B-type main-sequence star

A B-type main-sequence star (B V) 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.[2] B-type stars are extremely luminous and blue. Their spectra have neutral helium, which are most prominent at the B2 subclass, and moderate hydrogen lines. Examples include Regulus and Algol A.[3]

This class of stars was introduced with the Harvard sequence of stellar spectra and published in the Revised Harvard photometry catalogue. The definition of type B-type stars was the presence of non-ionized helium lines with the absence of singly ionized helium in the blue-violet portion of the spectrum. All of the spectral classes, including the B type, were subdivided with a numerical suffix that indicated the degree to which they approached the next classification. Thus B2 is 1/5 of the way from type B (or B0) to type A.[4][5]

Later, however, more refined spectra showed lines of ionized helium for stars of type B0. Likewise, A0 stars also show weak lines of non-ionized helium. Subsequent catalogues of stellar spectra classified the stars based on the strengths of absorption lines at specific frequencies, or by comparing the strengths of different lines. Thus, in the MK Classification system, the spectral class B0 has the line at wavelength 439 nm being stronger than the line at 420 nm.[6] The Balmer series of hydrogen lines grows stronger through the B class, then peak at type A2. The lines of ionized silicon are used to determine the sub-class of the B-type stars, while magnesium lines are used to distinguish between the temperature classes.[5]

Type-B stars don't have a corona and lack a convection zone in their outer atmosphere. They have a higher mass loss rate than smaller stars such as the Sun, and their stellar wind has velocities of about 3,000 km/s.[7] The energy generation in main-sequence B-type stars comes from the CNO cycle of thermonuclear fusion. Because the CNO cycle is very temperature sensitive, the energy generation is heavily concentrated at the center of the star, which results in a convection zone about the core. This results in a steady mixing of the hydrogen fuel with the helium byproduct of the nuclear fusion.[8] Many B-type stars have a rapid rate of rotation, with an equatorial rotation velocity of about 200 km/s.[9]

Avior
Part of the constellation of Carina, Epsilon Carinae is an example of a double star featuring a main-sequence B-type star.
Typical Stellar Properties[1]
Spectral
Type
Radius
R
Mass
M
Teff
(K)
log g
B0V 10 17 25,000 4
B1V 6.42 13.21 25,400 3.9
B2V 5.33 9.11 20,800 3.9
B3V 4.8 7.6 18,800 4
B5V 3.9 5.9 15,200 4
B6V 3.56 5.17 13,800 4
B7V 3.28 4.45 12,400 4.1
B8V 3 3.8 11,400 4.1
B9V 2.7 3.29 10,600 4.1

Be and B(e) stars

Spectral objects known as "Be stars" are massive yet non-supergiant entities that notably have, or had at some time, 1 or more Balmer lines in emission, with the hydrogen-related electromagnetic radiation series projected out by the stars being of particular scientific interest. Be stars are generally thought to feature unusually strong stellar winds, high surface temperatures, and significant attrition of stellar mass as the objects rotate at a curiously rapid rate, all of this in contrast to many other main-sequence star types.[10]

Though the related terminologies are confusingly ambiguous, spectral objects known as "B(e)" or "B[e] stars" are distinct from Be stars since said B(e) entities are in possession of distinctive neutral or low ionization emission lines that are considered to have 'forbidden mechanisms', something denoted by the use of brackets or parenthesis. In other words, these particular stars' emissions appear to undergo processes not normally allowed under 1st-order perturbation theory in quantum mechanics. The definition of a "B(e) star" can include objects that are large enough to be in Blue giant and Blue supergiant territory, beyond the size of standard main-sequence stars.

Spectral Standard Stars

The revised Yerkes Atlas system (Johnson & Morgan 1953)[11] listed a dense grid of B-type dwarf spectral standard stars, however not all of these have survived to this day as standards. The "anchor points" of the MK spectral classification system among the B-type main-sequence dwarf stars, i.e. those standard stars that have remain unchanged since at least the 1940s, are upsilon Orionis (B0 V), eta Aurigae (B3 V), eta Ursae Majoris (B3 V).[12][13] Besides these anchor standards, the seminal review of MK classification by Morgan & Keenan (1973)[13] listed "dagger standards" of Tau Scorpii (B0 V), Omega Scorpii (B1 V), 42 Orionis (B1 V), 22 Scorpii (B2 V), Rho Aurigae (B5 V), and 18 Tauri (B8 V). The Revised MK Spectra Atlas of Morgan, Abt, & Tapscott (1978)[14] further contributed the standards Beta2 Scorpii (B2 V), 29 Persei (B3 V), HD 36936 (B5 V), and HD 21071 (B7 V). Gray & Garrison (1994)[15] contributed two B9 V standards: omega For A and HR 2328. The only published B4 V standard is 90 Leonis, from Lesh (1968).[16] There has been little agreement in the literature on choice of B6 V standard.

