HSC basic information

HSC (Hyper Suprime-Cam) is a prime focus camera mounted on Subaru telescope. It uses 104 main science CCDs, which covers 1.8 deg FoV in diameter. This page shows the information of HSC CCD, filters, raw data naming rule, and the amount of data. Please refer Subaru Telescope - HSC for more information.


HSC CCDs

HSC has total 116 CCDs; 104 for science use, 8 for auto focus, and 4 for auto guider. The CCD data except 4 auto guider CCDs are output as raw data. The specific ID used for raw data of each CCD is SDO-ID in figure 1. DET-ID in the figure is used in hscPipe processing. The naming rule of raw data is described in Naming rules of raw data.

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Figure 1：CCD arrangement (excerpting from HSC page on the Subaru telescope web site)

Figure 2 shows the structure of each CCD. One CCD consists of 4 CHs and each has 536 x 4241 pixels, then total 2144 x 4241 pixels (in the raw data format). Each CH has also overscan, blank, and non-science use regions. After detrending, the size of 1 CCD becomes 2048 x 4176 pixels.

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Figure 2：Format of 1 CCD


HSC filters

The information of five Broad-band (g-, r2-, i2-, z-, y-band) and 11 Narrow-band filters (NB387, NB468, NB515, NB527, NB656, NB718, NB816, NB921, NB926, IB945, NB973) is publicly available. The latest information can be chacked here Figure 3 shows filter transmission characteristics.

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Figure 3：The transmission curves of in-service filters (excerpting from HSC page on the Subaru telescope web site)


Naming rules of raw data

The format of observed raw data is HSC+[A,B,C,...]+%6d+%2d.fits. Now we use HSCAxxxxxxxx.fits, but it will be HSCB, HSCC, and so on in the future. The next ‘%6d’ indicates the shot number (in hscPipe it is called “visit”) and ‘%2d’ CCD discrimination number. For the shot number, the continuous even and odd number are assigned. For example, both HSCA018200xx.fits and HSCA018201xx.fits are the data of one shot. CCD discrimination number is 00 to 57.

CCDs colored in cyan and purple in figure 1 denote CCDs with even and odd ‘%6d’ shot names, respectively. The double-digit number after under-bar on each CCD stands for a CCD discrimination number of raw data.

For instance, if you find a raw data named HSCA02234904.fits, its shot number (=visit) should be 22348, CCD discrimination number 04 (1_04 in figure 1), and CCD ID used in hscPipe processing 34.


Data amount

One pixel of HSC raw data can store 16 bit integer, then 1 CCD has ~18MB. The total number of CCD is 112, so the total amount of raw data in 1 shot becomes ~2GB. After hscPipe processing, each pixel has 32-bit data as well as a 32-bit image and a 16-bit flag image. Finally, one pixel of the reduced image stores 80 bit. The following table shows the data amount in each step.

Data amount
1 CCD of raw data 18 MB
1 shot of raw data 2 GB (112 CCDs)
1 CCD of reduced data 82 MB
1 shot of reduced data 11 GB (104 CCDs)
1 CCD’s catalog ~10MB - 30MB
1 shot’s catalog 1-2 GB
1 CCD（raw + reduced + catalog) 100 MB
1 shot（raw + reduced + catalog) 13 GB

If you took 100 shots per one object, the final size of data would be over 1 TB.