Wolf 359

Wolf 359
Leo constellation map.png
Wolf 359 is shown near the ecliptic in the southern region of Leo (bottom middle)
Observation data
Epoch J2000      Equinox J2000
Constellation Leo
Right ascension 10h 56m 28.99s[1]
Declination +07° 00′ 52.0″[1]
Apparent magnitude (V) 13.54[1]
Characteristics
Spectral type M6.5 Ve[1]
U−B color index +1.165[2]
B−V color index +2.034[2]
Variable type UV[3]
Astrometry
Radial velocity (Rv) +19±1[4] km/s
Proper motion (μ) RA: –3842[1] mas/yr
Dec.: –2725[1] mas/yr
Parallax (π) 419.10 ± 2.10[5] mas
Distance 7.78 ± 0.04 ly
(2.39 ± 0.01 pc)
Absolute magnitude (MV) 16.65[6]
Details
Mass 0.09[7] M☉
Radius 0.16[8] R☉
Surface gravity (log g) 5.5[9]
Luminosity 0.0009[10] to 0.0011[11] L☉
Temperature 2,800 ± 100[11] K
Rotational velocity (v sin i) < 3.0[4] km/s
Age (1–3.5) × 108[11] years
Other designations
CN Leonis, CN Leo, GJ 406, G 045-020, LTT 12923, LFT 750, LHS 36,[1] GCTP 2553.
Database references
SIMBAD data
Wolf 359 is the orange-hued star located just above the center of this 2009 astrophotograph.

Wolf 359 is a red dwarf star that is located in the constellation Leo, near the ecliptic. At a distance of approximately 7.8 light years from the Earth, Wolf 359 has an apparent magnitude of 13.5 and can only be seen with a large telescope. Wolf 359 is one of the nearest stars to the solar system; only the Alpha Centauri system and Barnard's star are known to be closer.

Wolf 359 is one of the faintest and lowest mass stars known. The photosphere of the star has a temperature of about 2,800 K, which is low enough for chemical compounds to form and survive. The absorption lines of compounds such as water and titanium(II) oxide have been observed.[12] The surface has a magnetic field that is stronger than the average magnetic field on the Sun. As a result of magnetic activity, Wolf 359 is a flare star that can undergo sudden increases in luminosity for several minutes. These flares emit strong bursts of X-ray and gamma ray radiation that have been observed by space telescopes. Wolf 359 is a relatively young star with an age of less than a billion years. No companions or debris has been detected in orbit around it.

Contents

Observation history

Wolf 359 first came to the attention of astronomers because of the relatively high rate of transverse motion against the background, known as the proper motion. A high rate of proper motion may indicate that a star is located nearby, as more distant stars must move at higher velocities in order to achieve the same rate of angular travel across the celestial sphere. The motion of Wolf 359 was first measured in 1917 by German astronomer Max Wolf, with the aid of astrophotography. In 1919 he published a catalog of over one thousand high proper motion stars, including this one, that are still identified by his name.[13] He listed this star as 359, and the star has since been referred to as Wolf 359 in reference to the position in Max Wolf's catalogue.[14]

The first parallax measurement of Wolf 359 was reported in 1928 from the Mount Wilson Observatory, yielding an annual shift in the star's position of 0.409 ± 0.009 arcseconds. From this shift, and the known size of the Earth's orbit, the distance to the star could be estimated. It was the lowest mass and faintest star known until the discovery of VB 10 in 1944.[15][16] The infrared magnitude of the star was measured in 1957.[17] In 1969, a brief flare in luminosity was observed on this star, linking it to the class of variable stars known as flare stars.[18]

Properties

Wolf 359 has a stellar classification of M6.5,[19] although various sources list a spectral class of M5.5,[20] M6[7] or M8.[21] An M-type star is known as a red dwarf because the energy emission of the star reaches a peak in the red and infrared parts of the spectrum.[22] Wolf 359 has a very low luminosity, emitting about 0.1% of the Sun's energy.[10][11] If this star were moved to the location of the Sun, it would appear ten times as bright as the full Moon.[23]

At an estimated 9% of the Sun's mass, Wolf 359 is just above the lowest limit at which a star can perform hydrogen fusion through the proton–proton chain reaction: 8% of the Sun's mass.[24] (Substellar objects below this limit are known as brown dwarfs.) The radius of Wolf 359 is an estimated 16% of the Sun's radius, or about 110,000 km.[25] For comparison, the equatorial radius of the planet Jupiter is 71,492 km, which is 65% as large as Wolf 359's.[26]

