Peering through the veil: near-infrared photometry and extinction for the Galactic nuclear star cluster

The aims of this work are to provide accurate photometry in multiple near-infrared broadband filters, to determine the power-law index of the extinction-law toward the central parsec of the Galaxy, to provide measurements of the absolute extinction toward the Galactic center, and finally to measure the spatial variability of extinction on arcsecond scales.We use adaptive optics observations of the central parsec of the Milky Way. Absolute values for the extinction in the H, Ks, and L'-bands as well as of the power-law indices of the H to Ks and Ks to L' extinction-laws are measured based on the well-known properties of red clump stars. Extinction maps are derived based on H-Ks and Ks-L' colors. We present Ks-band photometry for ~7700 stars (H and L' photometry for a subset). From a number of recently published values we compute a mean distance of the Galactic center of R_0=8.03+-0.15 kpc, which has an uncertainty of just 2%. Based on this R_0 and on the RC method, we derive absolute mean extinction values toward the central parsec of the Galaxy of A_H=4.48+-0.13 mag, A_Ks=2.54+-0.12$ mag, and A_L'=1.27+-0.18 mag. We estimate values of the power-law indices of the extinction-law of alpha_{H-Ks}=2.21+-0.24 and alpha_{Ks-L'}=1.34+-0.29. A Ks-band extinction map for the Galactic center is computed based on this extinction law and on stellar H-Ks colors. Mean extinction values in a circular region with 0.5" radius centered on Sagittarius A* are A_{H, SgrA*}=4.35+-0.12, A_{Ks, SgrA*}=2.46+-0.03, and A_{L', SgrA*}=1.23+-0.08.Comment: accepted for publication by Astronomy & Astrophysics; please contact RS for higher quality figure

The Position of Sgr A∗^* at the Galactic Center

The absolute position of the compact radio source at the dynamical center of the Galaxy, Sgr A$^*$, was known only to an accuracy of $0.2''$ in spite of its accurate location with respect to near-IR stellar sources to within 30 milliarcsecond (mas). To remedy this poor positional accuracy, we have selected 15 high-resolution, high-frequency VLA observations of Sgr A$^*$ carried out in the last 13 years and determined the weighted average position with the average epoch 1992.4 to be at $\alpha$, $\delta$[1950] = $17^{\rm h} 42^{\rm m}$ 29\dsec3076$\pm0.0007$, $-28^\circ 59^\prime 18.484\pm0.014^{\prime\prime}$, or $\alpha$, $\delta$[2000] = $17^{\rm h} 45^{\rm m}$ 40\dsec0383$\pm0.0007$, $-29^\circ 00^\prime 28.069\pm0.014^{\prime\prime}$ which agrees with earlier published values to within the $0.2''$ error bars of the earlier measurements. An accurate absolute position of Sgr A$^*$ can be useful for its identification with sources at other wavelengths, particularly, in soft and hard X-rays with implications for the models of a massive black hole at the Galactic center.Comment: 11 pages, one figure and one table. ApJL (in press

Proper Motions of Ionized Gas at the Galactic Center: Evidence for Unbound Orbiting Gas

We present radio continuum observations of the spiral-shaped ionized feature (Sgr A West) within the inner pc of the Galactic center at three epochs spanning 1986 to 1995. The VLA A-configuration was used at $\lambda$2cm (resolution of 0\dasec1$\times$0\dasec2). We detect proper motions of a number of features in the Northern and Eastern Arms of Sgr A West including the ionized gas associated with IRS 13 with V(RA)= 113 \pm 10, V(Dec)=150 \pm15 km/s, IRS 2 with V(RA)= 122 \pm 11, V(Dec)=24 \pm 34 km/s and the Norther Arm V(RA)= 126 \pm 30, V(Dec)=--207 \pm 58 km/s. We also report the detection of features having transverse velocities > 1000 km/s including a head-tail radio structure, the ``Bullet'', $\approx4''$ northwest of Sgr A$^*$ with V(RA)= 722 \pm 156, V(Dec)=832 \pm 203 km/s, exceeding the escape velocity at the Galactic center. The proper motion measurements when combined with previous H92$\alpha$ radio recombination line data suggest an unambiguous direction of the flow of ionized gas orbiting the Galactic center. The measured velocity distribution suggests that the ionized gas in the Northern Arm is not bound to the Galactic center assuming a 2.5 million solar mass of dark matter residing at the Galactic center. This implies that the stellar and ionized gas systems are not dynamically coupled, thus, supporting a picture in which the gas features in the Northern Arm and its extensions are the result of an energetic phenomenon that has externally driven a cloud of gas cloud into the Galactic center.Comment: 11 pages, three figures (one color) and one table. Astrophysical Journal Letters in pres

Simultaneous NIR/sub-mm observation of flare emission from SgrA*

We report on a successful, simultaneous observation and modeling of the sub-millimeter to near-infrared flare emission of the Sgr A* counterpart associated with the super-massive black hole at the Galactic center. Our modeling is based on simultaneous observations that have been carried out on 03 June, 2008 using the NACO adaptive optics (AO) instrument at the ESO VLT and the LABOCA bolometer at the APEX telescope. Inspection and modeling of the light curves show that the sub-mm follows the NIR emission with a delay of 1.5+/-0.5 hours. We explain the flare emission delay by an adiabatic expansion of the source components.Comment: 12 pages, 9 figures, 3 tables, in press with A&

