Setting the stage for solar system formation

Transcription

1 Setting the stage for solar system formation ALMA insights into the early years of young stars Jes Jørgensen! Niels Bohr Institute & Centre for Star and Planet Formation University of Copenhagen

2 Standard cartoon of star formation Embedded protostellar stages represent accretion/dispersal of 90% of mass + formation of circumstellar disks during few 100,000 years. after Shu et al Provide link back to parental molecular cloud and the star formation event and set the stage for the future evolution of the young stars, e.g., concerning the properties of their protoplanetary disks.

3 Early years of young stars: interesting questions When do protoplanetary disks form? Early on Are complex organic molecules formed around protostars?yes But everywhere? And is there a link between the physical and chemical evolution of embedded protostars?

4 Challenge: disk formation Aiming to probe disks expected to be forming on ~10s to ~100 AU scales around deeply embedded protostars. Need high spatial and spectral resolution as well as sensitivity to moderately high excited lines of less abundant species.

5 Challenge: astrochemistry -60 C Simple molecules turn to ice on surfaces of Complex organic dust grains. molecules formed in ices Ice evaporates; molecules injected into gas-phase -160 C -260 C Ice formed on surfaces of dust grains Based on figure by R. Visser / review by Herbst & van Dishoeck 2009

6 Challenge: astrochemistry NGC1333-IRAS2A in Perseus (Class 0 YSO - 20 L ; 250 pc) For typical low-mass YSOs the regions where molecules like H2O evaporates off dust grains are smaller than ~0.5-1 (diameter; AU). Need high spatial and spectral resolution as well as sensitivity to moderately high excited lines of less abundant species.

7 Atacama Large Millimeter/submillimeter Array (ALMA) 54x12 m + 12x7 m ant.; interferometry from mm (Eventual) highest angular resolution ~ (16 km baselines) Currently in early science stage; awaiting the Cycle 2 proposal results

8 Disk formation around young stars? Survey of 20 embedded protostars with the SMA. Most sources show more compact dust emission that what can be attributed to the larger scale infalling cores. Time Time Class 0 Class I Disks around Class I sources are not more massive than those around the younger Class 0 s rapid disk formation and growth. Jørgensen et al. (2009)

9 Studies of dynamics of disk formation L one of the youngest protostars with a disk showing Keplerian rotation. Tobin et al. (2012)

10 Studies of dynamics of disk formation ALMA observations of R CrA IRS7B: Menv = 2.2 Msun; Mstar = 2.0 Msun; Mdisk = Msun Dec ( 00 ) C 17 O J = 3! RA ( 00 ) AU Fig. 4. Moment 0 map (black contours at 3 43 mjy beam 1 km s 1 intervals) and moment 1 map (colour scale, velocities in km s 1 ) of the C 17 O emission centred at IRS7B, integrated between 11 km s 1 and +21 km s 1. The colour bar indicates LSR velocities in km s 1. The dust continuum emission is shown in green contours (logarithmically Johan E. Lindberg et al.: ALMA observations of chemistry and kinematics in 1 2 Fig. 5. Position-velocity (PV) diagram of the cleaned image data of the C 17 1 O emission 3 centred at IRS7B. The velocities are relative to the centroid velocity, which has a v LSR = 6.3 km s 1. The solid lines show the best test fits to Keplerian rotation (v / r 1/2 component in blue and v 1 / r component in green). The dashed lines show the best test fits to infall under conservation of angular momentum (v / r 1 component 0 in blue and v / r component in green). v 1 [(km s 1 ) 1 ] r [ 00 ] Fig. 7. Position-inverted-velocity (PIV) diagram of the uvmodelfit peaks in the C 17 O emission centred at IRS7B. The inverted velocity axis is used to make the origin of the diagram correspond to the central object. Blue dots are used for the v / r 1/2 and v / r 1 fits, green dots for the v / r fit. The velocities are given relative to the centroid velocity, which has a v LSR = 6.3 km s 1. The solid and dashes lines as in Fig. 5. Lindberg et al. (2014); + Johan s talk tomorrow Fig. 9. Posit ted versus i rotation an calculation

11 Protostellar disks with (claimed) Keplerian rotation Source M? M disk a R K b M? /M tot M disk /M? [M ] [M ] [AU] Class 0 NGC1333 IRAS4A Class L VLA Class I R CrA IRS7B Class I L1551 NE L1489-IRS IRS IRS Elias < TMC1A TMC TMR < f L1536 g Harsono, Jørgensen et al. (2014)

12 Follow the mass Comparison of inferred masses to evolutionary models (Visser et al. 2009). Generally much less massive disks relative to central stars than predicted from models in later stages and vice versa earlier? An indication of rapid processing of material from envelope through disk (Jørgensen 2009)? Predicted stellar and disk mass measured relative to the envelope mass in the models of Visser et al. (2009). Symbols indicate observations, arrow observed range for Class 0 s. Updated version of figure from Jørgensen+ (2009). ALMA should add hundreds(?) of sources to this diagram over the next years.

13 Is there a link between disk formation and chemistry? -60 C Molecules freeze-out -160 C Molecules freeze-out Molecules evaporate -260 C

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15 IRAS Protostellar binary with total luminosity of about 30 Lsun at a distance of 125 pc.

