A-type main-sequence star




See also: Stellar classification § Class A



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.


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. These stars have spectra which are defined by strong hydrogen Balmer absorption lines.[1][2] They have masses from 1.4 to 2.1 times the mass of the Sun and surface temperatures between 7600 and 11 500  K.[3]
Bright and nearby examples are Altair (A7 V), Sirius A (A1 V), and Vega (A0 V).[4] A-type stars do not have a convective zone and thus are not expected to harbor a magnetic dynamo. As a consequence, because they do not have strong stellar winds they lack a means to generate X-ray emission.[5]




Contents






  • 1 Spectral standard stars


  • 2 Planets


  • 3 See also


  • 4 References





Spectral standard stars































































Typical characteristics[6]
Stellar
Class
 Mass
(M☉)
 Radius
(R☉)
Mv
Teff
(K)
A0V 2.40 1.87 0.7 9727
A2V 2.19 1.78 1.3 8820
A5V 1.86 1.69 2.0 7880
A6V 1.80 1.66 2.1 7672
A7V 1.74 1.63 2.3 7483
A8V 1.66 1.60 2.4 7305
A9V 1.62 1.55 2.5 7112

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 remain unchanged over years and can be considered to define the system, are Vega (A0 V), Gamma Ursae Majoris (A0 V), and Fomalhaut (A3 V).[8][9] The seminal review of MK classification by Morgan & Keenan (1973)[9]
did not 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 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.[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. 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. 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.
[14]


A-type stars include planets like Fomalhaut, HD 15082, Beta Pictoris and HD 95086 b.



See also



  • Star count, survey of stars


References





  1. ^ Stellar Spectral Types, entry at hyperphysics.phy-astr.gsu.edu, accessed on line June 19, 2007.


  2. ^ "An Introduction to Modern Astrophysics" by B.W Caroll and D.A Ostlie 1996 edition, chapter 8


  3. ^ Empirical bolometric corrections for the main-sequence, G. M. H. J. Habets and J. R. W. Heintze, Astronomy and Astrophysics Supplement 46 (November 1981), pp. 193–237, Tables VII and VIII.


  4. ^ SIMBAD, entries on Sirius A and Vega, accessed June 19, 2007.


  5. ^ 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..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"""""""'""'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}


  6. ^ Adelman, S. J. (2005). "The physical properties of normal a stars". Proceedings of the International Astronomical Union. 2004. doi:10.1017/S1743921304004314.


  7. ^ 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


  8. ^ MK ANCHOR POINTS, Robert F. Garrison


  9. ^ ab Spectral Classification, W.W. Morgan & P.C. Keenan, 1973, Annual Review of Astronomy and Astrophysics, vol. 11, p.29


  10. ^ 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


  11. ^ The early A type stars – Refined MK classification, confrontation with Stroemgren photometry, and the effects of rotation, R.O. Gray & R.F. Garrison, 1987, Astrophysical Journal Supplement Series, vol. 65, p. 581


  12. ^ The late A-type stars – Refined MK classification, confrontation with Stromgren photometry, and the effects of rotation, R.O. Gray & R.F. Garrison, 1989, Astrophysical Journal Supplement Series, vol. 70, p. 623


  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


  14. ^
    Johnson, J. A. (2011). "The Stars that Host Planets". Sky & Telescope (April): 22–27.










-

Popular posts from this blog

Florida Star v. B. J. F.

Image
Florida Star v. B. J. F. From Wikipedia, the free encyclopedia Jump to navigation Jump to search United States Supreme Court case Florida Star v. B. J. F. Supreme Court of the United States Argued March 21, 1989 Decided June 21, 1989 Full case name The Florida Star v. B. J. F. Citations 491 U.S. 524 ( more ) 109 S. Ct. 2603; 105 L. Ed. 2d 443; 1989 U.S. LEXIS 3120; 57 U.S.L.W. 4816; 16 Media L. Rep. 1801 Prior history The Florida Star v. B.J.F., 530 So.2d 286 (1988) Supreme Court of Florida; Florida Star v. B.J.F., 499 So.2d 883 (1986) Fla. Dist. Court of Appeals Holding Florida Stat. § 794.03 is unconstitutional to the extent it makes the truthful reporting of information that was a matter of public record unlawful, as it violates the First Amendment. Court membership Chief Justice William Rehnquist Associate Justices William J. Brennan Jr.  · Byron White Thurgood Marshall  · Harry Blac
Read more

Danny Elfman

Image
Danny Elfman From Wikipedia, the free encyclopedia Jump to navigation Jump to search Danny Elfman Elfman at the 2010 San Diego Comic-Con Born Daniel Robert Elfman ( 1953-05-29 ) May 29, 1953 (age 65) Los Angeles, California, U.S. Spouse(s) Bridget Fonda ( m.  2003) Children 1 Musical career Genres Rock [1] ska [2] new wave film music video game music Occupation(s) Composer, singer, songwriter, record producer Instruments Trombone guitar percussion vocals keyboards [3] Years active 1972–present Associated acts Oingo Boingo James Newton Howard Daniel Robert Elfman (born May 29, 1953) is an American composer, singer, songwriter, and record producer. Elfman first became known for being the lead singer and songwriter for the band Oingo Boingo from 1974 to 1995. He is well known for scoring films and television shows, particularly his frequent collabora
Read more

Retrieve a Users Dashboard in Tumblr with R and TumblR. Oauth Issues

Image
.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty{ height:90px;width:728px;box-sizing:border-box; } 0 I am trying to use the TumblR package in R to set up the Oauth Authentication to Retrieve a user's dashboard using the second example in tumblR documentation However I get the following error, it seems that using twitter others have been able to use a different function to get around this, but I am not finding the same function available for Tumblr. See twitter package for R authentication: error 401 My code consumer_key <- OKey consumer_secret <- SKey appname <- App_name tokenURL <- 'http://www.tumblr.com/oauth/request_token' accessTokenURL <- 'http://www.tumblr.com/oauth/acces_token'
Read more