| 41. |
- Imig, Julie, et al.
(författare)
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A Tale of Two Disks : Mapping the Milky Way with the Final Data Release of APOGEE
- 2023
-
Ingår i: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 954:2
-
Tidskriftsartikel (refereegranskat)abstract
- We present new maps of the Milky Way disk showing the distribution of metallicity ([Fe/H]), alpha-element abundances ([Mg/Fe]), and stellar age, using a sample of 66,496 red giant stars from the final data release (DR17) of the Apache Point Observatory Galactic Evolution Experiment survey. We measure radial and vertical gradients, quantify the distribution functions for age and metallicity, and explore chemical clock relations across the Milky Way for the low-a disk, high-alpha disk, and total population independently. The low-alpha disk exhibits a negative radial metallicity gradient of -0.06 +/- 0.001 dex kpc(-1), which flattens with distance from the midplane. The high-alpha disk shows a flat radial gradient in metallicity and age across nearly all locations of the disk. The age and metallicity distribution functions shift from negatively skewed in the inner Galaxy to positively skewed at large radius. Significant bimodality in the [Mg/Fe]-[Fe/H] plane and in the [Mg/Fe]-age relation persist across the entire disk. The age estimates have typical uncertainties of similar to 0.15 in log(age) and may be subject to additional systematic errors, which impose limitations on conclusions drawn from this sample. Nevertheless, these results act as critical constraints on galactic evolution models, constraining which physical processes played a dominant role in the formation of the Milky Way disk. We discuss how radial migration predicts many of the observed trends near the solar neighborhood and in the outer disk, but an additional more dramatic evolution history, such as the multi-infall model or a merger event, is needed to explain the chemical and age bimodality elsewhere in the Galaxy.
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| 42. |
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| 43. |
- Jones, O. C., et al.
(författare)
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Probing the Dusty Stellar Populations of the Local Volume Galaxies with JWST/MIRI
- 2017
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 841:1, s. Article Number: 15-
-
Tidskriftsartikel (refereegranskat)abstract
- The Mid-Infrared Instrument (MIRI) for the James Webb Space Telescope (JWST) will revolutionize our understanding of infrared stellar populations in the Local Volume. Using the rich Spitzer-IRS spectroscopic data set and spectral classifications from the Surveying the Agents of Galaxy Evolution (SAGE)-Spectroscopic survey of more than 1000 objects in the Magellanic Clouds, the Grid of Red Supergiant and Asymptotic Giant Branch Star Model (GRAMS), and the grid of YSO models by Robitaille et al., we calculate the expected flux densities and colors in the MIRI broadband filters for prominent infrared stellar populations. We use these fluxes to explore the JWST/MIRI colors and magnitudes for composite stellar population studies of Local Volume galaxies. MIRI color classification schemes are presented; these diagrams provide a powerful means of identifying young stellar objects, evolved stars, and extragalactic background galaxies in Local Volume galaxies with a high degree of confidence. Finally, we examine which filter combinations are best for selecting populations of sources based on their JWST colors.
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| 44. |
- Landi, E., et al.
(författare)
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Hinode/EIS Coronal Magnetic Field Measurements at the Onset of a C2 Flare
- 2021
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 913:1
-
Tidskriftsartikel (refereegranskat)abstract
- We study Hinode/EIS observations of an active region taken before, during, and after a small C2.0 flare in order to monitor the evolution of the magnetic field and its relation to the flare event. We find that while the flare left the active region itself unaltered, the event included a large magnetic field enhancement (MFE), which consisted of a large magnetic field strength increase to values just short of 500 G in a rather small region where no magnetic field was measured before. This MFE is observed during the impulsive phase of the flare at the footpoints of flare loops, its magnetic energy is sufficient to power the radiative losses of the entire flare, and has completely dissipated after the flare. We argue that the MFE might occur at the location of the reconnection event triggering the flare, and note that it formed within 22 minutes of the flare start (as given by the EIS raster return time). These results open the door to a new line of studies aimed at determining whether MFEs can be flare precursor events or used for Space Weather forecasts, what advance warning time they could provide and if this time is long enough to allow for mitigation procedures to be implemented; as well as to explore which physical processes lead to MFE formation and dissipation, whether such processes are the same in both long-duration and impulsive flares, and whether they can be predicted by theoretical models.
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| 45. |
- Lee, Elspeth K.H., et al.
(författare)
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3D Radiative Transfer for Exoplanet Atmospheres. gCMCRT : A GPU-accelerated MCRT Code
- 2022
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 929:2
-
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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| 46. |
- Li, Daohai, et al.
(författare)
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Metal Pollution of the Solar White Dwarf by Solar System Small Bodies
- 2022
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 924:2
-
Tidskriftsartikel (refereegranskat)abstract
- White dwarfs (WDs) often show metal lines in their spectra, indicating accretion of asteroidal material. Our Sun is to become a WD in several gigayears. Here, we examine how the solar WD accretes from the three major small body populations: the main belt asteroids (MBAs), Jovian Trojan asteroids (JTAs), and trans-Neptunian objects (TNOs). Owing to the solar mass loss during the giant branch, 40% of the JTAs are lost but the vast majority of MBAs and TNOs survive. During the WD phase, objects from all three populations are sporadically scattered onto the WD, implying ongoing accretion. For young cooling ages ≲100 Myr, accretion of MBAs predominates; our predicted accretion rate ∼106 g s-1 falls short of observations by two orders of magnitude. On gigayear timescales, thanks to the consumption of the TNOs that kicks in ⪆100 Myr, the rate oscillates around 106-107 g s-1 until several gigayears and drops to ∼105 g s-1 at 10 Gyr. Our solar WD accretion rate from 1 Gyr and beyond agrees well with those of the extrasolar WDs. We show that for the solar WD, the accretion source region evolves in an inside-out pattern. Moreover, in a realistic small body population with individual sizes covering a wide range as WD pollutants, the accretion is dictated by the largest objects. As a consequence, the accretion rate is lower by an order of magnitude than that from a population of bodies of a uniform size and the same total mass and shows greater scatter.
