HD 75747

HD 75747
Location of HD 75747 (circled)
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]
Distance321.7 ± 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
Luminosity17.3±1.2[8] (combined) L☉
Metallicity [Fe/H]−0.38±0.06[9] or +0.17[10] dex
Age912±21[9] or 9.5[11] Myr
A
Mass1.86±0.02[7] M☉
Radius2.14±0.06[7] R☉
Surface gravity (log g)4.05±0.02[7] cgs
Temperature8,050±200[12] K
Rotational velocity (v sin i)64±6[10] km/s
B
Mass1.82±0.02[7] M☉
Radius2.34±0.06[7] R☉
Surface gravity (log g)3.96±0.02[7] cgs
Temperature7,444±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
SIMBADdata

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]

A light curve for RS Chamaeleontis, plotted from TESS data[17]

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]

  1. ^ a b c d e Cite error: The named reference GaiaDR3 was invoked but never defined (see the help page).
  2. ^ a b c Cite error: The named reference Samus2017 was invoked but never defined (see the help page).
  3. ^ Cite error: The named reference Jones1969 was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference Johnson1966 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference Gontcharov2006 was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference Anderson2012 was invoked but never defined (see the help page).
  7. ^ a b c d e f g h i j k l m Cite error: The named reference Andersen1975 was invoked but never defined (see the help page).
  8. ^ a b c d Cite error: The named reference Clausen1980 was invoked but never defined (see the help page).
  9. ^ a b c Cite error: The named reference Kovaleva2001 was invoked but never defined (see the help page).
  10. ^ a b c d Cite error: The named reference Alecian2005 was invoked but never defined (see the help page).
  11. ^ a b Cite error: The named reference Alecian2007 was invoked but never defined (see the help page).
  12. ^ a b Cite error: The named reference Releya1978 was invoked but never defined (see the help page).
  13. ^ a b Cite error: The named reference David2015 was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference Gould1879 was invoked but never defined (see the help page).
  15. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  16. ^ Cite error: The named reference Tycho2000 was invoked but never defined (see the help page).
  17. ^ Cite error: The named reference MAST was invoked but never defined (see the help page).
  18. ^ Cite error: The named reference Cousins1960 was invoked but never defined (see the help page).
  19. ^ Cite error: The named reference Wild1967 was invoked but never defined (see the help page).
  20. ^ Cite error: The named reference McInally1977 was invoked but never defined (see the help page).
  21. ^ Cite error: The named reference Murphy2013 was invoked but never defined (see the help page).