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Secondary target mask bits in SDSS-I, -II (for LEGACY_TARGET2, SEGUE1_TARGET2, SEGUE2_TARGET2, SPECIAL_TARGET2 or SECTARGET).
| Bit name | Binary digit | Description |
|---|---|---|
| LIGHT_TRAP | 0 | hole drilled for bright star, to avoid scattered light |
| REDDEN_STD | 1 | reddening standard star |
| TEST_TARGET | 2 | a test target |
| QA | 3 | quality assurance target |
| SKY | 4 | sky target |
| SPECTROPHOTO_STD | 5 | spectrophotometry standard (typically an F-star) |
| GUIDE_STAR | 6 | guide star hole |
| BUNDLE_HOLE | 7 | fiber bundle hole |
| QUALITY_HOLE | 8 | hole drilled for plate shop quality measurements |
| HOT_STD | 9 | hot standard star |
| SOUTHERN_SURVEY | 31 | a segue or southern survey target |