The STAGGER-grid: A grid of 3D stellar atmosphere models

Chiavassa, A.; Casagrande, Luca; Collet, Remo; Magic, Zazralt; Bigot, Lionel; Thévenin, F.; Asplund, Martin

doi:10.1051/0004-6361/201732147

Cited by 66 publications

(73 citation statements)

References 52 publications

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“…But these velocities were computed by comparing observed spectra against AMBRE model spectra which do not allow for convective motions in stellar atmospheres, resulting in blueshifts of many spectral lines. As a consequence, velocities of median spectra of dwarfs are found to be positive when compared to 3D stellar atmosphere models of the S grid (Chiavassa et al 2018). The effect is less pronounced in giants and is related to the fact that only synthetic spectra of dwarfs were used in computation of RV_synt values.…”

Section: Derivation Of the Final Valuesmentioning

confidence: 91%

The GALAH survey: accurate radial velocities and library of observed stellar template spectra

Zwitter

Kos

Chiavassa

et al. 2018

Monthly Notices of the Royal Astronomical Society

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GALAH is a large-scale magnitude-limited southern stellar spectroscopic survey. Its second data release (GALAH DR2) provides values of stellar parameters and abundances of 23 elements for 342,682 stars (Buder et al.). Here we add a description of the public release of radial velocities with a typical accuracy of 0.1 km s −1 for 336,215 of these stars, achievable due to the large wavelength coverage, high resolving power and good signal to noise ratio of the observed spectra, but also because convective motions in stellar atmosphere and gravitational redshift from the star to the observer are taken into account. In the process we derive medians of observed spectra which are nearly noiseless, as they are obtained from between 100 and 1116 observed spectra belonging to the same bin with a width of 50 K in temperature, 0.2 dex in gravity, and 0.1 dex in metallicity. Publicly released 1181 median spectra have a resolving power of 28,000 and trace the well-populated stellar types with metallicities between −0.6 and +0.3. Note that radial velocities from GALAH are an excellent match to the accuracy of velocity components along the sky plane derived by Gaia for the same stars. The level of accuracy achieved here is adequate for studies of dynamics within stellar clusters, associations and streams in the Galaxy. So it may be relevant for studies of the distribution of dark matter.

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Section: Derivation Of the Final Valuesmentioning

confidence: 91%

The GALAH survey: accurate radial velocities and library of observed stellar template spectra

Zwitter

Kos

Chiavassa

et al. 2018

Monthly Notices of the Royal Astronomical Society

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“…At this stage, the median spectrum is not guaranteed to be at zero velocity due to the combined effects of convective line shifts and gravitational redshifts (Asplund et al 2000;Allende Prieto et al 2013). We therefore use the grid of synthetic spectra (Chiavassa et al 2018) computed with 3D hydrodynamical stellar atmosphere models with the code (Magic et al 2013), which include the effects of convective motions in stellar atmospheres. Finally, we incorporate the effects of gravitational redshift, to put spectra of different stellar types on the same scale and thus allows us to speak about the accuracy and not just the precision of radial velocities.…”

Section: Alternate Radial Velocitiesmentioning

confidence: 99%

The GALAH Survey: second data release

Buder

Asplund

Duong

et al. 2018

Monthly Notices of the Royal Astronomical Society

364

447

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The Galactic Archaeology with HERMES (GALAH) survey is a large-scale stellar spectroscopic survey of the Milky Way and designed to deliver chemical information complementary to a large number of stars covered by the Gaia mission. We present the GALAH second public data release (GALAH DR2) containing 342,682 stars. For these stars, the GALAH collaboration provides stellar parameters and abundances for up to 23 elements to the community. Here we present the target selection, observation, data reduction and detailed explanation of how the spectra were analysed to estimate stellar parameters and element abundances. For the stellar analysis, we have used a multi-step approach. We use the physics-driven spectrum synthesis of Spectroscopy Made Easy (SME) to derive stellar labels (T eff , log g, [Fe/H], [X/Fe], v mic , v sin i, A K S ) for a representative training set of stars. This information is then propagated to the whole survey with the data-driven method of The Cannon. Special care has been exercised in the spectral synthesis to only consider spectral lines that have reliable atomic input data and are little affected by blending lines. Departures from local thermodynamic equilibrium (LTE) are considered for several key elements, including Li, O, Na, Mg, Al, Si, and Fe, using 1D stellar atmosphere models. Validation tests including repeat observations, Gaia benchmark stars, open and globular clusters, and K2 asteroseismic targets lend confidence to our methods and results. Combining the GALAH DR2 catalogue with the kinematic information from Gaia will enable a wide range of Galactic Archaeology studies, with unprecedented detail, dimensionality, and scope.

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“…The RHD simulations grid cover a large part of the HR diagram, including the evolutionary phases from the main sequence over the turnoff up to the red-giant branch for low-mass stars (Magic et al 2013). The simulation used in this work has been employed to compute synthetic spectra in the same spectral range as the observations with the multidimensional pure-LTE radiative transfer code Optim3D (Chiavassa et al 2009;Chiavassa et al 2018). The code takes into account the Doppler shifts occurring due to convective motions and solves monochromatically for the emerging intensity, including extensive atomic and molecular continuum and line opacity data from UV to far-IR.…”

Section: Observationsmentioning

confidence: 99%

The High-resolution Transmission Spectrum of HD 189733b Interpreted with Atmospheric Doppler Shifts from Three-dimensional General Circulation Models

Flowers¹,

Brogi²,

Rauscher³

et al. 2019

Self Cite

106

114

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The signature of wind patterns caused by the interplay of rotation and energy redistribution in hot Jupiters is detectable at high spectral resolution, yet no direct comparison has been attempted between predictions from general circulation models (GCMs) and observed high-resolution spectra. We present the first of such comparisons on nearinfrared transmission spectra of the hot Jupiter HD 189733b. Exploring twelve rotation rates and two chemical regimes, we have created model spectra from 3-D GCMs and cross-correlated them with the observed spectra. Comparing our models against those of HD 189733b, we obtain three key results: (1) we confirm CO and H 2 O in the planet's atmosphere at a detection significance of 8.2σ; (2) we recover the signature of ∼km/s day-to-night winds at ∼mbar pressures; and (3) we constrain the rotation period of the planet to between 1.2 and 4.69 days (synchronous rotation (2.2 days) remains consistent with existing observations). Our results do not suffer from the shortcomings of 1-D models as cross correlation templates -mainly that these models tend to over-constrain the slower rotation rates and show evidence for anomalous blue shifts. Our 3-D models instead match the observed line-of-sight velocity of this planet by self-consistently including the effects of high-altitude day-to-night winds. Overall, we find a high degree of consistency between HD 189733b observations and our GCM-based spectra, implying that the physics and chemistry are adequately described in current 3-D forward models for the purpose of interpreting observations at high spectral resolution.

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The STAGGER-grid: A grid of 3D stellar atmosphere models

Cited by 66 publications

References 52 publications

The GALAH survey: accurate radial velocities and library of observed stellar template spectra

The GALAH survey: accurate radial velocities and library of observed stellar template spectra

The GALAH Survey: second data release

The High-resolution Transmission Spectrum of HD 189733b Interpreted with Atmospheric Doppler Shifts from Three-dimensional General Circulation Models

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