RMS of the RV variations. In order to also include rotational components and their strong alias peaks introduced by nightly sampling gaps, the alias powers are accounted for by being redistributed to the central frequencies of the rotational harmonics. Conclusions. In order to enable a better understanding and mitigation of stellar activity sources, their respective impact on the total RV must be well-measured and characterized. We are able to recreate RV components up to rotational timescales, which can be further used to analyse the impact of each individual source of stellar signals on the detectability of exoplanets.Comment: Accepted for publication in A&

Atmospheric characterization of Proxima b by coupling the Sphere high-contrast imager to the Espresso spectrograph

Context. The temperate Earth-mass planet Proxima b is the closest exoplanet to Earth and represents what may be our best ever opportunity to search for life outside the Solar System. Aims. We aim at directly detecting Proxima b and characterizing its atmosphere by spatially resolving the planet and obtaining high-resolution reflected-light spectra. Methods. We propose to develop a coupling interface between the SPHERE high-contrast imager and the new ESPRESSO spectrograph, both installed at ESO VLT. The angular separation of 37 mas between Proxima b and its host star requires the use of visible wavelengths to spatially resolve the planet on a 8.2-m telescope. At an estimated planet-to-star contrast of ~10^-7 in reflected light, Proxima b is extremely challenging to detect with SPHERE alone. However, the combination of a ~10^3-10^4 contrast enhancement from SPHERE to the high spectral resolution of ESPRESSO can reveal the planetary spectral features and disentangle them from the stellar ones. Results. We find that significant but realistic upgrades to SPHERE and ESPRESSO would enable a 5-sigma detection of the planet and yield a measurement of its true mass and albedo in 20-40 nights of telescope time, assuming an Earth-like atmospheric composition. Moreover, it will be possible to probe the O2 bands at 627, 686 and 760 nm, the water vapour band at 717 nm, and the methane band at 715 nm. In particular, a 3.6-sigma detection of O2 could be made in about 60 nights of telescope time. Those would need to be spread over 3 years considering optimal observability conditions for the planet. Conclusions. The very existence of Proxima b and the SPHERE-ESPRESSO synergy represent a unique opportunity to detect biosignatures on an exoplanet in the near future. It is also a crucial pathfinder experiment for the development of Extremely Large Telescopes and their instruments (abridged).Comment: 16 pages, 7 figures, revised version accepted to A&

Validation of Messenger Ribonucleic Acid Markers Differentiating Among Human Acute Respiratory Distress Syndrome Subgroups in an Ovine Model of Acute Respiratory Distress Syndrome Phenotypes

BACKGROUND: The discovery of biological subphenotypes in acute respiratory distress syndrome (ARDS) might offer a new approach to ARDS in general and possibly targeted treatment, but little is known about the underlying biology yet. To validate our recently described ovine ARDS phenotypes model, we compared a subset of messenger ribonucleic acid (mRNA) markers in leukocytes as reported before to display differential expression between human ARDS subphenotypes to the expression in lung tissue in our ovine ARDS phenotypes model (phenotype 1 (Ph1): hypoinflammatory; phenotype 2 (Ph2): hyperinflammatory). METHODS: We studied 23 anesthetized sheep on mechanical ventilation with observation times between 6 and 24 h. They were randomly allocated to the two phenotypes (n = 14 to Ph1 and n = 9 to Ph2). At study end, lung tissue was harvested and preserved in RNAlater. After tissue homogenization in TRIzol, total RNA was extracted and custom capture and reporter probes designed by NanoString Technologies were used to measure the expression of 14 genes of interest and the 6 housekeeping genes on a nCounter SPRINT profiler. RESULTS: Among the 14 mRNA markers, in all animals over all time points, 13 markers showed the same trend in ovine Ph2/Ph1 as previously reported in the MARS cohort: matrix metalloproteinase 8, olfactomedin 4, resistin, G protein-coupled receptor 84, lipocalin 2, ankyrin repeat domain 22, CD177 molecule, and transcobalamin 1 expression was higher in Ph2 and membrane metalloendopeptidase, adhesion G protein-coupled receptor E3, transforming growth factor beta induced, histidine ammonia-lyase, and sulfatase 2 expression was higher in Ph1. These expression patterns could be found when different sources of mRNA – such as blood leukocytes and lung tissue – were compared. CONCLUSION: In human and ovine ARDS subgroups, similar activated pathways might be involved (e.g., oxidative phosphorylation, NF-κB pathway) that result in specific phenotypes

