| Object | (1)/(2) | M11  |
Grt 
 |
B-V
|
V-R
|
R-I
|
I-J
|
J-H
|
H-K
|
| 2060 Chiron | Cent/27 | 6.398
0.049 |
0.642
1.629 |
0.679
0.039 |
0.359
0.027 |
0.356
0.037 |
0.472
0.132 |
0.290
0.082 |
0.064
0.099 |
| 5145 Pholus | Cent/36 | 7.158
0.097 |
52.054
2.105 |
1.299
0.099 |
0.794
0.032 |
0.814
0.056 |
1.040
0.051 |
0.375
0.046 |
-0.037
0.047 |
| 7066 Nessus | Cent/17 | -- | 45.727
2.567 |
1.090
0.040 |
0.793
0.041 |
0.695
0.066 |
0.790
0.122 |
0.309
0.268 |
-0.089
0.385 |
| 8405 Asbolus | Cent/34 | 8.966
0.057 |
15.075
2.981 |
0.750
0.040 |
0.513
0.068 |
0.523
0.045 |
0.690
0.056 |
0.315
0.142 |
0.095
0.253 |
| 10199 Chariklo | Cent/38 | 6.486
0.033 |
13.677
1.548 |
0.802
0.049 |
0.479
0.029 |
0.542
0.030 |
0.730
0.040 |
0.411
0.044 |
0.093
0.046 |
| 10370 Hylonome | Cent/7 | -- | 10.667
4.090 |
0.643
0.082 |
0.464
0.059 |
0.490
0.122 |
0.390
0.173 |
-- | -- |
| 2P/Encke | SPC/4 | -- | 3.770
3.070 |
-- | 0.388
0.062 |
0.408
0.060 |
-- | -- | -- |
| 6P/d'Arrest | SPC/2 | -- | 15.138
2.886 |
0.770
0.040 |
0.565
0.067 |
0.450
0.040 |
-- | -- | -- |
| 10P/Tempel 2 | SPC/2 | -- | -- | -- | 0.575
0.048 |
-- | -- | -- | -- |
| 22P/Kopff | SPC/1 | -- | -- | -- | 0.533
0.022 |
-- | -- | -- | -- |
| 28P/Neujmin 1 | SPC/6 | -- | 11.687
3.947 |
-- | 0.508
0.079 |
0.440
0.079 |
-- | -- | -- |
| 46P/Wirtanen | SPC/1 | -- | -- | -- | 0.355
0.073 |
-- | -- | -- | -- |
| 53P/VanBiesbroek | SPC/1 | -- | -- | -- | 0.328
0.081 |
-- | -- | -- | -- |
| 86P/Wild3 | SPC/1 | -- | -- | -- | 0.116
0.144 |
-- | -- | -- | -- |
| 87P/Bus | SPC/1 | -- | -- | -- | 0.543
0.020 |
-- | -- | -- | -- |
| 93K2P/Helin-Law. | SPC/1 | -- | -- | -- | 0.267
0.075 |
-- | -- | -- | -- |
| 96P/Machholz 1 | SPC/1 | -- | -- | -- | 0.429
0.027 |
-- | -- | -- | -- |
| 107P/Wilson-Harr. | SPC/2 | -- | -- | -- | 0.406
0.017 |
-- | -- | -- | -- |
| 143P/Kowal-Mrkos | SPC/2 | -- | 20.983
1.167 |
0.820
0.028 |
0.580
0.020 |
0.560
0.022 |
-- | -- | -- |
| 1992 QB1 | QB1/8 | 6.864
0.121 |
37.328
6.651 |
0.836
0.145 |
0.713
0.098 |
0.672
0.197 |
-- | -- | -- |
| 1993 FW | QB1/8 | 6.533
0.151 |
12.172
5.517 |
0.932
0.089 |
0.517
0.101 |
0.431
0.127 |
-- | -- | -- |
| 1993 RO | Plut/6 | 8.488
