Beta Pictoris


Beta Pictoris

Starbox begin
name=Beta Pictoris
Starbox image


caption=Map of the Pictor constellation showing the position of Beta Pictoris.
Starbox observe
epoch=J2000
ra=05h 47m 17.1scite web|url=http://simbad.u-strasbg.fr/simbad/sim-id?protocol=html&Ident=bet+pic|title=* bet Pic -- Star|work=SIMBAD|accessdate=2008-09-06]
dec=-51° 03′ 59″
appmag_v=3.861
constell=Pictor
Starbox character
class=A6Vcite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2006AJ....132..161G&db_key=AST&nosetcookie=1|title=Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample|author=Gray, R. O. "et al."|year=2006|journal=The Astronomical Journal|volume=132|issue=1|pages=161–170|doi=10.1086/504637]
b-v=0.17cite web|url=http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=V/50/catalog&recno=2020|title=HR 2020|work=Bright Star Catalogue, 5th Revised Ed.|author=Hoffleit D. and Warren Jr W.H.|year=1991|accessdate=2008-09-06]
u-b=0.10
variable=Delta Scuti variablecite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2003MNRAS.341.1385K&db_key=AST&nosetcookie=1|title=δ Scuti pulsations in β Pictoris|author=Koen, C.|year=2003|journal=MNRAS|volume=341|issue=4|pages=1385–1387|doi=10.1046/j.1365-8711.2003.06509.x]
Starbox astrometry
radial_v=+20.0 ± 0.7cite web|url=http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=III/252/table8&recno=8252|title=HIP 27321|work=Pulkovo radial velocities for 35493 HIP stars|author=Gontcharov G.A.|year=2006|accessdate=2008-09-06]
prop_mo_ra=+4.66cite web|url=http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=I/311/hip2&recno=27251|title=HIP 27321|work=Hipparcos, the New Reduction|author=van Leeuwen, F.|year=2007|accessdate=2008-09-06]
prop_mo_dec=+84.16
parallax=50.98
p_error=0.12
parallax_footnote=
absmag_v=2.40The absolute magnitude MV of the star can be calculated from its apparent magnitude mV and distance d using the following equation:

extstyle M_V = m_V - 5log_{10} left(frac{d}{10mathrm{ parsecs ight)] Starbox detail
mass=1.75cite journal|url=http://cdsads.u-strasbg.fr/abs/1997A&A...320L..29C|title=β Pictoris revisited by Hipparcos. Star properties|author=Crifo, F. "et al."|year=1997|journal=Astronomy and Astrophysics|volume=320|pages=L29–L32]
radius=1.8cite conference|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2003IAUS..219E.127K&db_key=AST&nosetcookie=1|title=VINCI/VLTI Observations of Main Sequence Stars|author=Kervella, P.|year=2003|editor=A.K. Dupree and A.O. Benz|publisher=Astronomical Society of the Pacific|conference=IAUS 219: Stars as Suns: Activity, Evolution and Planets|booktitle=Proceedings of the 219th symposium of the International Astronomical Union|location=Sydney, Australia|pages=80|accessdate=2008-09-07]
luminosity_bolometric=8.7
temperature=8052
metal=112% solar
rotational_velocity=130cite web|url=http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=J/A%2bA/463/671/table4&recno=381|title=HD 39060|work=Rotational velocities of A-type stars. III. List of the 1541 B9- to F2-type stars, with their vsini value, spectral type, associated subgroup and classification|author=Royer F.; Zorec J. and Gomez A.E.|year=2007|accessdate=2008-09-07]
gravity=4.15
age=12±|8|4 millioncite journal|url=http://adsabs.harvard.edu/abs/2001ApJ...562L..87Z|title=The β Pictoris Moving Group|author=Zuckerman, B. "et al."|year=2001|journal=The Astrophysical Journal|volume=562|issue=1|pages=L87–L90|doi=10.1086/337968]
Starbox catalog
names=GJ 219, HR 2020, CD -51°1620, HD 39060, GCTP 1339.00, SAO 234134, HIP 27321

Beta Pictoris (β Pic / β Pictoris) is the second brightest star in the constellation Pictor. It is located 64 light years from our solar system and is significantly hotter, more massive and more luminous than our Sun. The Beta Pictoris system is very young, only 8-20 million years old although it is already in the main sequence stage of its evolution. Beta Pictoris is the title member of the Beta Pictoris moving group, an association of young stars which share the same motion through space and have the same age.

