LOCNES (LO-Cost NIR Extended Solar telescope) is a solar telescope installed at the TNG (Telescopio Nazionale Galileo) in the Canary Islands. It feeds the Sun’s light into the NIR spectrograph GIANO-B through a 40-m patch of optical fibers. LOCNES has been designed to obtain high signal-to-noise ratio spectra of the Sun as a star with an accurate wavelength calibration through molecular-band cells. This is an entirely new area of investigation that will provide timely results to improve the search of telluric planets with NIR spectrographs such as iSHELL, CARMENES, NIRPS, and GIANO-B. We will extract several disc-integrated activity indicators and average magnetic field measurements for the Sun in the NIR. These parameters will then be correlated with both the RV of the Sun as a star and the resolved images of the solar disc in visible and NIR. Such an approach will allow for a better understanding of the origin of activity-induced RV variations in the two spectral domains and will help in improving the techniques for their corrections. LOCNES has been installed on the outer part of the TNG dome and it started its operation in the 2023 Springtime when we performed the commissioning of the solar telescope. The main results of the commissioning will be highlighted in this paper.
The Large Interferometer For Exoplanets (LIFE) is a proposed space mission that enables the spectral characterization of the thermal emission of exoplanets in the solar neighborhood. The mission is designed to search for global atmospheric biosignatures on dozens of temperate terrestrial exoplanets and it will naturally investigate the diversity of other worlds. Here, we review the status of the mission concept, discuss the key mission parameters, and outline the trade-offs related to the mission’s architecture. In preparation for an upcoming concept study, we define a mission baseline based on a free-formation flying constellation of a double Bracewell nulling interferometer that consists of 4 collectors and a central beam-combiner spacecraft. The interferometric baselines are between 10–600m, and the estimated diameters of the collectors are at least 2m (but will depend on the total achievable instrument throughput). The spectral required wavelength range is 6–16μm (with a goal of 4–18.5μm), hence cryogenic temperatures are needed both for the collectors and the beam combiners. One of the key challenges is the required deep, stable, and broad-band nulling performance while maintaining a high system throughput for the planet signal. Among many ongoing or needed technology development activities, the demonstration of the measurement principle under cryogenic conditions is fundamentally important for LIFE.
In 2014 TNG also offered GIANO-B to the scientific community, providing a near-infrared (NIR) cross-dispersed echelle spectrograph covering 0.97 − 2.45 µm at a resolution of 50000. The possibility of simultaneously using GIANO-B together with the HARPS-N spectrograph (GIARPS observing mode) has been particularly appealing especially for the search of exoplanets by means high precision radial velocities. Moreover, GIANO-B triggered the possibility to observe in the NIR the Sun as a star by means of LOCNES, a solar telescope that feeds the spectrograph by a bundle of NIR fibers, for study the activity of the Sun as a star in the NIR wavelength range and its impact on the radial velocity measurements. Both science cases, include high-precision radial-velocity studies down to 3 m/s which demand for specialized, highly accurate wavelength calibration techniques. In this paper we present a developed absorption gas-cell to enable high-precision wavelength calibration for GIANO-B as a modified model of the CRIRES+ Absorbing Cell. We also discuss the manufacturing difficulties and the new design of the vessel. Furthermore, the AIT and the commissioning of the cells is also reported.
LOCNES (LOw-Cost NIR Extended Solar telescope) is a solar telescope installed at the TNG (Telescopio Nazionale Galileo). It feeds the light of the Sun into the NIR spectrograph GIANO-B through a 40-m patch of optical fibers. LOCNES has been designed to obtain high signal-to-noise ratio spectra of the Sun as a star with an accurate wavelength calibration through molecular-band cells. This is an entirely new area of investigation that will provide timely results to improve the search of telluric planets with NIR spectrographs such as iSHELL, CARMENES, and GIANO-B. We will extract several disc-integrated activity indicators and average magnetic field measurements for the Sun in the NIR. Eventually, they will be correlated with both the RV of the Sun-as-a -star and the resolved images of the solar disc in visible and NIR. Such an approach will allow for a better understanding of the origin of activity-induced RV variations in the two spectral domains and will help in improving the techniques for their corrections. In this paper, we outline the science drivers for the LOCNES project and its first commissioning results.
The search for telluric extrasolar planets with the Radial Velocity (RV) technique is intrinsically limited by the stellar jitter due to the activity of the star, because stellar surface inhomogeneities, including spots, plages and convective granules, induce perturbations hiding or even mimicking the planetary signal. This kind of noise is poorly understood in all the stars, but the Sun, due to their unresolved surfaces. For these reasons, the effects of the surface inhomogeneities on the measurement of the RV are very difficult to characterize. On the other hand, a better knowledge of these phenomena can allow us a step forward in our understanding of solar and stellar RV noise sources. This will allow to develop more tools for an optimal activity correction leading to more precise stellar RVs. Due to the high spatial resolution with which the Sun is observed, this noise is well known for it. Despite this, a link is lacking between the single observed photospheric phenomena and the behavior of the Sun observed as a star. LOCNES (Low Cost NIR Extended Solar Telescope) will allow to gather time series of RVs in order to disentangle the different contributions to the stellar (i.e., suns) RV jitter. Since July 2015, a Low Cost Solar Telescope (LCST) has been installed outside the TNG dome to feed solar light to the HARPS-N spectrograph (0.38-0.69 μm; R=115000). The refurbishment of the Near Infrared (NIR) High Resolution Spectrograph GIANO (now GIANO-B) and the new observing mode GIARPS at TNG (simultaneous observations in visible with HARPS-N and in NIR with GIANO-B) is a unique opportunity to extend the wavelength range up to 2.4 μm for measuring the RV time series of the Sun as a star. This paper outlines the LOCNES project and its scientific drivers.
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