RR Caeli

RR Caeli is an eclipsing binary star in the constellation Caelum. It is 69 light years from Earth.

RR Caeli

A white light light curve for RR Caeli, adapted from Maxted et al. (2007)[1]
Observation data
Epoch J2000      Equinox J2000
Constellation Caelum
Right ascension 04h 21m 05.563s[2]
Declination −48° 39′ 07.06″[2]
Apparent magnitude (V) 14.40[3]
Characteristics
Evolutionary stage White dwarf + red dwarf
Spectral type DA7.8 + M4[4]
U−B color index −0.42 [3]
B−V color index 0.52[3]
Variable type Algol[5]
Astrometry
Proper motion (μ) RA: 30.030[2] mas/yr
Dec.: −533.886[2] mas/yr
Parallax (π)47.2000 ± 0.0200 mas[2]
Distance69.10 ± 0.03 ly
(21.186 ± 0.009 pc)
Orbit[4]
Period (P)7.289 h
Semi-major axis (a)1.46 R☉
Eccentricity (e)0
Inclination (i)87.9°
Semi-amplitude (K1)
(primary)		48 km/s
Semi-amplitude (K2)
(secondary)		196 km/s
Details[1]
White dwarf
Mass0.448±0.002[4] M☉
Radius0.01568±0.00009[4] R☉
Luminosity (bolometric)0.0007 ± 0.00015[note 1] L☉
Surface gravity (log g)(7.67–7.72) ± 0.06 cgs
Temperature7540 ± 175 K
Red dwarf
Mass(0.182–0.183) ± 0.012 M☉
Radius(0.203–0.215) ± 0.015 R☉
Luminosity (bolometric)0.0038 ± 0.0013[note 1] L☉
Surface gravity (log g)(5.04–5.09) ± 0.04 cgs
Temperature3100 ± 113 K
Other designations
RR Caeli, LFT 349, WD 0419-487, GJ 2034, 2MASS J04210556-4839070, GSC 08072-01454, Gaia DR3 4788741548375134336[6]
Database references
SIMBADdata
Exoplanet Archivedata
ARICNSdata
Extrasolar Planets
Encyclopaedia		data

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.[7] The red dwarf is tidally locked with the white dwarf, meaning it displays the same side to the heavier star.[8] 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.[1] The white dwarf is likely to have a plain helium core, as its density is too low for the carbon-oxygen core.[4]

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.[7]

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.[9] More observations of the light curve are likely to help confirm the presence of one or both planets.[9] 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.[10] A two-planet model was presented in 2023.[11]

The RR Caeli planetary system[11]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(years)		 Eccentricity Inclination Radius
b (controversial) ≥3.0±0.3 MJ 5.2±0.1 15.0±0.6 0 >17.6° —
c (controversial) ≥2.7±0.7 MJ 9.7±0.9 39±5 0 — —

Notes
  1. From , where is the luminosity, is the radius, is the effective surface temperature and is the Stefan–Boltzmann constant.

References
  1. Maxted, P. F. L.; O'Donoghue, D.; Morales-Rueda, L.; Napiwotzki, R.; Smalley, B. (2007). "The mass and radius of the M-dwarf in the short-period eclipsing binary RR Caeli". Monthly Notices of the Royal Astronomical Society. 376 (2): 919–928. arXiv:astro-ph/0702005. Bibcode:2007MNRAS.376..919M. doi:10.1111/j.1365-2966.2007.11564.x. S2CID 3569936.
  2. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  3. Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
  4. Parsons, S. G.; Gänsicke, B. T.; Marsh, T. R.; Ashley, R. P.; Bours, M. C. P.; Breedt, E.; Burleigh, M. R.; Copperwheat, C. M.; Dhillon, V. S.; Green, M.; Hardy, L. K.; Hermes, J. J.; Irawati, P.; Kerry, P.; Littlefair, S. P.; McAllister, M. J.; Rattanasoon, S.; Rebassa-Mansergas, A.; Sahman, D. I.; Schreiber, M. R. (2017), "Testing the white dwarf mass–radius relationship with eclipsing binaries", Monthly Notices of the Royal Astronomical Society, 470 (4): 4473–4492, arXiv:1706.05016, doi:10.1093/mnras/stx1522
  5. Samus', N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
  6. "V* RR Caeli – Eclipsing binary of Algol type (detached)". SIMBAD. Retrieved 18 February 2013.
  7. Bruch, A.; Diaz, M. P. (1998). "The Eclipsing Precataclysmic Binary RR Caeli". The Astronomical Journal. 116 (2): 908–916. Bibcode:1998AJ....116..908B. doi:10.1086/300471.
  8. Ribeiro, T.; Baptista, R.; Kafka, S.; Dufour, P.; Gianninas, A.; Fontaine, G. (2013). "Accretion and activity on the post-common-envelope binary RR Caeli". Astronomy & Astrophysics. 556A: A34. arXiv:1307.5921. Bibcode:2013A&A...556A..34R. doi:10.1051/0004-6361/201220340. S2CID 55229588.
  9. Qian, S. B.; Liu, L.; Zhu, L. Y.; Dai, Z. B.; Fernández Lajús, E.; Baume, G. L. (2012). "A circumbinary planet in orbit around the short-period white dwarf eclipsing binary RR Cae". Monthly Notices of the Royal Astronomical Society: Letters. 422 (1): L24–L27. arXiv:1201.4205. Bibcode:2012MNRAS.422L..24Q. doi:10.1111/j.1745-3933.2012.01228.x. S2CID 119190656.
  10. Pulley, D.; Sharp, I. D.; Mallett, J.; von Harrach, S. (August 2022). "Eclipse timing variations in post-common envelope binaries: Are they a reliable indicator of circumbinary companions?". Monthly Notices of the Royal Astronomical Society. 514 (4): 5725–5738. arXiv:2206.06919. Bibcode:2022MNRAS.514.5725P. doi:10.1093/mnras/stac1676.
  11. Rattanamala, R.; Awiphan, S.; Komonjinda, S.; Phriksee, A.; Sappankum, P.; A-thano, N.; Chitchak, S.; Rittipruk, P.; Sawangwit, U.; Poshyachinda, S.; Reichart, D. E.; Haislip, J. B. (2021), Two circumbinary planets in RR Cae eclipsing binary system, arXiv:2109.09397
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