R Fornacis

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R Fornacis is a Mira variable carbon star in the constellation Fornax. It sits about 1,800 light-years away and is a type of old, cool star that has expanded and now shines with a lot of carbon in its atmosphere.

The star pulsates every roughly 389 days, causing its brightness to change by several magnitudes in visible light. It ranges from about magnitude 7.5 at its brightest to around 13.0 at its faintest. On average, its maximum brightness is around 8.9 and its minimum around 12.2.

What makes R Fornacis interesting: it was found variable in 1896. In 1983 it showed an unusually deep minimum, linked to a cloud of material ejected from its surface. Infrared observations reveal unusual brightness changes, and near-infrared measurements detected a shift in the star’s apparent position relative to its surrounding dust, which could be caused by a moving dust blob or possibly a companion with a long orbit.

Key facts
- Distance: about 1,810 light-years (550 parsecs)
- Period: about 389 days
- Brightness range (visible): 7.5 to 13.0; typical maximum ~8.9 and minimum ~12.2
- Type: carbon-rich Mira variable on the asymptotic giant branch (AGB), spectral type C4,3e
- Mass, radius, and luminosity: ~1.05 solar masses, ~575 solar radii, ~5,800 solar luminosities
- Temperature and gravity: ~2,100 K; log g ~ 0.12
- Metallicity: [Fe/H] ~ +0.21 dex
- Coordinates: RA 02h 29m 15.308s, Dec −26° 05′ 55.65″
- Other names: R For, IRAS 02270−2619, 2MASS J02291531−2605559