Astronomy:HD 75747

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Short description: Star in the constellation Chamaeleon
HD 75747
Location of HD 75747 (circled)
Observation data
Epoch J2000.0   Equinox (celestial coordinates)
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[1] mas/yr
Dec.: +28.179[1] mas/yr
Parallax (π)10.137 ± 0.0213[1] mas
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
RS Cha, CD−78°342, CPD−78°378, GC 12128, HD 75747, HIP 42794, HR 3524, SAO 256549, WDS 08413-7858CD[14]
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,[15] 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[16]

HD 75747 was known to be variable since 1960 based on observations by A. W. J. Cousins.[17] The system was first observed as an eclipsing binary in 1967 by astronomers P. A. T. Wild and H. C. Lagerweij. J.[18] 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.[19] 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.[20]

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]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  2. ↑ 2.0 2.1 2.2 Samus’, N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (January 2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports 61 (1): 80–88. doi:10.1134/S1063772917010085. ISSN 1063-7729. Bibcode: 2017ARep...61...80S. 
  3. ↑ Jones, D. H. P. (1969). "Spectroscopic Observations of two Eclipsing Binaries". Monthly Notes of the Astronomical Society of South Africa 28: 5. ISSN 0024-8266. Bibcode: 1969MNSSA..28....5J. 
  4. ↑ 4.0 4.1 Johnson, H. L.; Mitchell, R. I.; Iriarte, B.; Wisniewski, W. Z. (1966). "UBVRIJKL Photometry of the Bright Stars". Communications of the Lunar and Planetary Laboratory 4: 99–110. Bibcode: 1966CoLPL...4...99J. 
  5. ↑ 5.0 5.1 Gontcharov, G. A. (November 2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters 32 (11): 759–771. doi:10.1134/S1063773706110065. ISSN 1063-7737. Bibcode: 2006AstL...32..759G. 
  6. ↑ 6.0 6.1 Anderson, E.; Francis, Ch. (May 2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331–346. doi:10.1134/S1063773712050015. ISSN 1063-7737. Bibcode: 2012AstL...38..331A. 
  7. ↑ 7.00 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 7.10 7.11 7.12 Andersen, J. (November 1975). "Spectroscopic observations of eclipsing binaries. I. Description of methods, and results for RS Chamaeleontis and chi 2 Hydrae.". Astronomy and Astrophysics 44: 445–458. ISSN 0004-6361. Bibcode: 1975A&A....44..445A. 
  8. ↑ 8.0 8.1 8.2 8.3 Clausen, J. V.; Nordstrom, B. (March 1980). "Four-colour photometry of eclipsing binaries. XIa.". Astronomy and Astrophysics 83: 339–347. ISSN 0004-6361. Bibcode: 1980A&A....83..339C. 
  9. ↑ 9.0 9.1 9.2 Kovaleva, D. A. (December 2001). "Age and metallicity estimates for moderate-mass stars in eclipsing binaries". Astronomy Reports 45 (12): 972–983. doi:10.1134/1.1426128. ISSN 1063-7729. Bibcode: 2001ARep...45..972K. 
  10. ↑ 10.0 10.1 10.2 10.3 Alecian, E.; Catala, C.; Van't Veer-Menneret, C.; Goupil, M.-J.; Balona, L. (14 October 2005). "Pulsations and metallicity of the pre-main sequence eclipsing spectroscopic binary RS Cha". Astronomy & Astrophysics 442 (3): 993–1002. doi:10.1051/0004-6361:20041906. ISSN 0004-6361. Bibcode: 2005A&A...442..993A. 
  11. ↑ 11.0 11.1 Alecian, E.; Goupil, M.-J.; Lebreton, Y.; Dupret, M.-A.; Catala, C. (11 January 2007). "Calibration of the pre-main sequence RS Chamaleontis binary system". Astronomy & Astrophysics 465 (1): 241–248. doi:10.1051/0004-6361:20065822. ISSN 0004-6361. Bibcode: 2007A&A...465..241A. 
  12. ↑ 12.0 12.1 Relyea, L. J.; Kurucz, R. L. (May 1978). "A theoretical analysis of UVBY photometry". The Astrophysical Journal Supplement Series 37: 45. doi:10.1086/190517. ISSN 0067-0049. Bibcode: 1978ApJS...37...45R. 
  13. ↑ 13.0 13.1 David, Trevor J.; Hillenbrand, Lynne A. (12 May 2015). "The Ages of Early-type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets". The Astrophysical Journal 804 (2): 146. doi:10.1088/0004-637X/804/2/146. Bibcode: 2015ApJ...804..146D. 
  14. ↑ "RS Cha". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=RS+Cha. 
  15. ↑ Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P. et al. (March 2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics 355: L27–L30. ISSN 0004-6361. Bibcode: 2000A&A...355L..27H. 
  16. ↑ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html. 
  17. ↑ Cousins, A. W. J. (1960). "New Bright Variable Stars". Monthly Notes of the Astronomical Society of South Africa 19: 56. ISSN 0024-8266. Bibcode: 1960MNSSA..19...56C. 
  18. ↑ Wild, P. A. T.; Lagerweij, H. C. (1967). "Preliminary Photometric Elements of the Eclipsing Binary System 9 Cha". Monthly Notes of the Astronomical Society of South Africa 26: 144. ISSN 0024-8266. Bibcode: 1967MNSSA..26..144W. 
  19. ↑ McInally, C. J.; Austin, R. D. (September 1977). "RS Cha: a delta Scuti Variable". Information Bulletin on Variable Stars 1334: 1. ISSN 0374-0676. Bibcode: 1977IBVS.1334....1M. 
  20. ↑ Murphy, Simon J.; Lawson, Warrick A.; Bessell, Michael S. (20 August 2013). "Re-examining the membership and origin of the ϵ Cha association". Monthly Notices of the Royal Astronomical Society 435 (2): 1325–1349. doi:10.1093/mnras/stt1375. ISSN 0035-8711. Bibcode: 2013MNRAS.435.1325M. 
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