Stellar orbits at the Galactic Center provide a very clean probe of gravitational potential supermassive black hole. They can be studied with unique precision, beyond confusion limit single telescope, near-infrared interferometer GRAVITY. Imaging is essential to search field for faint, unknown stars on short which potentially could constrain hole spin. Furthermore, it provides starting point as...

Low-resolution LAMOST and Keck spectra of blue supergiant stars distributed over the disks Local Group spiral galaxies M 31 33 are analyzed to determine stellar effective temperatures, gravities, metallicities, reddening. Logarithmic metallicities at center (in solar units) $0.30\pm0.09$ $0.11\pm0.04$ metallicity gradients $-0.37\pm0.13$ dex/$R_{25}$ $-0.36\pm0.16$ measured for 33, respectively...