Low Mass star formation using high-J CO lines and WISH key program

ESO Colloquium, Santiago, Chile

Transcript

1. Low-mass star formation using high-J CO lines and WISH key program ALMA/ESO, Santiago, Jun 24, 2011 Umut A.Yıldız Ewine van Dishoeck Lars Kristensen Leiden Observatory Tuesday, June 28, 2011
2. Outline • Low-Mass Star-Formation • WISH KP • CO • Herschel-HIFI & APEX • Herschel & APEX Results Tuesday, June 28, 2011
3. • General Aim: • Understanding the formation of low-mass stars in the early phases by studying the physics and chemistry of star forming regions. • Specific Aim: • Most studies concentrated on the cold gas and dust around protostars (as probed by low-J lines). • Trace WARM gas by high-J CO observations with more efficient detectors, because warm gas is much more diagnostic of the energetic processes that shape these deeply embedded sources. Aims Tuesday, June 28, 2011
4. • How much warm gas is present in the inner regions of the protostellar envelopes and from which location does it originate? • What is the role of outflows and cavities on the protostellar envelope? • How is this warm gas distributed and heated? • How and where CO is formed and destroyed in the low-mass young stellar objects and how does its abundance evolve over the entire envelope? Open Questions? Tuesday, June 28, 2011
5. Molecular   Clouds Low  Mass  Star  Formation                  submm                                      IR                                        optical Deeply   Embedded  Phase T-­‐tauri  phase Planet  forming   disk Main-­‐sequence   star Tuesday, June 28, 2011
6. “WISH” Water In Star-forming Regions with Herschel PI: Ewine van Dishoeck http://www.strw.leidenuniv.nl/WISH/ • A 425 hr HIFI GT key-program with Herschel to study the physical and chemical structure of star forming regions focussing on H2O and its related species. • Both HIFI and PACS-spectroscopy are used • 80 team members in 35 institutes from 10 countries • Program covers ~80 sources ranging from pre-stellar cores, low- to high-mass protostars in different evolutionary stages as well as protoplanetary disks. Tuesday, June 28, 2011
7. A. Karska et al. 2010: APEX CHAMP+ high-J CO observations of L1527 and L483 7 Fig. 4. Top panel: CO 6-5 and CO 7-6 maps of L1527. Contour levels are 6σ, 12σ, 18σ etc. (σ(CO 6−5) = 1.5 K and σ(CO 7 − 6) = 4.1 K). Central position is marked with a X. Bottom panel: Spectral maps of L1527 in CO 6-5 (right) and CO 7-6 (left) transitions. Time Mass Prestellar Class 0 Class 1 Disks Intermediate- High-mass Low- ~80 sources ~80 sources WISH Sources (L. Kristensen) Tuesday, June 28, 2011
8. A. Karska et al. 2010: APEX CHAMP+ high-J CO observations of L1527 and L483 7 Fig. 4. Top panel: CO 6-5 and CO 7-6 maps of L1527. Contour levels are 6σ, 12σ, 18σ etc. (σ(CO 6−5) = 1.5 K and σ(CO 7 − 6) = 4.1 K). Central position is marked with a X. Bottom panel: Spectral maps of L1527 in CO 6-5 (right) and CO 7-6 (left) transitions. Time Mass Prestellar Class 0 Class 1 Disks Intermediate- High-mass Low- ~80 sources ~80 sources WISH Sources (L. Kristensen) Tuesday, June 28, 2011
9. • Water and high-J CO are natural filters of warm gas -unique probes of different physical regimes-. • H2O abundance shows large variations in star-formation regions: ~10-10 (cold) – 10-4 (warm) • CO abundance shows small variations • Both are complementary to each other. • Both are main coolants in the ISM (efficient). • Main reservoir of oxygen -affects chemistry of many other species-. pre-stellar cores - YSO’s - disks - comets - oceans Why Water and CO? Tuesday, June 28, 2011
