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We use an updated method for the detection of double-lined spectroscopic binaries (SB2s) using V sin  i values from spectral fits. The method is applied to all spectra from Large sky Area Multi-Object fiber Spectroscopic Telescope Medium Resolution Survey. Using this method, we detect 12 426 SB2 candidates, where 4321 are already known and 8105 are new discoveries. We check their spectra manually to minimize possible false positives. We also detect several cases of contamination of the spectra by solar light. Additionally, for candidates with multiple observations, we compute mass ratios with systemic velocities and determine Keplerian orbits. We present an updated catalogue of all SB2 candidates together with additional information for some of them in separate data tables. [ABSTRACT FROM AUTHOR]

We selected three double-lined spectroscopic binary systems which have extreme mass ratios, if measured using the Wilson method. We analysed medium resolution spectroscopic observations and space-based photometry and find that all these systems are not SB2, but rather triple systems and a chance alignment of another star with SB1 that have an unseen component. Therefore, suspicious mass ratios determined by the Wilson method for some double-lined spectroscopic binary systems aren't correct as these systems are more complex. [ABSTRACT FROM AUTHOR]

One-dimensional Y2Ti2O7:Cr3+/Yb3+ nano wire-embedded-tube structures composed of an outer nanotube with an outside diameter of 180–200 nm and a wall thickness of 30–36 nm and embedded wire with a diameter of 32–36 nm were fabricated via a simple single-nozzle electrospinning method at an air humidity of 45%. The Cr3+ content in the one-dimensional Y2Ti2O7:Cr3+/Yb3+ nanostructures is very low and accounts for approximately 0.5% of the total moles of Yb3+, Y3+, and Cr3+ ions. The energy transfer mechanism from Cr3+ to Yb3+ is systematically studied. The near-infrared luminescent properties of the one-dimensional Y2Ti2O7:Cr3+/Yb3+ nano wire-embedded-tube structures, especially the temperature sensing performance, were investigated. The one-dimensional Y2Ti2O7:Cr3+/Yb3+ nano wire-embedded-tube structures have emissions of 650–1100 nm and excellent temperature sensing properties. The maximum absolute sensitivity (Sa) and high relative sensitivity (Sr) values are 6.01–8.73%K−1 and 3.93–4.71%K−1, respectively, which are much higher than those of the previous Cr3+ and Cr3+/RE3+ co-doped near-infrared phosphors and other up-conversion phosphors doped by RE3+ ions. [ABSTRACT FROM AUTHOR]

Fluorescent CDs tend to undergo solid-state aggregation quenching in powder form. This is caused by the stacking of π–π conjugate structures and excessive resonant energy transfer. Moreover, various forms of N play an important role in white CDs suitable for LED applications. White, single-component, non-N-doped CDs have never been reported for LED application. In this study, to overcome this limitation, we developed Ga-doped CD powders containing no N element that exhibit ultra-wideband white emission in the range of 420–800 nm for LED applications and were able to resist solid-state aggregation quenching. Furthermore, the Ga-doped CD powders demonstrated excellent luminescence stability under high temperatures. Another strength of the Ga-doped CD powders is their large Stokes shift, where the peak center of white emission shifts from 550 nm to 650 nm under 365 nm excitation as the Ga doping concentration is adjusted from 0.05 to 0.6 (Ga : H2O, mass ratio). The full width at half-maximum can reach 262 nm. Additionally, the Ga-doped CD powders exhibit good luminescence stability under long-time exposure to an air atmosphere. Their luminescent intensity retained 70%–74% of the initial values even after being left in natural placement for 100 days. Moreover, the Ga-doped CDs demonstrate afterglow features. [ABSTRACT FROM AUTHOR]

Y2Ti2O7:Cr3+/Yb3+/Nd3+ phosphors with broadband near-infrared emission were developed by a high-temperature solid-state method. Under the excitation of 405 nm light, it shows broadband near-infrared emission from 650 to 1050 nm. Y2Ti2O7:Cr3+/Yb3+/Nd3+ phosphors present excellent bright luminescence and thermal quenching resistance. The energy transfer mechanism between Cr3+/Nd3+/Yb3+ ions was elucidated. By using the energy transfer from Cr3+-Nd3+-Yb3+, the excitation efficiency of Yb3+ at 405 nm is greatly improved, and the strong NIR emission centered at approximately 975 nm is well coupled with the absorption band of silicon solar cells. The Y2Ti2O7:0.005Cr3+/0.1Yb3+/0.01Nd3+ phosphors were assembled with a commercial 365 nm InGaN chip to fabricate a near-infrared LED device that can work under operating electric currents of 100–900 mA. In short, Y2Ti2O7:Cr3+/Yb3+/Nd3+ phosphors are suitable for near-infrared LED applications. [ABSTRACT FROM AUTHOR]

