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Free, publicly-accessible full text available November 11, 2025
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The reactivity of Bin−clusters (n= 2 to 30) with O2is found to display even-odd alternations. The open-shell even-sized Bin−clusters are more reactive than the closed-shell odd-sized clusters, except Bi18−, which exhibits no observable reactivity toward O2. We have investigated the structure and bonding of Bi18−to understand its remarkable resistance to oxidation. We find that the most stable structure of Bi18−consists of two Bi8cages linked by a Bi2dimer, where each atom is bonded to three neighboring atoms. Chemical bonding analyses reveal that each Bi uses its three 6pelectrons to form three covalent bonds with its neighbors, resulting in a Bi18−cluster without any dangling bonds. We find that the robust Bi18framework along with the totally delocalized unpaired electron is responsible for the surprising inertness of Bi18−toward O2. The Bi18framework is similar to that in Hittorf’s phosphorus, suggesting the possibility to create bismuth nanoclusters with interesting structures and properties.more » « lessFree, publicly-accessible full text available November 1, 2025
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Abstract Using proper motions from Gaia Early Data Release 3 (Gaia EDR3) and radial velocities from several surveys, we identify 60 candidate high-velocity stars with a total velocity greater than 75% of the escape velocity that probably originated from the Sagittarius dwarf spheroidal galaxy (Sgr) by orbital analysis. Sgr’s gravity has little effect on the results and the Large Magellanic Cloud’s gravity has a nonnegligible effect on only a few stars. The closest approach of these stars to the Sgr occurred when the Sgr passed its pericenter (∼38.2 Myr ago), which suggests they were tidally stripped from the Sgr. The positions of these stars in the Hertzsprung–Russell diagram and the chemical properties of 19 of them with available [Fe/H] are similar to the Sgr stream member stars. This is consistent with the assumption of their accretion origin. Two of the 60 are hypervelocity stars, which may also be produced by the Hills mechanism.more » « less
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Abstract We present the astrometric calibration of the Beijing–Arizona Sky Survey (BASS). The BASS astrometry was tied to the International Celestial Reference Frame via the Gaia Data Release 2 reference catalog. For effects that were stable throughout the BASS observations, including differential chromatic refraction and the low charge transfer efficiency of the CCD, we corrected for these effects at the raw image coordinates. Fourth-order polynomial intermediate longitudinal and latitudinal corrections were used to remove optical distortions. The comparison with the Gaia catalog shows that the systematic errors, depending on color or magnitude, are less than 2 milliarcseconds (mas). The position systematic error is estimated to be about −0.01 ± 0.7 mas in the region between 30° and 60° of decl. and up to −0.07 ± 0.9 mas in the region north of decl. 60°.more » « less