Astreaks: Astrometry of NEOs with trailed background stars

The detection and accurate astrometry of fast-moving near-Earth objects (NEOs) has been a challenge for the follow-up community. Their fast apparent motion results in streaks in sidereal images, thus affecting the telescope's limiting magnitude and astrometric accuracy. A widely adopted technique to mitigate trailing losses is non-sidereal tracking, which transfers the streaking to background reference stars. However, no existing publicly available astrometry software is configured to detect such elongated stars. We present Astreaks, a streaking source detection algorithm, to obtain accurate astrometry of NEOs in non-sidereal data. We validate the astrometric accuracy of Astreaks on 371 non-sidereally tracked images for 115 NEOs with two instrument set-ups of the GROWTH-India Telescope. The observed NEOs had V-band magnitude in the range [15, 22] with proper motion up to 140$^{\prime\prime}$/min, thus resulting in stellar streaks as high as 6.5$^\prime$ (582 pixels) in our data. Our method obtained astrometric solutions for all images with 100% success rate. The standard deviation in Observed-minus-Computed (O-C) residuals is 0.52$^{\prime\prime}$, with O-C residuals <2$^{\prime\prime}$(<1$^{\prime\prime}$) for 98.4% (84.4%) of our measurements. These are appreciable, given the pixel scale of $\sim$0.3$^{\prime\prime}$ and $\sim$0.7$^{\prime\prime}$ of our two instrument set-ups. This demonstrates that our modular and fully-automated algorithm helps improve the telescope system's limiting magnitude without compromising astrometric accuracy by enabling non-sidereal tracking on the target. This will help the NEO follow-up community cope with the accelerated discovery rates and improved sensitivity of the next-generation NEO surveys. Astreaks has been made available to the community under an open-source license.Comment: 10 pages, 7 figure

Enhancing the optical absorption of Ga

Optical and electronic properties of transition metal adsorbed Ga2SeTe Janus monolayer have been investigated in detail using DFT simulations. Results suggests that the pristine Janus monolayer of Ga2SeTe shows high absorption (− 15 × 104 1/cm) in few portions of the spectrum (− 380–430 nm). Metal adsorbed structures Ga2SeTe/Ni, Ga2SeTe/Pd, Ga2SeTe/Pt and Ga2SeTe/V results into redshift phenomena, which means that the absorption increases with the wavelength, or we can say that the absorption coefficient moved toward the red range of the spectrum. Absorption coefficient of Ni adsorbed structure is four times higher (− 60 × 104 1/cm) than the pristine Janus monolayer of Ga2SeTe. Considerably, higher absorption is also seen in other structures in the entire visible range (− 380–790 nm) of the spectrum. Dielectric function and refractive index of all metal adsorbed structures also calculated, and it is found that the absorption coefficient is in line with the dielectric constant. Due to its higher absorption peaks in the whole visible region, it is a potential candidate for optoelectronic applications and photovoltaic absorbers

Effect of Twisting and Stretching on Magneto Resistance and Spin Filtration in CNTs

Spin-dependent quantum transport properties in twisted carbon nanotube and stretched carbon nanotube are calculated using density functional theory (DFT) and non-equilibrium green’s function (NEGF) formulation. Twisting and stretching have no effect on spin transport in CNTs at low bias voltages. However, at high bias voltages the effects are significant. Stretching restricts any spin-up current in antiparallel configuration (APC), which results in higher magneto resistance (MR). Twisting allows spin-up current almost equivalent to the pristine CNT case, resulting in lower MR. High spin filtration is observed in PC and APC for pristine, stretched and twisted structures at all applied voltages. In APC, at low voltages spin filtration in stretched CNT is higher than in pristine and twisted ones, with pristine giving a higher spin filtration than twisted CNT

Tuning the tunneling magnetoresistance by using fluorinated graphene in graphene based magnetic junctions

Spin polarized properties of fluorinated graphene as tunnel barrier with CrO2 as two HMF electrodes are studied using first principle methods based on density functional theory. Fluorinated graphene with different fluorine coverages is explored as tunnel barriers in magnetic tunnel junctions. Density functional computation for different fluorine coverages imply that with increase in fluorine coverages, there is increase in band gap (Eg) of graphene, Eg ∼ 3.466 e V was observed when graphene sheet is fluorine adsorbed on both-side with 100% coverage (CF). The results of CF graphene are compared with C4F (fluorination on one-side of graphene sheet with 25% coverage) and out-of-plane graphene based magnetic tunnel junctions. On comparison of the results it is observed that CF graphene based structure offers high TMR ∼100%, and the transport of carrier is through tunneling as there are no transmission states near Fermi level. This suggests that graphene sheet with both-side fluorination with 100% coverages acts as a perfect insulator and hence a better barrier to the carriers which is due to negligible spin down current (I↓) in both Parallel Configuration (PC) and Antiparallel Configuration (APC)