| 1. |
- Lee, Elspeth K.H., et al.
(författare)
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3D Radiative Transfer for Exoplanet Atmospheres. gCMCRT : A GPU-accelerated MCRT Code
- 2022
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 929:2
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Tidskriftsartikel (refereegranskat)abstract
- Radiative transfer (RT) is a key component for investigating atmospheres of planetary bodies. With the 3D nature of exoplanet atmospheres being important in giving rise to their observable properties, accurate and fast 3D methods are required to be developed to meet future multidimensional and temporal data sets. We develop an open-source GPU RT code, gCMCRT, a Monte Carlo RT forward model for general use in planetary atmosphere RT problems. We aim to automate the post-processing pipeline, starting from direct global circulation model (GCM) output to synthetic spectra. We develop albedo, emission, and transmission spectra modes for 3D and 1D input structures. We include capability to use correlated-k and high-resolution opacity tables, the latter of which can be Doppler-shifted inside the model. We post-process results from several GCM groups, including ExoRad, SPARC/MITgcm THOR, UK Met Office UM, Exo-FMS, and the Rauscher model. Users can therefore take advantage of desktop and HPC GPU computing solutions. gCMCRT is well suited for post-processing large GCM model grids produced by members of the community and for high-resolution 3D investigations.
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| 2. |
- Nandakumar, Govind, et al.
(författare)
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Composition of Giants 1° North of the Galactic Center : Detailed Abundance Trends for 21 Elements Observed with IGRINS
- 2024
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Ingår i: Astrophysical Journal. - 0004-637X. ; 964:1
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Tidskriftsartikel (refereegranskat)abstract
- We report the first high-resolution, detailed abundances of 21 elements for giants in the Galactic bulge/bar within 1° of the Galactic plane, where high extinction has rendered such studies challenging. Our high-signal-to-noise-ratio and high-resolution, near-infrared spectra of seven M giants in the inner bulge, located at (l, b) = (0°, +1°), are observed using the IGRINS spectrograph. We report the first multichemical study of the inner Galactic bulge by investigating, relative to a robust new solar neighborhood sample, the abundance trends of 21 elements, including the relatively difficult to study heavy elements. The elements studied are: F, Mg, Si, S, Ca, Na, Al, K, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Ce, Nd, and Yb. We investigate bulge membership of all seven stars using distances and orbital simulations, and we find that the most metal-poor star may be a halo interloper. Our investigation also shows that the inner bulge as close as 1° north of the Galactic Center displays a similarity to the inner disk sequence, following the high-[α/Fe] envelope of the solar vicinity metal-rich population, though no firm conclusions for a different enrichment history are evident from this sample. We find a small fraction of metal-poor stars ([Fe/H] > −0.5), but most of our stars are mainly of supersolar metallicity. Fluorine is found to be enhanced at high metallicity compared to the solar neighborhood, but confirmation with a larger sample is required. We will apply this approach to explore the populations of the nuclear stellar disk and the nuclear star cluster.
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| 3. |
- Prinoth, Bibiana, et al.
(författare)
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Titanium oxide and chemical inhomogeneity in the atmosphere of the exoplanet WASP-189 b
- 2022
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 6:4, s. 449-457
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Tidskriftsartikel (refereegranskat)abstract
- The temperature of an atmosphere decreases with increasing altitude, unless a shortwave absorber that causes a temperature inversion exists. Ozone plays this role in the Earth’s atmosphere. In the atmospheres of highly irradiated exoplanets, the shortwave absorbers are predicted to be titanium oxide (TiO) and vanadium oxide (VO). Detections of TiO and VO have been claimed using both low-, and high- spectral-resolution observations, but subsequent observations have failed to confirm these claims or overturned them. Here we report the unambiguous detection of TiO in the ultra-hot Jupiter WASP-189 b using high-resolution transmission spectroscopy. This detection is based on applying the cross-correlation technique to many spectral lines of TiO from 460 to 690 nm. Moreover, we report detections of metals, including neutral and singly ionized iron and titanium, as well as chromium, magnesium, vanadium and manganese (Fe, Fe+, Ti, Ti+, Cr, Mg, V, Mn). The line positions of the detected species differ, which we interpret as a consequence of spatial gradients in their chemical abundances, such that they exist in different regions or dynamical regimes. This is direct observational evidence for the three-dimensional thermochemical stratification of an exoplanet atmosphere derived from high-resolution ground-based spectroscopy.
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| 4. |
- Ryde, Nils, et al.
