alma-corpus-mcp

virial_parameter

Calculates the virial parameter alpha_vir from velocity dispersion, radius, and mass to assess cloud gravitational boundedness, with FWHM, radius scaling, and density-profile corrections.

Instructions

Virial parameter alpha_vir = 5 sigma^2 R / (G M) (Bertoldi and McKee 1992), called alpha_5 here.

sigma: 1D velocity dispersion (km/s); pass a FWHM with sigma_is_fwhm. R: radius in pc, or give radius_from_sigma_r_pc so R = 1.91 sigma_r (Solomon et al. 1987 convention). For rho ~ r^-k: a = (1 - k/3)/(1 - 2k/5), alpha_E = 2 E_K/|E_G| = alpha_5 / a; equilibrium alpha_5 = a, bound if alpha_5 < 2a (equivalently alpha_E < 2). Never apply a profile-corrected coefficient and then also the 2a threshold. Limits: the mass conversion (alpha_CO, dust T and kappa) dominates; unresolved clouds give limits only; surface pressure and magnetic terms are ignored.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "sigma_kms": "<sigma_kms>",
      "radius_pc": "<radius_pc>",
      "mass_msun": "<mass_msun>"
    },
    "name": "virial_parameter"
  }
}

Input Schema

Name	Required	Description	Default
`mass_msun`	Yes
`radius_pc`	Yes
`sigma_kms`	Yes
`density_index`	No
`mass_err_msun`	No
`radius_err_pc`	No
`sigma_err_kms`	No
`sigma_is_fwhm`	No
`radius_from_sigma_r_pc`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Nov 9, 2026

TDQS

A4.3/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries the full burden and does well: it discloses assumptions about density profiles, the equilibrium condition, and important limits (mass conversion dominates, unresolved clouds give limits only, surface pressure and magnetic terms ignored). It does not describe error propagation behavior for the error parameters or the exact return format.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is dense but front-loads the formula and definitions, which suits a technical scientific tool. Every sentence adds useful context about conventions or caveats. Slightly more structure could improve readability, but it is not verbose.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the complexity of a 9-parameter scientific computation with no annotations or output schema, the description is largely complete: it covers the formula, profile correction, equilibrium criteria, and key limitations. The main missing piece is an explicit statement of return values and error propagation, which would help an agent understand the output.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0%, so the description must compensate. It explains the key inputs: sigma as 1D velocity dispersion, R as radius in pc, sigma_is_fwhm, radius_from_sigma_r_pc, and density_index through k. The three error parameters are not explicitly discussed, leaving a small gap.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific scientific computation: the virial parameter alpha_vir = 5 sigma^2 R / (G M), called alpha_5. It clearly distinguishes this calculation from sibling tools like dynamical_mass or toomre_q. The purpose is unambiguous without opening the schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives clear usage context: pass a FWHM with sigma_is_fwhm, or supply radius_from_sigma_r_pc for the Solomon et al. convention. It warns against combining profile-corrected coefficients with the 2a threshold and notes limits. However, it does not explicitly say when to prefer this tool over alternatives such as dynamical_mass.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.