GBT radiorecombination 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: 10.23 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

Results: W3A

• Total flux calculation: 11.35 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

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, 357-377