Delta Circini
Variable star in the constellation Circinus
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Delta Circini (δ Cir), is a multiple star system located in the constellation Circinus. Delta Circini is also known as HR 5664, and HD 135240. The system has a combined apparent visual magnitude of +5.09, and is located at a distance of about 700 pc (2,300ly) from the Sun.
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Circinus |
| Right ascension | 15h 16m 56.89591s[1] |
| Declination | −60° 57′ 26.1201″[1] |
| Apparent magnitude (V) | 5.09[2] (5.05 - 5.20[3]) |
| Characteristics | |
| Spectral type | O7.5III(f)[3] (O8IV[3] + O9.5V + B0.5V[4]) |
| U−B color index | −0.88[2] |
| B−V color index | −0.06[2] |
| Variable type | Eclipsing and ellipsoidal[3] |
| Astrometry | |
| Radial velocity (Rv) | −17.80[5] km/s |
| Proper motion (μ) | RA: −4.085[1] mas/yr Dec.: −3.758[1] mas/yr |
| Parallax (π) | 1.4345±0.1231 mas[1] |
| Distance | 2,641.5 ± 5.9 ly (809.9±1.8 pc)[6] |
| Orbit[6] | |
| Primary | Aa |
| Name | Ab |
| Period (P) | 3.90244719(52) days |
| Semi-major axis (a) | 34.56±0.01 R☉[a] |
| Eccentricity (e) | 0.06116±0.00010 |
| Inclination (i) | 78.7745±0.0088° |
| Periastron epoch (T) | 58,650.055430±0.00010 RJD |
| Argument of periastron (ω) (secondary) | 344.83±0.37° |
| Semi-amplitude (K1) (primary) | 156.8[3] km/s |
| Semi-amplitude (K2) (secondary) | 280.4[3] km/s |
| Orbit[6] | |
| Primary | Aab |
| Name | Ac |
| Period (P) | 1,603.24±0.19 days |
| Semi-major axis (a) | 10.065±0.018 au |
| Eccentricity (e) | 0.5291±0.0011 |
| Inclination (i) | 78.216±0.030° |
| Longitude of the node (Ω) | 256.87±0.07° |
| Argument of periastron (ω) (secondary) | 300.43±0.08° |
| Semi-amplitude (K1) (primary) | 24.37±0.10 km/s |
| Semi-amplitude (K2) (secondary) | 54.42±0.08 km/s |
| Details[6] | |
| Aa | |
| Mass | 23.358±0.030 M☉ |
| Radius | 9.647±0.013 R☉ |
| Luminosity | 153,000+27,000 −23,000[7] L☉ |
| Surface gravity (log g) | 3.8375±0.0013 cgs |
| Temperature | 33,750±300 K |
| Rotational velocity (v sin i) | 117±5 km/s |
| Age | 4.4±0.1 Myr |
| Ab | |
| Mass | 12.997±0.019 M☉ |
| Radius | 5.3997±0.0076 R☉ |
| Luminosity | 21,827+5,026 −4,085[7] L☉ |
| Surface gravity (log g) | 4.0871±0.0015 cgs |
| Temperature | 27,500±1,000 K |
| Rotational velocity (v sin i) | 96±10 km/s |
| Age | 4.7±0.2 Myr |
| Ac | |
| Mass | 16.41±0.12 M☉ |
| Radius | 5.79+0.46 −0.42 R☉ |
| Luminosity | 17,000[3] L☉ |
| Surface gravity (log g) | 4.09±0.06 cgs |
| Temperature | 29,000±2,000 K |
| Age | 4.3+1.1 −1.4 Myr |
| Other designations | |
| δ Cir, CD−60°5539, SAO 253084, HD 135240, HR 5664, HIP 74778, WDS J15169-6057 | |
| Database references | |
| SIMBAD | data |
Companions
δ Circini A is a spectroscopic triple star. The two inner components form an eclipsing binary system. The outer component has been resolved using the VLTI PIONIER instrument.[3]
δ Circini B is a 13th magnitude companion nearly an arc-second away. It is unclear whether the two are physically associated and little is known about the fainter star although it has been reported to be a G5 main sequence star or giant.[8]
HD 135160 is a 6th magnitude binary Be star that shares a common space motion with δ Circini and is only 4 arc minutes away. The two make a faint naked eye pair.
System properties
All three components of δ Circini A are hot luminous stars. The brightest is an O8 star just beginning to evolve away from the main sequence. It is in a very close orbit with an O9.5 main sequence star. The two stars are deformed into ellipsoidal shapes and eclipse each other every 3.9 days. The total brightness change is only 0.15 magnitudes.
The third component is a B0.5 main sequence star in a long eccentric orbit around the close pair. It is fainter and cooler than either of the two close stars.[3]
Notes
- Calculated from a sin i/sin(i). The same calculation is used for the uncertainty, although the value does not change significantly.