AU Microscopii

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AU Microscopii

Microscopii's debris disk.
Observation data
Epoch J2000
Constellation
(pronunciation)		 Microscopium
Right ascension 20h 45m 09.5318s
Declination -31° 20′ 27.238″
Apparent magnitude (V) 8.61
Characteristics
Spectral type M1 Ve
U-B color index 1.01
B-V color index 1.45
Variable type Flare star
Astrometry
Radial velocity (Rv) 1.2 km/s
Proper motion (μ) RA: 280.37 mas/yr
Dec.: -360.09 mas/yr
Parallax (π) 100.59 ± 1.35 mas
Distance 32.4 ± 0.4 ly
(9.9 ± 0.1 pc)
Absolute magnitude (MV) 8.61
Details
Radius 0.59 R☉
Luminosity 0.029 L☉
Temperature 3730 K
Other designations
GJ 803, HR , CD -31°17815, HD 197481, LHS , LTT 8214, GCTP 4939.00, SAO 212402, Vys 824, LDS 720. FK5 , HIP 102409.
Database references
SIMBAD data
ARICNS data

AU Microscopii (AU Mic) is a red dwarf star[1] located 10 parsecs (32 light-years) away -- about 8 times as far as our closest star after the sun.[2] AU Mic is a young star, only 12 million years old, less than 1% of the age of the sun.[3] It has only half the mass of the sun and is only one-tenth as bright. The star was given this name because it is in the constellation Microscopium and is a variable star. AU Microscopii is a member of the β Pictoris moving group.[4][5] AU Microscopii may be bound to the binary stars AT Microscopii[6] Like β Pictoris, AU Microscopi has a circumstellar dust disk known as a debris disk.

Contents

[edit] Stellar Properties

AU Micoscopii is a small M star, with a physical radius of only 60% that of the Sun and a mass only 50% that of the Sun.[7][8] AU Microscopii has an effective temperature of 3730 K.[9]

[edit] Variability

AU Microscopii has a nearly sinusoidal variation in its brightness with a period of 4.865 days. The amplitude of the variation changes slowly with time. The V band brightness variation was approximately 0.3 magnitudes in 1971, by 1980 it was merely 0.1 magnitudes.[10]

AU Microscopii has been observed in every part of the electromagnetic spectrum from radio to X-ray and is known to undergo flaring activity at all these wavelengths.[11][12][13][14] The flaring behaviour of AU Microscopii was first identified in 1973.[15][16]

[edit] Debris disk

Hubble Space Telescope image of the debris disk around AU Microscopii
Hubble Space Telescope image of the debris disk around AU Microscopii

AU Mic harbors its own disk of dust, first resolved at optical wavelengths in 2003 by Paul Kalas and collaborators using the University of Hawaii 2.2-m telescope on Mauna Kea, Hawaii.[2] This large debris disk faces the earth edge-on[17], and measures at least 200 AU in radius. At these large distances from the star, the lifetime of dust in the disk exceeds the age of AU Microscopii.[2] The disk has a gas to dust mass ratio of no more than 6:1, much lower than the usually assumed primordial value of 100:1.[18] The debris disk is therefore referred to as "gas-poor". The total amount of dust visible in the disk is estimated to be at least a lunar mass, while the larger planetesimals from which the dust is produced are inferred to has at least six lunar masses.[19]

The spectral energy distribution of AU Microscopii's debris disk at submillimetre wavelengths indicate the presence of an inner hole in the disk extending to 17 AU,[20] while scattered light images estimate the inner hole to be 12 AU in radius.[21] Combining the spectral energy distribution with the surface brightness profile yields a smaller estimate of the radius of the inner hole, 1 - 10 AU.[22]

The inner part of the disk is asymmetric and shows structure in the inner 40 AU.[23] The inner structure has been compared with that expected to be seen if the disk is influenced by larger bodies or has undergone recent planet formation.[23]

The presence of the inner hole and asymmetric structure has led a number of astronomers to search for planets. orbiting AU Microscopii. As of 2007, no searches have lead to any detections of planets.[22][24]

The surface brightness (brightness per area) of the disk as a function of projected distance b from the star follows a characteristic shape. The inner 15 AU of the disk appear approximately constant in density.[21]. Around b \approx 15 AU the density begins to decrease; first it decreases slowly as b − α where \alpha \approx 1.8; then outside b \approx 43 AU, the brightness drops more steeply, as b − α where \alpha \approx 4.8.[21] This "broken power-law" shape is similar to the shape of the profile of β Pic's disk.

