Radar Observations of the Volantids Meteor Shower Dr. Joel Younger 1,2 Prof. Iain Reid 1,2 Dr. Damian Murphy 3 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: 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 ~ 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 Davis Station Buckland Park

31 Dec – 2 Jan Buckland Park/Davis Station Combined VOL

Velocity Estimation Background estimate made using radiant in solar coordinates on non- shower 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 local zenith final trajectory original trajectory Earth vgvg vava

Daily Radiant Activity SNR detection threshold

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 radar Perpendicular detections are over the horizon, i.e. no detections when radiant is overhead

Detailed Radiant Activity 8-hour averages used to estimate shower duration Activity Estimate summary: – peak ~1300 UT 1 Jan 2016 – start no later ~ Dec – finish no earlier ~ 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 – E – 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 elementsymbolestimateuncertaintyCAMS semi-major axis a 2.11 AU AU eccentricity e 0.568± inclination i 47.2°± ° ascending node Ω 100.3° 99.26° perihelion argument ω 343.4°± ° perihelion distance q AU 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