Asteroid 86279 is probably a member of the
family of asteroids (based on the orbital radius and
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
brightness variation is 0.26 magnitude (±12.7% variation
the average). The rotational light curve is close to
meaning that the asteroid's shape is close to an oblate
brightness variation requires that the solid angle varies by
to min), and this implies that the ratio of longest axis to
at least as great as 1.27. The rotational axis is in the
ecliptic hemisphere (using the right-hand rule) since it
rotates in a
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
Since I like observing challenges this asteroid's faintness, at
magnitude, typically, was an added incentive for me to hone my
observing and analysis skills. This web page describes what a
amateur can learn about a faint asteroid if the motivation
Asteroid "86279 Brucegary" was discovered in 1999 by Jeff
David Healy using the Junk Bond Observatory (in Sierra Vista,
orbital elements and standard (1 a.u.) brightness are:
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
asteroid family is shown in the following scatter diagram of
asteroids observed by SDSS (reported by Ivezic et al, 2002).
. Scatter diagram of "sine(inclination"
semi-major axis for 10,592 asteroids observed with the SDSS
and reported by Ivezic et al, 2002. Each asteroid dot is
represent its SDSS g, r, i, z colors. Asteroid 86279 has
sine(inclination) = 0.374 and semi-major axis = 1.93 a.u.,
it within the upper-left group in this diagram (close and
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,
represented 1.6% of all 214,044 categorized asteroids (Faure,
What is the asteroid's size? We need to estimate the asteroid's
in order to convert its brightness to a diameter. The next plot
summary of measured albedos versus semi-major axis.
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
is 23% (range is 9 to 30%). As shown below, the asteroid's
brightness is V-mag = 15.76 (estimated SE = 0.05 mag). This
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
and period based on adjusted observation dates: 20060128,
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
angle and hypothetical rotation period. This second adjustment
similar rotational aspect to be observed either earlier than or
than an average periodic interval depending on whether the
before or after opposition. If the rotational vector pointed at
ecliptic north pole, for example, before opposition a given
would be viewed before a uniformly spaced schedule and after
it would be later. This means the asteroid's rotation direction,
prograde versus retrograde, can be determined. For the above
only the prograde hypothesis produced a good solution.
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
27% (i.e., the largest area projection was ~27% greater than the
smallest). This assumes a uniform albedo and similar shape for
sides. However, since the two minima are different the ends must
different shapse. The peaks are about the same, so the opposite
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
(assuming G = 0.15 is correct and my all-sky calibration
Image Subtraction Analysis
[Note: this section describes an image processing
procedure that removes a background star field image from
asteroid images that produces a residual image showing the
100% of its true value and stars at ~1% of their original
I wrote this I have made small improvements in analysis
the basic concept is the same. Later, when I settle on a
procedure, I'll update this section.]
An image subtraction technique was used to process observations
2006.01.28 UT with my 14-inch Celestron. Downslope winds cause
to vary from bad to poor, with FWHM ranging between 4.5 to 6.0
(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
of 2006.01.28. At the beginning (lower-left) the asteroid is
of a 19.1 magnitude star. The asteroid does not appear in this
because it is a median combine of 21 images during which the
astreroid's location changed. The faintest stars have CV
22.2 (SNR=3). The brightest star (saturated in this 8-bit
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
within the sky reference annulus. Any attempt to measure the
brightness would be affected by the nearby star. This is when
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
star is present as a ghost feature with an approximate
comparable to the 18.7 magnitude asteroid. Thus, the image
processing achieved a star subtraction of about 4 magnitudes
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
the ghost of the bright 14.6 magnitude star. This suggests that
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
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
predicted position of the asteroid for alignment. Unfiltered
corresponds to V-mag = 20.6 +/- 0.13 (SNR = 8). [Celestron
prime focus, f/1.86, SBIG ST-8XE; 2005.01.29; Hereford, AZ]
Measuring the brightnessof a stationary object with a
20.6 is easy for amateurs, but a moving object of the same
is more difficult. This asteroid was moving at the rate of 3.8
"arc/minute, which meant that exposures could not exceed ~1
asteroid's motion was known, so I added an "artificial star" to
image that was carefully offset from a nearby bright star by an
that corresponded to the asteroid's motion. I then used this
star for alignment of groups of 4 images while performing a
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
blemishes (such as cosmic ray features). These 12 images were
again using the artificial star for alignment. Voila! At the
location there appeared a 20.6 magnitude object which I assume
asteroid. It was located 1.6 pixel to the east and 0.1 pixel to
south of the predicted location.
Nearby Tycho stars were used to establish the magnitude scale,
estimate allowed me to establish a magnitude scale accurate to
mag, SE. The ephemeris predicted a magnitude on the observing
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
15.9). Of course, there are two other alternative
this brightness difference. The asteroid rotates, and I observed
near minimum, and the assumed opposition effect differs from the
adopted value describing the fall of of brightness with
sun-object-observer angle (G = 0.15). My observation was made
the time when the asteroid was on the opposite side of the sun
Earth. It was ~2.9 a.u. from Earth, whereas at opposition it
~1.3 a.u. away, and will be at 18.8 magnitude (at declination
Ivezic, Z., Lupton, R. H., Juric, M., Tabachnik, S., Quinn, T.,
J., Knapp, G. R., Rockosi, C. M., Brinkmann, J., "Color
Asteroid Families," A. J., 124
, 2943-2948, 2002
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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