An artist's impression of Sirius A and Sirius B, a binary star system. Sirius A, an A-type main-sequence star, is the larger of the two.
In July 2019, astronomers reported finding an A-type star, S5-HVS1, traveling 1,755 km/s (3,930,000 mph), faster than any other star detected so far. The star is in the constellation Grus (the Crane) in the southern sky, about 29,000 light-years from Earth, and may have been ejected out of the Milky Way after interacting with Sagittarius A*, the supermassive black hole at the center of the galaxy.[7][8][9][10][11]
The revised Yerkes Atlas system[14] 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), Gamma Ursae Majoris (A0 V), and Fomalhaut (A3 V).[15][16] The seminal review of MK classification by Morgan & Keenan (1973)[16] didn't provide any dagger standards between types A3 V and F2 V. HD 23886 was suggested as an A5 V standard in 1978.[17]
Richard Gray & Robert Garrison provided the most recent contributions to the A dwarf spectral sequence in a pair of papers in 1987[18] and 1989.[19] 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 Delta Leonis (A4 V) listed as a standard. There are no published A6 V and A8 V standard stars.
The Morgan-Keenan spectral classification
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.[20] 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.[21] 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.[21] 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. [22]
^"Stellar Spectral Types". hyperphysics.phy-astr.gsu.edu. Retrieved June 19, 2007.
^Dale A. Ostlie; Bradley W. Carroll (2007). An Introduction to Modern Stellar Astrophysics. Pearson Addison-Wesley. ISBN978-0-8053-0348-3.
^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
^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.
^Overbye, Dennis (14 November 2019). "A Black Hole Threw a Star Out of the Milky Way Galaxy – So long, S5-HVS1, we hardly knew you". The New York Times. Retrieved 18 November 2019.
^Koposov, Sergey E.; et al. (2019). "Discovery of a nearby 1700 km/s star ejected from the Milky Way by Sgr A*". Monthly Notices of the Royal Astronomical Society. arXiv:1907.11725. doi:10.1093/mnras/stz3081. S2CID 198968336.
^Starr, Michelle (31 July 2019). "Bizarre Star Found Hurtling Out of Our Galaxy Centre Is Fastest of Its Kind Ever Seen". ScienceAlert.com. Retrieved 18 November 2019.
^Irving, Michael (13 November 2019). "Fastest star ever found is being flicked out of the Milky Way". NewAtlas.com. Retrieved 18 November 2019.
^Plait, Phil (13 November 2019). "Our Local Supermassive Black Hole Shot A Star Right Out Of THe Galaxy". Bad Astronomy. Retrieved 19 November 2019.
^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.
^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.
^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.
^Robert F. Garrison. "MK ANCHOR POINTS". Retrieved 2022-01-05.
^ abMorgan, 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.
^Morgan, W. W.; Abt, Helmut A.; Tapscott, J. W. (1978). Revised MK Spectral Atlas for stars earlier than the sun. Bibcode:1978rmsa.book.....M.
^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.
^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.
^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.
^ abJohnson, 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: 785–793. arXiv:0704.2455. doi:10.1086/519677. S2CID 15076579.
^ Johnson, J. A. (2011). "The Stars that Host Planets". Sky & Telescope (April): 22–27.
^ Smalley, J. B. (2014). "Eclipsing Am binary systems in the SuperWASP survey". Astronomy and Astrophysics (April): 20.
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January 10, 2023
type, main, sequence, star, also, stellar, classification, class, dwarf, star, main, sequence, hydrogen, burning, star, spectral, type, luminosity, class, five, these, stars, have, spectra, defined, strong, hydrogen, balmer, absorption, lines, they, measure, b. See also Stellar classification Class A An A type main sequence star A V or A dwarf star is a main sequence hydrogen burning star of spectral type A and luminosity class V five These stars have spectra defined by strong hydrogen Balmer absorption lines 1 2 They measure between 1 4 and 2 1 solar masses M and have surface temperatures between 7 600 and 10 000 K 3 Bright and nearby examples are Altair A7 V Sirius A A1 V and Vega A0 V 4 5 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 emissions 6 An artist s impression of Sirius A and Sirius B a binary star system Sirius A an A type main sequence star is the larger of the two In July 2019 astronomers reported finding an A type star S5 HVS1 traveling 1 755 km s 3 930 000 mph faster than any other star detected so far The star is in the constellation Grus the Crane in the southern sky about 29 000 light years from Earth and may have been ejected out of the Milky Way after interacting with Sagittarius