Geoscience Reference
In-Depth Information
sampling rate and sampling phase, namely, the (random) start point
of each sampling, are the last two things to be considered before an
ensemble of (normalized) light curves can be derived.
The ensemble of normalized light curves will be integrated with some simu-
lated light curves at a given flux where various kinds of noise can be added
for further analysis. Photometry is the major part of the data pipeline. A
preliminary photometric algorithm can be used for testing.
A few concrete examples should be helpful in understanding some of the
steps above. The importance of the star level can be understood through
Table 1. The limiting magnitude is around 14 in a typical TAOS zipper
mode image. It is obvious that the angular size of a TAOS target star could
be compatible with a comet-size TNO itself. Another interesting feature is
that Fresnel diffraction could dominate a TAOS event. Suppose a TNO is
at a distance (
d
) of 50 AU. The related occultation is observed at a wave-
length (
λ
) of 500 nm. The size of a TNO (
s
) will satisfy
s
2
/λd
1if
s
is around 1 km. The code should be able to handle something like Fresnel
integrals rather than just a Fourier transformation. A diffraction code was
developed. It is now part of this simulator. Given all proper input param-
eters, a diffraction pattern and a CCD response at a certain sampling rate
with various sampling phase can be derived as illustrated in Fig. 4. Only
spherical TNOs of comet-size at trans-Neptunian distance are considered
∼
Table 1. Colors, magnitude, temperatures, and radius of normal stars are shown. The
projection of a stellar disk at 50 AU is estimated for various apparent magnitudes (
m
V
)
around 10-14. These are typical magnitudes of target stars in a TAOS zipper mode image.
Some of these stellar disks are similar to a comet-size TNO in their angular sizes.
R
(km) at 50 AU
S
p
M
V
T
eff
R/R
m
V
10
11
12
13
14
O5V
−
5
.
7
42,000
12
0.15
0.09
0.06
0.04
0.02
A0V
+0
.
65
9,790
2.4
0.55
0.35
0.22
0.14
0.09
F5V
+3
.
5
6,650
1.3
1.10
0.69
0.44
0.28
0.17
K0V
+5
.
9
5,150
0.85
2.17
1.37
0.86
0.55
0.34
K5V
+7
.
35
4,410
0.72
3.58
2.26
1.43
0.90
0.57
M0V
+8
.
8
3,840
0.60
5.83
3.68
2.32
1.46
0.92
M5V
+12
.
3
3,170
0.27
13.14
8.29
5.23
3.30
2.08
K0III
+0
.
7
4,660
15
3.49
2.20
1.39
0.88
0.55
K5III
−
0
.
2
4,050
25
3.85
2.43
1.53
0.97
0.61
M0III
−
0
.
4
3,690
40
5.61
3.54
2.23
1.41
0.89
Source
: Allen's Astrophysical Quantities, 4th Edition, ed. Cox, A. N. (Springer-Verlag,
New York, 2000).
