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OGLE-LMC-CEP0227
	; Artist’s impression of OGLE-LMC-CEP0227; Credit: ESO
Observation data; Epoch J2000 Equinox J2000
Constellation	Mensa
Right ascension	04h 52m 15.678s
Declination	−70° 14′ 31.33″
Apparent magnitude (V)	15.317
Characteristics
Spectral type	F7Ib + G4II
Apparent magnitude (J)	13.727
Apparent magnitude (H)	13.217
Apparent magnitude (K)	13.262
Variable type	Eclipsing binary, δ Cep
Astrometry
Distance	163,000 ly ; (50,000 pc)
Orbit
Period (P)	309.404±0.002 days
Semi-major axis (a)	389.86±0.77
Eccentricity (e)	0.1659±0.0006
Inclination (i)	86.833±0.016°
Argument of periastron (ω); (secondary)	342.0±0.6°
Details
A (Cepheid)
Mass	4.165±0.032 M☉
Radius	34.92±0.34 R☉
Luminosity	1,439 L☉
Surface gravity (log g)	1.971±0.011 cgs
Temperature	6,050±160 K
B
Mass	4.134±0.037 M☉
Radius	44.85±0.29 R☉
Surface gravity (log g)	1.751±0.010 cgs
Temperature	5,120±130 K
Rotational velocity (v sin i)	11.1±1.2 km/s
Other designations
	2MASS J04521567-7014313
Database references
SIMBAD	data

OGLE-LMC-CEP0227 is an eclipsing binary and Cepheid variable star,^[6] pulsating every 3.8 days.^[4] The star, in the Large Magellanic Cloud, was the first Cepheid star system found to be orbiting exactly edge on.^[4]

A near-infrared (I band) light curve for OGLE-LMC-CEP0227, adapted from Pietrzyński *et al.* (2010).^[4] The main plot shows the eclipse light curve, with the Cepheid variation removed, and the inset plot shows the Cepheid variation.

The OGLE-LMC-CEP0227 system contains two stars which orbit each other almost exactly 'edge on' to the line of sight from the Earth. This unique configuration has allowed astronomers to refine their understanding of classical Cepheid variable stars. Studies of this system have allowed astronomers to measure the Cepheid mass with unprecedented accuracy. There is still disagreement over whether the pulsational properties accurately match the mass derived from the observed orbit.^[4]^[6]

The two stars orbit each other every 309 days, and each has a mass close to 4.1 M_☉. The primary component has an effective temperature of 6,050 K and the secondary a temperature of 5,120 K.^[3]

Notes

^ ^a ^b The spectral type, radius, gravity, temperature, luminosity, and observed magnitudes for the Cepheid are mean values, since the star pulsates regularly.

References

^ ^a ^b ^c ^d ^e Cutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; Beichman, Charles A.; Carpenter, John M.; Chester, Thomas; Cambresy, Laurent; Evans, Tracey E.; Fowler, John W.; Gizis, John E.; Howard, Elizabeth V.; Huchra, John P.; Jarrett, Thomas H.; Kopan, Eugene L.; Kirkpatrick, J. Davy; Light, Robert M.; Marsh, Kenneth A.; McCallon, Howard L.; Schneider, Stephen E.; Stiening, Rae; Sykes, Matthew J.; Weinberg, Martin D.; Wheaton, William A.; Wheelock, Sherry L.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". CDS/ADC Collection of Electronic Catalogues. 2246: II/246. Bibcode:2003yCat.2246....0C.
^ Soszynski, I.; Poleski, R.; Udalski, A.; Szymanski, M. K.; Kubiak, M.; Pietrzynski, G.; Wyrzykowski, L.; Szewczyk, O.; Ulaczyk, K. (2008). "The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. I. Classical Cepheids in the Large Magellanic Cloud". Acta Astronomica. 58: 163. arXiv:0808.2210. Bibcode:2008AcA....58..163S.
^ ^a ^b ^c ^d Pilecki, B. (2013). "Physical parameters and the projection factor of the classical Cepheid in the binary system OGLE-LMC-CEP-0227". Monthly Notices of the Royal Astronomical Society. 436 (2): 953–967. arXiv:1308.5023. Bibcode:2013MNRAS.436..953P. doi:10.1093/mnras/stt1529. S2CID 119127008.
^ ^a ^b ^c ^d ^e Pietrzyński, G.; Thompson, I. B.; Gieren, W.; Graczyk, D.; Bono, G.; Udalski, A.; Soszyński, I.; Minniti, D.; Pilecki, B. (2010). "The dynamical mass of a classical Cepheid variable star in an eclipsing binary system". Nature. 468 (7323): 542–4. arXiv:1012.0231. Bibcode:2010Natur.468..542P. doi:10.1038/nature09598. PMID 21107425. S2CID 4413016.
^ Pietrzyński, G; D. Graczyk; W. Gieren; I. B. Thompson; B. Pilecki; A. Udalski; I. Soszyński; et al. (7 March 2013). "An eclipsing-binary distance to the Large Magellanic Cloud accurate to two per cent". Nature. 495 (7439): 76–79. arXiv:1303.2063. Bibcode:2013Natur.495...76P. doi:10.1038/nature11878. PMID 23467166. S2CID 4417699.
^ ^a ^b Neilson, H. R.; Langer, N. (2012). "Is there a mass discrepancy in the Cepheid binary OGLE-LMC-CEP0227?". Astronomy & Astrophysics. 537: A26. arXiv:1110.6657. Bibcode:2012A&A...537A..26N. doi:10.1051/0004-6361/201117829. S2CID 118394822.