Shell Star
A hot main-sequence star, usually of spectral class B-F, whose spectrum shows bright emission lines presumed to be due to a gaseous ring or shell surrounding the star.
Shock Wave ...
Shell Star
A type of star which is believed to be surrounded by a thin envelope of gas, which is often indicated by bright emission lines in its spectrum.
In shell stars, for instance in 48 Lib, sometimes one can see up to n = 41 (Merrill and Sanford 1944), although admittedly this is an extreme case. The narrowness of the lines indicates that the lines are formed in an extremely low-density medium.
To be that high, the star's rotation axis must be nearly perpendicular to the line of sight, which is consistent with 48 Lib's special Be-star status as a "shell star.
It is also classified as a "shell star" because it is surrounded by a shell of mostly hydrogen gas. The star may have about 1.75 times Sol's mass, 1.4 times its diameter, and 8.7 times its luminosity.
8A Lac is a BE variable (shell star) with unknown range and a period of about 16 to 18 years.
12 Lac (DD Lac) is a beta Cep type variable: 5.16 to 5.28 every 4h38m3.2s.
Deep Sky Objects: ...
The brightest star in Pictor is [6682] alpha Pictoris, an A-type star 660 million years old, lying 99 light-years from Earth. It is classified as a fast-rotating shell star, one surrounded by a disc of gas at the equator, ...
Shell star features
v
Variable spectral feature (also "var")
w
Weak lines (also "wl" & "wk")
d Del
Type A and F giants with weak calcium H and K lines, as in prototype Delta Delphini
d Sct ...
shell starv
variable spectral feature (also "var")w
weak lines (also "wl" & "wk)d Del
type A and F giants with weak calcium H and K lines, as in prototype ^delta Delphini//gr 310.8647916, 15.074694^d Sct ...
 See also: Light, Magnitude, Period, Solar, Distance
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