We present a study of the detached eclipsing binary J064726.39 + 223431.6 using spectra from the LAMOST medium-resolution spectra and Transiting Exoplanet Survey Satellite photometry. We use full-spectrum fitting to derive radial velocities and spectral parameters: |${T_{\rm eff}}_{A,B}=6177,\, 5820$| K, |$V \sin {i}_{A,B}=59,\, 50~\, {\rm km}\, {\rm s}^{-1}$|⁠ , and [Fe/H] A,B  = −0.19 dex. The orbital solution and light-curve analysis suggest that it is a close pair of fast rotating stars on a circular orbit. We measure their masses to be |$M_{A,B}=1.307\pm 0.007,\, 1.129\pm 0.005\, \mathrm{M}_\odot$| and their radii to be |$R_{A,B}=1.405\pm 0.052,\, 1.219\pm 0.060\, \mathrm{R}_\odot$|⁠ , resulting in surface gravities of |$\log {\rm (g)}_{A,B}=4.259\pm 0.033,\, 4.319\pm 0.042$| (cgs). Theoretical models cannot match all of these properties, predicting significantly higher T eff for a given metallicity. The derived age of the system is 1.56 Gyr, which indicates that both components are younger than Sun, which contradicts to much longer orbit's circularization time-scale. [ABSTRACT FROM AUTHOR]

We present a new method for the detection of double-lined spectroscopic binaries (SB2s) using V sin  i values from spectral fits. The method is tested on synthetic and real spectra from the Large Sky Area Multi-Object fiber Spectroscopic Telescope Medium Resolution Survey. It can reliably detect SB2 candidates for double-lined binaries with |$V \sin {i}_1+V \sin {i}_2\lt 300\, {\rm km}\, {\rm s}^{-1}$| if the radial velocity separation is large enough. Using this method, we detected 2460 SB2 candidates, 1410 of which are new discoveries. We confirmed the correlation between the radial velocity separation estimated by the binary model and V sin  i 0 estimated by the single-star model using the selected sample. Additionally, our method found one new SB2 candidate in open cluster M11. [ABSTRACT FROM AUTHOR]

Binaries consisting of a hot subdwarf star and an accreting white dwarf (WD) are sources of gravitational wave radiation at low frequencies and possible progenitors of Type Ia supernovae if the WD mass is large enough. Here, we report the discovery of the third binary known of this kind: It consists of a hot subdwarf O (sdO) star and a WD with an orbital period of 3.495 h and an orbital shrinkage of 0.1 s in 6 yr. The sdO star overfills its Roche lobe and likely transfers mass to the WD via an accretion disc. From spectroscopy, we obtain an effective temperature of |$T_{\mathrm{eff}}=54\, 240\pm 1840$| K and a surface gravity of log  g  = 4.841 ± 0.108 for the sdO star. From the light curve analysis, we obtain an sdO mass of M sdO = 0.55 M⊙ and a mass ratio of q  = M WD/ M sdO = 0.738 ± 0.001. Also, we estimate that the disc has a radius of |$\sim\!0.41\ \mathrm{R}_\odot$| and a thickness of |$\sim\!0.18\ \mathrm{R}_\odot$|⁠. The origin of this binary is probably a common envelope ejection channel, where the progenitor of the sdO star is either a red giant branch star or, more likely, an early asymptotic giant branch star; the sdO star will subsequently evolve into a WD and merge with its WD companion, likely resulting in an R Coronae Borealis (R CrB) star. The outstanding feature in the spectrum of this object is strong Ca H&K lines, which are blueshifted by ∼200 km s−1 and likely originate from the recently ejected common envelope, and we estimated that the remnant common envelope (CE) material in the binary system has a density |$\sim\!6\times 10^{-10}\ {\rm g\, cm}^{-3}$|⁠. [ABSTRACT FROM AUTHOR]

The lanthanide-based white light-emitting diodes excited by irradiation at a wavelength of 980 nm have attracted increasing attention because of their low photon frequency and ease of implementation. Here, we report on warm, white, Y2Ti2O7:Tm/Yb/Er nanotubes prepared by a simple single-needle electrospinning method. The Y2Ti2O7:Tm/Yb/Er nanotubes have an outer diameter of about 180 nm, and a wall thickness of 36 nm. Their color coordinates and chromaticity were controlled to yellow → red → warm white by adjusting the Tm3+ concentration from 0.5 to 2.0%. The luminescence properties and upconversion mechanism of Y2Ti2O7:Tm/Yb/Er nanotubes were investigated. The warm white Y2Ti2O7:Tm/Yb/Er nanotubes exhibit a strong correlated color temperature to a household incandescent lamp. [ABSTRACT FROM AUTHOR]