0.113 |
19.363
7.579 |
0.933
0.162 |
0.576
0.128 |
0.515
0.192 |
-- | -- | -- |
| 1993 SB | Plut/4 | 8.024
0.143 |
12.253
4.554 |
0.802
0.071 |
0.475
0.077 |
0.514
0.114 |
-- | -- | -- |
| 1993 SC | Plut/14 | 6.711
0.054 |
36.763
3.488 |
1.012
0.105 |
0.673
0.065 |
0.738
0.077 |
-- | 0.400
0.203 |
-0.040
0.197 |
| 1994 ES2 | QB1/2 | 7.525
0.115 |
80.403
7.434 |
0.710
0.150 |
0.940
0.150 |
0.970
0.150 |
-- | -- | -- |
| 1994 EV3 | QB1/4 | 7.108
0.089 |
27.511
7.555 |
1.500
0.150 |
0.516
0.124 |
0.840
0.199 |
-- | -- | -- |
| 1994 GV9 | QB1/1 | 6.815
0.091 |
-- | -- | 0.740
0.099 |
-- | -- | -- | -- |
| 1994 JQ1 | QB1/5 | 6.603
0.127 |
-- | -- | 0.945
0.097 |
-- | -- | -- | -- |
| 1994 JR1 | Plut/7 | 6.844
0.071 |
24.825
5.805 |
1.010
0.180 |
0.656
0.115 |
0.520
0.120 |
-- | -- | -- |
| 1994 JS | QB1/2 | 7.255
0.062 |
-- | -- | 0.850
0.070 |
-- | -- | -- | -- |
| 1994 JV | QB1/2 | 7.195
0.058 |
37.024
5.331 |
-- | 0.771
0.091 |
0.563
0.133 |
-- | -- | -- |
| 1994 TA | Cent/2 | 11.413
0.126 |
35.801
6.104 |
1.261
0.139 |
0.672
0.080 |
0.740
0.210 |
-- | -- | -- |
| 1994 TB | Plut/10 | 7.505
0.080 |
39.035
4.615 |
1.080
0.132 |
0.706
0.083 |
0.727
0.108 |
-- | -- | -- |
| 1994 VK8 | QB1/2 | 7.025
0.144 |
32.582
6.345 |
1.010
0.060 |
0.659
0.061 |
-- | -- | -- | -- |
| 1995 DA2 | QB1/7 | 7.964
0.118 |
17.189
7.292 |
1.310
0.270 |
0.547
0.131 |
0.515
0.172 |
-- | -- | -- |
| 1995 DB2 | QB1/2 | 8.112
0.085 |
-- | -- | -- | -- | -- | -- | -- |
| 1995 DC2 | QB1/6 | 6.848
0.148 |
36.530
7.927 |
-- | 0.770
0.160 |
0.580
0.160 |
-- | -- | -- |
| 1995 FB21 | QB1/4 | 7.017
0.099 |
-- | -- | -- | -- | -- | -- | -- |
| 1995 HM5 | Plut/7 | 7.881
0.111 |
6.761
4.993 |
0.649
0.102 |
0.463
0.096 |
0.370
0.108 |
-- | 1.200
0.470 |
-- |
| 1995 QY9 | Plut/6 | 7.487
0.126 |
10.588
4.022 |
0.696
0.121 |
0.520
0.093 |
0.400
0.060 |
-- | -- | -- |
| 1995 QZ9 | Plut/2 | 7.886
0.400 |
15.709
5.234 |
0.880
0.040 |
0.515
0.050 |
-- | -- | -- | -- |
| 1995 SM55 | QB1/3 | 4.333
0.053 |
1.269
2.875 |
0.645
0.034 |
0.394
0.052 |
0.310
0.066 |
-- | -- | -- |
| 1995 TL8 | Scat/1 | 4.585
0.056 |
33.942
3.051 |
1.045
0.072 |
0.695
0.051 |
0.641
0.076 |
-- | -- | -- |
