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Dainis Dravins - One of the best experts on this subject based on the ideXlab platform.
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spatially resolved spectroscopy across Stellar Surfaces iv f g and k stars synthetic 3d spectra at hyper high resolution
Astronomy and Astrophysics, 2021Co-Authors: Dainis Dravins, Hans-günter Ludwig, B FreytagAbstract:Context. High-precision Stellar analyses require hydrodynamic 3D modeling. Such models predict changes across Stellar disks of spectral line shapes, asymmetries, and wavelength shifts. For testing models in stars other than the Sun, spatially resolved observations are feasible from differential spectroscopy during exoplanet transits, retrieving spectra of those Stellar surface segments that successively become hidden behind the transiting planet, as demonstrated in Papers I, II, and III. Aims. Synthetic high-resolution spectra over extended spectral regions are now available from 3D models. Similar to other ab initio simulations in astrophysics, these data contain patterns that have not been specifically modeled but may be revealed after analyses to be analogous to those of a large volume of observations. Methods. From five 3D models spanning Teff = 3964-6726 K (spectral types ~K8 V-F3 V), synthetic spectra at hyper-high resolution (λ/Δλ >1 000 000) were analyzed. Selected Fe » I and Fe » II lines at various positions across Stellar disks were searched for characteristic patterns between different types of lines in the same star and for similar lines between different stars. Results. Spectral-line patterns are identified for representative photospheric lines of different strengths, excitation potentials, and ionization levels, thereby encoding the hydrodynamic 3D structure. Line profiles and bisectors are shown for various stars at different positions across Stellar disks. Absolute convective wavelength shifts are obtained as differences to 1D models, where such shifts do not occur. Conclusions. Observable relationships for line properties are retrieved from realistically complex synthetic spectra. Such patterns may also test very detailed 3D modeling, including non-LTE effects. While present results are obtained at hyper-high spectral resolution, the subsequent Paper V examines their practical observability at realistically lower resolutions, and in the presence of noise.
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Spatially resolved spectroscopy across Stellar Surfaces. IV. F, G, and K-stars: synthetic 3D spectra at hyper-high resolution
Astronomy & Astrophysics, 2021Co-Authors: Dainis Dravins, Hans-günter Ludwig, Bernd FreytagAbstract:High-precision Stellar analyses require hydrodynamic 3D modeling. Such models predict changes across Stellar disks of spectral line shapes, asymmetries, and wavelength shifts. For testing models in stars other than the Sun, spatially resolved observations are feasible from differential spectroscopy during exoplanet transits, retrieving spectra of Stellar surface segments that successively become hidden behind the transiting planet, as shown in Papers I, II, and III. Synthetic high-resolution spectra over extended spectral regions are now available from 3D models. Similar to other ab initio simulations, these data contain patterns that have not been specifically modeled but may be revealed after analyses analogous to those of a large volume of observations. From five 3D models spanning T=3964-6726K (approx. spectral types K8V-F3V), synthetic spectra at hyper-high resolution (R>1,000,000) were analyzed. Selected FeI and FeII lines at various positions across Stellar disks were searched for patterns between different lines in the same star and for similar lines between different stars. Such patterns are identified for representative photospheric lines of different strengths, excitation potential, and ionization level, encoding the hydrodynamic 3D structure. Line profiles and bisectors are shown for various stars at different positions across Stellar disks. Absolute convective wavelength shifts are obtained as differences to 1D models, where such shifts do not occur. Observable relationships for line properties are retrieved from realistically complex synthetic spectra. Such patterns may also test very detailed 3D modeling, including non-LTE effects. While present results are obtained at hyper-high spectral resolution, the subsequent Paper V examines their practical observability at realistically lower resolutions, and in the presence of noise.
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spatially resolved spectroscopy across Stellar Surfaces v observational prospects toward earth like exoplanet detection
arXiv: Earth and Planetary Astrophysics, 2021Co-Authors: Dainis Dravins, Hans-günter Ludwig, B FreytagAbstract:Testing 3D hydrodynamic models of Stellar atmospheres is feasible by retrieving spectral line shapes across Stellar disks, using differential spectroscopy during exoplanet transits. From synthetic data at hyper-high spectral resolution, characteristic patterns for FeI and FeII lines were identified in Paper IV from 3D models spanning T=3964-6726K (spectral types approx. K8V-F3V). The observability of patterns among lines of different strength, excitation potential and ionization level are now examined, as observed at ordinary spectral resolutions and in the presence of noise. Time variability in 3D atmospheres induces changes in spectral-line parameters, some of which are correlated. An adequate calibration could identify proxies for the jitter in apparent radial velocity to enable adjustments to actual Stellar radial motion. We also examined the center-to-limb temporal variability. Recovery of spatially resolved line profiles with fitted widths and depths is shown for various noise levels. Signals during exoplanet transit are simulated. In addition to Rossiter-McLaughlin type signatures in apparent radial velocity, analogous effects are shown for line depths and widths. From exoplanet transits, overall Stellar line parameters of width, depth and wavelength position can be retrieved already with moderate efforts, but a very good signal-to-noise ratio is required to reveal the more subtle signatures between subgroups of spectral lines, where finer details of atmospheric structure are encoded. In a solar model, temporal variability shows correlations between jittering in apparent radial velocity and fluctuations in line depth. Since both fluctuations in line depth and jittering in wavelength can be measured from the ground, searches for low-mass exoplanets should explore these to adjust apparent radial velocities to actual Stellar motion.