10. • Many CO lines are targeted with different Eup to probe range of temperatures. • Lower-J CO (Jup<3) transitions have been observed from ground-based telescopes. Energy Levels Rotational Lines CO Energy [K] HIFI APEX Tuesday, June 28, 2011
11. •Herschel Space Observatory • 3.5 meter submm and far-IR telescope in space • Launched in May 2009 with 3.5 year lifetime ✦ HIFI ✦ Single-pixel heterodyne instrument ✦ Covering 480-1910 GHz (157-625 µm) ✦ Ultra-high spectral resolution (dv = 0.1 km/s), line profiles are resolved => kinematic information Observations ✦ PACS ✦ 5x5 spaxels covering 47” x 47” (7000AU x 7000AU at a distance of 150 pc) ✦ Covering 47-220 µm ✦ Not too bad spectral resolution (dv = 150 km/s) Tuesday, June 28, 2011
12. Higher spatial resolution and sensitivity than previous instruments Space Submm Missions My Sources in NGC1333 star-formation region d=235 pc Tuesday, June 28, 2011
13. Decomposing CO ✦ Gauss decomposition reveals 2 components ✦ Broad (DV=25-30km/s) and Medium (5-10km/s) profiles corresponding to the outflow components seen in 12CO and H2O line profiles ✦ BC shocked gas on larger scales ✦ MC small scale shocks ✦ CO 10-9 profile is much broader than CO 2-1. ✦ By using both the ground- and space-based observations we constrained outflow temperatures to more than 100 K. Yildiz et al., 2010, A&A H2O 202-111 CO 10-9 CO 6-5 CO 4-3 NEW!! HIFI Observations d=235 pc CO 2-1 Tuesday, June 28, 2011
14. ✦ Isotopologue Lines ✦ 13CO: MC & NC ✦ C18O: NC (+MC) ✦ C18O 5-4 observed with deep H2 18O 110-101 ✦ Narrow widths indicates an origin in the quiescent envelope. Yildiz et al., 2010 13CO line profiles C18O line profiles Decomposing CO d=235 pc 13CO 10-9 C18O 9-8 C18O 5-4 C18O 2-1 Tuesday, June 28, 2011
15. Envelope Probed by CO, H2O Cavity Walls CO, H2O, OH, C II, O I C & J Shocks CO, H2O, OH?, O I Physical Structure Protostar Image Courtesy: R. Visser Tuesday, June 28, 2011
16. Passively Heated Envelope • Narrow Component • In dense envelope Tgas = Tdust • T < 200 K Image Courtesy: R. Visser Tuesday, June 28, 2011
17. Photon Heated Cavity Walls • Medium Component • More high-J CO (Jup>6) • 200 K < Tgas <1000 K, • Emission is originating in the higher density regions Image Courtesy: R. Visser Tuesday, June 28, 2011
18. C-Shocks in the Cavity Walls • Broad Component • C-shocks in the cavity walls into the envelope (extend over >100AU). • Tgas = a few 1000 K Image Courtesy: R. Visser Tuesday, June 28, 2011
19. Heating with J-Shocks • The outflow is directed by a J-type shock (creates molecular bullets). • No molecules can stand in front of a J-shock, quickly dissociate. • V ~ 200 km s-1 • T = thousands of Kelvins!! Image Courtesy: R. Visser Tuesday, June 28, 2011
20. 0 10 20 30 40 J u 10-19 10-18 10-17 10-16 10-15 Flux [W m-2] Passive C-shocks UV Total CO 0 10 20 30 40 J u 10-19 10-18 10-17 10-16 10-15 Flux [W m-2] 10 100 500 1000 2000 3000 4000 E u / k B [K] Decomposing CO Seen in all YSOs! van Kempen, Kristensen et al. (2010) Visser et al. (2011) Herczeg et al. in prep. • Three mechanisms: • Passively heated envelope • UV-heated cavity walls • Shocks • Free parameters: • UV-luminosity (0.1-1.0 L⊙◉☉⨀) • vshock (20 km/s) PACS Tuesday, June 28, 2011
