# Assessment Instructions: Problem Set 04 — Molecular Cloud Mass Estimators

## Inputs to Inspect
Student submission, this problem set, the solution key, the corresponding lecture slides/notes, and the referenced dataset(s) under `materials/ASTR360/data/`.

## Grading Standard
Award credit for correct method and units first, then for the specific numeric result. A student who shows correct reasoning with a small arithmetic slip should receive most of the available credit; a student with a correct-looking number but no visible derivation steps should not. Because this is a 300-level quantitative interstellar-medium course, full marks require a genuine derivation wherever the problem set asks for one, and a genuinely reasoned (not merely asserted) interpretation wherever the problem asks for scientific judgment (e.g., honestly characterizing an idealized model's disagreement with a real object).

## Problem-Level Criteria
- Problem 1: verify the algebraic factor-of-2 scaling is derived before the numeric answer is given.
- Problem 2: verify correct inversion of the X_CO conversion (mass to luminosity, not luminosity to mass).
- Problem 3: verify the M_vir ∝ sigma^2 scaling is confirmed numerically, not just asserted.
- Problem 4: verify the bound/unbound conclusion is stated comparatively and hedged given the model's known limitations, not as an absolute claim.

## Resubmission Policy
Students may resubmit within one week of receiving feedback. A resubmission must show a corrected derivation, not only a corrected final number, and should reference the specific feedback comment it addresses. Regrade to a maximum of 90% of the original point value unless the error was a grading mistake.

## Common Errors to Flag
- Forgetting the factor of 2 (H2 molecules, not H atoms) in the X_CO mass conversion.
- Treating M_vir=M_CO exactly as proof of virial equilibrium rather than a rough, hedged consistency check.
- Sign/direction errors in the sigma-doubling scaling check (reporting a factor of 2 instead of 4).