(författare)
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Fluorine in the Solar Neighborhood : The Need for Several Cosmic Sources
- 2020
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Ingår i: Astrophysical Journal. - : Institute of Physics (IOP). - 0004-637X .- 1538-4357. ; 893:1
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Tidskriftsartikel (refereegranskat)abstract
- The cosmic origin of fluorine is still not well constrained. Several nucleosynthetic channels at different phases of stellar evolution have been suggested, but these must be constrained by observations. For this, the fluorine abundance trend with metallicity spanning a wide range is required. Our aim is to determine stellar abundances of fluorine for -1.1 < [Fe H] < +0.4. We determine the abundances from HF lines in infrared K-band spectra ( 2.3 mm) of cool giants, observed with the IGRINS and Phoenix high-resolution spectrographs. We derive accurate stellar parameters for all our observed K giants, which is important as the HF lines are very temperaturesensitive. We find that [F/Fe] is flat as a function of metallicity at [ F/Fe]0, but increases as the metallicity increases. The fluorine slope shows a clear secondary behavior in this metallicity range. We also find that the [F/ Ce] ratio is relatively flat for -0.6 < [Fe H] < 0, and that for two metal-poor ([Fe H] < - 0.8), s-process element-enhanced giants, we do not detect an elevated fluorine abundance. We interpret all of these observational constraints as indications that several major processes are at play for the cosmic budget of fluorine over time: from those in massive stars at low metallicities, through the asymptotic giant branch star contribution at -0.6 < [Fe H] < 0, to processes with increasing yields with metallicity at supersolar metallicities. The origins of the latter, and whether or not Wolf-Rayet stars and/or novae could contribute at supersolar metallicities, is currently not known. To quantify these observational results, theoretical modeling is required. More observations in the metal-poor region are required to clarify the processes there.
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| 5. |
- Thorsbro, Brian
(författare)
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Atomic Data Needs in Astrophysics: The Galactic Center “Scandium Mystery”
- 2020
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Ingår i: Atoms. - : MDPI AG. - 2218-2004. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Investigating the Galactic center offers unique insights into the buildup and history of our Galaxy and is a stepping stone to understand galaxies in a larger context. It is reasonable to expect that the stars found in the Galactic center might have a different composition compared to stars found in the local neighborhood around the Sun. It is therefore quite exciting when recently there were reports of unusual neutral scandium, yttrium, and vanadium abundances found in the Galactic center stars, compared to local neighborhood stars. To explain the scandium abundances in the Galactic center, we turn to recent laboratory measurements and theoretical calculations done on the atomic oscillator strengths of neutral scandium lines in the near infrared. We combine these with measurements of the hyper fine splitting of neutral scandium. We show how these results can be used to explain the reported unusual scandium abundances and conclude that in this respect, the environment of the Galactic center is not that different from the environment in the local neighborhood around the sun.
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| 6. |
- Thorsbro, Brian
(författare)
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Clues to galaxy evolution from spectroscopic observations of Galactic centre stars
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this work we present results from spectroscopic observations of Galactic centre stars. High resolution stellar spectroscopy can be used to determine accurate stellar metallicities and abundances. Observing stars in the Galactic centre is challenging due to extreme extinction. However, observing bright M giants in the K band is viable with 10 m telescopes, which is what has been carried out in this work using the Keck II telescope at W. M. Keck Observatory, Hawai'i.We provide a metallicity distribution of a sample of stars observed in the Galactic centre and show that the sampled stars on average have a metallicity comparable to the Sun, with a subset of the sample having a very high metallicity. We also investigate the silicon abundance of the stars as an alpha tracer, and show that in general there is a similarity between the Galactic centre stars and stars further out. However, for the high metallicity subsample stars in the Galactic centre, there is evidence for a possible alpha enrichment beyond what is found elsewhere in the Galaxy.Alpha enrichment is a powerful diagnostic as it is central to chemical evolution models giving constraints important for the development of galactic formation and evolution theories. We model the determined alpha enrichment and suggest that there might have been a recent starburst event, or maybe there was a pause in star formation between 3 and 12 Gyr ago. We model different pause scenarios. Further observations of a larger number of stars, and other tracers of alpha elements, are required to verify this result.We also investigate claims of increased scandium abundances in the Galactic centre and find that the extremely strong scandium lines could be explained by a better understanding of the atomic physics properties of scandium, rather than a high scandium abundance. We find similarly strong scandium lines in stars further out in the Galaxy.We have thus demonstrated that the determination of abundances of Galactic centre stars is now possible and that future investigation of more stars and more elements will provide necessary and strong constraints to theories of how the Galactic centre have formed and evolved.
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