The entire star is undergoing convection, whereby the energy generated at the core is being transferred toward the surface by the convective motion of plasma, rather than by transmission through radiation. This circulation redistributes any accumulation of helium that is generated through stellar nucleosynthesis at the core throughout the star.[27] This will allow the star to remain on the main sequence as a hydrogen fusing star proportionately longer than a star such as the Sun where the helium steadily accumulates at the core. In combination with a lower rate of hydrogen consumption due to the low mass, the convection will allow Wolf 359 to remain a main sequence star for eight trillion years.[28]

A search of this star by the Hubble Space Telescope revealed no stellar companions, although this does not preclude the presence of smaller companions that are below the telescope's detection limit, such as a planet orbiting within one astronomical unit of the star.[29] No excess infrared emission has been detected, which may indicate the lack of a debris disk in orbit around this star.[30][31]

Outer atmosphere

Artist illustration of Wolf 359 generated by Celestia.

The outer light-emitting layer of a star is known as the photosphere. Temperature estimates of the photosphere of Wolf 359 range from 2,500 K to 2,900 K,[32] which is sufficiently cool for equilibrium chemistry to occur. The resulting chemical compounds survive long enough to be observed through their spectral lines.[33] Numerous molecular lines appear in the spectrum of Wolf 359, including those of carbon monoxide (CO),[34] iron hydride (FeH), chromium hydride (CrH), water (H2O),[12] magnesium hydride (MgH), vanadium(II) oxide (VO),[11] titanium(II) oxide (TiO) and possibly calcium hydroxide (CaOH).[35] Since there are no lines of lithium in the spectrum, this element must have already been consumed by fusion at the core. This indicates the star must be at least 100 million years old.[11]

Beyond the photosphere lies a nebulous, high temperature region known as the corona. In 2001, Wolf 359 became the first star other than the Sun to have the spectrum of its corona observed from a ground-based telescope. The spectrum showed emission lines of Fe XIII, which is heavily ionized iron that has been stripped of twelve of its electrons.[36] The strength of this line can vary over a time period of several hours, which may be evidence of microflare heating.[11]

Wolf 359 is classified as a UV Ceti-type flare star,[3] which is a star that undergoes brief, energetic increases in luminosity because of magnetic activity in the photosphere. Wolf 359 has a relatively high flare rate. Observations with the Hubble Space Telescope detected 32 flare events within a two hour period, with energies of 1027 ergs (1020 joules) and higher.[21] The mean magnetic field at the surface of Wolf 359 has a strength of about 2.2 kG (0.22 teslas), but this varies significantly on time scales as short as six hours.[20] By comparison, the magnetic field of the Sun averages 1 gauss (100 µT), although it can rise as high as 3 kG (0.3 T) in active sunspot regions.[37] During flare activity, Wolf 359 has been observed emitting X-rays and gamma rays.[38][39]

Motion

The rotation of a star causes a doppler shift to the spectrum. On average, this results in a broadening of the absorption lines in its spectrum, with the lines increasing in width with higher rates of rotation. However, only the rotational motion in the direction of the observer can be measured by this means, so the resulting data provides a lower limit on the star's rotation. This projected rotational velocity of Wolf 359's equator is less than 3 km/s, which is below the threshold of detection through spectral line broadening.[4] This low rate of rotation may have been caused by loss of angular momentum through a stellar wind. Typically, the time scale for the spin down of a star at spectral class M6 is roughly 10 billion years, because fully-convective stars like this lose their rotation more slowly than other stars.[40] However, evolutionary models suggest that Wolf 359 is a relatively young star with an age of less than a billion years.[11]

