Astronomy:A-type main-sequence star

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Short description: Stellar classification

Template:Infobox astronomical formation An A-type main-sequence star[lower-alpha 1] is a main-sequence (core hydrogen burning) star of spectral type A. The spectral luminosity class is V.[1][2] These stars have spectra defined by strong hydrogen Balmer absorption lines.[3] 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.

Spectral standard stars

The Morgan-Keenan spectral classification
Properties of typical A-type main-sequence stars[4][5][6][7][8]
Spectral
type 		Mass (M☉) Radius (R☉) Luminosity (L☉) Effective
temperature
(K) 		Color
index
(B − V)
A0V 2.33 2.193 38.37 9,700 0.00
A1V 2.17 2.136 30.76 9,300 0.04
A2V 2.06 2.117 24.21 8,840 0.07
A3V 1.92 1.861 17.06 8,600 0.10
A4V 1.88 1.794 13.43 8,250 0.14
A5V 1.86 1.785 12.36 8,100 0.16
A6V 1.83 1.775 11.12 7,910 0.19
A7V 1.76 1.750 10.00 7,760 0.21
A8V 1.67 1.747 9.12 7,590 0.25
A9V 1.63 1.747 8.24 7,400 0.27

The revised Yerkes Atlas system[9] 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).[10][11] The seminal review of MK classification by Morgan & Keenan (1973)[11] did not provide any dagger standards between types A3 V and F2 V. HD 23886 was suggested as an A5 V standard in 1978.[12]

Richard Gray & Robert Garrison provided the most recent contributions to the A dwarf spectral sequence in a pair of papers in 1987[13] and 1989.[14] 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.[15] 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.[16] 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.[16]

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 one in six stars having twice the mass of the Sun are orbited by one or more Jupiter-sized planets, compared to about one in sixteen for Sun-like stars.[17] A-type star systems known to feature planets include HD 15082, Beta Pictoris and HR 8799.[18]

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

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

Examples

Within 40 light-years:

Name Spectral
type 		Constellation vis Mag Mass
(M☉) 		Radius
(R☉) 		Luminosity
(L☉) 		Distance
(ly)
Sirius A0mA1 Va[39] 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[39] Aquila 0.76[43] 1.86±0.03[44] 2.007 × 1.565[44] 10.6[45] 16.73[46]
Vega A0 Va[39] Lyra 0.026[47] 2.15+0.10
−0.15[19] 		2.726±0.006 × 2.418±0.008[19] 47.2±0.2[19] 25.04[46]
Fomalhaut A3 V[48] 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[39] Leo 2.14[49] 1.78[50] 1.75±0.02[51] 12.9±0.1[51] 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. ↑ "Glossary term: Luminosity Class". 2020–2026. https://astro4edu.org/resources/glossary/term/503/. 
  2. ↑ "Glossary term: Dwarf Star". 2020–2026. https://astro4edu.org/resources/glossary/term/88/. 
  3. ↑ "Stellar Spectral Types". http://hyperphysics.phy-astr.gsu.edu/hbase/starlog/staspe.html. 
  4. ↑ 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. doi:10.1088/0067-0049/208/1/9. ISSN 0067-0049. Bibcode: 2013ApJS..208....9P. 
  5. ↑ Mamajek, Eric (2 March 2021). "A Modern Mean Dwarf Stellar Color and Effective Temperature Sequence". University of Rochester, Department of Physics and Astronomy. https://www.pas.rochester.edu/~emamajek/EEM_dwarf_UBVIJHK_colors_Teff.txt. 
  6. ↑ Ostlie, Dale A.; Carroll, Bradley W. (2007). An Introduction to Modern Stellar Astrophysics. Pearson Addison-Wesley. ISBN 978-0-8053-0348-3. https://books.google.com/books?id=BNpFAQAAIAAJ. 
  7. ↑ 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
  8. ↑ Schröder, C.; Schmitt, J. H. M. M. (November 2007). "X-ray emission from A-type stars". Astronomy and Astrophysics 475 (2): 677–684. doi:10.1051/0004-6361:20077429. Bibcode: 2007A&A...475..677S. 
  9. ↑ 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. doi:10.1086/145697. Bibcode: 1953ApJ...117..313J. 
  10. ↑ Garrison, Robert F.. "MK Anchor Points". http://www.astro.utoronto.ca/~garrison/mkstds.html. 
  11. ↑ 11.0 11.1 Morgan, W. W.; Keenan, P. C. (1973). "Spectral Classification". Annual Review of Astronomy and Astrophysics 11: 29. doi:10.1146/annurev.aa.11.090173.000333. Bibcode: 1973ARA&A..11...29M. 
  12. ↑ Morgan, W. W.; Abt, Helmut A.; Tapscott, J. W. (1978). Revised MK Spectral Atlas for stars earlier than the sun. Bibcode: 1978rmsa.book.....M. 
  13. ↑ 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. doi:10.1086/191237. Bibcode: 1987ApJS...65..581G. 
  14. ↑ 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. doi:10.1086/191349. Bibcode: 1989ApJS...70..623G. 
  15. ↑ Song, Inseok; Weinberger, A. J.; Becklin, E. E.; Zuckerman, B.; Chen, C. (2002). "M-Type Vega-like Stars". The Astronomical Journal 124 (1): 514–518. doi:10.1086/341164. Bibcode: 2002AJ....124..514S. 
  16. ↑ 16.0 16.1 Johnson, John Asher; Fischer, Debra A.; Marcy, Geoffrey W.; Wright, Jason T.; Driscoll, Peter; Butler, R. Paul; Hekker, Saskia; Reffert, Sabine et al. (2007). "Retired a Stars and Their Companions: Exoplanets Orbiting Three Intermediate-Mass Subgiants". The Astrophysical Journal 665 (1): 785–793. doi:10.1086/519677. Bibcode: 2007ApJ...665..785J. 
  17. ↑ Johnson, J. A. (2011). "The Stars that Host Planets". Sky & Telescope 121 (April): 22–27. Bibcode: 2011S&T...121d..22J. 
  18. ↑ "NASA Exoplanet Archive". https://exoplanetarchive.ipac.caltech.edu/. 
  19. ↑ 19.0 19.1 19.2 19.3 19.4 Monnier, J. D.; Che, Xiao; Zhao, Ming; Ekstrom, S.; Maestro, V.; Aufdenberg, J.; Baron, F.; Georgy, C. et al. (2012-12-10). "Resolving Vega and the inclination controversy with CHARA/MIRC". The Astrophysical Journal 761 (1): L3. doi:10.1088/2041-8205/761/1/L3. ISSN 2041-8205. Bibcode: 2012ApJ...761L...3M. 
  20. ↑ Su, K. Y. L.; Rieke, G. H.; Misselt, K. A. et al. (2005). "The Vega Debris Disk: A Surprise from Spitzer". The Astrophysical Journal 628 (1): 487–500. doi:10.1086/430819. Bibcode: 2005ApJ...628..487S. 
  21. ↑ Su, Kate Y. L.; Gaspar, Andras; Rieke, George H.; Malhotra, Renu; Matra, Luca; Wolff, Schuyler Grace; Leisenring, Jarron M.; Beichman, Charles et al. (31 Oct 2024). "Imaging of the Vega Debris System using JWST/MIRI". The Astrophysical Journal 977 (2): 277. doi:10.3847/1538-4357/ad8cde. Bibcode: 2024ApJ...977..277S. 
  22. ↑ Hurt, Spencer A.; Quinn, Samuel N.; Latham, David W.; Vanderburg, Andrew; Esquerdo, Gilbert A.; Calkins, Michael L.; Berlind, Perry; Angus, Ruth et al. (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. doi:10.3847/1538-3881/abdec8. Bibcode: 2021AJ....161..157H. 
  23. ↑ 23.0 23.1 23.2 23.3 23.4 Mamajek, E.E. (August 2012). "On the Age and Binarity of Fomalhaut". Astrophysical Journal Letters 754 (2): L20. doi:10.1088/2041-8205/754/2/L20. Bibcode: 2012ApJ...754L..20M. 
  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). doi:10.1088/0004-637X/775/1/56. Bibcode: 2013ApJ...775...56K. 
