4He Abundances: Optical vs Radio Dana S. Balser

Collaborators Tom Bania Bob Rood

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 ~ 0.081 * 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.

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

Green Bank Telescope Observations

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

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.

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.

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)

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.

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.

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=0.2384 and dY/dO=3.6 => dY/dZ = 1.6 (Peimbert et al. 2002) Top Dashed Line: Reverse ICF of 0.006 in Y (Gruenwald et al. 2002) Bottom Dashed Line: Clumping Effects with 3% decrease in Y (Mathis & Wood 2005)

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)

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

Extra Slides

Expanded View: M17N

Expanded View: S206

M17S

Expanded View: M17S