RR Caeli is an eclipsing binary star system, located 69

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s from Earth in the constellation

Caelum Caelum is a faint constellation in the southern sky, introduced in the 1750s by Nicolas Louis de Lacaille and counted among the 88 modern constellations. Its name means "chisel" in Latin, and it was formerly known as Caelum Sculptorium ("Engrave ...

. It is made up of a

red dwarf A red dwarf is the smallest kind of star on the main sequence. Red dwarfs are by far the most common type of fusing star in the Milky Way, at least in the neighborhood of the Sun. However, due to their low luminosity, individual red dwarfs are ...

star and a

white dwarf A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...

, which complete an orbit around each other every seven hours. There is evidence of two circumbinary planets orbiting even further away.

Properties

RR Caeli was first noted to be a high-proper motion star in 1955 by Jacob Luyten, and given the designation LFT 349. This star system consists of a

of spectral type M6 and a

that orbit each other every seven hours; the former is 18% as massive as the Sun, while the latter has 44% of the Sun's mass. The red dwarf is tidally locked with the white dwarf, meaning it displays the same side to the heavier star. The system is also a post-common-envelope binary, and the red dwarf star is transferring material onto the white dwarf. In approximately 9–20 billion years, RR Caeli will likely become a cataclysmic variable star due to the period's gradual shortening, leading to increasing rates of transfer of hydrogen to the surface of the white dwarf. The white dwarf is likely to have a plain helium core, as its density is too low for the carbon-oxygen core. Discovered to be an eclipsing binary in 1979, it has a baseline magnitude of 14.36, dimming markedly every 7.2 hours for an interval of around 10 minutes, due to the total eclipse of the hotter star by the cooler one. Its variability in brightness led to its being given the variable star designation RR Caeli in 1984. There are very shallow secondary eclipses where the white dwarf transits across the red dwarf.

Planetary system

In 2012, analysis of slight variations in the observed

light curve In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis ...

of the system showed that there was likely a

giant planet A giant planet, sometimes referred to as a jovian planet (''Jove'' being another name for the Roman god Jupiter (mythology), Jupiter), is a diverse type of planet much larger than Earth. Giant planets are usually primarily composed of low-boiling ...

about four times as massive as

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

orbiting the pair of stars with a period of 11.9 years, and that there was also evidence for a second possible substellar body further out. More observations of the light curve are likely to help confirm the presence of one or both planets. A 2022 study found that at least the 2012 model fails to predict recent changes in eclipse timing, suggesting that a different explanation for the eclipse timing variations may be needed. A two-planet model was presented in 2021.

Notes

References

{{DEFAULTSORT:RR Caeli Caelum Eclipsing binaries Caeli, RR M-type main-sequence stars White dwarfs Hypothetical planetary systems J04210556-4839070