| 1995 WY2 | QB1/3 | 6.861
0.110 |
21.766
9.753 |
1.004
0.206 |
0.648
0.190 |
0.458
0.208 |
-- | -- | -- |
| 1996 RQ20 | QB1/5 | 6.890
0.104 |
21.258
5.329 |
0.935
0.141 |
0.553
0.099 |
0.609
0.120 |
-- | -- | -- |
| 1996 RR20 | Plut/2 | 6.586
0.133 |
40.209
5.038 |
1.150
0.094 |
0.707
0.070 |
0.760
0.160 |
-- | -- | -- |
| 1996 SZ4 | Plut/2 | 8.181
0.159 |
19.062
4.832 |
0.783
0.124 |
0.531
0.062 |
0.620
0.170 |
-- | -- | -- |
| 1996 TC68 | QB1/1 | 6.734
0.073 |
-- | -- | 0.600
0.078 |
-- | -- | -- | -- |
| 1996 TK66 | QB1/2 | 6.281
0.074 |
27.932
3.716 |
1.002
0.060 |
0.640
0.050 |
0.590
0.120 |
-- | -- | -- |
| 1996 TL66 | Scat/10 | 5.227
0.133 |
3.355
3.011 |
0.694
0.056 |
0.334
0.052 |
0.428
0.079 |
-- | 0.350
0.117 |
-0.040
0.112 |
| 1996 TO66 | QB1/16 | 4.544
0.049 |
5.371
2.467 |
0.666
0.060 |
0.377
0.047 |
0.375
0.060 |
-- | -0.210
0.170 |
0.810
0.158 |
| 1996 TP66 | QB1/9 | 6.958
0.063 |
32.326
3.690 |
0.984
0.109 |
0.654
0.073 |
0.683
0.075 |
-- | 0.170
0.078 |
0.020
0.092 |
| 1996 TQ66 | Plut/6 | 7.137
0.078 |
35.809
4.398 |
1.186
0.118 |
0.655
0.081 |
0.750
0.100 |
-- | -- | -- |
| 1996 TS66 | QB1/9 | 5.986
0.112 |
28.922
5.214 |
1.010
0.082 |
0.635
0.110 |
0.645
0.097 |
-- | 0.650
0.071 |
-- |
| 1997 CQ29 | QB1/5 | 6.763
0.183 |
34.308
5.942 |
0.990
0.127 |
0.728
0.120 |
0.605
0.120 |
-- | -- | -- |
| 1997 CR29 | QB1/2 | 7.076
0.135 |
20.636
8.257 |
0.750
0.152 |
0.538
0.157 |
0.620
0.182 |
-- | -- | -- |
| 1997 CS29 | QB1/10 | 5.065
0.085 |
28.988
2.815 |
1.049
0.082 |
0.667
0.053 |
0.592
0.061 |
-- | 0.300
0.156 |
-0.100
0.233 |
| 1997 CT29 | QB1/2 | 6.498
0.230 |
-- | -- | 0.744
0.090 |
-- | -- | -- | -- |
| 1997 CU29 | QB1/4 | 6.206
0.108 |
28.730
3.680 |
1.157
0.145 |
0.634
0.058 |
0.638
0.098 |
-- | -- | -- |
| 1997 GA45 | QB1/1 | 7.744
0.500 |
-- | -- | -- | -- | -- | -- | -- |
| 1997 QH4 | QB1/3 | 6.983
0.133 |
28.694
6.173 |
1.039
0.131 |
0.628
0.103 |
0.649
0.159 |
-- | -- | -- |
| 1997 QJ4 | Plut/3 | 7.424
0.124 |
9.307
6.115 |
0.700
0.120 |
0.511
0.119 |
0.362
0.130 |
-- | -- | -- |
| 1997 RL13 | QB1/1 | 9.361
0.300 |
-- | -- | -- | -- | -- | -- | -- |
| 1997 RT5 | QB1/1 | 6.736
0.030 |
