Physics and chemistry of irradiated protostars Johan E. Lindberg 1,2 - PowerPoint PPT Presentation

Physics and chemistry of irradiated protostars Johan E. Lindberg 1,2 Jes K. Jørgensen 2,1 , J. D. Green 3 , G. J. Herczeg 4,5 , O. Dionatos 6 , N. J. Evans II 3 , A. Karska 5 , S. F. Wampfler 1,2 , C. Brinch 2,1 , T. Haugbølle 1 , E. A. Bergin 7 , D. Harsono 8,9 , M. V. Persson 8 , R. Visser 7 , S. Yamamoto 10 , Y. Watanabe 10 , S. E. Bisschop 1,2 , N. Sakai 10 1 Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen 2 Niels Bohr Institute, University of Copenhagen, 3 University of Texas at Austin, 4 Kavli Institute for Astronomy and Astrophysics, Beijing, 5 Max Planck Institute for Extraterrestrial Physics, 6 University of Vienna, 7 University of Michigan, 8 Leiden Observatory, 9 SRON Netherlands, 10 Department of Physics, University of Tokyo Lund, February 11th, 2014

Evolution of low-mass Young Stellar Objects Theory: Observations: Adapted from Lada (1987), André et al. (2000), and Smith (2004). Persson (2013), after Shu et al. (1987) T bol increases with time.

Stars form in clusters! ● Most stars form in clusters. ● Environmental effects on star formation must be considered. ● Irradiation → implications on physics (temperature). ● Also profound implications on Porras et al. (2003): A Catalog of the chemistry? Young Stellar Groups and Clusters within 1 Kiloparsec of the Sun

Stars with relatively high masses ● The Initial Mass Function (IMF; Salpeter 1955) describes the distribution of initial stellar masses. ● ~ 6% of all stars: M ★ > 2 M ☉ ( L ★ > 16 L ☉ ) ● ~ 1% of all stars: M ★ > 6 M ☉ ( L ★ > 800 L ☉ ) ● A large proportion of all stars will be formed close to a fairly massive star. Implications?

Chemistry in protostellar envelopes Jørgensen et al. 2002, A&A, 389, 908 Complex organics form in ice mantles of dust grains, but require CO, H 2 O (and other molecules) in these mantles. ? The presence of CO in the ice Hot corino mantles requires low T at large scales in the envelope. Modication of figure from Herbst & van Dishoeck 2009, ARA&A, 47, 1, 427

What is the physical impact from external irradiation on the envelope? What are the effects on the chemistry?

Our lab: Corona Australis ● One of the most nearby star-forming regions ( d ≈ 130 pc) ● Situated in the southern sky ( δ ≈ -37°) ● ~100 young stellar objects within the region. ● Most of the youngest sources (Class 0/I) situated nearby the luminous Herbig Be star R CrA (Peterson et al 2011).

SMA and APEX observations of H 2 CO ● SMA observations of molecular gas around R CrA showed very extended emission. ● APEX was used for zero-spacing observations. ● The two datasets were combined: High-resolved spectral images of all emission on 400 – 8 000 AU scales. 2000 AU + = H 2 CO 3 03 -2 02 at 218.2 GHz Lindberg & Jørgensen, 2012, A&A, 548, A24

Strong H 2 CO emission not associated with YSOs Northern ridge H 2 CO 3 03 -2 02 H 2 CO 3 22 -2 21 Southern ridge Greyscale: JCMT/SCUBA 850 µm dust continuum Lindberg & Jørgensen, 2012, A&A, 548, A24

Temperature map assuming Local Thermodynamic Equilibrium [K] The rotational temperatures were estimated using 3 H 2 CO lines at 218-219 GHz Lindberg & Jørgensen, 2012, A&A, 548, A24

Herschel /PACS 120 µm dust continuum Point source emission removed using POMAC deconvolution algorithm All emission Colour contours: PACS 120 µm continuum Greyscale: H 2 CO 3 03 → 2 02 (SMA+APEX) Lindberg et al., accepted (A&A)

