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Meeting on Asteroids and Comets Europe2006 May 14st-moving asteroids
Lightcurve photometry of fast-moving asteroidsby simultaneous V- and I-band calibration of field
stars
by
Richard MilesGolden Hill Observatory (MPC J77), United Kingdom
Observatory
Setup
Methodology-1
Observing Methodology
1) Utilise Hipparcos stars as secondary references in V (and I)
Hipparcos Coverage
Hipparcos to V
V-I vs B-V
Methodology-2
Observing Methodology
1) Utilise Hipparcos stars as secondary references in V (and I)
2) Calibrate using Hipparcos red-blue pairs
R-B Pairs Sky Distribution
Sky Distribution of Hipparcos Red-Blue Pairs
Cl to V coeff.
Transformation – Clear to V Transformation Coefficient
Cl to V calculated
Transformation – Clear to V Magnitude
Methodology-3
Observing Methodology
1) Utilise Hipparcos stars as secondary references in V (and I)
2) Calibrate using Hipparcos red-blue pairs
3) Calibrate unfiltered photometry (stars and asteroids)
Cl to V measured
Transformation – Clear to V MagnitudeDerived from Asteroid – Comparison Star Observations
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
V-I Color Index
Co
rrec
tion,
mag
Poly. (Observed correction)
Poly. (Red-blue pair calibration (X=1.2))
Methodology-4
Observing Methodology
1) Utilise Hipparcos stars as secondary references in V (and I)
2) Calibrate using Hipparcos red-blue pairs
3) Calibrate unfiltered photometry (stars and asteroids)
4) Simultaneous wide-field images in V and I-band
Methodology-5
Observing Methodology
1) Utilise Hipparcos stars as secondary references in V (and I)
2) Calibrate using Hipparcos red-blue pairs
3) Calibrate unfiltered photometry (stars and asteroids)
4) Simultaneous wide-field images in V and I-band
5) Unfiltered images with narrow-field telescope
Methodology-6
Observing Methodology
1) Utilise Hipparcos stars as secondary references in V (and I)
2) Calibrate using Hipparcos red-blue pairs
3) Calibrate unfiltered photometry (stars and asteroids)
4) Simultaneous wide-field images in V and I-band
5) Unfiltered images with narrow-field telescope
6) Determine V and (V-I) colours of stars near asteroid track
HIP 55101
HIP 55503
HIP 55182
79 x 1 minute stacked exposures 6-cm aperture + V filter
HIP 55101
HIP 55503
HIP 55182
Track of 2000 BD19
79 x 1 minute stacked exposures 6-cm aperture + V filter
Inset images using 28-cm aperture + no filter
a
d
ef
g
h
ij
m
no
p
q
r
st
a
10.86
14.8514.59
12.59
14.01
10.8211.85
13.16
13.1213.29
13.70
15.45
14.82
12.6612.86
Methodology-7
Observing Methodology
1) Utilise Hipparcos stars as secondary references in V (and I)
2) Calibrate using Hipparcos red-blue pairs
3) Calibrate unfiltered photometry (stars and asteroids)
4) Simultaneous wide-field images in V and I-band
5) Unfiltered images with narrow-field telescope
6) Determine V and (V-I) colours of stars near asteroid track
7) Carry out aperture photometry or PSF photometry of fast-
moving asteroid relative to an ensemble of stars in the same
field - Difficult - May need to stack groups of images
(Astrometrica, Lymm software) to get adequate SNR for
asteroid.
Methodology-8
Observing Methodology
1) Utilise Hipparcos stars as secondary references in V (and I)
2) Calibrate using Hipparcos red-blue pairs
3) Calibrate unfiltered photometry (stars and asteroids)
4) Simultaneous wide-field images in V and I-band
5) Unfiltered images with narrow-field telescope
6) Determine V and (V-I) colours of stars near asteroid track
7) Carry out aperture photometry or PSF photometry of fast-
moving asteroid relative to an ensemble of stars in the same
field - Difficult - May need to stack groups of images
(Astrometrica, Lymm software) to get adequate SNR for
asteroid.
8) Calculate V-magnitude zeropoint of unfiltered images using
ensemble of stars. May require photometry of trailed stars
using tilted elliptical aperture with AstPhot32 software
(Stefano Mottola) or Lymm8 software (John Saxton)
AstPhot32Software
StefanoMottola
Lymm softwareJohn Saxton
Features:
• Script-based running in Fortran
• Pattern recognition
• Models track of asteroid
• Tracks and stacks images (if required)
• Aperture or PSF photometry on calculated asteroid positions
• NEW! - Photometry on single images or on user-defined stacks
• NEW! - Novel sky background correction
2005 WC1 (diameter 500m approx)2005 Dec 06 23.8-24.8h UT
2005 WC1
2005 WC1
Sky BackgroundCorrection
Sky BackgroundCorrection
Effect of PA
2000 BD19
130 B&W
(130) Elektra – Composite Lightcurve
(130) Elektra in 2005
-0.2
-0.1
0.0
0.1
0.2
0.30.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Rotational Phase (Period = 5.2248 hr)
Rel
ativ
e V
Mag
nit
ud
e
999 measures on 17 nights
130 Electra Composite
Asteroid (130) Elektra [ 2005 Feb 14 - Apr 10, 17 nights ]
11.6
11.7
11.8
11.9
12
12.1
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Rotational Phase (Period = 5.2248 hours)
V m
ag
nit
ud
e (
Ph
as
e A
ng
le =
0.3
4 d
eg
)
Richard MilesGolden Hill Obs.
280 mm SCT (clear)60 mm Refr. (V filter)60 mm Refr. (I filter)
130 Phase Curve
(130) Elektra - Phase Curve
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 2 4 6 8 10 12 14 16 18 20
Phase Angle, deg
Re
du
ce
d M
ag
nit
ud
e (
rel.
to
Ph
. An
gle
= 0
.34
d
eg
)
280 mm SCT (clear)60 mm Refr. (V filter)60 mm Refr. (I filter)
Richard MilesGolden Hill Obs.
Phase brightening
ACKNOWLEDGMENTS
• Stefano Mottola – AstPhot32 photometry software
• John Saxton – Lymm photometry software
• Norman Walker – Provision of V and I filters
Acknowledgments
THANKS FOR YOUR ATTENTION
End of talk