-- | -- | -- | -- | -- | -- | -- |
| 1997 RX9 | QB1/1 | 7.800
0.100 |
-- | -- | -- | -- | -- | -- | -- |
| 1997 SZ10 | QB1/1 | 8.145
0.060 |
31.431
3.246 |
1.140
0.080 |
0.650
0.030 |
-- | -- | -- | -- |
| 1998 BU48 | Cent/1 | 7.033
0.057 |
26.985
3.102 |
1.105
0.074 |
0.648
0.052 |
0.570
0.078 |
-- | -- | -- |
| 1998 FS144 | QB1/1 | -- | 20.767
6.964 |
0.910
0.076 |
0.560
0.067 |
-- | -- | -- | -- |
| 1998 HK151 | Plut/3 | 6.879
0.039 |
8.017
3.404 |
0.510
0.090 |
0.469
0.065 |
0.398
0.073 |
-- | -- | -- |
| 1998 KG62 | QB1/2 | 6.065
0.078 |
23.450
3.122 |
1.000
0.060 |
0.561
0.074 |
0.640
0.040 |
-- | -- | -- |
| 1998 QM107 | Cent/1 | 10.226
0.060 |
16.299
3.246 |
0.730
0.060 |
0.520
0.030 |
-- | -- | -- | -- |
| 1998 SG35 | Cent/2 | 10.828
0.023 |
12.259
2.768 |
0.725
0.089 |
0.456
0.050 |
0.546
0.063 |
-- | -- | -- |
| 1998 SM165 | QB1/2 | 5.799
0.190 |
33.103
3.836 |
0.966
0.091 |
0.687
0.079 |
0.648
0.073 |
-- | -- | -- |
| 1998 SN165 | QB1/4 | 5.736
0.410 |
7.311
4.410 |
0.712
0.095 |
0.446
0.089 |
0.419
0.088 |
-- | -- | -- |
| 1998 TF35 | Cent/2 | 8.683
0.193 |
34.880
4.193 |
1.085
0.111 |
0.697
0.064 |
0.651
0.119 |
-- | -- | -- |
| 1998 UR43 | Plut/3 | 8.090
0.130 |
9.494
5.465 |
0.784
0.101 |
0.565
0.106 |
0.268
0.117 |
-- | -- | -- |
| 1998 VG44 | Plut/2 | 6.349
0.057 |
24.105
3.881 |
0.951
0.055 |
0.567
0.056 |
0.668
0.116 |
-- | -- | -- |
| 1998 WH24 | QB1/7 | 4.512
0.108 |
23.435
3.338 |
0.924
0.063 |
0.602
0.043 |
0.547
0.111 |
-- | -- | -- |
| 1998 WV24 | Plut/1 | 7.112
0.040 |
14.117
3.243 |
0.770
0.010 |
0.500
0.030 |
-- | -- | -- | -- |
| 1998 WV31 | Plut/1 | 7.643
0.070 |
10.197
4.283 |
0.834
0.089 |
0.513
0.069 |
0.357
0.114 |
-- | -- | -- |
| 1998 WX24 | QB1/1 | 6.232
0.090 |
37.747
5.234 |
1.090
0.050 |
0.700
0.050 |
-- | -- | -- | -- |
| 1998 WX31 | QB1/1 | 6.225
0.075 |
26.201
4.606 |
-- | 0.602
0.080 |
0.640
0.112 |
-- | -- | -- |
| 1998 XY95 | Scat/1 | 6.492
0.167 |
36.230
7.184 |
0.939
0.238 |
0.645
0.140 |
0.772
0.153 |
-- | -- | -- |
| 1999 CC158 | Scat/1 | 5.430
0.074 |
20.293
3.657 |
0.962
0.098 |
0.571
0.063 |
0.552
0.088 |
-- | -- | -- |
| 1999 CD158 | QB1/1 | 4.903
0.066 |
13.430
3.734 |
0.871
0.077 |
0.477
0.065 |
