They are;
Houkago no Pleiades Original Soundtrack https://vgmdb.net/album/61595
Houkago no Pleiades Original Soundtrack "Mutsuraboshi" α https://vgmdb.net/album/52145
and
Houkago no Pleiades Original Soundtrack "Mutsuraboshi" β https://vgmdb.net/album/52146
I can find them in mp3 format, but I’m not interested in them because of the poor sound quality.
Thanks in anticipation!