Observing

 

SAMI uses plug plates which consist of a steel plate (~30cm diameter) in which holes are drilled for each object to be observed in a given field (typically 2 fields can be drilled on the same plate). These plates must be manufactured at the AAT 6 weeks ahead of the observing run. Astronomers must have their plate configuration files for drilling the plates ready more than 6 weeks ahead of the observing time. 

Other steps in preparation for an observing run include preparing guide star and standard star lists (which may be needed for configuring the plates if one hexabudles is used to point to a secondary standard), preparing a detailed observing plan, and filling in the visitor booking form. 

Plate plugging can only be done by a trained plate plugger on the SAMI pluggers list (contact Julia Bryant for details; jbryant@aao.gov.au or jbryant@sydney.edu.au).  

Science target constraints: The minimum separation between two science targets in 1 field pointing is 229 arcsec. Therefore the hexabundles cannot be butted together to make a larger IFU.  Typically, the science target list should contain more than 13 objects per field so that objects which may not be able to be tiled due to collisions with each other or standard/guide stars can be removed during the configuration process.

Guide stars: Ideally 3 guide stars will need to be provided for each field, however it is possible to guide on just 1 guide star. In order to be bright enough to guide on through the polymer bundles, the brightness should be 9 < g < 14.5, with suggested colours of 0.5 < (g - r) or (r - i) < 2.0 and proper motions below 15 mas/yr. 

Standard stars: Primary standard stars can be observed through 1 of the hexabundles on any plate and hence a separate plate is not required to be drilled for primary standard stars. Typically 1 or 2 standard stars are observed in 1 or 2 hexabundles twice per night.  A secondary standard star can be observed in one of the hexabundles simultaneously with 12 science targets. As some guidance to standard star selection, the SAMI Galaxy Survey selects spectrophotometric standards which are chosen from SDSS imaging to be similar in colour to an F-star (to give a spectrum which is smooth near the telluric features), based on the equation

([(u - g) ? 0.82]^2 + [(g ? r) ? 0.30]^2+ [(r ? i) ? 0.09]^2 + [(i ? z) ? 0.02]^2)^0.5 < X

where colour values, X, are prioritised based on the table below for given psf r-band magnitudes. Higher priority stars should be used first.

Priority rpsf X
     
8 <= 17.25 <0.08
7 <= 17.25 0.08<X<0.16
5 17.25 < rpsf <=17.5 <0.16
4 17.5 < rpsf <=17.75 <0.16
3  <=17.25 0.16<=X<0.2
2 17.25 < rpsf <=17.5 <0.2
1 17.5 < rpsf <=17.75 <0.2