  25. ↑ "Planet Fomalhaut b - Exoplanet.eu - Encyclopaedia of exoplanetary systems". https://exoplanet.eu/catalog/fomalhaut_b--291/. 
  26. ↑ Kalas, Paul (2008-11-13). "Optical Images of an Exosolar Planet 25 Light-Years from Earth". Science 322 (5906): 1345–8. doi:10.1126/science.1166609. PMID 19008414. Bibcode: 2008Sci...322.1345K. 
  27. ↑ Ygouf, Marie et al. (October 2023). "Searching for Planets Orbiting Fomalhaut with JWST/NIRCam". The Astronomical Journal 167 (1): 26. doi:10.3847/1538-3881/ad08c8. Bibcode: 2024AJ....167...26Y. 
  28. ↑ Sepulveda, Aldo G.; Bowler, Brendan P. (2022-02-01). "Dynamical Mass of the Exoplanet Host Star HR 8799". The Astronomical Journal 163 (2): 52. doi:10.3847/1538-3881/ac3bb5. ISSN 0004-6256. Bibcode: 2022AJ....163...52S. 
  29. ↑ Baines, Ellyn K.; White, Russel J.; Huber, Daniel; Jones, Jeremy; Boyajian, Tabetha; McAlister, Harold A.; ten Brummelaar, Theo A.; Turner, Nils H. et al. (2012-12-10). "The Chara Array Angular Diameter of Hr 8799 Favors Planetary Masses for ITS Imaged Companions". The Astrophysical Journal 761 (1): 57. doi:10.1088/0004-637X/761/1/57. ISSN 0004-637X. Bibcode: 2012ApJ...761...57B. https://iopscience.iop.org/article/10.1088/0004-637X/761/1/57. 
  30. ↑ 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. doi:10.3847/1538-3881/abf4e0. Bibcode: 2021AJ....161..271F. 
  31. ↑ 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. doi:10.1126/science.1166585. PMID 19008415. Bibcode: 2008Sci...322.1348M. 
  32. ↑ 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. doi:10.1038/nature09684. PMID 21150902. Bibcode: 2010Natur.468.1080M. 
  33. ↑ Thompson, William; Marois, Christian; Do ó, Clarissa R.; Konopacky, Quinn; Ruffio, Jean-Baptiste; Wang, Jason; Skemer, Andy J.; De Rosa, Robert J. et al. (2023). "Deep Orbital Search for Additional Planets in the HR 8799 System". The Astronomical Journal 165 (1): 29. doi:10.3847/1538-3881/aca1af. Bibcode: 2023AJ....165...29T. 
  34. ↑ Crifo, F. (1997). "β Pictoris revisited by Hipparcos. Star properties". Astronomy and Astrophysics 320: L29–L32. Bibcode: 1997A&A...320L..29C. 
  35. ↑ Kervella, P. (2003). "VINCI/VLTI Observations of Main Sequence Stars". IAUS 219: Stars as Suns: Activity, Evolution and Planets. Sydney, Australia: Astronomical Society of the Pacific. pp. 80. Bibcode: 2003IAUS..219E.127K. 
  36. ↑ 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. doi:10.1046/j.1365-8711.2001.04212.x. Bibcode: 2001MNRAS.323..402L. 
  37. ↑ Lagrange, A.-M.; Gratadour, D.; Chauvin, G.; Fusco, T.; Ehrenreich, D.; Mouillet, D.; Rousset, G.; Rouan, D. et al. (2009). "A probable giant planet imaged in the β Pictoris disk". Astronomy and Astrophysics 493 (2): L21–L25. doi:10.1051/0004-6361:200811325. ISSN 0004-6361. Bibcode: 2009A&A...493L..21L. 
  38. ↑ 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. doi:10.1038/s41550-019-0857-1. Bibcode: 2019NatAs...3.1135L. https://hal.science/hal-02327499. 
  39. ↑ 39.0 39.1 39.2 39.3 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. doi:10.1086/378365. Bibcode: 2003AJ....126.2048G. 
  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. https://vizier.u-strasbg.fr/viz-bin/VizieR-S?HR%202491. 
  41. ↑ 41.0 41.1 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. doi:10.3847/1538-4357/aa6af8. Bibcode: 2017ApJ...840...70B. 
  42. ↑ 42.0 42.1 Davis, J. (October 2010). "The Angular Diameter and Fundamental Parameters of Sirius A". Publications of the Astronomical Society of Australia 28: 58–65. doi:10.1071/AS10010. 
  43. ↑ 43.0 43.1 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. ↑ 44.0 44.1 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. doi:10.1051/0004-6361/201936830. Bibcode: 2020A&A...633A..78B. 
  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. doi:10.1086/497981. Bibcode: 2006ApJ...636.1087P.  See Table 2 for stellar parameters.
  46. ↑ 46.0 46.1 46.2 46.3 van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V. 
  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. doi:10.1086/420715. Bibcode: 2004AJ....127.3508B. 
  48. ↑ Gray, R. O. 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. doi:10.1086/504637. Bibcode: 2006AJ....132..161G. 
  49. ↑ Samus, N. N. et al. (2017). "General Catalogue of Variable Stars". Astronomy Reports. 5.1 61 (1): 80–88. doi:10.1134/S1063772917010085. Bibcode: 2017ARep...61...80S. 
  50. ↑ Di Folco, E. et al. (2004). "VLTI near-IR interferometric observations of Vega-like stars". Astronomy and Astrophysics 426 (2): 601–617. doi:10.1051/0004-6361:20047189. Bibcode: 2004A&A...426..601D. 
  51. ↑ 51.0 51.1 Baines, Ellyn K.; Clark, James H. III; 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. doi:10.3847/1538-3881/ad08be. ISSN 0004-6256. Bibcode: 2023AJ....166..268B. 



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