Spectral Classification Tables for
TT.tt.LL.P1P2P3P4 Encodings

(from IVOA Note: An Encoding System to Represent Stellar Spectral Classes
in Archival Databases and Catalogs" by Smith, Thompson, Gray, Corbally, and Kamp.)

Table 1. Mapping of TT spectral types and tt subtypes

ENCODED SPECTRAL TYPES (TT):

    Sp           Code  Description                     Sp           Code   Description        

    Sp           Code  Description                     Sp           Code   Description        

Notes:

1. This table omits some obsolete usages. For example, R and N map to CN and CR, respectively. The scheme interprets “R” and “N” as these respective spectral types.

2. For the reader’s information (only), subdwarf A stars (sdA   TT=33) consist of two evolu-tionarily distinct groups: sdA0-sdA2 stars are products of advanced evolution (like sdO, sdB), whereas sdA3..sdA9  stars (like sdF-sdK stars) are old stars on the metal-weak main sequence.

3. “Undifferentiated C stars” are not a universally sanctioned spectral type, but because these designations continue in the literature they have been added to our table; TT=20.

ENCODED SUBTYPES ( tt ) FOR NON-EXPLODING STARS:

 Code       Subtype

ENCODED SUBTYPES ( tt ) FOR NOVAE AND SUPERNOVAE:

 Code   Nova Class            Code   SN Class                          

Table 2.  Mapping  of LL luminosity classes

Class            Code        Class            Code     Class                Code                  

Notes:

1.  Boldface are “base” classes, to which plain font classes are considered aliases.
2.  Ignore “–“ and “+” as in Va- , Va + . Retain for 1a +
3. ‘esd’ is used as a luminosity class for F, G, and K stars but as a peculiarity for M ,L, and T stars. In both cases it immediately precedes the spectral type.

Table 3. Mapping of P 1 P 2 P 3 P 4  spectral peculiarities

Table of “Global ” Peculiarities P 1  and P 2   (except for novae, CV, supernovae)

Code    Pec string                Description

NOTES ON “GLOBAL” PECULIARITIES (P1P2):

1. If two or more global peculiarities are present in the classification string, only the two with the lowest values in this table are selected.
2. If one global peculiarity is present, its value is assigned to P1 and P2 is given the value 0.
3. The values of two nonzero global peculiarities will be mapped to P1 and P2 in order of their values in this table (i.e. P1 < P2). The exception is that if “p” and “e” both appear they retain their original classification order.

4.  For composite spectra the following rules apply:

      a)  TT.tt.LL.P1P2 codes refer to the primary’s spectrum, and P1=1.

      b)  P3P4 refer to the spectral type of the secondary’s spectrum.

Table of Peculiarities P3, P4 determined by TT Spectral types

Wolf-Rayet Stars  (TT = 51-55)                          

 P3   Pec          Description                                            P4    Pec       Description

Types OB  (also OB, sdB, sdO,sDA; TT = 10,11, 31, 32, 33, 56)        

P3     Pec            Description                              P4       Pec                    Description

Note to previous table:

1. For O, B, OB, sdO, sdB stars, C, N peculiarities may immediately follow the spectral type, e.g. “OC9 V”.
2. These peculiarities strings and others in the following P3P4 tables may be denoted in different but generally obvious ways by some classifiers, e.g. “m” may be “metallic,” etc.
3. The “He” anomaly is recognized for B stars. In rare cases when “He” precedes type A, these characters are ignored.

Types AF (also sdF;  TT = 12, 13)                                          

P3     Pec           Description                               P4     Pec                     Description

Note:

1. The P4=3 “Fe-“ anomaly is triggered automatically for type sdF, as for metal-weak stars.

  Types  GK (also sdG, sdK; TT = 14, 15)

 P3    Pec             Description                     P4        Pec            Description        

Note:

1. The P4=5 “Fe-“ anomaly is triggered for the sdG, sdK types, as for metal-weak  starrs.

  Types MLT (TT = 16-18)

  P3     Pec             Description                               P4     Pec    Description      

White Dwarfs (“D” types TT = 40-49)

P3, P4    Peculiarity       Description                            

Notes:  

1.   As noted by Gray & Corbally (2009): “To the primary type can be added one or more secondary composition symbols

     (A, B, C, O, Z, or Q), indicating a trace of an element defined as for the primary ones [spectral types].” These

     compositional symbols as well as the P and d designations are also defined In the table.

2.   The same symbol may not be used for both spectral type and compositional purposes, e.g. “DAA” is not used.

 Type C* (Carbon Stars, TT = 20-25)                  

 P3  Pec     Description                         P4  Pec   Description    

Type S (S Stars, TT = 26)    

 P3         Pec                        Description                        P4      Pec             Description      

Notes affecting C and S star peculiarities:

1) There are two possible “peculiarity triggers for TT=26 (S and related) stars:  

             a) “SC” is a spectral type that triggers an SC anomaly, namely P3 = 4.

             b) “MS” is a spectral type that triggers P3=1.

2)  “MS” in the C and S star tables has two different meanings, as follows:

a) for C stars it refers to the presence of Merrill-Sanford (Si-C-C) bands; typically “MS”       occurs at the end of  a classification string.

b) for S stars it refers to a marginal S star.