1. FMOS astrometry plan
Masayuki Akiyama

2. Background: Base astrometric catalogs (USNO efforts)
USNO catalogs from Precision (plate) Measuring Machine
USNO-B1.0 : 1,000,000,000 objects, 0.2” accuracy
USNO-A2.0 : 526,230,881 objects from all sky (POSS-I+SRC-J,ESO-R)
HST Guide Star Catalog, Hipparcos Tycho catalog
Typical astrometric error is 0.25”, sufficiently bright stars in good regions (in the center of each plate) 0.15”
USNO-SA2.0 : Subset of A2.0 catalog
UCAC2 (USNO CCD Astrograph Catalog 2nd data release, AJ,127, , astro-ph/ ,
20mas accuracy for R=10-14 mag stars, R=16mag limit with 70mas accuracy
Release 2 cover limited region of sky, All sky coverage (3rd release, UCAC3) will be open to public early 2008

3. Background: Base astrometric catalogs (others ?)
2MASS near-infrared All-sky Catalog of Point Sources
Down to J=15.8, 70 mas accuracy.
SDSS catalog
Down to r=20mag with 45 mas and r=22mag with 100 mas.
However, they do not have proper motions information.

4. Background: Scam astrometry results, so far
Applying linear WCS description to the SDFRED resultant images results in up to 1” systematic residual at the edge of FoVs (Furusawa et al. SXDS paper, ApJS submitted).
Astrometry check with Scam archival data by SMOKA project : ASJ/2007/Fall poster presentation by Yoshino et al. (ADAC).
3rd order astrometric conversion between Scam(X,Y,chip) -> USNO-B1.0(RA,DEC)
Typical random residual 0.2 – 0.5 arcsec in the entire field of view of Scam.
>1” systematic difference from distortion pattern shown in Miyazaki et al. (2001)
The random residual can be affected by USNO-B1.0 uncertainty. Future check with USAC2 catalog (see below..) ?
Platais et al. (2006, PASP, 118, 107) Scam ESPfield1 vs. 400 UCAC stars
rms 40 mas or better, 30 mas from UCAC catalog itself, and 20 mas from Scam modeling residual.
10s exposure shows systematic atmospheric noise up to 50mas, >30s required.

5. FMOS: Astrometric standards for FMOS engineering
Select several fields for FMOS astrometric standard fields. We need high Galactic latitude astrometric fields for engineering obs.
Further check of the Scam astrometric model. Obtain Scam short exposure data (~1s) in selected fields with many UCAC2 stars. Better astrometry in the FMOS astrometric standard fields.
For open use observations, we need some sort of astrometry check software with UCAC3 catalog (not leave observer’s own risk…like VIMOS, DEIMOS…)
Galactic plane fields with >100 UCAC2 stars in Feb.
Galactic plane fields with >100 UCAC2 stars in Aug.

6. FMOS: UCAC catalog server
Currently check through Vizier.
UCAC2 CDs are requested ( , will be delibered ).
Use FMOS OBCP backup (mfmos) as temporary server ?
Preparation in contact with Furusawa-san.

7. For example: Deep Astrometric Standards
Platais et al. (2006) PASP, 118, 107
celestial equator, cross meridian, close to Galactic equator, free of dark cloud etc.
GOT (6:00, +21:45) (187.7, -0.9) 2260 UCAC2 stars /deg2
Hya (8:49, -15:25) (241.2, +17.4) 1440 UCAC2 stars /deg2
Oph (17:44, +11:15) (35.6, +34.6) 1510 UCAC2 stars / deg2
Sgr (19:20, -20:40) (17.2, -15.3) 3720 UCAC2 stars /deg2
(NGC188 (0:44:20, +85:18.9)
Feasibility in the next Feb.