Beta Pictoris shows an excess of infrared emission compared to normal stars of its type, which is caused by large quantities of dust near the star. Detailed observations reveal a large disk of dust and gas orbiting the star, which was the first debris disk to be imaged around another star.cite journal|url=http://adsabs.harvard.edu/abs/1984Sci...226.1421S|title=A circumstellar disk around Beta Pictoris|author=Smith, B. A. and Terrile, R. J.|year=1984|journal=Science|volume=226|pages=1421–1424] In addition to the presence of several planetesimal beltscite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2003ApJ...584L..27W&db_key=AST&nosetcookie=1|title=The Inner Rings of β Pictoris|author=Wahhaj, Z. "et al."|journal=The Astrophysical Journal|volume=584|issue=1|pages=L27–L31|year=2003] and cometary activity,cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?1990A%26A...236..202B&db_key=AST&nosetcookie=1|title=The Beta Pictoris circumstellar disk. X - Numerical simulations of infalling evaporating bodies|author=Beust, H.; Vidal-Madjar, A.; Ferlet, R. and Lagrange-Henri, A. M.|year=1990|journal=Astronomy and Astrophysics|volume=236|issue=1|pages=202–216] there are indications that planets have formed within this disk and that the processes of planet formation may still be ongoing.cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2007A%26A...466..389F&db_key=AST&nosetcookie=1|title=Planets of β Pictoris revisited|author=Freistetter, F.; Krivov, A. V. and Löhne, T.|year=2007|journal=Astronomy and Astrophysics|volume=466|issue=1|pages=389–393|doi=10.1051/0004-6361:20066746] Material from the Beta Pictoris debris disk is thought to be the dominant source of interstellar meteoroids in our solar system.cite journal|url=http://adsabs.harvard.edu/abs/2000JGR...10510353B|title=Advanced Meteor Orbit Radar observations of interstellar meteoroids|author=Baggaley, W. Jack|year=2000|journal=J. Geophys. Res.|volume=105|issue=A5|pages=10353–10362|doi=10.1029/1999JA900383]

Location and visibility

Beta Pictoris is a star in the southern constellation of Pictor (the Easel) and is located to the west of the bright star Canopus. [cite web|url=http://www.astro.uiuc.edu/~kaler/sow/betapic.html|title=Beta Pictoris|author=Kaler, Jim|work=STARS|accessdate=2008-09-08] The distance to Beta Pictoris was found by measuring the star's trigonometric parallax. The star has an apparent visual magnitude of 3.861, so is visible to the naked eye: indeed this star is the second brightest in its constellation, exceeded only by Alpha Pictoris with an apparent magnitude of 3.30. [cite web|url=http://www.daviddarling.info/encyclopedia/P/Pic.html|title=Pictor (abbr. Pic, gen. Pictoris)|author=Darling, David|work=The Internet Encyclopedia of Science|accessdate=2008-09-08]

The distance to Beta Pictoris (and many other stars) was measured by the Hipparcos satellite. This was done by measuring its trigonometric parallax: the slight displacement in its position observed as the Earth moves around this orbit. Beta Pictoris was found to exhibit a parallax of 51.87 milliarcseconds, [cite web|url=http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=I/239/hip_main&recno=27301|title=HIP 27321|work=The Hipparcos and Tycho Catalogues|author=ESA|year=1997|accessdate=2008-09-07] a value which was later revised to 50.98 milliarcseconds when the data was reanalysed taking systematic errors more carefully into account. The distance to Beta Pictoris is therefore 64.0 light years, with an uncertainty of 0.2 light years. [cite web|url=http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit1/distances.html|author=Pogge, Richard|title=Lecture 5: Distances of the Stars|work=Astronomy 162: Introduction to Stars, Galaxies, & the Universe|accessdate=2008-09-08] See the article on propagation of uncertainty for information on how errors on derived values can be calculated. The parallax can be converted into distance using the equation:

extstyle mathrm{Distance in parsecs} = frac{1}{mathrm{parallax in arcseconds]

The Hipparcos satellite also measured the proper motion of Beta Pictoris: it is travelling eastwards at a rate of 4.66 milliarcseconds per year, and northwards at a rate of 84.16 milliarcseconds per year. Measurements of the Doppler shift of the star's spectrum reveals it is moving away from us at a rate of 20 km/s. Several other stars share the same motion through space as Beta Pictoris and likely formed from the same gas cloud at roughly the same time: these comprise the Beta Pictoris moving group.