Transphere and RATRAN models of IRS7B envelope Dust radiative transfer code for spherically symmetric envelopes; Radiative transfer and molecular excitation Transphere model fitted to Herschel and SCUBA continuum data points. Images (ray-tracing) made using RATRAN. χ ISRF = 750, L c = 4 L ☉ : L c = 4 L ☉ , χ ISRF = 750 0 7 5 = CO evaporation T = 20 K χ ISRF , L c = 4 L ☉ , χ ISRF = 1 0 -4 L ☉ 1 = L c n ~ R -1.5 n = 1.3×10 6 cm -3 at 1000 AU R in = 200 AU Transphere: Dullemond et al. (2002), A&A, 389, 464 R out = 10 000 AU RATRAN: Hogerheijde & van der Tak (2000), A&A, 362, 697

APEX line surveys of IRS7B and other sources in CrA ● Motivation: Is the chemistry H 2 CO affected by the irradiation? ● APEX was used to survey IRS7B at 218-245 GHz CH 3 OH ● CH 3 CCH was the most complex species detected – no typical complex organic molecules. ● 17 additional Class 0/I sources in CrA were observed targeting H 2 CO, CH 3 OH, and c -C 3 H 2 c -C 3 H 2 Lindberg et al., in prep.

Results of 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 IRS7B: Low-mass young stellar object with strong CN emission and no complex organics except CH 3 OH Bisschop et al. (2013), A&A, 552, A122 Caux et al. (2011), A&A, 532, A23 Lindberg et al. (in prep.)

Rotational temperatures as function of distance to R CrA Transphere model of R CrA heating IRS7B H 2 CO VV CrA c -C 3 H 2 Lindberg et al., in prep.

Bright CH 3 OH – from where? ● The APEX and ASTE line surveys showed bright CH 3 OH lines (Schöier et al., 2006 – hot corino?; Watanabe et al, 2012)? ● The line survey provided strong upper limits on complex organic molecules with significantly lower abundances vs. CH 3 OH than seen in hot corinos. ● ALMA map shows extended CH 3 OH. ● Study the 30 AU scales! CH 3 OH 7 0 →6 0 Continuum

C 17 O line emission traces kinematics Position-inverted-velocity diagram [km s –1 ] Lower abs. velocities v ~ r -1/2 v ~ r -1 M env ≈ 2.2 M ☉ Solid lines: Keplerian rotation M star ≈ 2.0 M ☉ Dashed lines: Infall with conservation of M disc ≈ 0.024 M ☉ angular momentum Lindberg et al., submitted to A&A

RATRAN CH 3 OH models Spectra from IRS7B 1.2''*1.0'' box: Radiative transfer models Inner density: Power law show that CH 3 OH either has a X inner (CH 3 OH) = 1e-10 X outer (CH 3 OH) = 1e-10 low abundance or that the density profile is flat in the central envelope. Inner density: Power law X inner (CH 3 OH) = 1e-8 X outer (CH 3 OH) = 1e-10 A flattened envelope profile at R < 100 AU could be related to the presence of a circumstellar disc at those scales. Inner density: Flat X inner (CH 3 OH) = 1e-8 X outer (CH 3 OH) = 1e-10 Currently difficult to separate Model 1 from Models 3-4. Inner density: Flat X inner (CH 3 OH) = 1e-10 X outer (CH 3 OH) = 1e-12 Lindberg et al., submitted to A&A Data Model

Conclusions ● Intermediate-mass stars have a significant influence on the temperature in star-forming regions. The temperature is affected by R CrA on scales as large as 30 000 AU (0.15 pc). ● This seems to affect the large-scale chemistry in the IRS7 cloud. ● The absence of complex organics could either be caused by this, or by the flattening of the inner envelope by a newly-formed protoplanetary disc around IRS7B.

Outlook ● The effect should be studied in other, more massive, star-forming regions. How common is this effect? ● ALMA will provide higher-sensitivity images of discs and complex organic molecules. ● Stars are often formed in clusters, which seem to strongly affect the physics and chemistry of the star-forming envelope. What can this tell us about the formation of our own Solar System?