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Photometry of Transneptunian Objects for the HerschelKey Program ‘TNOs are Cool’
H. Boehnhardt • D. Schulz • S. Protopapa • C. Gotz
Received: 4 March 2014 / Accepted: 18 September 2014� Springer Science+Business Media Dordrecht 2014
Abstract Photometric measurements of 33 transneptunian objects (TNOs) and Centaurs
from the target list of the Herschel Key program ‘TNOs are cool’ are presented. Broadband
filter observations of 5 Plutinos, 14 classical disk objects (CDOs), 5 scattered disk
objects (SDOs), 5 detached disk objects (DDOs) and 4 Centaurs are used to determine
absolute magnitudes, broadband colours and spectral gradients in the visible wavelength
range. The diameters of the objects estimated with assumed average albedo values fall in the
typical range for the various dynamical populations. Deviations between our and published
measurements of the photometric brightnesses for three objects indicate larger lightcurve
amplitudes (0.4–0.8 mag) due to non-spherical shape and/or albedo. A statistical analysis of
photometric population properties using our data and those of the MBOSS2 database by
Hainaut et al. (A&A 546:A115, 2012) supports the results and conclusion of this group of
authors, namely it shows that dynamically cold CDOs are disjunct for their visible colours
from the other TNO populations and Centaurs. Six objects (2002 GV31, 2003 AZ84, 2003
MW12, 2003 OP32, 2003 UZ117, 2005 RM43) with neutral to bluish spectral gradients were
found, of which 2002 GV31 shows the smallest spectral slope among the dynamically cold
CDOs known so far. Three very red objects (2002 KY14, 2004 GV9, 2007 OR10) with
This article is based on observations obtained at the La Silla-Paranal observatory of the European SouthernObservatory ESO through programs 083.A-9032(A) and 085.A-9008(A) in Max-Planck-Society time as wellas through progams 086.C-0738(A) in ESO open time.
H. Boehnhardt (&) � D. SchulzMax-Planck-Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Gottingen,Germanye-mail: [email protected]
S. ProtopapaDepartment of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
C. GotzInstitute for Geophysics and Extraterrestrial Physics, Technical University, Mendelssohnstr. 3,38106 Braunschweig, Germany
123
Earth Moon PlanetsDOI 10.1007/s11038-014-9450-x
spectral gradients above 40 %/100 nm were found of which 2007 OR10 is by far the reddest
DDO measured so far.
Keywords Kuiper belt � Transneptunian objects � Centaurs �Bessell BVRI filter photometry � Spectral gradients
1 Introduction
Transneptunian objects (TNOs) are considered among the most primordial objects
accessible to Earth-based observations. They may represent the population of planetesi-
mals left behind from the formation period of the solar system and should contain widely
unmodified material from the origin of the planetary system. They are building stones that
may have created the atmospheres of the gas giants and they are an important source for
Jupiter family comets.
The several dynamical populations in the Transneptunian region (Gladman et al. 2008)
could be the result of gravitational scattering and migration processes during the early
phase of the planetary system (Morbidelli et al. 2008; Kenyon et al. 2008). The formation
and evolution history of the outer planetary system may also be reflected in the physical
and chemical constitution of TNOs, e.g., in sizes, albedos, and compositions. Composition
information of TNOs is obtained through spectral and photometric measurements of the
radiation scattered by these targets, while size and albedo estimations usually require
information not only on the reflected but also emitted light of these bodies. Both
approaches require the assessment of results from a larger sample of TNOs in order to
synthesize population properties. Photometric and spectroscopic results of TNOs are
available since two decades, however, still with insufficient coverage of the various
dynamical populations and moderate to small sample sizes for statistical significance. Size
and albedo estimations are even less abundant. In order to overcome this situation, a
Herschel Key program (Muller et al. 2009), was initiated with the aim to determine sizes,
albedo and thermal properties of about 130 TNOs and Centaurs and analyze links between
physical, chemical and dynamical properties of these objects in order to further understand
their formation and evolution history. It was soon realized that complementary photo-
metric—and spectroscopic—information of the program targets is required in order to
perform the analysis of the Herschel measurements and to put the results in a global
context. The observations and results described below are part of the complementary
ground-based support for the Herschel Key program and at the same time serve as inde-
pendent information for the analysis of individual objects and population properties in the
visible light.
TNOs from the target list of the Herschel Key Program ‘TNOs are Cool’ (Muller et al.
2009) were observed in order to provide photometric information on the objects in the
visible wavelength range and to improve the orbit information around the time of the
Herschel measurements. The TNOs’ visible photometry is used to determine the absolute
magnitude of the selected targets, which can be applied together with Herschel measure-
ments for estimations of their size and albedo. It also provides complementary physical
information of the objects, e.g., their global reflectance and intrinsic surface colours (Sect.
5) and integrates in the statistical characterization of the various populations of minor
bodies in the outer solar system (Sect. 6).
H. Boehnhardt et al.
123
2 Observations
The selection criteria for the targets of the ground-based imaging observations were: (1) the
TNO is in the target list of the Herschel Key Program ‘TNOs are Cool’, meaning it was
already measured or was meant to be measured by the space observatory and (2) the
photometric information of the target, like absolute magnitudes and/or colours and spectral
information in the visible wavelength range, is missing. This way, the obtained results could
also complement the MBOSS2 database (Hainaut et al. 2012) and thus be used for the
characterization of photometric properties of the TNO populations. In addition, targets for
which the predicted uncertainty of the ephemeris was critical for the Herschel observations
received high priority for implementation. In total 36 TNOs were included in the target list
of our observations of which 35 objects were actually pointed by Herschel. The remaining
TNO (2001 CZ31) was included in our target list for observations since by the time of the
imaging photometry it was still to be observed by Herschel, but at the end it was removed
from the Herschel target list. The objects selected belong to the dynamical groups of
Centaurs, Plutinos, classical disk objects (CDOs), scattered disk objects (SDOs) and
detached disk objects (DDOs). The classical disk objects are furthermore distinguished in
two groups, i.e. the dynamically cold ones with inclinations below 5 deg and the dynam-
ically hot ones with inclinations above 5�. This criterion addresses a possible different
formation region for both groups as suggested by dynamical models for the early planetary
system (see Morbidelli et al. 2008 and references therein) as well as by the diversity of other
physical properties (see Doressoundiram et al. 2008 and references therein).
The observations were performed at the La Silla-Paranal observatory operated by the
European Southern Observatory ESO during October 2009 to August 2011. Two telescope-
instrument combinations were used, i.e., the 2.2m MPG/ESO telescope plus the WFI
instrument at La Silla and the 8.2 m VLT Unit Telescope 1 Antu plus the FORS2 instrument
at Paranal. WFI is a wide field imager with a half-degree field of view with CCD pixel size of
0.238 arcsec. FORS2 is a focal reducer with a 6.8 arcmin field of view and a pixel resolution of
0.25 arcsec for the standard collimator optics used. Technical information on the telescopes
and instruments are found at http://www.eso.org/sci/facilities/lasilla/telescopes/2p2.html
and http://www.eso.org/sci/facilities/lasilla/instruments/wfi.html for the 2.2m ? WFI and at
http://www.eso.org/sci/facilities/paranal/instruments/overview.html and http://www.eso.
org/sci/facilities/paranal/instruments/fors/ for the VLT UT1 ? FORS2.