Innovative manufacturing technologies for the disassembly of consumer goods

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Ecological harmless disposal of used technical consumer products will become mandatory for producers and importing companies. This disposal policy will focus on product and material loops; used products will be disassembled and the parts and materials then recycled. Owing to environmental and legislative reasons, the importance of disassembly as a step in the process of recycling is steadily rising. The article presents developed technologies and tools for the disassembly of consumer goods. The aim is to recover materials and reusable components within a semiautomatic pilot disassembly system. Different destructive processes were optimized to disassemble washing machines

Coordinated NIR/mm observations of flare emission from Sagittarius A*

We report on a successful, simultaneous observation and modelling of the millimeter (mm) to near-infrared (NIR) flare emission of the Sgr A* counterpart associated with the supermassive black hole at the Galactic centre (GC). We present a mm/sub-mm light curve of Sgr A* with one of the highest quality continuous time coverages and study and model the physical processes giving rise to the variable emission of Sgr A*.Comment: 14 pages, 16 figure

Resolving the Host Galaxy of the Nearby QSO I Zw 1 with Sub-Arcsecond Multi-Transition Molecular Line Observations

We present the first sub-kpc 0.7" (~ 850 pc) resolution 12CO(1-0) molecular line observations of the ISM in the host galaxy of the QSO I Zw 1. The observations were obtained with the BIMA mm-interferometer in its compact A configuration. The BIMA data are complemented by new observations of the 12CO(2-1) and 13CO(1-0) line with IRAM Plateau de Bure mm-interferometer (PdBI) at 0.9" and 1.9" resolution, respectively. These measurements, which are part of a multi-wavelength study of the host galaxy of I Zw 1, are aimed at comparing the ISM properties of a QSO host with those of nearby galaxies as well as to obtain constraints on galaxy formation/evolution models. Our images of the 12CO(1-0) line emission show a ring-like structure in the circumnuclear molecular gas distribution with an inner radius of about 1.2 kpc. The presence of such a molecular gas ring was predicted from earlier lower angular resolution PdBI 12CO(1-0) observations. A comparison of the BIMA data with IRAM PdBI 12CO(2-1) observations shows variations in the excitation conditions of the molecular gas in the innermost 1.5" comprising the nuclear region of I Zw 1. The observed properties of the molecular cloud complexes in the disk of the host galaxy suggest that they can be the sites of massive circumnuclear star formation, and show no indications of excitation by the nuclear AGN. This all indicates that the molecular gas in a QSO host galaxy has similar properties to the gas observed in nearby low luminosity AGNs.Comment: to be published in ApJ 1 July 2004 issu

Astrometry of circumstellar masers

The circumstellar masers around evolved stars offer an interesting possibility to measure stellar parameters through VLBI astrometry. In this paper the application of this technique is discussed, including the accuracy and the uncertainties of the method. The different maser species (OH, H_2O, SiO) have slightly different characteristics and applications. This paper does not concern astrometry of maser spots to study the kinematics of the envelope, but concentrates on attempting to measure the motion of the underlying star.Comment: 8 pages, 2 figures, to appear in "Mass-losing Stars and their Circumstellar Matter", eds Y. Nakada & M. Honma, Kluwer ASSL serie

The Jet in the Galactic Center: An Ideal Laboratory for Magnetohydrodynamics and General Relativity

In this paper we review and discuss some of the intriguing properties of the Galactic Center supermassive black hole candidate Sgr A*. Of all possible black hole sources, the event horizon of Sgr A*, subtends the largest angular scale on the sky. It is therefore a prime candidate to study and image plasma processes in strong gravity and it even allows imaging of the shadow cast by the event horizon. Recent mm-wave VLBI and radio timing observations as well as numerical GRMHD simulations now have provided several breakthroughs that put Sgr A* back into the focus. Firstly, VLBI observations have now measured the intrinsic size of Sgr A* at multiple frequencies, where the highest frequency measurements have approached the scale of the black hole shadow. Moreover, measurements of the radio variability show a clear time lag between 22 GHz and 43 GHz. The combination of size and timing measurements, allows one to actually measure the flow speed and direction of magnetized plasma at some tens of Schwarzschild radii. This data strongly support a moderately relativistic outflow, consistent with an accelerating jet model. This is compared to recent GRMHD simulation that show the presence of a moderately relativistic outflow coupled to an accretion flow Sgr A*. Further VLBI and timing observations coupled to simulations have the potential to map out the velocity profile from 5-40 Schwarzschild radii and to provide a first glimpse at the appearance of a jet-disk system near the event horizon. Future submm-VLBI experiments would even be able to directly image those processes in strong gravity and directly confirm the presence of an event horizon.Comment: invited talk to appear in "Jets on All Scales", IAU Symposium 275, G.E. Romero, R.A. Sunyaev & T. Belloni, eds., Cambridge University Press, 9 pages, LaTex, 4 figure