Chemical peculiarities

Some of the B-type stars of stellar class B0–B3 exhibit unusually strong lines of non-ionized helium. These chemically peculiar stars are termed helium-strong stars. These often have strong magnetic fields in their photosphere. In contrast, there are also helium-weak B-type stars with understrength helium lines and strong hydrogen spectra. Other chemically peculiar B-types stars are mercury–manganese stars with spectral types B7-B9. Finally, the aforementioned Be stars show a prominent emission spectrum of hydrogen.[17]

Planets

B-type stars known to have planets include the main-sequence B-types HIP 78530 b, the subgiants Kappa Andromedae b and a few (19 are now known) B-type subdwarfs.

See also

References

  1. ^ Silaj, J.; et al. (November 2014), "The Hα Profiles of Be Shell Stars", The Astrophysical Journal, 795 (1): 12, Bibcode:2014ApJ...795...82S, doi:10.1088/0004-637X/795/1/82, 82.
  2. ^ Habets, G. M. H. J.; Heintze, J. R. W. (November 1981). "Empirical bolometric corrections for the main-sequence". Astronomy and Astrophysics Supplement. 46: 193–237. Bibcode:1981A&AS...46..193H., Tables VII and VIII.
  3. ^ SIMBAD, entries on Regulus and Algol A, accessed June 19, 2007.
  4. ^ Pickering, Edward Charles (1908). "Revised Harvard photometry : a catalogue of the positions, photometric magnitudes and spectra of 9110 stars, mainly of the magnitude 6.50, and brighter observed with the 2 and 4 inch meridian photometers". Annals of the Astronomical Observatory of Harvard College. 50. Bibcode:1908AnHar..50....1P. Retrieved 2009-09-21.
  5. ^ a b Gray, C. Richard O.; Corbally, J. (2009). Stellar Spectral Classification. Princeton University Press. pp. 115–122. ISBN 0691125112.
  6. ^ Morgan, William Wilson; Keenan, Philip Childs; Kellman, Edith (1943). An atlas of stellar spectra, with an outline of spectral classification. Chicago, Ill: The University of Chicago press. Bibcode:1943assw.book.....M.
  7. ^ Aschenbach, B.; Hahn, Hermann-Michael; Truemper, Joachim (1998). Hermann-Michael Hahn (ed.). The invisible sky: ROSAT and the age of X-ray astronomy. Springer. p. 76. ISBN 0387949283.
  8. ^ Böhm-Vitense, Erika (1992). Introduction to stellar astrophysics. 3. Cambridge University Press. p. 167. ISBN 0521348714.
  9. ^ McNally, D. (1965). "The distribution of angular momentum among main sequence stars". The Observatory. 85: 166–169. Bibcode:1965Obs....85..166M.
  10. ^ Slettebak, Arne (July 1988). "The Be Stars". Publications of the Astronomical Society of the Pacific. 100: 770–784. Bibcode:1988PASP..100..770S. doi:10.1086/132234.
  11. ^ Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas H.L. Johnson & W.W. Morgan, 1953, Astrophysical Journal, 117, 313
  12. ^ MK ANCHOR POINTS, Robert F. Garrison
  13. ^ a b Spectral Classification, W.W. Morgan & P.C. Keenan, 1973, Annual Review of Astronomy and Astrophysics, vol. 11, p.29
  14. ^ Revised MK Spectral Atlas for stars earlier than the sun, W.W. Morgan, W. W., H.A. Abt, J.W. Tapscott, 1978, Williams Bay: Yerkes Observatory, and Tucson: Kitt Peak National Observatory
  15. ^ The late B-type stars: Refined MK classification, confrontation with stromgren photometry, and the effects of rotation, R.F. Gray & R.O. Garrison, 1994, The Astronomical Journal, vol. 107, no. 4, p. 1556-1564
  16. ^ The Kinematics of the Gould Belt: an Expanding Group? J.R. Lesh, 1968, Astrophysical Journal Supplement, vol. 17, p.371 (Table 1)
  17. ^ Gray, Richard O.; Corbally, C. J. (2009). Stellar Spectral Classification. Princeton University Press. pp. 123–136. ISBN 0691125112.
12 Scorpii

