Summary of the SIM EPICS/Marcy Webpage

The SIM EPICS/Marcy target list Webpage is designed to be of use to SIM team members working on the 2 SIM Planet Search projects (Teams A & B). The primary focus is on the Tier 1 targets stars. This is a list of stars to be observed by SIM with the highest astrometric precision. Based on preliminary observatoins and considerations of the detectability of planets around each of these Target stars, the membership in this list will vary before SIM's launch.

The primary list of Tier 1 Target stars can be found here. Currently clicking on a star takes you to that star's page. Here you can find: basic info, link DSS image, a text list of REF stars and a map of the Target and nearby REF stars. Currently this map shows the "Merit" for each REF star in bold. Merit is proportional to an estimated astrometric error in micro arc seconds. (So smaller is better). It is weighted to include the effects of various factors: Theta (angular distance from the primary: smaller is better), D (estimated distance to the REF star: larger is better), V (smaller =more photons is better), and BMV (B-V of the REF star is currently not accounted for).

Another measure is shown in italics. This is the failure probability, in %. This is an estimate of percent chance that a REF star will have a greater than "acceptable" astrometric error, and thus depends upon what is an "acceptable" error, eg 1 uas, 2 uas, etc. One reason for a high failure probability would that the star is so close to us (eg 200 pc) than undetectable neptune mass companions would cause noticable astrometric wobbles. Since failure probability depends on a number of factors, these numbers are certainly not fixed, and other metrics could be considered.

Possible Future Improvements

  1. One important index which is not currently included on this page is an overall measure of the configuration of reference stars. A "configuration merit function" has been worked out by Joe Catanzerite & Angelle Tanner of JPL, who call it the geometric multiplier. It is a purely geometric factor governing the alignment of the REF stars. (For example having all REF stars on one side is bad). This could be improved by also accounting for the probability that one ref star should drop out due to high jitter, and the effect that would have on the overall configuration. In this sense a slightly noisy REF star alone on one side of the Target might be more valuable than a very stable REF star with several neighbors.
  2. The list of reference stars in text format could be made to show those which have been observed.
  3. The map of REF stars could be color coded to reveal the vetting status of the star: Not observed, Observed at least once, Vetted, or Rejected.
  4. A geometric multiplier (perhaps weighted) could be calculated for each Target star and its accompanying REF stars, and this be plotted below.

Internal Page