Physical properties

pectrum, luminosity and variability

According to measurements made as part of the Nearby Stars Project, Beta Pictoris has a spectral type of A6V. The A6 part is the spectral class: the A indicates this is a white star similar to Sirius and Vega, as opposed to our Sun which is a yellow star of spectral type G2Vcite web|url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html|title=Sun Fact Sheet|publisher=NASA|accessdate=2008-09-07] . The 6 means it is intermediate between the hottest A type stars (A0) and the coolest (A9). The Roman numeral V is the luminosity class and indicates that, like the Sun, the star is a main sequence star. Such stars are powered by the fusion of hydrogen in their cores.

The spectrum reveals that Beta Pictoris has an effective temperature of 8052 K (7780°C / 14000°F), which is hotter than our Sun's 5778 K (5505°C / 9941°F). Analysis of the spectrum reveals that the star contains a slightly higher ratio of heavy elements (termed metals in astronomy) to hydrogen than our Sun. This value is expressed as the quantity [M/H] , the base-10 logarithm of the ratio of the star's metal fraction to that of the Sun. In the case of Beta Pictoris, the value of [M/H] is 0.05, which means that the star's metal fraction is 12% greater than that of our Sun.

Analysis of the spectrum can also reveal the surface gravity of the star, usually expressed as log g, the base-10 logarithm of the gravitational acceleration given in CGS units (in this case, cm/s²). Beta Pictoris has log g=4.15, implying a surface gravity of 140 m/s² which is about half of the gravitational acceleration at the surface of our Sun (274 m/s²).

As an A-type main sequence star, Beta Pictoris is more luminous than our Sun: combining the apparent magnitude of 3.861 with the distance of 19.62 parsecs gives an absolute magnitude of 2.40, as compared to our Sun which has an absolute magnitude of 4.83. [cite web|url=http://astronomy.swin.edu.au/cosmos/A/Absolute+Magnitude|title=Absolute Magnitude|work=COSMOS - The SAO Encyclopedia of Astronomy|accessdate=2008-09-08] This corresponds to a visual luminosity 9.4 times greater than that of the Sun. When the entire spectrum of radiation from Beta Pictoris and the Sun is taken into account, Beta Pictoris is found to be 8.7 times more luminous than the Sun. [cite web|url=http://www.astronomynotes.com/starprop/s4.htm|author=Strobel, Nick|work=Astronomy Notes|title=Magnitude System|accessdate=2008-09-08] The visual luminosity can then be calculated by:

extstyle frac{L_{ast{L_{odot = 10^{0.4(M_{V_{odot - M_{V_{ast)}]

Many main sequence stars of spectral type A fall into a region of the Hertzsprung-Russell diagram called the instability strip, which is occupied by pulsating variable stars. In 2003, photometric monitoring of the star revealed variations in brightness of around 1-2 millimagnitudes on frequencies between about 30 and 40 minutes. Radial velocity studies of Beta Pictoris also reveal variability: there are pulsations at two frequencies, one at 30.4 minutes and one at 36.9 minutes.cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2006A%26A...447..355G&db_key=AST&nosetcookie=1|title=Extrasolar planets and brown dwarfs around A-F type stars. III. β Pictoris: looking for planets, finding pulsations|author=Galland, F. "et al."|year=2006|journal=Astronomy and Astrophysics|volume=447|issue=1|pages=355–359|doi=10.1051/0004-6361:20054080] As a result, the star is classified as a Delta Scuti variable.

