Cluster Deep Field - ISAAC Observations
ISAAC Observations of the Cluster Deep Field (MS1008-12)ISAAC was used in the SW Imaging mode (pixel size=0".147, fov=2.5'x 2.5' ).
Observations were done in on-off jitter mode, alternating 1 minute on-target and 1 minute off-target in Ks band in a series of 30 exposures, and 45 sec on-target and 45 sec off-target in J band,in a series of 40 exposures.
In Ks two full series andone prematurely aborted series were obtained. In J one full and one aborted series were obtained.
Dark-frames and twilight flats were obtained at the beginning of thenight. One set of observations of standard S165-E (Ks) and S312 (J) from the list ofHST standards were also obtained.
Unfortunately, the off-target images in Ks band included heavily vignetted exposuresdue to the guide-probe being in the field of view. Off-target exposureswere therefore ignored in further processing.
Each series of on-target images were reduced using the jitter programfrom the eclipse reductionpackage. The series of 8 Ks images is unfortunately too short to doa meaningful reduction with jitter. They were therefore ignored. In thismanner we obtained two de-jittered images with an effective exposure timeof 30 minutes each in Ks, and two images of 30 and 18 minutes respectively in J band.These images were astrometrically calibrated usingstandard EIS processing tools, and co-added using the drizzling procedure.
In Ks the total exposure time of the co-added image is 60 minutes with a seeingof 0.45 arcsec.In J the total exposure time is 48 minutes, with a seeing of 0.68 arcsec.
Zeropoints were obtained from single sets of standard starobservations on each night. The zeropoint are listed in the table.The uncertainty in the magnitude of the standard is approximately 0.01mag. The uncertainty in the measured mag is approximately 0.01mag. It should be noted that the position of the standard S165 (Ks) isoffset by 2 arcsec from the listed position in the HST standardslist. Moreover the star appears as an optical double.
No correction for extinction were made. However, variation betweenimages at different airmasses, and different nights is <0.05 mag,indicating that extinction can be savely ignored and that theaforementioned zeropoint is accurate to approximately 0.05 mag.
Note that zeropoint are mags/count in the images
All the on/off target and calibration frames in J-band and Ks-band can be retrieved from the VLT Science Archive. To request files, you have to register as a VLT/NTT archive user. If you are already a registered VLT/NTT archive user you don't need to register. The links below will senda query to the VLT/NTT data archive and provide a page where theactual request can be made.
Total ExpT ZP SeeingCo-added images MS1008_J.fits 48min 28.18 0.68MS1008_Ks.fits 60min 26.15 0.45Original de-jittered images. MS1008_J_1.fits 20x1.5=30min 28.17 0.60MS1008_J_2.fits 12x1.5=18min 28.19 0.75MS1008_Ks_1.fits 15x2 =30min 26.15 0.41MS1008_Ks_2.fits 15x2 =30min 26.15 0.39