| 1. |
- Currie, Thayne, et al.
(författare)
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RECOVERY OF THE CANDIDATE PROTOPLANET HD 100546 b WITH GEMINI/NICI AND DETECTION OF ADDITIONAL (PLANET-INDUCED ?) DISK STRUCTURE AT SMALL SEPARATIONS
- 2014
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 796:2, s. L30-
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Tidskriftsartikel (refereegranskat)abstract
- We report the first independent, second epoch (re-) detection of a directly imaged protoplanet candidate. Using L' high-contrast imaging of HD 100546 taken with the Near-Infrared Coronagraph and Imager on Gemini South, we recover HD 100546 b with a position and brightness consistent with the original Very Large Telescope/NAos-COnica detection from Quanz et al., although data obtained after 2013 will be required to decisively demonstrate common proper motion. HD 100546 b may be spatially resolved, up to approximate to 12-13 AU in diameter, and is embedded in a finger of thermal IR-bright, polarized emission extending inward to at least 0 ''.3. Standard hot-start models imply a mass of approximate to 15 M-J. However, if HD 100546 b is newly formed or made visible by a circumplanetary disk, both of which are plausible, its mass is significantly lower (e.g., 1-7 M-J). Additionally, we discover a thermal IR-bright disk feature, possibly a spiral density wave, at roughly the same angular separation as HD 100546 b but 90 degrees. away. Our interpretation of this feature as a spiral arm is not decisive, but modeling analyses using spiral density wave theory implies a wave launching point exterior to approximate to 0 ''.45 embedded within the visible disk structure: plausibly evidence for a second, hitherto unseen, wide-separation planet. With one confirmed protoplanet candidate and evidence for one to two others, HD 100546 is an important evolutionary precursor to intermediate-mass stars with multiple super-Jovian planets at moderate/wide separations like HR 8799.
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| 2. |
- Omoto, Kazuki, et al.
(författare)
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Neutron diffraction study of the crystal structure and structural phase transition of La0.7Ca0.3-xSrxCrO3 (0
- 2010
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 183:2, s. 392-401
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Tidskriftsartikel (refereegranskat)abstract
- The crystal structure of the La0.7Ca0.3-xSrxCrO3 series, including the compositional and temperature dependence of the structural parameters, has been Studied by variable temperature neutron diffraction measurements. The extent of the distortions from the ideal cubic perovskite structure has been evaluated quantitatively using the average bond lengths and the mean volumes of the [CrO6] octahedron and [(La/Ca/Sr)O-12] polyhedron, and has been shown to decrease with increase of Sr content or temperature. At the structural phase transition from the orthorhombic (Pnma) structure to the rhombohedral (R (3) over barc) one, the volume of the [CrO6] octahedron decreases whereas that of the [(La/Ca/Sr)O-12] polyhedron shows little difference, resulting in an overall decrease in the level of distortion. The change in the degree of distortion at the phase transition decreases with increase of Sr content, in agreement with the smaller variation of the enthalpy and volume for the specimens with higher Sr content.
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