The following document lists the file abstract/JKERP_HVC_9042.abs
from catalogue VI/111.
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Recently, after the first detection of High Velocity Clouds (HVCs) by Muller et al. (1963), it was anticipated that they interact with the galactic halo or the disk itself. This suggestion was based only on morphological arguments, derived from HI 21 cm line studies, but direct observational evidence for an interaction scenario was not found. The ROSAT mission (Truemper 1983) give us the opportunity to study the large scale distribution of galactic atomic hydrogen in soft X-ray absorption (Snowden et al. 1991, Kerp 1994). Additionally, in the case of HVC 90+42.5-130, we detect for the first time soft X-ray emission associated with a high-velocity-cloud (Kerp et al. 1994a). Kerp et al. (1994a) claimed that magnetic reconnection (Lesch 1991, Kahn and Brett 1993) is the heating process of the HVC boundaries. This suggestion is strongly emphasized by the detection of a strong magnetic field (larger than 20 my Gauss, Kerp and Guesten, in prep.) by HI 21-cm Zee- man observations with the Effelsberg telescope. Thus, based on the X-ray and HI 21-cm line data, we found evidence that the soft X-ray emission is physically associated with the HVC. Furthermore, magnetic reconnection can easily account for the detected energies, and is most probably the main heating process in these high temperature, low vol- ume density areas (Kerp et al. 1994b). Thus, apart from the very hot HVC boundaries, we expect cooling lines, especially via the CII and OI finestructure transitions. Moreover, the interaction zone of HVC with the galactic disk matter is an area of small scale density variations, with enhanced cooling and grain formation. Quite close to the area of the brightest soft X-ray emission, IRAS detected at 100 microns and 60 microns infrared emission. Due to the close positional correlation with the X-ray emission we expect colour gradients in the ISO bands. Also the line ratio of CII(158my) and OI(63my) will reveal appreciable variations over this IRAS cloud. An indication for the contribution of OI(63my) to the I(60) band is indicate by the high I(60)/I(100) ratio.