ASTR 340 Problem Set 03: CCD Noise Terms and Exposure-Time Trade-offs

Problem set for lecture unit 3.

Problems

1. Shot noise at 100 s 20 points

Compute the photon shot noise (in electrons) for the V=18 worked-scenario star (count rate 243408.201 e⁻/s) after a 100 s exposure.

2. Dominant noise term 15 points

Compare your Problem 1 result to the representative read noise (3.5 e⁻) and dark-current shot noise (0.3162 e⁻ at 100 s), and identify which of the three terms dominates the total noise at this exposure time.

3. Read-noise-limited crossover 15 points

Solve for the exposure time at which shot noise from this source equals the 3.5-electron read-noise floor, and confirm your answer against 0.0 s.

4. Interpreting the crossover 20 points

Explain what regime (read-noise-limited or shot-noise-limited) applies for exposures shorter than your Problem 3 answer, and what regime applies for longer exposures, and state which regime is more efficient to operate in for a faint, read-noise-sensitive measurement.

Due and Scope

Submit a complete derivation with equations, units, labeled quantities, and a short narrative interpretation for each problem. Show every step; a correct final number without a visible derivation receives partial credit at most, and quoting a lecture number without adapting it to this problem's specific inputs receives no credit for that step.

OpenStax Companion Reading

OpenStax Astronomy 2e (local reference copy: references/openstax-astronomy-2e-extracted.txt), Chapter 6 (astronomical instruments), descriptive only; this course exceeds that introductory treatment throughout.

References and Data Sources