A the supermassive black hole at the center of the galaxy 7 8 9 10 11 Contents 1 Spectral standard stars 2 Planets 3 Examples 4 See also 5 ReferencesSpectral standard stars EditProperties of typical A type main sequence stars 12 13 Spectraltype Mass M Radius R Luminosity L Effectivetemperature K Colorindex B V A0V 2 18 2 193 38 02 9 700 0 00A1V 2 05 2 136 30 90 9 300 0 04A2V 1 98 2 117 23 99 8 800 0 07A3V 1 93 1 861 16 98 8 600 0 10A4V 1 88 1 794 13 49 8 250 0 14A5V 1 86 1 785 12 30 8 100 0 16A6V 1 83 1 775 11 22 7 910 0 19A7V 1 81 1 750 10 00 7 760 0 21A8V 1 77 1 747 9 12 7 590 0 25A9V 1 75 1 747 8 32 7 400 0 27The revised Yerkes Atlas system 14 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 Gamma Ursae Majoris A0 V and Fomalhaut A3 V 15 16 The seminal review of MK classification by Morgan amp Keenan 1973 16 didn t provide any dagger standards between types A3 V and F2 V HD 23886 was suggested as an A5 V standard in 1978 17 Richard Gray amp Robert Garrison provided the most recent contributions to the A dwarf spectral sequence in a pair of papers in 1987 18 and 1989 19 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 amp Garrison papers one also occasionally sees Delta Leonis A4 V listed as a standard There are no published A6 V and A8 V standard stars The Morgan Keenan spectral classificationPlanets EditA 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 20 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 21 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 21 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 22 A type star systems known to feature planets include Fomalhaut HD 15082 Beta Pictoris HR 8799 and HD 95086 23 Examples EditWithin 40 light years Name Spectraltype Constellation vis Mag Mass M Radius R Luminosity L Distance ly Sirius A0mA1 Va Canis Major 1 47 2 063 1 711 25 4 8 60 0 04Altair A7 V Aquila 0 76 1 79 1 63 2 03 10 6 16 73Vega A0 Va Lyra 0 026 2 135 2 362 2 818 40 12 25 04Fomalhaut A3 V Piscis Austrinus 1 17 1 91 1 84 16 25 1Denebola A3 V Leo 2 14 1 78 1 73 15 35 8Delta Capricorni A5 IV Capricornus 2 83 2 0 1 91 11 38 6Delta Capricorni is likely a subgiant or giant star and Altair is a disputed subgiant In addition Sirius is the brightest star in the night sky See also EditStar count survey of stars B type main sequence starReferences Edit Stellar Spectral Types hyperphysics phy astr gsu edu Retrieved June 19 2007 Dale A Ostlie Bradley W Carroll 2007 An Introduction to Modern Stellar Astrophysics Pearson Addison Wesley ISBN 978 0 8053 0348 3 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 amp AS 46 193H Tables VII VIII Sirius A SIMBAD Centre de donnees astronomiques de Strasbourg Retrieved 2022 01 05 Vega SIMBAD Centre de donnees astronomiques de Strasbourg Retrieved 2022 01 05 Schroder C Schmitt J H M M November 2007 X ray emission from A type stars Astronomy and Astrophysics 475 2 677 684 Bibcode 2007A amp A 475 677S doi 10 1051 0004 6361 20077429 Overbye Dennis 14 November 2019 A Black Hole Threw a Star Out of the Milky Way Galaxy So long S5 HVS1 we hardly knew you The New York Times Retrieved 18 November 2019 Koposov Sergey E et al 2019 Discovery of a nearby 1700 km s star ejected from the Milky Way by Sgr A Monthly Notices of the Royal Astronomical Society arXiv 1907 11725 doi 10 1093 mnras stz3081 S2CID 198968336 Starr Michelle 31 July 2019 Bizarre Star Found Hurtling Out of Our Galaxy Centre Is Fastest of Its Kind Ever Seen ScienceAlert com Retrieved 18 November 2019 Irving Michael 13 November 2019 Fastest star ever found is being flicked out of the Milky Way NewAtlas com Retrieved 18 November 2019 Plait Phil 13 November 2019 Our Local Supermassive Black Hole Shot A Star Right Out Of THe Galaxy Bad Astronomy Retrieved 19 November 2019 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 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 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 Robert F Garrison MK ANCHOR POINTS Retrieved 2022 01 05 a b Morgan W W Keenan P C 1973 Spectral Classification Annual Review of Astronomy and Astrophysics 11 29 Bibcode 1973ARA amp A 11 29M doi 10 1146 annurev aa 11 090173 000333 Morgan W W Abt Helmut A Tapscott J W 1978 Revised MK Spectral Atlas for stars earlier than the sun Bibcode 1978rmsa book M 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 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 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 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 665 785 793 arXiv 0704 2455 doi 10 1086 519677 S2CID 15076579 Johnson J A 2011 The Stars that Host Planets Sky amp Telescope April 22 27 Smalley J B 2014 Eclipsing Am binary systems in the SuperWASP survey Astronomy and Astrophysics April 20 Portals Astronomy Spaceflight Outer space Solar System 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 amp oldid 1131801268, wikipedia, wiki, book, books, library,
