CH star

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CH stars are particular type of carbon stars which are characterized by the presence of exceedingly strong absorption bands due to CH (methylidyne) in their spectra. They belong to the stellar population II, [1] meaning they are metal poor and generally pretty middle-aged stars, and are under-luminous compared to the classical C–N carbon stars. The term 'CH star' was coined by Philip C. Keenan in 1942 as a sub-type of the C classification, which he used for carbon stars. The main molecular feature used in identifying the initial set of five CH stars lies in the Fraunhaufer G band. [2]

In 1975, Yasuho Yamashita noted that some higher temperature carbon stars displayed the typical spectral characteristics of a CH star, but did not have the same kinematic properties. That is, they did not have the higher space velocities characteristic of the older stellar population. These were dubbed CH-like stars. [3] Many CH stars are known to be members of binary star systems, and it is reasonable to believe this is (or was) the case for all CH stars. Like Barium stars, they are probably the result of a mass transfer from a former classical carbon star companion, now a degenerate white dwarf, to the current CH-classed star. [4]

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78 Ursae Majoris is a binary star system in the northern circumpolar constellation of Ursa Major. It is visible to the naked eye as a faint point of light with a combined apparent visual magnitude of 4.93. Parallax estimates by Hipparcos put it at a distance of 83 light-years (25 pc), but it is drifting closer with a radial velocity of −5 km/s. The system is a candidate member of the Ursa Major Moving Group.

5 Ursae Minoris is a star in the circumpolar constellation of Ursa Minor. It is a faint star but visible to the naked eye with an apparent visual magnitude of 4.253. The distance to this star, as determined from an annual parallax shift of 9.09±0.13 mas, is about 110 pc. It is moving further away with a heliocentric radial velocity of +9 km/s.

2 Persei is a binary star system in the northern constellation Perseus, located around 500 light years away from the Sun. It is visible to the naked eye as a faint, blue-white hued star with an apparent visual magnitude is 5.70. The system is moving further away from the Earth with a heliocentric radial velocity of 11 km/s.

16 Serpentis is a binary star system in the Serpens Caput portion of the equatorial constellation of Serpens, located 228 light years from the Sun. It is visible to the naked eye as a fain, orange-hued star with an apparent visual magnitude of 5.261. The system is moving further from the Earth with a heliocentric radial velocity of +3 km/s.

HD 2454 is a probable binary star system in the zodiac constellation of Pisces. With an apparent visual magnitude of 6.04, it is near the lower limit of visibility to the naked eye under good seeing conditions. An annual parallax shift of 26.3 mas as measured from Earth's orbit provides a distance estimate of 124 light years. It has a relatively high proper motion, traversing the celestial sphere at a rate of 0.208 arcseconds per year, and is moving closer to the Sun with a heliocentric radial velocity of −10 km/s.

KS Persei is a binary system in the equatorial constellation of Perseus. It is sometimes known as Bidelman's Star, named after William P. Bidelman. The star is invisible to the naked eye with a mean apparent visual magnitude of 7.70. As of 2018, the structure and evolutionary history of this system remain uncertain, although some form of mass transfer is likely to have occurred to explain the observed properties.

References

  1. McClure, Robert D.; Woodsworth, A. W. (April 1, 1990), "The binary nature of the barium and CH stars. III - Orbital parameters", Astrophysical Journal, Part 1, 352: 709–723, Bibcode:1990ApJ...352..709M, doi: 10.1086/168573 .
  2. Hearnshaw, John B. (2014), The Analysis of Starlight: Two Centuries of Astronomical Spectroscopy (2nd ed.), Cambridge University Press, p. 233, ISBN   978-1107782914.
  3. Sperauskas, J.; et al. (July 2016), "The Binary Nature of CH-Like Stars", The Astrophysical Journal, 826 (1): 13, Bibcode:2016ApJ...826...85S, doi: 10.3847/0004-637X/826/1/85 , 85.
  4. Goswami, Aruna (2005). "CH stars at high Galactic latitudes". Monthly Notices of the Royal Astronomical Society. 359 (2): 531–544. arXiv: astro-ph/0507202 . Bibcode:2005MNRAS.359..531G. doi:10.1111/j.1365-2966.2005.08917.x. S2CID   14521922.