Apparatus and Setup
You will use ../data/archive_query_sample.csv, a small excerpt of a Gaia-like source catalog with G magnitude, color (BP−RP), parallax, and parallax uncertainty for three sources.
Materials and Data
| source_id | G mag | BP−RP | Parallax (mas) | Parallax err (mas) | Parallax/err | Passes quality cut? |
|---|---|---|---|---|---|---|
| 1 | 12.1 | 0.8 | 5.1 | 0.2 | ||
| 2 | 15.3 | 2.1 | 1.2 | 0.5 | ||
| 3 | 10.7 | 0.3 | 8.8 | 0.1 |
Procedure
- Compute the fractional parallax quality (parallax/error) for each source and complete the table.
- Apply a documented quality cut of parallax/error > 5 and state which source(s) fail it.
- Apply a second, independent cut of G < 14 (a "bright and reliable" magnitude limit) and state which source(s) fail it.
- Combine both cuts and report the final retained sample, listing exactly which sources remain and why each excluded source was removed.
- For each retained source, compute distance in parsecs as d = 1000/parallax(mas), and report the result with the parallax uncertainty propagated into a distance uncertainty (σ_d ≈ d × σ_parallax/parallax for small fractional errors).
Analysis and Uncertainty
State explicitly, in a query-log paragraph, every cut you applied and in what order, so that a second student could reproduce your final retained sample exactly from the raw table above.
Deliverables
- Completed quality-cut table.
- A written query log documenting both cuts and their order.
- Distances with propagated uncertainties for the retained sources.
- One paragraph on what would change if the parallax quality cut were relaxed to > 3 instead of > 5.
Assessment Criteria
- Correct parallax/error ratios and correct pass/fail determination for both cuts.
- Query log is specific enough to be reproducible (states the exact numeric thresholds and order).
- Distances and propagated uncertainties are computed correctly for the retained sources only.
References and Provenance
- OpenStax Astronomy 2e (local reference copy: references/openstax-astronomy-2e.pdf), Chapter 19.2 (surveying the stars, parallax).
- Dataset:
materials/ASTR210/data/archive_query_sample.csv, logged inreference-log.mdas a synthetic instructional excerpt modeled on Gaia-style catalog columns.