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Traditional one-dimensional hydrostatic model atmospheres introduce systematic modelling errors into spectroscopic analyses of FGK-type stars. We present an updated version of the -grid of three-dimensional model atmospheres, and explore the accuracy of post-processing methods in preparation for spectral synthesis. New and old models were (re)computed following an updated workflow, including an updated opacity binning technique. Spectroscopic tests were performed in three-dimensional local thermodynamic equilibrium for a grid of 216 fictitious Fe I lines, spanning a wide range of oscillator strengths, excitation potentials, and central wavelengths, and eight model atmospheres that cover the stellar atmospheric parameter range ($ $, logg , and feh ) of FGK-type stars. Using this grid, the impact of vertical and horizontal resolutions, and temporal sampling of model atmospheres on spectroscopic diagnostics, was tested. We find that downsampling the horizontal mesh from its original size of $240 grid cells to $80 cells, in other words, sampling every third grid cell, introduces minimal errors on the equivalent width and normalised line flux across the line and stellar parameter space. Regarding temporal sampling, we find that sampling ten statistically independent snapshots is sufficient to accurately model the shape of spectral line profiles. For equivalent widths, a subsample consisting of only two snapshots is sufficient, introducing an abundance error of less than 0.015 dex. We have computed 32 new model atmospheres and recomputed 116 old ones present in the original grid. The public release of the -grid contains 243 models and the processed snapshots can be used to improve the accuracy of spectroscopic analyses.
Traditional one-dimensional hydrostatic model atmospheres introduce systematic modelling errors into spectroscopic analyses of FGK-type stars. We present an updated version of the -grid of three-dimensional model atmospheres, and explore the accuracy of post-processing methods in preparation for spectral synthesis. New and old models were (re)computed following an updated workflow, including an updated opacity binning technique. Spectroscopic tests were performed in three-dimensional local thermodynamic equilibrium for a grid of 216 fictitious Fe I lines, spanning a wide range of oscillator strengths, excitation potentials, and central wavelengths, and eight model atmospheres that cover the stellar atmospheric parameter range ($ $, logg , and feh ) of FGK-type stars. Using this grid, the impact of vertical and horizontal resolutions, and temporal sampling of model atmospheres on spectroscopic diagnostics, was tested. We find that downsampling the horizontal mesh from its original size of $240 grid cells to $80 cells, in other words, sampling every third grid cell, introduces minimal errors on the equivalent width and normalised line flux across the line and stellar parameter space. Regarding temporal sampling, we find that sampling ten statistically independent snapshots is sufficient to accurately model the shape of spectral line profiles. For equivalent widths, a subsample consisting of only two snapshots is sufficient, introducing an abundance error of less than 0.015 dex. We have computed 32 new model atmospheres and recomputed 116 old ones present in the original grid. The public release of the -grid contains 243 models and the processed snapshots can be used to improve the accuracy of spectroscopic analyses.
Context is one of the lowest-density gas giants known to date, making it an excellent target for atmospheric characterisation through the transmission spectroscopy technique. Aims . In the framework of the GAPS large programme, we collected four transit events of \, with the aim of studying the exoplanet atmosphere and deriving the orbital projected obliquity. Methods . We exploited the high-precision GIARPS (GIANO-B + HARPS-N) observing mode of the Telescopio Nazionale Galileo (TNG) along with additional archival TESS photometry to explore the activity level of the host star. We performed transmission spectroscopy, both in the visible (VIS) and in the near-infrared (NIR) wavelength range, and we analysed the RML effect when fitting both the radial velocities and the Doppler shadow. Based on the TESS photometry, we redetermined the transit parameters of Results . By modelling the RML effect, we derived a sky-projected obliquity of ($2.2 circ $, indicating an aligned planetary orbit. The chromospheric activity index $ prime HK $, the CCF profile, and the variability in the transmission spectrum of the H$ line suggest that the host star shows signatures of stellar activity and/or pulsation. We found no evidence of atomic or molecular species in the optical transmission spectra, with the exception of pseudo-signals corresponding to Cr I Fe I H$ Na I and Ti I . In the NIR range, we found an absorption signal of the triplet of $<!PCT!> (19.0sigma ), corresponding to an effective planetary radius of sim 3 $R (where $R 2 $R which extends beyond the planet's Roche lobe radius. Conclusions . Owing to the stellar variability and the high uncertainty of the model, we could not confirm the planetary origin of the signals found in the optical transmission spectrum. On the other hand, we were able to confirm previous detections of the infrared triplet, providing a 19.0sigma detection. Our finding indicates that the planet's atmosphere is evaporating.
The search for small exoplanets around solar-type stars is limited by stellar physical variability, such as a jittering in the apparent photospheric radial velocity. While chromospheric variability has been aptly studied, challenges remain for the observation, modeling. and understanding the much smaller fluctuations in photospheric spectral line strengths, shapes, and shifts. Extreme-precision radial-velocity spectrometers allow for highly precise stellar spectroscopy and time series of the Sun (seen as a star) enable the monitoring of its photospheric variability. Understanding such microvariability through hydrodynamic 3D models would require diagnostics from different categories of well-defined photospheric lines with specific formation conditions. Fluctuations in their line strengths may indeed be correlated with radial-velocity excursions and prove useful in identifying observable proxies for their monitoring. From three years of HARPS-N observations of the Sun-as-a-star at lambda /$ sim 100,000, we selected 1000 low-noise spectra and measured line absorption in Fe i Fe ii Mg i Mn i Halpha , Hbeta , Hgamma Na i and the G -band. We examined their variations and likely atmospheric origins, also with respect to simultaneously measured chromospheric emission and apparent radial velocity. Systematic line-strength variability is seen, largely shadowing the solar-cycle evolution of Ca ii H\ \,K emission, but to smaller extents (typically on a sub-percent level). Among iron lines, the greatest amplitudes have been seen for Fe ii in the blue, while the trends change sign among strong lines in the green Mg i triplet and between Balmer lines. Variations in the G -band core are greater than of the full G -band, in line with theoretical predictions. No variation is detected in the semi-forbidden Mg i lambda \,457.1 nm. Hyperfine split Mn i behaves largely similar to Fe i . For lines at longer wavelengths, telluric absorption limits the achievable precision. Microvariability in the solar photospheric spectrum displays systematic signatures among various features. These measure values that are different than the classical Ca ii H\ \,K index, while still reflecting a strong influence from magnetic regions. Although unprecedented precision can be achieved from radial-velocity spectrometers, current resolutions are not adequate to reveal changes in detailed line shapes; in addition, their photometric calibration is not perfect. A forthcoming priority will be to model microvariability in solar magnetic regions, which could also provide desired specifications for future instrumentation toward exoEarth detections.
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