POSSIBLE SHOCK-WAVE IN THE LOCAL INTERSTELLAR PLASMA, VERY CLOSE TO THE HELIOSPHERE

We show, using the HST - GHRS data on velocity and temperature in the nearby interstellar medium, that the observed 3 - 4 km s(-1) relative velocity between the Local Interstellar Cloud (LIC) and the so-called G-cloud located in the Galactic Center hemisphere can be quite natural ly explained assuming that the two clouds do interact with each other. In the proposed interpretation the two media are separated by a (quas iperpendicular) MHD shock front propagating from the LIC into the G-cl oud. The LIC plasma is then nothing else but the shocked (compression 1.3 - 1.4) gas of the G-cloud. A 1-D single-fluid solution of the Rank ine - Hugoniot equations can fit the most probable observed values of the relative velocity (3.75 km/s), LIC (6700 K) and G-cloud (5400 K) k inetic temperatures, if the plasma-beta of the LIC plasma is in the ra nge 1.3 - 1.5 (Table 1). This corresponds to a super - fast magnetoson ic motion of the heliosphere through the LIC, independently of LIC den sity. The LIC magnetic held strength is 1.9 (3.1) mu G for the LIC ele ctron density n(e) = 0.04 (0.10) cm(-3). In this case the shock is les s than 30 000 AU away and moves at about 10 km s(-1) relative to the L IC plasma. The Sun is chasing the shock and should catch up with it in about 10(4) years. If the heliospheric VLF emissions cutoff at 1.8 kH z is indicative of n(e) (LIC) = 0.04 cm(-3) (Gurnett et al., 1993), th e (pure plasma) bowshock ahead of the heliopause could be the source o f quasi-continuous heliospheric 2-kHz emission band. We believe that w ith the expected increase in the performance of modern spectroscopic i nstrumentation the proposed method of magnetic held evaluation may in the future find wider application in the studies of the interstellar m edium.