Apparatus and Setup
This lab performs a calibration-frame reduction sequence (Lecture 07) and derives a photometric zero point from a real Landolt standard star (Lecture 08), then applies it to recover an unknown target's calibrated V magnitude.
Materials and Data
| Frame / quantity | Representative value |
|---|---|
| Bias frame (mean level) | 400 ADU |
| Dark frame, matched 300 s exposure (mean level) | 480 ADU |
| Normalized flat-field frame (mean) | 1.000 (by construction) |
| Raw light frame, standard star SA 98-978 (mean, 300 s) | 811360668 ADU |
| Raw light frame, science target (mean, 300 s) | 40568033 ADU |
| SA 98-978 published V magnitude (Landolt 1992) | 9.061 |
Procedure
- Using I_cal=(raw-D)/F (matched-exposure master-dark workflow, Lecture 07), compute the calibrated ADU level for both the standard-star frame and the science-target frame from the data table.
- Convert each calibrated ADU level to an electron count rate using the representative gain g=1.8 e⁻/ADU and the 300 s exposure time.
- Using SA 98-978's published V=9.061 magnitude and its measured count rate, solve for the night's photometric zero point Z_pt via m=-2.5log₁₀(counts/s)+Z_pt.
- Apply the zero point from step 3 to the science target's measured count rate to compute its calibrated V magnitude, and confirm your value is consistent with 12.314.
Analysis and Uncertainty
State explicitly what would happen to the derived zero point, and therefore to every target magnitude computed from it that same night, if the flat-field frame used in step 1 had a mean far from 1.0 rather than being properly normalized (Lecture 07's flat-field pitfall).
Deliverables
- Both calibrated ADU-to-count-rate conversions.
- The derived zero point with full substituted values.
- The recovered science-target V magnitude.
Assessment Criteria
- Correct calibration-equation application (matched-exposure dark workflow, not double bias subtraction).
- Correct gain conversion and zero-point derivation.
- Correct final target magnitude consistent with the worked value.
References and Provenance
- 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.
- SA 98-978 UBVRI magnitudes: standard published Landolt (1992) photometric standard-star values, not independently re-verified this session; calibration-frame ADU levels are illustrative/synthetic, matching this course's Lecture 07 worked example; see
materials/ASTR340/reference-log.md. - Generated by
materials/ASTR340/src/generate_astr340_content.py.