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spatially resolved spectroscopy across Stellar Surfaces iv f g k stars synthetic 3d spectra at hyper high resolution
arXiv: Solar and Stellar Astrophysics, 2021Co-Authors: Dainis Dravins, Hans-günter Ludwig, B FreytagAbstract:High-precision Stellar analyses require hydrodynamic 3D modeling. Such models predict changes across Stellar disks of spectral line shapes, asymmetries, and wavelength shifts. For testing models in stars other than the Sun, spatially resolved observations are feasible from differential spectroscopy during exoplanet transits, retrieving spectra of Stellar surface segments that successively become hidden behind the transiting planet, as shown in Papers I, II, and III. Synthetic high-resolution spectra over extended spectral regions are now available from 3D models. Similar to other ab initio simulations, these data contain patterns that have not been specifically modeled but may be revealed after analyses analogous to those of a large volume of observations. From five 3D models spanning T=3964-6726K (approx. spectral types K8V-F3V), synthetic spectra at hyper-high resolution (R>1,000,000) were analyzed. Selected FeI and FeII lines at various positions across Stellar disks were searched for patterns between different lines in the same star and for similar lines between different stars. Such patterns are identified for representative photospheric lines of different strengths, excitation potential, and ionization level, encoding the hydrodynamic 3D structure. Line profiles and bisectors are shown for various stars at different positions across Stellar disks. Absolute convective wavelength shifts are obtained as differences to 1D models, where such shifts do not occur. Observable relationships for line properties are retrieved from realistically complex synthetic spectra. Such patterns may also test very detailed 3D modeling, including non-LTE effects. While present results are obtained at hyper-high spectral resolution, the subsequent Paper V examines their practical observability at realistically lower resolutions, and in the presence of noise.
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Spatially resolved spectroscopy across Stellar Surfaces. III. Photospheric Fe I lines across HD189733A (K1 V).
Astronomy & Astrophysics, 2018Co-Authors: Dainis Dravins, Martin Gustavsson, Hans-günter LudwigAbstract:Spectroscopy across spatially resolved Stellar Surfaces reveals spectral line profiles free from rotational broadening, whose gradual changes from disk center toward the Stellar limb reflect an atmospheric fine structure that is possible to model by 3-D hydrodynamics. Previous studies of photospheric spectral lines across Stellar disks exist for the Sun and HD209458 (G0 V) and are now extended to the planet-hosting HD189733A to sample a cooler K-type star and explore the future potential of the method. During exoplanet transit, Stellar surface portions successively become hidden and differential spectroscopy between various transit phases uncovers spectra of small surface segments temporarily hidden behind the planet. In Paper I, observable signatures were predicted quantitatively from hydrodynamic simulations. From observations of HD189733A with the ESO HARPS spectrometer at R=115,000, profiles for stronger and weaker Fe I lines are retrieved at several center-to-limb positions, reaching adequate S/N after averaging over numerous similar lines. Retrieved line profile widths and depths are compared to synthetic ones from models with parameters bracketing those of the target star and are found to be consistent with 3-D simulations. Center-to-limb changes strongly depend on the surface granulation structure and much greater line-width variation is predicted in hotter F-type stars with vigorous granulation than in cooler K-types. Such parameters, obtained from fits to full line profiles, are realistic to retrieve for brighter planet-hosting stars, while their hydrodynamic modeling offers previously unexplored diagnostics for Stellar atmospheric fine structure and 3-D line formation. Precise modeling may be required in searches for Earth-analog exoplanets around K-type stars, whose more tranquil surface granulation and lower ensuing microvariability may enable such detections.
Hans-günter Ludwig - One of the best experts on this subject based on the ideXlab platform.