The 2.2m ? WFI observations were done in visitor mode during observing periods of the
Max-Planck Society MPG, while the VLT observations were collected in normal open-time
ESO service observing mode. The imaging sequences of the TNOs used VRI or BVRI filters
and repeated the R filter during sequences that lasted significantly longer than 40–60 min in
order to follow possible object variability due to rotation. Typically, only a single epoch was
observed per target; multiple epochs were measured in some cases if the first attempt was
performed under unfavorable sky conditions. During the TNO observations telescope
tracking was set to compensate for the differential motion of the targets. For calibration
purposes photometric standard star fields from the ESO (for FORS2; http://www.eso.org/sci/
facilities/paranal/instruments/fors/tools/FORS_Std/FORS_Std.html) or the Landolt list (for
WFI; Landolt 1992) were observed and the usual bias, sky, and daytime flatfield exposures
were collected. TNO and standard stars were imaged as much as possible when clear sky
conditions prevailed according to the environmental monitor of the observing site. For the
WFI observations a set of standard star fields covering the airmass range from 1 to 2 was
imaged in order to allow for determination of the full set of photometric reduction parameters.
The FORS2 standard star calibrations followed the instrument calibration plan which
Photometry of Transneptunian Objects
123
foresees typically only one calibration field per night and relies on the determination and
stability of extinction parameters and colour transformations over longer timescales.
Table 1 provides the observing log for the TNO observations together with results for
the measured filter brightness of the objects. Note that not all target TNOs were measured
in all filters used at the respective telescope-instrument observations for the overall pro-
gram. In general, with 2.2m ? WFI TNOs were imaged through VRI-type instrument
filters, while for VLT ? FORS2 usually BVRI-type instrument filters were applied.
3 Data Processing
The data processing started with the basic reduction steps for photometry, i.e., bias sub-
traction, flatfield corrections, exposure time division and determination of the photometric
parameters for the observing sites and telescope-instrument combination used. For the
2.2m ? WFI photometric zeropoints, extinction parameters and colour transformations were
obtained on a nightly basis or for an observing interval of several nights for which stable sky
conditions could be assumed. Stable sky conditions were assessed via the nightly solutions
and information on the sky transparency from the environmental monitor of the site. For
VLT ? FORS2 nightly zeropoints only were determined since usually only a single standard
star field per night was taken for calibration purposes during service mode observations. Data
for the sky extinction and colour transformation of the FORS2 observing periods were taken
from the ESO FORS2 instrument calibration page (http://www.eso.org/observing/dfo/
quality/FORS2/qc/photocoeff/photocoeff_fors.html). The mean extinction coefficients for
the FORS2 filters over the observing period are: 0.21 mag/airmass for the B filter band, 0.13
mag/airmass for V, 0.09 mag/airmass for R and 0.03 mag/airmass for I with a scatter of well
below 0.02 mag/airmass for B and V and about 0.01 mag/airmass for R and I filters.
The TNOs were identified in the field of view by searching for moving objects at the
predicted object positions; this search was done by image blinking, and after identification
the accurate astrometric position of the TNO was measured and compared with the pre-
dicted one. A list of measured object (TNOs and Centaurs) positions and exposure mid-
points was reported to the IAU Minor Planet Center.
After measuring the photometry of the TNOs in relative units, the photometric mag-
nitudes of the objects were obtained for standard Bessell filter bands VRI for the WFI
observations and BVRI for the FORS2 observations. The measurement of the TNO pho-
tometry in relative units was performed on object-aligned median-averaged images by
applying the aperture growth method: The relative counts of the TNO were measured in a
series of apertures with increasing radius centered on the object and the mean magnitude of
the TNO was determined from the average ‘saturation level’ that the object brightness
reached for larger apertures well beyond the seeing limit. The same method was applied for
measuring the standard stars in order to determine the photometric parameters mentioned
above. The photometry used apertures without noticeable background objects included and
an object free annulus centered and close to the TNO or the standard star was chosen for
sky background estimation. The results of the TNO photometry are listed in Table 1.
From the filter magnitudes, when available, 2 or 3 object colours were calculated, i.e.,
V–R and R–I for objects observed with the 2.2m ? WFI and B–V, V–R and R–I for
objects observed with FORS2. When possible, the slope parameter (also known as spectral
gradient, S) is calculated (a) for four individual filter combinations BV, VR, RI and BI
applying the formula in Doressoundiram et al. (2008) and (b) by estimating it by linear
regression of the relative spectrum represented by the BVRI filters normalized to the V
H. Boehnhardt et al.
123
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Photometry of Transneptunian Objects
123
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H. Boehnhardt et al.
123
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1.0
30
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1,0
50
36
07
00
88
0
20
04
GV
91
1/0
4/2
01
13
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01
9.3
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OR
S2
90
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0.2
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8.2
80
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0.0
20
.01
0.0
1
1.0
4–
1.0
60
.56
90
30
60
90
Photometry of Transneptunian Objects
123
Ta
ble
1C
on
tin
ued
Ob
ject
iden
tifi
cati
on
Pre
lim
.IA
Udes
ignat
ion
IAU
Nu
mb
erIA
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ame
Ob
serv
ing
dat
e(U
T)
Tim
e(U
T)
Air
mas
sra
ng
e
Su
nd
ista
nce
(AU
)E
arth
dis
tan
ce(A
U)
Ph
ase
ang
le(d
eg)
B(m
ag)
Err
or
(mag
)T
exp
(s)
V(m
ag)
Err
or
(mag
)T
exp
(s)
R(m
ag)
Err
or
(mag
)T
exp
(s)
I(m
ag)
Err
or(
mag
)T
exp
(s)
