UNICS - An Unified Instrument Control System for Small/Medium Sized Astronomical Observatories

Although the astronomy community is witnessing an era of large telescopes, smaller and medium sized telescopes still maintain their utility being larger in numbers. In order to obtain better scientific outputs it is necessary to incorporate modern and advanced technologies to the back-end instruments and to their interfaces with the telescopes through various control processes. However often tight financial constraints on the smaller and medium size observatories limit the scope and utility of these systems. Most of the time for every new development on the telescope the back-end control systems are required to be built from scratch leading to high costs and efforts. Therefore a simple, low cost control system for small and medium size observatory needs to be developed to minimize the cost and efforts while going for the expansion of the observatory. Here we report on the development of a modern, multipurpose instrument control system UNICS (Unified Instrument Control System) to integrate the controls of various instruments and devices mounted on the telescope. UNICS consists of an embedded hardware unit called Common Control Unit (CCU) and Linux based data acquisition and User Interface. The Hardware of the CCU is built around the Atmel make ATmega 128 micro-controller and is designed with a back-plane, Master Slave architecture. The Graphical User Interface (GUI) has been developed based on QT and the back end application software is based on C/C++. UNICS provides feedback mechanisms which give the operator a good visibility and a quick-look display of the status and modes of instruments. UNICS is being used for regular science observations since March 2008 on 2m, f/10 IUCAA Telescope located at Girawali, Pune India.Comment: Submitted to PASP, 10 Pages, 5 figure

Structural and magnetic properties of the quantum magnet BaCuTe2O6

We investigate the structural and magnetic properties of the quantum magnet BaCuTe2O6. This compound is synthesized in powder and single crystal form for the first time. Synchrotron x ray and neutron diffraction reveal a cubic crystal structure P4132 where the magnetic Cu2 ions form a complex network. Heat capacity and static magnetic susceptibility measurements suggest the presence of antiferromagnetic interactions with a Curie Weiss temperature of amp; 8776; amp; 8722;33 K, while long range magnetic order occurs at the much lower temperature of amp; 8776;6.3 K. The magnetic structure, solved using neutron diffraction, reveals antiferromagnetic order along chains parallel to the a, b, and c crystal axes. This is consistent with the magnetic excitations which resemble the multispinon continuum typical of the spin 1 2 Heisenberg antiferromagnetic chain. A consistent intrachain interaction value of amp; 8776;34 K is achieved from the various techniques. Finally the magnetic structure provides evidence that the chains are coupled together in a noncollinear arrangement by a much weaker antiferromagnetic, frustrated hyperkagome interactio

Magnetic excitation spectrum and Hamiltonian of the quantum spin chain compound BaCuTe2O6

AbstractThe magnetic excitation spectrum and Hamiltonian of the quantum magnet BaCuTe2O6 is studied by inelastic neutron scattering (INS) and density functional theory (DFT). INS on powder and single crystal samples reveals overlapping spinon continua—the spectrum of an antiferromagnetic spin-1/2 spin chain—due to equivalent chains running along the a, b, and c directions. Long-range magnetic order onsets below TN=6.3 K due to interchain interactions, and is accompanied by the emergence of sharp spin-wave excitations, which replace the continua at low energies. The spin-wave spectrum is highly complex and was successfully modelled achieving excellent agreement with the data. The extracted interactions reveal an intrachain interaction, J3=2.9 meV, while the antiferromagnetic hyperkagome interaction J2 is the subleading interaction responsible for coupling the chains together in a frustrated way. DFT calculations reveal a similar picture for BaCuTe2O6 of dominant J3 and subleading J2 antiferromagnetic interactions and also indicate a high sensitivity of the interactions to small changes of structure, which could explain the very different Hamiltonians observed in the sister compounds SrCuTe2O6 and PbCuTe2O6

Strongly coupled charge, orbital, and spin order in TbTe3

We report a ground state with strongly coupled magnetic and charge density wave orders mediated via orbital ordering in the layered compound TbTe3. In addition to the commensurate antiferromagnetic (AFM) and charge density wave (CDW) orders, new magnetic peaks are observed whose propagation vector equals the sum of the AFM and CDW propagation vectors, revealing an intricate and highly entwined relationship. This is especially interesting given that the magnetic and charge orders lie in different layers of the crystal structure where the highly localized magnetic moments of the Tb3+ ions are netted in the Tb-Te stacks, while the charge order is formed by the conduction electrons of the adjacent Te-Te layers. Our results, based on neutron diffraction and resonant x-ray scattering, reveal that the charge and magnetic subsystems mutually influence each other via the orbital ordering of Tb3+ ions. © 2020 American Physical Society.S. C. thanks K. Prokes for the helpful insights regarding the heavy-fermion physics. This work has been partially supported by the Ministry of Education and Science of the Russian Federation, Contracts No. 02.A03.21.0006 and No. 02.A03.21.0011

Evidence for a three dimensional quantum spin liquid in PbCuTe2O6

The quantum spin liquid is a highly entangled magnetic state characterized by the absence of static magnetism in its ground state. Instead, the spins fluctuate in a highly correlated way down to the lowest temperatures. Quantum spin liquids are very rare and are confined to a few specific cases where the interactions between the magnetic ions cannot be simultaneously satisfied known as frustration . Lattices with magnetic ions in triangular or tetrahedral arrangements, which interact via isotropic antiferromagnetic interactions, can generate such a frustration. Three dimensional isotropic spin liquids have mostly been sought in materials where the magnetic ions form pyrochlore or hyperkagome lattices. Here we present a three dimensional lattice called the hyper hyperkagome that enables spin liquid behaviour and manifests in the compound PbCuTe2O6. Using a combination of experiment and theory, we show that this system exhibits signs of being a quantum spin liquid with no detectable static magnetism together with the presence of diffuse continua in the magnetic spectrum suggestive of fractional spinon excitation