SLIDE 1 Observational signatures of fragmenting protostellar disk
Olga Zakhozhay
Main Astronomical Observatory National Academy of Sciences of Ukraine zkholga@mail.ru
in collaboration with Eduard Vorobyov1 and Michael Dunham2
1Institute of Astrophysics, University Vienna, Austria 2Department of Astronomy , Yale University, USA
SLIDE 2 Disk formation and evolution, and planet formation, are integral parts of the star formation process
Pre-stellar phase Class 0 and I phases T Tauri phase
- 1+1D models (Hueso & Guillot 2005; Visser et al. 2009; Rice at al. 2010),
- 2D models (Yorke & Bodenheimer 1999; Boss & Hartmann 2001;
Vorobyov & Basu 2006, 2010, Zhu et al. 2009),
- 3D models (Krumholz et al. 2007; Kratter et al. 2010; Machida et al. 2009, 2010).
Global models that self-consistently follow Cloud => Disk transition
SLIDE 3
Gas surface density and temperature maps for the model with initial core mass M = 1.23 Msun
Gas surface density (g cm-2) Temperature (K)
SLIDE 4 Number of fragments vs. time
Characteristic time of mass infall onto the disc
Md – disk mass
– mass infall rate onto the disk
Md = 0.2 – 0.25 Msun
= (2 – 3) 10-6 Msun yr-1
tinfall = 0.07 – 0.12 Myr
SLIDE 5
Properties of fragments
SLIDE 6 Zoomed-in surface density images for four proto-BDs (characterized by midplane temperature >103 K)
Hill radius
Mf – mass of the fragment (proto-BD)
rf – radial distance from the protostar to the fragment
SLIDE 7 Calculation algorithm for the SEDs
* disk
F F F = +
disk d sc
F F F = +
Protostar
Disk
d – distance to YSO, 250 pc κν – opacity (Ossenkopf & Henning 1994, thin ice mantles (OH5 dust))
Disk Sink cell
SLIDE 8
Test of the code
where, T* = 4000 K R* = 2.5 Rsun rout = 200 AU (270 AU) Chiang & Goldreich 1997
SLIDE 9 Surface density maps and SEDs for the fragmenting disk
M = 55 MJup Tmp = 1660 K M = 64 MJup Tmp = 1375 K M = 52 MJup Tmp = 1190 K M = 32 MJup Tmp = 1180 K
proto-BD proto-BD proto-BD proto-BD
SLIDE 10 Surface density maps and SEDs for the fragmenting disk
Star+disk are embedded within a core
M = 55 MJup Tmp = 1660 K M = 64 MJup Tmp = 1375 K M = 52 MJup Tmp = 1190 K M = 32 MJup Tmp = 1180 K
proto-BD proto-BD proto-BD proto-BD
SLIDE 11
Surface density maps and SEDs for the non-fragmenting disk
SLIDE 12
Simulated ALMA images (log (mJy beam-1), 1 hour, 0.1″)
SLIDE 13
Simulated ALMA images, (mJy beam-1, 1 hour, 0.1″)
SLIDE 14
Simulated ALMA images, (log (mJy beam-1), 1 hour, 0.5″)
SLIDE 15 Conclusions
- Disk experiences multiple episodes of fragmentation in the embedded phase :
- mass distribution function: maxima around 5 MJ and 60-70 MJ,
- mass spectrum: from about Jupiter mass to very-low-mass stars.
- Majority of fragments surface temperatures Tsurf<100K due to high optical
depths.
- Some fragments: interior temperatures sufficient to evaporate dust grains.
These fragments have much higher surface densities and create a peak at ≈ 5μm in the SEDs.
- Fragments can be detected with ALMA (1 hour, 0.1").
- detection limit: 1.5 MJ (at 250 pc).
- use a log scaling to resolve the spiral structure and fragments at ≤ 100 AU.
- use oversaturated linear scaling to detect distant and low-mass fragments.
- with resolution of 0.5" fragments may be detected at distances ≤ 150 pc.
SLIDE 16
SLIDE 17 Model caveats
Uncertainties in dust opacity • Non-zero inclination
Dust sublimation temperature (1500K) Td.s. = 1000K, Fmax 18%, at λ = 1.2 μm Td.s. = 2000K, Fmax 46%, at λ = 1.75 μm
