62 research outputs found
Simultaneous radar and video meteors
The goal of this thesis is to better understand the physical and chemical properties of meteoroids by using simultaneous radar and video observations of meteors. The Canadian Meteor Orbit Radar (CMOR) and several Gen-III image-intensified CCD cameras were used to measure common meteors and validate metric errors determined through Monte Carlo modelling and to relate radar electron line density (q) to video photon radiant power (I). By adopting an ionisation coefficient from Jones (1997) and using recorded measurements of q/I, a corresponding estimate of the fraction of meteoroid kinetic energy loss converted into light (luminous efficiency) was found.
It was found that 7% ± 3% of video meteors were also simultaneously detected as specular echoes by radar, larger than the expected 2% − 5% from modelling. Errors in the fiducial picks for video meteors were found to be anisotropic, with video speeds being higher on average compared to radar speeds, consistent with more deceleration in specular radar measurements. Most radar detections occurred near the end of their meteor trails, suggesting simultaneous observations are biased towards larger, non-fragmenting meteoroids. The peak luminous efficiency was found to be 5.9% at 41 km/s. The magnitude scale and electron line density were found to relate as M = (38.7 ± 1.2) − 2.5 log10 q.
These results suggest the masses of higher speed meteoroids are an order of magnitude smaller than previously thought, implying the total meteoroid mass influx for small meteoroids is below earlier estimates. The main uncertainties associated with this analysis are the unknown spectra of individual meteors (which affects estimates of I), and assumptions of the initial meteor trail radius (which affects estimates of q). To improve future simultaneous comparisons, an automated video meteor observatory was constructed. This system, named the Canadian Automated Meteor Observatory (CAMO), features a guided camera which tracks meteors in real-time, giving higher precision video measurements of deceleration and fragmentation for comparison to radar measurements. CAMO can also be used to constrain numerical meteoroid ablation models and to measure the meteoroid mass in-flux at Earth
The return of the Andromedids meteor shower
The Andromedid meteor shower underwent spectacular outbursts in 1872 and
1885, producing thousands of visual meteors per hour and described as `stars
fell like rain' in Chinese records of the time. The shower originates from
comet 3D/Biela whose disintegration in the mid-1800's is linked to the
outbursts, but the shower has been weak or absent since the late 19th Century.
This shower returned in December 2011 with a zenithal hourly rate of
approximately 50, the strongest return in over a hundred years. Some 122
probable Andromedid orbits were detected by the Canadian Meteor Orbit Radar.
The shower outburst occurred during 2011 Dec 3-5. The radiant at RA
+ and Dec + is typical of the `classical' Andromedids of
the early 1800's, whose radiant was actually in Cassiopeia. The orbital
elements indicate that the material involved was released before 3D/Biela's
breakup prior to 1846. The observed shower in 2011 had a slow geocentric speed
(16 km s) and was comprised of small particles: the mean measured mass
from the radar is kg corresponding to radii of 0.5 mm at
a bulk density of 1000 kg/m.
Numerical simulations of the parent comet indicate that the meteoroids of the
2011 return of the Andromedids shower were primarily ejected during 3D/Biela's
1649 perihelion passage. The orbital characteristics, radiant, timing as well
as the absence of large particles in the streamlet are all consistent with
simulations. Predictions are made regarding other appearances of the shower in
the years 2000-2047 based on our numerical model. We note that the details of
the 2011 return can, in principle, be used to better constrain the orbit of
3D/Biela prior to the comets first recorded return in 1772.Comment: submitted to the Astronomical Journal Sep 22 201
Low thermal conductivity of the superfast rotator (499998) 2011 PT
Context: Asteroids with a diameter of up to a few dozen meters may spin very
fast and complete an entire rotation within a few minutes. These small and
fast-rotating bodies are thought to be monolithic objects because the
gravitational force due to their small size is not strong enough to counteract
the strong centripetal force caused by the fast rotation. Additionally, it is
not clear whether the fast spin prevents dust and small particles (regolith)
from being kept on their surface. Aims: We develop a model for constraining the
thermal conductivity of the surface of the small, fast-rotating near-Earth
asteroids. This model may suggest whether regolith is likely present on these
objects. Methods: Our approach is based on the comparison of the measured
Yarkovsky drift and a predicted value using a theoretical model that depends on
the orbital, physical and thermal parameters of the object. The necessary
parameters are either deduced from statistical distribution derived for
near-Earth asteroids population or determined from observations with associated
uncertainty. With this information, we performed Monte Carlo simulations and
produced a probability density distribution for the thermal conductivity.