Inst
rum
ent
20
04
PG
11
51
2/0
6/2
01
03
6.8
5n
u2
1.3
9n
mn
uW
FI
30
798
20
.36
8–
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86
36
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7–
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81
.40
10
65
23
0
20
04
PG
11
51
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03
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00
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,100
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04
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60
05
/11
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44
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21
.33
20
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FO
RS
2
12
034
70
.03
2–
0.0
53
43
.60
0.0
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.02
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10
.01
Sal
acia
1.3
5–
1.3
81
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42
01
50
30
05
40
20
05
EF
29
81
3/0
1/2
01
14
0.7
12
4.1
72
2.7
42
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72
1.4
7F
OR
S2
0.3
10
–0
.35
24
0.0
30
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0.0
30
.03
0.0
2
1.2
3–
1.2
21
.01
1,0
00
33
57
20
1,1
00
20
05
QU
18
22
6/1
2/2
01
04
8.8
72
2.0
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62
0.5
12
0.0
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OR
S2
30
377
50
.10
1–
0.1
15
48
.78
0.0
20
.02
0.0
10
.03
1.4
8–
1.6
21
.15
18
07
51
50
19
5
20
05
RM
43
26
/12
/20
10
35
.47
20
.82
20
.13
19
.80
19
.39
FO
RS
2
14
545
10
.11
9–
0.1
28
34
.69
0.0
20
.01
0.0
10
.02
1.1
8–
1.1
90
.97
90
35
60
90
20
05
RO
43
13
/12
/20
10
25
.42
22
.25
21
.53
21
.03
20
.52
FO
RS
2
0.1
21
–0
.16
12
4.6
30
.02
0.0
20
.01
0.0
2
1.0
8–
1.1
21
.36
1,0
50
36
07
00
88
0
20
05
RS
43
05
/11
/20
10
42
.36
22
.37
21
.45
20
.99
20
.48
FO
RS
2
30
837
90
.14
9–
0.1
92
41
.46
0.0
20
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0.0
10
.02
1.1
4–
1.2
40
.55
1,0
50
36
07
00
88
0
H. Boehnhardt et al.
123
Ta
ble
1C
on
tin
ued
Ob
ject
iden
tifi
cati
on
Pre
lim
.IA
Udes
ignat
ion
IAU
Nu
mb
erIA
UN
ame
Ob
serv
ing
dat
e(U
T)
Tim
e(U
T)
Air
mas
sra
ng
e
Su
nd
ista
nce
(AU
)E
arth
dis
tan
ce(A
U)
Ph
ase
ang
le(d
eg)
B(m
ag)
Err
or
(mag
)T
exp
(s)
V(m
ag)
Err
or
(mag
)T
exp
(s)
R(m
ag)
Err
or
(mag
)T
exp
(s)
I(m
ag)
Err
or(
mag
)T
exp
(s)
Inst
rum
ent
20
05
RS
43
13
/12
/20
10
42
.38
22
.48
21
.57
21
.16
20
.75
FO
RS
2
30
837
90
.07
1–
0.1
15
41
.93
0.0
50
.04
0.0
20
.03
1.1
9–
1.3
71
.18
1,0
50
36
07
00
88
0
20
05
TB
19
00
7/1
0/2
00
94
6.3
9n
u2
1.2
92
0.7
42
0.1
2W
FI
14
548
00
.11
7–
0.1
72
45
.53
0.1
70
.13
0.0
9
1.1
7–
1.2
80
.64
13
60
78
01
68
0
20
05
TB
19
00
5/1
1/2
01
04
6.3
42
2.0
82
1.3
52
0.7
52
0.0
9F
OR
S2
14
548
00
.05
9–
0.0
99
45
.81
0.0
20
.02
0.0
10
.02
1.1
3–
1.2
41
.04
1,0
50
36
07
00
88
0
20
05
UJ4
38
30
/11
/20
10
8.2
92
2.2
3n
u2
0.6
71
9.9
8F
OR
S2
14
548
60
.28
3–
0.2
91
7.7
20
.07
0.0
70
.05
1.5
1–
1.4
75
.81
90
50
90
20
06
HJ1
23
09
/05
/20
11
36
.33
23
.69
21
.84
21
.17
20
.48
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RS
2
0.2
91
–0
.33
23
5.3
20
.03
0.0
20
.01
0.0
1
1.1
5–
1.3
70
.13
1,0
50
36
07
00
88
0
20
06
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36
80
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0/2
00
91
1.9
9n
un
dn
dn
dW
FI
24
883
50
.12
6–
0.1
64
11
.26
––
–
1.7
5–
2.0
83
.39
61
53
15
78
0
20
07
OR
10
04
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/20
11
86
.39
23
.11
21
.72
20
.87
20
.07
FO
RS
2
22
508
80
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3–
0.2
06
85
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30
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10
.02
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3–
1.0
70
.25
42
01
50
30
55
40
20
07
RW
10
11
/08
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11
27
.66
22
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21
.31
20
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20
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RS
2
30
923
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66
26
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0.0
20
.07
0.0
40
.02
1.4
3–
1.2
61
.54
42
01
50
31
05
40
Photometry of Transneptunian Objects
123
Ta
ble
1C
on
tin
ued
Ob
ject
iden
tifi
cati
on
Pre
lim
.IA
Udes
ignat
ion
IAU
Nu
mb
erIA
UN
ame
Ob
serv
ing
dat
e(U
T)
Tim
e(U
T)
Air
mas
sra
ng
e
Su
nd
ista
nce
(AU
)E
arth
dis
tan
ce(A
U)
Ph
ase
ang
le(d
eg)
B(m
ag)
Err
or
(mag
)T
exp
(s)
V(m
ag)
Err
or
(mag
)T
exp
(s)
R(m
ag)
Err
or
(mag
)T
exp
(s)
I(m
ag)
Err
or(
mag
)T
exp
(s)
Inst
rum
ent
20
10
EK
139
17
/06
/20
10
39
.29
nu
nu
20
.49
nu
WF
I
0.0
34
–0
.11
73
8.8
10
.03
1.0
2–
2.7
01
.31
77
0
Ex
pla
nat
ion
s:T
he
tab
leli
sts,
in3
row
sp
ero
bje
ctan
do
bse
rvin
gep
och
,th
eo
bje
cts
ob
serv
edb
yit
sp
reli
min
ary
and
fin
alIA
Ud
esig
nat
ion
sin
clu
din
gob
ject
nam
es(i
fav
aila
ble
),th
eo
bse
rvin
gd
ate
and
tim
eas
dec
imal
day
sin
UT
and
the
airm
ass
ran
ge
of
the
ob
serv
atio
ns,
the
Su
nan
dE
arth
dis
tan
cein
AU
and
the
ph
ase
angle
ind
egre
es,
the
Bes
sell
B,
V,
R,
Ib
rig
htn
ess
of
the
ob
ject
inm
agn
itu
des
ifm
easu
red
/ob
serv
ed,
the
erro
ro
fth
efi
lter
mag
nit
ud
e(i
nm
ag)
plu
sth
ere
spec
tin
ve
tota
lin
teg
rati
on
tim
esT
exp
per
filt
erin
seco
nds,
and
the
inst
rum
enta
tion
use
dfo
rth
eobse
rvat
ions.
Ifth
eobje
cts
was
obse
rved
duri
ng
two
epoch
s,re
sult
sar
eli
sted
inse
par
ate
table
row
s.
nu
filt
ern
ot
use
d,
nd
ob
ject
no
td
etec
ted
,n
mo
bje
ctd
iffi
cult
tom
easu
rew
ith
un
reli
able
resu
lts,
usu
ally
du
eto
ab
lend
wit
ha
bac
kg
roun
do
bje
ct
H. Boehnhardt et al.
123
filter magnitude equal to one. Before the slope calculation, intrinsic colours of the TNOs
were calculated by removing the solar value for the respective filter combination. The
central wavelength of the filters provided the spectral reference for the slope calculation.
The slope estimation assumes a smooth and straight spectrum over the wavelength range
considered and, namely, the absence of absorption and emission features. This assumption
is justified—although not proven for the individual objects—since so far no strong
absorptions or emissions were identified in the visible wavelength range through spec-
troscopy of TNOs (Barucci et al. 2008). The BV, VR, RI and BI slope values allow the
comparison of the straightness of the spectral slopes over the visible wavelength range and
to assess whether deviations exist in particular towards the blue and red ends of the visible
spectrum. We have noted that some B filter measurements seem to be affected by relatively
low signal-to-noise level such that the BV spectral slope estimations lead to discrepancies
of more than 5–10 %/100 nm compared to the results from the other filters. In that case we
decided not to consider the B filter for the spectral slope calculation. We have considered
as final values for the spectral slope S, those measured using the method (b) described
above, after comparing the latter with the values obtained from individual filter band
combinations.
Absolute V and R magnitudes (HV and HR, respectively) are obtained by correcting the
measured brightness for Sun and Earth distances and for an average phase function. We
applied a linear phase function with slope parameter b = 0.16 ± 0.03 mag/deg for TNOs
and b = 0.11 ± 0.01 mag/deg for Centaurs as proposed by Sheppard and Jewitt (2002).
The absolute magnitudes, colours, and the spectral slopes of the TNOs and Centaurs are
reported in Table 2. Estimation of the result errors is done via error propagation using
measurement (relative count rates for the aperture photometry) and tabulated uncertainties
(for the atmospheric extinction and instrumental colours for the FORS2 photometry).
Flatfield inhomogeneities are considered in the error estimation for WFI data on TNOs and
standard stars, while for FORS2 only for the TNO photometry (relying on the proper
treatment for the photometry uncertainty in the course of the instrument calibration plan
and data quality control of ESO).
