Emission Signatures of a Young Protostellar Object M. Yamada(ASIAA) - PowerPoint PPT Presentation

Emission Signatures of a Young Protostellar Object M. Yamada(ASIAA) 、 M.N. Machida(NAOJ) 、 S. Inutsuka(Nagoya-U.), K. Tomisaka 、 Y. Kurono(NAOJ) I)magnetic flux problem II)morphology variance by diffusivity III)LTR(observational visualization) IV)pseudo-observation towards ALMA 1 2010 年 3 月 2 日火曜日 1

Introduction: Early Stage of Star Formation ✦ Unresolved problems in (low-mass) Star Formation: 1) angular-momentum problem J core >>J * ⇒ outflow launching that transfers J away 2) magnetic flux problem Φ core >> Φ * : how/when “extra” Φ B decreases by a factor of 10 4 -10 5 ? 3) ... and so on ✦ Low-mass star formation site: center of the parent molecular core observational study of earliest stages of star formation ✦ evolution time scale~free fall time: rapid evolution at the central region ( ρ ∝ r -2 ) ✦ ⇒ need to probe the emission embedded in an infalling envelope ✦ 3D MHD model + line transfer simulation Which line is the plausible tracer? How ALMA can reveal these problems realistically? 2 2010 年 3 月 2 日火曜日 2

Calculations: hydro. evolution 1D Radiative Hydrodynamics Larson (1969) Protostar Tohline (1982) Masunaga & Inutsuka (2000) Log T (K) Adiabatic Phase Second Collapse & Isothermal Phase Protostellar Phases To MS 10 4 Dead region B amplification B amplification B dissipation (10 12 cm -3 <n<10 15 cm -3 ) protostar (second core) 10 3 H 2 dissociation B B B (endoergic reaction) Molecular Cloud Core 10 2 Adiabatic core (First core) Formation 10 Gas Temperature Log n (cm -3 ) 10 5 10 10 10 15 10 20 3 Spatial Scale (AU) 10 4 100 1 0.1 2010 年 3 月 2 日火曜日 3

Magnetic Field in Star Formation ✦ “Magnetic flux problem” Φ core >> Φ * stellar magnetic flux is ~10 -4 ~10 -5 compared with the parent core ✦ How & where has φ B dissipated? dissipation: ambipolar diffusion, Ohmic dissipation ->dynamical evolution ✦ resistive MHD study: rapid diss. at the formation of outflows from the first core ✦ Machida et al.2006+ ideal MHD ohmic dissipation phase parameterize C η ・ η resistive MHD (Nakano et al. 2002) Can we observationally examine these expected 11 differences in morphology? 2010 年 3 月 2 日火曜日 4

Calculations ✦ Hydrodynamic simulations: 3D nest grid, resistive MHD ✦ initial condition: rotating Bonnor-Ebert sphere ✦ (M= 0.3Mo , R=2000AU, T kin =10K) EOS : taken from 1D radiation hydro. simulation ✦ (Masunaga & Inutsuka, 2000) + some modification long evolution, and large spatial extent ✦ 500AU stop calculations slightly after the first core ✦ formation ✦ Radiative Transfer: [ray tracing with long characteristics method] non-LTE level population up to J=16 for each grid ✦ assume uniform chemical abundance distribution ✦ abs. coeffs. profile : ✦ purely thermal velocity, no micro-turbulence HCO + HCN SiO n crit ~10 5 [1/cc] ~10 5 [1/cc] ~10 5 [1/cc] 13 E 10 4.2K 4.1K 2.08K Hogerheijde&van der Tak(2000) 2010 年 3 月 2 日火曜日 5

