{{short description|Double star in the constellation Caelum}} {{Starbox begin | name=RR Caeli }} {{Starbox image | image = 250px | caption = A white light light curve for RR Caeli, adapted from Maxted et al. (2007)<ref name="Maxted"/> }} {{Starbox observe | epoch=J2000 | ra={{RA|04|21|05.563}}<ref name=dr3/> | dec={{DEC|-48|39|07.06}}<ref name=dr3/> | appmag_v=14.40<ref name=ubv>{{cite journal|author1=Mermilliod, J.-C.|title=Compilation of Eggen's UBV data, transformed to UBV (unpublished)|journal=Catalogue of Eggen's UBV Data|date=1986|bibcode= 1986EgUBV........0M}}</ref> | constell=Caelum }} {{Starbox character | type = White dwarf + red dwarf | class=DA7.8 + M4<ref name=Parsons2017/> | r-i = | v-r = | b-v =0.52<ref name=ubv/> | u-b =−0.42 <ref name=ubv/> | variable=Algol<ref name=gcvs>{{cite journal |bibcode=2017ARep...61...80S |title=General catalogue of variable stars: Version GCVS 5.1 |last1=Samus' |first1=N. N. |last2=Kazarovets |first2=E. V. |last3=Durlevich |first3=O. V. |last4=Kireeva |first4=N. N. |last5=Pastukhova |first5=E. N. |journal=Astronomy Reports |year=2017 |volume=61 |issue=1 |page=80 |doi=10.1134/S1063772917010085 |s2cid=125853869 }}</ref> }} {{Starbox astrometry | radial_v= | prop_mo_ra=30.030<ref name=dr3/> | prop_mo_dec=−533.886<ref name=dr3/> | parallax=47.2 | p_error=0.02 | parallax_footnote = <ref name=dr3/> | absmag_v= }} {{Starbox orbit | reference = <ref name=Parsons2017/> | period = <!--Period (in years)--> | period_unitless = 7.289 h | axis = <!--Semimajor axis (in arcseconds)--> | axis_unitless = {{solar radius|1.46|link=y}} | eccentricity = 0 | inclination = 87.9 | node = <!--Longitude of node (in degrees)--> | periastron = <!--Periastron epoch--> | periarg = <!--Argument of periastron (in degrees), secondary --> | periarg_primary = <!--Argument of periastron (in degrees), primary --> | k1 = 48 | k2 = 196 }} {{Starbox detail | source = <ref name="Maxted"/> | component1 = White dwarf | mass = 0.453{{±|0.002}}<ref name=Rattanamala2021/> | radius = 0.01568{{±|0.00009}}<ref name=Parsons2017/> | luminosity_bolometric = {{nowrap|0.0007 ± 0.00015}}<ref name=bolometric_luminosity group=note/> | gravity = {{nowrap|(7.67–7.72) ± 0.06}} | temperature = {{nowrap|7540 ± 175}} | metal = <!--Metallicity (no units provided by template)--> | rotation = <!--Rotation (no units provided by template)--> | rotational_velocity = <!--Rotational velocity (v sin i, in km/s)--> | age = <!--Age (in years)--> | component2 = Red dwarf | mass2 = {{val|0.168|0.001}}<ref name=Rattanamala2021/> | radius2 = {{nowrap|(0.203–0.215) ± 0.015}} | luminosity_bolometric2 = {{nowrap|0.0038 ± 0.0013}}<ref name=bolometric_luminosity group=note/> | gravity2 = {{nowrap|(5.04–5.09) ± 0.04}} | temperature2 = {{nowrap|3100 ± 113}} | metal2 = <!--Metallicity (no units provided by template)--> | rotation2 = <!--Rotation (no units provided by template)--> | rotational_velocity2 = <!--Rotational velocity (v sin i, in km/s)--> | age2 = <!--Age (in years)-->
}} {{Starbox catalog | names=RR Caeli, LFT 349, WD 0419-487, GJ 2034, 2MASS J04210556-4839070, GSC 08072-01454, Gaia DR3 4788741548375134336<ref name="RRSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=RR+Cae |title = V* RR Caeli – Eclipsing binary of Algol type (detached) |publisher = SIMBAD | access-date = 18 February 2013}}</ref> }} {{Starbox reference | Simbad=RR+Caeli | ARICNS =02332 | EPE =RR+Cae | NSTED =RR Cae }} {{Starbox end}}
'''RR Caeli''' is an eclipsing binary star system, located 69 light-years (21.0 parsecs) from Earth in the constellation Caelum. It is made up of a red dwarf star and a white dwarf, 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 red dwarf of spectral type M6 and a white dwarf 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.<ref name="Bruch">{{Cite journal | last1 = Bruch | first1 = A. | last2 = Diaz | first2 = M. P. | doi = 10.1086/300471 | title = The Eclipsing Precataclysmic Binary RR Caeli | journal = The Astronomical Journal | volume = 116 | issue = 2 | pages = 908–916 | year = 1998 | bibcode=1998AJ....116..908B| doi-access = free }}</ref> The red dwarf is tidally locked with the white dwarf, meaning it displays the same side to the heavier star.<ref>{{cite journal|author=Ribeiro, T.|author2=Baptista, R.|author3=Kafka, S.|author4=Dufour, P.|author5=Gianninas, A.|author6=Fontaine, G.|date=2013|title=Accretion and activity on the post-common-envelope binary RR Caeli|journal=Astronomy & Astrophysics|volume=556A|bibcode=2013A&A...556A..34R|arxiv = 1307.5921|doi=10.1051/0004-6361/201220340|pages=A34|s2cid=55229588}}</ref> 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.<ref name="Maxted"/> The white dwarf is likely to have a plain helium core, as its density is too low for the carbon-oxygen core.<ref name=Parsons2017/>
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.<ref name="Bruch"/>
== Eclipse time variations and proposed planetary system ==
In 2012, analysis of slight variations in the observed light curve of the system showed that there was likely a giant planet about four times as massive as Jupiter 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.<ref name="Qian"/> More observations of the light curve are likely to help confirm the presence of one or both planets.<ref name="Qian"/> 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.<ref name="Pulley2022"/> A two-planet model was presented in 2021,<ref name=Rattanamala2021/> but it also fails to predict recent changes in eclipse timing as found in a 2025 study. This study does not rule out the presence of the planets, but suggest that the ETVs may have multiple causes.<ref name=Pulley2025/>
{{OrbitboxPlanet begin | name = RR Caeli (2021) | table_ref = <ref name=Rattanamala2021/> | period_unit = year }} {{OrbitboxPlanet hypothetical | status = controversial | exoplanet = b | mass = ≥3.0{{±|0.3}} | period = 15.0{{±|0.6}} | semimajor = 5.2{{±|0.1}} | eccentricity = 0 | inclination = >17.6 }} {{OrbitboxPlanet hypothetical | status = controversial | exoplanet = c | mass = ≥2.7{{±|0.7}} | period = 39{{±|5}} | semimajor = 9.7{{±|0.9}} | eccentricity = 0 | inclination = }} {{Orbitbox end}}
== Notes == {{reflist|group=note|refs= <ref name=bolometric_luminosity group=note>From <math>\begin{smallmatrix}L=4 \pi R^2 \sigma T_{\rm eff}^4 \end{smallmatrix}</math>, where <math>\begin{smallmatrix}L \end{smallmatrix}</math> is the luminosity, <math>\begin{smallmatrix}R \end{smallmatrix}</math> is the radius, <math>\begin{smallmatrix}T_{\rm eff}\end{smallmatrix}</math> is the effective surface temperature and <math>\begin{smallmatrix}\sigma \end{smallmatrix}</math> is the Stefan–Boltzmann constant.</ref> }}
==References== {{Reflist|refs=
<ref name=dr3>{{cite Gaia DR3|4788741548375134336}}</ref>
<ref name="Maxted">{{Cite journal | last1 = Maxted | first1 = P. F. L. | last2 = O'Donoghue | first2 = D. | last3 = Morales-Rueda | first3 = L. | last4 = Napiwotzki | first4 = R. | last5 = Smalley | first5 = B. | title = The mass and radius of the M-dwarf in the short-period eclipsing binary RR Caeli | doi = 10.1111/j.1365-2966.2007.11564.x| bibcode= 2007MNRAS.376..919M | arxiv = astro-ph/0702005| journal = Monthly Notices of the Royal Astronomical Society | volume = 376 | issue = 2 | pages = 919–928| year = 2007 | doi-access = free | s2cid = 3569936 }}</ref>
<ref name="Qian">{{Cite journal | last1 = Qian | first1 = S. B. | last2 = Liu | first2 = L. | last3 = Zhu | first3 = L. Y. | last4 = Dai | first4 = Z. B. | last5 = Fernández Lajús | first5 = E. | last6 = Baume | first6 = G. L. | doi = 10.1111/j.1745-3933.2012.01228.x | title = A circumbinary planet in orbit around the short-period white dwarf eclipsing binary RR Cae | journal = Monthly Notices of the Royal Astronomical Society: Letters | volume = 422 | pages = L24–L27 | year = 2012 | issue = 1 | doi-access = free |arxiv = 1201.4205 |bibcode = 2012MNRAS.422L..24Q | s2cid = 119190656 }}</ref>
<ref name=Pulley2025>{{Cite arXiv |last1=Pulley |first1=D. |last2=Sharp |first2=I. D. |last3=Mallett |first3=J. |last4=Harrach |first4=S. von |title=Eclipse timing variations in 7 post-common envelope binaries: an update on recent circumbinary models |date=2025-07-09 |class=astro-ph.SR |eprint=2507.06748 }}</ref>
<ref name=Parsons2017>{{cite journal|arxiv=1706.05016|title=Testing the white dwarf mass–radius relationship with eclipsing binaries|year=2017|doi=10.1093/mnras/stx1522|last1=Parsons|first1=S. G.|last2=Gänsicke|first2=B. T.|last3=Marsh|first3=T. R.|last4=Ashley|first4=R. P.|last5=Bours|first5=M. C. P.|last6=Breedt|first6=E.|last7=Burleigh|first7=M. R.|last8=Copperwheat|first8=C. M.|last9=Dhillon|first9=V. S.|last10=Green|first10=M.|last11=Hardy|first11=L. K.|last12=Hermes|first12=J. J.|last13=Irawati|first13=P.|last14=Kerry|first14=P.|last15=Littlefair|first15=S. P.|last16=McAllister|first16=M. J.|last17=Rattanasoon|first17=S.|last18=Rebassa-Mansergas|first18=A.|last19=Sahman|first19=D. I.|last20=Schreiber|first20=M. R.|journal=Monthly Notices of the Royal Astronomical Society|volume=470|issue=4|pages=4473–4492|doi-access=free }}</ref>
<ref name=Rattanamala2021>{{cite journal|last1=Rattanamala|first1=R.|last2=Awiphan|first2=S.|last3=Komonjinda|first3=S.|last4=Phriksee|first4=A.|last5=Sappankum|first5=P.|last6=A-thano|first6=N.|last7=Chitchak|first7=S.|last8=Rittipruk|first8=P.|last9=Sawangwit|first9=U.|last10=Poshyachinda|first10=S.|last11=Reichart|first11=D. E.|last12=Haislip|first12=J. B.|title=Eclipse timing variations in the WD+dM eclipsing binary RR Cae|arxiv=2109.09397|doi=10.1093/mnras/stad1733|year=2021|journal=Monthly Notices of the Royal Astronomical Society|issue=4|volume=523|pages=5086–5108|doi-access=free }}</ref>
<ref name="Pulley2022">{{cite journal |last1=Pulley |first1=D. |last2=Sharp |first2=I. D. |last3=Mallett |first3=J. |last4=von Harrach |first4=S. |date=August 2022 |title=Eclipse timing variations in post-common envelope binaries: Are they a reliable indicator of circumbinary companions? |journal=Monthly Notices of the Royal Astronomical Society |volume=514 |issue=4 |pages=5725–5738 |doi=10.1093/mnras/stac1676 |doi-access=free |arxiv=2206.06919 |bibcode=2022MNRAS.514.5725P}}</ref>
}}
{{Stars of Caelum}} {{2012 in space}}
Category:Caelum Category:Eclipsing binaries Caeli, RR Category:M-type main-sequence stars Category:White dwarfs Category:Hypothetical planetary systems