0.543
0.089 |
-- | -- | -- |
| 1999 CF119 | Scat/1 | 7.031
0.077 |
13.450
4.603 |
-- | 0.557
0.083 |
0.391
0.107 |
-- | -- | -- |
| 1999 DE9 | Scat/2 | 4.804
0.056 |
20.506
2.281 |
0.915
0.058 |
0.572
0.042 |
0.559
0.049 |
-- | -- | -- |
| 1999 HB12 | Scat/1 | -- | 8.150
3.096 |
0.870
0.060 |
0.500
0.050 |
0.320
0.080 |
-- | -- | -- |
| 1999 HR11 | QB1/1 | -- | 29.372
4.428 |
0.920
0.120 |
0.530
0.100 |
0.800
0.070 |
-- | -- | -- |
| 1999 HS11 | QB1/1 | -- | 30.142
4.784 |
1.010
0.160 |
0.680
0.100 |
0.600
0.090 |
-- | -- | -- |
| 1999 KR16 | QB1/1 | 5.505
0.020 |
44.581
1.577 |
1.100
0.050 |
0.740
0.030 |
0.770
0.030 |
-- | -- | -- |
| 1999 OX3 | Cent/3 | 7.272
0.196 |
28.215
3.746 |
1.072
0.117 |
0.692
0.055 |
0.475
0.109 |
-- | -- | -- |
| 1999 OY3 | QB1/1 | 6.303
0.040 |
0.952
2.294 |
0.710
0.010 |
0.370
0.020 |
-- | -- | -- | -- |
| 1999 RY215 | QB1/1 | -- | -- | 0.800
0.100 |
-- | 0.780
0.080 |
-- | -- | -- |
| 1999 RZ253 | QB1/2 | 5.428
0.056 |
29.962
3.002 |
0.820
0.170 |
0.646
0.058 |
0.647
0.062 |
-- | -- | -- |
| 1999 TC36 | Plut/5 | 4.920
0.070 |
32.331
2.382 |
1.008
0.050 |
0.687
0.041 |
0.625
0.056 |
-- | -- | -- |
| 1999 TD10 | Scat/2 | 8.706
0.022 |
11.893
1.908 |
0.770
0.050 |
0.495
0.040 |
0.470
0.032 |
-- | -- | -- |
| 1999 TR11 | Plut/1 | 8.058
0.140 |
44.369
7.259 |
1.020
0.080 |
0.750
0.070 |
-- | -- | -- | -- |
| 1999 UG5 | Cent/5 | 10.483
0.134 |
25.886
2.677 |
0.964
0.085 |
0.607
0.060 |
0.625
0.042 |
-- | -- | -- |
| 2000 EB173 | Plut/17 | 4.657
0.110 |
22.884
3.969 |
0.954
0.050 |
0.565
0.090 |
0.623
0.061 |
-- | -- | -- |
| 2000 OK67 | QB1/2 | 6.138
0.063 |
15.972
7.056 |
0.727
0.108 |
0.517
0.068 |
-- | -- | -- | -- |
| 2000 PE30 | Scat/1 | -- | 4.713
2.049 |
0.710
0.050 |
0.380
0.040 |
0.450
0.040 |
-- | -- | -- |
| 2000 QC243 | Cent/1 | 7.949
0.049 |
6.961
2.724 |
0.724
0.062 |
0.448
0.044 |
0.397
0.069 |
-- | -- | -- |
| 2000 WR106 | QB1/1 | 3.048
0.059 |
39.611
3.536 |
1.017
0.071 |
0.711
0.071 |
0.730
0.071 |
-- | -- | -- |
(1) Class: QB1 = Cubewano, Plut = Plutino,
Cent = Centaur, SPC = Short Period
Comet, LPC = Long Period Comet.
(2) Number of epochs. Grt is the spectral
gradient 
(%/100 nm).
