CW Leonis
A nearby carbon star shrouded in a thick, dusty envelope.
CW Leonis, also known as IRC +10216, is a variable carbon star wrapped in a thick shell of dust. It was first spotted in 1969 by a team led by Eric Becklin, using the 62-inch Caltech Infrared Telescope at Mount Wilson Observatory. The star radiates most of its energy in the infrared, and at a wavelength of 5 μm, it was recorded as having the highest flux of any object beyond the Solar System.
The star is thought to be in a late evolutionary stage, shedding its sooty outer layers as it heads toward becoming a white dwarf. Based on magnesium isotope ratios, its initial mass is estimated at 3 to 5 times that of the Sun, while its core—and eventual white dwarf mass—is about 0.7 to 0.9 solar masses. Its bolometric brightness fluctuates over a 649-day pulsation cycle, ranging from a minimum of roughly 6,250 times the Sun’s luminosity to a peak of about 15,800 times, with an average output around 11,300 L☉. The star’s brightness varies by about two magnitudes over this period, and it may have been brightening over several years; one study noted a mean increase of roughly one magnitude between 2004 and 2014. Because of its extremely red color, most observations are done at infrared wavelengths, and published visual magnitudes are rare and often inconsistent. The 2006 Guide Star Catalog lists an apparent visual magnitude of 19.23, while the ASAS-SN catalog (2014–2018) reports a mean magnitude of 17.56 with an amplitude of 0.68 magnitudes. A later study gives a mean magnitude of 14.5 and an amplitude of 2.0 magnitudes.
The carbon-rich gas envelope around CW Leonis is at least 69,000 years old, and the star is losing about 1 to 4 × 10⁻⁵ solar masses per year. The extended envelope contains at least 1.4 solar masses of material. Speckle observations from 1999 reveal a complex structure with partial arcs and unfinished shells, possibly caused by a magnetic cycle similar to the Sun’s solar cycle, leading to periodic increases in mass loss. About 50 molecules have been detected in the star’s outflows, including nitrogen, oxygen, water, silicon, and iron. One early theory suggested the star was once surrounded by comets that melted as it expanded, but water is now understood to form naturally in the atmospheres of all carbon stars.
If the star’s distance is at the lower end of its estimated range—120 parsecs—its astrosphere spans a radius of about 84,000 AU. CW Leonis an
- type
- Variable carbon star
- discovery_year
- 1969
- discoverers
- Eric Becklin and group
- distance_estimate
- 120 pc (lower end)
- luminosity
- 11,300 L☉ (best representation)
- pulsation_period
- 649 days
- mass_loss_rate
- (1–4) × 10⁻⁵ solar masses per year
Lore & Background
CW Leonis is believed to be in a late stage of its life, blowing off its own sooty atmosphere to form a white dwarf. Based on isotope ratios of magnesium, its initial mass has been constrained to lie between 3–5 solar masses, while the core mass and final white dwarf mass are about 0.7–0.9 solar masses. Its bolometric luminosity varies over a 649-day pulsation cycle, ranging from about 6,250 times the Sun's luminosity at minimum to around 15,800 times at peak, with a best-representation luminosity of 11,300 L☉. The star's brightness varies by about two magnitudes over its pulsation period and may have been increasing over a period of years; one study found an increase in mean brightness of about a magnitude between 2004 and 2014.
Reader's Guide
CW Leonis is significant as one of the most studied carbon stars due to its proximity and extreme infrared brightness. Its thick, carbon-rich envelope—at least 69,000 years old and containing at least 1.4 solar masses of material—provides a natural laboratory for studying stellar mass loss, dust formation, and chemical enrichment. Speckle observations from 1999 reveal a complex structure of partial arcs and unfinished shells, possibly driven by a magnetic cycle analogous to the solar cycle. The detection of about 50 molecules, including water, nitrogen, oxygen, silicon, and iron, has challenged earlier theories about water formation in carbon stars. Its high space velocity (over 91 km/s through the interstellar medium) and astrometric measurements suggesting a close binary companion make it a key object for understanding late stellar evolution and the dynamics of evolved stars in the Milky Way.
Did You Know?
- CW Leonis was discovered in 1969 using the 62-inch Caltech Infrared Telescope at Mount Wilson Observatory.
- At a wavelength of 5 μm, it has the highest flux of any object outside the Solar System.
- Its carbon-rich envelope is at least 69,000 years old and contains at least 1.4 solar masses of material.
- Astrometric measurements suggest CW Leonis may have a close binary companion and is the closest carbon star to Earth.
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