Asteroid 86279 is a member of the Hungaria
family of asteroids (based on the orbital radius and
eccentricity). Its diameter is estimated to be 1.26
± 0.20 km, which is based on H = 15.76 ± 0.10 and a
geometric albedo typical for the Hungaria family = 55 ±
18 % (based on Masiero et al, 2013). My light
curve measurements have established a rotation period of
8.84856 hours. The peak-to-peak brightness variation is 0.26
magnitude (±12.7% variation about the average). The
rotational light curve is close to sinusoidal, meaning that
the asteroid's shape is close to an oblate spheroid. The
brightness variation requires that the solid angle varies by
27% (max to min), and this implies that the ratio of longest
axis to shortest is at least as great as 1.27. The
rotational axis is in the northern ecliptic hemisphere
(using the right-hand rule) since it rotates in a prograde
direction. Another web
is used to describe ongoing observations during the
2015 apparition; the goal for these observations is
to create a phase curve with a slope usable for
inferring albedo, and hence size, using the B&S
Links internal to this web page:
2006 & 2007
2005 My First
Thanks, Dave Healy and Jeff Medkeff, for assigning my
name to this asteroid.
When someone names an asteroid for you it's incumbent upon the
recipient to try to determine as much about that asteroid as
possible. Since I like observing challenges this asteroid's
faintness, at ~18th magnitude, typically, was an added incentive
for me to hone my observing and analysis skills. This web page
describes what a dedicated amateur can learn about a faint
asteroid if the motivation exists.
Asteroid "86279 Brucegary" was discovered in 1999 by Jeff
Medkeff and David Healy using the Junk Bond Observatory (in
Sierra Vista, AZ). It's orbital elements and standard (1 a.u.)
a = 1.931865 a.u. (semi-major axis)
i = 21.9853 degrees (inclination)
e = 0.0679895 (eccentricity)
H = 15.9 (16.2 my suggested revision)
Based on the two orbital parameters a and i this asteroid can be
identified as a member of the "Hungaria" family. The smallness
of this asteroid family is shown in the following scatter
diagram of 10,592 asteroids observed by SDSS (reported by Ivezic
et al, 2002).
. Scatter diagram of "sine(inclination"
versus semi-major axis for 10,592 asteroids observed with the
SDSS telescope and reported by Ivezic et al, 2002. Each
asteroid dot is colored to represent its SDSS g, r, i, z
colors. Asteroid 86279 has sine(inclination) = 0.374 and
semi-major axis = 1.93 a.u., which places it within the
upper-left group in this diagram (close and highly inclined).
(Note: Mars orbits at 1.52 a.u., and at its farthest is at
As of mid-2004 there were 3375 Hungaria asteroids tabulated,
which represented 1.6% of all 214,044 categorized asteroids
What is the asteroid's size? We need to estimate the asteroid's
albedo in order to convert its brightness to a diameter. The
next plot is a summary of measured albedos versus semi-major
Figure 2. Albedo versus semi-major axis (Plot created
by Piotr Deuar, appearing in Wikipedia).
In this figure there are 7 Hungaria asteroids, and their median
albedo is 23% (range is 9 to 30%). As shown below, the
asteroid's standardized brightness is V-mag = 15.76 (estimated
SE = 0.05 mag). This corresponds to a diameter of 1.9 km (range
is 1.7 to 3.1 km).
However, a more recent analysis of albedos for the Hungaria
family, based on NEOWISE observations of 48 members, has been
published showing a median gemetrric albedo of 72.2 ± 15.6 %.
This result is based on 4 band thermal emission measurements
used to determine diameters and published photometric ata used
to derive H (assuming G = 0.15 for most cases). It is thought
that when phase slopes are better determined for the Hungarias
greater values for G will be derived (Warner, unpublished
private communication), which will brighten H, and lead to
albedos closer to 40%. My conservative approach is to adopt
albedo = 55 ± 18%. This leads to diameter = 1.26 ± 0.20 km.
