A-type main-sequence star

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A-type main-sequence star
Star-Vega.png
Vega, the second brightest star in the northern celestial hemisphere, is an A-type main-sequence star (field of view approx. 1°).
Characteristics
TypeClass of moderate-large main sequence star.
Mass range1.8–2.2 M☉
Temperature7400–9700 K
Average luminosity8–38 L☉
External links
Commons-logo.svg Media category
Wikidata-logo.svg Q471805

An A-type main-sequence star [a] is a main-sequence (core hydrogen burning) star of spectral type A. The spectral luminosity class is typically V. These stars have spectra defined by strong hydrogen Balmer absorption lines. [1] They measure between 1.7 and 2.1  solar masses (M☉), have surface temperatures between 7,600 and 10,000  K , and live for about a quarter of the lifetime of the Sun. Bright and nearby examples are Altair (A7), Sirius A (A1), and Vega (A0). A-type stars do not have convective zones and thus are not expected to harbor magnetic dynamos. As a consequence, because they do not have strong stellar winds; they lack a means to generate X-ray emission.

Contents

Spectral standard stars

The Morgan-Keenan spectral classification Morgan-Keenan spectral classification.svg
The Morgan-Keenan spectral classification
Properties of typical A-type main-sequence stars [2] [3] [4] [5] [6]
Spectral
type 		Mass (M☉) Radius (R☉) Luminosity (L☉) Effective
temperature
(K)		 Color
index
(B − V)
A0V2.182.19338.029,7000.00
A1V2.052.13630.909,3000.04
A2V1.982.11723.998,8000.07
A3V1.931.86116.988,6000.10
A4V1.881.79413.498,2500.14
A5V1.861.78512.308,1000.16
A6V1.831.77511.227,9100.19
A7V1.811.75010.007,7600.21
A8V1.771.7489.127,5900.25
A9V1.751.7478.327,4000.27

The revised Yerkes Atlas system [7] listed a dense grid of A-type dwarf spectral standard stars, but not all of these have survived to this day as standards. The "anchor points" and "dagger standards" of the MK spectral classification system among the A-type main-sequence dwarf stars, i.e. those standard stars that have remained unchanged over years and can be considered to define the system, are Vega (A0 V), Phecda (A0 V), and Fomalhaut (A3 V). [8] [9] The seminal review of MK classification by Morgan & Keenan (1973) [9] didn't provide any dagger standards between types A3 V and F2 V. HD 23886 was suggested as an A5 V standard in 1978. [10]

Richard Gray & Robert Garrison provided the most recent contributions to the A dwarf spectral sequence in a pair of papers in 1987 [11] and 1989. [12] They list an assortment of fast- and slow-rotating A-type dwarf spectral standards, including HD 45320 (A1 V), HD 88955 (A2 V), 2 Hydri (A7 V), 21 Leonis Minoris (A7 V), and 44 Ceti (A9 V). Besides the MK standards provided in Morgan's papers and the Gray & Garrison papers, one also occasionally sees Zosma (A4 V) listed as a standard. There are no published A6 V and A8 V standard stars.

Planets

A-type stars are young (typically few hundred million years old) and many emit infrared (IR) radiation beyond what would be expected from the star alone. This IR excess is attributable to dust emission from a debris disk where planets form. [13] Surveys indicate massive planets commonly form around A-type stars although these planets are difficult to detect using the Doppler spectroscopy method. This is because A-type stars typically rotate very quickly, which makes it difficult to measure the small Doppler shifts induced by orbiting planets since the spectral lines are very broad. [14] However, this type of massive star eventually evolves into a cooler red giant which rotates more slowly and thus can be measured using the radial velocity method. [14]

As of early 2011 about 30 Jupiter class planets have been found around evolved K-giant stars including Pollux, Gamma Cephei and Iota Draconis. Doppler surveys around a wide variety of stars indicate about 1 in 6 stars having twice the mass of the Sun are orbited by one or more Jupiter-sized planets, compared to about 1 in 16 for Sun-like stars. [15] A-type star systems known to feature planets include HD 15082, Beta Pictoris and HR 8799. [16]

Examples of A-type main-sequence stars with circumstellar disc and exoplanets:

