Harvard Astronomy 201b

Notes on Héctor Arce’s Guest Lecture on Outflows

In Uncategorized on March 29, 2011 at 10:00 pm

Slides, Part 1


Driving mechanism is MHD winds (not going to talk much about launching mechanism)


HH knots in the optical; NIR 2.12 micron H_2 emission (can trace slower ~50 km/s material than optical HH knots)

CO emission (redshifted & blueshifted) traces “molecular outflow” made of entrained and accelerated gas


  • Herbig & Haro’s observations 1950’s
  • shock-like spectra 1970’s (Schwartz 1975)
  • proper motions (fast!) late 70’s early 80’s
  • 1980’s observations showed very small extents ~0.1 pc
  • HST images 1990s, showing complex internal structure
  • “giant HH flows” found to be common in 1990’s, e.g. PV Ceph
  • episodicity appreciated/measured 1990’s/2000’s

Blackboard Discussion, Part 1

Basic Shock Physics

Radiative Shock: shock cools by emitting radiation more efficiently than by adiabatic expansion t_rc<t_ac ; typically v~a few 10’s of km/s, a few 100’s of km/s, n>~10^4 to 10^5 km/s

Non-radiative Shocks: …  typical of early phases of supernova remnant; n<10^3 to 10^4 cm-3; v~10^3 km/s…. mostly detected in X-rays  also–AGN jets are non-radiative UNLIKE proto-stellar jets

n_e=electron density from [SII], 6716, 6731 Angstroms

Jet Velocity from emission lines, using shock lines emission including strength & line shapes+shock models can give velocities

proper motions can also of course give velocities, but they take longer

X_e=ionization fraction (line ratios & models)

reviews: Hartigan et al. 1994; Baccioti et al. 1996, 1997, 1999, 2000; Hartigan et al. 2000 (Protostars and Planets IV)

Mass loss rate=v_jet•n_e•X_e•(pi r^2)(mu m_H)

typically 10^-8 to 10^-9 solar masses/year

best done with lines that are close in wavelength, so that reddening is not very different from one line to the next

drawing of anatomy of (jet) shock

Spectral-Line Mapping of Bipolar Flows

drawing…how outflow mapping is done

N_CO=column density

X_CO=abundance ratio, ~10^-4

M_H_2=mu • m_H • N_CO • X_CO

Total mass = Sum over x, y, z directions of M_H_2

P=M(v) • v

E=1/2 M(V_o) • v_o^2


  1. […] Lecture by Hector Arce. See this post for notes. See also this […]

  2. […] region in the image), but in the meantime some of the material is ejected in the form of bipolar outflows. Because the components of a star as it forms have different temperatures and velocities, […]

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