Interstellar dust
Interstellar dust, infrared light and polarization
A dark cloud redirects the story of starlight. Begin with where the absorbed power goes, calculate the grain response, then learn what real infrared colours can and cannot determine.
L1
Why a dark dust cloud shines in infrared
Follow absorbed starlight into grain heat and infrared emission, then see why a bright dust pixel need not contain more dust.
L1
From absorbed starlight to grain temperature
Derive the dust heating balance with spectral units, the four-pi cooling factor and a worked gray-grain example.
L2
Why transmitted and thermal polarization turn opposite ways
Build Stokes I, Q and U from two electric-field modes, then derive the perpendicular axes of transmission and thermal emission.
L3
How many temperatures do three infrared colours reveal?
Use one saved DustPedia galaxy record to see temperature–opacity tradeoffs, two-component degeneracy and a zero-amplitude boundary.
L3
Recompute a DustPedia infrared colour comparison
Fetch two fixed native rows and official SPIRE responses, preserve quality flags, and compare one- and two-temperature fits to the same saved data.
L4
Read an Astrodust model from cross sections to polarized emission
A guided reading of Hensley–Draine v1, with native mass and polarization audits, fixed-field limits and an unresolved covered-energy check.
Sources and calculation scope
- Hensley & Draine, arXiv:2208.12365v1 (2022)
Fixed first manuscript: sections 2.1–2.3, 4–6; equations 1–11/27 and Figures 6/11/12/18. Material cross sections, temperature distributions and prescribed size-dependent alignment are distinct from the teaching tensor. Its 2022 forecasts are not current-status claims.
- Astrodust+PAH Milky Way model, Dataverse version 2.0
CC0-1.0 complete small source tar and complete selected numeric FITS HDUs. Published model outputs, not new observations. Tar MD5 and SHA are checked; whole-FITS MD5 is not independently verified. Native maximum-polarized and random-orientation total references retain their separate geometries.
- Clark et al., DustPedia photometry, arXiv:1708.05335v1
Sections 2.1.1, 3.5–3.7, 4, 6.3.1 and 7.1: HIPE 13, reference spectrum, matched apertures, source flags, already-included calibration errors and aperture correction. No source-image re-reduction or flag clearance is claimed.
- DustPedia aperture-photometry catalog J/A+A/609/A37
Reader-local fixed NGC0628/NGC4254 queries through the official CfA VizieR mirror. Only declared query timestamps are excluded from the frozen identity. Raw and derived real tables are not redistributed while rights remain unresolved.
- Griffin et al., SPIRE photometer calibration, arXiv:1306.1778v1
Sections 2–3 and 6, equations 1/8–12/18–25: energy response, reference spectrum and point/extended beam distinctions. Power-law beam scenarios are conditional approximations, not an exact native catalog beam.
- ESA SPIRE context 14.3 RSRF and aperture-efficiency products
Exactly SPIRE_phot_RSRF_14_3.fits and SPIRE_phot_apertureEfficiency_14_3.fits, with fixed complete-file hashes. Context 14.3 differs from internal product versions 3 and 1. Reader fetch only; no uncleared response arrays are redistributed.
- Dust absorption, heat and polarization: standalone science
MIT scientific code plus separately licensed CC0 native inputs. Ten genuinely recomputed offline steps, retained coarse-grid failures, independent volume/Planck references and optional first-network real exercise. The site supplement records a later successful real first acquisition; the frozen archive remains unchanged.