Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.563p&link_type=abstract
Meteoritics, vol. 30, no. 5, page 563
Astronomy and Astrophysics
Astrophysics
Fireball, Meteor, Radiant
Scientific paper
On the morning of August 8, 1975, meteors were observed from a previously unrecognized radiant in Pegasus. The rates were approximately seven per hour [1]. The radiant was alpha = 350 degrees, delta = +19 degrees (2000.0). These meteors are characterized as swift, yellow-white and without significant ionization trains [1]. The average magnitude of several hundred meteors from this shower is approximately +3.50, slightly fainter than the Perseids which occur at the same time. A broad maximum seems to occur about August 8. The three active fireball networks (Prairie, MORP and European) were contacted in a search for previously recorded fireballs with negative results. Ceplecha [2] of the European Network computed the orbital elements using the FIRBAL program. On August 19, 1982 at 02:09:57 UT, a magnitude -14.76 f1reball occurred over the White Carpathian Mountains of Austria and Czechoslovakia. It was photographed by five cameras of the European Network. Reduction of this Upsilon Pegasid fireball (EN 190882A) showed it to be a type IIIb fireball [2] - that is, an extremely low density, cometary, snow-like material with a specific gravity of approximately 0.27 g/cm^3. This material ablates at high altitude and cannot produce sonic phenomena or meteorites. It is similar to the material in the Draconid meteor shower. The orbital elements derived from EN 190882A are given in Table I. Table I: Orbital elements for the Upsilon Pegasid stream from EN 190882A. omega = 305.9009 degrees Omega = 145.3431 degrees i = 85.0817 degrees q = 0.2022 e = 1.0 velocity = 51.8608 km/s Using these refined elements, Kronk [3] computed the radiant drift. The radiant drifts from the SSW to NNE at a relatively steep angle and at an average rate of 20 arc-min per day. An intensive literature search [3] revealed four double station Upsilon Pegasids which had previously been listed as sporadics. Institutions providing these data were Yale [4], Stalinabad [5], Tadjikistan [6] and Harvard [7]. These events showed a confirmed shower at least 20 days in length. The radiant appears to be approximately 3 degrees in diameter. Computer modeling using the D-criterion developed by Southworth and Hawkins [8] indicate that it could be much larger [3]. It is likely an old shower that is still intact, not disrupted by planetary perturbations due to its high inclination. These meteors cross the Earth's orbit while approaching the Sun. They arrive at perihelion about September 16.0 at a perihelion distance of 0.19 AU, half that of Mercury's orbit. The Earth travels through this nearly vertically inclined stream in almost the shortest possible interval. A shower duration as noted indicates a diameter of approximately 0.6 AU. References: [1] Povenmire H. (1980) Fireballs, Meteors and Meteorites, J.S.B. Enterprises Indian Harbour Beach, Florida, 215 pp. [2] Ceplecha Z. (1982) S.E.A.N. Bulletin, 7, 13-14. [3] Kronk G. (1988) Meteor Showers; A Descriptive Catalog, Enslow, Hillside, New Jersey, 281 pp. [4] Olivier C. P. (1937) Astrophys. J., 46, 41-56. [5] Simakina E. G. (1967) Solar System Res., 1, 96-121. [6] Babadzhanov P.B. (1963) Smithson. Contrib. Astrophys., 7, 287-291. [7] McCroskey R. and Posen A. (1961) Smithson. Contrib. Astrophys., 4, 15-84. [8] Southworth R. B. and Hawkins G. S. (1963) Smithson. Contrib. Astrophys., 7, 261-285.
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