Meteor Survey - Physics & Astronomylwa/users14/Cockrell.pdf · 2014-07-15 · meteor Meteors (as...
Transcript of Meteor Survey - Physics & Astronomylwa/users14/Cockrell.pdf · 2014-07-15 · meteor Meteors (as...
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LWA Users Meeting - July 2014Sophia Cockrell
Meteor Survey
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Survey overviewMeteor stream - closed loop orbit of cometary debris
• parallel orbits with same velocity
Our aim: a once-around-the-Sun survey of meteor streams along Earth’s orbit.
Why? To get a better census of material in our region.
Implications: Hopes to inform Solar System evolution studies.
A time sensitive opportunity! Major transmitters switching to digital next year.
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Detection
• Meteors create dense ionized gas column of gas in the lower ionosphere.
• Specular reflection - well established method
• A meteor stream should display an arc in all-sky image
meteor
Meteors (as small as 10-5 g) entering the atmosphere create dense quasi-linear structures of ionized gas in the lower ionosphere (85 - 105 km high) during ablation 10s of km long.
A meteor stream should display as an arc in all-sky image who's characteristics are determined by orientation of the stream and locations of the receiver and transmitter.
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radiant
• Detection occurs on an ellipse surface with the transmitter and receiver as foci.
• For a given meteor orientation, specular reflection only occurs at a fixed distance.
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PASI - raw at 55.25 MHz
• Analog TV stations broadcasting at 55.25 MHz together with LWA1 TBN mode detect ~9,500 meteors per hour (Helmboldt et al. 2013).
• Hour long observations every 40 hrs.
Point out features and what they represent
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MethodologyEach image made:
• 5.079s of data
• 32 frequency channels
• each 6.10 Hz wide
Mean image over all channels identifies brightest meteor trails.
Beam form to each source with a single 195.3 Hz wide channel.
The peak channel, sky position, flux density, intensity, and image RMS are recorded separately for X and Y polarization
Helmboldt et al. 2013
For a single 5.079s period:
Mean images over all channels compared with maximum S/N.
Each image is made using 5.079s of data imaged within 32 frequency channels, each 6.10 Hz wide. Initially, a mean image is made over all channels to identify the brightest meteor trails. For each of these detections, the antenna data are used to generate high-resolution(5.12ms) by beam forming to each source using a single 195.3 Hz wide channel.
For each significant detection within each cube, the peak channel, sky position, flux density/intensity, and image RMS are recorded. Separately for X and Y polarization
IMAGE: For a single 5.079s period, (upper) the mean images over all channels in X and Y polarization as compared with (lower) images of the maximum S/N over the entire image cube, with the image from each channel normalized by its own estimated noise level.
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Strong spectra:
• “non-trails”
• trails with smooth exponential decays
• substantial deviations from smooth decays
Helmboldt et al. 2013
Filtering strong signals
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How streams develop
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Detected streams• All-sky image of an hour
long TBN mode observation
• 25 stream-like detections to date.
E-W direction cosine
N-S
dire
ction
cosin
e
• Radiant - point where meteors seems to originate
• Determined by averaging (based on geometry and signal strength) potential transmitters.
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Radiant analysis
Radiants with same Alt/Az probably airplane artifacts
Az and Alt of stream radiants
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Radiant analysis
Displaying only radiants with unique Az and Alt
Az and Alt of stream radiants
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Radiant analysisAz and Alt of stream radiants
Displaying only radiants that grow in sporadic fashion
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Sporadic - E
• Clouds of unusually ionized atmospheric gas in the lower E region.
• Activity peaks in summer months.
• First detected on May 18. Since then, 16% of observations contain this feature with 75% of them occurring at 9pm.
• Confirmed sporadic-E activity during these times with Boulder, CO digisonde data.
• Concentrated toward the Northern arc, perhaps due to increased concentration of meteors.
• See Joe Helmboldt’s talk.
E-W direction cosine
N-S
dire
ction
cosin
e
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Zodiacal dustInterplanetary dust particles 10-300 µm in diameter confined to ecliptic plane
• Arc present in only and all early morning observations (leading edge)
• Radiant close to zenith
• RA increases gradually with Earth’s orbital direction.
• Stream grows gradually and sporadically
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Conclusions and Future Work• We have no potentially new, un-catalogued streams to date.
BUT…
• Density profile survey of the Zodiacal dust could be promising.
• Meteor and sporadic-E relationship determination may be possible.
In the Future:
• Continue survey at 55.25 MHz
• Work on a better identification method for separating artifacts from real streams.
• Need to catch a catalogued meteor shower!
• Attempting 15 MHz and 20 MHz frequencies for distance measurements and hopefully decrease airplane artifacts.