Abstract
Some evolved binaries, namely post–asymptotic giant branch (AGB) binaries, are surrounded by stable and massive circumbinary disks similar to protoplanetary disks found around young stars. ...Around 10% of these disks are transition disks: they have a large inner cavity in the dust. Previous interferometric measurements and modeling have ruled out these cavities being formed by dust sublimation and suggested that they are due to massive circumbinary planets that trap dust in the disk and produce the observed depletion of refractory elements on the surfaces of the post-AGB stars. In this study, we test an alternative scenario in which the large cavities could be due to dynamical truncation from the inner binary. We performed near-infrared interferometric observations with the CHARA Array on the archetype of such a transition disk around a post-AGB binary: AC Her. We detect the companion at ten epochs over 4 yr and determine the three-dimensional orbit using these astrometric measurements in combination with a radial velocity time series. This is the first astrometric orbit constructed for a post-AGB binary system. We derive the best-fit orbit with a semimajor axis of 2.01 ± 0.01 mas (2.83 ± 0.08 au), inclination (142.9 ± 1.1)°, and longitude of the ascending node (155.1 ± 1.8)°. We find that the theoretical dynamical truncation and dust sublimation radii are at least ∼3× smaller than the observed inner disk radius (∼21.5 mas or 30 au). This strengthens the hypothesis that the origin of the cavity is due to the presence of a circumbinary planet.
Abstract
We present measurements of the interferometrically resolved binary star system 12 Com and the single giant star 31 Com in the cluster Coma Berenices. 12 Com is a double-lined spectroscopic ...binary system consisting of a G7 giant and an A3 dwarf at the cluster turnoff. Using an extensive radial velocity data set and interferometric measurements from the Palomar Testbed Interferometer and the Center for High Angular Resolution Astronomy array, we measured masses
M
1
= 2.64 ± 0.07
M
⊙
and
M
2
= 2.10 ± 0.03
M
⊙
. Interferometry also allows us to resolve the giant and measure its size as
R
1
= 9.12 ± 0.12 ± 0.01
R
⊙
. With the measured masses and radii, we find an age of 533 ± 41 ± 42 Myr. For comparison, we measure the radius of 31 Com to be 8.36 ± 0.15
R
⊙
. Based on the photometry and radius measurements, 12 Com A is likely the most evolved bright star in the cluster, large enough to be in the red giant phase, but too small to have core helium burning. Simultaneous knowledge of 12 Com A’s mass and photometry puts strong constraints on convective core overshooting during the main-sequence phase, which in turn reduces systematic uncertainties in the age. Increased precision in measuring this system also improves our knowledge of the progenitor of the cluster white dwarf WD1216+260.
A combination of sol–gel Pechini method and flame synthesis was used to prepare yttrium aluminate glass microspheres with the garnet composition (YAG, 62.5 mol% aluminium oxide, 37.5 mol% yttrium ...oxide). Prepared glass microbeads were studied by optical microscopy, SEM, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and high-temperature (HT) XRD analysis. Formation of YAG as the only crystalline phase was observed during HT XRD experiment in the temperature interval (750–1200 °C), with the onset of YAG phase crystallization in the temperature interval 860–870 °C and most prominent increase in the YAG phase content between 905 and 910 °C. The experimental data obtained by DSC analysis and the Johnson–Mehl–Avrami–Kolmogorov model were used for determination of crystallization behaviour of the studied system. The frequency factor
A
= 5.2 × 10
48
± 9.6 × 10
48
min
−1
, apparent activation energy
E
app
= 1100 ± 10 kJ mol
−1
and the Avrami coefficient
m
= 4 were determined. The linear temperature dependence of nucleation rate, reaction-controlled crystal growth interface and a 3-D crystal growth were confirmed in the studied system.