Mass, radius and rotation

The mass of Beta Pictoris has been determined by using models of stellar evolution and fitting them to the star's observed properties. This method yields a stellar mass between 1.7 and 1.8 solar masses. The star's angular diameter has been measured using interferometry with the Very Large Telescope and was found to be 0.84 milliarcseconds. Combining this value with the distance of 64 light years gives a radius 1.8 times that of our Sun.

The rotational velocity of Beta Pictoris has been measured to be at least 130 km/s. Since this value is derived by measuring radial velocities, this is a lower limit on the true rotational velocity: the quantity measured is actually v sin(i), where i represents the inclination of the star's axis of rotation to the line of sight. If it is assumed that Beta Pictoris is viewed from Earth in its equatorial plane (a reasonable assumption since the circumstellar disk is seen edge-on), the rotation period can be calculated as 17 hours, which is significantly shorter than that of our Sun (609.12 hours).The rotation period can be calculated using the equations of circular motion:

extstyle P_{mathrm{rot = frac{2pi r}{v_{mathrm{rot}]

Age and formation

The presence of significant amounts of dust around the starcite book|last=Croswell|first=Ken|authorlink=Ken Croswell|title=Planet Quest|year=1999|publisher=Oxford University Press|isbn=0-19-288083-7|accessdate=2008-09-05] implies a young age of the system and led to debate about whether it had joined the main sequence or was still a pre-main sequence star [cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?1995ApJ...447L..41L&db_key=AST&nosetcookie=1|title=HST/GHRS Observations of the beta Pictoris System: Basic Parameters of the Age of the System|author=Lanz, Thierry; Heap, Sara R. and Hubeny, Ivan|year=1995|journal=The Astrophysical Journal Letters|volume=447|pages=L41] However when the star's distance was measured by Hipparcos it was revealed that Beta Pictoris was located further away than previously thought and hence was more luminous than originally believed. Once the Hipparcos results were taken into account, it was found that Beta Pictoris was located close to the zero age main sequence and was not a pre-main sequence star after all. Analysis of Beta Pictoris and other stars within the Beta Pictoris moving group suggests that they are around 12 million years old. Allowing for uncertainties, the age may range between 8 and 20 million years.

Beta Pictoris may have been formed near the Scorpius-Centaurus Association.cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2004ApJ...609..243O&db_key=AST&nosetcookie=1|title=New Aspects of the Formation of the β Pictoris Moving Group|author=Ortega, V. G. "et al."|year=2004|journal=The Astrophysical Journal|volume=609|issue=1|pages=243–246|doi=10.1086/420958] The collapse of the gas cloud which resulted in the formation of Beta Pictoris may have been triggered by the shockwave from a supernova explosion: the star which went supernova may have been a former companion of HIP 46950, which is now a runaway star. Tracing the path of HIP 46950 backwards suggests that it would have been in the vicinity of the Scorpius-Centaurus Association about 13 million years ago.

Circumstellar environment

Debris disks

Excess infrared radiation from Beta Pictoris was detected with the IRAS spacecraft in 1983. Along with Vega, Fomalhaut and Epsilon Eridani, it was one of the first four stars from which such an excess was detected: these stars are called "Vega-like" after the first of these stars from which such an excess was discovered. Since A-type stars like Beta Pictoris tend to radiate most of their energy at the blue end of the spectrum,From Wien's displacement law and a temperature of 8052 K the peak wavelength emission from Beta Pictoris would be around 360 nanometres which is in the ultraviolet region of the spectrum.] , this implied the presence of cool matter in orbit around the star, which would radiate at infrared radiations and produce the excess. This hypothesis was verified in 1984 when Beta Pictoris became the first star to have its circumstellar disk imaged optically.

