G-type main-sequence star

A G-type main-sequence star (Spectral type: G-V), often (and imprecisely) called a yellow dwarf, or G dwarf star, is a main-sequence star (luminosity class V) of spectral type G. Such a star has about 0.84 to 1.15 solar masses and surface temperature of between 5,300 and 6,000 K.[2], Tables VII, VIII. Like other main-sequence stars, a G-type main-sequence star is converting the element hydrogen to helium in its core by means of nuclear fusion.[3] The Sun, the star to which the Earth is gravitationally bound in the Solar System and the object with the largest apparent magnitude, is an example of a G-type main-sequence star (G2V type). Each second, the Sun fuses approximately 600 million tons of hydrogen to helium, converting about 4 million tons of matter to energy.[4][5] Besides the Sun, other well-known examples of G-type main-sequence stars include Alpha Centauri A, Tau Ceti, and 51 Pegasi.[6][7][8]

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 yellow for the less massive and luminous G-type main-sequence stars.[9] The Sun is in fact white, and its spectrum peaks in blue and green light, but it can often appear yellow, orange or red through Earth's atmosphere due to atmospheric Rayleigh scattering, especially at sunrise and sunset.[10][11][12] In addition, although the term "dwarf" is used to contrast yellow main-sequence stars from giant stars, yellow dwarfs like the Sun outshine 90% of the stars in the Milky Way (which are largely much dimmer orange dwarfs, red dwarfs, and white dwarfs, the last being a stellar remnant).

A G-type main-sequence star will fuse hydrogen from a few billion years to approximately 20 billion years, until it is exhausted at the center of the star. For example a star like the Sun will live on the main sequence for 10 billion years. When this happens, the star expands to many times its previous size and becomes a red giant, such as Aldebaran (or Alpha Tauri).[13] Eventually the red giant sheds its outer layers of gas, which become a planetary nebula, while the core rapidly cools and contracts into a compact, dense white dwarf.[3]

Sun white
The Sun, a typical example of a G-type main-sequence star.
Properties of typical G-type main-sequence stars[1]
Spectral
type
Mass (M) Surface
gravity

(log g)
Effective
temperature

(K)
Color
index

(B − V)
G0V 1.15 4.32 5,980 0.583
G1V 1.10 4.34 5,900 0.608
G2V 1.07 4.35 5,800 0.625
G3V 1.04 4.37 5,710 0.642
G4V 1.00 4.38 5,690 0.657
G5V[note 1] 0.98 4.40 5,620 0.672
G6V 0.93 4.42 5,570 0.690
G7V 0.90 4.44 5,500 0.713
G8V 0.87 4.46 5,450 0.740
G9V 0.84 4.48 5,370 0.776

Spectral standard stars

The revised Yerkes Atlas system (Johnson & Morgan 1953)[14] listed 11 G-type dwarf spectral standard stars; however, not all of these have survived to this day as standards.

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).[15] Other primary MK standard stars include HD 115043 (G1V) and 16 Cygni B (G3V).[16] 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 (G8V). There are not yet any generally agreed upon G7V and G9V standards.

Planets

Some of the nearest G-type stars known to have planets include the Sun, 61 Virginis, HD 102365, HD 147513, 47 Ursae Majoris, Mu Arae, Tau Ceti and Alpha Centauri.

See also

Notes

  1. ^ The Sun is not in this class because even though it corresponds to the same mass, the Sun is slightly hotter than the typical temperature for a G5V star (at 5,778 K), so it is a G2V star, which is normally slightly more massive than the Sun

References

  1. ^ Vardavas, Ilias M.; et al. (2011), "Chapter 5. Incoming Solar Radiation", Radiation and Climate: Atmospheric Energy Budget from Satellite Remote Sensing, International Series of Monographs on Physics, 138, OUP Oxford, p. 130, ISBN 0199697140
  2. ^ 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.
  3. ^ a b Stellar Evolution: Main Sequence to Giant, class notes, Astronomy 101, Valparaiso University, accessed on line June 19, 2007.
  4. ^ Why Does The Sun Shine?, lecture, Barbara Ryden, Astronomy 162, Ohio State University, accessed on line June 19, 2007.
  5. ^ Sun Archived 2007-06-16 at the Wayback Machine, entry at ARICNS, accessed June 19, 2007.
  6. ^ Alpha Centauri A, SIMBAD query result. Accessed on line December 4, 2007.
  7. ^ Tau Ceti, SIMBAD query result. Accessed on line December 4, 2007.
  8. ^ 51 Pegasi, SIMBAD query result. Accessed on line December 4, 2007.
  9. ^ What Color Are the Stars?, Mitchell N. Charity's webpage, accessed November 25, 2007
  10. ^ Cain, Frazer. "WHAT COLOR IS THE SUN?". Universe Today.
  11. ^ "What Color is the Sun?". Stanford University.
  12. ^ Dissanaike, George (19 October 1991). "Painting the sky red". New Scientist. 132 (1791): 31–33.
  13. ^ SIMBAD, entry for Aldebaran, accessed on line June 19, 2007.
  14. ^ 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
  15. ^ MK ANCHOR POINTS, Robert F. Garrison
  16. ^ The Perkins Catalog of Revised MK Types for the Cooler Stars, 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 Also known as G2V

75 Cancri

75 Cancri (abbreviated to 75 Cnc) is a binary star in the constellation of Cancer. The system is located about 102 light-years (31 parsecs) away, based on its stellar properties.75 Cancri is a spectroscopic binary, which means the two stellar components are too close to be resolved, but periodic Doppler shifts in their spectra indicate orbital motion. In this case, light from both stars can be detected, and it is a double-lined spectroscopic binary. The orbital period of the system is 19.41 days, and the eccentricity of the system is 0.19494, implying a slightly elliptical orbit. The primary has a mass of 1.173 M☉, and is a G-type main-sequence star or subgiant. The secondary is less massive, at 1.011 M☉.

