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Star in the constellation Chamaeleon From Wikipedia, the free encyclopedia
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]
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]
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