Humason 2-1 (Hu 2-1) is a bipolar planetary nebula with an elongated shape. This nebula has a radius of ~4.5 pc and was discovered by astronomer Milton Lassel Humason on June 23, 1992 at the Mount Wilson Observatory in California.
Humason 2-1 has a angular radius of ~0.4, which corresponds to a liner radius of ~4.5 10-3 pc if the distance of Hu 2-1 is 2.35 kpc.The expansion velocity of Hu 2-1 is approximately 10-15 km s⁻¹, this gave a electron density of ~10⁴ cm⁻³. Hu 2-1 has a rather high 5-GHz temperature of ~3455 K. The structure of Hu 2-1 is revealed by VLA radio continuum observations, which displays an elongated shape with a major axis oriented at position angle (PA) of ~320° and ~230°. A small ring close to the central star with a major axis of ~0.7" long and a PA of 135° was discovered.
The central star Central star of Hu 2-1 has a temperature of ~25-40 10³ K and a luminosity of , placing it at the beginning of the PNe evolutionary track on the H–R diagram. The axisymmetric structure of Hu 2-1 is caused by the interaction of a binary companion with the primary stars envelope during the common envelope (CE) evolution. The moderate density between the equatorial and polar reigons indicate the progenitor star evolved to a late AGB stage before entering the CE phase.
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