Note that not all observations of the TNO and Centaur targets of the program provided
useful results from the data analysis. 2001 CZ31 and 2006 SX436 were not detected in the
pointed fields, 2003 CO1 showed unrealistic colours, which may be due to variable sky
conditions. It is noted that the measurements of 2002 GV31, 2005 UJ438, 2007 OR10 and
2007 RW10 are affected by blends with background objects. In general, the photometry of
TNOs measured with the WFI instrument is less accurate given the lower signal-to-noise
ratio of the exposures, due to the smaller aperture of the 2.2m telescope, and due the
relatively unstable atmospheric conditions during the observing runs at La Silla.
4 Results
The data from the observations at ESO telescopes allowed to obtain photometric mea-
surements of in total 33 TNOs and Centaurs, i.e., 5 Plutinos, 14 CDOs, 5 SDOs, 5 DDOs
and 4 Centaurs. Of the 14 CDOs, 8 belong to the dynamically hot group and 6 to the
dynamically cold population. The dynamical classification used here follows the one
proposed by Gladman et al. (2008). Five objects have three filters (Bessell VRI or BRI)
measured, and two TNOs have only one filter (Bessell R) observed; the rest of the sample
(26 objects) has results in four filters (Bessell BVRI). In the following sections we describe
the results for individual objects and consider photometric population properties for the
Photometry of Transneptunian Objects
123
Ta
ble
2D
yn
amic
pro
per
ties
and
ph
oto
met
ric
resu
lts
of
the
ob
serv
edT
NO
san
dC
enta
urs
Ob
ject
des
ign
atio
ns
and
nam
eD
yn
amic
alty
pe
HV
(mag
)H
R(m
ag)
B–V
(mag
)V
–R
(mag
)R
–I
(mag
)S
pec
tral
gra
die
nt
(%/1
00
nm
)C
om
men
ts
19
98
SG
35
Cen
tau
r1
0.8
31
0.3
00
.74
0.5
30
.53
14
52
872
Ok
yrr
ho
e0
.01
0.0
10
.02
0.0
10
.02
2
19
99
OX
3S
DO
–6
.07
––
––
44
594
0.1
9
20
01
QG
29
8P
luti
no
6.8
16
.11
1.0
20
.70
0.6
53
3
13
977
50
.03
0.0
20
.05
0.0
40
.03
3a
20
01
QS
32
2C
DO
cold
ou
ter
dis
k7
.25
6.5
40
.69
0.7
10
.87
23
0.1
70
.09
0.2
20
.19
0.1
28
a
20
01
QT
322
CD
Oco
ldin
ner
dis
k8
.17
7.6
20
.81
0.5
40
.34
9
13
518
20
.04
0.1
00
.08
0.1
10
.10
3
20
02
GV
31
CD
Oco
ldo
ute
rd
isk
3.9
23
.42
0.5
50
.50
0.3
32
Ble
nd
sfr
om
bac
kg
roun
do
bje
ct
0.0
30
.04
0.0
30
.05
0.0
53
20
02
KX
14
CD
Oco
ldin
ner
dis
k5
.07
4.4
70
.77
0.6
10
.68
29
11
995
10
.03
0.0
10
.01
0.0
10
.01
1a
20
02
KY
14
Cen
tau
r1
0.5
09
.80
–0
.71
0.8
34
7
25
011
20
.08
0.1
20
.14
0.1
33
a
20
03
AZ
84
Plu
tin
o3
.54
3.0
80
.60
0.4
50
.33
1
20
899
60
.03
0.0
10
.04
0.0
30
.02
2
20
03
FB
12
8P
luti
no
7.2
66
.76
0.6
20
.50
0.5
01
3
13
306
70
.05
0.0
30
.06
0.0
60
.04
1a
20
03
FE
12
8C
DO
cold
ou
ter
dis
k6
.94
6.2
61
.04
0.6
80
.53
23
0.0
70
.02
0.0
80
.08
0.0
35
a
20
03
FX
12
8S
DO
6.6
06
.02
0.7
50
.57
0.5
21
7
H. Boehnhardt et al.
123
Ta
ble
2C
on
tin
ued
Ob
ject
des
ign
atio
ns
and
nam
eD
yn
amic
alty
pe
HV
(mag
)H
R(m
ag)
B–V
(mag
)V
–R
(mag
)R
–I
(mag
)S
pec
tral
gra
die
nt
(%/1
00
nm
)C
om
men
ts
65
489
Cet
o0
.01
0.0
10
.02
0.0
20
.02
3a
20
03
FY
12
8D
DO
5.3
65
.03
–0
.33
0.5
79
12
013
20
.08
0.0
50
.07
0.0
95
a
5.4
14
.99
–0
.42
0.3
74
0.0
80
.05
0.0
90
.08
1a
20
03
GH
55
CD
Oco
ldo
ute
rd
isk
6.1
85
.67
1.0
70
.52
0.6
42
2
38
543
70
.04
0.0
10
.05
0.0
40
.02
2a
20
03
MW
12
CD
Oh
ot
ou
ter
dis
k3
.93
3.6
3–
0.3
00
.38
0
17
456
7V
ard
a0
.07
0.0
50
.08
0.0
82
a
20
03
OP
32
CD
Oh
ot
ou
ter
dis
k3
.79
3.5
1–
0.2
80
.21
-7
12
017
80
.08
0.1
10
.14
0.1
41
a
4.2
2–
––
––
0.0
7
20
03
UR
29
2C
DO
cold
inner
dis
k7
.37
6.8
41
.15
0.5
30
.70
25
12
018
10
.03
0.0
20
.04
0.0
40
.04
3a
20
03
UZ
117
CD
Oh
ot
ou
ter
dis
k5
.27
4.8
60
.67
0.4
20
.33
2
0.0
20
.01
0.0
30
.03
0.0
31
20
04
EW
95
Plu
tin
o6
.52
6.0
90
.67
0.4
30
.39
4
12
021
60
.01
0.0
10
.02
0.0
20
.01
1
20
04
GV
9C
DO
ho
to
ute
rd
isk
4.0
33
.40
0.7
30
.63
0.8
84
6
90
568
0.0
30
.01
0.0
10
.01
0.0
16
a
20
04
PG
11
5D
DO
5.5
3–
––
––
30
798
20
.05
5.4
65
.15
–0
.31
0.4
74
0.0
50
.06
0.0
80
.11
3a
Photometry of Transneptunian Objects
123
Ta
ble
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H. Boehnhardt et al.
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Photometry of Transneptunian Objects
123
TNOs and Centaurs. For comparison we make use of data compiled in the MBOSS2
database of minor bodies in the outer solar system as described in Hainaut et al. (2012) and
available at http://www.eso.org/*ohainaut/MBOSS/ (database version for the paper of
Hainaut et al. 2012). It is noted that these authors have performed a critical data evaluation
of individual objects for which results are published. Thus, for comparison with our data
we take the MBOSS2 results as reference in the text and tables below. The publications for
the photometry of the individual objects used in MBOSS2 are listed here: 1998 SG35—
Delsanti et al. (2001), Doressoundiram et al. (2001), Bauer et al. (2003), Dotto et al.
