Location of HD 75747 (circled) | |
Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
---|---|
Constellation | Chamaeleon |
Right ascension | 08h43m 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, also known as HR 3524orRS 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 velocityof16.1 km/s.[5] It has an absolute magnitude of +1.21.[6]
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 photosphereateffective temperaturesof8,050 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 velocitiesof64 km/s and 70 km/s respectively.[10]