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        

 --

 00

 Unknown

 Y

 19

 For future cool brown dwarfs

 O, OC, ON

 10

 O type

 C

 20

 Undifferentiated C stars

 B, BC,BN

 11

 B type

 CR

 21

 R carbon stars

 A

 12

 A type

 CN

 22

 N carbon stars

 F, sdF

 13

 F type

 CJ

 23

 J carbon stars

 G, sdG

 14

 G type

 CH

 24

 CH stars

 K, sdK

 15

 K type

 CHd

 25

 Hydrogen deficient carbon stars

 M

 16

 M type

 S, SC, MS

 26

 S-type stars

 L

 17

 L type

 CV

 27

 Novae

 T

 18

 T type

 ??

 28

 Open for future


    Sp           Code  Description                     Sp           Code   Description        

 SN

 29

 Supernovae

 DQ

 46

 white dwarfs with carbon lines

 sd

 30

 subdwarf without type

 PG

 47

 PG1159 stars

 sdO, sdON,  sdOC, sdOB

 31

 O-type subdwarfs

 D?

 48

 reserved for new WD type

 sdB, sdBN,  sdBC

 32

 B-type subdwarfs

 D??

 49

 reserved for new WD type

 sdA

 33

 A-type subdwarfs

 NS

 50

 neutron stars

 D, WD, wd

 40

 white dwarf without type

 WR

 51

 Wolf Rayet without type

 DA

 41

 white dwarf with hydrogen lines

 WN

 52

 N-sequence Wolf Rayet

 DB

 42

 white dwarf with  He I lines

 WC

 53

 C-sequence Wolf Rayet

 DC

 43

 white dwarfs with continuous spectrum

 WO

 54

 O-sequence Wolf Rayet

 DO

 44

 white dwarf with He II lines

 55

 Open for new Wolf Rayet type

 DZ, DF, DG,  DK, DM, DX

 45

 White dwarf with metal lines

 OB, OBN,  OBC

 56

 OB stars

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

  00

 Unknown

  10-19

 0-9

  20

 9.5-9.9 for hot stars (TT=10, 11, 31, 32, 52-54, 56)

 10 for other spectral types (e.g. A-M)

ENCODED SUBTYPES ( tt ) FOR NOVAE AND SUPERNOVAE:

 Code   Nova Class            Code   SN Class                          

 00

 Unknown

 00

 Unknown

 10

 He/N

 10

 Ia

 11

 Fe IIn

 11

 Ib

 12

 Fe IIb

 12

 Ic

 13

 Ib/Ic

 14

 II

 15

 IIb

 16

 IIn

Table 2.  Mapping  of LL luminosity classes

Class            Code        Class            Code     Class                Code                  

 Unknown

 00

 IIa

 18

 IV, IVab, III-V, III/V

 27

 0

 10

 II, IIab, I-III, I/III

 19

 IVb

 28

 0-Ia, Ia0, Ia-0, Ia+

 11

 IIb

 20

 IV/V, IV-V, IVa-V,  IVa/V

 29

 Ia, Ia0-Ia, Ia0/Ia

 12

 II-III, II/III, IIb-III,  IIb-IIIa

 21

 Va, V, Va+, Va-, d,  Va-V, Vab

 30

 Ia-Iab, Ia/Iab, Ia-ab

 13

 IIIa

 22

 Vb, Vz, Vb-Vz

 31

 Iab, I, c

 14

 III, IIIa-III, IIIab,  III-IIIa, g

 23

 VI

 32

 Iab-Ib, Iab/Ib, Iab-b

 15

 IIIb, III-IIIb

 24

 VII, esd

 33

 Ib, I-II, I/II

 16

 III-IV, IIIb-IV,  IIIb-IVa, III/IV

 25

 VIII

 34

 Ib-II, Ib-IIa, Ib/II

 17

 IVa

 26

 IX

 35

 

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

 0

 Unspecified

 1

 +

 Composite  (P3,P4 describe secondary)

 2

 p, pec

 Peculiarity

 3

 e, em

 Emission lines

 4

 [e], q

 Forbidden line emission

 5

 v, var

 Variable

 6

 s

 Sharp lines

 7

 n, nn

 Broad lines

 8

 Open for future

 9

 Open for future

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

 0

 No peculiarity

 0

 