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spatially resolved spectroscopy across Stellar Surfaces iv f g and k stars synthetic 3d spectra at hyper high resolution
Astronomy and Astrophysics, 2021Co-Authors: Dainis Dravins, Hans-günter Ludwig, B FreytagAbstract:Context. High-precision Stellar analyses require hydrodynamic 3D modeling. Such models predict changes across Stellar disks of spectral line shapes, asymmetries, and wavelength shifts. For testing models in stars other than the Sun, spatially resolved observations are feasible from differential spectroscopy during exoplanet transits, retrieving spectra of those Stellar surface segments that successively become hidden behind the transiting planet, as demonstrated in Papers I, II, and III. Aims. Synthetic high-resolution spectra over extended spectral regions are now available from 3D models. Similar to other ab initio simulations in astrophysics, these data contain patterns that have not been specifically modeled but may be revealed after analyses to be analogous to those of a large volume of observations. Methods. From five 3D models spanning Teff = 3964-6726 K (spectral types ~K8 V-F3 V), synthetic spectra at hyper-high resolution (λ/Δλ >1 000 000) were analyzed. Selected Fe » I and Fe » II lines at various positions across Stellar disks were searched for characteristic patterns between different types of lines in the same star and for similar lines between different stars. Results. Spectral-line patterns are identified for representative photospheric lines of different strengths, excitation potentials, and ionization levels, thereby encoding the hydrodynamic 3D structure. Line profiles and bisectors are shown for various stars at different positions across Stellar disks. Absolute convective wavelength shifts are obtained as differences to 1D models, where such shifts do not occur. Conclusions. Observable relationships for line properties are retrieved from realistically complex synthetic spectra. Such patterns may also test very detailed 3D modeling, including non-LTE effects. While present results are obtained at hyper-high spectral resolution, the subsequent Paper V examines their practical observability at realistically lower resolutions, and in the presence of noise.
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Spatially resolved spectroscopy across Stellar Surfaces. IV. F, G, and K-stars: synthetic 3D spectra at hyper-high resolution
Astronomy & Astrophysics, 2021Co-Authors: Dainis Dravins, Hans-günter Ludwig, Bernd FreytagAbstract:High-precision Stellar analyses require hydrodynamic 3D modeling. Such models predict changes across Stellar disks of spectral line shapes, asymmetries, and wavelength shifts. For testing models in stars other than the Sun, spatially resolved observations are feasible from differential spectroscopy during exoplanet transits, retrieving spectra of Stellar surface segments that successively become hidden behind the transiting planet, as shown in Papers I, II, and III. Synthetic high-resolution spectra over extended spectral regions are now available from 3D models. Similar to other ab initio simulations, these data contain patterns that have not been specifically modeled but may be revealed after analyses analogous to those of a large volume of observations. From five 3D models spanning T=3964-6726K (approx. spectral types K8V-F3V), synthetic spectra at hyper-high resolution (R>1,000,000) were analyzed. Selected FeI and FeII lines at various positions across Stellar disks were searched for patterns between different lines in the same star and for similar lines between different stars. Such patterns are identified for representative photospheric lines of different strengths, excitation potential, and ionization level, encoding the hydrodynamic 3D structure. Line profiles and bisectors are shown for various stars at different positions across Stellar disks. Absolute convective wavelength shifts are obtained as differences to 1D models, where such shifts do not occur. Observable relationships for line properties are retrieved from realistically complex synthetic spectra. Such patterns may also test very detailed 3D modeling, including non-LTE effects. While present results are obtained at hyper-high spectral resolution, the subsequent Paper V examines their practical observability at realistically lower resolutions, and in the presence of noise.
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spatially resolved spectroscopy across Stellar Surfaces v observational prospects toward earth like exoplanet detection
arXiv: Earth and Planetary Astrophysics, 2021Co-Authors: Dainis Dravins, Hans-günter Ludwig, B FreytagAbstract:Testing 3D hydrodynamic models of Stellar atmospheres is feasible by retrieving spectral line shapes across Stellar disks, using differential spectroscopy during exoplanet transits. From synthetic data at hyper-high spectral resolution, characteristic patterns for FeI and FeII lines were identified in Paper IV from 3D models spanning T=3964-6726K (spectral types approx. K8V-F3V). The observability of patterns among lines of different strength, excitation potential and ionization level are now examined, as observed at ordinary spectral resolutions and in the presence of noise. Time variability in 3D atmospheres induces changes in spectral-line parameters, some of which are correlated. An adequate calibration could identify proxies for the jitter in apparent radial velocity to enable adjustments to actual Stellar radial motion. We also examined the center-to-limb temporal variability. Recovery of spatially resolved line profiles with fitted widths and depths is shown for various noise levels. Signals during exoplanet transit are simulated. In addition to Rossiter-McLaughlin type signatures in apparent radial velocity, analogous effects are shown for line depths and widths. From exoplanet transits, overall Stellar line parameters of width, depth and wavelength position can be retrieved already with moderate efforts, but a very good signal-to-noise ratio is required to reveal the more subtle signatures between subgroups of spectral lines, where finer details of atmospheric structure are encoded. In a solar model, temporal variability shows correlations between jittering in apparent radial velocity and fluctuations in line depth. Since both fluctuations in line depth and jittering in wavelength can be measured from the ground, searches for low-mass exoplanets should explore these to adjust apparent radial velocities to actual Stellar motion.
