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re: IMO new working list
Boy, is this guy trying to sell plotting or what! :-)!
George, I think you should post this on Meteorobs.
By explaining the rationale for shower additions,deletions and
modifications, I think this would be the perfect capper for the minor
shower discussion. Since so many of us have joined recently, they probably
have not seen this information. I now feel I have a much clearer
understanding of the process that IMO uses in making these decisions, and
am much more comfortable with them.As I always tried to explain to the Old
Man during my youth, don't give me that because I said so....explain it!
Thanks for the enlightenment!!!
Wayne
-------------
Original Text
>From GeoZay@aoldot com, on 6/7/96 9:31 AM:
To: <dedalus@latradedot com>, <wayne.t.hally@bangate1.tekdot com>
Wayne and Lew,
I don't know if you got a copy of this article from the WGN Journal. You
might want to read what Rainer had to say about the SAG complex and other
adjustments.
George
---------
METEOR NETWORK ARTICLE # 7
The following article was published in IMO's Journal in the august 1995
issue. The author is Rainer Arlt (Germany).
THE NEW WORKING LIST OF VISUAL METEOR SHOWERS
A look at the past issues of IMO's working list of visual meteor radiants
shows a gradual evolution of both the selection of showers and their
parameters. The Shower Calendar of 1992 contains a number of components of
large radiant complexes like the Sagittarids and the Puppid/Velids. Many of
these sub-radiants were removed from the list because no radiant analysis
of
plotted meteors from the appropriate latitudes resolved the radiants until
now, and the observations made by the counting method did not prove a
distinct activity of the specific radiant above the sporadic background.
Additionally, some slight changes were necessary regarding the activity
periods and the maximum ZHR's, which will represent the expectations of
visual observers better. The following is a list of changes for a number
of
radiants as well as some items pro or contra the inclusion of a shower in
the
list. Radiants with # designates inclusion into the new working list while
(
-)
designates it's removal. Do not forget that the omission of a shower does
not necessarily mean this radiant does not exist. Rather, visual
observations cannot provide us with reliable information about this meteor
stream. They may nevertheless be interesting for telescopic, photographic,
video, or radio observations.
# Quadrantids (QUA): The maximum ZHR was changed to 120 according to last
years results.
# delta-Cancrids (DCA): Although the activity of this radiant is low, it
represents the ecliptical background activity which is notably more or less
striking throughout the year. Observations during the Quadrantid activity
period showed quite a number of perfect delta-Cancrids whence the activity
period was prolonged to start from January 1.
(-) alpha-Crucids (ACR): A ZHR profile of 97 IMO observations shows a value
of
2-3 throughout the activity period. No photographic or radar orbits have
been associated with this radiant.
(-) alpha-Carinids (ACN): The profile of 74 IMO observations shows ZHR's of
around 2 with very large scatters. Photographic or radar meteors
associated
with the alpha-Carinids are not known.
# alpha-Centaurids (ACE): This shower produced varying activity in the last
decades. An activity profile from 178 IMO observations of 1988-1994 shows
a
distinct maximum with a ZHR of 5.5 +or- 0.8. No alpha-Centaurids have been
reported before February 1, therefore, the beginning of the activity period
was set to this date.
# delta-Leonids (DLE): Since 1911 it is known that there is a separate
radiant
north of the ecliptical radiants, and it has been detected by several
observers hitherto (Denning, Prentice, Hoffmeister, Whitney, Wood). 24
photographic meteors could be associated with the delta-Leonids by
Lindblad.
According to 70 IMO observations the shower reaches ZHR's around 2 in the
period February 15 to March 10. In this period most of the mentioned
sources
report distinct activity.
# gamma-Normids (GNO): The shower was observed visually since 1929. Radar
technique allowed the determination of the orbital elements. Australian
observers determined maximum ZHR's of 10 +or- 2 and 3.5 +or- 1.5 for 1983
and
1986 respectively. An average profile of 53 IMO observations shows a peak
rate of 8.
(-) beta-Pavonids (BPA): (Also called delta-Pavonids.) Very low ZHR's did
not
prove the visual significance of this radiant. The shower was observed by
the
West Australian Meteor Section in the 1980's. The maximum ZHR was reported
to
be 1.9 +or- 0.2. No photographic orbit was associated with the
beta-Pavonids.
# Virginids (VIR): This ecliptical shower has been observed since the last
century. The delta-Cancrid activity period ends on January 24 whereas the
Virginids started on February 1 in the 1994 shower list. As there is no
reason why the ecliptical activity should pause for a few days, the
Virginids now starts on January 25. The Virginid activity ends on April 15
and is taken over by the Sagittarids on the same day.
