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