The binary Kuiper Belt Object 1998 WW31 - Chapter 1

1998 WW31 is a double TNO!...

C. Veillet - CFHT
2001 April 14
 
 
Back to the 1998WW31 story

 
Recovery Detection of the possible pair Processed image Raw images Image quality check Astrometry
Archive Processed image Raw images Astrometry

IAUC 7610

S/2000 (1998 WW_31) 1
     C. Veillet, Canada-France-Hawaii Telescope (CFHT), reports:
"Recovery images of the transneptunian object (TNO) 1998 WW_31
(see MPEC 2001-G29) taken by C. Veillet, A. Doressoundiram, and J.
Shapiro with the 3.6-m CFHT show that two objects were within <
1".3 and moving together over the two nights of observations (2000
Dec. 22 and 23 UT) without any detectable relative motion.  CFHT
public archive observations of the same field taken nearly a year
previously by J. J. Kavelaars and A. Morbidelli show 1998 WW_31 as
double or elongated on four images, with the two components at a
different distance and position angle than on the discovery images.
A very preliminary reduction shows the brighter component to be 0.4
mag brighter than the secondary in R on 2000 Dec. 22, with the
secondary being 1".2 from the primary in p.a. 45 deg (with seeing
0".7-1".1).  The archival images taken on 2000 Jan. 7.3 show the
secondary to be 0".8 from the primary in p.a. 25 deg.  Images taken
on 2000 Jan. 6 show the same elongation, but the pair is embedded
in a bright star halo, making any measurement difficult.  The
maximum distance between the two components is thus at least 40 000
km.  This indicates that 1998 WW_31 is the second TNO to have a
satellite (after Pluto).  The analysis of other images from the
CFHT, from Kitt Peak (1998 Nov. 18, 1999 Jan. 14, 2000 Nov. 23),
and from the Nordic Optical Telescope (1998 Dec. 18) may allow a
full orbit determination, leading to physical parameters of the
pair.  Images and details on the data are available at
http://cfht.hawaii.edu/~veillet/WW31.html."

Reprinted by authorization of the CBAT


WW31 appears double or elongated on the three recovery images
 

The TNO has moved by around 48" between images 1 and 2, and 5" between images 2 and 3.

Processed images (CFH12K images)
 
Recovery images 
(2000 Dec. 22/23)
Archive data
(2000 Jan. 6)
Separation: 1.2" 
Position angle: +45 deg.
one 8mn and two 10 mn exposures 
Separation: 0.8" 
Position angle: +25 deg.
two 8mn exposures 


Interpretation

With the recovery data only:

- Two TNO's could be on different orbits, with apparent motions close enough to be indistinguishable over one day, and be 1.2" apart on these two nights. Unlikely, but there are even less probable coincidences happening!

- 1998 WW31 could be a double TNO (like Pluto-Charon). The distance between the two components would then be ~40,000 km (if at elongation).

Using the archive data...

- 1998 WW31 is definitely elongated (and even seen double on an image). Position angle and estimated distance between the two components have changed... 1998 WW31 is a double asteroid!


Raw images - recovery data (00BF52)
 
Image 1     2000 12 22.41014 
Image 2     2000 12 23.34323 
Image 3     2000 12 23.43105 

On I1, the TNO is clearly seen as two objects.
On the following night, the image is still seen as double on 2, and elongated on 3.
No apparent change in position angle in one day (data not good enough to detect a significant one).


Raw images - CFHT public archive data

2000 01 07.3
 
The pair is seen on this sequence of four 8 mn exposures 
over 1.2 hr

2000 01 06.3

On the three images of that night, 1998 WW31 is embedded in the halo of a very bright star.
More processing will be needed to extract quantitative measurements. However, the TNO
is elongated in a similar way as on the following night.
 
WW31 is seen only by going far into the halo of the star...
It is however clearly elongated like on the next night.

 


Image quality check (recovery data)

1/ fwhm of a sample of stars around

Image 1 - fwhm = 0.70"
Image 2 - fwhm = 1.10"
Image 3 - fwhm = 0.94"


2/ Contour maps of a nearby star (for possible telescope tracking and oscillation problems)
 


Recovery positions

     J98W31W  C2000 12 22.41014 03 28 34.73 +19 07 25.6                      568
     J98W31W  C2000 12 23.34323 03 28 31.48 +19 07 12.3                      568
     J98W31W  C2000 12 23.43105 03 28 31.14 +19 07 11.1                      568


Archive positions

     J98W31W  C2000 01 06.33309 03 23 09.10 +18 55 31.9                      568
     J98W31W  C2000 01 07.27523 03 23 06.76 +18 55 22.0                      568
     J98W31W  C2000 01 07.29704 03 23 06.70 +18 55 21.7                      568
     J98W31W  C2000 01 07.30363 03 23 06.69 +18 55 21.5                      568
     J98W31W  C2000 01 07.32440 03 23 06.63 +18 55 21.2                      568


Past observations

Observations:
     J98W31W* C1998 11 18.21509 03 21 32.64 +18 59 07.3          22.6 R      695
     J98W31W  C1998 11 18.37940 03 21 31.90 +18 59 04.6                      695
     J98W31W  C1998 11 18.45365 03 21 31.53 +18 59 03.2                      695
     J98W31W  C1998 12 18.06375 03 19 25.75 +18 50 26.5          23.4 R      950
     J98W31W  C1998 12 18.10505 03 19 25.63 +18 50 25.4                      950
     J98W31W  C1998 12 18.14633 03 19 25.49 +18 50 24.1                      950
     J98W31W  C1999 01 14.13690 03 18 10.23 +18 44 50.3          23.3 R      695
     J98W31W  C1999 01 14.25171 03 18 10.01 +18 44 49.2                      695

Observer details:
695 Kitt Peak.  Observers R. L. Millis, M. W. Buie, R. M. Wagner, J. L.
    Elliot, D. W. Willmarth, P. S. Smith, D. L. Harmer, A. Saha.  Measurers
    M. W. Buie, R. L. Millis, J. L. Elliot.  4-m reflector + CCD, 3.6-m
    WIYN Telescope + CCD.
950 La Palma.  Observers M. J. Holman, T. Grav.  2.6-m Nordic Optical
    Telescope + CCD.

MPEC here...