Observational studies of intermediate-mass protostars with PdBI, 30m and Herschel

Transcription

1 Observational studies of intermediate-mass protostars with PdBI, 30m and Herschel Asunción Fuente, Roberto Neri, Aina Palau, José Cernicharo and many excellent collaborators

2 Low-mass star formation Pre-stellar dense core Tbol = K M*=0 Accreting Protostar Thick envelopes and disks Infall and outflow simultaneously dm/dt = 0.975cs3/G dm/dt = Msun yr-1 (T=10 K) t = yr to form a 1 Msun star Pre-main sequence star Contraction to the main sequence tkh= GM*2/(R*L*) tkh = 107 yr for a 1 Msun star Modified from André et al. (2000)

3 Unresolved Problems Clustering 50 % of all low-mass stars are binaries Stars with M* > 5 Msun form in clusters Most of the low-mass stars have very likely been formed in clusters Accretion models cannot explain the formation of stars with M >10 Msun Radiation pressure would stop the accretion before reaching the final mass (tkh<tacc). New accretion models (McKee & Tan 2002) The turbulent velocity provides for the high accretion rate required for the formation of a massive star. Coalescence models (Stahler 2000) The massive star is formed by collisions of stars (protostars) of low and intermediate mass stars.

4 Intermediate mass (IM) stars are stars with masses between 2 and 10 Msun. Why study IM stars? i) The understanding of their formation process of IM stars is intereresting by itself. In fact, the IM stars dominate the UV field in our Galaxy (Wofire et al. 2002). ii) They constitute a link between low-mass and highmass star formation. They share properties (clustering) with high mass stars but are located closer to the Sun (D<2 Kpc).

5 1.- Clustering November, 29th IPAG, Grenoble (France)

6 Clustering in the NIR (Testi et al. 1999, A&A 342, 515) 44 HAeBe Msun <1000 AU

7 Clustering in the NIR (Testi et al. 1999, A&A 342, 515) The clustering degree seems to continously increase with the spectral type of the star, increasing with the stellar mass (or luminosity). The transition from isolated to clustered star formation occurs in the 1 10 M sun stellar mass range. The typical size of the cluster is ~0.2 pc

8 How clusters are formed? 1- The distribution of the stellar masses in the cluster is the consequence of the IMF (Testi et al. 2000; Parker & Goodwin 2007). 2.- The most massive stars need a rich cluster to be formed (Krumholz and Bonnel 2007). 3.- A massive star increase the number of members in its surroundings by inducing the formation of new stars (e.g. Hester & Desch 2005; Deharveng et al. 2012). The study of the earliest phases of cluster formation is necessary to determine their formation.

9 Clustering at mm wavelengths - Even for the closest targets (D< 3 Kpc), very few telescopes are able to reach mass sensitivities and spatial resolutions similar to NIR studies (PdBI, SMA, ALMA) - The imaging is too time consuming to observe large samples of protosclulster that allows to make statistics. - Most works centered on only one single source (e.g Beuther et al. 2004; Zapata et al. 2005; Fuente et al. 2005, 2009; Teixeira et al ) - Very few surveys: Neri et al (3 sources); Motte et al (5 sources)

10 Our project Mass sensitivity = 0.1 Msun Spatial resolution < 1000 AU Cont 1mm + 12CO (2-1) Selection criteria: (i) Previous interferometric observations in a compact configuration (7 ) showed the existence of a massive core (>20 Msun at 0.1 pc) associated with a protostar. (ii) D < 3 kpc (iii) Luminosities spanning from 300 to 10 5 Lsun (iv) Sources located in different clouds

11 Our project Red contour= 6xσ 0.52 x 0.36

12 IRAS (I22198) Class 0 L=300 Lsun D=0.76 kpc Tbol=59 K Quadrupolar outflow Hot core (Sánchez-Monge et al. 2010, ApJ 721, L107)

13 IRAS (I22198) Palau et al. 2011, ApJ 743, L32

14 AFGL 5142 (A5142) Class 0 L=2200 Lsun D=1.80 kpc Tbol=55 K Multiple outflows Hot core (Palau et al. 2011,ApJ 743, L32)

