Wikipedia

A-type main-sequence star

(Redirected from A-type main sequence star)
See also: Stellar classification § Class

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.

A-type main-sequence star
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
inline Media category
inline Q471805

Spectral standard stars

edit
 
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)
A0V 2.18 2.193 38.02 9,700 0.00
A1V 2.05 2.136 30.90 9,300 0.04
A2V 1.98 2.117 23.99 8,800 0.07
A3V 1.93 1.861 16.98 8,600 0.10
A4V 1.88 1.794 13.49 8,250 0.14
A5V 1.86 1.785 12.30 8,100 0.16
A6V 1.83 1.775 11.22 7,910 0.19
A7V 1.81 1.750 10.00 7,760 0.21
A8V 1.77 1.748 9.12 7,590 0.25
A9V 1.75 1.747 8.32 7,400 0.27

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

edit

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

edit

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

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

See also

edit

References

edit
  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. ^ a b 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. ^ a b 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. ^ a b c d e 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. ^ a b c d e 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. ^ a b c 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.
  23. ^ a b c d e Mamajek, E.E. (August 2012). "On the Age and Binarity of Fomalhaut". Astrophysical Journal Letters. 754 (2): L20. arXiv:1206.6353. Bibcode:2012ApJ...754L..20M. doi:10.1088/2041-8205/754/2/L20. S2CID 119191190.
  24. ^ Kalas, Paul; Graham, James R.; Fitzgerald, Michael P.; Clampin, Mark (2013). "STIS Coronagraphic Imaging of Fomalhaut: Main Belt Structure and the Orbit of Fomalhaut b". The Astrophysical Journal. 775 (1) 56. arXiv:1305.2222. Bibcode:2013ApJ...775...56K. doi:10.1088/0004-637X/775/1/56. S2CID 62877509.
  25. ^ "Planet Fomalhaut b - Exoplanet.eu - Encyclopaedia of exoplanetary systems". exoplanet.eu. Retrieved 2025-12-16.
  26. ^ Kalas, Paul; et al. (2008-11-13). "Optical Images of an Exosolar Planet 25 Light-Years from Earth". Science. 322 (5906): 1345–8. arXiv:0811.1994. Bibcode:2008Sci...322.1345K. doi:10.1126/science.1166609. PMID 19008414. S2CID 10054103.
  27. ^ Ygouf, Marie; Beichman, Charles; et al. (October 2023). "Searching for Planets Orbiting Fomalhaut with JWST/NIRCam". The Astronomical Journal. 167 (1): 26. arXiv:2310.15028. Bibcode:2024AJ....167...26Y. doi:10.3847/1538-3881/ad08c8.
  28. ^ Gray, Richard O.; Kaye, Anthony B. (December 1999). "HR 8799: A Link between γ Doradus Variables and λ Bootis Stars". The Astronomical Journal. 118 (6): 2993–2996. Bibcode:1999AJ....118.2993G. doi:10.1086/301134.
  29. ^ Sepulveda, Aldo G.; Bowler, Brendan P. (2022-02-01). "Dynamical Mass of the Exoplanet Host Star HR 8799". The Astronomical Journal. 163 (2): 52. arXiv:2111.12090. Bibcode:2022AJ....163...52S. doi:10.3847/1538-3881/ac3bb5. ISSN 0004-6256.
  30. ^ Baines, Ellyn K.; White, Russel J.; Huber, Daniel; Jones, Jeremy; Boyajian, Tabetha; McAlister, Harold A.; ten Brummelaar, Theo A.; Turner, Nils H.; Sturmann, Judit; Sturmann, Laszlo; Goldfinger, P. J.; Farrington, Christopher D.; Riedel, Adric R.; Ireland, Michael; von Braun, Kaspar (2012-12-10). "The Chara Array Angular Diameter of Hr 8799 Favors Planetary Masses for ITS Imaged Companions". The Astrophysical Journal. 761 (1): 57. arXiv:1210.0556. Bibcode:2012ApJ...761...57B. doi:10.1088/0004-637X/761/1/57. ISSN 0004-637X.
  31. ^ Faramaz, Virginie; Marino, Sebastian; Booth, Mark; Matrà, Luca; Mamajek, Eric E.; Bryden, Geoffrey; et al. (2021). "A Detailed Characterization of HR 8799's Debris Disk with ALMA in Band 7". The Astronomical Journal. 161 (6): 271. arXiv:2104.02088. Bibcode:2021AJ....161..271F. doi:10.3847/1538-3881/abf4e0. S2CID 233033512.
  32. ^ Marois, Christian; Macintosh, Bruce; Barman, Travis; Zuckerman, B.; Song, Inseok; Patience, Jennifer; Lafrenière, David; Doyon, René (November 2008). "Direct imaging of multiple planets orbiting the star HR 8799". Science. 322 (5906): 1348–1352. arXiv:0811.2606. Bibcode:2008Sci...322.1348M. doi:10.1126/science.1166585. PMID 19008415. S2CID 206516630.
  33. ^ Marois, Christian; Zuckerman, B.; Konopacky, Quinn M.; Macintosh, Bruce; Barman, Travis (December 2010). "Images of a fourth planet orbiting HR 8799". Nature. 468 (7327): 1080–1083. arXiv:1011.4918. Bibcode:2010Natur.468.1080M. doi:10.1038/nature09684. PMID 21150902. S2CID 4425891.
