Van Maanen 2
Epoch J2000.0 Equinox J2000.0 (ICRS)
|Right ascension||00h 49m 09.90175s|
|Declination||+05° 23′ 19.0117″|
|Apparent magnitude (V)||12.374|
|U−B color index||0.064|
|B−V color index||0.546|
|V−R color index||0.268|
|R−I color index||0.4|
|Radial velocity (Rv)||–38 km/s|
|Proper motion (μ)|| RA: +1,236.90 mas/yr |
Dec.: −2709.19 mas/yr
|Parallax (π)||234.60 ± 5.90 mas|
|Distance||13.9 ± 0.3 ly |
(4.3 ± 0.1 pc)
|Absolute magnitude (MV)||14.23 ± 0.05|
|Mass||0.68 ± 0.02 M☉|
|Radius||0.011 ± 0.001 R☉|
|Surface gravity (log g)||8.16 ± 0.03 cgs|
|Temperature||6,220 ± 240 K|
Van Maanen 2 (van Maanen's Star //) is a white dwarf. It is a dense, compact stellar remnant that is no longer generating energy, having about 68% of the Sun's mass but only 1% of the Sun's radius. Out of the white dwarfs known, it is, at 13.9 light-years, the third closest to the Sun, after Sirius B and Procyon B, in that order, and the closest known solitary white dwarf. Discovered in 1917 by Dutch–American astronomer Adriaan van Maanen, Van Maanen 2 was the third white dwarf identified, after 40 Eridani B and Sirius B, and the first that was not a member of a multi-star system. A spectrographic plate made in 1917 shows evidence of planetary matter around the star.
While searching for a companion to the large-proper-motion star Lalande 1299, in 1917 Dutch–American astronomer Adriaan van Maanen discovered a star with an even larger proper motion located a few arcminutes to the northeast. He estimated the annual proper motion of the latter as 3 arcseconds. This star had been previously recorded on a plate taken November 11, 1896 for the Carte du Ciel Catalog of Toulouse, and it showed an apparent magnitude of 12.3. The initial spectral classification was type F0.
In 1918, American astronomer Frederick Seares obtained a refined visual magnitude of 12.34, but the distance to the star remained unknown. Two years later, van Maanen published a parallax estimate of 0.246″, giving it an absolute magnitude of +14.8. This made it the faintest F-type star known at that time. In 1923, Dutch-American astronomer Willem Luyten published a study of stars with large proper motions in which he identified what he called "van Maanen's star" as one of only three known white dwarfs, a term he coined. These are stars that have an unusually low absolute magnitude for their spectral class, lying well below the main sequence on the Hertzsprung–Russell diagram of stellar temperature vs. luminosity.
The high mass density of white dwarfs was demonstrated in 1925 by American astronomer Walter Adams when he measured the gravitational redshift of Sirius B as 21 km/s. In 1926, British astrophysicist Ralph Fowler used the new theory of quantum mechanics to show that these stars are supported by electron gas in a degenerate state. British astrophysicist Leon Mestel demonstrated in 1952 that the energy emitted by a white dwarf is the surviving heat from a prior period of nuclear fusion. He showed that nuclear burning no longer occurs within a white dwarf, and calculated the internal temperature of van Maanen 2 as 6 × 106 K. He gave a preliminary age estimate of 1011/A years, where A is the mean atomic weight of the nuclei in the star.
In 2016, it was discovered that a spectrographic plate of van Maanen 2 made in 1917 has evidence – the earliest known – of planetary matter outside the Solar System. No actual planet has been detected, but the plate reveals the existence of a circumstellar ring of debris, and such rings in other cases have been associated with planets.
Van Maanen 2 is located 13.9 light-years (4.3 parsecs) from the Sun in the constellation Pisces, about 2° to the south of the star Delta Piscium, with a relatively high proper motion of 2.978″ annually along a position angle of 155.538°. It is too faint to be seen with the naked eye. Like other white dwarfs, it is a very dense star: its mass has been estimated to be about 68% of the Sun's, yet it has only 1% of the Sun's radius. The outer atmosphere has a temperature of approximately 6,220 K, which is relatively cool for a white dwarf. As all white dwarfs steadily radiate away their heat over time, this temperature can be used to estimate its age, thought to be around 3 billion years.
The progenitor of this white dwarf had an estimated 2.6 solar masses and remained on the main sequence for about 9 × 108 years. This gives the star a combined age of about 4.1 billion years. When this star left the main sequence, it expanded into a red giant that reached a maximum radius of 650 times the current radius of the Sun, or about 3 astronomical units. Any planets that were orbiting within this radius would have interacted directly with the star's extended envelope.
The stellar classification of Van Maanen 2 is DZ8, where the DZ prefix indicates the presence of elements heavier than helium in its spectrum—what astronomers term metals. Indeed, this star is the prototype for white dwarfs of this class. Based upon physical models of white dwarfs, elements with mass greater than helium should sink below the photosphere of the star, leaving only hydrogen and helium to be visible in the spectrum. Hence, for heavier elements to appear, there must have been an external source. It is unlikely that the heavy elements were obtained from the interstellar medium. Instead, the surface of the star was likely polluted by circumstellar material, such as by the remains of a rocky, terrestrial planet.