12 Scorpii is a probable triple star system in the zodiac constellation of Scorpius, located about 300 light years away from the Sun. It has the Bayer designation c1 Scorpii; 12 Scorpii is the Flamsteed designation. This system is faintly visible to the naked eye with a combined apparent visual magnitude of 5.67. It is a probable (82% chance) member of the Sco OB2 moving group. The primary component is a B-type main-sequence star with a stellar classification of B9V.

22 Aurigae

22 Aurigae is a star located 537 light years away from the Sun in the northern constellation Auriga. It is just bright enough to be barely visible to the naked eye under good viewing conditions, appearing as a blue-white hued star with an apparent visual magnitude of 6.45. At the distance of this object, the brightness is diminished by an extinction of 0.57 due to interstellar dust. The star is moving further from the Earth with a heliocentric radial velocity of +10 km/s, and it is a member of the Taurion OB association, located between Orion and Taurus.This object is a B-type main-sequence star with a stellar classification of B9 Vs. The 's' notation indicates the spectrum appears "sharp"-lined, due to its relatively moderate projected rotational velocity of 66 km/s. It has 2.9 times the mass of the Sun and about 3.1 times the Sun's radius. The star is radiating 90 times the luminosity of the Sun from its photosphere at an effective temperature of 10,764 K.

22 Scorpii

22 Scorpii (i Scorpii) is a single star in the southern zodiac constellation of Scorpius. It is faintly visible to the naked eye with an apparent visual magnitude of 4.78. The distance to this star can be estimated from its annual parallax shift of 7.89±0.24 mas, which yields a value of around 410 light years. The star is embedded in, or adjacent to, a diffuse nebulous cloud.This is a B-type main-sequence star with a stellar classification of B3 V. It is ten million years old and has a high rate of spin with a projected rotational velocity of 169 km/s. The star has about six times the mass of the Sun and is radiating 335 times the Sun's luminosity from its photosphere at an effective temperature of 19,600 K.

30 Persei

30 Persei is a binary star system in the northern constellation Perseus. It is faintly visible to the naked eye with an apparent visual magnitude of 5.49. Based upon an annual parallax shift of 4.46±0.39 mas, is located roughly 730 light years from the Sun. It is a member of the Perseus OB3 association, which includes the Alpha Persei Cluster.This is a single-lined spectroscopic binary star system with an orbital period of 36.5 days and an eccentricity of roughly 0.3. The visible component is a B-type main-sequence star with a stellar classification of B7 V. It is spinning rapidly with a projected rotational velocity of 212 km/s. The star has 4.2 times the mass of the Sun and is radiating around 611 times the Sun's luminosity from its photosphere at an effective temperature of 9,908 K.

36 Tauri

36 Tauri (abbreviated to 36 Tau) is a binary star in the constellation of Taurus. Parallax measurements made by the Hipparcos spacecraft put it at a distance of over 1,000 light years (350 parsecs) from Earth. The combined apparent magnitude of the system is about 5.5, meaning it can barely be seen with the naked eye, according to the Bortle scale.

36 Tauri is a spectroscopic binary. The two stars are close enough that periodic Doppler shifts in their spectra can be made out. In this case, light from both stars can be detected (and they overlap in the spectrum), so it is a double-lined system. The primary star, designated HD 25555, is a K-type bright giant, and the secondary star, designated HD 25556, is a B-type main-sequence star. However, the spectrum has also been interpreted as a G-type star and an A-type main-sequence star. The two stars have been resolved using speckle interferometry and are thought to have similar masses.

4 Aquilae

4 Aquilae, abbreviated 4 Aql, is a single, white-hued star in the equatorial constellation of Aquila. 4 Aquilae is the Flamsteed designation. It has an apparent visual magnitude of 5.02, making it a faint star visible to the naked eye. The distance to 4 Aql can be estimated from its annual parallax shift of 6.7 mas, yielding an estimated range of around 480 light years. It is moving closer to the Earth with a heliocentric radial velocity of −13 km/s.This is a B-type main-sequence star with a stellar classification of B9 V. It was classed as a Be star by Arne Sletteback in 1982, indicating it has ionized circumstellar gas. The star is spinning rapidly, showing a projected rotational velocity of 259 km/s, and is being viewed almost equator-on. It has 3.6 times the mass of the Sun and 3 times the Sun's radius. The star is radiating 294 times the Sun's luminosity from its photosphere at an effective temperature of 10,965 K.