  34. ^ Thompson, William; Marois, Christian; Do ó, Clarissa R.; Konopacky, Quinn; Ruffio, Jean-Baptiste; Wang, Jason; Skemer, Andy J.; De Rosa, Robert J.; MacIntosh, Bruce (2023). "Deep Orbital Search for Additional Planets in the HR 8799 System". The Astronomical Journal. 165 (1): 29. arXiv:2210.14213. Bibcode:2023AJ....165...29T. doi:10.3847/1538-3881/aca1af.
  35. ^ Crifo, F.; et al. (1997). "β Pictoris revisited by Hipparcos. Star properties". Astronomy and Astrophysics. 320: L29 – L32. Bibcode:1997A&A...320L..29C.
  36. ^ Kervella, P. (2003). "VINCI/VLTI Observations of Main Sequence Stars". In A.K. Dupree; A.O. Benz (eds.). Proceedings of the 219th symposium of the International Astronomical Union. IAUS 219: Stars as Suns: Activity, Evolution and Planets. Sydney, Australia: Astronomical Society of the Pacific. p. 80. Bibcode:2003IAUS..219E.127K.
  37. ^ Larwood, J. D. & Kalas, P. G. (2001). "Close stellar encounters with planetesimal discs: the dynamics of asymmetry in the β Pictoris system". MNRAS. 323 (2): 402–416. arXiv:astro-ph/0011279. Bibcode:2001MNRAS.323..402L. doi:10.1046/j.1365-8711.2001.04212.x. S2CID 1844824.
  38. ^ Lagrange, A.-M.; Gratadour, D.; Chauvin, G.; Fusco, T.; Ehrenreich, D.; Mouillet, D.; Rousset, G.; Rouan, D.; Allard, F.; Gendron, É.; Charton, J.; Mugnier, L.; Rabou, P.; Montri, J.; Lacombe, F. (2009). "A probable giant planet imaged in the β Pictoris disk". Astronomy and Astrophysics. 493 (2): L21 – L25. arXiv:0811.3583. Bibcode:2009A&A...493L..21L. doi:10.1051/0004-6361:200811325. ISSN 0004-6361. S2CID 16548235.
  39. ^ Lagrange; Meunier, Nadège; Rubini, Pascal; Keppler, Miriam; Galland, Franck; Chapellier, eric (2019). "Evidence for an additional planet in the β Pictoris system". Nature. 3 (12): 1135–1142. Bibcode:2019NatAs...3.1135L. doi:10.1038/s41550-019-0857-1. S2CID 202126059.
  40. ^ Hoffleit, D.; Warren, W. H. Jr. (1991). "Entry for HR 2491". Bright Star Catalogue (5th Revised Ed. (Preliminary Version) ed.). CDS. Bibcode:1991bsc..book.....H.
  41. ^ a b Bond, Howard E.; Schaefer, Gail H.; Gilliland, Ronald L.; Holberg, Jay B.; Mason, Brian D.; Lindenblad, Irving W.; et al. (2017). "The Sirius system and its astrophysical puzzles: Hubble Space Telescope and ground-based astrometry". The Astrophysical Journal. 840 (2): 70. arXiv:1703.10625. Bibcode:2017ApJ...840...70B. doi:10.3847/1538-4357/aa6af8. S2CID 51839102.
  42. ^ a b Davis, J.; et al. (October 2010). "The Angular Diameter and Fundamental Parameters of Sirius A". Publications of the Astronomical Society of Australia. 28: 58–65. arXiv:1010.3790. doi:10.1071/AS10010.
  43. ^ a b Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237: 0. Bibcode:2002yCat.2237....0D.
  44. ^ a b Bouchaud, K.; Domiciano De Souza, A.; Rieutord, M.; Reese, D. R.; Kervella, P. (2020). "A realistic two-dimensional model of Altair". Astronomy and Astrophysics. 633: A78. arXiv:1912.03138. Bibcode:2020A&A...633A..78B. doi:10.1051/0004-6361/201936830. S2CID 208857428.
  45. ^ Peterson, D. M.; Hummel, C. A.; Pauls, T. A.; et al. (2006). "Resolving the Effects of Rotation in Altair with Long-Baseline Interferometry". The Astrophysical Journal. 636 (2): 1087–1097. arXiv:astro-ph/0509236. Bibcode:2006ApJ...636.1087P. doi:10.1086/497981. S2CID 18683397. See Table 2 for stellar parameters.
  46. ^ a b c d van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
  47. ^ Bohlin, R. C.; Gilliland, R. L. (2004). "Hubble Space Telescope Absolute Spectrophotometry of Vega from the Far-Ultraviolet to the Infrared". The Astronomical Journal. 127 (6): 3508–3515. Bibcode:2004AJ....127.3508B. doi:10.1086/420715.
  48. ^ Samus, N. N.; et al. (2017). "General Catalogue of Variable Stars". Astronomy Reports. 5.1. 61 (1): 80–88. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
  49. ^ Di Folco, E.; et al. (2004). "VLTI near-IR interferometric observations of Vega-like stars". Astronomy and Astrophysics. 426 (2): 601–617. Bibcode:2004A&A...426..601D. doi:10.1051/0004-6361:20047189.
  50. ^ a b Baines, Ellyn K.; Clark III, James H.; Schmitt, Henrique R.; Stone, Jordan M.; von Braun, Kaspar (2023-12-01). "33 New Stellar Angular Diameters from the NPOI, and Nearly 180 NPOI Diameters as an Ensemble". The Astronomical Journal. 166 (6): 268. arXiv:2505.23514. Bibcode:2023AJ....166..268B. doi:10.3847/1538-3881/ad08be. ISSN 0004-6256.
 
Wikimedia Commons has media related to White main-sequence stars.
Retrieved from "https://en.wikipedia.org/w/index.php?title=A-type_main-sequence_star&oldid=1327976236"