Transcript Meteor Radar Including First Observations of the Camelopardalids

Radar Observations of the
Volantids Meteor Shower
Dr. Joel Younger 1,2 [email protected]
Prof. Iain Reid 1,2 [email protected]
Dr. Damian Murphy 3 [email protected]
1 ATRAD
Pty. Ltd., Thebarton, Australia
2 University of Adelaide, Adelaide, Australia
3 Australian Antarctic Division, Kingston, Australia
Volantids
• First detected by CAMS
New Zealand video
network
– 2 sites on South Island,
16 cameras each
• Likely Volantids
detections also from
Desert Fireball Network
(Curtin University) in
Australia
CAMS New Zealand radiants for 31 December 2015, image
from: http://cams.seti.org
Paper: Jenniskens, P., J. Baggaley, I. Crumpton, P. Aldous, P. S.
Gural, D. Samuels, J. Albers, and R. Soja (2016), A surprise
southern hemisphere meteor shower on New-Year’s Eve 2015:
the Volantids (IAU#758, VOL), WGN, J. IMO, 44(3), 35–41.
VHF All-Sky Meteor Radar
• Uses radio scatter to detect
plasma in meteor trails in
~70-110 km height range.
• Five antenna receive array
determines direction to
echo using interferometry.
• Primarily used for
– Winds: based on echo phase
drift
– Temperature/density:
inferred from estimates of
diffusion rates from echo
decay times
The Challenge to Mapping Radiant
Activity
• Objective: use single station
interferometric VHF meteor
radar to determine meteor
shower radiants and orbits
?
• Problem: specular meteor
detections are perpendicular
to trajectory – specific
direction is not known
outside a plane of ambiguity
?
?
Radar
Great Circle Mapping
•
For each possible radiant in celestial coordinates, count detections in a band
perpendicular to the radiant
–
•
•
Apply weighting function to reduce effect of cross-counting (smearing of narrow features)
Sense of the possible radiant vector determined by radar zenith’s hemisphere
Result is a measure of the relative activity of each radiant
Radars Used for Volantids Detection
• Davis Station, Antarctica
–
–
–
–
Australian Antarctic Division
33 MHz
6.8 kW peak power
14,000 meteors per day
• Buckland Park, Australia
–
–
–
–
University of Adelaide
55 MHz
40 kW peak power
Used as riometer during 1/3 of
time during Volantids
– 4,000 meteors per day
Buckland Park
Davis Station
31 Dec. 2015 – 2 Jan. 2016
Buckland Park/Davis Station Combined
Velocity Estimation
• Background estimate made using radiant in solar coordinates on nonshower days, subtracted from distribution of active shower velocities
– Strong background contamination, shower embedded in Southern Toroidal
source
– Approximately 730 shower detections in remaining peak
• Detections above median height used to minimize deceleration
Radiant Correction
•
1.
Gravitational acceleration affects shower
measurements two ways:
Infall acceleration: Observed meteoroid
velocity is higher than unperturbed
relative orbital velocity due to gravitational
acceleration during Earth approach.
Earth
va
𝑣𝑔 =
2.
𝑣𝑎2 −
vg
𝐺𝑀⊕
𝑟𝑎
Zenith attraction: Meteoroid trajectories
are bent towards the local zenith due to
gravitational acceleration towards the
center of Earth.
original
trajectory
∆𝜑
final
trajectory
local zenith
∆𝜑 = 2 tan−1
𝑣𝑎 −𝑣𝑔
𝑣𝑎 +𝑣𝑔
tan
𝜑
2
Daily Radiant Activity SNR
14
12
10
8
6
detection
threshold
4
2
0
31 Dec 15
1 Jan 16
Davis Station
2 Jan 16
Buckland Park
Radiant Activity Challenges
• Difficult to directly monitor
Volantids activity with the
radars used
– BP counts to low for reliable
activity estimates
– Radiant passes directly over
Davis Station
Perpendicular detections are over
the horizon, i.e. no detections
when radiant is overhead
radar
Detailed Radiant Activity
• 8-hour averages used to
estimate shower duration
• Activity Estimate
summary:
– peak ~1300 UT 1 Jan 2016
– start no later ~0000 31 Dec
– finish no earlier ~2200 2
Jan
Comparison: Camelopardalids
• New shower predicted from
comet 209P/LINEAR
– R.A. = 129.1° ± 9.8
– dec. = 79.4° ± 1.6
• Observed with radar at
Mohe, China
– 122.34 E
– 53.49 N
• Ideal viewing geometry for
shower entire duration
enabled detailed activity
monitoring
From: Younger et al. (2015), Observations of the
new Camelopardalids meteor shower using a 38.9
MHz radar at Mohe, China, Icarus, 253
Orbit Summary
• Orbits calculated from
radiant, velocity
– Good match with video
derived observations
• Smaller value of a, likely
due to decelerated
meteoroids seen by radar
– Radar configured to find
underdense meteors, i.e.
smaller meteoroid
population
– Visible meteors are
larger, decelerate less
during trail formation
element
semi-major
axis
eccentricity
inclination
ascending
node
perihelion
argument
perihelion
distance
symbol estimate
a
2.11 AU
uncertainty
+ 0.50
- 0.18
± 0.069
± 2.6
CAMS
2.23 AU
± 3.4
347.7°
e
i
Ω
0.568
47.2°
100.3°
ω
343.4°
q
0.970 AU + 0.004
- 0.009
0.563
47.8°
99.26°
0.975 AU
Orbit Statistics
•
Propogation of uncertainty in orbital
calculations complicates expression
of uncertainties in orbital elements.
– e, i, and ω maintain close to Normal
statistics
– a and q acquire assymetric probability
distributions
•
Monte Carlo method used to
estimate uncertainties:
– 50,000 runs using randomized radiant
values
– Distribution of input radiants based on
uncertainties in measurements
– Uncertainty in a and q inferred from
0.34 cumulative probability in each
direction
Conclusions
• Radar detections of Volantids at two locations
– Even modest perfomance radars capable of
shower detection
• Good agreement with CAMS data
– CAMS likely has better velocity data
– Radar shows longer extent, daytime activity