Sintering by viscous flow in a “kinetic window” between Tg and Tx temperatures was used to prepare bulk glass/glass‐ceramic luminescent materials from rapidly quenched glass microspheres in the ...system Y2O3–Al2O3 doped with Ce3+ ions. The glass microspheres were prepared from sol–gel synthesized precursor powders in a high‐temperature methane‐oxygen flame. The crystallization of the glasses was analyzed using differential scanning calorimetry and high‐temperature X‐ray diffraction. The crystallization behavior of quenched glass microspheres was found to be strongly dependent on glass composition. The glass microspheres were consolidated into bulk material by hot‐pressing technique at a temperature of up to 1100℃ with the applied pressure 40MPa. The optimized time‐temperature‐pressure regime enables the preparation of bulk glass, and glass‐ceramic with a high fraction of crystalline Ce3+‐doped YAG phase embedded in the Al2O3‐enriched glass matrix. The glass/glass‐ceramics emit blue/yellow light with high intensity under excitation in UV and/or blue spectral region.
Interaction of organic dyes with layered silicates can cause various changes in dye properties, such as metachromasia (color change), fluorescence quenching, resonance energy transfer, or even ...fluorescence enhancement. These phenomena are caused by the molecular aggregation or adsorption of dye molecules on silicate particles. The present work studied the photophysical properties of pseudoisocyanine (PIC) in colloidal dispersions of five samples of layered silicates (smectites) at variable PIC/smectite loadings. The silicates of variable composition and layer charge included one synthetic saponite, one synthetic hectorite, two synthetic Laponites, and one montmorillonite. Chemometric analysis of the absorption spectra revealed the formation of four spectral species: monomers and three types of molecular aggregates exhibiting light absorption in both H- and J-band regions. In addition, the samples of hybrid systems with silicates of lower layer charge under the condition of the lowest PIC/silicate ratio (0.01 mmol g–1) exhibited strong fluorescence surpassing that of J-aggregates. The luminescent species achieving quantum yields of about 50% were assigned to the adsorbed PIC monomers, a phenomenon that has never been observed for this dye. Theoretical calculations found that in water solution bending of the molecule supports nonradiative deactivation of the excited state of the free molecule. Adsorption of PIC molecules on the surface of silicate particles caused the change of the dihedral angle between pyridine subunits, which hinders the nonradiative deactivation channel and favors emission. Fluorescence from adsorbed monomers exhibited a maximum at ≈535 nm, which is at significantly lower wavelengths with respect to the J-aggregates emitting at ≈570 nm and thus cannot be related to dye aggregation as supported by the fact that this phenomenon occurs only at the lowest surface concentrations of the dye.
The Cu-doped mesoporous silica-based particles (Cu-BMS) were prepared using an evaporation-induced self-assembly sol-gel procedure as a heterogeneous catalyst for the activation of peroxydisulfate ...(PDS). The formation of well-organized mesoporous structures with amorphous nature and high surface area of 286 m2/g was demonstrated. The catalytic activity of Cu-BMS in the degradation of Methylene Blue (MB) and the effects of operating parameters, including Cu-BMS dosage, initial PDS amount, initial MB concentration, temperature and initial pH, were investigated in details. The Cu-BMS demonstrated a remarkable catalytic activity (93.5% degradation efficiency within 60 min) and good stability.
Display omitted
•Cu-BMS achieves 93.5% MB degradation within 60 min.•Enhancement of the catalytic activity of Cu(II) by immobilization on BMS.•Acidic pH enhanced the Cu-BMS catalytic performance.•SO4•− radicals play the main role in degradation of MB in the Cu-BMS/PDS system.•The Cu-BMS catalyst showed good activity over 12 continuous cycles.
The paper deals with the synthesis and characterisation of binary aluminate glasses in the La2O3–Al2O3 system with Al2O3 contents changing between 74.6 and 86.9mol% (48–65wt.%), and of ternary ...glasses with 75.7mol% Al2O3 doped with 1mol% of Nd2O3 or Er2O3. Six binary and two ternary compositions were prepared. Flame synthesis facilitated the preparation of X-ray amorphous microspheres in the systems with 58wt.% Al2O3, and with eutectic composition in the pseudobinary LaAlO3–LaAl11O18 system doped with Er. Other systems contained low fractions of crystalline LaAlO3 perovskite, regardless of the composition. The diameter of prepared microspheres ranged between 2 and 10μm. They were transparent for visible light, as well as in the IR wavenumber range from 1300 to 4000cm−1.
