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1.
  • Lindgren, Sara, et al. (författare)
  • A photometric calibration for M dwarfs based on high-resolution infrared spectrscopy
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Context. M dwarfs are, by number, the dominant stellar population in the local Galaxy. We have previously shown that the stellar parameters of individual M dwarfs can be determined with good accuracy using high-resolution infrared spectroscopy. Since this method is time-consuming the use of empirical calibrations based on photometry or low-resolution spectra is preferable for studies of large samples. In earlier work we showed that available photometric calibrations for M dwarfs have offsets compared to our high- resolution metallicity results.Aims. We use a sample of 33 late K and M dwarfs with accurately determined metallicities to derive a new photometric calibration for M dwarfs. The aim is to achieve a calibration with lower uncertainty and better agreement with spectroscopic results.Methods. We explored the B, V, J, H, K, g, r, i magnitudes to find combinations that show a correlation between the metallicity and the position in a color-magnitude diagram. We used 5-fold cross-validation and the corrected Akaike information criterion to find a polynomial model that minimizes the information lost, exploring different polynomial degrees, with and without cross-terms. The coefficients were determined through a weighted least-squares solution against our calibration sample.Results. We present a new photometric metallicity calibration for M dwarfs, where the metallicity is given by a linear relation and onecross-termoftheMKSmagnitudeandtheV−(JHK) or B−(JHK) colors. The new calibration relations have root-mean-square deviation values with respect to the calibration sample of 0.11-0.12 dex, which is about 0.1 dex lower than for previous photometric calibrations, and we also achieve a substantial improvement of the value of the adjusted squared multiple correlation coefficient. We furthermore show that our calibration compares well with two spectroscopic calibrations. Comparing synthetic calculated iso- metallicity lines with our empirical calibration, we find a good agreement of the shapes and slopes.Conclusions. Compared to previous calibrations our new photometric calibration shows improvement in all statistical tests performed. Through our testing of several polynomials we conclude that the inclusion of a cross-term between absolute magnitude and color is important for the performance of the photometric calibration. Applying our photometric calibration to a sample of M dwarfs known to host planets points towards a possible giant planet-metallicity correlation for M dwarfs.
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2.
  • Wehrhahn, Ansgar, et al. (författare)
  • CRIRES+ detection of H2O and CO in the transmission spectra of WASP-107 b
  • 2022
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • WASP-107 b is a warm super-Neptune with a large extended atmosphere orbiting a bright K dwarf of solar composition. The planet's size and the brightness of its stellar host make it highly amenable to atmospheric characterisation, with previous detections of both He and H2O. We observe it here for the first time in high-resolution spectroscopy in the K-band. To obtain a transmission spectrum of the exoplanet atmosphere, we observe a transit event of WASP-107 b for a total of 5.4 hours (2.7 hours in transit) in the K-band with an average SNR = 64 for each exposure using the high-resolution infrared CRIRES+ spectrograph on the Very Large Telescope on Cerro Paranal, Chile. We aim to demonstrate the capabilities of this new instrument for exoplanet characterisation by searching for the presence of molecular features of key chemical species in the atmosphere with spectral lines detectable in this band, such as CO, CO2, H2O, and CH4. The search for particular chemical species is conducted by using the cross-correlation method on the observed spectra. The transit spectroscopy observations are first cleaned from the stellar and telluric features using the SYSREM algorithm, and the remaining spectral information is then compared to a model transmission spectrum. The model transmission spectrum is obtained using the petitRADTRANS code based on expectations for a warm Neptune-class planet and the observed orbital parameters. We report the detection of H2O in the atmosphere of WASP-107 b with 4.71 sigma significance, as well as a detection of CO at 3.46 sigma. The velocities of these detections show signs of atmospheric weather patterns, such as day-to-night-side temperature gradients. We do not detect the presence of CO2 or CH4. Our results confirm the chemical composition of the WASP-107 b's atmosphere and pave the way for efficient atmospheric studies of other planets of the same class. They show that the newly upgraded high-resolution spectrograph CRIRES+ is suitable for exoplanet transit observations. All detections and non-detections are in agreement with previous transmission studies of WASP-107 b based on low-resolution spectroscopy.
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