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spatially resolved spectroscopy across Stellar Surfaces iv f g k stars synthetic 3d spectra at hyper high resolution
arXiv: Solar and Stellar Astrophysics, 2021Co-Authors: Dainis Dravins, Hans-günter Ludwig, B FreytagAbstract:High-precision Stellar analyses require hydrodynamic 3D modeling. Such models predict changes across Stellar disks of spectral line shapes, asymmetries, and wavelength shifts. For testing models in stars other than the Sun, spatially resolved observations are feasible from differential spectroscopy during exoplanet transits, retrieving spectra of Stellar surface segments that successively become hidden behind the transiting planet, as shown in Papers I, II, and III. Synthetic high-resolution spectra over extended spectral regions are now available from 3D models. Similar to other ab initio simulations, these data contain patterns that have not been specifically modeled but may be revealed after analyses analogous to those of a large volume of observations. From five 3D models spanning T=3964-6726K (approx. spectral types K8V-F3V), synthetic spectra at hyper-high resolution (R>1,000,000) were analyzed. Selected FeI and FeII lines at various positions across Stellar disks were searched for patterns between different lines in the same star and for similar lines between different stars. Such patterns are identified for representative photospheric lines of different strengths, excitation potential, and ionization level, encoding the hydrodynamic 3D structure. Line profiles and bisectors are shown for various stars at different positions across Stellar disks. Absolute convective wavelength shifts are obtained as differences to 1D models, where such shifts do not occur. Observable relationships for line properties are retrieved from realistically complex synthetic spectra. Such patterns may also test very detailed 3D modeling, including non-LTE effects. While present results are obtained at hyper-high spectral resolution, the subsequent Paper V examines their practical observability at realistically lower resolutions, and in the presence of noise.
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Spatially resolved spectroscopy across Stellar Surfaces. III. Photospheric Fe I lines across HD189733A (K1 V).
Astronomy & Astrophysics, 2018Co-Authors: Dainis Dravins, Martin Gustavsson, Hans-günter LudwigAbstract:Spectroscopy across spatially resolved Stellar Surfaces reveals spectral line profiles free from rotational broadening, whose gradual changes from disk center toward the Stellar limb reflect an atmospheric fine structure that is possible to model by 3-D hydrodynamics. Previous studies of photospheric spectral lines across Stellar disks exist for the Sun and HD209458 (G0 V) and are now extended to the planet-hosting HD189733A to sample a cooler K-type star and explore the future potential of the method. During exoplanet transit, Stellar surface portions successively become hidden and differential spectroscopy between various transit phases uncovers spectra of small surface segments temporarily hidden behind the planet. In Paper I, observable signatures were predicted quantitatively from hydrodynamic simulations. From observations of HD189733A with the ESO HARPS spectrometer at R=115,000, profiles for stronger and weaker Fe I lines are retrieved at several center-to-limb positions, reaching adequate S/N after averaging over numerous similar lines. Retrieved line profile widths and depths are compared to synthetic ones from models with parameters bracketing those of the target star and are found to be consistent with 3-D simulations. Center-to-limb changes strongly depend on the surface granulation structure and much greater line-width variation is predicted in hotter F-type stars with vigorous granulation than in cooler K-types. Such parameters, obtained from fits to full line profiles, are realistic to retrieve for brighter planet-hosting stars, while their hydrodynamic modeling offers previously unexplored diagnostics for Stellar atmospheric fine structure and 3-D line formation. Precise modeling may be required in searches for Earth-analog exoplanets around K-type stars, whose more tranquil surface granulation and lower ensuing microvariability may enable such detections.
Hiva Pazira - One of the best experts on this subject based on the ideXlab platform.