Morphology variations with eta C η =1 C η =0 (ideal) (a) (b) 12.80 12.80 200 200 11.80 11.80 log 10 n [cm -3 ] log 10 n [cm -3 ] 100 100 10.80 10.80 z[AU] z[AU] outflow 0 0 9.80 9.80 8.80 8.80 -100 -100 7.80 7.80 -200 -200 6.80 6.80 -200 -100 0 100 200 -200 -100 0 100 200 C η =10 x[AU] x[AU] C η =100 (c) (d) 12.80 12.80 200 200 11.80 11.80 log 10 n [cm -3 ] log 10 n [cm -3 ] 100 100 10.80 10.80 z[AU] z[AU] 0 0 9.80 9.80 Strong B 8.80 8.80 -100 -100 7.80 7.80 -200 -200 Wide Opening Angle 6.80 6.80 -200 -100 0 100 200 -200 -100 0 100 200 x[AU] x[AU] ✦ density distribution - “hole” near the first core (launching point) for η >0 cases 14 B-field dissipation at the center -> launching point of the magneto-centrifugal force ✦ goes OUTWARD 2010 年 3 月 2 日火曜日 6

Results: integrated intensity(I) H 13 CO + (4-3), y=2x10 -10 C η =1 C η =0 (ideal) (a) (b) 32.0 32.0 200 26.7 26.7 200 I [K km sec -1 ] I [K km sec -1 ] 21.3 21.3 100 100 z[AU] z[AU] 16.0 16.0 0 0 10.7 10.7 -100 -100 5.3 5.3 -200 -200 0.0 0.0 -200 -100 0 100 200 -200 -100 0 100 200 C η =10 C η =100 x[AU] x[AU] (c) (d) 32.0 32.0 200 26.7 200 26.7 ✦ required I [K km sec -1 ] I [K km sec -1 ] 21.3 21.3 100 100 resolution z[AU] z[AU] 16.0 16.0 0 0 ~10AU@140pc 10.7 10.7 -100 -100 = 0.07”: 5.3 5.3 resolvable -200 -200 0.0 0.0 -200 -100 0 100 200 -200 -100 0 100 200 x[AU] x[AU] ✦ Integrated intensity distributions show differences in the widths of “cavities” of outflows 15 B-field dissipation at the center -> launching point of the magneto-centrifugal force ✦ goes OUTWARD 2010 年 3 月 2 日火曜日 7

Results: integrated intensity(II) H 13 CO + (4-3), y=2x10 -10 , θ =30deg C η =0 (ideal) C η =0.1 C η =1 (a) (b) (c) 32.0 32.0 32.0 200 200 200 26.7 26.7 26.7 I [K km sec -1 ] I [K km sec -1 ] I [K km sec -1 ] 100 100 100 21.3 21.3 21.3 z[AU] z[AU] z[AU] 0 0 0 16.0 16.0 16.0 10.7 10.7 10.7 -100 -100 -100 5.3 5.3 5.3 -200 -200 -200 0.0 0.0 0.0 -200 -100 0 100 200 -200 -100 0 100 200 -200 -100 0 100 200 x[AU] x[AU] x[AU] ✦ pole-on ~ close-to-pole-on views show morphology differences due to η filled cone ( η =0) ⇔ “empty” cone ( η ≠ 0) ✦ Strong B significant difference in ideal/resistive MHD ✦ results Wide Opening Angle А 16 η =0 η ≠ 0 2010 年 3 月 2 日火曜日 8

磁気遠心力風モデル Eta effects in Vel. channel maps eta=0(ideal MHD) eta=1 Wider opening outflows from outer launching ✦ loci form “cavity” structure in (x, y, v) space Strong B -> appears as arm-like structures in nearly 17 pole-on view Wide Opening Angle 2010 年 3 月 2 日火曜日 9

Results: opacity of surrounding envelope C η =1 H 13 CO + (4-3), y=2x10 -10 C η =0 (ideal) n crit (4-3)~10 6 -10 7 cm -3 ⇔ 10 6 cm -3 <n<10 12 cm -3 in this C η =10 snapshot, +n ∝ r -2 C η =100 ⇒ T ex and τ are smaller in outer part l=8 ( Δ L~400AU) ✦ < τ > in the comp. domain is reasonably small for H 13 CO + (4-3) line H 13 CO + (4-3)@356GHz → falls in the band of the receiver on ALMA (Band 8) ✦ 18 < τ > in the larger grid ~ < τ > of the envelope < 10 : OBSERVABLE!! ✦ 2010 年 3 月 2 日火曜日 10