The debris disk around Beta Pictoris is orientated edge-on to observers on Earth, and is orientated in a northeast-southwest direction. The disk is asymmetric: in the northeast direction it has been observed out to 1835 astronomical units from the star, while the southwest direction the extent is 1450 AU.cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2001MNRAS.323..402L&db_key=AST&nosetcookie=1|title=Close stellar encounters with planetesimal discs: the dynamics of asymmetry in the β Pictoris system|author=Larwood, J. D. and Kalas, P. G.|journal=MNRAS|volume=323|issue=2|pages=402–416|year=2001|doi=10.1046/j.1365-8711.2001.04212.x] Several elliptical rings of material have been observed in the outer regions of the debris disk between 500 and 800 AU: these may have formed as a result of the system being disrupted by a passing star. [cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2000ApJ...530L.133K&db_key=AST&nosetcookie=1|title=Rings in the Planetesimal Disk of β Pictoris|author=Kalas, P.; Larwood, J.; Smith, B. A. and Schultz, A.|year=2000|journal=The Astrophysical Journal|volume=530|issue=2|pages=L133–L137|doi=10.1086/312494] Astrometric data from the Hipparcos mission reveal that the red giant star Beta Columbae passed within 2 light years of Beta Pictoris about 110,000 years ago, but a larger perturbation would have been caused by Zeta Doradus, which passed at a distance of 3 light years about 350,000 years ago. [cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2001ApJ...553..410K&db_key=AST&nosetcookie=1|title=Stellar Encounters with the β Pictoris Planetesimal System|author=Kalas, Paul; Deltorn, Jean-Marc and Larwood, John|year=2001|journal=The Astrophysical Journal|volume=553|issue=1|pages=410–420|doi=10.1086/320632] However computer simulations favour a lower encounter velocity than either of these two candidates, which suggest that the star responsible for the rings may have been a companion star of Beta Pictoris on an unstable orbit. The simulations suggest a perturbing star with a mass of 0.5 solar masses (which would make it a red dwarf of spectral type M0V) is likely to blame for the structures. [cite press release|url=http://hubblesite.org/newscenter/archive/releases/2000/02/text/|title=Beta Pictoris Disk Hides Giant Elliptical Ring System|publisher=NASA|date=2000-01-15|accessdate=2008-09-02]

In 2006, imaging of the system with the Hubble Space Telescope's Advanced Camera for Surveys revealed the presence of a secondary dust disk inclined at an angle of about 5° to the main disk and extending at least 130 AU from the star.cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2006AJ....131.3109G&db_key=AST&nosetcookie=1|author=Golimowski, D. A. "et al."|title=Hubble Space Telescope ACS Multiband Coronagraphic Imaging of the Debris Disk around β Pictoris|journal=The Astronomical Journal|volume=131|issue=6|pages=3109–3130|year=2006|doi=10.1086/503801] The secondary disk is asymmetrical: the southwest extension is more curved and less inclined than the northeast. The imaging was not good enough to distinguish between the main and secondary disks within 80 AU of Beta Pictoris, however the northeast extension of the dust disk is predicted to intersect with the main disk at about 30 AU from the star. The secondary disk may be produced by a massive planet in an inclined orbit removing matter from the primary disk and causing it to move in an orbit aligned with the planet.cite press release|url=http://hubblesite.org/newscenter/archive/releases/2006/25/full/|title=Hubble Reveals Two Dust Disks Around Nearby Star Beta Pictoris|publisher=NASA|date=2006-06-27|accessdate=2008-09-02]

Studies made with the NASA Far Ultraviolet Spectroscopic Explorer have discovered that the disk around Beta Pictoris contains an extreme overabundance of carbon-rich gas.cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2006Natur.441..724R&db_key=AST&nosetcookie=1|title=Stabilization of the disk around β Pictoris by extremely carbon-rich gas|author=Roberge, Aki "et al."|year=2006|journal=Nature|volume=441|issue=7094|pages=724–726|doi=10.1038/nature04832] This helps stabilise the disk against radiation pressure which would otherwise blow the material away into interstellar space. Currently, there are two suggested explanations for the origin of the carbon overabundance. Beta Pictoris might be in the process of forming exotic carbon-rich planets, in contrast to the terrestrial planets in our solar system, which are rich in oxygen instead of carbon.cite press release|url=http://www.nasa.gov/vision/universe/starsgalaxies/betapic.html|title=NASA's Fuse Finds Infant Solar System Awash in Carbon|date=2006-06-07|publisher=NASA|accessdate=2006-07-03] Alternatively it may be passing through an unknown phase that might also have occurred early in the development of our solar system: in our solar system there are carbon-rich meteorites (the enstatite chondrites are candidates for forming in a carbon-rich environment) and it has been proposed that Jupiter may have formed around a carbon-rich core.

