Unbiased line surveys of protostellar envelopes A study of the physics and chemistry of the youngest protostars in Corona Australis Johan E. Lindberg Astrochemistry Laboratory NASA Goddard Space Flight Center Green Bank, September 22, 2015 in collaboration with: Steven B. Charnley (NASA Goddard), Jes K. Jørgensen (Uni. of Copenhagen), Yoshimasa Watanabe (Uni. of Tokyo), Suzanne E. Bisschop (Uni. of Copenhagen), Nami Sakai (Uni. of Tokyo), Satoshi Yamamoto (Uni. of Tokyo)
Outline Low-mass star formation and astrochemistry Line surveys with single-dish telescopes R CrA IRS7B survey with APEX and ASTE Intermezzo: ALMA observations H2CO and c-c3h2 surveys in CrA and Oph with APEX
Evolution of Young Stellar Objects Theory: SED observations: Adapted from Lada (1987), André et al. (2000), and Smith (2004). Persson (2013), after Shu et al. (1987)
Chemistry in protostellar envelopes Jørgensen et al. 2002, A&A, 389, 908? Hot corino ~10 000 AU The grains are typically 0.1 µm and are not drawn to scale. Complex organics are thought to form in ice mantles of dust grains, but require CO, H2O (and other molecules) in these mantles. The presence of CO in the ice mantles requires low T at large scales in the envelope. Adapted from Herbst & van Dishoeck 2009, ARA&A, 47, 1, 427
Where do the complex organics come from? Grain surface chemistry Gas-phase ion-molecule chemistry Öberg et al. (2009), A&A, 504, 891 Charnley (1997) IAU Colloq. 161, 89 Complex organics also detected in prestellar cores! (Bacmann et al. 2012, A&A, 541, L12)
Complex molecules in low-mass Class 0 protostars: Hot corino vs. Warm Carbon Chain Chemistry sources Hot corino sources Complex organic molecules (CH3OCH3, CH3CHO,...) Long pre-stellar phase: WCCC sources C CO before freezeout Long carbon chain species (C4H, HC5N, C6H-,...) Short pre-stellar phase: C freezes out as atoms Tex ~ 100 K (COMs: high Tevap) Tex ~ 30 K (CH4: low Tevap) Four known sources: Two known sources: IRAS 16293-2422 (Ophiuchus) NGC 1333 IRAS2A (Perseus) NGC 1333 IRAS4A (Perseus) NGC 1333 IRAS4B (Perseus) L1527 IRAS 04368+2557 (Taurus) IRAS 15398-3357 (Lupus) Sakai et al. (2009), ApJ, 697,769
Observations of protostellar envelopes Several low-mass star-forming regions 100-150 pc away Typically: 1'' ~ 100 AU T(R) in low-mass protostar APEX GBT ARGUS ALMA Jørgensen et al. 2002, A&A, 389, 908
TIMASSS: The IRAS 16293-2422 Millimeter and Submillimeter Spectral Survey Class 0 protostar in Ophiuchus IRAM 30 m and JCMT 15 m (10''-30'') Total range of 200 GHz rms: 5-17 mk in 1 km/s channels > 4000 lines detected 70 identified molecular species, many of them complex organic molecules (COMs, 6 atoms) Ideal to characterise the cool (10-100 K) chemistry of protostellar envelopes Hot corino source: chemistry similar to hot cores Caux et al. (2011), A&A, 532, A23 Jaber et al. (2014), ApJ, 791, 29
BVR optical image Credit: ESO/MPG 2.2 m telescope at La Silla, Chile 60.000 AU 1 ly R CrA cloud Spitzer: 3.6 µm, 4.5 µm, 8.0 µm Peterson et al. (2011) Distance: 130 pc ~100 protostars in CrA, ~10 near R CrA Declination: -37
The R CrA cloud in continuum Greyscale: Spitzer 4.5 µm (Peterson et al. 2011) Blue contours: Herschel 70 µm (Lindberg et al. 2013) Red contours: SMA 1.3 mm (Peterson et al. 2011; Lindberg & Jørgensen 2012) Distance: 130 pc (Neuhäuser & Forbrich 2008) Lindberg & Jørgensen, 2012, A&A, 548, A24
Rotational diagrams CH3CCH spectrum Inclination gives Trot Proportional to line strength Assumptions for Tkin = Trot : Local Thermodynamic Equilibrium (LTE) Optically thin emission Similar source size for all lines See e.g. Goldsmith & Langer (1999), ApJ, 517, 109 Upper energy level of transition Lindberg et al. (2015), arxiv:1509.02514
