1. 1
Image: SH 206, Adam Block, Mount Lemmon Sky Center, University of Arizona 2008
A Model For Narrow C+
Emission Discovered
By Herschel
Marcus Hughes
Williams College
2014 STSCI SASP Presentation

2. 2
(Pineda et al. 2013)
(Pineda et al. 2013)
Milky Way Schematic: R. Hurt, Courtesy NASA/JPL-Caltech
ESA

3. Inputs:
• Electron density
• Hydrogen density
• Star Spectral Type
• Gas kinetic temperature
Outputs:
• Radius of HII and PDR
• Emission measure
• C+ intensity
Assumptions:
• HII region is pure hydrogen
• Ratio of C to H
• Constant density
• Temperature regime
• Collision rate coefficients
(Wiesenfeld & Goldsmith 2014)
3
HIIPDR
Ioniz. Front
Dissoc. Front
C and C+
C2+ and C3+
H2HI
CO and C+
1017 cm0 cm1017cm 1019 cm1019 cm

4. 4
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60
C+Intensity(Kkm/s)
Star Effective Temperature (103 K)
C+ Emission from O and B Main Sequence Stars
n = 103 cm-3
ne = 80 cm-3
Input SD and SLYC from Diaz-Miller, Franco, & Shore (1998)
<p> = 0.15
Tkinetic = 103 K

5. 5
150.6, -1.0:
• O6V type star at right velocity (Crampton & Fisher 1994)
• Observed C+ intensity: 19.4 K km/s
• Predicted C+ intensity: 85 K km/
• Predicted C+ Intensity with Dust: 20 K km/s
Example Regions:
• 087.2, -0.5
• 109.8, +0.0
• 109.8, +2.0
• 150.6, -1.0
• 202.6, +2.0
• 207.2, -2.0
• 265.5, -2.0
Background Image: 1420 MHz Continuum
(Diaz-Miller, Franco, & Shore 1998)

6. Future Possibilities
• Predict emission measures
• Compare to observed emission measures
• Compare to OH measures
• An additional tracer of molecular gas
• Consider effects of dust more generally
• Decreases region radius, decreases C+ intensity
• Apply model to narrower inner galaxy pointings
• Consider the variable density and temperature case
6

7. Bibliography
• Balser, D.S., Bania, T.M., Rood, R. T., & Wilson, T.L. 1995,
ApJS, 100, 371
• Crampton & Fisher 1974, Pub. Of the Dominion Astrophysical
Observatory, 14, 283
• Diaz-Miller, R. I., Franco, J., & Shore, S. N. 1998, ApJ, 501,
192
• Goldsmith, P.F., Langer, W.D., Pineda, J.L, & Velusamy, T.
2012, ApJS, 203,13
• Langer, W.D., Velusamy, T., Pineda, J.L, Willacy, K., &
Goldsmith, P.F. 2014, A&A, 561, A122
• Pineda, J.L, Langer, W.D., Veulsamy, T., & Goldsmith, P.F.
2013, A&A 554, A103
• Wiesenfeld, L. & Goldsmith, P.F. 2014, ApJ, 780, 183
• Special Thanks: Philip Engelke & Paul Goldsmith
7