Do we need the temperature? Might be worth keeping.
For groups of stars - binaries and the like - we need the base data required to construct orbital elements in case they become important. Ideally this will be consistent with at least the well known binary system parameters. For that I will need a binary or variable star catalog with the appropriate cross-identifications. And all of this needs to be compactly encoded.
- Using bit fields, 16 bits will be plenty for the "classic" spectral type including interesting features
- Real (4 bytes in Derby) will be plenty of precision for floating point numbers.
- Integer (4 bytes) will be plenty for "object IDs"