[edit] Methods of Observation

AU Mic's disk has been observed at a variety of different wavelengths, giving us different types of information about the system. The light from the disk observed at optical wavelengths is stellar light that has reflected (scattered) off dust particles into our line of sight. Observations at these wavelengths utilize a coronagraphic spot to block the bright light coming directly from the star. Such observations provide high-resolution images of the disk. Because light having a wavelength longer than the size of a dust grain is scattered only poorly, comparing images at different wavelengths (visible and near-infrared, for example) gives us information about the sizes of the dust grains in the disk.[25]

Artist's impression of AU Microscopii Credit: NASA/ESA/G. Bacon (STScI)
Artist's impression of AU Microscopii Credit: NASA/ESA/G. Bacon (STScI)

Optical observations have been made with the Hubble Space Telescope and Keck Telescopes. The system has also been observed at infrared and sub-millimeter wavelengths. This light is emitted directly by dust grains as a result of their internal heat (modified blackbody radiation). The disk cannot be resolved at these wavelengths, so such observations are measurements of the amount of light coming from the entire system. Observations at increasingly longer wavelengths give information about dust particles of larger sizes and at larger distances from the star. These observations have been made with the James Clerk Maxwell Telescope and Spitzer Space Telescope.

[edit] References

  1. ^ Maran, S. P., Woodgate, B. E., Carpenter, K. G., Robinson, R. D., Shore, S. N., and Linsky, J. L. (September 1991). "An Investigation of the Flare Star AU Mic with the Goddard High Resolution Spectrograph on the Hubble Space Telescope". Bulletin of the American Astronomical Society 23: 1382. 
  2. ^ a b c Paul Kalas, Michael C. Liu and Brenda C. Matthews (26 March 2004). "Discovery of a Large Dust Disk Around the Nearby Star AU Microscopii". Science 303: 1990 - 1992. doi:10.1126/science.1093420. 
  3. ^ Peter Plavchan, M. Jura, and S. J. Lipsc (October 1, 2005). "Where Are the M Dwarf Disks Older Than 10 Million Years?". The Astrophysical Journal 631 (2): 1161 - 1169. doi:10.1086/432568. 
  4. ^ B Zuckerman and Inseok Song (September 2004). "Young Stars Near the Sun". Annual Review of Astronomy &Astrophysics 42 (1): 685 - 721. doi:10.1146/annurev.astro.42.053102.134111. 
  5. ^ Barrado y Navascués, David; Stauffer, John R.; Song, Inseok; Caillault, J.-P. (August 1, 1999). "The Age of beta Pictoris". The Astrophysical Journal 520 (2): L123 - L126. doi:10.1086/312162. 
  6. ^ Monsignori Fossi, B. C.; Landini, M.; Drake, J. J.; Cully, S. L. (October 1995). "The EUV spectrum of AT Microscopii.". Astronomy & Astrophysics 302: 193. 
  7. ^ Del Zanna, G.; Landini, M. and Mason, H. E. (April 2002). "Spectroscopic diagnostics of stellar transition regions and coronae in the XUV: AU Mic in quiescence". Astronomy and Astrophysics 385: 968 - 985. doi:10.1051/0004-6361:20020164. 
  8. ^ David Mouillet (26 March 2004). "Nearby Planetary Disks". Science 303: 1982-1983. doi:10.1126/science.1095851. 
  9. ^ Linsky, J. L., Bornmann, P. L., Carpenter, K. G., Hege, E. K., Wing, R. F., Giampapa, M. S. (15 September 1982). "Outer atmospheres of cool stars. XII - A survey of IUE ultraviolet emission line spectra of cool dwarf stars". The Astrophysical Journal 260: 670 - 694. doi:10.1086/160288. 
  10. ^ Butler, C. J., Doyle, J. G., Andrews, A. D., Byrne, P. B., Linsky, J. L., Bornmann, P. L. (March 1987). "Rotational modulation and flares on RS CVn and BY DRA systems. II - IUE observations of BY Draconis and AU Microscopii". Astronomy and Astrophysics 174: 139 - 157. 