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Spatially resolved spectroscopy across Stellar Surfaces. II. High-resolution spectra across HD209458 (G0V)
Astronomy & Astrophysics, 2017Co-Authors: Dainis Dravins, Hans-günter Ludwig, Erik Dahlén, Hiva PaziraAbstract:CONTEXT: High-resolution spectroscopy across spatially resolved Stellar Surfaces aims at obtaining spectral-line profiles that are free from rotational broadening; the gradual changes of these profiles from disk center toward the Stellar limb reveal properties of atmospheric fine structure, which are possible to model with 3-D hydrodynamics. AIMS: Previous such studies have only been carried out for the Sun but are now extended to other stars. In this work, profiles of photospheric spectral lines are retrieved across the disk of the planet-hosting star HD209458 (G0V). METHODS: During exoplanet transit, Stellar surface portions successively become hidden and differential spectroscopy provides spectra of small surface segments temporarily hidden behind the planet. The method was elaborated in Paper I, with observable signatures quantitatively predicted from hydrodynamic simulations. RESULTS: From observations of HD209458 with spectral resolution R=80,000, photospheric FeI line profiles are obtained at several center-to-limb positions, reaching adequately high S/N after averaging over numerous similar lines CONCLUSIONS: Retrieved line profiles are compared to synthetic line profiles. Hydrodynamic 3-D models predict, and current observations confirm, that photospheric absorption lines become broader and shallower toward the Stellar limb, reflecting that horizontal velocities in Stellar granulation are greater than vertical velocities. Additional types of 3-D signatures will become observable with the highest resolution spectrometers at large telescopes.
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Spatially resolved spectroscopy across Stellar Surfaces : I. Using exoplanet transits to analyze 3D Stellar atmospheres
Astronomy & Astrophysics, 2017Co-Authors: Dainis Dravins, Hans-günter Ludwig, Erik Dahlén, Hiva PaziraAbstract:Context. High-precision Stellar analyses require hydrodynamic modeling to interpret chemical abundances or oscillation modes. Exoplanet atmosphere studies require Stellar background spectra to be known along the transit path while detection of Earth analogs require Stellar microvariability to be understood. Hydrodynamic 3D models can be computed for widely different stars but have been tested in detail only for the Sun with its resolved surface features. Model predictions include spectral line shapes, asymmetries, and wavelength shifts, and their center-To-limb changes across Stellar disks. Aims. We observe high-resolution spectral line profiles across spatially highly resolved Stellar Surfaces, which are free from the effects of spatial smearing and rotational broadening present in full-disk spectra, enabling comparisons to synthetic profiles from 3D models. Methods. During exoplanet transits, successive Stellar surface portions become hidden and differential spectroscopy between various transit phases provides spectra of small surface segments temporarily hidden behind the planet. Planets cover no more than ~1% of any main-sequence star, enabling high spatial resolution but demanding very precise observations. Realistically measurable quantities are identified through simulated observations of synthetic spectral lines. Results. In normal stars, line profile ratios between various transit phases may vary by 0.5%, requiring S/N 5000 for meaningful spectral reconstruction. While not yet realistic for individual spectral lines, this is achievable for cool stars by averaging over numerous lines with similar parameters. Conclusions. For bright host stars of large transiting planets, spatially resolved spectroscopy is currently practical. More observable targets are likely to be found in the near future by ongoing photometric searches.
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spatially resolved spectroscopy across Stellar Surfaces ii high resolution spectra across hd 209458 g0 v
Astronomy and Astrophysics, 2017Co-Authors: Dainis Dravins, Hans-günter Ludwig, Svenerik Dahlen, Hiva PaziraAbstract:Context. High-resolution spectroscopy across spatially resolved Stellar Surfaces aims at obtaining spectral-line profiles that are free from rotational broadening; the gradual changes of these profiles from disk center toward the Stellar limb reveal properties of atmospheric fine structure, which are possible to model with 3D hydrodynamics. Aims. Previous such studies have only been carried out for the Sun but are now extended to other stars. In this work, profiles of photospheric spectral lines are retrieved across the disk of the planet-hosting star HD 209458 (G0 V). Methods. During exoplanet transit, Stellar surface portions successively become hidden and differential spectroscopy provides spectra of small surface segments temporarily hidden behind the planet. The method was elaborated in Paper I, with observable signatures quantitatively predicted from hydrodynamic simulations. Results. From observations of HD 209458 with spectral resolution λ/ Δλ ~ 80 000, photospheric Fe I line profiles are obtained at several center-To-limb positions, reaching adequately high S/N after averaging over numerous similar lines. Conclusions. Retrieved line profiles are compared to synthetic line profiles. Hydrodynamic 3D models predict, and current observations confirm, that photospheric absorption lines become broader and shallower toward the Stellar limb, reflecting that horizontal velocities in Stellar granulation are greater than vertical velocities. Additional types of 3D signatures will become observable with the highest resolution spectrometers at large telescopes. (Less)
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spatially resolved spectroscopy across Stellar Surfaces i using exoplanet transits to analyze 3 d Stellar atmospheres
