1. 4He Abundances: Optical vs Radio Dana S. Balser

2. Collaborators
Tom Bania
Bob Rood

3. Radio Recombination Lines
Sensitivity
Spectral Baselines
Departures from LTE
Ionization Structure
Density Structure
Sensitivity: RRLs are much weaker than ORLs (hard to detect H RRLs in extragalactic objects). Improvements in Spectrometers allow stacking of adjacent RRLs to increase signal-to-noise ratio.
Spectral Baselines: Have limited accurate measure of line profiles. The off-axis design of the GBT significant improves the spectral baselines.
Departures from LTE: It is typically assumed that the Rydberg levels of H and He are affected by collisonal/radiative effects in the same way so that the ratio of the ionic abundances is just the ratio of the line area. For high-n, where the levels are controlled by collisions and are in LTE this should be the case. HII regions models indicate that the n~90 lines are approximately in LTE (Shaver 1980; Balser et al. 1999). Also, note consistent 4He/H ratio for n=91,114,130 (plot).
Freq_LTE ~ * EM^0.36  Freq_LTE ~ 6.9 +/- 3.6 GHz
Ionization Structure: There is no way to directly measure neutral H or He. Typically one uses other diagnostics to measure ionization structure. Q(He)/Q(H); He++/He+; O+S++/S+O++; [OIII]5007/[OI]6300 (e.g., Ballantyne et al. 2000; Gruenwald et al. 2002; Sauer & Jadamzik 2002).
N(He)/N(H) = ICF * (N(He+) + N(He++))/N(H+) in some cases ICF < 1.
Density Structure: Inhomogeneous density models effect the ICF. Models by Viegas et al. (2000) predict that inhomogeneities will decrease the ICF. Models by Mathis & Wood (2005) indicate that clumping will produce neutral He even in very hot stars as a sharp increase in density will allow H to compete more effectively for He-ionizing photons.

4. 4He/H: RRLs with the 140 Foot Telescope
No significant difference in Y with n.
Includes 3% systematic error.
Peimbert et al. (1992)

5. Green Bank Telescope Observations

6. Planetary Nebulae 50” Balick et al. NGC 3242 NGC 6543 NGC 6826
All from Balick’s web page (all Hubble data)
NGC3242: WFPC2; NII red, OIII green, starlight filter blue
NGC6543: WFPC2; NII red; OIII green; OI blue
NGC6826: WFPC2; NII red, OIII green, starlight filter blue
NGC7009: WFPC2; NII red, OIII green, starlight filter blue
GBT’s HPBW is larger than RRL emission region.
These PNe have large halos but we are not sensitive to this gas.
Balick et al.
NGC 6826
NGC 7009

7. GBT: PNe Radio Recombination Lines
NGC 3242
NGC 6543
NGC 6826
NGC 7009
Average of 91a + 92a bands (re-grid with sinx/x kernel)
Third-order polynomial baseline fit removed
Dv = 2.1 km/s (smoothed 5 channels)
One expects a Gaussian profile if the thermal motions dominate any large-scale motions (e.g., expansion). If there exists a significant expansion velocity relative to these thermal motions then the profile will be double peaked if the telescope’s beam is smaller than the emission region or a square profile if the telescope’s beam is similar or larger than the emission region.
Although we measure the He++ (146a) line we do not measure the H146a (at 2091 MHz); thus we cannot determine He++/H+ directly. We can model the PNe and estimate the H146a based on the H91a.
NGC3242: Square-wave profile (use area under curve for 4He/H). He++ detected. Only a limit.
NGC6543: Gaussian profile (use ratio of Gaussian fit area). No He++ detected. O++/C++ detected.
NGC6543: Gaussian profile (use ratio of Gaussian fit area). No He++ detected.
NGC7009: Square-wave profile (use area under curve for 4He/H). He++ detected (maybe blended with O++/C++ or it has a different velocity). Only a limit.

8. HII Regions: M17 Optical (Halpha) Radio Continuum (9GHz) 30’ 60’
M17 (optical): MacQuarrie; Halpha; 4.3” f/7 refractor
M17 (radio); Maddalena et al.; 9 GHz; 54x54 arcmin; GBT
30’
60’
MacQuarrie
Maddalena et al.

9. HII Regions: S206 Optical (Halpha) Radio Continuum (9 GHz)
S206 (optical): from Pismis & Mampaso (1991); Halpha; 1.0 m Observatorio de Tonantzintla (Mexico)
S206 (radio): from Balser (2006); 9 GHz; GBT
Pismis & Mampaso (1991)
Balser (2006)

10. GBT: HII Region Radio Recombination Lines
M17N
S206
S206
M17N
Average of 87a-93a bands (re-grid with sinx/x kernel)
Third-order polynomial baseline fit removed
Dv = 0.43 km/s (no smoothing)
M17N: fit C, 2He, 2H (fixed both He line centers based on H fit)
S206: fit C, He, H
No measurement of He++ line.

11. 4He/H: Planetary Nebulae
4He/H data is not comprehensive but includes studies that estimate an uncertainty.
Barker (1983,1985,1988): ~3” diameter aperture toward 5-8 positions; diffraction grating.
Perinotto et al. (2004): New analysis of past data
Krabble & Copetti (2006): Long slit spectrophotometry.

12. 4He/H: HII Regions
Blue Compact Dwarfs (BCD): Isotov & Thuan (2004); ORL
SMC/LMC: Peimbert et al. (2003); ORL
S206: Deharveng et al. (2000); ORL; Fabry-Perot with 1-4 arcmin diaphram
M17: Garcia-Rojas et al. (2007); ORL (position 14)
Sun: Basu & Anita (2004); Heliosiesmology
Solid Line: Yp= and dY/dO=3.6 => dY/dZ = 1.6 (Peimbert et al. 2002)
Top Dashed Line: Reverse ICF of in Y (Gruenwald et al. 2002)
Bottom Dashed Line: Clumping Effects with 3% decrease in Y (Mathis & Wood 2005)

13. 4He/H differences as large as 20% between Optical and Radio
Summary
4He/H differences as large as 20% between Optical and Radio
Galactic dY/dZ ~ 1 (M17, S206)

14. Models of PNe and HII Regions EVLA
Future Work
Explore 4He/H with n
Models of PNe and HII Regions
EVLA

15. Extra Slides

16. Expanded View: M17N

17. Expanded View: S206

18. M17S

19. Expanded View: M17S