GSC 03089-00929

GSC 03089-00929 is a magnitude 12 star located approximately 760 light-years away in the constellation of Hercules. This star is a G type main sequence star that is similar to but slightly cooler than our sun.

This star is identified in SIMBAD as a variable star per the 1SWASP survey.

HD 156411

HD 156411 is a 7th magnitude G-type main sequence star located approximately 179 light years away in the constellation Ara. This star is larger, hotter, brighter, and more massive than our Sun. Also its metal content is three-fourths as much as the Sun. In 2009, a gas giant planet was found in orbit around the star.

HD 156846

HD 156846 is a G-type main sequence star of magnitude 6.5, located approximately 160 light-years away in the Ophiuchus constellation. The star has an M4 companion and a planet.

HD 171238

HD 171238 is a 9th magnitude G-type main sequence star located approximately 146 light years away in the constellation Sagittarius. This star is a little bit cooler, less massive, older, and more metallic than the Sun. In August 2009, it was announced that this star has a planet.

HD 181720

HD 181720 is an 8th magnitude G-type main sequence star located approximately 190 light years away in the constellation Sagittarius. This star is larger, hotter, brighter, and less massive than our Sun. Also its metal content is three-tenths as much as the Sun. In 2009, a gas giant planet was found in orbit around the star.

HD 204313

HD 204313 is an 8th magnitude G-type main sequence star located approximately 155 light years away in the constellation Capricornus.

HD 208487

HD 208487 is a 7th magnitude G-type main sequence star located approximately 144 light-years away in the constellation of Grus. It has the same spectral type as our sun, G2V. However, it is probably slightly less massive and more luminous, indicating that it is slightly older. As of 2008, there is one known extrasolar planet confirmed to be orbiting the star.

HD 34445

HD 34445 is a 7th-magnitude G-type main-sequence star located in the constellation Orion. Parallax measurements made by Gaia put the star at about 150.5 light-years (46.15 parsecs) away.

At an age of 8.5 billion years, this star is larger, hotter, brighter, and more massive than our Sun. Also its metal content is roughly 40% greater than the Sun. In 2004, a gas giant planet was found in orbit around the star, but it was not until 2009 that this planet was confirmed. In 2017, five more planets were found. All have minimum masses significantly greater than that of the Earth, between 16.8 M⊕ and 200.0 M⊕.

HD 45184

HD 45184 is a 6th magnitude G-type main sequence star located approximately 71 light years away in the constellation Canis Major. It has a planet around 12 times as massive as Earth that takes 5.88 days to complete an orbit around its host star. The planet was detected by radial velocity.

HD 49674

HD 49674 is an 8th magnitude G-type main-sequence star (spectral type G5V) located approximately 144 light years away in the constellation of Auriga. It has a very similar mass to our Sun. It is orbited by a recently discovered planet.

HD 63765

HD 63765 is an 8th-magnitude G-type main sequence star located approximately 106 light years away in the constellation Carina. This star is smaller, cooler, dimmer, and less massive than the Sun. It has a lower iron content than our Sun, with approximately 69% of the Sun's iron-to-hydrogen ratio. In 2009, a gas giant planet was found in orbit around the star.

HD 65216

HD 65216 is an 8th magnitude G-type main sequence star located approximately 34.3 parsecs (112 ly) away in the constellation of Carina. It is a Sun-like yellow dwarf, 8% less massive and somewhat less luminous. It cannot be seen without technical aid, but with binoculars or telescope it should be visible.

HD 73526

HD 73526 is a G-type main-sequence star. It is about 310 light-years away in the constellation Vela.

HD 76151

HD 76151 is a G-type main sequence star in the constellation of Hydra. It has an apparent visual magnitude of approximately 6.00.An infrared excess has been detected around this star, most likely indicating the presence of a circumstellar disk at a radius of 7.9 AU. The temperature of this dust is 99 K.

HD 90156

HD 90156 is a 7th magnitude G-type main sequence star located approximately 73 light years away in the constellation Hydra. This star is smaller, cooler, fainter, and less massive than our Sun. Also its metal content is over half as much as the Sun. In 2009, a gas giant planet was found in orbit around the star.

This star was designated as Gamma Antliae by Lacaille, and Gould intended to keep it in that constellation. However, the delineating of constellation boundaries in 1930 saw it transferred to Hydra.

HIP 14810

HIP 14810 is a G-type main-sequence star located approximately 165 light-years away in the constellation of Aries.

KIC 11026764

KIC 11026764 is a G-type main sequence star whose characteristics have been extensively measured by the Kepler spacecraft because of its similarity to our Sun. Its diameter is 2.18 times the Sun and is aged at 5.94 billion years, slightly older than our Sun.

Kepler-15

Kepler-15 is a star that is host to the planet Kepler-15b. It is a G-type main sequence star with a mass of 1.018 M☉. It is also known as KOI-128, or KIC 11359879.

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