2006 and 2007 Light
Here's a chi-squared "solution" for the rotation light curve
shape and period based on adjusted observation dates: 20060128,
20060131, 20071008, 20071011, 20071101 and 20071107 (UT).
The "adjustments" consist of two things: 1) magnitude offsets to
compensate for distance and sun-asteroid-earth geometry (from an
ephemeris), and 2) time shifts caused by the same
sun-asteroid-earth angle and hypothetical rotation period. This
second adjustment causes a similar rotational aspect to be
observed either earlier than or later than an average periodic
interval depending on whether the asteroid is before or after
opposition. If the rotational vector pointed at the ecliptic
north pole, for example, before opposition a given aspect would
be viewed before a uniformly spaced schedule and after
opposition it would be later. This means the asteroid's rotation
direction, prograde versus retrograde, can be determined. For
the above solution only the prograde hypothesis produced a good
Based on these observations it appears that the asteroid's
rotation period is 8.84856 ± 0.00003 hours. The average
peak-to-peak brightness variation is 0.26 magnitude, implying
that the asteroid's projected solid angle varied by 27% (i.e.,
the largest area projection was ~27% greater than the smallest).
This assumes a uniform albedo and similar shape for all sides.
However, since the two minima are different the ends must have
different shapse. The peaks are about the same, so the opposite
sides probably have the same projected area and albedo.
The measured magnitude offsets from ephemeris values predicted a
magnitude average -0.14 magnitude. In other words the average
V-magnitude is brighter than the ephemeris values by ~14%. This
requires that the ephemeris H value be changed from 15.9 to
15.76 (assuming G = 0.15 is correct and my all-sky
calibration is correct).
Image Subtraction Analysis
[Note: this section describes an image processing
procedure that removes a background star field image from
individual asteroid images that produces a residual image
showing the asteroid at 100% of its true value and stars at
~1% of their original value. Since I wrote this I have made
small improvements in analysis procedure, but the basic
concept is the same. Later, when I settle on a final
procedure, I'll update this section.]
An image subtraction technique was used to process observations
made 2006.01.28 UT with my 14-inch Celestron. Downslope winds
cause seeing to vary from bad to poor, with FWHM ranging between
4.5 to 6.0 "arc (for 4-minute exposures).
Let's begin with an image of the star field showing the path of
the asteroid during the 3-hour observing period.
Figure 2. Path of asteroid during the 3-hour
observing period of 2006.01.28. At the beginning (lower-left)
the asteroid is just north of a 19.1 magnitude star. The
asteroid does not appear in this image because it is a median
combine of 21 images during which the astreroid's location
changed. The faintest stars have CV magnitudes of 22.2
(SNR=3). The brightest star (saturated in this 8-bit image,
but not saturated in the 16-bit FITS image) has CV = 14.59
with FWHM = 6.0 "arc. The FOV is 8.6 x 6.6 'arc (cropped from
the original 15 x 10 'arc image). North up, east left. [Total
exposure = 84 minutes.]
The next image is a median combine of the first 3 images
(cropped the same as the previous image).
Figure 3. Median combine of first 3 images, showing
asteroid (cicled) at the beginning of its path for the night.
The asteroid is close to a 19.1 magnitude star, located to its
south within the sky reference annulus. Any attempt to measure
the asteroid's brightness would be affected by the nearby star.
This is when "image subtraction" is useful.
Figure 4. Same star field after image subtraction,
showing the asteroid without interference from nearby stars.
Let's show the before and after versions of the previous two
images for a smaller FOV.
Figure 5. Before and after image subtraction (for a
smaller FOV) for the first 3-image set.
Notice that the 19th magnitude star to the asteroid's south is
completely removed after image subtraction. Only the 14.6
magnitude star is present as a ghost feature with an approximate
brightness comparable to the 18.7 magnitude asteroid. Thus, the
image subtraction processing achieved a star subtraction of
about 4 magnitudes (40-fold reduction).
