structure, star formation and magnetic fields in the omc 1 region
DESCRIPTION
Structure, star formation and magnetic fields in the OMC 1 region. Coppin et al., A&A, 356, 1031 (2000). UMEKAWA Michihisa (ASAFAS). Plasma seminar Feb. 2. Observation of OMC1 using 450 and 850 micro m clump mass function polarimetry (direction of magnetic fields). - PowerPoint PPT PresentationTRANSCRIPT
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Structure, star formation and magnetic fields in the OMC 1 region
UMEKAWA Michihisa (ASAFAS)
Plasma seminar Feb. 2
Coppin et al., A&A, 356, 1031 (2000)
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• Observation of OMC1 using 450 and 850 micro m• clump mass function• polarimetry (direction of magnetic fields)
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Orion star forming region
•~ 450pc•5h20m-6h00m•+5°- -10°
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OMC1
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James Clerk Maxwell Telescope (JCMT)SCUBA (Submillimetre Common-User Bolometer Array)Dec. 1997Jan. 1999 for polarimetry data, with a rotating half-wave plate and a fixed etched grid in front of the SCUBA
15m, the largest submillimetre tele-scope in the world.
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SCUBA 450 micro m: hexagonal array of 91 bolometers850 micro m: 37 bolometersfield of view: 2’.3Calibration sources: Uranus, Mars, OH231.8, CRL618......Nine over lapping fields of view over two nightsBright bar region could be observed only second night
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north-east bar KL
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Clump identification
1. part of a clump being truncated by the map edge2. having a negative flux3. having a higher mean signal in larger areas4. having a peak flux above the local background lower than the noise cut-offreject criteria
The fluxes of the peaks above the local backgroud for clumps
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•39 clumps at 850 micro m, 28 clumps at 450 micro m 55 source are finally listed•3 clumps are on common regions 850 and 450 micro m covered, but not seen on 450 micro m map. All have some emission on 450 micro m map although not a distinct centroid.•Clumps are generally circle, however at 850 micro m 7 clumps and at 450 micro m 4 clumps are elongated.•~ 20% of the flux within their beam size region•<7% of the total flux of the whole jiggle-map region.•S_ν ν^(2+β) (black body). The mean βis 0.5.∝This is small than 1.75 to 2.5 of the previous work at 350 and 1100 micro m. For clouds This is 1.8 to 2.3.Expecting the growth of grains?
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Clump mass function
•The number of clumps dN in mass bin M to M+dM is dN/dM M^(-α)∝
•S_clumps directly traces mass of the clumps. β and temperature of dust are approximately constant. log(dN/dS_clump) vs log S_clump is plotted.
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α= 1.51 at 850 micro m and 1.54 at 450 micro m.
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Polarimetry data
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Conclusions
•4 clouds larger than 0.1 pc contain most of the mass and flux in the region, while the 55 clumps identified on ~0.02pc scales have <7% of the total flux.•magnetic field may have influenced the formation of the brightest cores, Orion-KL and Orion-S, but overall the HII region expansion and fragmentation on the Jeans length appear to be more important dynamically.•a single power-law function of slope -1.5 provides a good fit to the clump masses over a very wide range from 0.1 to 100 Msun.• One more NEXT
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Cloud mass function in Motte et al. (1998)
Motte et al., A&A 336, 150 (1998)ρOphiuchi dark cloud : 160pc from the sun.IRAM 30-m telescope located near Granada Spain1.3mm dust continuum emission from the ρOphiuchi main cloudMPIfR 19-channel bolometerrun: 1995 Mar. 17 to 21, 1996 Mar. 13 to 17, 1996 Apr. 3 to 4, and 1997 Feb. 17 to 23
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Results
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• dN/dM M^-α∝
• α~2.5 for 1 – 10 Msun• α~1.5 for less than 1Msun
• The mass distribution for clumps mimics the behavior of the stellar initial mass function.
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• Motte et al. found two slopes of cloud mass function in ρOphiuchi. In contrust their result has only -1.5.
• The changes in mas function slope are potentially a difference between regions of high-mass and low-mass star formation.
Statistical problem: only afew high mass objects identified in each cloud.
Comments in Coppin et al.
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Umekawa’s simulations
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(a)
(b)
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• (a) Mc~3.5x10 Msun
• (b) Mc~1.1x10^-1Msun
• 微妙である
Umekawa’s simulations