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| 47. |
- Li, W., et al.
(författare)
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A Theoretical Investigation of the Magnetic-field-induced Transition in Fe X, of Importance for Measuring Magnetic Field Strengths in the Solar Corona
- 2021
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 913:2
-
Tidskriftsartikel (refereegranskat)abstract
- The use of the magnetic-field-induced transition (MIT) in Fe X for the measurement of the magnetic field strength in the solar corona has been discussed and demonstrated in a number of recent studies. This diagnostic technique depends on, among other conditions, the accuracy of the atomic data for Fe X. In the present work, we carry out a large-scale calculation for the atomic properties needed for the determination of the MIT rate using the multiconfiguration Dirac-Hartree-Fock method. Four computational schemes are employed to study the convergence of the atomic properties of interest. Comparison with other experimental and theoretical sources are performed and recommended values are suggested for important properties, e.g., the magnetic induced transition probabilities as a function of magnetic field strengths. The present calculations affect magnetic field measurements by decreasing the magnetic field strengths by 10%-15%, leading to differences in magnetic energy up to 30%. We recommend that the current data should be employed in magnetic field measurements in the future.
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| 48. |
- Lyra, Wladimir, et al.
(författare)
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An Analytical Theory for the Growth from Planetesimals to Planets by Polydisperse Pebble Accretion
- 2023
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 946:2
-
Tidskriftsartikel (refereegranskat)abstract
- Pebble accretion is recognized as a significant accelerator of planet formation. Yet only formulae for single-sized (monodisperse) distribution have been derived in the literature. These can lead to significant underestimates for Bondi accretion, for which the best accreted pebble size may not be the one that dominates the mass distribution. We derive in this paper the polydisperse theory of pebble accretion. We consider a power-law distribution in pebble radius, and we find the resulting surface and volume number density distribution functions. We derive also the exact monodisperse analytical pebble accretion rate for which 3D accretion and 2D accretion are limits. In addition, we find analytical solutions to the polydisperse 2D Hill and 3D Bondi limits. We integrate the polydisperse pebble accretion numerically for the MRN distribution, finding a slight decrease (by an exact factor 3/7) in the Hill regime compared to the monodisperse case. In contrast, in the Bondi regime, we find accretion rates 1-2 orders of magnitude higher compared to monodisperse, also extending the onset of pebble accretion to 1-2 orders of magnitude lower in mass. We find megayear timescales, within the disk lifetime, for Bondi accretion on top of planetary seeds of masses 10−6 to 10−4 M ⊕, over a significant range of the parameter space. This mass range overlaps with the high-mass end of the planetesimal initial mass function, and thus pebble accretion is possible directly following formation by streaming instability. This alleviates the need for mutual planetesimal collisions as a major contribution to planetary growth.
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| 49. |
- Mousis, Olivier, et al.
(författare)
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Jupiter's Formation in the Vicinity of the Amorphous Ice Snowline
- 2019
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 875:1
-
Tidskriftsartikel (refereegranskat)abstract
- Argon, krypton, xenon, carbon, nitrogen, sulfur, and phosphorus have all been measured and found to be enriched by a quasi uniform factor in the 2-4 range, compared to their protosolar values, in the atmosphere of Jupiter. To elucidate the origin of these volatile enrichments, we investigate the possibility of an inward drift of particles made of amorphous ice and adsorbed volatiles, and their ability to enrich in heavy elements the gas phase of the protosolar nebula, once they cross the amorphous-to-crystalline ice transition zone, following the original idea formulated by Monga & Desch. To do so, we use a simple accretion disk model coupled to modules depicting the radial evolution of icy particles and vapors, assuming growth, fragmentation, and crystallization of amorphous grains. We show that it is possible to accrete supersolar gas from the nebula onto proto-Jupiter's core to form its envelope, and allowing it to match the observed volatile enrichments. Our calculations suggest that nebular gas, with a metallicity similar to that measured in Jupiter, can be accreted by its envelope if the planet is formed in the ∼0.5-2 Myr time range and in the 0.5-20 au distance range from the Sun, depending on the adopted viscosity parameter of the disk. These values match a wide range of Jupiter's formation scenarios, including in situ formation and migration/formation models.
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| 50. |
- Price-Whelan, Adrian, et al.
(författare)
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The Astropy Project : Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package*
- 2022
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 935:2
-
Tidskriftsartikel (refereegranskat)abstract
- The Astropy Project supports and fosters the development of open-source and openly developed Python packages that provide commonly needed functionality to the astronomical community. A key element of the Astropy Project is the core package astropy, which serves as the foundation for more specialized projects and packages. In this article, we summarize key features in the core package as of the recent major release, version 5.0, and provide major updates on the Project. We then discuss supporting a broader ecosystem of interoperable packages, including connections with several astronomical observatories and missions. We also revisit the future outlook of the Astropy Project and the current status of Learn Astropy. We conclude by raising and discussing the current and future challenges facing the Project.
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