(-) theta-Centaurids (TCE): Although the ZHR profile of 190 IMO
observations
shows maximum ZHR's around 4, no distinct maximum could be found. The
scatters of these maximum values is larger than 1. About the same picture
appears in with maximum ZHR <4.5. No photographic or radar orbits were
found
for this shower.
(-) omicron-Centaurids (OCE): ZHR's are between 2 and 3. No photographic
or
radar orbits could be associated with this radiant.
# Lyrids (LYR): Although high activity with ZHR's over 50 has been observed
in the past, the list gives a ZHR of 15 as the usual value which can be
expected by the observer.
(-) alpha-Bootids (ABO): An analysis of 220 IMO observations with only
plotted
meteors shows a distinct activity profile with a maximum ZHR of 1. No
clear
ZHR profile could be obtained from the remaining 624 observations of this
period with counted meteors. Although careful observations and shower
association might thus be able to detect this shower, a huge number of
reports would be needed to get a reliable physical information about the
stream.
# pi-Puppids (PPU): No changes were applied to this periodically active
radiant.
# eta-Aquarids (ETA): The time of maximum was changed to May 6 (solar
longitude = 45.5 degrees) with a ZHR of 60. This is the result of 523
observations.
# Sagittarids (SAG): This ecliptical radiant complex takes the place of the
Virginids on April 15. The Virginid radiant is about 20 degrees west of
the
Sagittarids. However, as the ZHR of the Virginids falls below 2 on April
we
assume that the Sagittarid radiant is a better representation of the center
of ecliptical activity. As they also interfere with the Capricornids in
the
end of July, the activity period was restricted to July 15. The ZHR of a
mean profile of 129 IMO observations did not exceed 5. In order to fit the
possible sub-radiants described below better, the declination of the
radiant
positions was set onto the ecliptic.
(-) alpha-Scorpids (ASC), kappa-Scorpids (KSC), omega-Scorpids (OSC),
chi-Scorpids (CSC), beta-Corona Australids (CAU), Northern Ophiuchids (NOP),
Southern Ophiuchids (SOP), theta-Ophiuchids (TOP), lambda-Sagittarids
(LSA):
A lot of radiants have been proposed in the regions of Scorpius,
Sagittarius,
and Ophiuchus. I found over 100 different radiants in the literature for
the
period April to June. The main component, the alpha-Scorpids, is well
represented by the gradually moving radiation area of the Sagittarids (See
above). This large complex also comprehends the notable activity of the
omega-Scorpids and the gamma-Sagittarids. It is likely that no distinct
radiant can be found even from a large number of meteor plots in this area
and period.
(-) June Lyrids (JLY): This shower was discovered by two independent
observers
in 1966 and observed in detail in 1969. A weaker return is known from
1974.
The present annual activity calculated from 64 IMO records is at 1.5 +or-
0.4
without distinct maximum, i.e., at the detection limit.
(-) June Bootids (JBO): The stream is associated with comet Pons-Winnecke,
and
a strong meteor shower was observed in 1916 as well as enhanced activity in
1921 and 1927. Since then, no visually significant rates have been
observed.
# July Phoenicids (PHE): High radio echo rates were observed in the 1950's
with several tens of echos per hour. The activity profile of 87 IMO
observations shows a maximum ZHR of 4.4 +or- 0.6. The activity period was
changed to July 10-July 16. The maximum occurs on July 14 according to
several sources with a radiant at RA = 2h30m, dec.= -48 degrees.
# July Pegasids (JPE): Very few data are available for this shower. It's
activity period was slightly prolonged to July 13. The ZHR turned out to be
3
but might not represent the very short maximum.
# Piscis Austrinids (PAU): The activity period was shrunk to July 15 to
August 10. Before and after this period ZHR's were below 1, the maximum
ZHR
being 5.
# Southern delta-Aquarids (SDA): The activity period starts later, on July
12, as rates are below visual significance before.
# alpha-Capricornids (CAP): According to the ZHR profile of 1625 IMO
observations and radiant studies, the activity period ends on August 15
with
a ZHR of 0.5. The maximum ZHR is 4.
# Southern iota-Aquarids (SIA): Since the ZHR's of this shower are very low,
the activity period was shortened to the visually detectable period July 25
to August 15. The maximum ZHR did not exceed 2.
# Northern delta-Aquarids (NDA): This radiant appeared well in the Aquarid
analysis throughout the activity period with a maximum ZHR of 4.