The total mass of metals in the atmosphere of Van Maanen 2 is estimated to be around 1021 g—about the same mass as a large moon such as Ariel. These pollutants will sink deeper into the atmosphere on time scales of around three million years, which indicates the material is being replenished at a rate of 107 g/s. These materials could have been accreted in the form of multiple planetesimals smaller than around 84 km colliding with the star.
White dwarfs with a spectrum that indicates high levels of metal contamination often possess a circumstellar disk. In the case of van Maanen 2, observations of the star at a wavelength of 24 μm do not show the infrared excess that might be generated by a dusty disk. Instead there is a noticeable deficit. The predicted flux at 24 μm is 0.23 mJy, whereas the measured value is 0.11 ± 0.03 mJy. This deficit may be explained by collision-induced absorption in the atmosphere of the star. However, this is normally only known to happen with white dwarfs that have temperatures below 4,000 K, as a result of collisions between hydrogen molecules or between hydrogen molecules and helium.
The possible existence of a substellar companion remains uncertain. As recently as 2004, there was one paper confirming and one denying its detection. As of 2008, observations with the Spitzer Space Telescope appear to rule out any companions within 1,200 AU of the star that have four Jupiter masses or greater.
- van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357
- Koen, C.; et al. (April 2010), "UBV(RI)C JHK observations of Hipparcos-selected nearby stars", Monthly Notices of the Royal Astronomical Society, 403 (4): 1949–1968, Bibcode:2010MNRAS.403.1949K, doi:10.1111/j.1365-2966.2009.16182.x
- McCook, G. P.; Sion, E. M. (August 2006), Spectroscopically Identified White Dwarfs, Bibcode:2006yCat.3235....0M, retrieved 2010-12-04 VizieR On-line Data Catalog: III/235B
- "Van Maanen's star", SIMBAD Astronomical Object Database, Centre de Données astronomiques de Strasbourg, retrieved 2008-12-08
- Aannestad, Per A.; et al. (March 1993), "Cool metallic-line white dwarfs, radial velocities, and interstellar accretion", Astronomical Journal, 105 (3): 1033–1044, Bibcode:1993AJ....105.1033A, doi:10.1086/116491.
- Giammichele, N.; Bergeron, P.; Dufour, P. (April 2012), "Know Your Neighborhood: A Detailed Model Atmosphere Analysis of Nearby White Dwarfs", The Astrophysical Journal Supplement, 199 (2): 29, arXiv:1202.5581, Bibcode:2012ApJS..199...29G, doi:10.1088/0067-0049/199/2/29. Based on log L/L☉ = −3.77.
- Sion, Edward M.; et al. (December 2009), "The White Dwarfs Within 20 Parsecs of the Sun: Kinematics and Statistics", The Astronomical Journal, 138 (6): 1681–1689, arXiv:0910.1288, Bibcode:2009AJ....138.1681S, doi:10.1088/0004-6256/138/6/1681
- David Dickinson, Astro-Challenge: Hunting for Van Maanen's Star, Astro Guyz, December 17, 2012
- The One Hundred Nearest Star Systems, RECONS, 2008-01-01, retrieved 2008-12-08
- Holberg, J. B.; Oswalt, Terry D.; Sion, E. M. (May 2002), "A Determination of the Local Density of White Dwarf Stars", The Astrophysical Journal, 571 (1): 512–518, arXiv:astro-ph/0102120, Bibcode:2002ApJ...571..512H, doi:10.1086/339842
- van Maanen, A. (December 1917), "Two Faint Stars with Large Proper Motion", Publications of the Astronomical Society of the Pacific, 29 (172): 258–259, Bibcode:1917PASP...29..258V, doi:10.1086/122654
- Schatzman, Évry (1958), White Dwarfs, North Holland Publishing Company, p. 2
- Seares, F. H. (1918), "Magnitudes and Colors of Three Faint Stars of Large Proper Motion", Publications of the Astronomical Society of the Pacific, 30 (175): 191–192, Bibcode:1918PASP...30..191S, doi:10.1086/122724
- van Maanen, Adriaan (1920), "No. 182. The photographic determination of stellar parallaxes with the 60-inch reflector. Fourth series.", Contributions from the Mount Wilson Observatory, 182: 1–35, Bibcode:1920CMWCI.182....1V—van Maanen identified the star as "Anon. 1".
- Holberg, J. B. (2005), "How Degenerate Stars Came to be Known as White Dwarfs", Bulletin of the American Astronomical Society, 37: 1503, Bibcode:2005AAS...20720501H
- Luyten, Willem J. (1923), "Bulletin Number 344 - A study of stars with large proper motions", Lick Observatory Bulletin, 11: 1–32, Bibcode:1923LicOB..11....1L, doi:10.5479/ADS/bib/1923LicOB.11.1L—See p. 20.