If you want to learn more about the image processing procedure
used on this data go to IS for 6128
Animation of Asteroid Motion
Figure 6. Animation of asteroid's 3-hour motion,
using cropped versions of the image subtraction images.
Notice that in this animation there is no hint of other stars
besides the ghost of the bright 14.6 magnitude star. This
suggests that the image subtraction process did what it was
suppsoed to do.
Here's an animation from "smoothed" versions of the same images
(only 10 frames).
Figure 7. Same animation but with smoothing applied.
2005 January Observation
The discovery of "86279 Brucegary" was made 1999.10.17 by Jeff
Medkeff and Dave Healy. They used Dave's Junk Bond Observatory
20-inch Ritchey-Chritien (loaner) telescope in Sierra Vista, AZ
(3 miles from my place).
The asteroid has the following known properties:
Semi-major axis = 1.932 a.u.
Eccentricity = 0.068
Inclination = 21.8 degrees (unusually large)
Absolute magnitude = 15.9 (my suggested
revision calls for 15.8)
The brightness implies a diameter of ~3.0 km (based on the H
value and an albedo of 0.15).
Of course, I had to take a "picture" of it as soon as I learned
about the official naming.
Stack of 48 one-minute exposures, using
the predicted position of the asteroid for alignment. Unfiltered
brightness corresponds to V-mag = 20.6 +/- 0.13 (SNR = 8). [Celestron
14-inch, prime focus, f/1.86, SBIG ST-8XE; 2005.01.29;
Measuring the brightnessof a stationary object with a
V-magnitude of 20.6 is easy for amateurs, but a moving object of
the same brightness is more difficult. This asteroid was moving
at the rate of 3.8 "arc/minute, which meant that exposures could
not exceed ~1 minute. The asteroid's motion was known, so I
added an "artificial star" to each image that was carefully
offset from a nearby bright star by an amount that corresponded
to the asteroid's motion. I then used this artificial star for
alignment of groups of 4 images while performing a median
combine. Since there were 48 one-minute images, this led to a
set of 12 median combined images, each of which was cleansed of
any artifact blemishes (such as cosmic ray features). These 12
images were averaged, again using the artificial star for
alignment. Voila! At the predicted location there appeared a
20.6 magnitude object which I assume is the asteroid. It was
located 1.6 pixel to the east and 0.1 pixel to the south of the
Nearby Tycho stars were used to establish the magnitude scale,
which I estimate allowed me to establish a magnitude scale
accurate to 0.07 mag, SE. The ephemeris predicted a magnitude on
the observing date of 20.3, so based on my measured magnitude I
am suggesting that the asteroid is 0.3 magnitude fainter than
assumed by the ephemeris program. In other words, I am
suggesting that H = 16.2 (instead of 15.9). Of course, there are
two other alternative reconciliations of this brightness
difference. The asteroid rotates, and I observed it near
minimum, and the assumed opposition effect differs from the
adopted value describing the fall of of brightness with
increasing sun-object-observer angle (G = 0.15). My observation
was made close to the time when the asteroid was on the opposite
side of the sun from the Earth. It was ~2.9 a.u. from Earth,
whereas at opposition it will be ~1.3 a.u. away, and will be at
18.8 magnitude (at declination +42 degreese).
Ivezic, Z., Lupton, R. H., Juric, M., Tabachnik, S., Quinn, T.,
Gunn, J., Knapp, G. R., Rockosi, C. M., Brinkmann, J., "Color
Confirmation of Asteroid Families," A. J., 124
2943-2948, 2002 November.
Masiero, Joseph R., A. K. Mainzer, J. M. Bauer, T> Grav, C.
R. Nugent and R. Stevenson, 2014, arXiv:1305.1607v1.
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Webmaster: Bruce L. Gary. Nothing
on this web page is copyrighted. First created:
2005.02.13. Last revised: 2007.11.07