 No peculiarity

 1

 b

 broad-lined

 2

 (h)

 weak hydrogen

 3

 h

 hydrogen emis. present

 4

 ha

 hydrogen emis + abs present

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

P3     Pec            Description                              P4       Pec                    Description

 0

 No peculiarity

 0  

 No peculiarity

 1

 He

 He strong or He weak

 1

 PCyg , w

 wind

 2

 HgMn, Hg, Mn

 Hg and/or Mn

 2

 f

 emission line class

 3

 Si, SiSr

 Si or Sr strong

 3

 f+

 emission line class

 4

 SiCrEu, SiCr

 SiCrEu or SiCr strong

 4

 f*

 emission line class

 5

 SrCrEu

 SrCrEu strong

 5

 Fe+, Fe, m+, m

 metal strong

 6

 SiEu

 SiEu strong

 6

 Fe-, m-, wk

 metal weak

 7

 Cr

 Cr strong

 7

 sh, shell

 shell lines

 8

 Sr, SrSi

 Sr or SrSi strong

 8

 C, N

 CN peculiarities are

 triggered by  above TT’s

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

 0

 No peculiarity

 0          

 No peculiarity

 1

 HgMn, Mn, Hg

 Hg and/or Mn strong

 1

 P Cyg

 P Cygni  profiles

 2

 Si

 Si strong

 2

 lam Boo, l Boo, lambda Boo

 lambda Boo star

 3

 SiCrEu

 SiCrEu strong

 3

 Fe-, m-, w, wk

 metal-weak or subwarf

 4

 SrCrEu

 SrCrEu strong

 4

 Fe+, m+

 metal-strong

 5

 SiEu

 SiEu strong

 5

 m

 metallic lined

 6

 Cr

 Cr strong

 6

 sh, shell

 shell lines

 7

 Sr

 Sr strong

 7

 Ba

 Ba dwarf

 8

rho Pup

rho Puppis star

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        

 0

 No peculiarity

 0

 No pecuiarity

 1

 CN+, CN

 strong CN

 1

 Ba+, Ba

 barium star

 2

 CN-

 weak CN

 2

 Ba Fe+

 metal-strong barium star

 3

 CH+, CH

 strong CH

 3

 Ba Fe-

 metal-weak barium star

 4

 CH-

 weak CH

 4

 Fe+, m+

 metal-strong

 5

 CN+ CH+

 (self-explanatory)

 5

 Fe-, m-

 metal-weak or subdwarf

 6

 CN+CH-

 (self-explanatory)

 6

 C2

 strong Swan bands

 7

 CN- CH+

 (self-explanatory)

 7

 Ba C2

 Ba star, strong Swan bands

 8

 CN- CH-

 (self-explanatory)

 8

 Ca

 calcium peculiarity

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      

 0

 No peculiarity

 0

No peculiarity

 1

 Ba+, Ba

 Ba strong

 1

 Fe+

 Fe strong

 2

 sd

 subdwarf

 2

 Fe-

 Fe weak

 3

 esd, usd  

 Extreme or ultra subdwarf

White Dwarfs (“D” types TT = 40-49)

P3, P4    Peculiarity       Description                            

 0

No peculiarity

 1

 A

trace H I lines

 2

 B

trace He I lines

 3

 O

trace He II lines

 4

 Q

trace carbon lines

 5

 Z

trace metal lines

 6

 H

magnetic, w/o visible polarization

 7

 P

magnetic with visible polarization

 8

 d

dust

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    

 0

No peculiarity

 0

No peculiarity

 1

 MS

Merrill-Sanford bands

 1

 j

enhanced C13

 2

 dC

Dwarf carbon star

 

Type S (S Stars, TT = 26)    

 P3         Pec                        Description                        P4      Pec             Description      

 0

No peculiarity

No peculiarity

 0

No peculiarity

 1

MS

MS (marginal S-type) stars

 1

Tc+, Tc

Tc-strong

 2

/1, /2, /3

CO index= 1,2 or 3

 2

Tc-

Tc-weak

 3

/4, /5, /6

CO index =4, 5 or 6

 4

SC, /7, /8, /9, /10

CO index =7,8,9 or 10

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.