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 http://youngstars.nbi.dk http://starplan.dk
Standard cartoon of star formation • Embedded protostellar stages represent accretion/dispersal of 90% of mass + formation of circumstellar disks during few 100,000 years. • 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. after Shu et al. 1987
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?
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.
Challenge: astrochemistry -60 °C Simple molecules turn to ice on surfaces of Complex organic dust grains. molecules formed in ices -160 °C Ice evaporates; molecules injected into gas-phase -260 °C Ice formed on surfaces of dust grains Based on figure by R. Visser / review by Herbst & van Dishoeck 2009
Challenge: astrochemistry NGC1333-IRAS2A in Perseus (Class 0 YSO - 20 L ☉ ; 250 pc) • For typical low-mass YSOs the regions where molecules like H 2 O evaporates o ff dust grains are smaller than ~0.5-1” (diameter; 100-200 AU). • Need high spatial and spectral resolution as well as sensitivity to moderately high excited lines of “less abundant” species.
Atacama Large Millimeter/submillimeter Array (ALMA) 54x12 m + 12x7 m ant.; interferometry from 0.3-3 mm (Eventual) highest angular resolution ~ 0.01-0.02” (16 km baselines) Currently in early science stage; awaiting the Cycle 2 proposal results
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)
Studies of dynamics of disk formation • L1527 - one of the youngest protostars with a disk showing Keplerian rotation. Tobin et al. (2012)
Studies of dynamics of disk formation • ALMA observations of R CrA IRS7B: M env = 2.2 M sun ; M star = 2.0 M sun ; M disk = 0.024 M sun C 17 O J = 3 ! 2 15 . 0 1 2 2 12 . 5 1 3 10 . 0 1 1 5 v � 1 [(km s � 1 ) � 1 ] 7 . 5 1 ∆ Dec ( 00 ) 10 0 0 5 . 0 � 1 10 2 . 5 � 1 5 -1 0 . 0 � 1 3 � 2 . 5 -2 100 AU � 1 2 � 5 . 0 0 . 4 0 . 2 0 . 0 � 0 . 2 � 0 . 4 2 1 0 -1 -2 r [ 00 ] ∆ RA ( 00 ) Lindberg et al. (2014); + Johan’s talk tomorrow
Protostellar disks with (claimed) Keplerian rotation R K a M ? / M tot b Source M ? M disk M disk / M ? [ M � ] [ M � ] [AU] Class 0 NGC1333 IRAS4A2 0.08 0.25 310 0.02 3.1 L1527 0.19 0.029–0.075 90 0.2 0.13–0.34 Class I VLA1623 0.20 0.02 150 0.4–0.6 ... R CrA IRS7B 1.7 0.024 50 0.43 0.01 L1551 NE 0.8 0.026 300 0.65 0.032 L1489-IRS 1.3 0.004 200 0.83–0.93 0.0030 IRS43 1.9 0.004 190 0.89 0.002 IRS63 0.8 0.099 165 0.83 0.12 Elias29 2.5 0.011 200 0.98 < 0 . 003 TMC1A 0.53 0.045–0.075 100 0.75–0.78 0.08–0.14 TMC1 0.54 0.005–0.024 100 0.76–0.79 0.01–0.06 0.72 f TMR1 0.7 0.01–0.015 < 50 0.02–0.03 L1536 g 0.4 0.007–0.024 80 0.95–0.97 0.02–0.06 Harsono, Jørgensen et al. (2014)
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 • ALMA should add hundreds(?) of to the envelope mass in the models of Visser et sources to this diagram over the al. (2009). Symbols indicate observations, arrow next years. observed range for Class 0’s. Updated version of figure from Jørgensen+ (2009).
Is there a link between disk formation and chemistry? -60 °C Molecules freeze-out -160 °C Molecules freeze-out -260 °C Molecules evaporate
IRAS 16293-2422 • Protostellar binary with total luminosity of about 30 L sun at a distance of 125 pc.
IRAS 16293-2422 - an astrochemical testbed • Protostellar binary with total luminosity of about 30 L sun 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. 2011. IRAM PdBI (Bottinelli et al. 2004) SMA (Bisschop et al. 2008)
SV observations of chemistry in IRAS16293-2422 • All features seen in the ALMA data represent molecular lines. • Rich spectrum with many complex organics; ~30% of lines remain unassigned. • Molecular gas at 200-300 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)
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 G34.41+0.31 (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 methanol- containing ices) - plus, link to cometary compositions.
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 di ffi cult to detect in protostars with more extensive disks (e.g., Lindberg+ 2014 ).
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 di ffi cult to detect in protostars with more extensive disks (e.g., Lindberg+ 2014 ). • But still… more and more actually do show (signs o ff ) complex organics with increasing sensitivity. ALMA Cycle 0 observations of the “Warm Carbon-Chain Chemistry Source” IRAS15398-3359 (Jørgensen et al. 2013)
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).
How about chemistry? L acc ∼ GM star ˙ M R star • Variations in accretion rates will a ff ect 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 di ffi cult to observe from ground. Molecules freeze-out Molecules evaporate
Linking (accretion) physics and chemistry • Example from ALMA Cycle 0 CO & CH 3 OH program: imaging protostellar HCO + physics and chemistry. • Absence of HCO + emission toward location of protostar: why not correlated with CO? • Likely destroyed by reactions with H 2 O: but where is it present in the 150 AU gas-phase? Jørgensen et al. (2013)
Where is H 2 O present in the gas-phase Increase in luminosity by 100x Increase in luminosity by 10x H 2 O sublimation
Linking (accretion) physics and chemistry • Example from ALMA Cycle 0 CO & CH 3 OH program: imaging protostellar HCO + physics and chemistry. • Absence of HCO + emission toward location of protostar: why not correlated with CO? • Likely destroyed by reactions with H 2 O: but where is it present in the 150 AU gas-phase? • Requires an increase in luminosity by a factor 100 above current Jørgensen et al. (2013) luminosity... and...
H 2 O of course should not have frozen-out (again) yet H 2 O sublimation Increase in luminosity by 100x Increase in luminosity by 10x n H2 ~10 7 cm -3 ( ⇒ t dep ~ 100-1000 years)
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