Our central Galactic supermassive black hole, Sgr A*, exists mostly in a very stable, extremely low-luminosity (∼ 10LEdd), thermal quiescent state, which is interrupted roughly daily by a brief, nonthermal X-ray flare. Because they are not accompanied by significant changes in the radio wavelengths, the flares make Sgr A* unusual in the context of black holes accreting at slightly higher rates....

With 10 years of high-resolution imaging data now available on the stellar cluster in the Galactic Center, we present proper motions for >40 stars at projected distances ≤ 1.2 ′′ from Sagittarius A* (Sgr A*). We find evidence on a ≥ 2σ level for radial anisotropy of the cluster of stars within 1 ′′ of Sgr A*. For a brightness limit of K ∼ 15.5 we find no evidence for a stationary source at the ...

We present deep color-magnitude diagrams for two Subaru Suprime-Cam fields in the Virgo Stellar Stream(VSS)/Virgo Overdensity(VOD) and compare them to a field centred on the highest concentration of Sagittarius (Sgr) Tidal Stream stars in the leading arm, Branch A of the bifurcation. A prominent population of main sequence stars is detected in all three fields and can be traced as faint as g ≈ ...

We investigate the evolutionary status of four stars: V348 Sgr, DY Cen and MV Sgr in the Galaxy and HV 2671 in the LMC. These stars have in common random deep declines in visual brightness which are characteristic for R Coronae Borealis (RCB) stars. RCB stars are typically cool, hydrogen deficient supergiants. The four stars studied in this paper are hotter (Teff = 15-20 kK) than the majority o...

Observations of two H2CO (303−202 and 321−220) lines and continuum emission at 1.3 mm towards Sgr B2(N) and Sgr B2(M) have been carried out with the SMA. The mosaic maps of Sgr B2(N) and Sgr B2(M) in both continuum and lines show a complex distribution of dust and molecular gas in both clumps and filaments surrounding the compact star formation cores. We have observed a decelerating outflow ori...

We present new absolute trigonometric parallaxes and relative proper motions for nine Galactic Cepheid variable stars: l Car, ζ Gem, β Dor, W Sgr, X Sgr, Y Sgr, FF Aql, T Vul, and RT Aur. We obtain these results with astrometric data from Fine Guidance Sensor 1r, a white-light interferometer on Hubble Space Telescope. We find absolute parallaxes in milliseconds of arc: l Car, 2.01± 0.20 ; ζ Gem...

We summarize the results of 7 mm VLBA imaging of Sgr A* and discuss some of the diiculties of accurately constraining the size of Sgr A* with VLBI observations. Our imaging results are fully consistent with the hypothesis that the VLBA image of Sgr A* is a resolved elliptical Gaussian caused by the scattering of an intervening thermal plasma. We show that determination of the minor axis size at...

We observed Sgr A* at 1.3 cm on 1992 November 8 with a 14 station VLBI array and, using data from 10 of these stations, obtained a high-dynamic range image with a beam of 3.35×1.7 milliarcseconds in position angle 14◦. The observed surface brightness distribution of Sgr A* is best modelled by an elliptically shaped gaussian component with parameter values: flux density 1.05 ± 0.10 Jy, major axi...

We report on recent near-IR observations of V4332 Sgr the nova-like variable that erupted in 1994. Its rapid, post-outburst evolution to a cool M type giant/supergiant, soon after its outburst, had showed that it was an unusual object differing from other eruptive variables like classical/symbiotic novae or born-again AGB stars. The present study of V4332 Sgr was motivated by the keen interest ...

The rapidly varying non-thermal X-ray emission observed from Sgr A⋆ points to particle acceleration taking place close to the supermassive black hole. The TeV γ-ray source HESS J1745−290 is coincident with Sgr A⋆ and may be closely related to the X-ray emission. Simultaneous X-ray and TeV observations are required to elucidate the relationship between these two objects. Here we report on joint ...