M11 is the
absolute R magnitude.
In order to get the most significant results, the statistical analysis presented in this paper were based on a complete compilation of all the TNO and Centaur colors that have been reported in the "Distant EKO'' web page (Parker 2001), as of 2001. Several additional papers, preprint and private communications about TNOs and Comets were also added. We realize that such a compilation can never be complete and up-to-date; the current database is frozen in its current state, and we plan to add new and missing papers in future versions. Refer to Appendix A for the references that were used for each object. Authors are encouraged to send us their measurements electronically (ohainaut@eso.org), so that we can include them in this database.
When available, the individual magnitudes were used, so that
non-standard color indexes (i.e. not the traditional B-V, V-R...)
can be computed (we hereby encourage the authors to publish these
individual magnitudes). Where the magnitudes were not available, we
used the published color indexes. In this compilation, no correction
has been made for the different photometric systems used. Only the name
of the filter is taken into account, so that
,
K=K'=Ks, etc. We assume that the errors introduced by these
assumptions are small compared to the measurement errors. As all the
TNO measurements were obtained after 1992, a large fraction of them
were calibrated using the standard stars by Landolt (1992). If the
authors computed the color term of their system and applied them, the
magnitude they published are de facto in the Bessel system as
described by Landolt, further reducing possible color discrepancies
between the different filter system used.
For a given epoch (loosely defined as "within a few hours''), we computed all the possible colors and magnitudes based on the available colors and magnitudes. It is important to note that no additional color indexes were computed at that stage (i.e. if V is available at one epoch, and R at another, the V-R index is not computed mixing these epochs). Some publications list colors obtained by combining magnitudes obtained at different epochs. These were not entered in the database. We also checked for and removed multiple entries for the same measurements that appeared in different papers.
The magnitudes and colors from different epochs (and different authors) were combined in order to obtain one average magnitude and color set per object. However, no new color indexes are computed even if we now have enough data (e.g. if an author reported a R-I and another I-J, we do not compute nor use the resulting R-J), as these would not be obtained from simultaneous data. In this way, even if the object presents some intrinsic magnitude variability, we do not introduce any additional color artifacts. The average magnitude that we publish here corresponds to the average of the (possibly varying) magnitudes, and the average colors is the average of the measured colors. The variations of magnitude will not contribute to the color error.
For this combination, 
,
the average magnitude or color is
obtained by weighted average of the individual magnitudes and
colors. We did not a priori reject any published measurement, nor
give a stronger or lighter weight to the measurements from a given
author or team. We did not give a larger weight to measurements
obtained on a larger telescope. For this study, we fully trust and
rely on the published error bars: the weight of a measurement is set
to 
:
)
will be given a strong weight compared to approximate
values. In case of multiple measurements
xi, i=1... N of an item
(magnitude or color), the error
is computed as a combination
of the individual errors 
and of the dispersion of the
measurements around their mean ,
using
level taking into account the sum of the considered error bars). The
current database did not trigger this warning.
The classical color indexes are reported in Table 1. In this table, the un-named objects are identified by their temporary MPC designation (e.g. 1992 QB1), while the named objects are identified with their number and name. For uniformity, we don't use the number of numbered but still un-named object. In the case of the numbered comets, their IAU designation is used.
The table also lists the number of independent epochs that were combined for each object.
For each epoch, we attempted to compute an absolute R magnitude: for
this purpose, we used either the measured R magnitude, when
available, or another magnitude and the corresponding color index with
R. The helio- and geo-centric distances (r and 
,
resp., [AU])
were computed using a two-body ephemerides program with the orbital
elements available at MPC, and the absolute magnitude M(1,1) was
computed using
is the R magnitude of the Sun and M(1,1) is the
absolute R magnitude from Eq. (3). As the albedo p is not
known (except for a couple of objects), and in particular because
neutral-grey objects could either correspond to extremely old surfaces
(with p as low as 0.02, Thompson et al. 1987) or to objects covered
with fresh ice (therefore having a higher albedo, possibly as high as
that of Pluto, 0.3, or Chiron, 0.1), we do not give a generic
conversion of M(1,1) into a radius.
