[Prev][Next][Index][Thread]

RE: (meteorobs) Sporadic Flux Variations (long)



This is to add to Jim Richardson's helpful post.

The latest results known to me were published in Jim Jones and Peter
Brown's paper (MNRAS, 265, p.524) from an analysis of 10 surveys
ranging from fireballs, through visual to radar meteors.  They first
removed the six most-prominent streams by comparing the orbits of the
survey meteors with these showers and using the Southworth D criterion
(D>0.5 defined as sporadic).

There are believed to be a number of concentrations in the sporadic
meteor flux.  As is normal, their positions are defined with respect
to the Sun-centred ecliptic longitude (L), and ecliptic latitude (B).
Here is a tabulation of the mean positions and radii for the sources
as found by Jones & Brown.


Name               L      B    Radius   Comments
                  (o)    (o)     (o)
Northern Apex     271    +19     18     Long-period comets, mostly radar
Southern Apex     273    -11     16     Probably same as Northern Apex

Helion            342      0     19     } Short-period comets &
Antihelion        198      1     16     } some asteroidal material

North Toroidal    271    +58     21     } Circular orbits (P-R effect)
South Toroidal    274    -60      -     } of long-period comets? Radar
                                        } meteors


The comparative strengths of the these concentrations vary with the
survey.  The differences are partially due to the different
populations of bodies involved, but technical selection effects and
other biases appear to be the major factors.  The origins of the
sources are not well understood.


I first heard about the northern toroidal source in articles on
telescopic meteors written by Keith Hindley around 1970 in "The
Astronomer".  Given that this source produces mostly faint meteors, we
thought that a large statistical survey involving around 25000
telescopic meteors should reveal more information about the
distribution of the sporadic flux.  We were aiming to include casual
observations (e.g. seen during variable star estimations or comet
hunting), but it never quite panned out.  "Insufficient data,
captain".  It is still something we can do, but it does require
observations throughout the year and different times through the night
by numerous observers.  Of course we can't measure orbits.  As it was
such a long-term programme I've concentrated on showers in recent
years in the hope that this will attract more observers, and then
obtain a sporadic survey as a by-product.

Malcolm

Follow-Ups: References: