Low-mass star formation in CG1: a diffraction limited search for pre-main sequence stars next to NX Puppis

Using adaptive optics at the ESO 3.6m telescope, we obtained diffraction limited JHK-images of the region around the Herbig AeBe star NX Pup. We clearly resolved the close companion (sep. 0.128") to NX Pup -- originally discovered by HST -- and measured its JHK magnitudes. A third object at a separation of 7.0" from NX Pup was identified as a classical T Tauri star so that NX Pup may in fact form a hierarchical triple system. We discuss the evolutionary status of these stars and derive estimates for their spectral types, luminosities, masses and ages.Comment: Latex using l-aa-ps.sty with links to 5 postscript figures. Complete postscript version also available at http://lucky.astro.uni-wuerzburg.de/ Accepted for publication in A&

INFLUENCE OF DIFFERENT SURFACE MATERIALS ON THE FOULING PROCESS IN A MICROSTRUCTURED HEAT EXCHANGER UNDER LAMINAR REGIME

Microstructure devices are well known for their excellent performance with regard to heat and mass transfer. Microstructured heat exchangers show significant advantages in comparison with conventional heat exchangers. The unique properties of a microreaction system show high overall heat transfer coefficients for example. Small characteristic dimensions are in the order of a few hundred μm (Schubert et al., 1998, 2001; Worz et al, 1998). Due to the small dimensions, an increased pressure drop is combined with excellent heat transfer properties. But the small channels are prone to fouling processes. The accumulation of crystalline deposits is a severe problem. An additional wall layer causes a decrease of the overall heat transfer coefficient. Therefore the attention has been directed to the reduction of possible fouling processes within the channels. The fouling can be subdivided in two parts: First into the induction period and second into the so-called fouling period itself (Lund et al., 1981; Forster et al., 1999a, 1999b, and 2000). For the investigations a special electrically heated micro heat exchanger with changeable foils of different surface materials (stainless steel, FEP, DLC) was developed. The foil temperature is electronically controlled to a constant level of 100°C. A solution of calciumnitrate/sodiumhydrogencarbonate is pumped under laminar flow conditions through the channels of the microstructured part. The high temperature causes the precipitation of solid calciumcarbonate on the surface. The results for all materials, the uncoated stainless steel and the DLC and FEP coated heat transfer surfaces, show typical fouling behaviour with an induction period, followed by an asymptotic built-up of the deposited calcium carbonate. The fouling plot of DLC and FEP coated heat transfer surfaces contradict the hypothesis that the use of such materials leads to much longer induction periods. There is no influence of the surface material found on the induction period and the gradient of the fouling period in the laminar flow regime

METALLIC MICRO HEAT EXCHANGERS: PROPERTIES, APPLICATIONS AND LONG TERM STABILITY

Micro heat exchangers, which until recently have been implemented only at laboratory scale, are now being available for industrial applications. They are well known for their superior heat transfer properties due to the large surface-to-volume ratio. But there are little data available on the long term stability of these devices. In this paper application several application examples for micro heat exchangers made of stainless steel are presented. The devices consist of stainless steel foils providing numerous micro channels generated by mechanical micromachining or wet chemical etching. A number of the foils are arranged in a specific way and bonded together. Device property descriptions as well as some possible application examples show the potential of metallic microstructure devices. Results on two crossflow microstructure heat exchangers running in long term tests are presented. Both devices have been tested for more than 8000 hours each, using deionised water as test fluid. Experimental data on the heat transfer properties and the pressure drop are given and compared. It was found that the heat transfer capabilities were significantly decreased within the first few hundred hours of testing and then run into a saturation state. Performance degradation may be due to a fouling layer deposited on the heat exchange surface. Some other experimental applications in which fouling was expected to cause problems are described briefly

The GRAVITY fringe tracker: correlation between optical path residuals and atmospheric parameters

After the first year of observations with the GRAVITY fringe tracker, we compute correlations between the optical path residuals and atmospheric and astronomical parameters. The median residuals of the optical path residuals are 180 nm on the ATs and 270 nm on the UTs. The residuals are uncorrelated with the target magnitudes for Kmag below 5.5 on ATs (9 on UTs). The correlation with the coherence time is however extremely clear, with a drop-off in fringe tracking performance below 3 ms.Comment: submitted to SPIE Astronomical Telescopes & Instrumentation 201

The proper motion of the Arches cluster with Keck Laser-Guide Star Adaptive Optics

We present the first measurement of the proper motion of the young, compact Arches cluster near the Galactic center from near-infrared adaptive optics (AO) data taken with the recently commissioned laser-guide star (LGS) at the Keck 10-m telescope. The excellent astrometric accuracy achieved with LGS-AO provides the basis for a detailed comparison with VLT/NAOS-CONICA data taken 4.3 years earlier. Over the 4.3 year baseline, a spatial displacement of the Arches cluster with respect to the field population is measured to be 24.0 +/- 2.2 mas, corresponding to a proper motion of 5.6 +/- 0.5 mas/yr or 212 +/- 29 km/s at a distance of 8 kpc. In combination with the known line-of-sight velocity of the cluster, we derive a 3D space motion of 232 +/- 30 km/s of the Arches relative to the field. The large proper motion of the Arches cannot be explained with any of the closed orbital families observed in gas clouds in the bar potential of the inner Galaxy, but would be consistent with the Arches being on a transitional trajectory from x1 to x2 orbits. We investigate a cloud-cloud collision as the possible origin for the Arches cluster. The integration of the cluster orbit in the potential of the inner Galaxy suggests that the cluster passes within 10 pc of the supermassive black hole only if its true GC distance is very close to its projected distance. A contribution of young stars from the Arches cluster to the young stellar population in the inner few parsecs of the GC thus appears increasingly unlikely. The measurement of the 3D velocity and orbital analysis provides the first observational evidence that Arches-like clusters do not spiral into the GC. This confirms that no progenitor clusters to the nuclear cluster are observed at the present epoch.Comment: 22 pdflatex pages including 12 figures, reviewed version accepted by Ap