The information contained in the color indexes can be converted into a
very low resolution reflectivity spectrum
(Jewitt & Meech 1986), using
are the magnitude of the object and of the Sun
at the considered wavelength. Normalizing the reflectivity to 1 at a
given wavelength (in our case, the V central wavelength), we have
Boehnhardt et al. (2001) have compared such magnitude-based reflectivity
spectra with real spectra (i.e. obtained with a spectrograph) for
10 objects observed quasi-simultaneously with a large telescope
(one of ESO's 8 m VLTs) through broad-band filters and with a low
resolution spectrograph. He found a excellent agreement between real
and magnitude-based spectra.
| Color | Value |
| U-B | 0.204 |
| U-V | 0.845 |
| V-R | 0.36 |
| V-I | 0.69 |
| V-K | 1.486 |
| J-H | 0.23 |
| H-K | 0.06 |
We can introduce a description of the reflectivity spectrum: the
reddening ,
also called slope parameter or spectral index, which is
expressed in percent of reddening per 100 nm:
,
describing the spectrum over the V-R-I range. We obtained the value
of ,
together with its uncertainty, by linear regression of
as given in Eq. (6). We restricted this fit to the
objects having at least two color indexes measured. The values of
and its error are listed in
Table 3.
We
also restricted the fit to the V, R and I filters, excluding
B, because the B reflectivity shows a systematic trend, as
described below. The error on
is a combination of the error
on each
(obtained by propagation of the errors on
the colors) and on the linear regression. In order to further
characterize the shape of the spectrum, we introduced d, the total
deviation of the reflectivity with respect to the linear regression:
is the reflectivity expected from the linear
fit. Positive values of d correspond to spectra with a global
concavity, while negative values correspond to a convexity. The
concavity d can be interpreted in two ways: either i) one
considers that the result published by Boehnhardt et al. (2001) can be
generalized to all MBOSSes; in that case, objects with a large |d|suffer from large uncertainties and should be re-measured with a
better S/N, or ii) it is considered as real, and large values of
|d| denote objects whose spectral characteristic are intrinsically
different and worth a more detailed study. In both cases, observers
should take a closer look at the objects identified by a large
deviation |d| in Table 3. These objects are
(7066) Nessus, 1991 QB1, 1993 SC, 1994 ES2, 1994 TB,
1996 RR20 and 1999 KR16.
![\begin{figure}
\par\mbox{\includegraphics[width=6.8cm,clip]{hainaut_fig2a_tno_B-...
...includegraphics[width=6.8cm,clip]{hainaut_fig2f_tno_J-H_H-K.eps} }\end{figure}](/articles/aa/full/2002/26/aa1991/img39.gif) |
Figure 2: MBOSS color-color diagrams. The meaning of the different symbols is given in Fig. 4. The reddening line ranges gradients from -10 to 70%/100 nm; a tick mark is placed every 10 units. The outliers objects in the B-V, R-I are 1994 ES2 (top left), 1994 EV3(top right), 1998 HK151 (bottom left), and 1995 DA2 (middle right). All other combinations of colors are available on the MBOSS web site. |
![\begin{figure}
\par\includegraphics[width=7.8cm,clip]{hainaut_fig3a_tnoOrbit_B-V...
