AU Microscopii

Starbox begin
name=AU Microscopii Starbox image


caption=Microscopii's debris disk. Starbox observe
epoch=J2000
ra=RA|20|45|09.5318
dec=DEC| -31|20|27.238
appmag_v=8.61
constell=Microscopium Starbox character
class=M1 Ve
b-v=1.45
u-b=1.01
variable=Flare star Starbox astrometry
radial_v=1.2
prop_mo_ra=280.37
prop_mo_dec=-360.09
parallax=100.59
p_error=1.35
absmag_v=8.61 Starbox detail
radius=0.59
luminosity=0.029
temperature = 3730 Starbox catalog
names=GJ 803, HR , CD -31°17815, HD 197481, LHS , LTT 8214, GCTP 4939.00, SAO 212402, Vys 824, LDS 720. FK5 , HIP 102409. Starbox reference
Simbad=AU+Microscopii
ARICNS=01685

AU Microscopii (AU Mic) is a red dwarf star [cite journal|author = Maran, S. P., Woodgate, B. E., Carpenter, K. G., Robinson, R. D., Shore, S. N., and Linsky, J. L.|title = An Investigation of the Flare Star AU Mic with the Goddard High Resolution Spectrograph on the Hubble Space Telescope|month = September | year = 1991|journal = Bulletin of the American Astronomical Society|volume = 23|pages = 1382|url = http://adsabs.harvard.edu/abs/1991BAAS...23.1382M|accessdate = 2007-05-30] located 10 parsecs (32 light-years) away -- about 8 times as far as our closest star after the sun.cite journal|url = http://www.sciencemag.org/cgi/content/full/303/5666/1990|title = Discovery of a Large Dust Disk Around the Nearby Star AU Microscopii|author = Paul Kalas, Michael C. Liu and Brenda C. Matthews|date = 26 March 2004|journal = Science|volume = 303|number = 5666|pages = 1990–1992|doi = 10.1126/science.1093420|pmid = 14988511] AU Mic is a young star, only 12 million years old, less than 1% of the age of the sun.cite journal|author = Peter Plavchan, M. Jura, and S. J. Lipsc|title = Where Are the M Dwarf Disks Older Than 10 Million Years?|journal = The Astrophysical Journal|date = October 1 2005|volume = 631|issue = 2|pages = 1161–1169|url = http://adsabs.harvard.edu/abs/2005ApJ...631.1161P|doi = 10.1086/432568] 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. [cite journal|title = Young Stars Near the Sun|author = B Zuckerman and Inseok Song|journal = Annual Review of Astronomy &Astrophysics|month = September | year = 2004|volume = 42|issue = 1|pages = 685–721|url = http://adsabs.harvard.edu/abs/2004ARA%26A..42..685Z|doi = 10.1146/annurev.astro.42.053102.134111] [cite journal|author = Barrado y Navascués, David; Stauffer, John R.; Song, Inseok; Caillault, J.-P.|title = The Age of beta Pictoris|journal = The Astrophysical Journal|date = August 1 1999|volume = 520|issue = 2|pages = L123–L126|url = http://adsabs.harvard.edu/abs/1999ApJ...520L.123B|accessdate = 2007-05-14|doi = 10.1086/312162] AU Microscopii may be bound to the binary stars AT Microscopii [cite journal|author = Monsignori Fossi, B. C.; Landini, M.; Drake, J. J.; Cully, S. L.|title = The EUV spectrum of AT Microscopii|month = October | year = 1995|journal = Astronomy & Astrophysics|volume = 302|pages = 193|url = http://adsabs.harvard.edu/abs/1995A&A...302..193M|accessdate = 2007-06-08] Like β Pictoris, AU Microscopi has a circumstellar dust disk known as a debris disk.

