Geoscience Reference
In-Depth Information
3.2.
Observation results
The resulting time variation of the surface color of (832) Karin in our
2003 observation
12
is summarized in Fig. 3(b). For reference, we show
the lightcurve of this asteroid during the summer to autumn of 2003
obtained from a couple of telescopes including VATT (Fig. 3(a), equiva-
lent to Fig. 1(a)). As seen in Fig. 3(b), we obtained the color data of this
asteroid for over more than 80% of its rotational period at this observation.
The results of our 2004 multi-color observation are summarized in
Fig. 3(e), as well as this asteroid's lightcurve obtained at this observation
(Fig. 3(d), equivalent to Fig. 1(b)). This time we obtained the color data
of this asteroid over almost the entire period of its rotation.
Looking at Fig. 3(b), which shows major results of the 2003 observation,
the
V
-
R
value is almost constant throughout the rotation. The change in
B
-
V
is slight in the early phase of rotation, then gradually becomes larger
during the period of this observation. What most draws our attention in
this data is an obvious anomaly in
V
-
I
value at phase
0.2. To inspect
this anomaly in more detail, we calculated the wavelength dependence of
the relative reflectance of this asteroid by subtracting the solar colors of
B
-
V
=0
.
665,
V
-
R
=0
.
367, and
V
-
I
=0
.
705
13
from our original color
data. The relative reflectance is normalized at a wavelength of the
V
filter,
5394.84 A. Then, as shown in Fig. 3(c), we found that the relative reflectance
of this asteroid at long wavelengths (i.e. in the
I
-band) is much larger at the
rotation phase
∼
0.2 than at other phases. The steep slope of the relative
reflectance in Fig. 3(c) at phase
∼
0.2 should be called “red”, as is often
seen in regular S-type asteroids.
14
,
15
Note that the magnitude errors in Fig. 3(b) look smaller than the mag-
nitude errors in Fig. 3(a), which might seem strange. This is because we
have used lightcurve data from many other smaller telescopes in Fig. 3(a),
not only that from the 1.8-m VATT, while we drew Fig. 3(b) with only the
data from the 1.8-m VATT. If you compare Figs. 3(d) and (e) for both of
which we used the only data from VATT, you can see that the magnitude
errors in Fig. 3(e) are as large as, or larger than, those in Fig. 3(d), which
seems reasonable.
In our 2004 observation results, lightcurve of (832) Karin (Fig. 3(d))
looks different from what we saw a year before (Fig. 3(a)). This is reason-
able because the relative orbital configuration of (832) Karin and the Earth
is different from our 2003 observation. A remarkable fact of this observa-
tion is that we no longer saw a particularly “red” surface on this asteroid.
∼
