TPF-I SWG Report - Exoplanet Exploration Program - NASA
TPF-I SWG Report - Exoplanet Exploration Program - NASA
TPF-I SWG Report - Exoplanet Exploration Program - NASA
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C HAPTER 2<br />
Lines of constant<br />
stellar type<br />
30.00<br />
Diameter of circle<br />
proportional to intrinsic<br />
diameter of star<br />
25.00<br />
F0<br />
Distance / pc<br />
20.00<br />
15.00<br />
G0<br />
F9<br />
10.00<br />
G9<br />
K0<br />
5.00<br />
K9<br />
M0<br />
0.00<br />
0 50 100 150 200<br />
Projected IHZ / mas<br />
Figure 2-7. Candidate targets for <strong>TPF</strong>-I. Each of the 1014 candidate stars is represented by a<br />
circle with a diameter proportional to the diameter of the star (intrinsic, not angular diameter).<br />
Curves show loci of a given spectral type.<br />
Beyond the distance criterion, at this early phase it is desirable to keep the number of culling criteria as<br />
small as possible. The scientific target stars can be summarized quite simply: bright, nearby, solar-like,<br />
main-sequence stars for which a binary companion is not too close. This statement translates in<br />
straightforward fashion to the detailed technical requirements listed in Table 2-3.<br />
The final column in this table gives the number of potential target stars remaining after the set of culls<br />
down to a given line has been applied. Even after all applicable science culls have been applied, over<br />
1000 suitable targets remain. These 1014 stars are plotted in Fig. 2-7 on a space of stellar distance vs.<br />
projected inner habitable zones size, from which it can be seen, e.g., that for a sizable candidate<br />
population of stars to be observable, an inner working angle of 50 milliarcsecond (mas) or smaller is<br />
needed. The final candidate list of 1014 stars was used to predict the performance of different <strong>TPF</strong>-I<br />
architectures.<br />
2.5.2 Engineering Criteria<br />
Next one also needs to include instrumental or engineering constraints which can eliminate certain classes<br />
of stars. With the current baseline design of <strong>TPF</strong>-I, these fall into two categories. First, sunshade<br />
constraints limit observations to stars within 45° of the ecliptic. Second, control of stray light implies that<br />
any bright companion stars must be more than 10 arcsec away from the target star of interest. As<br />
Table 2-2 shows, this eliminates about 40% of the scientifically interesting stars.<br />
24
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