Presentation on theme: "Meteors from 209P/LINEAR A Summary by Rob McNaught, based on simulations by David Asher Expanded and amended (May 20) from a presentation to the TA meeting."— Presentation transcript:
Meteors from 209P/LINEAR A Summary by Rob McNaught, based on simulations by David Asher Expanded and amended (May 20) from a presentation to the TA meeting 2014 May 10, Basingstoke
209P/LINEAR 2004 Feb 03 - NEA 2004 CB discovered by LINEAR (MPEC 2004-C16) 2004 Mar 30 - Found to be a comet by Rob McNaught (IAUC 8314) West Animation of three 10sec exps Tail 1 arcmin long 2004 Mar m reflector Siding Spring Observatory R. H. McNaught North q = AU e = i = 21.2 deg a = 2.96 (P = 5.09 yrs)
Meteor Shower Jenniskens (2004) 1 st to note possibility Lyytinen/Jenniskens (2006) made dust trail calculations Vaubaillon (2012) used supercomputer to calculate millions of particle motions Maslov (2013) made dust trail calculations Ye and Wiegert (2013) modelled dust tail of 209P and particle stream Asher (2014) made dust trail calculations All indicate a shower over N America
209P meteor shower Daylight Night Galapagos Hawaii Fiji Samoa Observed radiant elevation May 24 07:00UT
True RADIANT RA 122 +/- 1d Dec +79 +/- 1d (Ye and Wiegert) km/s (Maslov,Asher) (Vaubaillon) (J2000) Atmospheric velocity – very slow meteors The observed (apparent) radiant will be higher in the sky due to the gravitational bending of the incoming meteors by the Earth (to a max. of 11 deg). This is called Zenithal Attraction.
Nearby dust trails 2014 Encounter Very consistent with the dust trails, but saturation of this plot allows no interpretation of the shower profile or peak time. Vaubaillon
Asher’s dust trails Note: profile through Ye and Wiegert’s plot has peak after the dust trails 20-rev21-rev 22-rev 23-rev rev 46-rev 47-rev rev Dust trails with |r E -r D |>0.0200AU are not plotted, but high density region is confirmed by 1 to 16-rev trails
Dust trails and binning The modern variant of dust trail calculations developed following limitations of some Leonid research that used significant binning Asher’s dust trail calculations for both the Leonids and 209P indicate that unperturbed dust trails retain their profile between returns However, they can shift significantly in nodal distance and longitude over + /- 1day Binning is not wrong, it’s just less precise
Dust trails and binning Binning +/- 7 days will diffuse the reality of what is happening at the instant of the nodal encounter Dust trail calculations are much simpler to do and detail precisely where the core of a dust trail is at the instant it crosses the node If the trail is wide enough, it will produce meteors at that instant
Dust trail theory Developed by Miroslav Plavec in 50s Demonstrated successfully by Reznikov, Kondrat'eva and colleagues in 80s and 90s for many streams Rediscovered several times
Dust trail theory Start with ejection at prior perihelion Alter orbital period to estimate particle arrival at node at same time as Earth in 2014 Perturbations change this arrival time Iterate the starting period to produce arrival at node at exactly the instant the Earth is at that same solar longitude. Note the distance (r E -r D ) of the particle from the Earth
Earth at node, time = T 1 Dust trail theory Earth’s orbit Particle orbit Node Particle at time = T 0 Particle at time = T 1 Particle at time = T final To Sun Modified particle orbit Final particle orbit Earth at node, time = T 0 (Initial P too short) (Initial P too long) (Initial P correct) Earth at node, time = T final r E -r D r E = distance of Earth from Sun r D = distance of dust trail from Sun
Asher’s 209P dust trails Dust trails <20-rev old have large r E -r D i.e. too distant for meteors, but lie mostly in the Ye and Wiegert highest density zone The 22 and 47-rev trails have ~direct hits Trails between 27 and 45-revs are almost coincident, but offset from the Earth’s orbit Dust trails >52-rev old are still in the Earth’s vicinity, but strongly disrupted and not well suited for dust trail prediction
The trails align across the Earth’s orbit almost perpendicularly, so peak at similar times (Leonid trails were more scattered). The first trails to be encountered are older, then younger and finally much older. Dust trail calculations are based on the centre of the Earth. A time adjustment is needed for when a specific location passes through the dust sheet. Asher’s 209P dust trails
