Related Research Articles
A star is an astronomical object comprising a luminous spheroid of plasma held together by self-gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make them appear as fixed points of light. The most prominent stars have been categorised into constellations and asterisms, and many of the brightest stars have proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. The observable universe contains an estimated 1022 to 1024 stars. Only about 4,000 of these stars are visible to the naked eye, all within the Milky Way galaxy.
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with spectral lines. Each line indicates a particular chemical element or molecule, with the line strength indicating the abundance of that element. The strengths of the different spectral lines vary mainly due to the temperature of the photosphere, although in some cases there are true abundance differences. The spectral class of a star is a short code primarily summarizing the ionization state, giving an objective measure of the photosphere's temperature.
Beta Arietis, officially named Sheratan, is a star system and the second-brightest star in the constellation of Aries, marking the ram's second horn.
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.
Zeta Puppis, formally named Naos, is a star in the constellation of Puppis.
A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution of a star.
A B-type main-sequence star is a main-sequence (hydrogen-burning) star of spectral type B and luminosity class V. These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10,000 and 30,000 K. B-type stars are extremely luminous and blue. Their spectra have strong neutral helium absorption lines, which are most prominent at the B2 subclass, and moderately strong hydrogen lines. Examples include Regulus and Algol A.
Chi Carinae, Latinised from χ Carinae, is a star in the southern constellation of Carina. It is a third-magnitude star and is one of the brighter members of the constellation. The distance to the star can be determined directly through parallax measurements, yielding an estimate of roughly 450 light-years with a 6.7% margin of error. This star is a suspected astrometric binary, although nothing is known about the companion.
A yellow hypergiant (YHG) is a massive star with an extended atmosphere, a spectral class from A to K, and, starting with an initial mass of about 20–60 solar masses, has lost as much as half that mass. They are amongst the most visually luminous stars, with absolute magnitude (MV) around −9, but also one of the rarest, with just 20 known in the Milky Way and six of those in just a single cluster. They are sometimes referred to as cool hypergiants in comparison with O- and B-type stars, and sometimes as warm hypergiants in comparison with red supergiants.
Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface.
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.
A hypergiant (luminosity class 0 or Ia+) is a very rare type of star that has an extremely high luminosity, mass, size and mass loss because of its extreme stellar winds. The term hypergiant is defined as luminosity class 0 (zero) in the MKK system. However, this is rarely seen in literature or in published spectral classifications, except for specific well-defined groups such as the yellow hypergiants, RSG (red supergiants), or blue B(e) supergiants with emission spectra. More commonly, hypergiants are classed as Ia-0 or Ia+, but red supergiants are rarely assigned these spectral classifications. Astronomers are interested in these stars because they relate to understanding stellar evolution, especially star formation, stability, and their expected demise as supernovae.
AB7, also known as SMC WR7, is a binary star in the Small Magellanic Cloud. A Wolf–Rayet star and a supergiant companion of spectral type O orbit in a period of 19.56 days. The system is surrounded by a ring-shaped nebula known as a bubble nebula.
BI 253 is an O2V star in the Large Magellanic Cloud and is a primary standard of the O2 type. It is one of the hottest main-sequence stars known and one of the most-massive and most-luminous stars known.
68 Cygni is the Flamsteed designation for a star in the constellation Cygnus. Located approximately 1,400 parsecs (4,600 ly) distant, the star is a hot blue giant of spectral type O7.5IIIn( ), a massive star that is likely currently expanding to become a supergiant. The star is surrounded by a ring-shaped nebula named S 119.
HR 6819, also known as HD 167128 or QV Telescopii, is a double star system in the southern constellation of Telescopium. It is in the south-western corner of the constellation, near Pavo to the south and Ara to the west. The system appears as a variable star that is dimly visible to the naked eye with an apparent magnitude that ranges from 5.32 down to 5.39, which is comparable to the maximum brightness of the planet Uranus. It is about 1,120 light years from the Sun, and is drifting farther away at a rate of 9.4 km/s. Due to its location in the sky, it is visible only to observers south of 33°N latitude.
The Balmer jump, Balmer discontinuity, or Balmer break is the difference of intensity of the stellar continuum spectrum on either side of the limit of the Balmer series of hydrogen, at approximately 364.5 nm. It is caused by electrons being completely ionized directly from the second energy level of a hydrogen atom, which creates a continuum absorption at wavelengths shorter than 364.5 nm.
HD 133002 is a possible binary star in the northern constellation of Ursa Minor. With an apparent visual magnitude of 5.65, it is faintly visible to the naked eye. The high declination of +82.5° means it is hidden from view from most of the southern hemisphere. Parallax measurements yield an estimated distance of around 142 light years from the Sun. If it was instead positioned at a distance of 33 ly (10 pc), this would be a second magnitude star. The system is drifting closer with a heliocentric radial velocity of −44 km/s.
AB8, also known as SMC WR8, is a binary star in the Small Magellanic Cloud (SMC). A Wolf-Rayet star and a main sequence companion of spectral type O orbit in a period of 16.638 days. It is one of only nine known WO stars, the only Wolf-Rayet star in the SMC not on the nitrogen sequence, and the only Wolf-Rayet star in the SMC outside the main bar.
WR 30a is a massive spectroscopic binary in the constellation Carina. The primary is an extremely rare star on the WO oxygen sequence and the secondary a massive class O star. It appears near the Carina Nebula but is much further away.
References
- ↑ De Jager, C. (1954). "High-energy Microturbulence in the Solar Photosphere". Nature. 173 (4406): 680–1. Bibcode:1954Natur.173..680D. doi:10.1038/173680b0. S2CID 4188420.
- ↑ Montalban, J.; Nendwich, J.; Heiter, U.; Kupka, F.; et al. (1999). "The Effect of the microturbulence parameter on the Color-Magnitude Diagram". Reports on Progress in Physics. 61 (S239): 77–115. Bibcode:2007IAUS..239..166M. doi: 10.1017/S1743921307000361 .
- ↑ Cantiello, M. et al. (2008). "On the origin of Microturbulence in hot stars" (PDF).
{{cite journal}}: Cite journal requires|journal=(help) - ↑ Cantiello, M. et al. (2009); Langer, N.; Brott, I.; De Koter, A.; Shore, S. N.; Vink, J. S.; Voegler, A.; Lennon, D. J.; Yoon, S.-C. (2009). "Sub-surface convection zones in hot massive stars and their observable consequences". Astronomy and Astrophysics. 499 (1): 279. arXiv: 0903.2049 . Bibcode:2009A&A...499..279C. doi:10.1051/0004-6361/200911643. S2CID 55396719.
- ↑ Briley, Michael (July 13, 2006). "Stellar Properties from Spectral Lines: Introduction". University of Wisconsin. Archived from the original on November 23, 2007. Retrieved 2007-05-21.
- ↑ Nevins, W.M. (August 21, 2006). "The Plasma Microturbulence Project". Lawrence Livermore National Laboratory. Archived from the original on July 20, 2011. Retrieved 2007-05-21.
