CfAO Summer Internship

1. CfAO Summer Internship Michelle Darrah Smithsonian SubMillimeter Array Supervisor: Alison Peck • Dual Track Internship: • Observing Assistant - learned how to prime and operate the array for observations • Research

2. Observing and Priming

3. Quasar Calibration at Submillimeter Wavelengths SMA Michelle Darrah

4. SMA Calibration • Optical telescopes adjust for bad seeing due to thermal problems, radio interferometer telescopes adjust for phase differences due to H2O in the atmosphere and turbulence. • Creating an image of an astronomical source, we must compensate for phase changes by observing bright point-like source.

5. Path Length and Phase Shift The signal at each antenna is going to arrive slightly out of phase due to different path through the atmosphere. • The signals from each telescope is going to arrive slightly out of phase from intermittent and unsmooth atmospheric interference.

6. Precise Calibration Benefits • Better Image Fidelity • Increased Data Accuracy • Quality Assessment of Data • Ability to Take Data From Dimmer or More Distant Objects

7. Calibrator Requirements • Stability • Comprehensive Documentation • Minimal Weather Dependence • Bright at Multiple Wavelengths

8. Quasars • Intrinsically brighter than their surroundings at multiple wavelengths

9. Calibration Publication • At each new wavelength a list of calibrators must be established. • A published list of calibrators and their accepted flux values gives future telescopes a step ahead in their calibrations and data collection.

10. Steps • Observe quasar candidates with the observations spanning at least six months • Use Miriad or MIR software to reduce data • Plot data and check for stability • Narrow the list to those quasars that there is sufficient data on, and observe more data for those that do not make that list.

11. Observing • Observing script nflux.pl • Long list of quasars calibrated against Callisto or Ganymede. • Edited daily (using VI), to update priority rating for each quasar.

12. Data • Data from observing gets reduced using Miriad or MIR and then plotted; observed time (MJD) vs. flux (Jy) • Plots analyzed for stability and brightness • Sorted into stable objects, useful for calibrations, and unstable objects that are interesting for their own intrinsic scientific value. • Cross referenced to VLA data to look for correlation in time of flux change to frequency. • Repeatedly observed to ensure continued stability

13. Plots 0402-014 Flux Variability 62% at 850mm Unstable for Calibrations 3c273 Flux Variability 11% at 850mm Stable

14. Continued Observations 3c454.3 Was a stable calibrator until the end of 2004. Good example of why to continually observe and re-evaluate.

15. From more than 330 calibrators, the list was analyzed for comprehensive data over 6 months or more, and then separated into 2 lists, stable and unstable, at both 1mm and 850mm.

16. Results • Maximum flux variation 30% for stability • 16 stable calibrators at 850 mm • 18 stable calibrators at 1mm • Not enough correlation in timing between the VLA data and SMA data to draw conclusions.

17. Acknowledgements • Alison Peck, Shelbi Hostler, Ant Schinckel • SMA Staff • CfAO • University of Hawaii at Hilo • Funding provided through the Center for Adaptive Optics, a NSF Science and Technology Center (STC) AST-987683