15 AFGL 5142 (A5142)

16 AFGL 5142 (A5142) Hot cores/corinos at scales of < 500 AU Palau et al. 2011, ApJ 743, L32

17 IRAS (I22172N) Class 0 L=830 Lsun D=2.40 kpc Tbol=195 K Multiple outflows No hot core

18 IRAS (I22134) Class 0 L=11800 Lsun D=2.60 kpc Tbol=93 K Multiple outflows No hot core

19 Our survey 830 Lsun Lsun 300 Lsun 2200 Lsun

20 Completing our survey 1.- We search in the literature for interferometric observations of massive dense core with spatial resolutions of < 1000 AU and mass sensitivities < 0.5 Msun. 2.- We found 18 regions spanning a wide range of luminosities and evolutionary stages which were re-analized to determine the number of mm sources, source sizes and source masses following uniform criteria. 3.- For their interest, we added the 4 Cygnus protostars analyzed by Motte et al. (2010) although they have a slightly different spatial scale.

21 Fragmentation of massive dense core down to < 1000 AU (Palau et al. 2012, ArXiv )

22 Fragmentation of massive dense core down to < 1000 AU (Palau et al. 2012, ArXiv )

23 Fragmentation of massive dense core down to < 1000 AU (Palau et al. 2012, ArXiv )

24 Source parameters 1.- Lbol and Tbol using 2MASS, Spitzer/IRAC and MIPS, WISE, MSX, IRAS and JCMT 2.- Mass (M), mean surface density (Ʃ) and mean density of the core (T=20 K, kappa= cm2 g-1 at 850 μm) 3.- Mass of the strongest millimeter source (Mmax) assuming T=50 K 4.- Core formation efficiency (CFE) as the ratio of the sum of the masses of the fragments (high spatial resolution interferometry) and the single dish mass. 5.- Non-thermal velocity dispersion (σnon-th) 6.- Jeans mass and Jeans number (MJeans, Njeans) assuming Tgas=20 K and thermal dispersion and thermal+non thermal dispersion. 7. -Rotational to gravitational energy ratio (βrot) following the expression of Chen et al. (2012, ApJ 747, L43). Fragmentation expected for βrot>0.01.

25 Fragmentation of massive dense core down to < 1000 AU (Palau et al. 2012, ArXiv ) - The number of fragments is not correlated with the luminosity, single-dish mass, βrot, density and σnth. - Only Nmm and NIR are correlated.

26 Fragmentation of massive dense core down to < 1000 AU (Palau et al. 2012, ArXiv ) Low Core Formation Efficiency (10% - 20%) for most sources

27 Implications for star formation models New accretion models (McKee & Tan 2002, 2003) The turbulent velocity provides for the high accretion rate required for the formation of a massive star. The low CFE contradicts the monolithic accretion models Coalescence/competitive accretion models (Bonnel 2004) The massive star is formed by collisions of stars (protostars) of low and intermediate mass stars. The correlation between the mass of the most massive member of the cluster and the bolometric luminosity is in contradiction with competitive accretion models Does magnetic field play a role?

28 Magnetohydrodynamical model - We use the MHD model of Commercon et al. (2011, ApJ 742, L9) to model our representative cases I22198 and A The simulations include the magnetic fields, turbulence and take into account the radiative feedback from the accretion shock and thermal emision. - From the output, we compute the column density maps and transform them into 1mm continuum maps assuming the temperature derived from simulations (assuming dust temperature=gas temperature) and the standard dust opacities from Ossenkopf and Henning (1994). - We used the GILDAS task uv_model to calculate the visibilities we would obtain by observing the model britghtness distribution with the same uv-coverage as our observations, to eventually produce the synthetic maps.