(2003), Doressoundiram et al. (2007); 1999 OX3—Tegler and Romanishin (2000), Dor-
essoundiram et al. (2001), Delsanti et al. (2001), Boehnhardt et al. (2002), Doressoundiram
et al. (2002), Bauer et al. (2003), McBride et al. (2003), Peixinho et al. (2004),
Table 3 Comparison of results of our TNO and Centaur photometry with MBOSS 2 data
Objectdesignation
ModifiedHR(a) (mag)
B–V (mag) V–R (mag) R–I (mag) Spectral gradient(%/100 nm)
1998 SG35 10.80 ± 0.01 0.74 ± 0.02 0.53 ± 0.01 0.53 ± 0.02 14 ± 2
52872 10.77 ± 0.09 0.74 ± 0.07 0.49 ± 0.06 0.47 ± 0.07 11 ± 3
1999 OX3 6.33 ± 0.19 – – – –
44594 7.06 ± 0.08 1.14 ± 0.06 0.70 ± 0.05 0.65 ± 0.06 34 ± 2
2002 KX14 4.64 ± 0.01 0.77 ± 0.01 0.61 ± 0.01 0.68 ± 0.01 29 ± 1
119951 – 1.05 ± 0.03 0.61 ± 0.02 – 26 ± 2
2002 KY14 10.19 ± 0.12 – 0.71 ± 0.14 0.83 ± 0.13 47 ± 3
250112a 9.75 ± 0.04 – – – 41 ± 3
2003 FX128 6.11 ± 0.01 0.75 ± 0.02 0.57 ± 0.02 0.52 ± 0.02 17 ± 3
65489 6.28 ± 0.04 0.86 ± 0.03 0.56 ± 0.03 – 16 ± 1
2003 FY128 5.23 ± 0.05 – 0.38 ± 0.09 0.47 ± 0.09 7 ± 3
120132 4.48 ± 0.01 1.05 ± 0.03 0.60 ± 0.02 0.55 ± 0.03 21 ± 1
2003 GH55 5.84 ± 0.01 1.07 ± 0.05 0.52 ± 0.04 0.64 ± 0.02 22 ± 2
385437 5.95 ± 0.06 1.12 ± 0.05 0.63 ± 0.06 – 26 ± 6
2003 OP32 3.72 ± 0.11 – 0.28 ± 0.14 0.21 ± 0.14 -7 ± 1
120178 – 0.70 ± 0.05 – – 3 ± 2
2004 GV9 3.49 ± 0.01 0.73 ± 0.01 0.63 ± 0.01 0.88 ± 0.01 46 ± 6
90568 – 0.84 ± 0.03 – – 21 ± 1
2004 SB60 3.71 ± 0.01 0.82 ± 0.02 0.47 ± 0.02 0.39 ± 0.02 9 ± 1
120347 – – – – 7 ± 0
2005 RM43 4.35 ± 0.01 0.69 ± 0.02 0.33 ± 0.02 0.41 ± 0.02 1 ± 1
145451 – 0.59 ± 0.04 – – 1 ± 1
2005 TB190 4.12 ± 0.03 0.99 ± 0.03 0.60 ± 0.03 0.39 ± 0.02 27 ± 1
145480 4.17 ± 0.02 0.98 ± 0.04 0.56 ± 0.04 0.56 ± 0.03 19 ± 2
2005 UJ438 11.64 ± 0.07 – – 0.69 ± 0.09 31 ± 5
145486* 11.72 ± 0.03 – – – 30 ± 3
Explanations: For the column headings see Tables 1, 2 except HR(a) which is the modified absolutebrightness of the object at unity Earth and Sun distance and phase angle as for the observations (seeTable 1). The upper value (in roman) per entry field provides the results from our observations, the lowervalue (in italics) the corresponding value from the MBOSS2 database. Objects marked by symbol a:comparison values are based on results published in Bauer et al. (2013), otherwise comparison values arefrom MBOSS2 database
H. Boehnhardt et al.
123
Doressoundiram et al. (2005, 2007), Jewitt et al. (2007), Sheppard (2010); 2002 KX14—
Rabinowitz et al. (2007), DeMeo et al. (2009), Romanishin et al. (2010); 2003 FX128—
Tegler et al. (2003), Jewitt et al. (2007), Benecchi et al. (2009); 2003 FY128—DeMeo
et al. (2009), Sheppard (2010); 2003 GH55—Jewitt et al. (2007); 2003 OP32—Rabinowitz
et al. (2008); 2004 GV9—Rabinowitz et al. (2008), DeMeo et al. (2009); 2004 SB60—
Benecchi et al. (2009); 2005 RM43—Rabinowitz et al. (2008), DeMeo et al. (2009); 2005
TB190—Sheppard (2010).
4.1 Comparison of Individual TNOs in MBOSS2 Database
11 objects in our target list have entries in the MBOSS2 database, 2 more in a recent paper
by Bauer et al. (2013). Both are used for comparison of the absolute brightness and the
spectral gradients of the objects—see Table 3. In order to be compatible with the MBOSS2
database the result listed in Table 3 provides the ‘modified’ absolute magnitude not cor-
rected for the phase function. From the eight objects with listed absolute magnitudes in
three datasets (i.e. ours, that from MBOSS2 and from Bauer et al.) five objects (1995
SG35, 2003 FX128, 2003 GH55, 2005 TB190, 2005 UJ438) have small differences
(\0.2 mag) for the modified HR such that one may speculate on a small amplitude of the
rotation lightcurve. The other three objects (1999 OX3, 2002 KY14, 2003 FX128) display
deviations of 0.4–0.8 mag which may indicate larger amplitudes of rotation variability and/
or contributions from phase effects or activity of the objects.
For the spectral gradients S our values agree—within the estimated uncertainties—with
those of the MBOSS2 database and Bauer et al. (2013) for eight objects (1995 SG35, 2002
KX14, 2002 KY14, 2003 FX128, 2003 GH55, 2004 SB60, 2005 RM43, 2005 UJ438) and
they are compatible (i.e., close in amplitude though outside of the formal uncertainties) for
two TNOs (2003 OP32, 2005 TB190). Disagreement is found for two objects (2003 FY128
and 2004 GV9) which may indicate large-scale surface heterogeneity and deserves con-
firmation by new observations.
4.2 Individual Objects
In the following we provide brief comments on individual objects, grouped by dynamical
types as estimated from the orbital elements and orbit integrations and applying the
dynamical classification criteria as described by Gladman et al. (2008).
4.2.1 3:2 Resonance Objects (Plutinos): 2001 QG298, 2003 AZ84, 2003 FB128, 2004
EW95, 2006 HJ123 (see Tables 1, 2)
From the HR magnitudes and assuming an average albedo of 0.1 (Mommert et al. 2012, gave
0.08 ± 0.03 as average geometric albedo for a sample of 18 Plutinos), 2001 QG298, 2003
FB128, 2004 EW95 and 2006 HJ123 belong to the medium-large objects (order 200–500 km
diameter) while 2003 AZ84 seems to have a larger size (order 800–900 km). The quantitative
analysis of Herschel and other ground-based measurements of Plutinos (Mommert et al.
2012) provides sizes of 727 km for 2003 AZ84 and 291 and 216 km for 2004 EW95 and 2006
HJ123, respectively. It is noted that 2006 HJ123 has a relatively high albedo of 0.28, while
2003 AZ84 and 2004 EW95 show albedo of 0.11 and 0.04, respectively.
The spectral slopes of the Plutinos in our sample cover a wide range from 1 to 34 %/
100 nm. Two Plutinos, 2003 AZ84 and 2004 EW95, have close to neutral intrinsic colours
Photometry of Transneptunian Objects
123
which may indicate the presence of ices on their surfaces. At least for 2003 AZ84 the neutral
spectral gradient in the visible and the relatively high albedo is nicely compatible with the
presence of water ice on its surface which is claimed by Barkume et al. (2008) based on near-
IR spectroscopy of this object. 2001 OG298 and 2006 HJ123 belong to the very red Plutino
objects (S above 30 %/100 nm); their sizes, albedos and spectral properties are not known.
