KI Nulling Data Products

In the Nuller mode the main science data measurement is the coherent null leakage, approximately equal to one minus 1/2 of the visibility amplitude squared for a given source. Integrations on the target source and calibrators are interleaved in time. Each integration includes all local (detector, background) calibrations.

As with the V² mode, the NExScI will reduce the raw data and provide average null values (Level 1 data) in a set of files available through the KI database as either ASCII or FITS files. The NExScI will also provide the programs necessary to calibrate the Level 1 data for the system response. After this calibration, the data are ready for astrophysical modeling and interpretation.

Level 1 Nulling files

filename	contents
YYYYDDD.nullsum	Wide-band nulling data
YYYYDDD.nullspec	Spectrometer nulling data
YYYYDDD.nullbaseline	A priori baseline model
YYYYDDD.nullinfo	Reduction configuration info, etc.
YYYYDDD.nullanc	Ancillary data
YYYYDDD.nulllog	Observer log
YYYYDDD.nullrpt	Nightly report
YYYYDDD.nullcat	Source catalog file

In addition to the Nulling files, during Nulling observing a set of L1 files is produced that correspond to the near-infrared fringe tracker (needed to stabilize the fringes on the Nuller camera). We call this the "NIRV2-Null" mode, and those L1 files can also be downloaded from the KI archive. The format of the files is identical to those obtained during standard V2 operations ( NIRV2 mode).

There are two sets of NIRV2-Null files for each Nulling night, corresponding to each of the two Keck-Keck baselines formed between halves of the Keck telescopes (as described in Colavita et al 2008). The two baselines are often termed "primary" and "secondary". In our database, the L1 files for the primary baseline have the suffixes .sum, .spec etc; while the files for the secondary baseline have the suffixes .sum2, .spec2, etc.

The two sets of NIRV2-Null L1 files are in principle equivalent, and users are encouraged to form an average of the L1 data from both sets.

However, differences in the fringe tracker servo between standard V2 and Nulling make the wideband pixel NIRV2-Null data unusable for science. Therefore users are asked to ONLY use NIRV2-Null spectrometer data for science purposes.

Level 2 Nulling files

Last updated: 31 July 2009