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We present a large ${\sim 30" \times 30"}$ spectroscopic survey of the Galactic Center using the SINFONI IFU at the VLT. Combining observations of the last two decades we compile spectra of over $2800$ stars. Using the Bracket-$\gamma$ absorption lines we identify $195$ young stars, extending the list of known young stars by $79$. In order to explore the angular momentum distribution of the young stars, we introduce an isotropic cluster prior. This prior reproduces an isotropic cluster in a mathematically exact way, which we test through numerical simulations. We calculate the posterior angular momentum space as function of projected separation from Sgr~A*. We find that the observed young star distribution is substantially different from an isotropic cluster. We identify the previously reported feature of the clockwise disk and find that its angular momentum changes as function of separation from the black hole, and thus confirm a warp of the clockwise disk ($p \sim 99.2\%$). At large separations, we discover three prominent overdensities of angular momentum. One overdensity has been reported previously, the counter-clockwise disk. The other two are new. Determining the likely members of these structures, we find that as many as $75\%$ of stars can be associated with one of these features. Stars belonging to the warped clockwise-disk show a top heavy K-band luminosity function, while stars belonging to the larger separation features do not. Our observations are in good agreement with the predictions of simulations of in-situ star formation, and argue for common formation of these structures., Comment: Accepted for Publication in APJL

With the upgrade from GRAVITY to GRAVITY$^+$ the instrument will evolve into an all-sky interferometer that can observe faint targets, such as high redshift AGN. Observing the faintest targets requires reducing the noise sources in GRAVITY as much as possible. The dominant noise source, especially in the blue part of the spectrum, is the backscattering of the metrology laser light onto the detector. To reduce this noise we introduce two new metrology modes. With a combination of small hardware changes and software adaptations, we can dim the metrology laser during the observation without losing the phase referencing. For single beam targets, we can even turn off the metrology laser for the maximum SNR on the detector. These changes lead to an SNR improvement of over a factor of two averaged over the whole spectrum and up to a factor of eight in the part of the spectrum currently dominated by laser noise., Comment: Proceeding of SPIE Astronomical Telescopes + Instrumentation 2022

We present the successful demonstration of world's first large-separation ~30" off-axis fringe tracking with four telescopes in October 2019. With this technique we increase the sky-coverage for optical interferometry by orders of magnitude compared to current technology. Following the early work at the Palomar Testbed Interferometer, the first demonstration of off-axis fringe tracking at the Keck Interferometer and with PRIMA at the ESO Very Large Telescope Interferometer, and the breakthrough with the GRAVITY Galactic Center observations, we enhanced the VLTI infrastructure for GRAVITY to take advantage of the PRIMA Star separators and Differential Delay Lines for off-axis fringe tracking. In our presentation we give an introduction to the subject, present the enhancements of the VLTI, and present our results from the first on-sky operation in October 2019, with observations of the Orion Trapezium Cluster, a field brown dwarf, and a high redshift quasar.