H2CO as a temperature and density probe H2CO lines with same Ju give Tkin Ratios between different Ju give n(h2) Ju rot. diag. RA DE X Ju = 3 =5 N = 1014 cm-2 ) 2 02 03 ) 4 04 (5 05 )/I 2 02 3 I(3 0 I(3 Lindberg et al. (2015), arxiv:1509.02514 see also Mangum & Wootten (1993), ApJS, 89, 123 RADEX: van der Tak et al. (2007), A&A, 468, 627
SMA+APEX H2CO rotational temperature map [K] The rotational temperatures were estimated using the three H2CO lines at 218 GHz Lindberg & Jørgensen, 2012, A&A, 548, A24
APEX and ASTE line surveys of IRS7B ASTE survey: 332-364 GHz (Watanabe et al. 2012) APEX survey: 218-245 GHz (Lindberg et al. 2015) c APEX (Atacama Pathfinder EXperiment) ASTE (Atacama Submillimeter Telescope Experiment)
1.3 mm survey of R CrA IRS7B with APEX 102 lines and 20 molecular species detected Beam size: 26'' 29'' c rms levels ~ 10 mk per km/s reached in 1.5 hours per setting. APEX SHeFI today: 4 GHz coverage, 76 khz (~0.1 km/s) resolution Lindberg et al. (2015), arxiv:1509.02514
0.8 mm survey of R CrA IRS7B with ASTE 89 lines and 16 molecular species detected; in total 22 species in ASTE+APEX Beam size: 21'' 23'' Watanabe et al. (2012), ApJ, 745, 126
Results of IRS7B line survey Hot core: High-mass star- forming region with lots of complex organics Hot corino: Low-mass young stellar object with lots of complex organics (TIMASSS survey) IRS7B: Low-mass young stellar object with strong CN emission and very little complex organics Bisschop et al. (2013), A&A, 552, A122 Caux et al. (2011), A&A, 532, A23 Lindberg et al. (2015) arxiv:1509.02514
Low COM abundances in IRS7B IRS7B: X(CH3OH) ~ a few 10-9, ~1% of value in IRAS 16293-2422 Some gas-phase reactions suppressed by low X(CH3OH): CH3OH2+ + HCOOH CH3OCHO + H2O + H+ CH3OH2+ + CH3OH CH3OCH3 + H2O + H+ (Charnley 1997, Peeters et al. 2006, Taquet et al. in prep.) References: Lindberg et al. (2015), van Dishoeck et al (1995), Schöier et al. (2002), Cazaux et al. (2003), Sakai & Yamamoto (2013), Agúndez et al. (2008), Öberg et al. (2010), Bachiller & Pérez Gutiérrez (1997), Arce et al. (2008)
Most CH3OH emission resolved out by ALMA ASTE 22'' beam at IRS7B Watanabe et al. (2012) ApJ, 745, 126 33 Jy 8 Jy ALMA CH3OH (colour scale) ALMA continuum (red contours) 16 Jy IRS7B 35 Jy 10 mjy/beam ALMA 1.2''x1'' box at IRS7B 5.5 hours of ALMA Cycle 0 (18 antennas) Lindberg et al. (2014) A&A, 566, A74 Strongest CH3OH line integrated over ALMA primary beam < 1 Jy
CH3OH: ALMA spectrum and RATRAN models Spectra from IRS7B 1.2''x1.0'' box: Inner density: Power law Xinner(CH3OH) = 1e-10 Xouter(CH3OH) = 1e-10 Inner density: Power law Xinner(CH3OH) = 1e-8 Xouter(CH3OH) = 1e-10 Inner density: Flat Xinner(CH3OH) = 1e-8 Xouter(CH3OH) = 1e-10 No hot corino Hot corino Typical hot corino does not fit with data Hot corino + disc? r100 K ~ Mstar1/2 rdisc ~ Mstar Disc eventually outgrows hot corino. Inner density: Flat Xinner(CH3OH) = 1e-10 Xouter(CH3OH) = 1e-12 Data Model CH3OH deficiency from irradiation history? High T at early time => No CO at grains => No complex organic grain chemistry Lindberg et al. (2014), A&A, 566, A74
Survey of all 17 embedded protostars in CrA H2CO (formaldehyde) c-c3h2 (cyclopropenylidene)
Rotational temperatures as function of distance to R CrA Spherical (1-D) Transphere model of R CrA heating SMA map around IRS7B (Lindberg & Jørgensen 2012) IRS7B H2CO VV CrA c-c3h2 Transphere: Dullemond et al. (2002), A&A, 389, 464 Lindberg et al. (2015), arxiv:1509.02514
Conclusions Unbiased line surveys are ideal to characterise chemistry of protostellar sources ARGUS receiver can be used to acquire such line surveys at high spatial resolution. Line surveys can also be used to characterise physical parameters such as temperature. Origin of complex organic molecules needs further investigation R CrA (M = 3M ) governs the chemical and physical properties in a ~ 10 000 AU radius. c-c3h2 tends to be more shielded than H2CO