tellar 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.cite journal|author = Del Zanna, G.; Landini, M. and Mason, H. E.|title = Spectroscopic diagnostics of stellar transition regions and coronae in the XUV: AU Mic in quiescence|journal = Astronomy and Astrophysics|volume = 385|month = April | year = 2002|pages = 968–985|url = http://adsabs.harvard.edu/abs/2002A%26A...385..968D|accessdate = 2007-05-30|doi = 10.1051/0004-6361:20020164] [cite journal|url = http://www.sciencemag.org/cgi/content/full/sci;303/5666/1982|title = Nearby Planetary Disks|author = David Mouillet|journal = Science|volume = 303|number = 5666|pages = 1982–1983|date = 26 March 2004|doi = 10.1126/science.1095851|pmid = 15044792] AU Microscopii has an effective temperature of 3730 K.cite journal|author = Linsky, J. L., Bornmann, P. L., Carpenter, K. G., Hege, E. K., Wing, R. F., Giampapa, M. S.|title = Outer atmospheres of cool stars. XII - A survey of IUE ultraviolet emission line spectra of cool dwarf stars|journal = The Astrophysical Journal|date = 15 September 1982|part = 1|volume = 260|pages = 670–694|url = http://adsabs.harvard.edu/abs/1982ApJ...260..670L|accessdate = 2007-06-14|doi = 10.1086/160288]

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. [cite journal|author = Butler, C. J., Doyle, J. G., Andrews, A. D., Byrne, P. B., Linsky, J. L., Bornmann, P. L.|title = Rotational modulation and flares on RS CVn and BY DRA systems. II - IUE observations of BY Draconis and AU Microscopii|journal = Astronomy and Astrophysics|month = March | year = 1987|volume = 174|number = 1-2|pages = 139–157|url = http://adsabs.harvard.edu/abs/1987A%26A...174..139B|accessdate = 2007-05-28]

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. [cite journal|author = 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.|title = Observing stellar coronae with the Goddard High Resolution Spectrograph. 1: The dMe star AU microscopoii|journal = The Astrophysical Journal|volume = 421|number = 2|pages = 800–808|date = 1 February 1994|accessdate = 2007-05-28|url = http://adsabs.harvard.edu/abs/1994ApJ...421..800M|doi = 10.1086/173692] [cite journal|author = Cully, Scott L.; Siegmund, Oswald H. W.; Vedder, Peter W.; Vallerga, John V.|title = Extreme Ultraviolet Explorer deep survey observations of a large flare on AU Microscopii|journal = The Astrophysical Journal|url = http://adsabs.harvard.edu/abs/1993ApJ...414L..49C|volume = 414|number = 2|pages = L49–L52|date = September 10 1993|accessdate = 2007-05-28|doi = 10.1086/156986] [cite journal|author = Kundu, M. R., Jackson, P. D., White, S. M., & Melozzi, M.|title = Microwave observations of the flare stars UV Ceti, AT Microscopii, and AU Microscopii|journal = The Astrophysical Journal|date = 15 January 1987|volume = 312|pages = 822–829|url = http://adsabs.harvard.edu/abs/1987ApJ...312..822K|accessdate = 2007-05-28|doi = 10.1086/164928] cite journal|author = Tsikoudi, V. and Kellett, B. J.|title = ROSAT All-Sky Survey X-ray and EUV observations of YY Gem and AU Mic|journal = Monthly Notices of the Royal Astronomical Society|volume = 319|issue = 4|pages = 1147–1153|url = http://adsabs.harvard.edu/abs/2000MNRAS.319.1147T|accessdate = 2007-05-30|month = December | year = 2000|doi = 10.1046/j.1365-8711.2000.03905.x] The flaring behaviour of AU Microscopii was first identified in 1973. [cite journal|author = W.E. Kunkel|title = Activity in Flare Stars in the Solar Neighborhood|journal = The Astrophysical Journal Supplement|year = 1973|volume = 25|url = http://adsabs.harvard.edu/abs/1973ApJS...25....1K|accessdate = 2007-05-28|pages = 1|doi = 10.1086/190263] [cite journal|author = Butler, C. J.; Byrne, P. B.; Andrews, A. D.; Doyle, J. G.|title = Ultraviolet spectra of dwarf solar neighbourhood stars. I|journal = Monthly Notices of the Royal Astronomical Society|month = December | year = 1981|volume = 197|pages = 815–827|url = http://adsabs.harvard.edu/abs/1981MNRAS.197..815B|accessdate = 2007-05-28]

