GBT radio recombination lines (GBT-5) Single Dish Summer School July 2009

Project Team Advisor: – Toney Minter (NRAO, Green Bank) Project Team: – Daniel Angles-Alcazar ( Univ. of Puerto Rico) – Joseph Richards (Caltech) – Marty Bloss (NRAO, Green Bank)

Project Description Use the GBT spectrometer to observe the radio recombination lines of Hydrogen, Helium, and Carbon Sources: – planetary nebula NGC 7027 – HII regions DR 21, W3A Measurements – Electron temperature of the emitted gas – Turbulent velocity of the gas

N = 103 H103 α N = 104 N = 102 N = 105 Recombination Lines

Techniques Required GBT calibration, pointing and observing control Position switching Spectral line observations Use GBT “vector calibrated" data to compare the result obtained from the cross-scans to estimate the accuracy of the calibration Identify and flag RFI in observations Reduce observation data via GBTIDL

Observing Procedures Modify pointing & observing scripts Peaked up for pointing and focus Calibrate on source and balance IF Execute multiple spectral scans “Sanity-check” results using GBTIDL during observations

Data Reduction For each source: – Derive flux density scale from calibrator (3C286) – Estimate continuum level – Collect and average multiple scans (flagging RFI) – Fit baseline – Fit Gaussians to potential recombination line areas Multiple Gaussians in some H103 recombinations

Data Reduction (cont.) For each source: – Confirm line detections and calculate power and velocity – Calculate electron temperature – Calculate nonthermal velocity

Results DR 21

Results: DR 21 Total flux calculation: Jy Potential lines detected: – Hydrogen – Helium – Carbon Electron temperature: 3,500 K Kinetic temperature: 17,500 K Turbulent velocity: 20.8 km/s Abundance: He 4.9%, C 19.8%

Results: W3A

Total flux calculation: Jy Potential lines detected: – Hydrogen – Helium – Carbon Electron temperature: 2,400 K Kinetic temperature: 4,300 K Turbulent velocity: 17.3 km/s Abundance: He 8.7%, C 19.8%

Results: NGC 7027

Total flux calculation: 2.93 Jy Potential lines detected: – Hydrogen Electron temperature: 8,400 K Three sigma limit of 63% for He or C abundance

Findings Hydrogen (H103a) recombination line was detected in W3A, DR 21, & NGC 7027 Helium (He103a) and Carbon (C103a) recombination lines were detected in W3A and DR 21 Electron temperatures were calculated using Hydrogen in all three sources Turbulent velocities were calculated for W3A and DR 21

Bibliography A survey of H 109 a Recombination Line Emission in Galactic H II Regions of the Northern Sky, E.C Reifenstein III, et al., Astron & Astrophysics, Vol 4,