...cm}
\includegraphics[width=7.8cm,clip]{hainaut_fig3f_tnoGrad.eps}
\end{figure}](/articles/aa/full/2002/26/aa1991/img40.gif) |
Figure 3:
Visible color distributions as
functions of the absolute magnitude M(1,1), the orbit semi-major
axis a [AU], the eccentricity e, the inclination i and the
orbit excitation 
(see text for definition). The meaning
of the different symbols is given in Fig. 4. Other
colors are available electronically and on line at the MBOSS web
site. |
It is interesting to note that the coordinates
of an
object are very similar to the "principal components'' (PC1,PC2) that
Barucci et al. (2001) have obtained from an analysis of the colors of 22
objects: the position of a MBOSS in a multi-dimensional color diagram
is determined primarily by PC1 (which can physically be associated to
)
and to a much lesser extent by PC2 (which would be related
to d). The additional dimension of the multi-dimensional color diagram
contain little information. We intent to apply a similar analysis to
this dataset.
Figure 2 shows a selection of color-color diagrams; the
whole collection, for all possible color indexes, is available on the
MBOSS web site. To guide the eye, the reddening line is drawn on each
diagram. This line is constructed computing the colors for an object
of a given reddening
using Eq. (7), and then
connecting all the points for
70%/100 nm (a tick is
placed every 10%). An object located directly on this line has a
perfectly linear reflectivity spectrum, and its slope
can be
estimated using the tick-marks on the line. Objects above the line
have a concave spectrum (positive d), while objects below the line
have a convex spectrum (negative d) over the spectral
range considered.
As it was noted in Sect. 1.2, the three physical processes that are suspected to effect the color of a MBOSS surface independently produce linear reflectivity spectra (in first approximation, over the visible wavelength range). The average over the complete surface of an object will therefore also be a linear spectrum. Within that hypothesis, if no other physical processes plays an important role, and if the MBOSSes have the same original intrinsic composition, the objects should all lie on the reddening line. A young-surfaced object would have solar-like colors, and the aging will move the object up the reddening line, while collision and activity will move it back down. Similarly, an object left undisturbed long enough would evolve moving up the reddening line till it reaches the maximum possible reddening, then, the continued irradiation of its surface would cause it to further darken (Thompson et al. 1987), possibly moving back down on the reddening line. In that case, one could expect to find among the neutral objects some MBOSSes covered with fresh ice, together with objects with ancient ice, with a very dark albedo. This is tested later (cf. Sect. 3.4).
The diagrams from Fig. 2 are in agreement with this simple interpretation of the reddening line: the MBOSSes are clustered along that line. For the (B-V) and (V-R) colors, the deviations from the line are compatible with the error bars of the individual points, indicating that the spectra are linear over this wavelength range. The plots involving the (R-I) color, however, show a systematic deviation from the line for the reddest objects (particularly visible in the (B-R) vs. (R-I) diagram). This corresponds to the fact that the spectrum of the reddest objects flattens toward the IR, where it is typically flat/neutral (Davies 2000; McBride et al. 1999). One also notes a systematic deviation from the reddening line of the neutral to neutral-red points in the B-V vs. V-R diagram: the bulk of these points are significantly above the line; this corresponds to the bend observed around the B wavelength in many reflection spectra from Fig. 1. This bend is not observed in the "fresh ice'' laboratory spectra published by Thompson et al. (1987), suggesting that in spite of their low reddening, the surface of these objects could be significantly processed.
It is also interesting to note a small group of 5 objects clustered
very near the solar colors in the
diagram, i.e. in
the range corresponding to fresh ice surface. Two of these objects are
either known or suspected to be cometary active, i.e. (2060) Chiron
(Tholen et al. 1988; Meech & Belton 1989) and 1996 TO66 (Hainaut et al. 2000). A
detailed study of the others (1995 SM55, 1996 TL66 and
1999 OY3) is well deserved.
In addition to the simple "reddening line'', it would be interesting to produce an evolution track of the color of laboratory ices, for increasing irradiation doses. Such work will be presented in another paper by the same authors.
The diagrams show notable outliers (i.e. isolated points, far from the reddening line and the general cluster of objects):
Copyright ESO 2002
![\begin{figure}
\par\includegraphics[width=8.8cm,clip]{hainaut_fig1_tnoGradSpecExample.eps}
\end{figure}](/articles/aa/full/2002/26/aa1991/img34.gif)