16 IRAS an astrochemical testbed Protostellar binary with total luminosity of about 30 Lsun at a distance of 125 pc. Complex organic molecules observed on small scales toward two binary components. Target for large campaign at the SMA - thus obvious choice for ALMA Science Verification observations. E.g., Bottinelli et al. 2004; Kuan et al. 2004; Schöier et al. 2004; Chandler et al. 2005; Takakuwa et al. 2007; Bisschop et al. 2008; Jørgensen et al IRAM PdBI (Bottinelli et al. 2004) SMA (Bisschop et al. 2008)

17 SV observations of chemistry in IRAS All features seen in the ALMA data represent molecular lines. Rich spectrum with many complex organics; ~30% of lines remain unassigned. Molecular gas at K in the two components of binary. Key discovery: 6 lines of glycolaldehyde in band 6 (here) + another 7 in band 9. Jørgensen et al. (2012)

18 Glycolaldehyde s claim to fame... The first sugar (or a simple sugar-like molecule ); under Earth-like condition the first step in the formose reaction leading to ribose - the backbone of RNA. Thus, a real prebiotic molecule... Previously seen toward the Galactic center (Hollis et al. 2000) and tentatively the high-mass hot core G (Beltran et al. 2009). ALMA detection, the first for a solar-type protostar - with imaging constraining the origin to Solar System scales. Simultaneous detection of other complex organics and relative abundances constrain their origin (photochemistry of methanolcontaining ices) - plus, link to cometary compositions.

19 Do all sources show complex organics? Formation of disks will be related to a flattened inner envelope and consequently reduction of column density on small scales. Complex organics may be more difficult to detect in protostars with more extensive disks (e.g., Lindberg+ 2014).

20 Do all sources show complex organics? Formation of disks will be related to a flattened inner envelope and consequently reduction of column density on small scales. Complex organics may be more difficult to detect in protostars with more extensive disks (e.g., Lindberg+ 2014). But still more and more actually do show (signs off) complex organics with increasing sensitivity. ALMA Cycle 0 observations of the Warm Carbon-Chain Chemistry Source IRAS (Jørgensen et al. 2013)

21 Young disks The fairly massive disks in the early stages are unlikely to be stable - and accretion from them onto the central star consequently highly non-steady. Predicted stellar and disk mass measured relative to the envelope mass in the models of Visser et al. (2009). Symbols indicate observations, arrow observed range for Class 0 s. Updated version of figure from Jørgensen+ (2009).

22 How about chemistry? L acc G M starṁ R star Molecules freeze-out Variations in accretion rates will affect the protostellar luminosity and consequently the formation and sublimation of ices (as well as the surface reactions taking place). Molecules freeze-out The main constituent of those ices is water, which is difficult to observe from ground. Molecules evaporate

23 Linking (accretion) physics and chemistry Example from ALMA Cycle 0 program: imaging protostellar physics and chemistry. CO & CH3OH HCO + Absence of HCO + emission toward location of protostar: why not correlated with CO? Likely destroyed by reactions with H2O: but where is it present in the gas-phase? 150 AU Jørgensen et al. (2013)

24 Where is H2O present in the gas-phase H2O sublimation Increase in luminosity by 100x Increase in luminosity by 10x

25 Linking (accretion) physics and chemistry Example from ALMA Cycle 0 program: imaging protostellar physics and chemistry. CO & CH3OH HCO + Absence of HCO + emission toward location of protostar: why not correlated with CO? Likely destroyed by reactions with H2O: but where is it present in the gas-phase? 150 AU Requires an increase in luminosity by a factor 100 above current luminosity... and... Jørgensen et al. (2013)

26 H2O of course should not have frozen-out (again) yet H2O sublimation Increase in luminosity by 100x Increase in luminosity by 10x nh2 ~10 7 cm -3 ( tdep ~ years)

27 Linking physics and chemistry of protostars? IRAS15398 is among a small group of protostellar sources showing little evidence for compact dust continuum emission (i.e., disks ). - One scenario could be that one builds up an disk early in the evolution, which becomes unstable, collapses and dumps all of its material onto the central star thereby increasing the luminosity in a short period of time. The same sources interestingly also show the presence of large carbon-chain molecules (C4H2, C4H2, HC5N, CH3CCH ) tracing lukewarm temperatures (~20 30 K) on large ( AU) scales. - Natural consequence of accretion burst (heating) is the release of these molecules on larger scales. Assuming a reset time for the chemistry of 1000 years ( duration of the effects in the post-burst ) and typical lifetimes for deeply embedded phases of 100,000 years simple (small-number) statistics suggest that they undergo of order 10 such bursts during the embedded protostellar phases.

28 Summary An increasing number of deeply embedded protostars show evidence for the presence of Keplerian disks: those disks are formed early in the protostellar evolution. Complex organics: those molecules are formed early in the protostellar evolution. It is an interesting task both from an observational (technical) as well as a theoretical point of view to relate the two. We should be (and are) taking steps toward a much more dynamic picture of the physical - and chemical - evolution of young stars.