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RISS 인기검색어
- 검색키워드
- 저자 : Prato, Mirko (검색결과 2 건)
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RADIAL VELOCITY VARIABILITY OF FIELD BROWN DWARFS
Prato, L.,Mace, G. N.,Rice, E. L.,McLean, I. S.,Kirkpatrick, J. Davy,Burgasser, A. J.,Kim, Sungsoo S. IOP Publishing 2015 The Astrophysical journal Vol.808 No.1
<P>We present paper six of the NIRSPEC Brown Dwarf Spectroscopic Survey, an analysis of multi-epoch, high-resolution (R similar to 20,000) spectra of 25 field dwarf systems (3 late-type M dwarfs, 16 L dwarfs, and 6 T dwarfs) taken with the NIRSPEC infrared spectrograph at the W. M. Keck Observatory. With a radial velocity (RV) precision of similar to 2 km s(-1), we are sensitive to brown dwarf companions in orbits with periods of a few years or less given a mass ratio of 0.5 or greater. We do not detect any spectroscopic binary brown dwarfs in the sample. Given our target properties, and the frequency and cadence of observations, we use a Monte Carlo simulation to determine the detection probability of our sample. Even with a null detection result, our 1 sigma upper limit for very low mass binary frequency is 18%. Our targets included seven known, wide brown dwarf binary systems. No significant RV variability was measured in our multi-epoch observations of these systems, even for those pairs for which our data spanned a significant fraction of the orbital period. Specialized techniques are required to reach the high precisions sensitive to motion in orbits of very low-mass systems. For eight objects, including six T dwarfs, we present the first published high-resolution spectra, many with high signal to noise, that will provide valuable comparison data for models of brown dwarf atmospheres.</P>
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Akkerman, Quinten A.,Park, Sungwook,Radicchi, Eros,Nunzi, Francesca,Mosconi, Edoardo,De Angelis, Filippo,Brescia, Rosaria,Rastogi, Prachi,Prato, Mirko,Manna, Liberato American Chemical Society 2017 NANO LETTERS Vol.17 No.3
<P/><P>We have developed a colloidal synthesis of nearly monodisperse nanocrystals of pure Cs<SUB>4</SUB>PbX<SUB>6</SUB> (X = Cl, Br, I) and their mixed halide compositions with sizes ranging from 9 to 37 nm. The optical absorption spectra of these nanocrystals display a sharp, high energy peak due to transitions between states localized in individual PbX<SUB>6</SUB><SUP>4–</SUP> octahedra. These spectral features are insensitive to the size of the particles and in agreement with the features of the corresponding bulk materials. Samples with mixed halide composition exhibit absorption bands that are intermediate in spectral position between those of the pure halide compounds. Furthermore, the absorption bands of intermediate compositions broaden due to the different possible combinations of halide coordination around the Pb<SUP>2+</SUP> ions. Both observations are supportive of the fact that the [PbX<SUB>6</SUB>]<SUP>4–</SUP> octahedra are electronically decoupled in these systems. Because of the large band gap of Cs<SUB>4</SUB>PbX<SUB>6</SUB> (>3.2 eV), no excitonic emission in the visible range was observed. The Cs<SUB>4</SUB>PbBr<SUB>6</SUB> nanocrystals can be converted into green fluorescent CsPbBr<SUB>3</SUB> nanocrystals by their reaction with an excess of PbBr<SUB>2</SUB> with preservation of size and size distributions. The insertion of PbX<SUB>2</SUB> into Cs<SUB>4</SUB>PbX<SUB>6</SUB> provides a means of accessing CsPbX<SUB>3</SUB> nanocrystals in a wide variety of sizes, shapes, and compositions, an important aspect for the development of precisely tuned perovskite nanocrystal inks.</P>
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