The orbit of the star S2 around SgrA* from VLT and Keck data

Two recent papers (Ghez et al. 2008, Gillessen et al. 2009) have estimated the mass of and the distance to the massive black hole in the center of the Milky Way using stellar orbits. The two astrometric data sets are independent and yielded consistent results, even though the measured positions do not match when simply overplotting the two sets. In this letter we show that the two sets can be brought to excellent agreement with each other when allowing for a small offset in the definition of the reference frame of the two data sets. The required offsets in the coordinates and velocities of the origin of the reference frames are consistent with the uncertainties given in Ghez et al. (2008). The so combined data set allows for a moderate improvement of the statistical errors of mass of and distance to Sgr A*, but the overall accuracies of these numbers are dominated by systematic errors and the long-term calibration of the reference frame. We obtain R0 = 8.28 +- 0.15(stat) +- 0.29(sys) kpc and M(MBH) = 4.30 +- 0.20(stat) +- 0.30(sys) x 10^6 Msun as best estimates from a multi-star fit.Comment: submitted to ApJ

Calcium isotopic composition of high-latitude proxy carrier Neogloboquadrina pachyderma (sin.)

The accurate reconstruction of sea surface temperature (SST) history in climate-sensitive regions (e.g. tropical and polar oceans) became a challenging task in palaeoceanographic research. Biogenic shell carbonate SST proxies successfully developed for tropical regions often fail in cool water environments. Their major regional shortcomings and the cryptic diversity now found within the major high latitude proxy carrier Neogloboquadrina pachyderma (sin.) highlight an urgent need to explore complementary SST proxies for these cool-water regions. Here we incorporate the genetic component into a calibration study of a new SST proxy for the high latitudes. We found that the calcium isotopic composition (δ44/40Ca) of calcite from genotyped net catches and core-top samples of the planktonic foraminifera Neogloboquadrina pachyderma (sin.) is related to temperature and unaffected by genetic variations. The temperature sensitivity has been found to be 0.17 (±0.02)‰ per 1°C, highlighting its potential for downcore applications in open marine cool-water environments. Our results further indicate that in extreme polar environments, below a critical threshold temperature of 2.0 (±0.5)°C associated with salinities below 33.0 (±0.5)‰, a prominent shift in biomineralization affects the δ44/40Ca of genotyped and core-top N. pachyderma (sin.), becoming insensitive to temperature. These findings highlight the need of more systematic calibration studies on single planktonic foraminiferal species in order to unravel species-specific factors influencing the temperature sensitivity of Ca isotope fractionation and to validate the proxies' applicability

A new era of spectroscopy: SINFONI, NIR integral field spectroscopy at the diffraction limit of an 8m telescope

SINFONI, the SINgle Faint Object Near-infrared Investigation, is an instrument for the Very Large Telescope (VLT), which will start its operation mid 2002 and allow for the first time near infrared (NIR) integral field spectroscopy at the diffraction limit of an 8-m telescope. SINFONI is the combination of two state-of-the art instruments, the integral field spectrometer SPIFFI, built by the Max-Planck-Institut fuer extraterrestrische Physik (MPE), and the adaptive optics (AO) system MACAO, built by the European Southern Observatory (ESO). It will allow a unique type of observations by delivering simultaneously high spatial resolution (pixel sizes 0.025arcsec to 0.25arcsec) and a moderate spectral resolution (R~2000 to R~4500), where the higher spectral resolution mode will allow for software OH suppression. This opens new prospects for astronomy.Comment: 9 pages, 4 figures, to appear in SPIE proceedings "Astronomical Telescopes and Instrumentation 2000". More recent sensitivity estimates are available at http://www.mpe.mpg.de/www_ir/ir_instruments/sinfoni/spiffi.ht

The power of monitoring stellar orbits

The center of the Milky Way hosts a massive black hole. The observational evidence for its existence is overwhelming. The compact radio source Sgr A* has been associated with a black hole since its discovery. In the last decade, high-resolution, near-infrared measurements of individual stellar orbits in the innermost region of the Galactic Center have shown that at the position of Sgr A* a highly concentrated mass of 4 x 10^6 M_sun is located. Assuming that general relativity is correct, the conclusion that Sgr A* is a massive black hole is inevitable. Without doubt this is the most important application of stellar orbits in the Galactic Center. Here, we discuss the possibilities going beyond the mass measurement offered by monitoring these orbits. They are an extremely useful tool for many scientific questions, such as a geometric distance estimate to the Galactic Center or the puzzle, how these stars reached their current orbits. Future improvements in the instrumentation will open up the route to testing relativistic effects in the gravitational potential of the black hole, allowing to take full advantage of this unique laboratory for celestial mechanics.Comment: Proceedings of the Galactic Center Workshop 2009, Shangha