Planetesimal belts

s from the star were detected, which alternate in inclination with respect to the main disk.

Observations in 2004 revealed the presence of an inner belt containing silicate material at a distance of 6.4 AU from the star. Silicate material was also detected at 16 and 30 AU from the star, with a lack of dust between 6.4 and 16 AU providing evidence that a massive planet may be orbiting in this region. [cite journal|url=http://www.nature.com/nature/journal/v431/n7009/abs/nature02948.html|title=An early extrasolar planetary system revealed by planetesimal belts in β Pictoris|author=Okamoto, Yoshiko Kataza "et al."|journal=Nature|year=2004|volume=431|issue=7009|pages=660–663|doi=10.1038/nature02948] cite web|url=http://www.astronomy.com/asy/default.aspx?c=a&id=2512|title=Making planets at Beta Pictoris|year=2004|publisher=Astronomy Magazine|author=Burnham, Robert|accessdate=2008-09-02]

Modelling of the dust disk at 100 AU from the star suggests the dust in this region may have been produced by a series of collisions initiated by the destruction of planetesimals with radii of about 180 kilometers. After the initial collision, the debris undergoes further collisions in a process called a collisional cascade. Similar processes have been inferred in the debris disks around Fomalhaut and AU Microscopii. [cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2007MNRAS.380.1642Q&db_key=AST&nosetcookie=1|title=Planetary embryos and planetesimals residing in thin debris discs|author=Quillen, Alice C.; Morbidelli, Alessandro and Moore, Alex|journal=MNRAS|year=2007|volume=380|issue=4|pages=1642–1648|doi=10.1111/j.1365-2966.2007.12217.x]

Falling evaporating bodies

The spectrum of Beta Pictoris shows strong short-term variability which was first noticed in the red-shifted part of various absorption lines, which was interpreted as being caused by material falling onto the star. [cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?1988A%26A...190..275L&db_key=AST&nosetcookie=1|title=The Beta Pictoris circumstellar disk. VI - Evidence for material falling on to the star|author=Lagrange-Henri, A. M.; Vidal-Madjar, A. and Ferlet, R.|journal=Astronomy and Astrophysics|volume=190|pages=275–282|year=1988] The source of this material was suggested to be small comet-like objects on orbits which take them close to the star where they begin to evaporate, termed the "falling evaporating bodies" model. Transient blue-shifted absorption events were also detected, though less frequently: these may represent a second group of objects on a different set of orbits. [cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?1998MNRAS.294L..31C&db_key=AST&nosetcookie=1|title=Detection of a strong transient blueshifted absorption component in the Beta Pictoris disc|author=Crawford, I. A.; Beust, H. and Lagrange, A.-M.|year=1998|journal=MNRAS|volume=294|pages=L31–L34] Detailed modelling indicates the falling evaporating bodies are unlikely to be mainly icy like comets, but instead are probably composed of a mixed dust and ice core with a crust of refractory material. [cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2001A%26A...372..616K&db_key=AST&nosetcookie=1|title=The physico-chemical history of Falling Evaporating Bodies around beta Pictoris: investigating the presence of volatiles|author=Karmann, C.; Beust, H. and Klinger, J.|year=2001|journal=Astronomy and Astrophysics|volume=372|pages=616–626|doi=10.1051/0004-6361:20010528] These objects may have been perturbed onto their star-grazing orbits by the gravitational influence of a planet in a mildly eccentric orbit around Beta Pictoris at a distance of roughly 10 AU from the star.cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2001A%26A...376..621T&db_key=AST&nosetcookie=1|title=Falling evaporating bodies in the β Pictoris system. Resonance refilling and long term duration of the phenomenon|author=Thébault, P. and Beust, H.|year=2001|journal=Astronomy and Astrophysics|volume=376|pages=621–640|doi=10.1051/0004-6361:20010983] Falling evaporating bodies may also be responsible for the presence of gas located high above the plane of the main debris disk. [cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2007A%26A...466..201B&db_key=AST&nosetcookie=1|title=High latitude gas in the β Pictoris system. A possible origin related to falling evaporating bodies|author=Beust, H. and Valiron, P.|year=2007|journal=Astronomy and Astrophysics|volume=466|issue=1|pages=201–213|doi=10.1051/0004-6361:20053425]

Possible planetary system

The radial velocity method used to discover the majority of currently-known extrasolar planets is not well suited to studying A-type stars like Beta Pictoris. Current limits derived from this method are enough to rule out close-orbiting giant planets (planets more massive than 2 Jupiter masses are ruled out at a distance of 0.05 AU from the star) but for planets orbiting at 1 AU, planets with less than 9 Jupiter masses would have evaded detection. Therefore to find planets in the Beta Pictoris system, astronomers look for the effects that the planet has on the circumstellar environment.

