SETI [ASTRO] IMO-NEWS: 1999 Beta Taurids Alert - Possible Swarm Appearance (fwd)


Larry Klaes (lklaes@bbn.com)
Mon, 21 Jun 1999 15:38:58 -0400


>X-Authentication-Warning: brickbat12.mindspring.com: majordom set sender to owner-astro using -f >Date: Sat, 19 Jun 1999 08:33:09 -0300 (ADT) >From: Michael Boschat <andromed@ATM.DAL.CA> >To: ASTRO <astro@lists.mindspring.com> >Subject: [ASTRO] IMO-news: 1999 Beta Taurids Alert - Possible Swarm Appearance (fwd) >Sender: owner-astro@brickbat12.mindspring.com >Reply-To: Michael Boschat <andromed@ATM.DAL.CA> > >May be of interest! > >Mike >Halifax Center >============================================= > >------- Forwarded Message > >Date: Wed, 16 Jun 1999 15:55:49 +0100 >From: Alastair McBeath <mcbal.gwyvre@virgin.net> >To: imo-news@imo.net >Subject: 1999 Beta Taurids Alert - Possible Swarm Appearance > >1999 Beta Taurids Alert - Possible Swarm Appearance > >>From Alastair McBeath, IMO Vice-President, e-mail: >vice_president@imo.net > >In 1993 David Asher presented a paper to the International Meteor >Conference in Puimichel [1] describing a theoretical resonant swarm of >particles within the Taurid/Beta Taurid stream which could account for >various meteor shower enhancements, increased fireball fluxes and even >meteoritic impacts associated with the Taurid Complex of meteoroid >streams, asteroids and comets. He used this theory to suggest times when >future returns of the proposed "swarm" might lead to increased activity >from the nighttime Taurid showers active in October-November, and the >daytime Beta Taurids of June-July. He suggested that 1999 could see a >return of the swarm during the Beta Taurid activity period, which is the >purpose of this reminder warning now. > Results from late October 1998 [2] suggested an enhanced Taurid period >had been detected by radio and visual observers in the closing days of >the month, along with an increased flux of minor Taurid fireballs >(magnitudes -3 to -8). Another of David's predictions for the swarm was >that a recurrence might be expected in October-November 1998, which may >well be what was recorded. > The Beta Taurids are usually assumed to last from about June 5 to July >17, reaching an ill-defined single maximum around June 28 (solar >longitude 96.7 degrees (all solar longitudes given here are for eq. >J2000.0)) from a radiant at approximately alpha = 086 degrees, delta = >+19 degrees. There is some disagreement in the published data on the >shower concerning most of these parameters however (cf. [3]). Most >authors suggest a lengthy, flat maximum occurs in late June to early >July. Forward scatter radio results from 1994-1997 [4] indicated a >moderate-strength echo count enhancement occurred between roughly solar >longitudes 91-93 degrees, with signs of weaker activity bracketing this >"peak" between solar longitudes 89-99 degrees. It is not clear if this >activity belongs to the Beta Taurids, nor whether this represents a >shift in the maximum time by several days if so, but the 89-99 degrees >spell is at least comparable in length to the Taurid maximum time in >early November. > From their orbital parameters, it is clear the Taurids and Beta Taurids >are linked, either as two encounters by the Earth with the same stream, >or as two separate streams which follow very similar orbits, so it is >not unreasonable we may extrapolate details for the Beta Taurids from >what we know of the Taurids. If we can do this, it is possible any swarm >enhancement of the Beta Taurids this June might occur up to 5-8 days >before the expected maximum, following the relative timings of events >seen last October. > To identify what happens with the Beta Taurids this year, whether a >swarm event or not, I would suggest radio observers should be especially >alert between June 18-19 through to July 2-3 at least (still later in >July might be better, as some earlier results suggested a Beta Taurid >maximum around July 2 or 3; this has not been found in data from the >1990s so far, however), as continuously as possible. This should cover >whatever the shower produces and also provide non-peak data for >calibration. Ideally, 24-hour-a-day monitoring should be carried out, >but if this is not possible, try to make your observing runs at the same >time every day. The Beta Taurid radiant is above the horizon between >roughly 03-04h local time to about 18-19h, for northern hemisphere