EFOSC2 quick reductions for acquisition images to ID target

Common problem is identifying the target in an acquisition image.

The coordinates in the marshall from the major surveys such as Gaia, Pan-STARRS and ATLAS are all

good to better than about 1" (Gaia much better of course, and the other two are Gaia based). Because of

its large pixels, ASASSN can return coords which are a few arcsec out, but normally they are also good to 1-2".

A rapid astrometric calibration of EFOSC2 can give you the target unambiguously. Here's a run through :

Run the pipeline task PESSTOEFOSCPHOT

/Users/sjs/data/pessto/2018May>PESSTOEFOSCPHOT EFOSC.2018-05-05T01_42_19.980.

Will produce a file called something like 'OTHER_20180504_V641_58243_1.fits'

Open in ds9

    • click Scale and zscale to automatically set the grey scale levels to reasonably sensible values

    • Go to Zoom, then Align which will align N up and E to left

  • Make sure you have Region selected ( check this with ... Edit and then Region)

  • Click anywhere on image, and a green circle should appear

  • Double click on the green circle and the coord box will pop up :

Put in the coords to align the circle to the astrometric position. Normally this will be right on your target, if the astrometric

calibration has worked in PESSTOEFOSCPHOT.

If you are still not sure then if the target is above dec = -30 degrees, get a Pan-STARRS image to check what is

different in EFOSC2 acquisition image and the Pan-STARRS archive image.

Set the image size to 984 pixels, so you get exactly 4.1 arcmins to match EFOSC2 finder - and g is closest to EFOSC2 V band filter image

Download this FITS image

Now also load that up into ds9 - and align the two with Frame -> Match -> Frame -> WCS

Should now be obvious which object is your target . For example, PS1 on left and EFOSC2 on right here :

If the target is below dec = -30 then use the DSS in ds9 to get an image to check

Go to Analysis -> Image Servers and ESO DS1/II (or any others) and then put in the coords and 4.1 arcmin to match EFOSC2 field of view.

Do the WCS alignment again to get the two images astrometrically aligned.