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Subject
- nebulae[remove]100
- photometry31
- h ii regions20
- infrared photometry19
- spectroscopy16
- interstellar medium15
- magellanic clouds12
- molecular clouds11
- optical astronomy11
- infrared astronomy10
- infrared sources10
- young stellar objects10
- open star clusters8
- radio astronomy8
- x-ray sources8
- stellar spectral types7
- pre-main sequence stars6
- radial velocity6
- stellar associations6
- surveys6
