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Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very high surface enhancement of heavy elements, depletion of hydrogen, and strong stellar winds. The surface temperatures of known Wolf–Rayet stars range from 20,000 K to around 210,000 K, hotter than almost all other kinds of stars. They were previously called W-type stars referring to their spectral classification.
A carbon star is typically an asymptotic giant branch star, a luminous red giant, whose atmosphere contains more carbon than oxygen. The two elements combine in the upper layers of the star, forming carbon monoxide, which consumes most of the oxygen in the atmosphere, leaving carbon atoms free to form other carbon compounds, giving the star a "sooty" atmosphere and a strikingly ruby red appearance. There are also some dwarf and supergiant carbon stars, with the more common giant stars sometimes being called classical carbon stars to distinguish them.
Omicron Virginis is a star in the zodiac constellation of Virgo. It is visible to the naked eye with an apparent visual magnitude of +4.12. Based upon parallax measurements, it is about 163 light years from the Sun.
24 Aquilae is a star in the equatorial constellation of Aquila. 24 Aquilae is its Flamsteed designation. It is located at a distance of around 434 light-years from Earth and has an apparent visual magnitude of 6.4. According to the Bortle Dark-Sky Scale, this star is just visible to the naked eye in dark rural skies. It is drifting closer to the Sun with a radial velocity of −26 km/s.
Omicron Boötis is a yellow-hued star in the northern constellation of Boötes. With an apparent visual magnitude of +4.60, it is a fifth magnitude star that is visible to the naked eye. Based upon an annual parallax shift of 13.42 mas as seen from the Earth, it is located about 243 light years from the Sun. The star is moving closer to the Sun with a radial velocity of −9 km/s.
Zeta Capricorni, Latinised from ζ Capricorni, is a binary star system in the southern constellation of Capricornus. It is visible to the naked eye with an apparent visual magnitude of 3.77. The system is located at a distance of approximately 386 light-years from the Sun based on parallax. It is drifting further away with a radial velocity of +2 km/s. The absolute magnitude of this system is −1.59.
Barium stars are spectral class G to K stars whose spectra indicate an overabundance of s-process elements by the presence of singly ionized barium, Ba II, at λ 455.4 nm. Barium stars also show enhanced spectral features of carbon, the bands of the molecules CH, CN and C2. The class was originally recognized and defined by William P. Bidelman and Philip Keenan. Initially, after their discovery, they were thought to be red giants, but the same chemical signature has been observed in main-sequence stars as well.
72 Ophiuchi is a binary star system in the equatorial constellation of Ophiuchus. It is visible to the naked eye as a faint, white-hued point of light with a combined apparent visual magnitude of 3.73. It is located approximately 86.9 light years away from the Sun based on parallax, but is moving closer with a heliocentric radial velocity of -23.9 km/s.
An S-type star is a cool giant with approximately equal quantities of carbon and oxygen in its atmosphere. The class was originally defined in 1922 by Paul Merrill for stars with unusual absorption lines and molecular bands now known to be due to s-process elements. The bands of zirconium monoxide (ZrO) are a defining feature of the S stars.
2 Vulpeculae is a binary star system in the northern constellation of Vulpecula, located around 1,800 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 of 5.43.
SU Andromedae is a carbon star in the constellation of Andromeda. It is a variable star classified as a slow irregular pulsating supergiant, and varies from an apparent visual magnitude of 8.5 at minimum brightness to a magnitude of 8.0 at maximum brightness with no clear period.
Xi1 Ceti , Latinized from ξ1 Ceti, is a binary star system located in the equatorial constellation of Cetus. It is visible to the naked eye with a combined apparent visual magnitude of +4.36. The distance to this system is approximately 340 light years based on parallax measurements, and it is drifting closer to the Sun with a radial velocity of −4 km/s. The proximity of the star to the ecliptic means it is subject to lunar occultations.
U Camelopardalis is a semiregular variable star in the constellation Camelopardalis. Based on parallax measurements made by the Hipparcos spacecraft, it is located about 3,000 light-years away from the Earth. Its apparent visual magnitude is about 8, which is dim enough that it cannot be seen with the unaided eye.
U Hydrae is a single star in the equatorial constellation of Hydra, near the northern constellation border with Sextans. It is a semiregular variable star of sub-type SRb, with its brightness ranging from visual magnitude (V) 4.7 to 5.2 over a 450-day period, with some irregularity. This object is located at a distance of approximately 680 light years from the Sun based on parallax. It is drifting closer with a radial velocity of −26 km/s.
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.
56 Persei is at least a triple star and possibly a quadruple star system in the northern constellation of Perseus. It is visible to the naked eye as a dim point of light with a combined apparent visual magnitude of 5.77. The system is located 139 light-years (42.5 pc) distant from the Sun based on parallax, but is drifting closer with a radial velocity of −32 km/s.
A CN star has unusually strong cyano radical bands in its spectrum compared to other stars of its stellar class. Cyano radical is a simple molecule of one carbon atom and one nitrogen atom, with absorption bands around wavelengths 388.9 and 421.6 nanometer. This group of stars was first noticed in certain G and K-type giants by J. J. Nassau and W. W. Morgan in 1949, then a further 4,150 were identified by Nancy G. Roman in 1952. They can be distinguished from barium stars by the lack of s-process elements, and from other types of luminous stars by the general weakness of features other than the CN lines.
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
- ↑ 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 .
- ↑ Hearnshaw, John B. (2014), The Analysis of Starlight: Two Centuries of Astronomical Spectroscopy (2nd ed.), Cambridge University Press, p. 233, ISBN 978-1107782914.
- ↑ 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.
- ↑ 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.