Other observable indications? strong 4.20 60 coll. 2.80 40 R out 20 1.40 Vz [km s -1 ] y[AU] 0 0.00 -20 -1.40 Z out -40 -2.80 -60 -4.20 -60 -40 -20 0 20 40 60 x[AU] outflow length ✦ Shift in launching point → evolution of aspect ratio of outflow width/ length easier than direct detection of relatively small differences in the launching points ✦ 19 from images 2010 年 3 月 2 日火曜日 11

Pseudo-Observation in Computer ✦ line transfer simulation of YSO outflow ✦ rotation of magnetocentrifugal-force driven flow appears in velocity channel maps SiO(7-6), 30deg 2000AU 20 Yamada, Machida, Inutsuka & outflow axis Tomisaka, 2009 2010 年 3 月 2 日火曜日 12

Pseudo-Observation in Computer Y.Kurono & MY, private comm. SMA ALMA @140pc, dec=-30 ✦ diffuse component from the geometrically thick protostellar disk: the total power array is inevitably necessary in ALMA obs. 21 exposure time: ~14 hours for SiO(7-6) @0.1”, 0.3K sensitivity w/ALMA ✦ 2010 年 3 月 2 日火曜日 13

Summary ✦ We examined the emission signatures of very young objects w/ 3D MHD +nonLTE simulations magneto-centrifugal force driven flow: rotation of outflows appears as vel. grad./ ✦ velocity channel maps complicated velocity (rot, infall, outflow) ✦ ->complex morphology, a new criterion for identification of embedded outflows ✦ degree of resistivity shifts the launching point of the outflows “thickness” of the outflows (R out /Z out ) v.s. R out would be an indicator of eta ✦ ..or velocity moment map also helps rather than integrated intensity maps ✦ ✦ Opacity of surrounding envelope is quite severe ( ⇔ necessary to examine the VERY young stage) high-J lines having high n crit , or low abundance isotopologue mid-J lines could probe ✦ the compact & embedded signatures e.g., HCO + (7-6) (624GHz), H 13 CO +/ HC 18 O + (4-3) (356GHz) are good candidate ✦ ALMA can resolve the structure (at least in nearby low-mass star formation regions) ✦ 22 required observational time - ~8 hours(0.07”) for J=4-3, & ~40 hours for J=7-6 lines ✦ 2010 年 3 月 2 日火曜日 14

23 Excitation Temperature: CO adopt “standard” mol. ✦ 12 abundance y=3x10 -4 10 8 n crit (1-0)~10 2 cm -3 , n crit ∝ J 3 ✦ 6 4 J=1-0 J=2-1 J=3-2 J=1-0 J=2-1 J=3-2 huge optical thickness ( τ 0 up ✦ 1-0 2-1 3-2 2 to 4,000) and high density 0 12 (10 6 cm -3 < n < 10 11 cm -3 ) in the T ex [K] T ex [K] 10 simulation box, pop. energy 8 distribution becomes LTE 6 even at high J (J=10-9) J=4-3 J=5-4 J=6-5 4 (T ex = T kin ~10K) J=4-3 J=5-4 J=6-5 4-3 5-4 6-5 2 0 12 coll. dominant: 10 CO, 13 CO, C 18 O are 8 J=7-6 J=8-7 J=9-8 6 improper tracers for 4 young objects J=7-6 J=8-7 J=9-8 7-6 8-7 9-8 n[cm -3 ] 2 0 10 6 10 7 10 8 10 9 10 10 10 6 10 7 10 8 10 9 10 10 10 6 10 7 10 8 10 9 10 10 10 11 10 11 10 11 n[cm -3 ] 2010 年 3 月 2 日火曜日 15