Five compositions in the system Al2O3–Y2O3 with high level of homogeneity were prepared in the form of glass microspheres by flame synthesis. The amorphous nature of prepared glasses with highly ...disordered structure was confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman and nuclear magnetic resonance (NMR) spectroscopy. In the NMR spectra, typical signals with chemical shifts of 75, 42 and 12 ppm were observed, which were attributed to the presence of AlO4, AlO5 and AlO6 motifs in the glass structure. The ratio of individual motifs in glass samples did not change significantly with the composition. The crystallization of yttrium-aluminium garnet (YAG) phase was observed as a major process in the glasses thermally treated up to 1450 °C, with slow crystallization of θ- and α-Al2O3 phases detected in the temperature interval 980–1450 °C. IR and Raman spectra of the microspheres crystallized at 998, 1300 and 1500 °C for 4 h contained typical bands, that were assigned to the vibrations of AlO4 and AlO6 groups in YAG and Al2O3 structures. The comparison of 27Al and 89Y magic angle spinning (MAS) NMR spectra showed the presence of only YAG and α-Al2O3 phase in the samples crystallized at 1500 °C and the presence of a trace amount of θ-Al2O3 in the sample crystallized at 998 and 1300 °C. The yttrium aluminium perovskite (YAP) and yttrium aluminium monoclinic (YAM) phases, expected in this system, were no detected.
Transparent spinel with high real in-line transmittance (RIT up to 79%) was prepared from commercial spinel powder by capsule-free hot isostatic pressing (HIP). Optimal pre-sintering conditions were ...found in order to enhance the RIT values and doping with Cr3+ (0.01–0.04 at%) and Tb3+ (0.05–0.125 at%) secured photoluminescence. The incorporation of the dopants in tested range does not noticeably reduced the RIT. The Cr3+-doped MgAl2O4 shows efficient narrow red emission at about 685 nm (R-line) due to the 2Eg→4A2g transition of Cr3+ ions located in octahedral sites of D3d local symmetry with a strong crystal field. The Tb3+-doped MgAl2O4 ceramics have shown emissions from blue to red spectral range (5D4→7F3–6 transitions), with prominent green emission centered at 545 nm. The maximal emission intensity was achieved at 0.075 at% of Tb3+, Further increase of Tb3+ content led to the concentration quenching caused by Tb3+ ions segregation at the grain boundaries.
Yttrium aluminate glasses (76.8 mol% of Al
2
O
3
, 23.2 mol% of Y
2
O
3
) doped with Er
3+
and Nd
3+
ions at different concentration levels (0.25 mol%, 0.5 mol% and 0.75 mol% Er
2
O
3
/Nd
2
O
3
) ...were prepared by flame synthesis in the form of glass microspheres. The prepared samples were XRD amorphous, without presence of any crystalline phases in measured patterns. The two exothermic effects (~ 940, ~ 1010 °C), which can be assigned to the two steps of YAG crystallization, were observed in the DSC records of all prepared samples. The high temperature XRD measurements showed YAG (900–1200 °C) and α-Al
2
O
3
(1300–1450 °C) phase crystallization. The emission spectra were measured in the VIS and NIR regions for Er-doped samples and in the NIR region for Nd-doped samples. All measured emission spectra contain of characteristic bands due to the typical 4
f
–4
f
transitions within the Er
3+
and Nd
3+
ions. Comparison of the measured intensities of Er-doped samples made it evident that the highest intensities were obtained for the 0.5 mol% Er
2
O
3
-doped sample (in both the NIR and VIS spectral regions). The maximum intensity for Nd-doped samples was found when the sample was doped with 0.75 mol% of Nd
2
O
3
. The slowly increasing of emission intensities in samples after 20 min annealing at 1000 °C and Stark splitting of emission bands in samples after 40 and 60 min annealing at 1000 °C and after 20, 40 and 60 min annealing at 1500 °C was observed.
