What happens when we stop assuming what can't be assumed?
Astrophotography by GrandpaJunkrat ----- Classification
Cosmology from my armchair..............................
I do it metric .............................................................. Location:
bastion@protonmail.com The Netherlands
Bortle 7 - 9
New classification Framework: Domain‑Prefixed O‑M‑E‑F System
Legacy terminology — YSO, T Tauri, Herbig Ae/Be, Class I/II/III — is inconsistent and physically ambiguous. This survey uses a domain‑prefixed O‑M‑E‑F system that classifies every object based solely on its physical state and observable properties, independent of catalogue labels.
Each object receives exactly one domain prefix.
Domains are mutually exclusive and follow a strict physical priority order.
Entry Meaning
C Compact remnant
White dwarf, neutron star, pulsar, cataclysmic variable, black hole, supernova remnant
EV Evolved star
Post‑main‑sequence object (giants, supergiants)
Y Pre‑equilibrium object
Pre‑main‑sequence star with infrared excess + accretion
XP Substellar post‑contraction object
Mass < 0.075 M☉ (brown dwarfs, planetary‑mass objects)
MS Main‑sequence star
Stable hydrogen‑burning star
N Nebula / extended source
Diffuse emission, not point‑like
After the domain prefix, each object receives a tuple of four orthogonal axes:
D:(O, M, E; F)
These axes describe independent observable properties.
Entry Meaning
O(phot.point) Point‑source photometric detection
O(phot.IRex.point) Point source with infrared excess
O(phot.noIRex.point) Point source without infrared excess
Extended sources are placed in domain N, not given an O‑label.
Entry Meaning
M(high) Mass > 5 M☉
M(int) Mass 1.5–5 M☉
M(low) Mass 0.8–1.5 M☉
M(very_low) Mass < 0.8 M☉
M(unknown) Insufficient data to estimate mass
Mass is derived from SIMBAD spectral type or Gaia absolute magnitude.
Entry Meaning
F(disc.full.acc) Full disc with active accretion
F(disc) Disc present (no accretion detected)
F(none) No circumstellar material
F(unknown) Insufficient data
Envelope‑based labels (F(env), F(env+disc)) are removed in v4.5.
The complete classification has the fixed form:
RA,Dec → D:(O, M, E; F)
Where:
D is the domain prefix (C, EV, Y, XP, MS, N)
Commas separate O, M, and E
A semicolon separates E and F
F: Fine structure (circumstellar environment)
Entry Meaning
F(disc.full.acc) Full disc with active accretion
F(disc.full.noacc) Full disc without accretion
F(disc.trans.acc) Transitional disc with accretion
F(disc.trans.noacc) Transitional disc without accretion
F(env) Envelope‑dominated
F(env+disc) Envelope + disc
F(none) No circumstellar material
F(unknown) Insufficient data
Each classification consists of equatorial coordinates (RA, Dec) followed by the domain prefix and the O‑M‑E‑F tuple. The complete notation has the fixed form:
RA,Dec → D:(O, M, E; F) [V=…]
- D is the domain prefix (Y, MS, EV, XP, C, N, or V)
- Commas separate O, M, and E
- Semicolon separates E and F
- The variability flag V (optional) indicates observed variability.
Examples:
A pre‑main‑sequence object with IR excess and a full disc:
Y:(O(phot.IRex.point), M(low), E(II); F(disc.full.acc))
A main‑sequence star without circumstellar material:
MS:(O(phot.point), M(low), E(n.a.); F(none))
V582 Cep (coordinates 21:45:28.35 +66:00:16.6) has clear infrared excess, is a point source (Gaia RUWE < 1.4), and is classified as a low‑mass pre‑equilibrium object with a disc and active accretion.
Its full classification is:
21:45:28.35 +66:00:16.6 Y:(O(phot.IRex.point), M(low), E(II); F(disc.full.acc))
This replaces ambiguous legacy labels such as "Long‑Period Variable" or "YSO".
A Python script that performs the full O‑M‑E‑F classification from coordinates (RA, Dec) is available under the CC0 license. It queries Gaia, 2MASS, and WISE, applies the rules above, and outputs the classification string. The script can be downloaded from the page Python code classification page.
