Apparatus and Setup
You will use ../data/variable_star_lightcurve.csv, containing normalized target and comparison-star fluxes at six times (in fractional Barycentric Julian Date offset, t_bjd) spanning one observing sequence.
Materials and Data
| t (BJD offset) | Target flux | Comparison flux | Δm (mag) |
|---|---|---|---|
| 0.00 | 0.995 | 1.000 | |
| 0.05 | 0.992 | 1.001 | |
| 0.10 | 0.970 | 0.999 | |
| 0.15 | 0.955 | 1.000 | |
| 0.20 | 0.972 | 1.002 | |
| 0.25 | 0.994 | 1.001 |
Procedure
- Compute Δm = −2.5log10(F_target/F_comp) at each of the six times and complete the table.
- Plot Δm versus t. Identify the time of minimum light (largest Δm, i.e. faintest target) and its approximate depth relative to the t = 0.00 baseline.
- Estimate a noise floor for Δm from the two flattest points in the comparison star’s own flux (should be within about 0.2% of 1.000); convert that flux scatter to an equivalent Δm scatter and compare it to the dip depth you measured.
- State, with a number, whether the dip is statistically significant relative to your estimated noise floor.
- Discuss what would make this comparison star unsuitable (e.g., if its own flux had varied by 2% instead of 0.2%).
Analysis and Uncertainty
Report the dip depth (in millimagnitudes) relative to the pre-dip baseline, and the estimated noise floor, and state their ratio as a rough significance (dip depth / noise floor).
Deliverables
- Completed six-row Δm table.
- Light-curve plot with the dip clearly marked.
- Dip depth, noise floor, and significance ratio, each with a number.
- One paragraph judging whether the comparison star was a good choice.
Assessment Criteria
- Correct Δm for all six rows.
- Dip correctly identified near t ≈ 0.15 with a depth consistent with the data (roughly 0.03–0.05 mag).
- Noise floor estimated from actual comparison-star scatter, not assumed.
- Significance judgment is quantitative, not just descriptive.
References and Provenance
- OpenStax Astronomy 2e (local reference copy: references/openstax-astronomy-2e.pdf), Chapter 17.1 (brightness/magnitudes) and Chapter 21.4 (transiting exoplanet evidence).
- Dataset:
materials/ASTR210/data/variable_star_lightcurve.csv, logged inreference-log.md.