  11. ^ Maran, S. P.; Robinson, R. D.; Shore, S. N.; Brosius, J. W.; Carpenter, K. G.; Woodgate, B. E.; Linsky, J. L.; Brown, A.; Byrne, P. B.; Kundu, M. R.; White, S.; Brandt, J. C.; Shine, R. A.; Walter, F. M. (1 February 1994). "Observing stellar coronae with the Goddard High Resolution Spectrograph. 1: The dMe star AU microscopoii". The Astrophysical Journal 421: 800 - 808. doi:10.1086/173692. 
  12. ^ Cully, Scott L.; Siegmund, Oswald H. W.; Vedder, Peter W.; Vallerga, John V. (September 10, 1993). "Extreme Ultraviolet Explorer deep survey observations of a large flare on AU Microscopii". The Astrophysical Journal 414: L49-L52. doi:10.1086/156986. 
  13. ^ Kundu, M. R., Jackson, P. D., White, S. M., & Melozzi, M. (15 January 1987). "Microwave observations of the flare stars UV Ceti, AT Microscopii, and AU Microscopii". The Astrophysical Journal 312: 822 - 829. doi:10.1086/164928. 
  14. ^ Tsikoudi, V. and Kellett, B. J. (December 2000). "ROSAT All-Sky Survey X-ray and EUV observations of YY Gem and AU Mic". Monthly Notices of the Royal Astronomical Society 319 (4): 1147 - 1153. doi:10.1046/j.1365-8711.2000.03905.x. 
  15. ^ W.E. Kunkel (1973). "Activity in Flare Stars in the Solar Neighborhood". The Astrophysical Journal Supplement 25: 1. 
  16. ^ Butler, C. J.; Byrne, P. B.; Andrews, A. D.; Doyle, J. G. (December 1981). "Ultraviolet spectra of dwarf solar neighbourhood stars. I". Monthly Notices of the Royal Astronomical Society 197: 815 - 827. 
  17. ^ Paul Kalas, James R. Graham and Mark Clampin (23 June 2005). "A planetary system as the origin of structure in Fomalhaut's dust belt". Nature: 1067 - 1070. doi:10.1038/nature03601. 
  18. ^ Aki Roberge, Alycia J. Weinberger, Seth Redfield, and Paul D. Feldman (20 June 2005). "Rapid Dissipation of Primordial Gas from the AU Microscopii Debris Disk". The Astrophysical Journal 626 (2): L105 - L108. doi:10.1086/431899. 
  19. ^ C. H. Chen, B. M. Patten, M. W. Werner, C. D. Dowell, K. R. Stapelfeldt, I. Song, J. R. Stauffer, M. Blaylock, K. D. Gordon, and V. Krause (December 1, 2005). "A Spitzer Study of Dusty Disks around Nearby, Young Stars". The Astrophysical Journal (2): 1372 - 1384. doi:10.1086/497124. 
  20. ^ Michael C. Liu, Brenda C. Matthews, Jonathan P. Williams, and Paul G. Kalas (June 10, 2004). "A Submillimeter Search of Nearby Young Stars for Cold Dust: Discovery of Debris Disks around Two Low-Mass Stars". The Astrophysical Journal 608 (1): 526 - 532. doi:10.1086/392531. 
  21. ^ a b c John E. Kirst, D. R. Ardila, D. A. Golimowski, M. Clampin, H. C. Ford, G. D. Illingworth, G. F. Hartig, F. Bartko, N. Benítez, J. P. Blakeslee, R. J. Bouwens, L. D. Bradley, T. J. Broadhurst, R. A. Brown, C. J. Burrows, E. S. Cheng, N. J. G. Cross, R. Demarco, P. D. Feldman, M. Franx, T. Goto, C. Gronwall, B. Holden, N. Homeier, L. Infante, R. A. Kimble, M. P. Lesser, A. R. Martel, S. Mei, F. Mennanteau, G. R. Meurer, G. K. Miley, V. Motta, M. Postman, P. Rosati, M. Sirianni, W. B. Sparks, H. D. Tran, Z. I. Tsvetanov, R. L. White, AND W. Zheng (February 2005). "Hubble Space Telescope Advanced Camera for Surveys Coronagraphic Imaging of the AU Microscopii Debris Disk". The Astronomical Journal 129 (2): 1008 - 1017. 
  22. ^ a b Stanimir A. Metchev, Joshua A. Eisner, and Lynne A. Hillenbrand (March 20, 2005). "Adaptive Optics Imaging of the AU Microscopii Circumstellar Disk: Evidence for Dynamical Evolution". The Astrophysical Journal 622 (1): 451 - 462. doi:10.1086/427869. 
  23. ^ a b Michael C. Liu (3 September 2004). "Substructure in the Circumstellar Disk Around the Young Star AU Microscopii". Science 305: 1442 - 1444. 
  24. ^ E. Masciadri, R. Mundt, Th. Henning, and C. Alvarez (1 June 2005). "A Search for Hot Massive Extrasolar Planets around Nearby Young Stars with the Adaptive Optics System NACO". The Astrophysical Journal 625 (2): 1004 - 1018. doi:10.1086/429687. 
  25. ^ Sanders, Robert. "Dust around nearby star like powder snow", UC Berkeley News, January 8, 2007. Retrieved on 2007-01-11. 

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