4 Sagittarii

4 Sagittarii is a suspected astrometric binary star system in the zodiac constellation of Sagittarius, located approximately 390 light years away based on parallax. It is visible to the naked eye as a faint, blue-white hued star with an apparent visual magnitude of 4.74, The system is moving closer to the Earth with a heliocentric radial velocity of −18 km/s.The visible component is a B-type main-sequence star with a stellar classification of B9 V. It has a high rate of spin, displaying a projected rotational velocity of 149 km/s. This is giving it an oblate shape with a equatorial bulge that is an estimated 14% larger than the polar radius. 4 Sagittarii has 3.23 times the mass of the Sun and is radiating 240 times the Sun's luminosity from its photosphere at an effective temperature of 9,661 K.

50 Boötis

50 Boötis is a single star located 275 light years away from the Sun in the northern constellation of Boötes. It is visible to the naked eye as a dim, blue-white hued star with an apparent visual magnitude of 5.38. The object is moving closer to the Earth with a heliocentric radial velocity of −9 km/s.This is a B-type main-sequence star with a stellar classification of B9 Vn, where the 'n' notation indicates "nebulous" lines due to rapid rotation. It is 174 million years old with a projected rotational velocity of 232 km/s. The star has 3.31 times the mass of the Sun and about 3.1 times the Sun's radius. It is radiating 55 times the Sun's luminosity from its photosphere at an effective temperature of 12,140 km/s.

52 Hydrae

52 Hydrae is a triple star system in the constellation Hydra. It has the Bayer designation l Hydrae; 52 Hydrae is the Flamsteed designation. This system is visible to the naked eye as a faint, blue-white hued star with an apparent visual magnitude of 4.97. It is a probable (80% chance) member of the Sco OB2 moving group of stars, and is moving away from the Earth with a heliocentric radial velocity of 5 km/s.The primary component is a binary system consisting of two nearly equal components with an orbital period of around 15 years and an angular separation of 0.1″. It shows a combined stellar classification of B7/8V, which matches a B-type main-sequence star. The third component is a magnitude 10.0 star at a separation of 4.2″ with a mass similar to the Sun. It is orbiting the inner pair with a period of around 3,900 years.

53 Aurigae

53 Aurigae is a binary star in the constellation Auriga. Its apparent magnitude is 5.74. Parallax estimates made by the Hipparcos spacecraft put it at a distance of 350 light-years (106 parsecs) away.The two components of 53 Aurigae orbit each other every 39 years. The primary component, 53 Aurigae A, is chemically peculiar since it contains higher-than-normal amounts of manganese, but also europium, chromium, and mercury. It is a B-type main-sequence star, while the secondary component, 53 Aurigae B, is an early F-type main-sequence star. The total mass of the system is estimated to be 4.8 M☉.

55 Persei

55 Persei is a single, blue-white hued star in the northern constellation Perseus. It is faintly visible to the naked eye under good seeing conditions, having an apparent visual magnitude of 5.73. Based upon an annual parallax shift of 8.50±0.38 mas as seen from Earth's orbit, the star is located about 380 light years from the Sun. At that distance, the visual magnitude is diminished by an extinction of 0.39 due to interstellar dust.

This is a B-type main-sequence star with a stellar classification of B8 V; a massive star that is generating energy through hydrogen fusion at its core. It has 3.44 times the mass of the Sun and about 3 times the Sun's radius. The star is about 197 million years old and is spinning rapidly with a projected rotational velocity of 288 km/s. It is radiating roughly 193 times the Sun's luminosity from its photosphere at an effective temperature of 12,246 K.

HD 108541

HD 108541, also known by its Bayer designation u Centauri is a star located in the constellation Centaurus, It is also known as HR 4748. The apparent magnitude of the star is about 5.4, meaning it is only visible to the naked eye under excellent viewing conditions. Its distance is about 440 light-years (140 parsecs), based on its parallax measured by the Hipparcos astrometry satellite. The spectral type of HD 108541 is B8/9V, meaning it is a late B-type main sequence star. These types of stars are a few times more massive than the Sun, and have effective temperatures of about 10,000 to 30,000 K. HD 108541 is just under 3 times more massive than the Sun and has a temperature of about 11,000 K.