Shadows cast on the transition disk of HD 135344B. Multiwavelength VLT/SPHERE polarimetric differential imaging

The protoplanetary disk around the F-type star HD 135344B (SAO 206462) is in a transition stage and shows many intriguing structures both in scattered light and thermal (sub-)millimeter emission which are possibly related to planet formation processes. We study the morphology and surface brightness of the disk in scattered light to gain insight into the innermost disk regions, the formation of protoplanets, planet-disk interactions traced in the surface and midplane layers, and the dust grain properties of the disk surface. We have carried out high-contrast polarimetric differential imaging (PDI) observations with VLT/SPHERE and obtained polarized scattered light images with ZIMPOL in R- and I-band and with IRDIS in Y- and J-band. The scattered light images reveal with unprecedented angular resolution and sensitivity the spiral arms as well as the 25 au cavity of the disk. Multiple shadow features are discovered on the outer disk with one shadow only being present during the second observation epoch. A positive surface brightness gradient is observed in the stellar irradiation corrected images in southwest direction possibly due to an azimuthally asymmetric perturbation of the temperature and/or surface density by the passing spiral arms. The disk integrated polarized flux, normalized to the stellar flux, shows a positive trend towards longer wavelengths which we attribute to large aggregate dust grains in the disk surface. Part of the the non-azimuthal polarization signal in the Uphi image of the J-band observation could be the result of multiple scattering in the disk. The detected shadow features and their possible variability have the potential to provide insight into the structure of and processes occurring in the innermost disk regions.Comment: Accepted for publication in A&A, 20 pages, 15 figure

CHEOPS launch in 2019! – Payload Capabilities and In-Orbit Commissioning Preview

ESA Science Programme Committee (SPC) selected CHEOPS as the first small class science mission in 2012. CHEOPS is considered as a pilot case for the implementation of “small science missions” and its success is key for the continuation of fast-paced, small missions. The mission has been developed and brought into a flight readiness state within 5-6 years from selection, which is about half the time of other ESA missions. This paper focuses on the CHEOPS payload and its predicted capabilities. The 300mm effective aperture Ritchey-Chretien telescope provided by the CHEOPS consortium has been tested and characterized on ground in a 2 months calibration campaign after the qualification for flight. The results have led to performance estimations, which are discussed here. We show that the performance requirements in flight are expected to be met by the instrument. A preview is given towards the 2 months lasting In Orbit Commissioning (IOC) phase of the CHEOPS payload after LEOP and platform check-out. The activities in orbit range from dark current measurements, PSF characterization and parasitic stray light determination to AOCS and instrument performance verifications to science validation using reference transits

Shadows and spirals in the protoplanetary disk HD 100453

Understanding the diversity of planets requires to study the morphology and the physical conditions in the protoplanetary disks in which they form. We observed and spatially resolved the disk around the ~10 Myr old protoplanetary disk HD 100453 in polarized scattered light with SPHERE/VLT at optical and near-infrared wavelengths, reaching an angular resolution of ~0.02", and an inner working angle of ~0.09". We detect polarized scattered light up to ~0.42" (~48 au) and detect a cavity, a rim with azimuthal brightness variations at an inclination of 38 degrees, two shadows and two symmetric spiral arms. The spiral arms originate near the location of the shadows, close to the semi major axis. We detect a faint spiral-like feature in the SW that can be interpreted as the scattering surface of the bottom side of the disk, if the disk is tidally truncated by the M-dwarf companion currently seen at a projected distance of ~119 au. We construct a radiative transfer model that accounts for the main characteristics of the features with an inner and outer disk misaligned by ~72 degrees. The azimuthal brightness variations along the rim are well reproduced with the scattering phase function of the model. While spirals can be triggered by the tidal interaction with the companion, the close proximity of the spirals to the shadows suggests that the shadows could also play a role. The change in stellar illumination along the rim, induces an azimuthal variation of the scale height that can contribute to the brightness variations. Dark regions in polarized images of transition disks are now detected in a handful of disks and often interpreted as shadows due to a misaligned inner disk. The origin of such a misalignment in HD 100453, and of the spirals, is unclear, and might be due to a yet-undetected massive companion inside the cavity, and on an inclined orbit.Comment: A&A, accepte