29 Fragmentation of massive dense core down to < 1000 AU (Palau et al. 2012, ArXiv )

30 Fragmentation of massive dense core down to < 1000 AU (Palau et al. 2012, ArXiv )

31 Conclusions 1.- No correlation between the number of fragments and any of the parameters determined for the massive cores, in particular there is no correlation with the bolometric luminosity. 2.- Weak correlation between the CFE and the density which suggests that gravity dominates the core stability for high densities. 3.- The good correlation between Nmm and NIR which suggests that the fragmentation efficiency does not vary significantly among different star formation episodes. 4.- Low fragmentation and high fragmentation cases are well explained by differences in the magnetic field/tubulence ratio in the scenario of magnetohydrodynamical models.

32 2.- Chemistry November, 29th IPAG, Grenoble (France)

33 Herschel data on NGC 7129 (WISH GTKP) out 2 Fuente et al A&A 433, Fuente et al A&A 444, 481. out 1 L=460 Lsun; Tbol=58 K; D=1250 pc Hot core Two bipolar ouflows: Two bipolar outflows. The SiO emission is detected in out1. Evidence for deuteration. molecular depletion and high

34 Herschel data on NGC 7129 (WISH GTKP) The emission of the C18O 3-2 line peaks towards the protostar. The linewidths of the C18O lines increase from 1.3 km s-1 (J=1-0) to 2.1 km s-1 (J=5-4).

35 C18O Modelling in NGC 7129 FIRS 2 (Fuente et al. 2012, A&A 540, 75) - n-t profiles from the SED fitting (Crimier et al. 2010, A&A 518,52) 100 K - Chemical model: Modified version of Caselli et al. (2008, A&A 392, 703) - Ray tracing code (Alonso-Albi et al A&A 518, 52), 20 K

36 Standard CO+H2O matrix PDR CO trapped

37 Other evidences for low CO abundances in hot cores 1.- Yildiz et al (A&A 521, 40) found the the C18O abundance should be a factor of 5 lower then the starndard value in the hot corino NGC 1322 IRAS 2A to explain Herschel observations. (WISH program) 2.-Zernikel et al (A&A 546, 87) estimated a CO abundance 10 times lower than the standard in the massive hot core NGC6334I. (CHESS program) 3.-Kim et al (ApJ 758, 38), on basis of C18O observations and CO2 ice absorption lines, came to the conclusion that episodic mass accretion events could trap CO into pure CO2 ice hindering from evaporation at 20 K.

38 1.- Circumstellar disks November, 29th IPAG, Grenoble (France)

39 GV Tau (Haro 6-10) Devine et al. 1999, ApJ 117, 2931 Leinert et al. 2001, A&A 369, 215

40 Warm HCN in the planet forming zone of GV Tau N GV Tau N GV Tau S Gibb et al. 2007, ApJ 660, First high resolution, ground base detection of HCN and C2H2 in the inner disk of GV Tau N HCN/CO ~ 0.6 %

41 Warm HCN in the planet forming zone of GV Tau N (Fuente, Cernicharo & Agúndez, 2012, ApJ 754,L6) PdB observations ~0.49 x 0.29 ( ~ 69 AU x 36 AU) Continuum, HCN 3->2 & HCO+ 3->2

42 Warm HCN in the planet forming zone of GV Tau N (Fuente, Cernicharo & Agúndez, 2012, ApJ 754,L6) HCN/HCO+> AU HCN/HCO+<1.6

43 Can we explain the high HCN abundances? Model calculations by Agúndez, Cernicharo & Goicoechea (2008) using a gas-phase chemical model applied to a disk. To include grain surface chemistry does not change the results in the inner R< 10 AU region (Walsh et al. 2010). The HCN abundance is well explained by PDR chemistry in a very dense (n > 107 cm-3) region.

44 References 1.- Palau, A., Fuente, A., Girart, J.M., et al. 2012, arxiv: Fuente, A., Cernicharo, J., & Agúndez, M. 2012, ApJL, 754, L6 3.- Fuente, A., Caselli, P., McCoey, C., et al. 2012, A&A, 540, A Palau, A., Fuente, A., Girart, J.M., et al. 2011, ApJL, 743, L32