A G-type main-sequence star (spectral type: G-V), also often, and imprecisely called a yellow dwarf, or G star, is a main-sequence star (luminosity class V) of spectral type G. Such a star has about 0.9 to 1.1 solar masses and an effective temperature between about 5,300 and 6,000 K. Like other main-sequence stars, a G-type main-sequence star converts the elementhydrogen to helium in its core by means of nuclear fusion, but can also fuse helium when hydrogen runs out. The Sun, the star in the center of the Solar System to which the Earth is gravitationally bound, is an example of a G-type main-sequence star (G2V type). Each second, the Sun fuses approximately 600 million tons of hydrogen into helium in a process known as the proton–proton chain (4 hydrogens form 1 helium), converting about 4 million tons of matter to energy.[1][2] Besides the Sun, other well-known examples of G-type main-sequence stars include Alpha Centauri, Tau Ceti, Capella and 51 Pegasi.[3][4][5][6]
The Sun, a typical example of a G-type main-sequence star
The term yellow dwarf is a misnomer, because G-type stars actually range in color from white, for more luminous types like the Sun, to only very slightly yellowish for the less massive and luminous G-type main-sequence stars lower down.[7] The Sun is in fact white, but it can often appear yellow, orange or red through Earth's atmosphere due to atmospheric Rayleigh scattering, especially at sunrise and sunset.[8][9][10] In addition, although the term "dwarf" is used to contrast G-type main-sequence stars with giant stars or bigger, stars similar to the Sun still outshine 90% of the stars in the Milky Way (which are largely much dimmer orange dwarfs, red dwarfs, and white dwarfs which are much more common, the latter being stellar remnants).[11]
A G-type main-sequence star will fuse hydrogen for approximately 10 billion years, until the hydrogen element is exhausted at the center of the star. When this happens, the star rapidly expands, cooling and darkening as it passes through the subgiant branch and ultimately expanding into many times its previous size at the tip of the red giant phase, about 1 billion years after leaving the main sequence. After this, the star's degenerate helium core abruptly ignites in a helium flash fusing helium, and the star passes on to the horizontal branch, and then to the asymptotic giant branch. Expanding even further as helium starts running out as it pulses violently, the star's gravity is not sufficient to hold its outer envelope, resulting in significant mass loss and shedding. The ejected material remains as a planetary nebula, radiating as it absorbs energetic photons from the photosphere. Eventually, the core begins to fade as nuclear reactions cease, and becomes a dense, compact white dwarf, which cools slowly from its high initial temperature as the nebula fades.[12][13]
Spectral standard stars
Properties of typical G-type main-sequence stars[14][15]
The revised Yerkes Atlas system (Johnson & Morgan 1953)[16] listed 11 G-type dwarf spectral standard stars; however, not all of these still exactly conform to this designation.
The "anchor points" of the MK spectral classification system among the G-type main-sequence dwarf stars, i.e. those standard stars that have remained unchanged over years, are beta CVn (G0V), the Sun (G2V), Kappa1 Ceti (G5V), 61 Ursae Majoris (G8V).[17] Other primary MK standard stars include HD 115043 (G1V) and 16 Cygni B (G3V).[18] The choices of G4 and G6 dwarf standards have changed slightly over the years among expert classifiers, but often-used examples include 70 Virginis (G4V) and 82 Eridani (G6V). There are not yet any generally agreed upon G7V and G9V standards.
^"Sun" 2007-06-16 at the Wayback Machine, entry at ARICNS, accessed June 19, 2007.
^"Alpha Centauri A" 2019-04-28 at the Wayback Machine, SIMBAD query result. Accessed on line December 4, 2007.
^"Tau Ceti" 2019-04-28 at the Wayback Machine, SIMBAD query result. Accessed on line December 4, 2007.
^"51 Pegasi" 2019-04-28 at the Wayback Machine, SIMBAD query result. Accessed December 4, 2007.
^"Type G Stars". www.whillyard.com. Retrieved 2022-04-22.
^What Color Are the Stars? 2017-08-06 at the Wayback Machine, Mitchell N. Charity's webpage, accessed November 25, 2007
^Cain, Frazer. "WHAT COLOR IS THE SUN?". Universe Today. from the original on 2012-03-20. Retrieved 2017-11-06.