Name Spectral
type 		Mass
(M☉)		 Radius
(R☉)		 Disk extent
(AU)		 exoplanets
Vega A0V [17] 2.15 [18] 2.73 [18] 170 [19] / 815 [20] Vega b (candidate) [21]
Fomalhaut A3V [22] 1.92 [23] 1.84 [23] 209 [24] Fomalhaut b (controversial [25] ), [26] unnamed candidate [27]
HR 8799 A5V [28] 1.43 [29] 1.44 [30] 360 [31] HR 8799 b, HR 8799 c, HR 8799 d, [32] HR 8799 e, [33] HR 8799 f (candidate) [34]
Beta Pictoris A6V [22] 1.75 [35] 1.73 [36] 1835 [37] Beta Pictoris b, [38] Beta Pictoris c [39]

Examples

Within 40 light years:

Name Spectral
type 		Constellation vis Mag Mass
(M☉)		 Radius
(R☉)		 Luminosity
(L☉)		 Distance
(ly)
Sirius A0mA1 Va [17] Canis Major −1.46 [40] 2.063 [41] 1.713±0.009 [42] 24.7±0.7 [42] 8.61±0.03 [41]
Altair A7 V [17] Aquila 0.76 [43] 1.86±0.03 [44] 2.007 × 1.565 [44] 10.6 [45] 16.73 [46]
Vega A0 Va [17] Lyra 0.026 [47] 2.15+0.10
−0.15 [18] 		2.726±0.006 × 2.418±0.008 [18] 47.2±0.2 [18] 25.04 [46]
Fomalhaut A3 V [22] Piscis Austrinus 1.17 [43] 1.92±0.02 [23] 1.842±0.019 [23] 16.63±0.48 [23] 25.1 [46]
Denebola A3 Va [17] Leo 2.14 [48] 1.78 [49] 1.75±0.02 [50] 12.9±0.1 [50] 35.8 [46]

Sirius is the brightest star in the night sky.

Notes

  1. ↑ also called an "A-type dwarf" or "white main-sequence star" to distinguish it from a white dwarf.