4.2.2 Dynamically ‘Hot’ Classical Disk Objects (Hot CDOs): 2003 MW12, 2003 OP32,
2003 UZ117, 2004 GV9, 2004 SB60, 2005 RS43 (see Tables 1, 2)
With absolute magnitudes HR between 3.4 and 4.9 mag, the hot CDOs measured may fall
in the size range of 500–900 km (assuming the mean albedo of 0.1 for hot CDOs; Vilenius
et al. 2012, give a mean geometric albedo of 0.11 ± 0.04). Based on Herschel and ground-
based measurements, Vilenius et al. (2012) and Fornasier et al. (2013) determined sizes
and albedos of 680 km and 0.077 for 2004 GV9 and 901/874 km and 0.044 for 2004 SB60,
respectively. The majority, i.e., 4 hot CDOs (2003 MW12, 2003 UZ117, 2004 SB60, 2005
RS43), have neutral to moderately red (0–12 %/100 nm) spectral gradients in the visible
wavelength range; one hot CDO displays a slightly bluish slope (2003 OP32 with -7 %/
100 nm), one seems to be very red (2004 GV9 with 46 %/100 nm)—and none of the
measured CDOs falls in the intermediate to red colour range with a mean value of about
20 %/100 nm (Hainaut et al. 2012). It is noted that 2003 OP32 and 2003 UZ117 are
members of the Haumea collision family; the bluish and close to neutral spectral gradients
of both TNOs are very much compatible with that of the possible parent body 136108
Haumea (Jewitt et al. 2007, Rabinowitz et al. 2007) and may thus support the interpretation
as collision fragments.
4.2.3 Dynamically ‘Cold’ Classical Disk Objects (Cold CDOs): 2001 QS322, 2001
QT322, 2002 GV31, 2002 KX14, 2003 FE128, 2003 GH55, 2003 UR292, 2005
EF298 (see Tables 1, 2)
From the absolute brightness range determined (3.4–7.6 mag in R) the eight dynamically
cold CDOs in our observing list belong to the medium large TNOs (80–550 km for a
geometric albedo of 0.15, see Vilenius et al. 2012). 2002 QT322 is the brightest (and
possibly largest) cold CDO found so far. For 2002 KX14, the second brightest cold CDO in
our sample, diameter and albedo estimations by Vilenius et al. (2012) gave 455 km and
0.01, respectively; 2002 GV31 seems to be a smaller TNO (\130 km diameter) though
with a brighter albedo ([0.22). The spectral gradients of the 6 cold CDOs in the visible fall
in the range between 22 and 29 %/100 nm, i.e., they belong to the red TNO population and
are quite typical for members of the cold Classical Disk (see Hainaut et al. 2012). 2001
QT322 and 2002 GV31 displayed moderately red (9 %/100 nm) and quasi-neutral (2 %/
100 nm) spectral gradients, respectively, which fall below the currently known lowest
values for CDOs. It is however noted, that the measurements of 2002 GV31 might be
affected by blends from a background object close to the TNO.
4.2.4 Scattered Disk Objects (SDOs): 1999 OX3, 2003 FX128, 2005 QU182, 2005 RM43,
2007 RW10 (see Tables 1, 2)
The five SDOs measured cover an absolute R brightness range from 3.4 to 6.3 mag
corresponding to size of about 300–900 km when assuming the mean albedo for SDOs of
H. Boehnhardt et al.
123
0.07 as given by Santos-Sanz et al. (2012). For two TNOs diameter and albedo were
published (300 km and 0.05 for 2003 FX128 and 247 km and 0.08 for 2007 RW10;
Santos-Sanz et al. 2012). The four SDOs for which spectral gradients are obtained from our
photometry show no (2005 RM43), moderate (2007 RW10) and medium reddening (2003
FX128, 2005 QU182) within the range found from the measured SDO population.
4.2.5 Detached Disk Objects (DDOs): 2003 FY128, 2004 PG115, 2005 TB190, 2007
OR10, 2010 EK139 (see Tables 1, 2)
The absolute magnitudes of the measured DDOs (range is 1.5–5.5 mag in R) indicate large
to medium size bodies (300–1400 km) when assuming a mean albedo of 0.17 (Santos-Sanz
et al. 2012). This conclusion does not apply for 2010 EK139 since the higher geometric
albedo of 0.25 results in a size of almost 1,000 km as estimated based upon Herschel
observations (Pal et al. 2012). The size and albedo estimates reveal a rather wide range for
diameter and albedo (460 km and 0.08 for 2003 FY128, 464 km and 0.15 for 2005 TB190,
1,280 km and 0.19 for 2007 OR10; see Santos-Sanz et al. 2012). The reddening of the
DDOs is either small (4 and 9 %/100 nm for 2003 FY128 and 2004 PG115) or red (25 %/
100 nm for 2005 TB190). 2007 OR10 is found with a very red spectral slope of 50 %/
100 nm, although the reliability of this results is somehow jeopardized by the blend of a
background object close to the TNO. It is noted that 2005 TB190 and 2007 OR10 seem to
be redder than other DDOs measured so far (see Hainaut et al. 2012).
4.2.6 Centaurs: 1998 SG35, 2002 KY14, 2005 RO43, 2005 UJ438 (see Tables 1, 2)
With absolute magnitudes between 6.9 and 11.0 mag in R the Centaurs in our list are
among the smaller objects (diameter of 25–200 km for an assumed geometric albedo of
0.07; Stansberry et al. 2008). With 7.4 and 6.9 mag in V and R, respectively, 2005 RO43
has the lowest absolute brightness among the Centaurs for which photometry is published.
Diameter and albedo are measured for 1998 SG35 (52 km and 0.025; Stansberry et al.
2008). Two Centaurs each have moderately red (1998 SG35 and 2005 RO43) and very red
(2002 KY14 and 2005 UJ438) spectral gradients S, i.e., representing the bimodal colour
population put forth by Peixinho et al. (2012).
5 Population Statistics
Adding our results to those of the MBOSS2 database on TNO photometry in the visible
wavelength range, we have performed a similar statistical assessment of the spectral
gradients S for the different dynamical groups as described in Hainaut et al. (2012) and best
illustrated in their Table 4. The assessment included the t test, the F test, and the Kol-
mogorov–Smirnov test of the spectral gradients distributions for Plutinos, hot and cold
CDOs, SDOs, DDOs and Centaurs plus Jupiter Trojans. The key findings confirm those of
Hainaut et al. (2012), i.e., the cold CDOs and the Trojans are clearly disjoint from each
other and from the other TNO populations for their colour distributions. The red colour
population among the CDOs was first suggested by Tegler and Romanishin (2000) and
further analyzed by Doressoundiram et al. (2002), Trujillo and Brown (2002). The spectral
gradient distributions of the dynamical TNO populations and of the Centaurs is shown in
Fig. 1; obviously, the cold CDOs show a very wide distribution of spectral gradients
peaking in the 25/30 %/100 nm bin. The bimodal gradient distribution of the Centaurs as
Photometry of Transneptunian Objects
123
suggested first by Peixinho et al. (2003) and Tegler et al. (2003) and reanalyzed for
instance by Peixinho et al. (2012) is also noticeable in the figure, although the statistical
tests performed did not address it specifically. From our statistical tests the spectral gra-
dient distribution of the Centaurs is indistinguishable from those of the Plutinos, hot CDOs,
SDOs and DDOs.
6 Concluding Remarks
Photometric measurements of 33 TNOs and Centaurs in BVRI filters are presented. The
measured objects are all from the target list of the Herschel Key program ‘TNOs are cool’.
