HD 75747
Star in the constellation Chamaeleon
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HD 75747, also known as HR 3524 or RS Chamaeleontis (RS Cha), is a binary star located in the southern circumpolar constellation Chamaeleon. It has an average apparent magnitude of 6.05,[16] making it barely visible to the naked eye. The system is located relatively close at a distance of 322 light years based on Gaia DR3 parallax measurements[1] but is receding with a somewhat constrained heliocentric radial velocity of 16.1 km/s.[5] It has an absolute magnitude of +1.21.[6]
  | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Chamaeleon |
| Right ascension | 08h 43m 12.19841s[1] |
| Declination | −79° 04′ 12.3685″[1] |
| Apparent magnitude (V) | 6.02 to 6.68[2] |
| Characteristics | |
| Spectral type | A8 IV + A8 IV[3] |
| U−B color index | +0.08[4] |
| B−V color index | +0.24[4] |
| Variable type | Algol + δ Scuti[2] |
| Astrometry | |
| Radial velocity (Rv) | 16.1±4.3[5] km/s |
| Proper motion (μ) | RA: −27.263 mas/yr[1] Dec.: +28.179 mas/yr[1] |
| Parallax (π) | 10.137±0.0213 mas[1] |
| Distance | 321.7 ± 0.7 ly (98.6 ± 0.2 pc) |
| Absolute magnitude (MV) | +1.21[6] |
| Orbit | |
| Period (P) | 1.6699 d[7] |
| Semi-major axis (a) | 9.14 R☉[8] |
| Eccentricity (e) | 0.00[7] |
| Inclination (i) | 83.4[8]° |
| Periastron epoch (T) | 2,438,380.526 JD[7] |
| Argument of periastron (ω) (secondary) | 0.00° |
| Semi-amplitude (K1) (primary) | 136.1[7] km/s |
| Semi-amplitude (K2) (secondary) | 138.9[7] km/s |
| Details | |
| Luminosity | 17.3±1.2[8] (combined) L☉ |
| Metallicity [Fe/H] | −0.38±0.06[9] or +0.17[10] dex |
| Age | 912±21[9] or 9.5[11] Myr |
| A | |
| Mass | 1.86±0.02[7] M☉ |
| Radius | 2.14±0.06[7] R☉ |
| Surface gravity (log g) | 4.05±0.02[7] cgs |
| Temperature | 8,050±200[12] K |
| Rotational velocity (v sin i) | 64±6[10] km/s |
| B | |
| Mass | 1.82±0.02[7] M☉ |
| Radius | 2.34±0.06[7] R☉ |
| Surface gravity (log g) | 3.96±0.02[7] cgs |
| Temperature | 7,444±129[13] K |
| Rotational velocity (v sin i) | 70±6[10] km/s |
| Other designations | |
| 9 G. Chamaeleontis[14], RS Cha, CD−78°342, CPD−78°378, GC 12128, HD 75747, HIP 42794, HR 3524, SAO 256549, WDS 08413-7858CD[15] | |
| Database references | |
| SIMBAD | data |
HD 75747 was known to be variable since 1960 based on observations by A. W. J. Cousins.[18] The system was first observed as an eclipsing binary in 1967 by astronomers P. A. T. Wild and H. C. Lagerweij. J.[19] Andersen deduced a circular orbit with a period of 1.66 days for the system.[7] Subsequent observations revealed that one of the components as a δ Scuti variable.[20] RS Cha is an Algol-type eclipsing binary ranging from 6.02 to 6.58 or 6.68 within 1.6699 days, depending on the eclipse.[2] This system is part of the η Chamaeleontis association, a group of young stars moving with Eta Cha, and Eta Cha is just eight arc-minutes to the northwest of RS Cha.[21]
Both components have a stellar classification of A8 IV, indicating that both objects are slightly evolved A-type subgiants. RS Cha A and B have masses nearly double of the Sun's and 2.14 - 2.34 times the radius of the Sun.[7] They radiate 17.3 times the luminosity of the Sun[8] from its photosphere at effective temperatures of 8,050 K[12] and 7,444 K respectively,[13] giving the object a white hue. RS Cha was originally thought to be 912 million years old,[9] meaning that both stars were evolving off the main sequence. However, astronomer E. Alecian and colleagues re-examined the age of the system and it turns out that HD 75747 is only 9 million years old,[11] making them pre-main sequence stars. The components rotation periods are synchronous to the orbital period, having projected rotational velocities of 64 km/s and 70 km/s respectively.[10]