RR Caeli is an
eclipsing binary star
A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...
in the
constellation
A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object.
The origins of the e ...
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 Sculptoriu ...
. It is 69
light years
A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...
from
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
.
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
red dwarf
''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. T ...
of
spectral type
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...
M6 and a
white dwarf
A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes ...
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
Tidal locking between a pair of co-orbiting astronomical bodies occurs when one of the objects reaches a state where there is no longer any net change in its rotation rate over the course of a complete orbit. In the case where a tidally locked bo ...
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
In astronomy, cataclysmic variable stars (CVs) are stars which irregularly increase in brightness by a large factor, then drop back down to a quiescent state. They were initially called novae (), since ones with an outburst brightness visible t ...
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
A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in w ...
in 1979, it has a baseline magnitude
Magnitude may refer to:
Mathematics
*Euclidean vector, a quantity defined by both its magnitude and its direction
*Magnitude (mathematics), the relative size of an object
*Norm (mathematics), a term for the size or length of a vector
*Order of ...
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 of light intensity of a celestial object or region as a function of time, typically with the magnitude of light received on the y axis and with time on the x axis. The light is usually in a particular frequ ...
of the system showed that there was likely a giant planet
The giant planets constitute a diverse type of planet much larger than Earth. They are usually primarily composed of low-boiling-point materials (volatiles), rather than rock or other solid matter, but massive solid planets can also exist. The ...
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 mass more than two and a half times that of all the other planets in the Solar System combined, but ...
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.preprint
In academic publishing, a preprint is a version of a scholarly or scientific paper that precedes formal peer review and publication in a peer-reviewed scholarly or scientific journal. The preprint may be available, often as a non-typeset versio ...
, but has not been published in a journal or peer-reviewed.[ 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.]
Notes
References
{{DEFAULTSORT:RR Caeli
Caelum
Eclipsing binaries
Caeli, RR
M-type main-sequence stars
White dwarfs
Hypothetical planetary systems
J04210556-4839070