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SIM GRID

SIM GRID. What is the Grid?. A regularly spaced set of ~12 mag stars that cover the whole sky, along with 25~50 QSO’s that form a reference frame for SIM global and narrow angle observations. Grid stars: Moderately bright (12 mag) ~1300 stars in a regular grid pattern

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SIM GRID

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  1. SIM GRID

  2. What is the Grid? • A regularly spaced set of ~12 mag stars that cover the whole sky, along with 25~50 QSO’s that form a reference frame for SIM global and narrow angle observations. • Grid stars: Moderately bright (12 mag) ~1300 stars in a regular grid pattern • K giants were chosen because they are intrinsically bright, hence distant, 1~2 Kpc • At such a distance jovian planets would in general would produce non-linear motions over 5 years < 4 uas.

  3. Follow up Status

  4. Grid Observartion Plans • CCD imaging (multiband) to identify potential K giants • Follow up with low resolution spectroscopy for confirmation Generate several candidate K Giants per grid location. • Final selection based on large RV survey of K giant candidates • RV survey RFP (request for proposals in the works) • Use ~3 RV measurements to elminate K Giant candidates • Cut off ~50m/sec • Grid star RV program will hopefully start in fy 03 continue for ~ 5 years • QSO’s in the grid will be selected by a sub-team of the SIM science team. Two key projects (Johnston, Werhle) have QSO’s in their observing lists. These two key projects are tasked to pick the 25~50 QSO’s that will be observed as part of the Grid. • Observation of the Grid QSO’s will not be charged against the key project teams.

  5. Planets in the SIM Grid Joe Catanzarite Caltech Interferometry Science Center 26 February 2002

  6. Overview • We present new results from Monte Carlo simulations quantifying the expected contamination of the SIM grid† with planetary companions • We have considered cases of an absolute Brown Dwarf Desert, as well as a Brown Dwarf Oasis at long periods. • Dropout rate due to planetary companions is < 1.5%, or 6.3% combined with stellar companions. • With acceleration fit, the total companion contamination rate drops to < 2.5% • Preliminary simulation results from Ray Swartz indicate that the grid is robust against dropout rates below 6% † K giants at 2 kiloparsecs

  7. What We Know About Planetary Companions to Solar-type Stars • 3% of G stars have planets with 0.3 < log[period(days)] < 3.6 and 3 < log[mass(Suns)] < 2 • Brown Dwarf Desert: there are very few planets of more than 10 Jupiter masses out to a few AU

  8. Extrapolating the Planetary Companion Distribution for Solar-type Stars • Assume planet population with 0.3 < log[ period(days) ] < 5 and –6 < log[ mass(Suns) ] < –1 • Assume distribution is uniform in both log(M) and log(P) [cf. Tabachnik & Tremaine 2001] • Fraction of stars with planets follows: • Absolute Brown Dwarf desert – there are no planets beyond 3 AU: (18.8 dex2 )(3% per 3.3 dex2) ~ 17% • Brown Dwarf Oasis – planets with M > 10 MJupiter orbit beyond 3 AU: (20.8 dex2 )(3% per 3.3 dex2) ~ 19%

  9. Planetary Companions to SIM Grid Stars

  10. Simulation Parameters • Pre-mission radial-velocity screening • survey precision 50 m/s • 5 year duration, 3 epochs per star • fit to constant velocity model • detection threshold at reduced 2 = 2 • Astrometric detection by SIM • 5 year duration, 25 epochs per star • astrometric signal  RMS residual in fit to model with position and proper motion • threshold set to 3 as, as grid must be accurate to 4 as

  11. A Peek at the Problem Planets • If Brown Dwarf Desert is absolute, planets surviving the RV survey whose astrometric jitter is detectable by SIM have periods between 1.4 and 22 years and masses between 2.5 and 10 Jupiters. • Almost all of this population is within detection limits of current RV surveys and thus has already been characterized statistically. • Even with a Brown Dwarf Oasis, half the SIM-detectable planets are from the known population. • The problem planets are for the most part not in the long-period regime, so their jitter cannot be fitted out with an acceleration term.

  12. Results: RV-Screened Final Grid Sample

  13. Conclusion and Future Work • A radial velocity survey at 50 m/s precision eliminates most stars with planetary companions detectable by SIM • Fewer than 1.5% of the stars in an RV-screened grid show SIM-detectable reflex motion due to planetary companions • Total dropout rate for stellar and planetary companions is 6.3% • With acceleration fit, the total companion contamination rate drops to < 2.5% • Preliminary simulation results from Ray Swartz indicate that the grid is robust against losses of < 6% • Future Work • Include effects of parallax and eccentricity • Obtain results for 10 year SIM mission • Confirm results of Ray’s SIM grid simulations

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