Issue |
A&A
Volume 378, Number 2, November I 2001
|
|
---|---|---|
Page(s) | 653 - 667 | |
Section | Celestial mechanics and astrometry | |
DOI | https://doi.org/10.1051/0004-6361:20011212 | |
Published online | 15 November 2001 |
Visible and near-IR observations of transneptunian objects *
Results from ESO and Calar Alto Telescopes
1
European Southern Observatory ESO, Alonso de Cordova 3107, Santiago de Chile, Chile e-mail: ohainaut@eso.org; tsekiguc@eso.org; mvair@eso.org
2
Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 50125 Firenze, Italy e-mail: tozzi@arcetri.astro.it
3
Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: birkle@mpia-hd.mpg.de
4
National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588, Japan e-mail: watanabe@nao.jp.ac
5
European Southern Observatory ESO, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany e-mail: grupprec@eso.org
6
Landessternwarte Heidelberg, Königstuhl, 69117 Heidelberg, Germany e-mail: iappenze@lsw.uni-heidelberg.de (FORS Principle Investigator)
7
Universitäts-Sternwarte Göttingen, Geismarlandstr. 11, 81679 Göttingen, Germany
8
Universitäts-Sternwarte München, Scheinerstr. 1, 81679 München, Germany
Corresponding author: H. Boehnhardt, hboehnha@eso.org
Received:
10
January
2001
Accepted:
21
August
2001
We present visible (BVRI) and near-IR (JHKs) broadband photometry and visible
low-dispersion spectroscopy of Transneptunian Objects (TNOs) and Centaurs. In total,
16 TNOs and 1 Centaur were observed over the past two years at ESO
telescopes in La Silla and Paranal in Chile as well as at the Calar Alto
Observatory in Spain. The sample consists of objects measured for the first
time and those for which comparison data is available from literature. The
targets were: 1992QB1, 1993RO, 1994EV3, 1995HM5, 1995SM55, 1996RQ20, 1996TL66,
1996TO66, 1996TP66, 1997CQ29, 1997CS29, 1998HK151, 1998TF35, 1998VG44, 1998WH24,
1998XY95, 1999TC36.
The spectra of 5 TNOs (1995SM55, 1996TO66, 1997CQ29, 1997CS29, 1998HK151) show
almost constant gradients over the visible wavelength range with only marginal
indication for a flatter slope beyond 750-800 nm. The photometric colour
gradients obtained quasi-simultaneously are in good agreement with the spectral
data. This suggests that in general photometric colour gradients are a valuable
diagnostic tool for spectral type classification of TNOs.
The photometric study revealed a number of new objects with neutral and red
colours. For re-measured objects the published broadband colours were -in
general -confirmed, although a few remarkable exceptions exist. Two TNOs appear
to be outlyers according to the available broadband colours: 1993EV3 and
1995HM5. 1995SM55 is the bluest TNO measured so far.
No clear global correlation between colour and absolute R filter brightness
of our TNO targets is found. However, the data for the 5 brightest TNOs
(brighter than 5 mag absolute magnitude) could also be interpreted with
a linear increase of
colour by about 0.75 mag per brightness magnitude.
The colour-colour diagrams show continuous reddening of the TNOs in
vs.
,
vs.
and
vs.
. The bimodality suggested from earlier measurements
of Tegler & Romanishin ([CITE]) is not confirmed. According to our colour
gradient statistics (number of objects per gradient interval) most of the TNOs
have surface reddening between 0 and 40% /100 nm. For the Cubewanos the
major population falls between 20-40% /100 nm.
The Plutinos and Centaurs show a bifold grouping, i.e. a neutral/slightly
reddish group (reddening <20% /100 nm) and a red group (reddening 30-40% /100 nm). The
statistical significance of the various populations found
is suffering -for the Centaurs and scattered disk objects very severely -
from the small number
of objects measured. However, the diversity of the reddening distribution of
Centaurs/Plutinos and Cubewanos, if confirmed by new observations, may indicate a different
balancing of resurfacing processes for these object types: for instance, for Centaurs
a possibility is that re-condensed frost from coma activity may be dominant over impact
re-surfacing and
high energy surface processing.
Key words: minor planets, asteroids / solar system: general / Kuiper Belt
© ESO, 2001
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