Multiple lines of evidence suggest the existence of a massive planet orbiting in the region around 10 AU from the star: the dust-free gap between the planetesimal belts at 6.4 AU and 16 AU suggest this region is being cleared out; a planet at this distance would explain the origin of the falling evaporating bodies; and the warps and inclined rings in the inner disk suggest a massive planet on an inclined orbit is disrupting the disk. [cite journal|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?1997MNRAS.292..896M&db_key=AST&nosetcookie=1|title=A planet on an inclined orbit as an explanation of the warp in the Beta Pictoris disc|author=Mouillet, D.; Larwood, J. D.; Papaloizou, J. C. B. and Lagrange, A. M.|year=1997|journal=MNRAS|volume=292|pages=896–904] Modelling accounting for all of these phenomena suggest that the planet is orbiting in a mildly eccentric orbit (eccentricity less than 0.1) with a semimajor axis of 12 AU and has a mass between 2 and 5 times that of Jupiter.

The 12 AU planet by itself cannot explain the structure of the planetesimal belts at 30 AU and 52 AU from the star. These belts might be associated with smaller planets at 25 and 44 AU, with masses around 0.5 and 0.1 Jupiter masses respectively. Such a system of planets, if it exists, would be close to a 1:3:7 orbital resonance. It may also be that the rings in the outer disc at 500-800 AU are indirectly caused by the influence of these planets.

Dust stream

In 2000, observations made with the Advanced Meteor Orbit Radar facility revealed the presence of a stream of particles coming from the direction of Beta Pictoris, which appears to be the dominant source of interstellar meteoroids in our solar system. The particles in the Beta Pictoris dust stream are relatively large, with radii exceeding 20 microns, and their velocities suggest that they must have left the Beta Pictoris system at roughly 25 km/s. These particles may have been ejected from the Beta Pictoris debris disk as a result of the migration of gas giant planets within the disk and may be an indication that the Beta Pictoris system is forming an Oort cloud. [cite journal|url=http://adsabs.harvard.edu/abs/2003A%26A...402L...5K|title=A stream of particles from the β Pictoris disc: A possible ejection mechanism|author=Krivova, N. A. and Solanki, S. K.|year=2003|journal=Astronomy and Astrophysics|volume=402|pages=L5–L8|doi=10.1051/0004-6361:20030369] Numerical modelling of dust ejection also suggests radiation pressure may also be responsible and suggests that planets further than about 1 AU from the star cannot directly cause the dust stream. On the other hand, planets in close-in orbits around Beta Pictoris better fit the planetary scenario for the stream's origin. [cite journal|url=http://adsabs.harvard.edu/abs/2004A%26A...417..341K|title=Towards understanding the β Pictoris dust stream|author=Krivov, A. V. "et al."|year=2004|journal=Astronomy and Astrophysics|volume=417|pages=341–352|doi=10.1051/0004-6361:20034379]

Notes

References

External links

* [http://www.disksite.com/ The Circumstellar Disk Learning Site]
* [http://www.alcyone.de/SIT/bsc/bsc_search.html Bright Star Catalog]
* [http://www.astro.uiuc.edu/~kaler/sow/betapic.html Beta Pictoris]
* [http://www.ifa.hawaii.edu/faculty/jewitt/beta.html Dr. David Jewitt's page on Beta Pic]
* [http://www.solstation.com/stars2/beta-pic.htm Beta Pictoris] at SolStation.
* [http://www.ari.uni-heidelberg.de/aricns/cnspages/4c00467.htm ARICNS]
* [http://www.seds.org/~spider/spider/Misc/betaPic.html SEDS entry]


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