11 research outputs found
Asteroid (3200) Phaethon: colors, phase curve, limits on cometary activity and fragmentation
We report on a multi-observatory campaign to examine asteroid 3200 Phaethon
during its December 2017 close approach to Earth, in order to improve our
measurements of its fundamental parameters, and to search for surface
variations, cometary activity and fragmentation. The mean colors of Phaethon
are B-V = 0.702 +/- 0.004, V-R = 0.309 +/- 0.003, R-I = 0.266 +/- 0.004,
neutral to slightly blue, consistent with previous classifications of Phaethon
as a F-type or B-type asteroid. Variations in Phaethon's B-V colors (but not
V-R or R-I) with observer sub-latitude are seen and may be associated with
craters observed by the Arecibo radar. High cadence photometry over phases from
20 to 100 degrees allows a fit to the values of the HG photometric parameters;
H = 14.57 +/- 0.02, 13.63 +/- 0.02, 13.28 +/- 0.02, 13.07 +/- 0.02; G = 0.00
+/- 0.01, -0.09 +/- 0.01, -0.10 +/- 0.01, -0.08 +/- 0.01 in the BVRI filters
respectively; the negative G values are consistent with other observations of F
type asteroids. Light curve variations were seen that are also consistent with
concavities reported by Arecibo, indicative of large craters on Phaethon's
surface whose ejecta may be the source of the Geminid meteoroid stream. A
search for gas/dust production set an upper limit of 0.06 +/- 0.02 kg/s when
Phaethon was 1.449 AU from the Sun, and 0.2 +/- 0.1 kg/s at 1.067 AU. A search
for meter-class fragments accompanying Phaethon did not find any whose on-sky
motion was not also consistent with background main belt asteroids.Comment: Accepted by the Astronomical Journal, 15 pages, 8 figures, 1 animated
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Asteroid (3200) Phaethon: Colors, Phase Curve, Limits on Cometary Activity, and Fragmentation
We report on a multiobservatory campaign to examine asteroid 3200 Phaethon during its 2017 December close approach to Earth, in order to improve our measurements of its fundamental parameters, and to search for surface variations, cometary activity, and fragmentation. The mean colors of Phaethon are B – V = 0.702 ± 0.004, V – R = 0.309 ± 0.003, and R – I = 0.266 ± 0.004, neutral to slightly blue, consistent with previous classifications of Phaethon as a F-type or B-type asteroid. Variations in Phaethon's B – V colors (but not V – R or R – I) with observer sublatitude are seen and may be associated with craters observed by the Arecibo radar. High-cadence photometry over phases from 20° to 100° allows a fit to the values of the HG photometric parameters; H = 14.57 ± 0.02, 13.63 ± 0.02, 13.28 ± 0.02, 13.07 ± 0.02; G = 0.00 ± 0.01, −0.09 ± 0.01, −0.10 ± 0.01, −0.08 ± 0.01 in the BVRI filters respectively; the negative G values are consistent with other observations of F-type asteroids. Light-curve variations were seen that are also consistent with concavities reported by Arecibo, indicative of large craters on Phaethon's surface whose ejecta may be the source of the Geminid meteoroid stream. A search for gas/dust production sets an upper limit of 0.06 ± 0.02 kg s^(−1) when Phaethon was 1.449 au from the Sun, and 0.2 ± 0.1 kg s^(−1) at 1.067 au. A search for meter-class fragments accompanying Phaethon did not find any whose on-sky motion was not also consistent with background main-belt asteroids
Debris Disks: Probing Planet Formation
Debris disks are the dust disks found around ~20% of nearby main sequence
stars in far-IR surveys. They can be considered as descendants of
protoplanetary disks or components of planetary systems, providing valuable
information on circumstellar disk evolution and the outcome of planet
formation. The debris disk population can be explained by the steady
collisional erosion of planetesimal belts; population models constrain where
(10-100au) and in what quantity (>1Mearth) planetesimals (>10km in size)
typically form in protoplanetary disks. Gas is now seen long into the debris
disk phase. Some of this is secondary implying planetesimals have a Solar
System comet-like composition, but some systems may retain primordial gas.
Ongoing planet formation processes are invoked for some debris disks, such as
the continued growth of dwarf planets in an unstirred disk, or the growth of
terrestrial planets through giant impacts. Planets imprint structure on debris
disks in many ways; images of gaps, clumps, warps, eccentricities and other
disk asymmetries, are readily explained by planets at >>5au. Hot dust in the
region planets are commonly found (<5au) is seen for a growing number of stars.
This dust usually originates in an outer belt (e.g., from exocomets), although
an asteroid belt or recent collision is sometimes inferred.Comment: Invited review, accepted for publication in the 'Handbook of
Exoplanets', eds. H.J. Deeg and J.A. Belmonte, Springer (2018
Modeling non-motorized travel demand at intersections based on traffic counts and GIS data in Calgary, Canada
In September 2009 the City of Calgary Council approved Plan It Calgary, which proposes policies that focus on the development of resilient neighborhoods through the intensification and diversification of urban activities around transit stations and routes. More intensive development and mixed land use encourage non-motorized trips and reinforce comfortable, safe and walkable streets. The development of high-density, mixed-use and transit- and pedestrian-oriented communities has the potential to generate trips with shorter destinations, which are expected to result in a higher share of active travel modes, such as biking and walking. Thus, there is a growing need to estimate the impact of land-use development scenarios and transportation policies on bicycle and pedestrian demand to predict future non-motorized trip volumes and adequately design the related infrastructure.
This study calibrates multiple linear and Poisson regression models to estimate non-motorized travel demand based on GIS, transportation data and road characteristics. The empirical models that have been developed in this research can be used to assess the impacts of urban design and built environments, such as developing high-density and mix-land-use areas, and building complete streets in the middle ring communities of the City of Calgary in influencing the demand for active travel modes. The developed models show the benefits of improved pedestrian infrastructure, such as improved network connectivity and increases in the length of pedestrian pathways, as well as the integration of transit and walking modes and transit and bicycle modes in encouraging more non-motorized travel demand. The method employed herein is a straightforward statistical analysis method, and the needed data are relatively easy to access