HD 28375

HD 28375 is a star in the zodiac constellation of Taurus. Its apparent magnitude is 5.53. Based on parallax estimates made by the Hipparcos spacecraft, the star is located fairly close, about 380 light-years (117 parsecs) away.HD 28375 has a spectrum matching that of a B-type main-sequence star. Its effective temperature is about 13,000 K. An infrared excess has been detected, indicating the presence of a circumstellar disk. The dust would have a temperature of about 119 K, located about 67 astronomical units away from the star.HD 28375 is also known as 44 Eridani, although the name has fallen out of use because constellations were redrawn, placing the star out of Eridanus and into Taurus.

HR 1884

HR 1884 is a spectroscopic binary star in the constellation Auriga. The primary is a G type supergiant star while the secondary is probably a B type main sequence star.The possible spectroscopic binary nature of the star was first noted in 1983 by Gilbert Burki and Michel Mayor in a paper on the rate of binaries among supergiant stars. In the same year William P. Bidelman noted that the stellar spectrum was composite indicating a companion star. Confirmation of spectroscopic binary status and a preliminary orbit was published in 1998 by R. Paul Butler, a much more accurate orbit was published in 2015 by Roger Griffin.

HR 6902

HR 6902 (also designated V2291 Oph) is a binary system located 790 light years away from the Sun in the Ophiuchus constellation. The system includes an orange bright giant star and a B-type main sequence star, forming an eclipsing binary of Zeta Aurigae type. The system is also surrounded by a warm circumstellar envelope and the spectra show silicon and carbon absorption up to a distance of 3.3 giant radii.

H Centauri

H Centauri (H Cen), also known as V945 Centauri, is probable triple star system located in the constellation Centaurus. From parallax measurements, it is located 113 parsecs (370 light years) from the sun. It is a member of the Lower Centaurus-Crux (LCC) subgroup of the Scorpius–Centaurus Association.This system is a double-lined spectroscopic binary formed by two B-type main-sequence star with spectral types B7V and B8.5V. They are in a close (but detached) circular orbit with a period of 0.6496 days and a separation of 5.63 solar radii. Observed at an inclination of 24°, the system is an ellipsoidal variable whose apparent visual magnitude varies from 5.14 to 5.17 over the course of an orbit as the star's visible surface area changes. The system's spectrum contains a third set of spectral lines that are probably from a third star, also of type B.

Iota Andromedae

Iota Andromedae (ι And, ι Andromedae) is a star in the constellation Andromeda. It has an apparent magnitude of +4.29 and is approximately 500 light years from Earth.Iota Andromedae is a B-type main sequence star with a stellar classification of B8 V. It is among the least variable stars observed during the Hipparcos mission.

X1 Centauri

x1 Centauri is a star located in the constellation Centaurus. It is also known by its designations HD 107832 and HR 4712. The apparent magnitude of the star is about 5.3, meaning it is only visible to the naked eye under excellent viewing conditions. Its distance is about 440 light-years (140 parsecs), based on its parallax measured by the Hipparcos astrometry satellite.x1 Centauri's spectral type is B8/9V, meaning it is a late B-type main sequence star. These types of stars are a few times more massive than the Sun, and have effective temperatures of about 10,000 to 30,000 K. x1 Centauri is just over 3 times more massive than the Sun and has a temperature of about 11,300 K. The star x2 Centauri, which lies about 0.4′ away from x1 Centauri, may or may not form a physical binary star system with x1 Centauri, as the two have similar proper motions and distances.

X2 Centauri

x2 Centauri is a star located in the constellation Centaurus. It is also known by its designations HD 108114 and HR 4724. The apparent magnitude of the star is about 5.7, meaning it is only visible to the naked eye under excellent viewing conditions. Its distance is about 440 light-years (140 parsecs), based on its parallax measured by the Hipparcos astrometry satellite.x2 Centauri's spectral type is B9IV/V, meaning it is a late B-type main sequence star or subgiant. These types of stars are a few times more massive than the Sun, and have effective temperatures of about 10,000 to 30,000 K. x2 Centauri has a temperature of about 11,500 K. The star x1 Centauri, which lies about 0.4′ away from x2 Centauri, may or may not form a physical binary star system with x2 Centauri, as the two have similar proper motions and distances.

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Evolution
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