Lab 03: Aperture Photometry

Apparatus and Setup

You will use ../data/photometry_standard_stars.csv, containing V-band aperture counts for three photometric standard stars observed in the same field and night, plus one unidentified target measured with the identical aperture and sky annulus.

Materials and Data

Procedure

1. Compute the count rate (counts/exposure time) for STD-A and derive the zero point ZP using m = −2.5log10(rate) + ZP and the catalog magnitude.
2. Apply your derived ZP to STD-B and STD-C and compare your predicted magnitudes to the catalog values. State the agreement in millimagnitudes.
3. If the agreement for either star is worse than about 0.02 mag, identify a plausible cause (aperture too small, contaminating neighbor, misreported exposure time) before proceeding.
4. Apply your verified ZP to TARGET-X and report its calibrated V magnitude.
5. Estimate the uncertainty on the TARGET-X magnitude from Poisson statistics on its count rate, and combine it in quadrature with a zero-point uncertainty of ±0.02 mag (Lecture 13’s method).

Analysis and Uncertainty

Report TARGET-X’s magnitude as m ± σ_total, following the quadrature-combination rule, not as a bare number.

Deliverables

• Derived zero point with the arithmetic shown.
• Verification table comparing predicted and catalog magnitudes for STD-B and STD-C.
• TARGET-X magnitude with combined uncertainty.
• One sentence stating whether you trust this zero point for other targets in the same field, and why.

Assessment Criteria

• Zero point correctly derived from STD-A.
• Verification against STD-B/STD-C shown with numeric agreement stated.
• TARGET-X magnitude correct to the precision of the input data, with an uncertainty explicitly combined in quadrature.

References and Provenance

• OpenStax Astronomy 2e (local reference copy: references/openstax-astronomy-2e.pdf), Chapter 17.1 (the brightness of stars).
• Dataset: materials/ASTR210/data/photometry_standard_stars.csv, logged in reference-log.md.