Astronomy:HD 75747

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Short description: Star in the constellation Chamaeleon
HD 75747
Chamaeleon constellation map.svg
Red circle.svg
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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