^"What Color is the Sun?". Stanford University. from the original on 2017-10-30. Retrieved 2017-11-06.
^Dissanaike, George (19 October 1991). "Painting the sky red". New Scientist. 132 (1791): 31–33.
^"More G Stars | StarDate Online". stardate.org. Retrieved 2022-04-22.
^Hurley, J. R.; Pols, O. R.; Tout, C. A. (1 July 2000). "Comprehensive analytic formulae for stellar evolution as a function of mass and metallicity". Monthly Notices of the Royal Astronomical Society. 315 (3): 543–569. arXiv:astro-ph/0001295. Bibcode:2000MNRAS.315..543H. doi:10.1046/j.1365-8711.2000.03426.x. S2CID 18523597.
^"Evolution from the Main Sequence to Red Giants | Astronomy". courses.lumenlearning.com. Retrieved 2022-04-22.
^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.
^Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas 2019-04-02 at the Wayback Machine H.L. Johnson & W.W. Morgan, 1953, Astrophysical Journal, 117, 313
^MK ANCHOR POINTS 2019-06-25 at the Wayback Machine, Robert F. Garrison
^The Perkins Catalog of Revised MK Types for the Cooler Stars 2017-10-11 at the Wayback Machine, P.C. Keenan & R.C McNeil, "Astrophysical Journal Supplement Series" 71 (October 1989), pp. 245–266.
External links
Media related to Yellow dwarfs at Wikimedia Commons
type, main, sequence, star, spectral, type, also, often, imprecisely, called, yellow, dwarf, star, main, sequence, star, luminosity, class, spectral, type, such, star, about, solar, masses, effective, temperature, between, about, like, other, main, sequence, s. A G type main sequence star spectral type G V also often and imprecisely called a yellow dwarf or G star is a main sequence star luminosity class V of spectral type G Such a star has about 0 9 to 1 1 solar masses and an effective temperature between about 5 300 and 6 000 K Like other main sequence stars a G type main sequence star converts the element hydrogen to helium in its core by means of nuclear fusion but can also fuse helium when hydrogen runs out The Sun the star in the center of the Solar System to which the Earth is gravitationally bound is an example of a G type main sequence star G2V type Each second the Sun fuses approximately 600 million tons of hydrogen into helium in a process known as the proton proton chain 4 hydrogens form 1 helium converting about 4 million tons of matter to energy 1 2 Besides the Sun other well known examples of G type main sequence stars include Alpha Centauri Tau Ceti Capella and 51 Pegasi 3 4 5 6 The Sun a typical example of a G type main sequence star Contents 1 Description 2 Spectral standard stars 3 Planets 4 See also 5 References 6 External linksDescription EditThe term yellow dwarf is a misnomer because G type stars actually range in color from white for more luminous types like the Sun to only very slightly yellowish for the less massive and luminous G type main sequence stars lower down 7 The Sun is in fact white but it can often appear yellow orange or red through Earth s atmosphere due to atmospheric Rayleigh scattering especially at sunrise and sunset 8 9 10 In addition although the term dwarf is used to contrast G type main sequence stars with giant stars or bigger stars similar to the Sun still outshine 90 of the stars in the Milky Way which are largely much dimmer orange dwarfs red dwarfs and white dwarfs which are much more common the latter being stellar remnants 11 A G type main sequence star will fuse hydrogen for approximately 10 billion years until the hydrogen element is exhausted at the center of the star When this happens the star rapidly expands cooling and darkening as it passes through the subgiant branch and ultimately expanding into many times its previous size at the tip of the red giant phase about 1 billion years after leaving the main sequence After this the star s degenerate helium core abruptly ignites in a helium flash fusing helium and the star passes on to the horizontal branch and then to the asymptotic giant branch Expanding even further as helium starts running out as it pulses violently the star s gravity is not sufficient to hold its outer