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The Serpens Star Forming Region in HCO +, HCN, and N 2 H + Michiel R. Hogerheijde Steward Observatory The University of Arizona.

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Presentation on theme: "The Serpens Star Forming Region in HCO +, HCN, and N 2 H + Michiel R. Hogerheijde Steward Observatory The University of Arizona."— Presentation transcript:

1 The Serpens Star Forming Region in HCO +, HCN, and N 2 H + Michiel R. Hogerheijde Steward Observatory The University of Arizona

2 Outline Molecular clouds and star formation The Serpens star-forming region Single-dish images Interferometer images Combination single-dish and interferometer Abundances A shock model for HCN and N 2 H + Conclusions

3 Molecular clouds and star formation Stars form in condensations in interstellar clouds Cloud structure determines stellar masses Jets, outflows affect cloud chemistry and structure

4 The Serpens star-forming region Dense cluster of pre– main-sequence stars Two condensations, NW and SE ~Dozen submm continuum peaks Many associated with YSOs, some starless cores SCUBA 850 µm on DSS image Davis et al. (1999)

5 JCMT/SCUBA images of Serpens Davis et al. (1999) SMM4 SMM11 SMM6 SMM2 SMM3 SMM1/ FIRS1 SMM8 SMM9/ S68N SMM10 SMM5

6 Many outflows ‘Tangle’ of outflows Intermediate velocities: ±7 km s -1 Extreme velocities: ±11 km s -1 Davis et al. (1999)

7 How do outflows affect structure and chemistry in Serpens? J=1–0 transitions ( ≈3 mm) of HCO +, HCN, N 2 H + Common tracers of dense [n(H 2 )≈10 5–6 cm -3 ] and cool (T kin ≈30 K) gas Morphology  chemistry 4 Single-dish on-the-fly maps from Kitt Peak 12-meter telescope 4 Interferometer mosaics from the Berkeley- Illinois-Maryland array (SE region only)

8 Single-dish maps HCO + 1–0HCN 1–0N 2 H + 1–0 Resolution 1 = 0.12 pc = 21,000 AU

9 Single-dish maps N 2 H + equally strong in NE and SE –Follows submillimeter continuum HCO + and HCN peak in SE –Where most embedded YSOs and their outflows are E-W velocity gradient –Solid-body rotation, also noted by Olmi & Testi (2002)

10 Interferometer mosaics Higher resolution: 10–20 arcsec; 140 arcsecs primary field of view Filters out large-scale emission ~ 115 arcsec 13-point ‘mosaic’: overlapping pointings

11 Interferometer mosaics: N 2 H + Resolution 17  = pc = 7000 AU

12 Interferometer mosaics: N 2 H + Color: N 2 H + Contours: 850 µm

13 Interferometer mosaics: HCN Resolution 21  = pc = 8500 AU

14 Interferometer mosaics: HCO + Resolution 12  = pc = 4600 AU

15 Interferometer mosaics N 2 H + : –At continuum peaks –Ahead of SMM3’s jet –North of ‘shock position’ HCO + and HCN: –near YSOs, outflows Strong blue-shifted HCN west of SMM4: –‘shock position’

16 Combining single-dish and interferometer data Interferometers filter out emission on scales larger ~ shortest antenna spacing Missing ‘zero-spacing’ flux KP12m well matched to 6-m BIMA antennas Method: joint deconvolution

17 Combined BIMA and KP12m

18 Combined maps qualitatively look as expected High resolution of BIMA brings out velocity details on small scales ‘Washed out’ in KP12m map BIMA recovers ~30% of line flux

19 Abundances Are HCO + and HCN enhanced by outflow action? Throughout core, or only locally?

20 Abundances Olmi & Testi (2002) C 18 O 1–0 map FCRAO: 1 arcmin resolution T ex N(H 2 ) Use to derive abundances on 1 arcmin scales

21 Abundances HCO + HCNN2H+N2H+

22 Abundances Average Serpens Peak positions Dark cloud values a N2H+N2H+ 3.8x x (5–10)x HCO + 3.0x x (2–8)x10 -9 HCN 5.4x x (0.5–5)x10 -8 Factor 2 enhancement near YSOs (outflows) Abundances HCN, HCO + << dark clouds: depletion; T ex ? a) van Dishoeck et al. 1993; Ohishi et al. 1992; Turner 2000

23 Shock model for HCN and N 2 H + Offsets between HCN (color) and N 2 H + (contours) SMM3’s jetShock position

24 Shock model for HCN and N 2 H + C-type shock Magnetic precursor Ions accelerate, compress, and heat before neutrals N 2 H + emission up in precursor HCN abundance up in warm region: evaporation of ices Accompanying H 2 O destroys N 2 H + Draine & Katz (1986)

25 Two models for shock position: 1 Jet driven by SMM4, deflected by dense material. N 2 H + in magnetic precursor of C-type shock.

26 Two models for shock position: 2 Jet driven by SMM1, hitting dense matter. HCN at bow shock, N 2 H + along the sides where shock speeds are lower.

27 Conclusions HCN, HCO + locally enhanced by shocks Depleted in rest of cloud compared to dark- cloud values Unresolved observations would trace outflow- affected material preferrentially N 2 H + undepleted: traces condensations N 2 H + emission ahead of shocks: enhancement in magnetic precursor, destruction in warm region?

28 Future work C 18 O on 10–20 arcsec scales, fully sampled Higher-J lines: excitation HCN, HCO +, and N 2 H + High-resolution interferometry shock region; additional species Time-dependent shock-chemistry model

29 Many thanks to… Staff of the Kitt Peak 12 meter Radio Telescope Staff of the Berkeley-Illinois-Maryland Association millimeter array Chris Davis and Luca Olmi for making their data available electronically


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