Subject
- novae3
- o stars3
- ob stars6
- observational astronomy34
- open star clusters20
- optical astronomy521
- optical observation13
- peculiar variable stars2
- photographic magnitude10
- photographic photometry11
- photometry870
- photometry, sdss1
- planetary nebulae11
- polarimetry22
- population ii stars5
- pre-main sequence stars13
- proper motions93
- protostars1
- pulsars18
- qsos1