Humason 2-1
Bipolar planetary nebula discovered by Milton Lassel Humason in 1992.
Humason 2-1 (Hu 2-1) is a bipolar planetary nebula with an elongated shape, first spotted by astronomer Milton Lassel Humason on June 23, 1992, from the Mount Wilson Observatory in California. The nebula has a radius of about 4.5 parsecs and an angular radius of roughly 0.4 arcseconds, which translates to a linear radius of about 4.5 × 10⁻³ parsecs if its distance is 2.35 kiloparsecs. Its expansion velocity falls between 10 and 15 kilometers per second, and the electron density is around 10⁴ particles per cubic centimeter. The nebula has a notably high 5-gigahertz temperature of approximately 3455 Kelvin. VLA radio continuum observations reveal its structure as elongated, with a major axis oriented at position angles of roughly 320° and 230°. A small ring near the central star has a major axis about 0.7 arcseconds long and a position angle of 135°.
The central star of Hu 2-1 has a temperature between 25,000 and 40,000 Kelvin and a luminosity of about 11,500 times that of the Sun, placing it at the beginning of the planetary nebula evolutionary track on the Hertzsprung-Russell diagram. The nebula’s axisymmetric shape results from the interaction of a binary companion with the primary star’s envelope during common envelope evolution. The moderate density difference between the equatorial and polar regions suggests the progenitor star had evolved to a late asymptotic giant branch stage before entering the common envelope phase.
- Radius
- ~4.5 pc
- Angular radius
- ~0.4 arcsec
- Linear radius
- ~4.5 × 10⁻³ pc (at distance 2.35 kpc)
- Distance
- 2.35 kpc
- Expansion velocity
- 10–15 km s⁻¹
- Electron density
- ~10⁴ cm⁻³
- 5 ghz temperature
- ~3455 K
- Central star temperature
- 25–40 × 10³ K
- Central star luminosity
- ~11.5 × 10³ L☉
Lore & Background
Humason 2-1 was discovered on June 23, 1992 by Milton Lassel Humason at the Mount Wilson Observatory in California. The nebula has a radius of approximately 4.5 pc and an angular radius of about 0.4 arcsec, which corresponds to a linear radius of roughly 4.5 × 10⁻³ pc assuming a distance of 2.35 kpc. Its expansion velocity is estimated at 10–15 km s⁻¹, and it possesses an electron density of about 10⁴ cm⁻³. VLA radio continuum observations reveal an elongated shape with a major axis oriented at position angles of approximately 320° and 230°, and a small ring near the central star with a major axis of about 0.7 arcsec and a position angle of 135°.
Reader's Guide
Humason 2-1 is significant as a bipolar planetary nebula whose structure is shaped by binary interaction during common envelope evolution. The central star, with a temperature of 25–40 × 10³ K and a luminosity of about 11.5 × 10³ L☉, is placed at the beginning of the planetary nebula evolutionary track on the Hertzsprung–Russell diagram. The moderate density contrast between equatorial and polar regions indicates that the progenitor star had evolved to a late asymptotic giant branch stage before entering the common envelope phase. The nebula's rather high 5-GHz temperature of approximately 3455 K and its detailed radio morphology from VLA observations provide constraints on the physical conditions and evolutionary history of this object. Its discovery by Milton Lassel Humason at Mount Wilson Observatory adds to the catalog of planetary nebulae studied in the late 20th century.
Did You Know?
- Humason 2-1 was discovered by Milton Lassel Humason on June 23, 1992 at Mount Wilson Observatory.
- The nebula has a bipolar shape with an elongated structure revealed by VLA radio observations.
- Its central star has a temperature of 25–40 × 10³ K and a luminosity of ~11.5 × 10³ L☉.
- The axisymmetric structure is caused by binary interaction during common envelope evolution.
Frequently Asked Questions
What is Humason 2-1?
Humason 2-1 (abbreviated Hu 2-1) is a bipolar planetary nebula distinguished by its elongated, two-lobed morphology. It sits at an estimated distance of roughly 2.35 kiloparsecs from Earth.
Who discovered Humason 2-1 and when?
Astronomer Milton Lassel Humason first identified the object on June 23, 1992, while conducting observations at the Mount Wilson Observatory in California. The nebula was subsequently catalogued under his name and the designation Hu 2-1.
What are the key physical measurements of Humason 2-1?
The nebula shows an angular radius of about 0.4 arcseconds, an expansion velocity between 10 and 15 km/s, and an electron density near 10⁴ particles per cubic centimeter. At the stated 2.35-kpc distance, its linear radius works out to approximately 4.5 × 10⁻³ parsecs.
What makes Humason 2-1's shape distinctive compared to other planetary nebulae?
Its bipolar geometry produces a stretched, elongated profile rather than the rounder or elliptical outlines typical of many other planetary nebulae. This two-lobed structure generally reflects collimated outflows shaped by the central star's rotation axis or a binary companion.
How far is Humason 2-1 from Earth, and how big does it appear?
At roughly 2.35 kiloparsecs, the nebula subtends only about 0.4 arcseconds of angular radius, making it a challenging target for small telescopes. Its physical size at that distance corresponds to a linear radius on the order of a few thousandths of a parsec.
More in Planetary Nebulae 1-24
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