# Perseids (PER): The time of maximum is given for the traditional maximum
with a ZHR of 100.
# kappa-Cygnids (KCG): The visual activity period now ends on August 25
when
ZHR's fall below 1.0 according to a profile of 5585 IMO observations. The
maximum ZHR is 3.
# Northen iota-Aquarids (NIA): As this radiant is probably the prominent
representative of the ecliptical background showers, the activity period
was
connected to that of the Piscids and ends on August 31. This is about the
result of the Aquarid analysis.
- pi-Eridanids (ERI): No clear activity profile was obtained by Jenniskens,
where ZHR's were around 2. The same pictures occurs in the activity
profile
of 42 IMO observations of 1988-1994 with ZHR's even lower than 2.
# alpha-Aurigids (AUR): The maximum ZHR was set to 10, although
occasionally
higher peaks may occur.
# delta-Aurigids (DAU): The mean maximum ZHR of 186 IMO observations is 6.
# (Southern) Piscids (SPI): Connecting to the Northern iota-Aquarids the
Piscids start on September 1 and end on September 30 to be continued by the
Taurids.
(-) kappa-Aquarids (KAQ): The activity profile of 195 IMO observations of
this
shower shows a maximum ZHR of 0.9 +or- 0.2. This low rate is likely to be
not
significant for visual observations by both the counting and plotting
method.
No photographic records could be associated with the radiant.
(-) October Capricornids (OCC): A maximum ZHR of 1.0 +or- 0.1 was derived
from
122 observations. No clear activity profile can be seen.
(-) sigma-Orionids (SOR): This radiant was not mentioned by Kronk in 1988
and
Jenniskens in 1994. The activity profile of 174 IMO observations shows
maximum ZHR's of 2.0 +or- 0.6 with large variations from day to day.
# Draconids or Giacobinids (GIA): this shower is known for periodic
activity.
It is noted as a periodic shower; the annual activity is below the visual
detection limit.
# epsilon-Geminids (EGE): Several observers had already detected this
shower
in the first half of this century. A number of photographic orbits were
associated with the epsilon-Geminids. The activity profile of 239 IMO
observations shows a maximum ZHR of 3.
# Orionids (ORI): No changes were applied.
# Northern and Southern Taurids (NTA and STA): The activity period starts
on
October 1 to take over the ecliptical radiation area of the Piscids.
# Leonids (LEO): The Leonids promise increasing maximum ZHR's in the
forthcoming years, hence, no ZHR is given.
# alpha-Monocerotids (AMO): No changes were applied. The shower produced
rich displays in 1925, 1935, 1985, and 1994. Two photographic and two
radar
orbits could be associated with this radiant.
# chi-Orionids (XOR): No changes were applied.
# December Phoenicids (PHE): Since the maximum ZHR of this shower is
strongly
variable, no value is given in the working list.
# Puppid-Velids (PUP): This radiant should represent the major part of the
numerous radiants in Puppis and Vela suggested in recent years. The
activity
period of December 1 to December 15 was the only time for which significant
ZHR's and photographic orbits could be found. Several sources indicate a
maximum ZHR around 10 on December 6.
(-) sigma-Puppids I (SPU), tau-Puppids I (TPU), pi-Puppids I (PIP),
lambda-Velids I (LVL): These radiants constituted the major components of
the
Puppid-Velid complex active from October to January, and they were already
a
compromise between a jumble of radiants in that region. However, no
systematic activity was found for none of the showers, and no photographic
or
radar orbits could be associated either. Regarding visual observations,
only
meteor plots can prove one or the other radiant.
# December Monocerotids (MON): The declination of this radiant was
erroeneously given as delta = +14 degrees in the working lists of 1993 to
1995 in accordance with a different radiant found by Sekanina from radar
meteors. The actual value, however, is delta = +8 degrees. Hence,
activity
calculations will be affected by this error.
# sigma-Hydrids (HYD): This radiant was not discovered by visual
observations
but by an association of seven photographic orbits. A total of 393 visual
IMO observations show a maximum ZHR of 2.
# Geminids (GEM): No changes were applied.
# Coma Berenicids (COM): No changes were applied. More than 20
photographic
and radar orbits count be associated with this stream. The Western Meteor
Section reports a maximum ZHR of 6.4 +or- 3.2 in 1980, an activity profile
of
679 IMO observations reaches a maximum of 3.9 +or- 0.2.
# Ursids (URS): Although the Ursids may produce enhanced activity, the list
value for the maximum ZHR was set to 10.