arXiv: Solar and Stellar Astrophysics, 2017Co-Authors: Dainis Dravins, Hans-günter Ludwig, Erik Dahlén, Hiva PaziraAbstract:CONTEXT: High-precision Stellar analyses require hydrodynamic modeling to interpret chemical abundances or oscillation modes. Exoplanet atmosphere studies require Stellar background spectra to be known along the transit path while detection of Earth analogs require Stellar microvariability to be understood. Hydrodynamic 3-D models can be computed for widely different stars but have been tested in detail only for the Sun with its resolved surface features. Model predictions include spectral line shapes, asymmetries, and wavelength shifts, and their center-to-limb changes across Stellar disks. AIMS: To observe high-resolution spectral line profiles across spatially highly resolved Stellar Surfaces, which are free from the effects of spatial smearing and rotational broadening present in full-disk spectra, enabling comparisons to synthetic profiles from 3-D models. METHODS: During exoplanet transits, successive Stellar surface portions become hidden and differential spectroscopy between various transit phases provides spectra of small surface segments temporarily hidden behind the planet. Planets cover no more than about 1% of any main-sequence star, enabling high spatial resolution but demanding very precise observations. Realistically measurable quantities are identified through simulated observations of synthetic spectral lines. RESULTS: In normal stars, line profile ratios between various transit phases may vary by some 0.5%, requiring S/N ratios of 5,000 or more for meaningful spectral reconstruction. While not yet realistic for individual spectral lines, this is achievable for cool stars by averaging over numerous lines with similar parameters. CONCLUSIONS: For bright host stars of large transiting planets, spatially resolved spectroscopy is currently practical. More observable targets are likely to be found in the near future by ongoing photometric searches.
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Exoplanet transits enable high-resolution spectroscopy across spatially resolved Stellar Surfaces
arXiv: Solar and Stellar Astrophysics, 2016Co-Authors: Dainis Dravins, Hans-günter Ludwig, Erik Dahlén, Hiva PaziraAbstract:Observations of Stellar Surfaces - except for the Sun - are hampered by their tiny angular extent, while observed spectral lines are smeared by averaging over the Stellar surface, and by Stellar rotation. Exoplanet transits can be used to analyze Stellar atmospheric structure, yielding high-resolution spectra across spatially highly resolved Stellar Surfaces, free from effects of spatial smearing and the rotational wavelength broadening present in full-disk spectra. During a transit, Stellar surface portions successively become hidden, and differential spectroscopy between various transit phases provides spectra of those surface segments then hidden behind the planet. The small area subtended by even a large planet (about 1% of a main-sequence star) offers high spatial resolution but demands very precise observations. We demonstrate the reconstruction of photospheric FeI line profiles at a spectral resolution R=80,000 across the surface of the solar-type star HD209458. Any detailed understanding of Stellar atmospheres requires modeling with 3-dimensional hydrodynamics. The properties predicted by such models are mapped onto the precise spectral-line shapes, asymmetries and wavelength shifts, and their variation from the center to the limb across any Stellar disk. This method provides a tool for testing and verifying such models. The method will soon become applicable to more diverse types of stars, thanks to new spectrometers on very large telescopes, and since ongoing photometric searches are expected to discover additional bright host stars of transiting exoplanets.
B Freytag - One of the best experts on this subject based on the ideXlab platform.
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spatially resolved spectroscopy across Stellar Surfaces iv f g and k stars synthetic 3d spectra at hyper high resolution
Astronomy and Astrophysics, 2021Co-Authors: Dainis Dravins, Hans-günter Ludwig, B FreytagAbstract:Context. High-precision Stellar analyses require hydrodynamic 3D modeling. Such models predict changes across Stellar disks of spectral line shapes, asymmetries, and wavelength shifts. For testing models in stars other than the Sun, spatially resolved observations are feasible from differential spectroscopy during exoplanet transits, retrieving spectra of those Stellar surface segments that successively become hidden behind the transiting planet, as demonstrated in Papers I, II, and III. Aims. Synthetic high-resolution spectra over extended spectral regions are now available from 3D models. Similar to other ab initio simulations in astrophysics, these data contain patterns that have not been specifically modeled but may be revealed after analyses to be analogous to those of a large volume of observations. Methods. From five 3D models spanning Teff = 3964-6726 K (spectral types ~K8 V-F3 V), synthetic spectra at hyper-high resolution (λ/Δλ >1 000 000) were analyzed. Selected Fe » I and Fe » II lines at various positions across Stellar disks were searched for characteristic patterns between different types of lines in the same star and for similar lines between different stars. Results. Spectral-line patterns are identified for representative photospheric lines of different strengths, excitation potentials, and ionization levels, thereby encoding the hydrodynamic 3D structure. Line profiles and bisectors are shown for various stars at different positions across Stellar disks. Absolute convective wavelength shifts are obtained as differences to 1D models, where such shifts do not occur. Conclusions. Observable relationships for line properties are retrieved from realistically complex synthetic spectra. Such patterns may also test very detailed 3D modeling, including non-LTE effects. While present results are obtained at hyper-high spectral resolution, the subsequent Paper V examines their practical observability at realistically lower resolutions, and in the presence of noise.