They were selected for observations since visible photometry was missing either to support
the immediate size and albedo estimation to be performed together with flux measurements
from Herschel observations or to complement the object characterization by multi-colour
data. They are thus providing valuable information and input for the analysis of Herschel
data of individual objects and of the whole sample of objects measured through this
program.
Indications of brightness variations are found by comparison of published results with
our data for 3 objects. The suggested variations may result from non-spherical rotating
objects of minimum main axes ratios between 1.2 and 2. However, no lightcurve can be
compiled from the available measurements. Alternatively, parts of the variation amplitude
may also be due to the phase function and/or intrinsic activity.
Fig. 1 The distributions of spectral gradients for the TNO populations and Centaurs. The histogram showsthe number of objects per spectral gradient bin for the dynamical populations of TNOs and for Centaurs.Abscissa bin of spectral gradient range (for instance: 5\10 means spectral gradients from 5 to 10 %/100 nm).Ordinate number of objects per spectral gradient bin
H. Boehnhardt et al.
123
Rough size estimations are performed based upon the absolute R magnitudes of the
objects and assumed average geometric albedo values for the respective dynamical pop-
ulation of the TNOs or Centaurs. These estimations fall in the size ranges known so far for
the respective populations.
The statistical analysis of the spectral gradients of the measured objects added to the
much larger sample of the MBOSS2 database confirmed the diversity of the spectral
gradient distributions of the cold CDOs (and Trojans) from those of the other TNO and
Centaur populations.
A few objects show spectral gradients at the extreme ends of the known ranges for
TNOs and Centaurs. 6 objects were found to show neutral spectral gradient (S \ 3 %/
100 nm), i.e., 2002 GV31, 2003 AZ84, 2003 MW12, 2003 OP32, 2003 UZ117 and 2005
RM43, half of them from the population of dynamically hot CDOs. Neutral colours may
indicate the presence of surface ice (suggested by spectroscopic results for 2003 AZ84).
2003 OP32 has a rather negative spectral slope (S = -7 %/100 nm) in the visible
wavelength range. It is interesting to note that among the objects with neutral spectral
slopes is one cold CDO (2002 GV31). Towards the very red end of the spectral slope
distributions (S [ 40 %/100 nm) we find three objects, i.e. 2002 KY14, 2004 GV9 and
2007 OR10. The latter object is by far the reddest DDO measured so far.
References
K.M. Barkume, M.E. Brown, E.L. Schaller, Near-infrared spectra of Centaurs and Kuiper belt objects. AJ135, 55–67 (2008)
M.A. Barucci, M.E. Brown, J.P. Emery, F. Merlin, Composition and surface properties of transneptunianobjects and centaurs, in The Solar System Beyond Neptune, ed. by M.A. Barucci, H. Boehnhardt, D.P.Cruikshank, A. Morbidelli (The University of Arizona Press, Tucson, 2008), pp. 143–160
J.M. Bauer, K.J. Meech, Y.R. Fernandez, J. Pittichova, O.R. Hainaut, H. Boehnhardt, A.C. Delsanti,Physical survey of 24 Centaurs with visible photometry. Icarus 166, 195–211 (2003)
J.M. Bauer, T. Grav, E. Blauvelt, A.K. Mainzer, J.R. Masiero, R. Stevenson, E. Kramer, Y.R. Fernandez,C.M. Lisse, R.M. Cutri, P.R. Weissman, J.W. Bailey, F.J. Masci, R. Walker, A. Waszczak, C.R.Nugent, K.J. Meech, A. Lucas, G. Pearman, A. Wilkins, J. Watkins, S. Kulkarni, E.L. Wright, and theWISE and PTF Teams, Centaurs and scattered disk objects in the thermal infrared: analysis of WISE/NEOWISE observations. ApJ 773, 22 (2013)
S.D. Benecchi, K.S. Noll, W.M. Grundy, M.W. Buie, D.C. Stephens, H.F. Levison, The correlated colors oftransneptunian binaries. Icarus 200, 292–303 (2009)
H. Boehnhardt, A. Delsanti, M.A. Barucci, O.R. Hainaut, A. Doressoundiram, M. Lazzarin, L. Barrera, C.deBergh, K. Birkle, E. Dotto, K.J. Meech, J.E. Ortiz, J. Ramon, T. Sekiguchi, N. Thomas, G.P. Tozzi,J. Watanabe, R.M. West, ESO large program on physical studies of transneptunian objects and Cen-taurs: visible photometry—first results. A&A 395, 297–303 (2002)
A.C. Delsanti, H. Boehnhardt, L. Barrera, K.J. Meech, T. Sekiguchi, O.R. Hainaut, BVRI photometry of 27Kuiper Belt objects with ESO/Very Large Telescope. A&A 340, 347–358 (2001)
F.E. DeMeo, S. Fornasier, M.A. Barucci, D. Perna, S. Protopapa, A. Alvarez-Candal, A. Delsanti, A.Doressoundiram, F. Merlin, C. de Bergh, Visible and near-infrared colors of transneptunian objects andCentaurs from the second ESO large program. A&A 493, 283–290 (2009)
A. Doressoundiram, M.A. Barucci, J. Romon, C. Veillet, Multicolor photometry of trans-neptunian objects.Icarus 154, 277–286 (2001)
A. Doressoundiram, N. Peixinho, C. deBergh, S. Fornasier, P. Thebault, M.A. Barucci, C. Veillet, The colordistribution in the Edgeworth-Kuiper belt. AJ 124, 2279–2296 (2002)
A. Doressoundiram, N. Peixinho, C. Doucet, O. Mousis, M.A. Barucci, J.M. Petit, C. Veillet, The MeudonMulticolor Survey (2MS) of Centaurs and trans-neptunian objects: extended dataset and status on thecorrelations reported. Icarus 174, 90–104 (2005)
A. Doressoundiram, N. Peixinho, A. Moullet, S. Fornasier, M.A. Barucci, J.-L. Beuzit, C. Veillet, TheMeudon Multicolor Survey (2MS) of Centaurs and trans-neptunian objects: from visible to infraredcolors. AJ 134, 2186–2199 (2007)
Photometry of Transneptunian Objects
123
A. Doressoundiram, H. Boehnhardt, S.C. Tegler, C. Trujillo, Color properties and trends of the transnep-tunian objects, in The Solar System Beyond Neptune, ed. by M.A. Barucci, H. Boehnhardt, D.P.Cruikshank, A. Morbidelli (The University of Arizona Press, Tucson, 2008), pp. 91–104
E. Dotto, M.A. Barucci, H. Boehnhardt, J. Romon, A. Doressoundiram, N. Peixinho, C. de Bergh, M.Lazzarin, Searching for water ice on 47171 1999 TC36, 1998 SG35, and 2000 QC243: ESO largeprogram on TNOs and centaurs. Icarus 162, 408–414 (2003)
