next previous
Up: The classification of

3. Classification of 10 Å spectra

Drilling (1996) discussed the classification of the spectra of hot subdwarfs of 1.5 to 10 Å resolution and has identified 8 distinct classes, all of which had been previously defined in the literature. The spectra of ALL hot subdwarfs classified to date fit into one of these 8 classes which can be arranged in a two-parameter sequence of HeI/HeII versus He/H. Some duplicity of nomenclature exists, which Drilling sought to rationalise with a provisional scheme which is amplified here.

(smallest HeII/HeI). "Stars with colours corresponding to those of a B star and in which the Balmer lines are abnormally broad for the colour as compared with Pop. I main-sequence stars. Some, but not all, subdwarf B stars have HeI lines that are weak for their colour'' (Sargent & Searle 1968). Closer examination suggests that there is little to distinguish classes sdB2 and sdB3 quantitatively. In terms of our classification lines, both classes fulfil the criterion that HeI 4471 is present but weaker than Htex2html_wrap_inline1957.
(intermediate HeII/HeI)
(largest HeII/HeI)

The two-dimensional sequence is illustrated schematically in Fig. 1 (click here). It should be noted that the Green et al. (1986) classifications refer to 10 Å resolution spectra. It should also be noted that this spectral classification system remains incomplete after more than a decade of use. Standard stars observed at a specified resolution and S/N have still to be established. In the following, we shall adopt the Drilling notation to refer to 10 Å classifications.


Object Green Moehler Us
et al. et al.
PG0902+058 sdO(D) sdO6:He3
PG0909+276 sdO(A) sdO7:He1
PG0921+311 sdO(B) sdO7:He3
HS1000+4704 sdO6:He2
PG1127+019 sdO(D) sdO6:He4
PG1230+067 sdO(B) sdO6:He3
TON107 sdO(D) sdO7:He2
PG1413+113 sdO(D) sdO6:He4
PG1415+492 sdO(D) sdO9:He4
PG1437+727 sdO(D) sdO7?:He3tex2html_wrap_inline1923
PG1441+407 sdO(D) sdO5:He4
PG1526+440 sdO(D) sdO7:He2
PG1544+488 sdO(D) He-sdB sdO9:He4
PG1552+464 sdO(D) DBA
PG1554+408 sdO(D) sdO7:He4
PG1559+222 sdO(D) sdO7:He3
PG1600+171 sdO(D) sdO5:He4
PG1607+173 sdO(A) sdB:He2
PG1615+413 sdO(D) sdO8:He3
PG1629+466 sdO(D) sdO8:He3
PG1648+315 sdO(D) sdO8:He2
PG1658+273 sdO(D) sdO7:He4
PG1715+273 sdO(D) sdO7:He3
HS1843+6343 sdO8:He4
LS IV-14 116 sdO7:He1
PG2215+151 sdO(C) sdO6:He4
Table 2: Classification of "helium-rich'' subdwarfs

tex2html_wrap_inline1923 4686/4713 not measured.

next previous
Up: The classification of

Copyright by the European Southern Observatory (ESO)