Year Mo Da UT Revs a 0 r E -r D f M : : : : : : : : : : : : : : : : : : : : : : : Revs – number of orbits of dust from ejection to 2014 a 0 –difference between semi-major axis (a 0 ) of the comet and the particle at ejection. a 0 ~0.0 => large particles r E -r D – distance of the dust trail node from Earth’s orbit. (Earth radius = AU) (Impact radius= AU) f M – estimate of the along-trail dispersion. For a 1-rev trail, f M = 1.0, but for an unperturbed n-rev trail, f M = 1/n Asher’s 209P dust trails
Year Mo Da UT Revs a 0 r E -r D f M : : : : : : : : : : The 46-rev trail would combine with the main 22-rev peak. The 47-rev trail will be a direct hit but this and older trails are encountered much later. This should give a second lower peak with a slow tail off. Revs – number of orbits of dust from ejection to 2014 a 0 –difference between semi-major axis (a 0 ) of the comet and the particle at ejection. a 0 ~0.0 => large particles r E -r D – distance of the dust trail node from Earth’s orbit. (Earth radius = AU) (Impact radius= AU) f M – estimate of the along-trail dispersion. For a 1-rev trail, f M = 1.0 but for an unperturbed n-rev trail, f M = 1/n
A time = T x, (a short time before the encounter, but with the particles sufficiently far from the Earth for the particle’s orbit to be essentially unperturbed by the Earth), predict the position of three particles that differed at this location after 1-rev by a tiny amount, dM 0, in their mean anomaly. Calculating f M Earth’s orbit Particle orbit Particle 0 at time = T x (Nominal dust trail) Particle 1 at time = T x Particle 2 at time = T x dM x (2) dM x (1) dM 0
The extent of the increase of dM x (1) and dM x (2) over dM 0 indicates the dilution of the dust trail density by stretching, f M = 2*dM 0 /(dM x (1)+dM x (2)) If dM x (1) differs significantly from dM x (2), this indicates a significant non-linearity in the dust trail stretching, as a result of perturbations. Calculating f M Earth’s orbit Particle orbit Particle 0 at time = T x (Nominal dust trail) Particle 1 at time = T x Particle 2 at time = T x dM x (2) dM x (1) dM 0
Calculating f M Earth’s orbit Particle orbit Particle 0 at time = T x (Nominal dust trail) Particle 1 at time = T x Particle 2 at time = T x dM x (2) dM x (1) dM 0 Asher uses more particles for this parameter and checks uniformity as well as the level of stretching. Non-uniform distribution indicates perturbations and unreliability of the f M value. -ve values of f M indicate that the trail has bent backwards on itself.
da 0 and particle size For 3mm particles of typical density, solar radiation pressure ratio, beta= beta= would be the equivalent of a tangential ejection velocity from 209P of 2m/s & da 0 = Period is key as particles with same period roughly comove in space, experiencing similar perturbations For most of the dust trail encounters, da 0 < Particles in such orbits would have low beta and/or low ejection velocity, implying large particles and bright meteors.
Shower profile Ye and Wiegert (08:15UT) (06:29UT) Asher’s dust trails suggest a similar but narrower spread comprising 2 peaks. Approximates to ZHR Average fluence should be unaffected by binning but peak rates and width probably are.
What will happen? All studies suggest the encountered particles will be large – bright meteors Rates are very uncertain, as nothing is known of the comet’s historical activity. Rates will be ZHR=0 to storm! Estimated ZHR= from comet’s current activity Differences in peak (06:29-07:40UT) and duration (FWHM~0.4 day to rather less)
When is the peak? Ye and Wiegert -06:29UT (modelling) Lyytinen -07:00UT (dust trail) Asher (1 st peak) -07:09UT (dust trail) Maslov -07:21UT (dust trail) Vaubaillon -07:40UT (modelling) Asher (2 nd peak) -07:47UT (dust trail) Predictions are for the Earth’s centre. Peak will be 8 mins earlier from N America
Correction to Peak times Daylight Night 2014 May 24 07:00UT Galapagos Hawaii Fiji Samoa
Ye and Wiegert have probably too large a bin size which diffuses the reality I trust Asher’s dust trail timings Main peak centred around the 22-rev trail at 07:09UT (unadjusted), superimposed on a broader shower with slow rise and sharper fall off A lower peak from the 47-rev trail at 07:47UT (unadjusted) should have a sharp rise and slower decline Conclusion
Finally Staying in the UK? Don’t let daylight ruin a good shower Core of the 22-rev dust trail will pass the daylight side of the Earth Should fireballs occur, they will be visible if the sky is clear Peaks at 07:00UT & 07:38UT (adjusted) for central UK, the apparent radiant will be at: Az=10 deg Alt=50 deg