Setting the stage for solar system formation ALMA insights into - - PowerPoint PPT Presentation

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%

• f 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?
• Are complex organic molecules formed around protostars?
• But everywhere? And is there a link between the physical and chemical evolution of

embedded protostars? Early on… Yes…

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

Ice evaporates; molecules injected into gas-phase Ice formed on surfaces of dust grains

Based on figure by R. Visser / review by Herbst & van Dishoeck 2009

• 260 °C
• 160 °C
• 60 °C

Complex organic molecules formed in ices Simple molecules turn to ice on surfaces of dust grains.

Challenge: astrochemistry

• For typical low-mass YSOs the regions where molecules like H2O evaporates off 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.

NGC1333-IRAS2A in Perseus (Class 0 YSO - 20 L☉; 250 pc)

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?

“Disks” around Class I sources are not more massive than those around the younger Class 0’s ⇒ rapid “disk” formation and growth.

Class 0 Class I

• 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

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: Menv = 2.2 Msun; Mstar = 2.0 Msun; Mdisk = 0.024 Msun

C17O J = 3 ! 2

100 AU 5.0 2.5 0.0 2.5 5.0 7.5 10.0 12.5 15.0

• 2
• 1

1 2 ∆RA (00)

• 2
• 1

1 2 ∆Dec (00)

0.4 0.2 0.0 0.2 0.4 r [00]

1 2 1 3 1 5 1 10

1

10

1

5

1

3

1

2

v1 [(km s1)1]

Lindberg et al. (2014); + Johan’s talk tomorrow

Protostellar disks with (claimed) Keplerian rotation

Harsono, Jørgensen et al. (2014)

Source M? Mdisk RKa M?/Mtotb Mdisk/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 VLA1623 0.20 0.02 150 0.4–0.6 ... Class I 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 TMR1 0.7 0.01–0.015 < 50 0.72f 0.02–0.03 L1536g 0.4 0.007–0.024 80 0.95–0.97 0.02–0.06

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)?

• ALMA should add hundreds(?) of

sources to this diagram over the next years.

Predicted stellar and disk mass measured relative to the envelope mass in the models of Visser et

• al. (2009). Symbols indicate observations, arrow
• bserved range for Class 0’s. Updated version of

figure from Jørgensen+ (2009).

Molecules freeze-out

Is there a link between disk formation and chemistry?

Molecules evaporate Molecules freeze-out

• 260 °C
• 160 °C
• 60 °C

• Protostellar binary with total

luminosity of about 30 Lsun at a distance of 125 pc.

IRAS 16293-2422

IRAS 16293-2422 - an astrochemical testbed

SMA (Bisschop et al. 2008) IRAM PdBI (Bottinelli et al. 2004)

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.

• Protostellar binary with total

luminosity of about 30 Lsun at a distance of 125 pc.

• Complex organic molecules
• bserved on small scales

toward two binary components.

• Target for large campaign at the

SMA - thus obvious choice for ALMA Science Verification

• bservations.

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

• rganics may be more difficult 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

• rganics 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” 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

• nto 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
• bserved range for Class 0’s. Updated version of

figure from Jørgensen+ (2009).

Molecules freeze-out

How about chemistry?

Molecules evaporate Molecules freeze-out

Lacc ∼ GMstar ˙ M Rstar

• 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).

• The main constituent of those ices

is water, which is difficult to

• bserve from ground.

Linking (accretion) physics and chemistry

• Example from ALMA Cycle 0

program: imaging protostellar physics and chemistry.

• 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?

Jørgensen et al. (2013)

150 AU HCO+ CO & CH3OH

Where is H2O present in the gas-phase

H2O sublimation

Increase in luminosity by 10x Increase in luminosity by 100x

Linking (accretion) physics and chemistry

• Example from ALMA Cycle 0

program: imaging protostellar physics and chemistry.

• 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?

• Requires an increase in luminosity by

a factor 100 above current luminosity... and...

Jørgensen et al. (2013)

150 AU HCO+ CO & CH3OH

H2O of course should not have frozen-out (again) yet

H2O sublimation

Increase in luminosity by 10x Increase in luminosity by 100x

nH2 ~107 cm-3 (⇒ tdep ~ 100-1000 years)

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 (1000-2000 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.

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.