  | |
| Observation data EpochJ2000.0 Equinox | |
|---|---|
| Constellation | Canis Major |
| Right ascension | 07h 19m 28.18202s[1] |
| Declination | −16° 23′ 42.8773″[1] |
| Apparent magnitude (V) | 5.70 - 6.34[2] |
| Characteristics | |
| Spectral type | F0V + G8IV[3] |
| U−Bcolor index | +0.01[3] |
| B−Vcolor index | +0.34[3] |
| Variable type | Algol[4] |
| Astrometry | |
| Radial velocity (Rv) | −39.0[5] km/s |
| Proper motion (μ) | RA: +165.37[1]mas/yr Dec.: −136.18[1]mas/yr |
| Parallax (π) | 23.38±0.54 mas[1] |
| Distance | 140 ± 3 ly (42.8 ± 1.0 pc) |
| Absolute magnitude (MV) | +2.57[6] |
| Details[3] | |
| primary | |
| Mass | 1.67 M☉ |
| Radius | 1.78 R☉ |
| Luminosity | 8.2 L☉ |
| Surface gravity (log g) | 4.16 cgs |
| Temperature | 7,300 K |
| Rotational velocity (v sin i) | 78.3±3.9[6] km/s |
| secondary | |
| Mass | 0.22 M☉ |
| Radius | 1.22 R☉ |
| Luminosity | 0.49 L☉ |
| Surface gravity (log g) | 3.60 cgs |
| Temperature | 4,350 K |
| tertiary | |
| Mass | 0.8 M☉ |
| Radius | 0.83 R☉ |
| Luminosity | 0.4 L☉ |
| Surface gravity (log g) | 4.50 cgs |
| Other designations | |
| R Canis Majoris,BD−16°1898,HR 2788,HD 57167,HIP 35487,SAO 152724,GC 9758 | |
| Database references | |
| SIMBAD | data |
R Canis Majoris is an eclipsinginteracting binary star system in theconstellationCanis Major. It varies from magnitude 5.7 to 6.34.[7] The system is unusual in the low mass ratio (ie. big mass difference) between the main two components and shortness of the orbital period.[3] It is faintly visible to thenaked eye of an observer with very good observing conditions.
In 1887,Edwin Forrest Sawyer discovered that the star, then generally referred to as 155 Canis Majoris (after its listing inUranometria Argentina), is avariable star.[4] It appears with itsvariable star designation, R Canis Majoris, inAnnie Jump Cannon'sSecond catalogue of variable stars, published in 1907.[9]
Eclipse timings for R Canis Majoris have been being measured since 1887, and whilst at present the time period appears constant at 1.1359 days, periodic quasi-sinusoidal variations of the eclipse arrival times have been taking place with a periodicity of around 93 years. This has led to the suggestion that there exists a third non-eclipsing body in the system whose gravitational pull is responsible for these variations.[10]
R Canis Majoris is thought to be aninteracting binary star. The secondary star, originally the more massive of the two, has evolved away from themain sequence, expanded, and exceeded itsRoche lobe. The primary has stripped away mass from the secondary, with much of it being lost completely from the system. The secondary now has a very reduced mass relative to its temperature and luminosity, while the primary has gained helium-rich material and become hotter and more luminous.[11]
Reanalysis of the system using high-resolution spectroscopy yields its two main components to have masses1.67±0.08 and0.22±0.07 timesthat of the Sun respectively and radii1.78±0.03 and1.22±0.07 timesthat of the Sun respectively. Their surface temperatures are7,300 K and4,350 K. A third star in the system is very faint, presumed to be anorange dwarf. A tentative orbit has been derived with a period of 102 years. The third star has a mass 80% that of the Sun and a radius around 83% that of the Sun.[3]