The proper motion of this star against the background is 4.696 arcseconds per year, and it is moving away from the Sun at a velocity of 19 km/s.[7][4] When translated into the galactic coordinate system, this motion corresponds to a space velocity of (U, V, W) = (–26, –44, –18) km/s.[41] The space velocity of this star implies that it belongs to the population of old disk stars. It is following an orbit through the Milky Way galaxy that will carry it as close as 20.5 kly (6.3 kpc) and as distant as 28 kly (8.6 kpc) from the galactic core. The galactic orbit has an eccentrity of 0.156, and the star can travel as far as 444 light-years (136 pc) away from the galactic plane.[42] The closest stellar neighbor to Wolf 359 is the red dwarf star Ross 128, 3.79 ly (1.16 pc) away.[43] Approximately 13,850 years ago, Wolf 359 was at its minimal distance of about 7.35 ly (2.25 pc) from the Sun.[44]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 "V* CN Leo -- Flare Star". SIMBAD. Centre de Données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-id?protocol=html&Ident=Wolf+359. Retrieved 2007-07-16. 
  2. ↑ 2.0 2.1 Landolt, Arlo U. (May 2009). "UBVRI Photometric Standard Stars Around the Celestial Equator: Updates and Additions". The Astronomical Journal 137 (5): 4186–4269. doi:10.1088/0004-6256/137/5/4186. Bibcode: 2009AJ....137.4186L.  See table II.
  3. ↑ 3.0 3.1 Gershberg, R. E.; Shakhovskaia, N. I. (1983). "Characteristics of activity energetics of he UV Cet-type flare stars". Astrophysics and Space Science 95 (2): 235–253. doi:10.1007/BF00653631. Bibcode: 1983Ap%26SS..95..235G. 
  4. ↑ 4.0 4.1 4.2 4.3 Mohanty, Subhanjoy; Basri, Gibor (2003). "Rotation and Activity in Mid-M to L Field Dwarfs". The Astrophysical Journal 583 (1): 451–472. doi:10.1086/345097. Bibcode: 2002astro.ph..1455M. 
  5. ↑ Henry, Todd J.; Subasavage, John P.; Brown, Misty A.; Beaulieu, Thomas D.; Jao, Wei-Chun; Hambly, Nigel C. (November 2004). "The Solar Neighborhood. X. New Nearby Stars in the Southern Sky and Accurate Photometric Distance Estimates for Red Dwarfs". The Astronomical Journal 128 (5): 2460–2473. doi:10.1086/425052. Bibcode: 2004AJ....128.2460H. 
  6. ↑ The absolute magnitude M is determined as follows:
    M = m – 5(log10( D ) – 1)
    = 13.54 – 5(log10( 2.39 ) – 1)
    = 13.54 – 5(0.378 – 1) = 16.65

    where m is the apparent magnitude, D is the distance in parsecs and log10 is the base-10 logarithm. See:

    Lang, Kenneth R. (2006). Astrophysical Formulae. Astronomy and Astrophysics Library. 1 (3 ed.). Birkhäuser. p. 31. ISBN 3540296921. 
  7. ↑ 7.0 7.1 7.2 Staff (June 8, 2007). "List of the Nearest 100 Stellar Systems". Research Consortium on Nearby Stars. http://joy.chara.gsu.edu/RECONS/. Retrieved 2007-07-16. 
  8. ↑ Doyle, J. G.; Butler, C. J. (1990). "Optical and infrared photometry of dwarf M and K stars". Astronomy and Astrophysics 235 (1-2): 335–339. Bibcode: 1990A&A...235..335D. 
  9. ↑ Fuhrmeister, B.; Schmitt, J. H. M. M.; Hauschildt, P. H. (September 2005). "PHOENIX model chromospheres of mid- to late-type M dwarfs". Astronomy and Astrophysics 439 (3): 1137–1148. doi:10.1051/0004-6361:20042338. 
  10. ↑ 10.0 10.1 West, Frederick R. (2002). "Letter to the Editor: The Corona of CN Leonis (Gliese 406) and its Possible Detection at Radio Frequencies". The Journal of the American Association of Variable Star Observers 30 (2): 149–150. Bibcode: 2002JAVSO..30..149W. 
  11. ↑ 11.0 11.1 11.2 11.3 11.4 11.5 11.6 11.7 Pavlenko, Ya. V.; Jones, H. R. A.; Lyubchik, Yu.; Tennyson, J.; Pinfield, D. J. (2006). "Spectral energy distribution for GJ406". Astronomy and Astrophysics 447 (2): 709–717. doi:10.1051/0004-6361:20052979. Bibcode: 2006A&A...447..709P. 
  12. ↑ 12.0 12.1 McLean, Ian S.; McGovern, Mark R.; Burgasser, Adam J.; Kirkpatrick, J. Davy; Prato, L.; Kim, Sungsoo S. (October 2003). "The NIRSPEC Brown Dwarf Spectroscopic Survey. I. Low-Resolution Near-Infrared Spectra". The Astrophysical Journal 596 (1): 561–586. doi:10.1086/377636. 
  13. ↑ Wolf, M. (1919). "Katalog von 1053 staerker bewegten Fixsternen". Veroeffentlichungen der Badischen Sternwarte zu Heidelberg 7 (10): 195–219. Bibcode: 1919VeHei...7..195W.  See p. 206.
  14. ↑ Wolf, M. (July 1917). "Eigenbewegungssterne". Astronomische Nachrichten 204: 345. Bibcode: 1917AN....204..345W. 
  15. ↑ van Maanen, Adriaan (1928). "The Photographic Determination of Stellar Parallaxes with the 60- and 100-INCH Reflectors. Fifteenth Series". Contributions from the Mount Wilson Observatory 356: 1–27. Bibcode: 1928CMWCI.356....1V. 
  16. ↑ van Biesbroeck, G. (August 1944). "The star of lowest known luminosity". The Astronomical Journal 51: 61–62. doi:10.1086/105801. Bibcode: 1944AJ.....51...61V. 
  17. ↑ Kron, G. E.; Gascoigne, S. C. B.; White, H. S. (1957). "Red and infrared magnitudes for 282 stars with known trigonometric parallaxes.". Astronomical Journal 62: 205–220. doi:10.1086/107521. Bibcode: 1957AJ.....62..205K. 
  18. ↑ Greenstein, Jesse L.; Neugebauer, G.; Becklin, E. E. (August 1970). "The Faint End of the Main Sequence". Astrophysical Journal 161: 519. doi:10.1086/150556. Bibcode: 1970ApJ...161..519G. 
  19. ↑ Mukai, K.; et al. (August 1990). "Spectroscopy of faint, high latitude cataclysmic variable candidates". Monthly Notices of the Royal Astronomical Society 245 (3): 385–391. Bibcode: 1990MNRAS.245..385M. 
  20. ↑ 20.0 20.1 Reiners, A.; Schmitt, J. H. M. M.; Liefke, C. (2007). "Rapid magnetic flux variability on the flare star CN Leonis". Astronomy and Astrophysics 466 (2): L13–L16. doi:10.1051/0004-6361:20077095. Bibcode: 2007A&A...466L..13R. 
  21. ↑ 21.0 21.1 Robinson, R. D.; Carpenter, K. G.; Percival, J. W.; Bookbinder, J. A. (1995). "A Search for Microflaring Activity on dMe Flare Stars. I. Observations of the dM8e Star CN Leonis". Astrophysical Journal 451: 795–805. doi:10.1086/176266. Bibcode: 1995ApJ...451..795R. 
  22. ↑ Jones, Lauren V. (2009). Stars and Galaxies. Greenwood Guides to the Universe. ABC-CLIO. p. 50. ISBN 0313340757. 
  23. ↑ Borgia, Michael P. (2006). Human vision and the night sky: hot [i.e. how] to improve your observing skills. Patrick Moore's practical astronomy series. Springer. p. 208. ISBN 0387307761. 
  24. ↑ Dantona, F.; Mazzitelli, I. (September 15, 1985). "Evolution of very low mass stars and brown dwarfs. I - The minimum main-sequence mass and luminosity". Astrophysical Journal, Part 1 296: 502–513. doi:10.1086/163470. Bibcode: 1985ApJ...296..502D. 