Results: Applying our model to the superfast rotator asteroid (499998) 2011 PT,
we find that the measured Yarkovsky drift can only be achieved when the thermal
conductivity of the surface is low. The resulting probability density
function for the conductivity is bimodal, with two most likely values being
around 0.0001 and 0.005 W m K. Based on this, we find that the
probability that is lower than 0.1 W m K is at least 95\%.
This low thermal conductivity might indicate that the surface of 2011 PT is
covered with a thermal insulating layer, composed of a regolith-like material
similar to lunar dust.Comment: Accepted for publication in A&A. 13 pages, 7 figures, 2 table
Improvement of digest2 NEO Classification Code -- utilizing the Astrometry Data Exchange Standard
We describe enhancements to the digest2 software, a short-arc orbit
classifier for heliocentric orbits. Digest2 is primarily used by the Near-Earth
Object (NEO) community to flag newly discovered objects for a immediate
follow-up and has been a part of NEO discovery process for more than 15 years.
We have updated the solar system population model used to weight the digest2
score according to the 2023 catalog of known solar system orbits and extended
the list of mean uncertainties for 140 observatory codes. Moreover, we have
added Astrometry Data Exchange Standard (ADES) input format support to digest2,
which provides additional information for the astrometry, such as positional
uncertainties for each detection. The digest2 code was also extended to read
the roving observer astrometric format as well as the ability to compute a new
parameter from the provided astrometric uncertainties () that can serve
as an indicator of in-tracklet curvature when compared with tracklet's
great-circle fit RMS. Comparison with the previous version of digest2 confirmed
the improvement in accuracy of NEO identification and found that using ADES XML
input significantly reduces the computation time of the digest2.Comment: 14 pages, 8 tables, 6 figures, appendi
Fragmentation Kinematics in Comet 332P/Ikeya-Murakami
We present initial time-resolved observations of the split comet
332P/Ikeya-Murakami taken using the Hubble Space Telescope. Our images reveal a
dust-bathed cluster of fragments receding from their parent nucleus at
projected speeds in the range 0.06 to 3.5 m s from which we estimate
ejection times from October to December 2015. The number of fragments with
effective radii 20 m follows a differential power law with index
= -3.60.6, while smaller fragments are less abundant than
expected from an extrapolation of this power-law. We argue that, in addition to
losses due to observational selection, torques from anisotropic outgassing are
capable of destroying the small fragments by driving them quickly to rotational
instability. Specifically, the spin-up times of fragments 20 m in
radius are shorter than the time elapsed since ejection from the parent
nucleus. The effective radius of the parent nucleus is 275 m
(geometric albedo 0.04 assumed). This is about seven times smaller than
previous estimates and results in a nucleus mass at least 300 times smaller
than previously thought. The mass in solid pieces, kg, is about
4% of the mass of the parent nucleus. As a result of its small size, the parent
nucleus also has a short spin-up time. Brightness variations in time-resolved
nucleus photometry are consistent with rotational instability playing a role in
the release of fragments.Comment: 19 pages, 1 table, 4 figures, To be published on ApJ
Observations of an Unexpected Meteor Shower Outburst at High Ecliptic Southern Latitude and Its Potential Origin
A strong and unexpected meteor shower outburst was observed by the Southern Argentina Agile MEteor Radar Orbital System (SAAMER-OS) at high southern ecliptic latitude within the South Toroidal region. The outburst, which was active throughout solar longitudes 351° and 352°, peaked at 09:30 UT on 2020 March 12, has a mean Sun-centered ecliptic radiant of λ-λ 0 ∼ 307.°5 and β ∼-77.°2 and a geocentric velocity of 30.7 km s-1. Using the D′parameter criterion, we find the corresponding orbital elements of the outburst to match well with both the β Tucanid and δ Mensid meteor showers, suggesting these are in fact the same shower. We also find a promising parent candidate in asteroid (248590) 2006 CS, a large (D ∼ 2 km) highly inclined 52° near-Earth object.Fil: Janches, Diego. Nasa Goddard Space Flight Center; Estados UnidosFil: Bruzzone, Juan Sebastian. Nasa Goddard Space Flight Center; Estados UnidosFil: Weryk, Robert J.. University of Hawaii at Manoa; Estados UnidosFil: Hormaechea, José Luis. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y GeofÃsicas; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro Austral de Investigaciones CientÃficas; ArgentinaFil: Wiegert, Paul. Public Health Ontario; CanadáFil: Brunini, Claudio Antonio. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y GeofÃsicas; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - la Plata. Laboratorio Geo - Aggo.; Argentin
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