HST data set numbering

jhargisjhargis Member, Administrator, Institute_Staff, Moderator_MAST, Admin_MAST Posts: 30 admin
We have a list of our data in dataset form and need to be able to access all
raw files associated with a dataset. If the dataset ends in q or s this is
trivial as the raw file has the same root as the dataset. If the dataset
ends in 0 we can read the _asn.fits file to find the raw exposures.

However, when the dataset ends in a nonzero number, we find that there is
never an association table with the same root. There is, however, always an
assocaition table with that n>0 changed to a zero. An example is the


There is no j8v301011_asn.fits. However there is a j8v301010_asn.fits (and
no dataset j8v301010). Does this mean that all raw files for j8v301011 are
listed in j8v301010_asn.fits? Is this true no matter what the last number
of a dataset is?


  • scflemingscfleming Member, Institute_Staff, Moderator_MAST, Admin_MAST Posts: 35
    You've encountered a situation that results from a decision to reserve the trailing 0 for dither products for ACS. So, yes, the j8v301010_asn.fits association table lists all the raw files that make up product j8v301011_crj.fits. When you read the asn file (look at the end of the header), you'll see which datasets form the products.

    Do be careful; it's dangerous to assume that 010_asn.fits always describes a 011 product. There are datasets where a pattern is used to dither, and at each dither point, a CR-split was taken.
    Each pair of CR-splits will produce a product (011, 012, etc.) AND there will be dither product (010_drz.fits).

    For example, J90201010 is a dither product made up of 10 exposures. J90201011, 012, 013, 014 and 015 are CR-split products, each of which is made from 2 exposures. Below is an extract from the J90201010_asn.fits header. Look at the column labeled type. EXP is an exposure, PROD is a product. CR means CR-split and DTH means dither. You tell what exposures go with which product by looking at the trailing number of type. Exposures J90201EFQ and J90201EGQ form PROD-CR1 (J90201011), while J90201EMQ and J90201EOQ form
    PROD-CR3 (J90201013). All 10 exposures form the dither product.

    dataset type
    J90201EFQ EXP-CR1
    J90201EGQ EXP-CR1
    J90201EIQ EXP-CR2
    J90201EKQ EXP-CR2
    J90201EMQ EXP-CR3
    J90201EOQ EXP-CR3
    J90201EQQ EXP-CR4
    J90201ESQ EXP-CR4
    J90201EUQ EXP-CR5
    J90201EWQ EXP-CR5
    J90201010 PROD-DTH
    J90201011 PROD-CR1
    J90201012 PROD-CR2
    J90201013 PROD-CR3
    J90201014 PROD-CR4
    J90201015 PROD-CR5
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