S. Fornasier, E. Lellouch, T. Muller, P. Santos-Sanz, P. Panuzzo, C. Kiss, T. Lim, M. Mommert, D.Bockelee-Morvan, E. Vilenius, J. Stansberry, G.P. Tozzi, S. Mottola, A. Delsanti, J. Crovisier, R.Duffard, F. Henry, P. Lacerda, A. Barucci, A. Gicquel, ‘‘TNOs are cool’’: a survey of the trans-neptunian region VIII. Combined Herschel PACS and SPIRE observations of nine bright targets at70–500 lm. A&A 555, A15 (2013)
B. Gladman, B.G. Marsden, C. VanLaerhoven, Nomenclature in the outer solar system, in The Solar SystemBeyond Neptune, ed. by M.A. Barucci, H. Boehnhardt, D.P. Cruikshank, A. Morbidelli (The Universityof Arizona Press, Tucson, 2008), pp. 43–57
O. Hainaut, H. Boehnhardt, S. Protopapa, Colours of minor bodies in the outer solar system. II. A statisticalanalysis revisited. A&A 546, A115 (2012)
D. Jewitt, N. Peixinho, H.H. Hsieh, U-band photometry of Kuiper belt objects. AJ 134, 2046–2053 (2007)S.J. Kenyon, B.C. Bromley, D.P. O’Brien, D.R. Davis, Formation and collisional evolution of Kuiper belt
objects, in The Solar System Beyond Neptune, ed. by M.A. Barucci, H. Boehnhardt, D.P. Cruikshank,A. Morbidelli (The University of Arizona Press, Tucson, 2008), pp. 293–314
A.U. Landolt, UBVRI photometric standard stars in the magnitude range 11.5 \ V \ 16.0 around thecelestial equator. AJ 104, 340–491 (1992)
N. McBride, S.F. Green, J.K. Davies, D.J. Tholen, S.S. Sheppard, R.J. Whiteley, J.K. Hillier, Visible andinfrared photometry of Kuiper belt objects: searching for evidence of trends. Icarus 161, 501–510(2003)
M. Mommert, A.W. Harris, C. Kiss, A. Pal, P. Santos-Sanz, J. Stansberry, A. Delsanti, E. Vilenius, T.G.Muller, N. Peixinho, E. Lellouch, N. Szalai, F. Henry, R. Duffard, S. Fornasier, P. Hartogh, M.Mueller, J.L. Ortiz, S. Protopapa, M. Rengel, A. Thirouin, TNOs are cool: a survey of the trans-neptunian region V. Physical characterization of 18 Plutinos using Herschel—PACS observations.A&A 541, A93 (2012)
A. Morbidelli, H.H. Levison, R. Gomez, The dynamical structure of the Kuiper belt and its primordialorigin, in The Solar System Beyond Neptune, ed. by M.A. Barucci, H. Boehnhardt, D.P. Cruikshank, A.Morbidelli (The University of Arizona Press, Tucson, 2008), pp. 275–292
T. Muller, E. Lellouch, H. Boehnhardt, J. Stansberry, A. Barucci, J. Crovisier, A. Delsanti, A. Doresso-undiram, E. Dotto, R. Duffard, S. Fornasier, O. Groussin, P. Gutierrez, O. Hainaut, A.W. Harris, P.Hartogh, D. Hestroffer, J. Horner, D. Jewitt, M. Kidger, C. Kiss, P. Lacerda, L. Lara, T. Lim, M.Mueller, R. Moreno, J.L. Ortiz, M. Rengel, P. Santos-Sanz, B. Swinyard, N. Thomas, A. Thirouin, D.Trilling, TNOs are cool: a survey of the transneptunian region, EMP 105, 209–219 (2009)
A. Pal, C. Kiss, T.G. Muller, P. Santos-Sanz, E. Vilenius, N. Szalai, M. Mommert, E. Lellouch, M. Rengel,P. Hartogh, S. Protopapa, J. Stansberry, J.-L. Ortiz, R. Duffard, A. Thirouin, F. Henry, A. Delsanti,‘‘TNOs are cool’’: a survey of the trans-neptunian region VII. Size and surface characteristics of(90377) Sedna and 2010 Ek129. A&A 541, L6 (2012)
N. Peixinho, H. Boehnhardt, I. Belskaya, A. Doressoundiram, M.A. Barucci, A. Delsanti, ESO large pro-gram on Centaurs and TNOs: visible colors—final results. Icarus 170, 153–166 (2004)
N. Peixinho, A. Doressoundiram, A. Delsanti, H. Boehnhardt, M.A. Barucci, I. Belskaya, Reopening theTNOs color controversy: Centaurs bimodality and TNOs unimodality. A&A 410, L29–L32 (2003)
N. Peixinho, A. Delsanti, A. Guilbert-Lepoutre, R. Gafeira, P. Lacerda, The bimodal colors of Centaurs andsmall Kuiper belt objects. A&A 546, A86 (2012)
D.L. Rabinowitz, B.E. Schaefer, S.W. Tourtellotte, The diverse solar phase curves of distant icy bodies.I. Photometric observations of 18 trans-neptunian objects, 7 Centaurs, and Nereid. AJ 133, 26–43(2007)
D.L. Rabinowitz, B.E. Schaefer, M. Schaefer, S.W. Tourtellotte, The youthful appearance of the 2003 EL61collisional family. AJ 136, 1502–1509 (2008)
W. Romanishin, S.C. Tegler, G.J. Consolmagno, Colors of inner disk classical Kuiper belt objects. AJ 140,29–33 (2010)
P. Santos-Sanz, E. Lellouch, S. Fornasier, C. Kiss, A. Pal, T.G. Muller, E. Vilenius, J. Stansberry, M.Mommert, A. Delsanti, M. Mueller, N. Peixinho, F. Henry, J.L. Ortiz, A. Thirouin, S. Protopapa, R.Duffard, N. Szalai, T. Lim, C. Ejeta, P. Hartogh, A.W. Harris, M. Rengel, ‘‘TNOs are cool’’: a surveyof the trans-neptunian region IV. Size/albedo characterization of 15 scattered disk and detached objectsobserved with Herschel-PACS. A&A 541, A92 (2012)
H. Boehnhardt et al.
123
S.S. Sheppard, The colors of extreme outer solar system objects. AJ 139, 1394–1405 (2010)S.S. Sheppard, D.C. Jewitt, Time-resolved photometry of Kuiper belt objects: rotations, shapes, and phase
functions. AJ 124, 1757–1775 (2002)J. Stansberry, W. Grundy, M. Brown, D. Cruikshank, J. Spencer, D. Trilling, J.-L. Margot, Physical
properties of Kuiper belt and centaur objects: constraints from the spitzer space telescope, in The SolarSystem Beyond Neptune, ed. by M.A. Barucci, H. Boehnhardt, D.P. Cruikshank, A. Morbidelli (Uni-versity of arizona Press, Tucson, 2008), pp. 164–179
S.C. Tegler, W. Romanishin, Extremely red Kuiper-belt objects in near-circular orbits beyond 40 AU.Nature 407, 979–981 (2000)
S.C. Tegler, W. Romanishin, Resolution of the Kuiper belt object color controversy: two distinct colorpopulations. Icarus 161, 181–191 (2003)
S.C. Tegler, W. Romanishin, G.J. Consolmagno, Color patterns in the Kuiper belt: a possible primordialorigin. ApJ 599, L49–L52 (2003)
C.A. Trujillo, M.E. Brown, A correlation between inclination and color in the classical Kuiper belt. ApJ 566,L125–L128 (2002)
E. Vilenius, C. Kiss, M. Mommert, T. Muller, P. Santos-Sanz, A. Pal, J. Stansberry, M. Mueller, N.Peixinho, S. Fornasier, E. Lellouch, A. Delsanti, A. Thirouin, J.L. Ortiz, R. Duffard, D. Perna, N.Szalai, S. Protopapa, F. Henry, D. Hestroffer, M. Rengel, E. Dotto, P. Hartogh, ‘‘TNOs are cool’’: asurvey of the trans-neptunian region VI. Herschel/PACS observations and thermal modeling of 19classical Kuiper belt objects. A&A 541, A94 (2012)
Photometry of Transneptunian Objects
123