- Adams, W. S. (1925), "The relativity displacement of the spectral lines in the companion of Sirius", The Observatory, 48: 337–342, Bibcode:1925Obs....48..337A
- Fowler, R. H. (1926), "On Dense Matter", Monthly Notices of the Royal Astronomical Society, 87: 114–122, Bibcode:1926MNRAS..87..114F, doi:10.1093/mnras/87.2.114
- Harman, Peter Michael; Mitton, Simon (2002), Cambridge Scientific Minds, Cambridge University Press, pp. 230–232, ISBN 0-521-78612-6
- Mestel, L. (1952), "On the theory of white dwarf stars. I. The energy sources of white dwarfs", Monthly Notices of the Royal Astronomical Society, 112: 583–597, Bibcode:1952MNRAS.112..583M, doi:10.1093/mnras/112.6.583
- Farihi, J. (2016-03-12). "Circumstellar debris and pollution at white dwarf stars". New Astronomy Reviews. 71: 9–34. arXiv:1604.03092. Bibcode:2016NewAR..71....9F. doi:10.1016/j.newar.2016.03.001. Retrieved 2016-04-15.
- "1917 astronomical plate has first-ever evidence of exoplanetary system". ScienceDaily. Retrieved 2016-04-15.
- Burnham, Robert (1978), Burnham's celestial handbook: an observer's guide to the universe beyond the solar system, Dover books explaining science, 3 (2nd ed.), Courier Dover Publications, pp. 1474–1477, ISBN 0-486-23673-0
- Sion, Edward M.; et al. (June 2014), "The White Dwarfs within 25 pc of the Sun: Kinematics and Spectroscopic Subtypes", The Astronomical Journal, 147 (6): 11, arXiv:1401.4989, Bibcode:2014AJ....147..129S, doi:10.1088/0004-6256/147/6/129, 129.
- Burleigh, M. R.; et al. (May 2008), "The 'DODO' survey - I. Limits on ultra-cool substellar and planetary-mass companions to van Maanen's star (vMa2)", Monthly Notices of the Royal Astronomical Society: Letters, 386 (1): L5–L9, arXiv:0801.2917, Bibcode:2008MNRAS.386L...5B, doi:10.1111/j.1745-3933.2008.00446.x
- Farihi, J.; et al. (June 2010), "Rocky planetesimals as the origin of metals in DZ stars", Monthly Notices of the Royal Astronomical Society, 404 (4): 2123–2135, arXiv:1001.5025, Bibcode:2010MNRAS.404.2123F, doi:10.1111/j.1365-2966.2010.16426.x
- Jacobson, R. A.; et al. (June 1992), "The masses of Uranus and its major satellites from Voyager tracking data and earth-based Uranian satellite data", The Astronomical Journal, 103 (6): 2068–2078, Bibcode:1992AJ....103.2068J, doi:10.1086/116211.
- Wyatt, M. C.; Farihi, J.; Pringle, J. E.; Bonsor, A. (April 2014), "Stochastic accretion of planetesimals on to white dwarfs: constraints on the mass distribution of accreted material from atmospheric pollution", Monthly Notices of the Royal Astronomical Society, 439 (4): 3371–3391, arXiv:1401.6173, Bibcode:2014MNRAS.439.3371W, doi:10.1093/mnras/stu183.
- Farihi, J.; Jura, M.; Zuckerman, B. (April 2009), "Infrared Signatures of Disrupted Minor Planets at White Dwarfs", The Astrophysical Journal, 694 (2): 805–819, arXiv:0901.0973, Bibcode:2009ApJ...694..805F, doi:10.1088/0004-637X/694/2/805
- Farihi, J. (May 2005), "Cool versus Ultracool White Dwarfs", The Astronomical Journal, 129 (5): 2382–2385, arXiv:astro-ph/0502134, Bibcode:2005AJ....129.2382F, doi:10.1086/429527
- Bailer-Jones, C. A. L. (March 2015), "Close encounters of the stellar kind", Astronomy & Astrophysics, 575: 13, arXiv:1412.3648, Bibcode:2015A&A...575A..35B, doi:10.1051/0004-6361/201425221, A35.
- Makarov, Valeri V. (2004), "A Substellar Companion to van Maanen 2", The Astrophysical Journal Letters, 600 (1): L71–L73, Bibcode:2004ApJ...600L..71M, doi:10.1086/381544
- Farihi, J.; Becklin, E. E.; Macintosh, B. A. (June 2004), "Mid-Infrared Observations of van Maanen 2: No Substellar Companion", Astrophysical Journal Letters, 608 (2): L109–L112, arXiv:astro-ph/0405245, Bibcode:2004ApJ...608L.109F, doi:10.1086/422502
- Farihi, J.; Becklin, E. E.; Zuckerman, B. (July 2008), "Spitzer IRAC Observations of White Dwarfs. II. Massive Planetary and Cold Brown Dwarf Companions to Young and Old Degenerates", The Astrophysical Journal, 681 (2): 1470–1483, arXiv:0804.0237, Bibcode:2008ApJ...681.1470F, doi:10.1086/588726