21. APEX/CHAMP+ CO • Leading campaign to observe CO 6-5, 7-6 + isotopologues in large sample of low-mass YSOs • Disentangling heating mechanisms on scales > 1000 AU • Complementary to HIFI CO observations and proposed ALMA band 9 observations van Kempen et al. (2009a,b), Yildiz et al. (2010), Yildiz et al. in prep., Karska et al. in prep. Umut A. Yıldız et al.: NGC 1333 IRAS 4A/4B envelope and outflow Spectral map of IRAS 4A and IRAS 4B is shown in 12CO 6–5 transition at 240 ×240 mapping area. Individual spectra are shown on TMB om -2 to 11 K and velocity scale from -25 to 35 km s−1. The outflow of IRAS 4A and 4B are overplotted over the entire spectral map. The re centered on IRAS 4A. The contour levels are 3σ, 6σ, 9σ,... L483 L1527 R Cr A BHR71 NGC2071 Serpens NGC1333 Beam ~ 7-9” Maps ~ 2’ x 2’ Tuesday, June 28, 2011
22. • NGC 1333 IRAS 4A/4B • 9’’ spatial resolution • In the CO map, the lines are spectrally resolved and provide crucial information regarding the dynamics of the region. • Our observations allow us to trace and reveal effects of shock and UV excitation. CHAMP+ CO 6-5 Yildiz et al., in prep. Tuesday, June 28, 2011
23. • NGC 1333 IRAS 4A/4B • 9’’ spatial resolution • In the CO map, the lines are spectrally resolved and provide crucial information regarding the dynamics of the region. • Our observations allow us to trace and reveal effects of shock and UV excitation. CHAMP+ CO 6-5 Yildiz et al., in prep. Tuesday, June 28, 2011
24. • High resolution data gives idea of inclination of IRAS 4B outflow CHAMP+ CO 6-5 Yildiz et al., in prep. Tuesday, June 28, 2011
25. T for outflowing gas Yildiz et al., 2010, A&A ✦ Temperatures inferred from CO 6-5/10-9 & CO 3-2/10-9 ratio indicates high temperature range for low-mass protostars 70-200 K ✦ Column Densities are different in BC and MC Broad C. Medium C. IRAS 2A 6x1019 2x1020 IRAS 4A 4x1020 6x1020 IRAS 4B 1x1020 2x1020 Tuesday, June 28, 2011
26. Envelope ✦ Higher-J lines sensitive to warm parts but 50% come from outer envelope with T < 50K so that traces lower temperatures. ✦ 90% of the emission for the low-J lines originates at T<25-30K (sensitive to outer parts of the envelope). IRAS 2A ✦ C18O 9-8 Eup: 238 K 200 K 10 K ✦ C18O 9-8 Eup: 238 K Tuesday, June 28, 2011
27. Abundance Studies ✦ RATRAN models run for IRAS 2A Tuesday, June 28, 2011
28. Abundance Studies ✦ Constant: cannot reproduce simultaneously Tuesday, June 28, 2011
29. Abundance Studies ✦ Constant: cannot reproduce simultaneously ✦ Anti-jump: low-J OK but not higher-J Tuesday, June 28, 2011
30. Abundance Studies ✦ Constant: cannot reproduce simultaneously ✦ Anti-jump: low-J OK but not higher-J ✦ Drop: Best fit to all data Tuesday, June 28, 2011
31. Take-home Messages • Herschel-HIFI and APEX open new era of high-J CO observations for tracing warm gas. • In the CO map, the lines are spectrally resolved and provide crucial information regarding the dynamics of the region. • Broad CO emission line profiles trace shock excited gas along the outflow axis. Surrounding the outflow and the protostar, the line profiles are narrow indicating UV excitation. • H2O and CO data reveal surprises: • Lines are broader than expected (shocks) and multiple components can be traced • Higher-J lines sensitive to warm parts but 50% come from outer envelope with T < 50K so that traces lower temperatures (high-J C18O observations). • Herschel provides key numbers in terms of gas-phase abundances, physical conditions, etc. Tuesday, June 28, 2011