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spatially resolved spectroscopy across Stellar Surfaces v observational prospects toward earth like exoplanet detection
arXiv: Earth and Planetary Astrophysics, 2021Co-Authors: Dainis Dravins, Hans-günter Ludwig, B FreytagAbstract:Testing 3D hydrodynamic models of Stellar atmospheres is feasible by retrieving spectral line shapes across Stellar disks, using differential spectroscopy during exoplanet transits. From synthetic data at hyper-high spectral resolution, characteristic patterns for FeI and FeII lines were identified in Paper IV from 3D models spanning T=3964-6726K (spectral types approx. K8V-F3V). The observability of patterns among lines of different strength, excitation potential and ionization level are now examined, as observed at ordinary spectral resolutions and in the presence of noise. Time variability in 3D atmospheres induces changes in spectral-line parameters, some of which are correlated. An adequate calibration could identify proxies for the jitter in apparent radial velocity to enable adjustments to actual Stellar radial motion. We also examined the center-to-limb temporal variability. Recovery of spatially resolved line profiles with fitted widths and depths is shown for various noise levels. Signals during exoplanet transit are simulated. In addition to Rossiter-McLaughlin type signatures in apparent radial velocity, analogous effects are shown for line depths and widths. From exoplanet transits, overall Stellar line parameters of width, depth and wavelength position can be retrieved already with moderate efforts, but a very good signal-to-noise ratio is required to reveal the more subtle signatures between subgroups of spectral lines, where finer details of atmospheric structure are encoded. In a solar model, temporal variability shows correlations between jittering in apparent radial velocity and fluctuations in line depth. Since both fluctuations in line depth and jittering in wavelength can be measured from the ground, searches for low-mass exoplanets should explore these to adjust apparent radial velocities to actual Stellar motion.
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spatially resolved spectroscopy across Stellar Surfaces iv f g k stars synthetic 3d spectra at hyper high resolution
arXiv: Solar and Stellar Astrophysics, 2021Co-Authors: Dainis Dravins, Hans-günter Ludwig, B FreytagAbstract:High-precision Stellar analyses require hydrodynamic 3D modeling. Such models predict changes across Stellar disks of spectral line shapes, asymmetries, and wavelength shifts. For testing models in stars other than the Sun, spatially resolved observations are feasible from differential spectroscopy during exoplanet transits, retrieving spectra of Stellar surface segments that successively become hidden behind the transiting planet, as shown in Papers I, II, and III. Synthetic high-resolution spectra over extended spectral regions are now available from 3D models. Similar to other ab initio simulations, these data contain patterns that have not been specifically modeled but may be revealed after analyses analogous to those of a large volume of observations. From five 3D models spanning T=3964-6726K (approx. spectral types K8V-F3V), synthetic spectra at hyper-high resolution (R>1,000,000) were analyzed. Selected FeI and FeII lines at various positions across Stellar disks were searched for patterns between different lines in the same star and for similar lines between different stars. Such patterns are identified for representative photospheric lines of different strengths, excitation potential, and ionization level, encoding the hydrodynamic 3D structure. Line profiles and bisectors are shown for various stars at different positions across Stellar disks. Absolute convective wavelength shifts are obtained as differences to 1D models, where such shifts do not occur. Observable relationships for line properties are retrieved from realistically complex synthetic spectra. Such patterns may also test very detailed 3D modeling, including non-LTE effects. While present results are obtained at hyper-high spectral resolution, the subsequent Paper V examines their practical observability at realistically lower resolutions, and in the presence of noise.
Bernd Freytag - One of the best experts on this subject based on the ideXlab platform.