sites >between approximately 35-55 degrees north near June 28. > There are likely to be problems because of Sporadic-E interference, >other atmospheric events (storms, etc.), and potentially Auroral-E as >activity builds in Solar Cycle 23. Times when any of these occurred >should also be included in your reports. Furthermore, there is the >possibility that the June Bootids, which produced their sudden, and >quite unexpected, outburst on 1998 June 27-28, may recur this year >(again on June 27-28 if their timing is the same as in 1998). So far, it >has not been possible to say why the Bootid outburst happened last June, >so telling when another one might transpire is presently impossible. The >overlap in radio-visibilities between the Beta Taurids and the June >Bootids is significant for sites north of about +45 degrees latitude, >which created problems in analysing the Bootid outburst by radio in >1998. This means any unexpected radio peak around June 28 this year need >not have resulted from the Beta Taurids. Only careful analysis of a >large enough body of data will reveal this. > Non-radio observers are faced with a very difficult prospect, because >the centre of the Beta Taurid radiant is just 10 degrees or so west of >the Sun on June 28. Tropical or near-equator observers might possibly >see a few slow-moving shower fireballs in the strong predawn twilight an >hour or two before sunrise at some point during the dates given above, >if anything unusual happens from the shower this year. As even the outer >fringes of the radiant will be on or below the horizon however, the >meteors will probably have exceptionally long paths across the sky. > For particularly northern hemisphere observers, there is the additional >possibility that a few daylight fireballs might occur if a swarm >appearance manifests. This is because the Beta Taurid radiant will be >high to very high above the horizon for a large part of the day near the >shower's expected best from such places. Those who routinely handle the >American DoD satellite reports which feature especially brilliant >meteors (Zdenek Ceplecha's "superbolides") should pay particular >attention to any events that occur during the late June to early July >period as well; an increased flux could represent something unusual from >the Beta Taurids. Although the nighttime Taurids do not have much of a >reputation for producing these especially brilliant fireballs, the Beta >Taurids may be capable of doing so, assuming for example that the major >clustering event of lunar impacts, detected by the Apollo programme's >seismometers, of about ten days' duration centred on 1975 June 22 was >due to this source. > There are of course no guarantees that anything unusual will happen >from the Beta Taurids this year, but even establishing that no swarm >recurrence happened in 1999 June-July with some degree of certainty >would help refine David Asher's model of the Taurid Complex swarm. Even >a swarm appearance is not guaranteed to produce spectacularly high rates >or dozens of bright meteors. If the 1998 late October Taurid event was >due to a recurrence of the swarm, it should be noted that the visual >ZHRs from the shower were enhanced only to the level of normal maximum >rates (combined ZHRs ~9-10; usually no better than ~5-7 in late >October), while the Taurid fireball percentage was roughly double that >in normal years. > Observations should be submitted to all the usual places you routinely >do, but copies can also be e-mailed to me as well. Please bear in mind >that I am still most unwell however (as noted in WGN 27:2), so do not >expect a rapid response. Good luck, and clear, Sporadic-E-free skies for >your data collection! > >References: >[1] D. Asher, "Meteoroid Swarms and the Taurid Complex", in: >"Proceedings IMC, Puimichel 1993", ed. P. Roggemans, IMO, 1993, >pp.88-91. > >[2] A. McBeath, "SPA Meteor Section Results: September-October 1998", >WGN (in press). > >[3] G. W. Kronk, "Meteor Showers: A Descriptive Catalog", Enslow, 1988, >pp.115-118. > >[4] A. McBeath, "The Forward Scatter Meteor Year", in: "Proceedings IMC, >Petnica 1997", eds. A. Knoefel & A. McBeath, IMO, 1998, pp.39-54. > > > >------- End of Forwarded Message > > > >To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at: >http://www.tiac.net/users/lewkaren/meteorobs/subscribe.html > > >



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