Wednesday, 1 July 2015

Deep Sky column 5/2015: Dwarfs and Giants

Summer and non-deep sky oriented column due to midnight sun.

Massive star: LBV candidate Cyg OB2 #12 (HIP 101364). 11.4 magnitude star with ~110 M☉ and bolometric magnitude ~10.9. Dwarfed by R136a1 (~256 solar masses) in NGC 2070 (LMC - Dorado).

A star close to us: Lalande 21185 in Ursa Major. The star is only 8,3 light years away. At magnitude 7.5 is it also a naked eye object under excellent conditions. Absolute magnitude is quite faint: ~10.5.

Tiny star: Barnard's star. Closer to us than Lalande 21185 but a lot smaller: 0.14 M☉and with an absolute magnitude of only 13,2. The star has only 150 times more mass the Jupiter. Moves 10" in the sky per year - that's 90 km/s. Not discovered by E. E. Barnard.

Far far away: 6th magnitude Rho Cassiopeia. Distance estimates vary greatly: between 6000 and 16 000 light years. Commonly referred as the most distant (single) star visible to the naked eye. Radius is at least 400 R☉ then again dwarfed by UY Scuti (~1700 solar radii). Another distant star to the naked eye: V762 Cas, possibly even 15 000 light years away.