Frequently Asked Questions

From where can I get accurate coordinates?

Very accurate coordinates are available from the UCAC2 catalog (Zacharias et al. 2004). You can setup you skycat tool to query around the target. The search radius in case of Sinfoni would be 2 to 7.4 arcminutes for telescope guide stars (11 to 13.5 magnitudes in R) and 0.0 to 0.5 arcminutes for AO natural guide stars.

include in .skycat/skycat.cfg:

serv_type:      catalog
long_name:      UCAC2_wgsarc
short_name:     UCAC2_wgsarc
url:            http://archive.eso.org:8080/skycat/servers/ucac2?c=%ra%dec&r=%r1,%r2&f=8
symbol:         Jmag {circle {} {} {} {} {}} {{18-$Jmag} {}}
sort_order:     increasing
copyright:      USNO

More on skycat setup for 2MASS, GSC2 and DSS2:

The 2MASS catalog (Cutri et al. 2003) can be read from skycat as well:

include in .skycat/skycat.cfg:

serv_type:      catalog
long_name:      2MASS catalog
short_name:     2MASS@CDS
url:            http://vizier.u-strasbg.fr/viz-bin/asu-acl?-source=II/246&-c.ra=%ra&-c.dec=%dec&-c.rm=%r2&-out.max=%n
symbol:         Jmag {circle red {} {} {} {$Jmag > 0.}} {{(25-$Jmag)/2.} {}}
copyright:      2MASS: IPAC,UMASS,NASA,Caltech on-line at CDS

Once you started to update the skycat configuration you may want to include also GSC-2 and DSS-2 (the later doesn't cover the full sky):

include in .skycat/skycat.cfg:

serv_type:      catalog
long_name:      GSC-2 at ESO
short_name:     gsc2@eso
url:            http://archive.eso.org/skycat/servers/gsc2query?ra=%ra&dec=%dec&r2=%r2&%cond
symbol:         Fmag {square {} {} {} {} {$Fmag > 0.}} {{(23-$Fmag)/3000} {deg 2000}} 
search_cols:    m1 Jmag(Brightest) : m2 Jmag(Faintest)

serv_type:      imagesvr
long_name:      DSS2 Blue (45%)
short_name:     dss2b@eso
url:            http://archive.eso.org/dss/dss?ra=%ra&dec=%dec&mime-type=%mime-type&x=%w&y=%h&Sky-Survey=DSS2-blue
copyright:      Digitized Sky Survey (c) by AURA, provided online by ESO

serv_type:      imagesvr
long_name:      DSS2 IR  (27%)
short_name:     dss2ir@eso
url:            http://archive.eso.org/dss/dss?ra=%ra&dec=%dec&mime-type=%mime-type&x=%w&y=%h&Sky-Survey=DSS2-ir
copyright:      Digitized Sky Survey (c) by AURA, provided online by ESO

serv_type:      imagesvr
long_name:      DSS2 Red (98%)
short_name:     dss2r@eso
url:            http://archive.eso.org/dss/dss?ra=%ra&dec=%dec&mime-type=%mime-type&x=%w&y=%h&Sky-Survey=DSS2-red
copyright:      Digitized Sky Survey (c) by AURA, provided online by ESO

How can I align and coadd stacks of image cubes taken in different nights or OBs?

There are no acquisition images of targets (or reference stars for blind offsets) stored on disk with SINFONI. For observations of very faint objects it may not be possible to see the target within the execution time of an observation block (OB) and the relative position of the target in jittered image cubes will be only known from the fits headers of the files:

SEQ CUMOFFSETX  =    -0.000000 
SEQ CUMOFFSETY  =    -0.000000 

The cummulated offsets are defined from the original position where the target was centered during the target acquisition. If the target acquisition was repeated (like in one of the next nights) then the cummulated offsets may not be accurate enough to combine the different stacks of image cubes. The observation and data reduction strategy can be improved in the following way:

For closed loop (NGS) observations:

An accurate reference for closed loop observation is the position of the field selector mirror which can be read from the fits header of the SINFONI files :

INS1 FSEL1 ALPHA=     0.000000 
INS1 FSEL1 DELTA=     0.000000 

Alternatively an image of the natural guide star (NGS) can be taken with template SINFONI_ifs_cal_NGS which will offset the telescope to the NGS and center the field selector mirror:

SINFONI_ifs_acq_NGS    
SINFONI_ifs_cal_NGS    (optional)     
SINFONI_ifs_obs_****    
SINFONI_ifs_cal_NGS    (optional)     
...

For open loop (noAO) observations with blind offsets to the target:

After the target acquisition and the execution of the blind offset the instrument will remain at the position of the faint target. The observing sequence of science exposures will as well end such that the instrument points to the faint science target (return to origin by default). The best way to get a reference image to define the center of a stack of image cubes would be to add template SINFONI_ifs_cal_PSF with the inverse blind offset. It will then take an exposure of the bright reference star which was previously used for the blind offset. The template can be included either before or after the science exposure template:

SINFONI_ifs_acq_noAO    with offset +alpha,+delta from reference star to target
SINFONI_ifs_cal_PSF     with offset -alpha,-delta from target to reference star (optional)
SINFONI_ifs_obs_****    
SINFONI_ifs_cal_PSF     with offset -alpha,-delta from target to reference star (optional)
...