Massive binaries in the vicinity of Sgr A*

A long-term spectroscopic and photometric survey of the most luminous and massive stars in the vicinity of the super-massive black hole Sgr A* revealed two new binaries; a long-period Ofpe/WN9 binary, GCIRS 16NE, with a modest eccentricity of 0.3 and a period of 224 days and an eclipsing Wolf-Rayet binary with a period of 2.3 days. Together with the already identified binary GCIRS 16SW, there are now three confirmed OB/WR binaries in the inner 0.2\,pc of the Galactic Center. Using radial velocity change upper limits, we were able to constrain the spectroscopic binary fraction in the Galactic Center to $F_{\rm SB}=0.27^{+0.29}_{-0.19}$ at a confidence level of 95%, a massive binary fraction similar to that observed in dense clusters. The fraction of eclipsing binaries with photometric amplitudes $\Delta m>0.4$ is $F^{\rm GC}_{\rm EB}=3\pm2$, which is consistent with local OB star clusters ($F_{\rm EB}=1$). Overall the Galactic Center binary fraction seems to be close to the binary fraction in comparable young clusters.Comment: 5 figures, submitted to Ap

On the nature of the fast moving star S2 in the Galactic Center

We analyze the properties of the star S2 orbiting the supermassive black hole at the center of the Galaxy. A high quality SINFONI H and K band spectrum obtained from coadding 23.5 hours of observation between 2004 and 2007 reveals that S2 is an early B dwarf (B0-2.5V). Using model atmospheres, we constrain its stellar and wind properties. We show that S2 is a genuine massive star, and not the core of a stripped giant star as sometimes speculated to resolve the problem of star formation so close to the supermassive black hole. We give an upper limit on its mass loss rate, and show that it is He enriched, possibly because of the presence of a magnetic field.Comment: 4 pages, 5 figures, ApJ letters accepte

Pericenter passage of the gas cloud G2 in the Galactic Center

We have further followed the evolution of the orbital and physical properties of G2, the object currently falling toward the massive black hole in the Galactic Center on a near-radial orbit. New, very sensitive data were taken in April 2013 with NACO and SINFONI at the ESO VLT . The 'head' of G2 continues to be stretched ever further along the orbit in position-velocity space. A fraction of its emission appears to be already emerging on the blue-shifted side of the orbit, past pericenter approach. Ionized gas in the head is now stretched over more than 15,000 Schwarzschild radii RS around the pericenter of the orbit, at ~ 2000 RS ~ 20 light hours from the black hole. The pericenter passage of G2 will be a process stretching over a period of at least one year. The Brackett-{\gamma} luminosity of the head has been constant over the past 9 years, to within +- 25%, as have the line ratios Brackett-{\gamma} / Paschen-{\alpha} and Brackett-{\gamma} / Helium-I. We do not see any significant evidence for deviations of G2's dynamical evolution, due to hydrodynamical interactions with the hot gas around the black hole, from a ballistic orbit of an initially compact cloud with moderate velocity dispersion. The constant luminosity and the increasingly stretched appearance of the head of G2 in the position-velocity plane, without a central peak, is not consistent with several proposed models with continuous gas release from an initially bound zone around a faint star on the same orbit as G2.Comment: 10 figures, submitted to Ap

Improving Monolithic Perovskite Silicon Tandem Solar Cells From an Optical Viewpoint

Perovskite silicon tandem solar cells are the most promising concept for a future photovoltaic technology. We report on recent progress from an optical viewpoint and disucss how we achieved more than 25 device efficienc

Hydrodynamical simulations of a compact source scenario for G2

The origin of the dense gas cloud G2 discovered in the Galactic Center (Gillessen et al. 2012) is still a debated puzzle. G2 might be a diffuse cloud or the result of an outflow from an invisible star embedded in it. We present here detailed simulations of the evolution of winds on G2's orbit. We find that the hydrodynamic interaction with the hot atmosphere present in the Galactic Center and the extreme gravitational field of the supermassive black hole must be taken in account when modeling such a source scenario. We find that the hydrodynamic interaction with the hot atmosphere present in the Galactic Center and the extreme gravitational field of the supermassive black hole must be taken in account when modeling such a source scenario. We also find that in this scenario most of the Br\gamma\ luminosity is expected to come from the highly filamentary densest shocked wind material. G2's observational properties can be used to constrain the properties of the outflow and our best model has a mass outflow rate of Mdot,w=8.8 x 10^{-8} Msun/yr and a wind velocity of vw = 50 km/s. These values are compatible with those of a young TTauri star wind, as already suggested by Scoville & Burkert (2013).Comment: 4 pages, 3 figures; Proceeding of the IAU 303: "The GC: Feeding and Feedback in a Normal Galactic Nucleus" / September 30 - October 4, 2013, Santa Fe, New Mexico (USA