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(meteorobs) Excerpts from "CCNet, 15 December 1999"
------- Forwarded Message
From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet, 15 December 1999
Date: Wed, 15 Dec 1999 09:33:36 -0500 (EST)
CCNet, 15 December 1999
-------------------------------
[...]
(4) IT WASN'T A GEMINID
Tony Beresford <starman@camtechdot net.au>=20
[...]
(8) X-RAY & EXTREME ULTRAVIOLET EMISSION FROM COMET P/ENCKE
C.M. Lisse et al., UNIVERSITY OF MARYLAND
(9) COMETARY EVIDENCE OF A MASSIVE BODY=20
IN THE OUTER OORT CLOUD
J.J. Matese et al., UNIVERSITY OF LOUISIANA
(10) THE DYNAMICS OF PLUTINOS
Q.J. Yu & S. Tremaine, PRINCETON UNIVERSITY=20
OBSERVATORY
============================================================
(4) IT WASN'T A GEMINID
>From Tony Beresford <starman@camtechdot net.au>=20
Benny,
The channel ten news report relayed by Robert Clements contained
typical inaccuracies of Mr Ross Dowe. Firstly is was quite clear to me
from the reports I had by telephone, about the fireball widely seen
over South Australia, that it wasn't a Geminid, and Mr. Dowe had even
more information of course.
The object was moving mainly West to East. It was seen from Pt Lincoln
on our west coast. It disintegrated to the NE of Adelaide. It occured
at local time 21:22-23 on December 13 (1052or 1053UT). The Geminid
radiant didn't rise till 02:00am on December 14.
Secondly, of course, is the overpromotion of the Geminid
shower at our latitudes. The ZHR for the Geminids is 100 or
so, but the unfavourable geometry considerably reduces the
observable rate to more like 50. Since most Australians
live in an urban environment, light pollution cuts into
this rate for most. Using these words the public expect the
natural eqivalent of a fireworks display and will be
disappointed when they dont get it.
Tony Beresford
============================================================
(8) X-RAY & EXTREME ULTRAVIOLET EMISSION FROM COMET P/ENCKE
C.M. Lisse*), D. Christian, K. Denneel, J. Englhauser, J. Trumper,=20
M. Desch, F.E. Marshall, R. Petre, S. Snowden: X-ray and extreme=20
ultraviolet emission from comet P/Encke 1997. ICARUS, 1999,=20
Vol.141, No.2, pp.316-330
*) UNIVERSITY OF MARYLAND,DEPT ASTRON,COLLEGE PK,
MD,20742
In an effort to understand the newly discovered phenomenon=20
of cometary X-ray emission, we have obtained observations=20
of the short period (3.3 years), well-studied comet 2P/Encke=20
(Encke) during its July 1997 close approach to Earth. Extended,=20
variable emission on the sunward side of the nucleus was found=20
in the Rontgen X-ray satellite High Resolution Imager (HRI)=20
at 0.090-0.75 keV and in the Extreme Ultraviolet Explorer=20
(EUVE) scanner telescopes' Lexan B 0.090- to 0.28-keV and=20
Al/Ti/C 0.050- to 0.16-keV bandpasses; useful upper limits=20
were found in the Ti/Sb/Al 0.020- to 0.040-eV bandpass.=20
Similar to our results for C/Hyakutake. the emission morphology=20
was roughly symmetric with respect to a vector from the comet's=20
nucleus toward the Sun, with a light curve consisting of a slowly=20
varying baseline emission and a large impulsive event on 7 July=20
1997 with a time scale of similar to 3 h and an amplitude=20
of similar to 3 times the baseline. A count rate of similar=20
to 0.17 counts s(-1) in the HRI was measured for the slowly=20
varying emission, corresponding to a total luminosity L-x=20
of 4 x 10(14) erg s(-1). Unlike Hyahutake, however the bulk=20
of the emission clearly originates outside the comet's=20
bow-shock, arguing against the magnetic reconnection and=20
plasma dust emission models. The comet's lightcurve does=20
not correlate with the solar X-ray lightcurve, ruling out=20
scattering of solar X-rays as the emission mechanism. The=20
multiwavelength HRI/EUVE photometry is inconsistent with=20
the Haberli et al. (1997, Science 276, 939-942) charge=20
transfer, plasma dust, and attogram dust models of cometary=20
X-ray emission and is consistent with the Wegmann et al.=20
(1988, Planet. Space Sci. 46, 603-612) charge exchange,=20
0.15- to 0.45-keV thermal bremsstrahlung, and photon index=20
1.6-2.0 power law models. While the impulsive event=20
correlates very well with the passage of a solar magnetic=20
field boundary at the Earth and an increase in the solar=20
wind particle flux, it is not coincident, according to=20
current models of the solar wind magnetic current sheet,=20
with the passage of the sector boundary by the comet,=20
suggesting that new models of the current sheet are=20
necessary. (C) 1999 Academic Press.