envelope resulting in significant mass loss and shedding The ejected material remains as a planetary nebula radiating as it absorbs energetic photons from the photosphere Eventually the core begins to fade as nuclear reactions cease and becomes a dense compact white dwarf which cools slowly from its high initial temperature as the nebula fades 12 13 Spectral standard stars EditProperties of typical G type main sequence stars 14 15 Spectraltype Mass M Radius R Luminosity L Effectivetemperature K Colorindex B V G0V 1 06 1 100 1 35 5 930 0 60G1V 1 03 1 060 1 20 5 860 0 62G2V 1 00 1 012 1 02 5 770 0 65G3V 0 99 1 002 0 98 5 720 0 66G4V 0 985 0 991 0 91 5 680 0 67G5V 0 98 0 977 0 89 5 660 0 68G6V 0 97 0 949 0 79 5 600 0 70G7V 0 95 0 927 0 74 5 550 0 71G8V 0 94 0 914 0 68 5 480 0 73G9V 0 90 0 853 0 55 5 380 0 78The revised Yerkes Atlas system Johnson amp Morgan 1953 16 listed 11 G type dwarf spectral standard stars however not all of these still exactly conform to this designation The anchor points of the MK spectral classification system among the G type main sequence dwarf stars i e those standard stars that have remained unchanged over years are beta CVn G0V the Sun G2V Kappa1 Ceti G5V 61 Ursae Majoris G8V 17 Other primary MK standard stars include HD 115043 G1V and 16 Cygni B G3V 18 The choices of G4 and G6 dwarf standards have changed slightly over the years among expert classifiers but often used examples include 70 Virginis G4V and 82 Eridani G6V There are not yet any generally agreed upon G7V and G9V standards Planets EditBesides the Sun and its planets some of the nearest G type stars known to have planets include 61 Virginis HD 102365 HD 147513 47 Ursae Majoris Mu Arae and Tau Ceti See also EditHertzsprung Russell diagram G dwarf problem Yellow hypergiant Solar twin Star count survey of starsReferences Edit Why Does The Sun Shine Archived 2006 09 09 at the Wayback Machine lecture Barbara Ryden Astronomy 162 Ohio State University accessed on line June 19 2007 Sun Archived 2007 06 16 at the Wayback Machine entry at ARICNS accessed June 19 2007 Alpha Centauri A Archived 2019 04 28 at the Wayback Machine SIMBAD query result Accessed on line December 4 2007 Tau Ceti Archived 2019 04 28 at the Wayback Machine SIMBAD query result Accessed on line December 4 2007 51 Pegasi Archived 2019 04 28 at the Wayback Machine SIMBAD query result Accessed December 4 2007 Type G Stars www whillyard com Retrieved 2022 04 22 What Color Are the Stars Archived 2017 08 06 at the Wayback Machine Mitchell N Charity s webpage accessed November 25 2007 Cain Frazer WHAT COLOR IS THE SUN Universe Today Archived from the original on 2012 03 20 Retrieved 2017 11 06 What Color is the Sun Stanford University Archived from the original on 2017 10 30 Retrieved 2017 11 06 Dissanaike George 19 October 1991 Painting the sky red New Scientist 132 1791 31 33 More G Stars StarDate Online stardate org Retrieved 2022 04 22 Hurley J R Pols O R Tout C A 1 July 2000 Comprehensive analytic formulae for stellar evolution as a function of mass and metallicity Monthly Notices of the Royal Astronomical Society 315 3 543 569 arXiv astro ph 0001295 Bibcode 2000MNRAS 315 543H doi 10 1046 j 1365 8711 2000 03426 x S2CID 18523597 Evolution from the Main Sequence to Red Giants Astronomy courses lumenlearning com Retrieved 2022 04 22 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 Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas Archived 2019 04 02 at the Wayback Machine H L Johnson amp W W Morgan 1953 Astrophysical Journal 117 313 MK ANCHOR POINTS Archived 2019 06 25 at the Wayback Machine Robert F Garrison The Perkins Catalog of Revised MK Types for the Cooler Stars Archived 2017 10 11 at the Wayback Machine P C Keenan amp R C McNeil Astrophysical Journal Supplement Series 71 October 1989 pp 245 266 External links Edit Media related to Yellow dwarfs at Wikimedia Commons Portals Astronomy Stars Outer space Solar System Retrieved from https en wikipedia org w index php title G type main sequence star amp oldid 1135284872, wikipedia, wiki, book, books, library,