  25. ↑ Brown, T. M.; Christensen-Dalsgaard, J. (1998). "Accurate Determination of the Solar Photospheric Radius". Astrophysical Journal Letters 500: L195. doi:10.1086/311416. Bibcode: 1998ApJ...500L.195B.  The radius of the Sun is 695.5 Mm. 16% of this is 111 Mm.
  26. ↑ Harvey, Samantha (March 4, 2010). "Jupiter: Facts & Figures". Solar System Exploration. NASA. http://solarsystem.nasa.gov/planets/profile.cfm?Object=Jupiter&Display=Facts. Retrieved 2010-05-28. 
  27. ↑ McCook, G. P.; Jewell, E. R. (1995). "Fully Convective M Dwarfs". Villanova University. http://www.csc.villanova.edu/~astronom/obs95/node12.html. Retrieved 2010-05-017. 
  28. ↑ Adams, Fred C.; Laughlin, Gregory; Graves, Genevieve J. M. (December 2004). "Red Dwarfs and the End of the Main Sequence". Gravitational Collapse: From Massive Stars to Planets. Revista Mexicana de Astronomía y Astrofísica. pp. 46–49. Bibcode: 2004RMxAC..22...46A. 
  29. ↑ Schroeder, Daniel J.; et al. (2000). "A Search for Faint Companions to Nearby Stars Using the Wide Field Planetary Camera 2". The Astronomical Journal 119 (2): 906–922. doi:10.1086/301227. Bibcode: 2000AJ....119..906S. 
  30. ↑ Gautier, T. N.; et al.; MIPS (2007). "Far Infrared Properties of M Dwarfs". The Astrophysical Journal 667: 527-. doi:10.1086/520667. http://arxiv.org/abs/0707.0464v1. Retrieved 2007-11-29. 
  31. ↑ Lestrade, J.-F.; Wyatt, M. C.; Bertoldi, F.; Menten, K. M.; Labaigt, G. (November 2009). "Search for cold debris disks around M-dwarfs. II". Astronomy and Astrophysics 506 (3): 1455–1467. doi:10.1051/0004-6361/200912306. Bibcode: 2009A&A...506.1455L. 
  32. ↑ Casagrande, Luca; Flynn, Chris; Bessell, Michael (September 2008). "M dwarfs: effective temperatures, radii and metallicities". Monthly Notices of the Royal Astronomical Society 389 (2): 585–607. doi:10.1111/j.1365-2966.2008.13573.x. Bibcode: 2008MNRAS.389..585C. 
  33. ↑ Verschuur, Gerrit L. (2003). Interstellar matters: essays on curiosity and astronomical discovery. Springer. pp. 253–254. ISBN 0387406069. 
  34. ↑ Pavlenko, Y. V.; Jones, H. R. A. (December 2002). "Carbon monoxide bands in M dwarfs". Astronomy and Astrophysics 396: 967–975. doi:10.1051/0004-6361:20021454. Bibcode: 2002A&A...396..967P. 
  35. ↑ Pesch, Peter (June 1972). "CaOH, a New Triatomic Molecule in Stellar Atmospheres". Astrophysical Journal 174: L155. doi:10.1086/180970. 
  36. ↑ Schmitt, J. H. M. M. ; Wichmann, R. (2001). "Ground-based observation of emission lines from the corona of a red-dwarf star". Nature 412 (2): 508–510. doi:10.1038/35087513. PMID 11484044. http://www.nature.com/nature/journal/v412/n6846/abs/412508a0.html. Retrieved 2007-07-18. 
  37. ↑ Staff (January 7, 2007). "Calling Dr. Frankenstein! : Interactive Binaries Show Signs of Induced Hyperactivity". National Optical Astronomy Observatory. http://www.noao.edu/outreach/press/pr07/pr0701.html. Retrieved 2006-05-24. 
  38. ↑ Schmitt, J.H.M.M.; Fleming, T.A.; Giampapa, M.S. (September 1995). "The X-Ray View of the Low-Mass Stars in the Solar Neighborhood". Astrophysical Journal 450 (9): 392–400. doi:10.1086/176149. Bibcode: 1995ApJ...450..392S/0000392.000.html. 
  39. ↑ Cwiok, M.; et al. (March 2006). "Search for Optical Counterparts of Gamma Ray Burst". Acta Physica Polonica B 37 (3): 919. Bibcode: 2006AcPPB..37..919C. 
  40. ↑ Röser, Siegfried (2008). Reviews in Modern Astronomy, Cosmic Matter. Wiley-VCH. pp. 49–50, 57. ISBN 3527408207. 
  41. ↑ Gliese, W. (1969). "Catalogue of Nearby Stars". Veröffentlichungen des Astronomischen Rechen-Instituts Heidelberg. Bibcode: 1969VeARI..22....1G. 
  42. ↑ Allen, C.; Herrera, M. A. (1998). "The galactic orbits of nearby UV Ceti stars". Revista Mexicana de Astronomia y Astrofisica 34: 37–46. Bibcode: 1998RMxAA..34...37A. 
  43. ↑ "Wolf 359". SolStation Company. http://www.solstation.com/stars/wolf359.htm. Retrieved 2006-08-10. 
  44. ↑ "Annotations on V* CN Leo object". Centre de Données astronomiques de Strasbourg. http://cdsannotations.u-strasbg.fr/annotations/simbadObject/1769389. Retrieved 2010-04-13. 

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