Debris disk

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. This large debris disk faces the earth edge-on [cite journal|author = Paul Kalas, James R. Graham and Mark Clampin|title = A planetary system as the origin of structure in Fomalhaut's dust belt|journal = Nature|voulme = 435|date = 23 June 2005|pages = 1067–1070|url = http://adsabs.harvard.edu/abs/2005Natur.435.1067K|doi = 10.1038/nature03601|issue = 7045|volume = 435] , 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. 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.planetesimals from which the dust is produced are inferred to has at least six lunar masses. [cite journal|author = 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|title = A Spitzer Study of Dusty Disks around Nearby, Young Stars|journal = The Astrophysical Journal|date = December 1 2005|voume = 634|issue = 2|pages = 1372–1384|url = http://adsabs.harvard.edu/abs/2005ApJ...634.1372C|doi = 10.1086/497124|volume = 634]

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, [cite journal|title = A Submillimeter Search of Nearby Young Stars for Cold Dust: Discovery of Debris Disks around Two Low-Mass Stars|author = Michael C. Liu, Brenda C. Matthews, Jonathan P. Williams, and Paul G. Kalas|journal = The Astrophysical Journal|date = June 10 2004|volume = 608|issue = 1|pages = 526–532|url = http://adsabs.harvard.edu/abs/2004ApJ...608..526L|doi = 10.1086/392531] while scattered light images estimate the inner hole to be 12 AU in radius.cite journal|author = 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|title = Hubble Space Telescope Advanced Camera for Surveys Coronagraphic Imaging of the AU Microscopii Debris Disk|month = February | year = 2005|journal = The Astronomical Journal|volume = 129|issue = 2|pages = 1008–1017|url = http://adsabs.harvard.edu/abs/2005AJ....129.1008K|doi = 10.1086/426755] Combining the spectral energy distribution with the surface brightness profile yields a smaller estimate of the radius of the inner hole, 1 - 10 AU.cite journal|author = Stanimir A. Metchev, Joshua A. Eisner, and Lynne A. Hillenbrand|title = Adaptive Optics Imaging of the AU Microscopii Circumstellar Disk: Evidence for Dynamical Evolution|journal = The Astrophysical Journal|date = March 20 2005|volume = 622|issue = 1|pages = 451–462|url = http://adsabs.harvard.edu/abs/2005ApJ...622..451M|doi = 10.1086/427869]

The inner part of the disk is asymmetric and shows structure in the inner 40 AU.cite journal|title = Substructure in the Circumstellar Disk Around the Young Star AU Microscopii|author = Michael C. Liu|journal = Science|date = 3 September 2004|volume = 305|number = 5689|pages = 1442–1444|url = http://www.sciencemag.org/cgi/content/full/305/5689/1442|doi = 10.1126/science.1102929|pmid = 15308766] 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.

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.cite journal|author = E. Masciadri, R. Mundt, Th. Henning, and C. Alvarez|title = A Search for Hot Massive Extrasolar Planets around Nearby Young Stars with the Adaptive Optics System NACO|journal = The Astrophysical Journal|date = 1 June 2005|volume = 625|issue = 2|pages = 1004–1018|url = http://adsabs.harvard.edu/abs/2005ApJ...625.1004M|doi = 10.1086/429687]

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.. Around $b\; approx\; 15\; AU$ the density begins to decrease; first it decreases slowly as $b^\{-alpha\}$ where $alpha\; approx\; 1.8$; then outside $b\; approx\; 43\; AU$, the brightness drops more steeply, as $b^\{-alpha\}$ where $alpha\; approx\; 4.8$. This "broken power-law" shape is similar to the shape of the profile of β Pic's disk.

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. Wikimedia Foundation. 2010.