============================================================
(9) COMETARY EVIDENCE OF A MASSIVE BODY=20
IN THE OUTER OORT CLOUD
J.J. Matese*), P.G. Whitman, D.P. Whitmire: Cometary=20
evidence of a massive body in the outer Oort cloud. ICARUS,=20
1999, Vol.141, No.2, pp.354-366
*) UNIVERSITY OF LOUISIANA,DEPT PHYS,LAFAYETTE,LA,70504
Approximately 25% of the 82 new class I Oort cloud comets=20
have an anomalous distribution of orbital elements that can=20
best be understood if there exists a bound perturber in the=20
outer Oort cloud. Statistically significant correlated=20
anomalies include aphelia directions, energies, perihelion=20
distances, and signatures of the angular momentum change=20
due to the Galaxy. The perturber, acting in concert with=20
the galactic tide, causes these comets to enter the loss=20
cylinder-an interval of Oort cloud comet perihelion=20
distances in the planetary region which is emptied by=20
interactions with Saturn and Jupiter. More concisely, the=20
impulse serves to smear the loss cylinder boundary inward=20
along the track of the perturber. Thus it is easier for the=20
galactic tide to make these comets observable. A smaller=20
number of comets are directly injected by the impulsive=20
mechanism. We estimate that the perturber-comet=20
interactions take place at a mean distance of approximate=20
to 25,000 AU. The putative brown dwarf would have a mass of=20
3 (x)(divided by) 2M(Jupiter) and an orbit whose normal=20
direction is within 5 degrees of the galactic midplane.=20
This object would not have been detected in the IRAS=20
database, but will be detectable in the next generation of=20
planet/brown dwarf searches, including SIRTE It is also=20
possible that its radio emissions would make it=20
distinguishable in sensitive radio telescopes such as the=20
VLA. (C) 1999 Academic Press.
============================================================
(10) THE DYNAMICS OF PLUTINOS
Q.J. Yu*) & S. Tremaine: The dynamics of Plutinos.=20
ASTRONOMICAL JOURNAL, 1999, Vol.118, No.4, pp.1873-1881
*) PRINCETON UNIVERSITY OBSERVATORY,PEYTON HALL, PRINCETON,=20
NJ, 08544
Plutinos are Kuiper belt objects that share the 3:2 Neptune=20
resonance with Pluto. The long-term stability of Plutino orbits
depends on their eccentricity. Plutinos with eccentricities=20
close to Pluto's (fractional eccentricity difference Delta=20
e/e(P) =3D \ e - e(P)\/e(P) less than or similar to 0.1) can be=20
stable because the longitude difference librates, in a manner=20
similar to the tadpole and horseshoe libration in co-orbital=20
satellites. Plutinos with Delta e/e(P) greater than or similar=20
to 0.3 can also be stable; the longitude difference circulates=20
and close encounters are possible, but the effects of Pluto are
weak because the encounter velocity is high. Orbits with=20
intermediate eccentricity differences are likely to be unstable
over the age of the solar system, in the sense that encounters=20
with Pluto drive them out of the 3:2 Neptune resonance and thus
into close encounters with Neptune. This mechanism may be a=20
source of Jupiter-family comets. Copyright 1999, Institute=20
for Scientific Information Inc.
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