See also

References

  1. ↑ "Stellar Spectral Types". hyperphysics.phy-astr.gsu.edu. Retrieved June 19, 2007.
  2. ↑ Pecaut, Mark J.; Mamajek, Eric E. (1 September 2013). "Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-main-sequence Stars". The Astrophysical Journal Supplement Series. 208 (1): 9. arXiv: 1307.2657 . Bibcode:2013ApJS..208....9P. doi:10.1088/0067-0049/208/1/9. ISSN   0067-0049. S2CID   119308564.
  3. ↑ Mamajek, Eric (2 March 2021). "A Modern Mean Dwarf Stellar Color and Effective Temperature Sequence". University of Rochester, Department of Physics and Astronomy. Retrieved 5 July 2021.
  4. ↑ Ostlie, Dale A.; Carroll, Bradley W. (2007). An Introduction to Modern Stellar Astrophysics. Pearson Addison-Wesley. ISBN   978-0-8053-0348-3.
  5. ↑ Habets, G. M. H. J.; Heintze, J. R. W. (1981). "Empirical bolometric corrections for the main-sequence". Astronomy and Astrophysics Supplement Series. 46: 193. Bibcode:1981A&AS...46..193H.Tables VII, VIII
  6. ↑ Schröder, C.; Schmitt, J. H. M. M. (November 2007). "X-ray emission from A-type stars". Astronomy and Astrophysics. 475 (2): 677–684. Bibcode:2007A&A...475..677S. doi: 10.1051/0004-6361:20077429 .
  7. ↑ Johnson, H. L.; Morgan, W. W. (1953). "Fundamental stellar photometry for standards of spectral type on the Revised System of the Yerkes Spectral Atlas". The Astrophysical Journal. 117: 313. Bibcode:1953ApJ...117..313J. doi:10.1086/145697.
  8. ↑ Garrison, Robert F. "MK Anchor Points". Archived from the original on 2019-06-25. Retrieved 2022-01-05.
  9. 1 2 Morgan, W. W.; Keenan, P. C. (1973). "Spectral Classification". Annual Review of Astronomy and Astrophysics. 11: 29. Bibcode:1973ARA&A..11...29M. doi:10.1146/annurev.aa.11.090173.000333.
  10. ↑ Morgan, W. W.; Abt, Helmut A.; Tapscott, J. W. (1978). Revised MK Spectral Atlas for stars earlier than the sun. Bibcode:1978rmsa.book.....M.
  11. ↑ Gray, R. O.; Garrison, R. F. (1987). "The Early A-Type Stars: Refined MK Classification, Confrontation with Stroemgren Photometry, and the Effects of Rotation". The Astrophysical Journal Supplement Series. 65: 581. Bibcode:1987ApJS...65..581G. doi: 10.1086/191237 .
  12. ↑ Gray, R. O.; Garrison, R. F. (1989). "The Late A-Type Stars: Refined MK Classification, Confrontation with Stroemgren Photometry, and the Effects of Rotation". The Astrophysical Journal Supplement Series. 70: 623. Bibcode:1989ApJS...70..623G. doi: 10.1086/191349 .
  13. ↑ Song, Inseok; et al. (2002). "M-Type Vega-like Stars". The Astronomical Journal. 124 (1): 514–518. arXiv: astro-ph/0204255 . Bibcode:2002AJ....124..514S. doi:10.1086/341164. S2CID   3450920.
  14. 1 2 Johnson, John Asher; Fischer, Debra A.; Marcy, Geoffrey W.; Wright, Jason T.; Driscoll, Peter; Butler, R. Paul; Hekker, Saskia; Reffert, Sabine; Vogt, Steven S. (2007). "Retired a Stars and Their Companions: Exoplanets Orbiting Three Intermediate-Mass Subgiants". The Astrophysical Journal. 665 (1): 785–793. arXiv: 0704.2455 . Bibcode:2007ApJ...665..785J. doi:10.1086/519677. S2CID   15076579.
  15. ↑ Johnson, J. A. (2011). "The Stars that Host Planets". Sky & Telescope . 121 (April): 22–27. Bibcode:2011S&T...121d..22J.
  16. ↑ "NASA Exoplanet Archive". exoplanetarchive.ipac.caltech.edu. Retrieved 2025-11-20.
  17. 1 2 3 4 5 Gray, R.O.; Corbally, C.J.; Garrison, R.F.; McFadden, M.T.; Robinson, P.E. (2003). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of stars earlier than M0 within 40 parsecs: The Northern Sample. I". Astronomical Journal. 126 (4): 2048–2059. arXiv: astro-ph/0308182 . Bibcode:2003AJ....126.2048G. doi:10.1086/378365. S2CID   119417105.
  18. 1 2 3 4 5 Monnier, J. D.; Che, Xiao; Zhao, Ming; Ekstrom, S.; Maestro, V.; Aufdenberg, J.; Baron, F.; Georgy, C.; Kraus, S.; McAlister, H.; Pedretti, E.; Ridgway, S.; Sturmann, J.; Sturmann, L.; Brummelaar, T. ten (2012-12-10). "Resolving Vega and the inclination controversy with CHARA/MIRC". The Astrophysical Journal. 761 (1): L3. arXiv: 1211.6055 . Bibcode:2012ApJ...761L...3M. doi:10.1088/2041-8205/761/1/L3. ISSN   2041-8205.
  19. ↑ Su, K. Y. L.; et al. (2005). "The Vega Debris Disk: A Surprise from Spitzer". The Astrophysical Journal. 628 (1): 487–500. arXiv: astro-ph/0504086 . Bibcode:2005ApJ...628..487S. doi:10.1086/430819. S2CID   18898968.
  20. ↑ Su, Kate Y. L.; Gaspar, Andras; Rieke, George H.; Malhotra, Renu; Matra, Luca; Wolff, Schuyler Grace; Leisenring, Jarron M.; Beichman, Charles; Ygouf, Marie (31 Oct 2024). "Imaging of the Vega Debris System using JWST/MIRI". The Astrophysical Journal. 977 (2): 277. arXiv: 2410.23636 . Bibcode:2024ApJ...977..277S. doi: 10.3847/1538-4357/ad8cde .
  21. ↑ Hurt, Spencer A.; Quinn, Samuel N.; Latham, David W.; Vanderburg, Andrew; Esquerdo, Gilbert A.; Calkins, Michael L.; Berlind, Perry; Angus, Ruth; Latham, Christian A.; Zhou, George (21 January 2021). "A Decade of Radial-velocity Monitoring of Vega and New Limits on the Presence of Planets". The Astronomical Journal. 161 (4): 157. arXiv: 2101.08801 . Bibcode:2021AJ....161..157H. doi: 10.3847/1538-3881/abdec8 . S2CID   231693198.
  22. 1 2 3 Gray, R. O.; Corbally, C. J.; et al. (July 2006). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc – The Southern Sample". The Astronomical Journal . 132 (1): 161–170. arXiv: astro-ph/0603770 . Bibcode:2006AJ....132..161G. doi:10.1086/504637. S2CID   250741593.
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