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Spatially resolved spectroscopy across Stellar Surfaces. IV. F, G, and K-stars: synthetic 3D spectra at hyper-high resolution
Astronomy & Astrophysics, 2021Co-Authors: Dainis Dravins, Hans-günter Ludwig, Bernd FreytagAbstract:High-precision Stellar analyses require hydrodynamic 3D modeling. Such models predict changes across Stellar disks of spectral line shapes, asymmetries, and wavelength shifts. For testing models in stars other than the Sun, spatially resolved observations are feasible from differential spectroscopy during exoplanet transits, retrieving spectra of Stellar surface segments that successively become hidden behind the transiting planet, as shown in Papers I, II, and III. Synthetic high-resolution spectra over extended spectral regions are now available from 3D models. Similar to other ab initio simulations, these data contain patterns that have not been specifically modeled but may be revealed after analyses analogous to those of a large volume of observations. From five 3D models spanning T=3964-6726K (approx. spectral types K8V-F3V), synthetic spectra at hyper-high resolution (R>1,000,000) were analyzed. Selected FeI and FeII lines at various positions across Stellar disks were searched for patterns between different lines in the same star and for similar lines between different stars. Such patterns are identified for representative photospheric lines of different strengths, excitation potential, and ionization level, encoding the hydrodynamic 3D structure. Line profiles and bisectors are shown for various stars at different positions across Stellar disks. Absolute convective wavelength shifts are obtained as differences to 1D models, where such shifts do not occur. Observable relationships for line properties are retrieved from realistically complex synthetic spectra. Such patterns may also test very detailed 3D modeling, including non-LTE effects. While present results are obtained at hyper-high spectral resolution, the subsequent Paper V examines their practical observability at realistically lower resolutions, and in the presence of noise.
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Pathways for Observing Stellar Surfaces Using 3D Hydrodynamical Simulations of Evolved Stars
EAS Publications Series, 2015Co-Authors: Andrea Chiavassa, Bernd FreytagAbstract:Evolved stars are among the largest and brightest stars and they are ideal targets for the new generation of sensitive, high resolution instrumentation that provides spectrophotometric, interferometric, astrometric, and imaging observables. The interpretation of the complex Stellar surface images requires numerical simulations of Stellar convection that take into account multi-dimensional time-dependent radiation hydrodynamics with realistic input physics. We show how the evolved star simulations are obtained using the radiative hydrodynamics code CO5BOLD and how the accurate observables are computed with the post-processing radiative transfer code Optim3D. The synergy between observations and theoretical work is supported by a proper and quantitative analysis using these simulations, and by strong constraints from the observational side.
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3d hydrodynamical simulations of evolved stars and observations of Stellar Surfaces
Conference on Why Galaxies Care About AGB Stars III: A Closer Look in Space and Time JUL 28-AUG 01 2014 Univ Vienna Vienna AUSTRIA, 2015Co-Authors: A Chiavassa, Bernd FreytagAbstract:Evolved stars are among the largest and brightest stars and they are ideal targets for the new generation of sensitive, high resolution instrumentation that provides spectrophotometric, interferome ...
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3D hydrodynamical simulations of evolved stars and observations of Stellar Surfaces
arXiv: Solar and Stellar Astrophysics, 2014Co-Authors: Andrea Chiavassa, Bernd FreytagAbstract:Evolved stars are among the largest and brightest stars and they are ideal targets for the new generation of sensitive, high resolution instrumentation that pro- vides spectrophotometric, interferometric, astrometric, and imaging observables. The interpretation of the complex Stellar surface images requires numerical simulations of Stellar convection that take into account multi-dimensional time-dependent radiation hydrodynamics with realistic input physics. We show how the evolved star simulations are obtained using the radiative hydrodynamics code CO5BOLD and how the accurate observables are computed with the post-processing radiative transfer code Optim3D. The synergy between observations and theoretical work is supported by a proper and quantitative analysis using these simulations, and by strong constraints from the obser- vational side.
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3D hydrodynamical simulations to interpret observations of Stellar Surfaces of red supergiant stars
EAS Publications Series, 2013Co-Authors: Andrea Chiavassa, Bernd Freytag, Bertrand PlezAbstract:As red supergiants are the largest and brightest stars, they are ideal targets for the new generation of sensitive, high resolution instrumentation that provides spectrophotometric, interferometric, astrometric, and imaging observables. The interpretation of the complex Stellar surface images requires numerical simulations of Stellar convection that take into account multi-dimensional time-dependent radiation hydrodynamics with realistic input physics. We show the results obtained with the synergy between the radiative hydrodynamics code CO5BOLD and the post-processing radiative transfer code Optim3D. Such simulations support a proper and quantitative analysis of these observations, and the observations provide the theoretical work with strong constraints.
