Low Resolution Spectroscopy Of Be Type Stars
Jim Ferreira, Livermore CA   bakerst@comcast.net

Be stars [B type stars that have emission lines in their spectrum] are particularly fascinating.  Like most B type stars their surface temperature falls between 10,000K and 30,000K, but they are in a luminosity class of III to V so they are not supergiant stars.  Be stars are rapidly rotating stars [up to several hundred kilometers/second] with circumstellar disks extending out from their equators.  The disk is a decretion disk, which means it is made up of ejected star material not material incoming from a neighboring star.  The disk is predominantly Hydrogen with some Helium.  Since most of the B type star light is in the Ultra Violet, the Hydrogen and Helium in the decretion disk is heavily ionized.  The most prominent lines in the visual portion of the spectrum are H-alpha and H-beta, but He emission lines are also present and in some cases detectable with modest amateur equipment.  The resulting spectrum is an overlay of the decretion disk emission lines on the stars photosphere absorption line continuum.


Be stars have been studied spectroscopically since the mid 1800s, however, they are still poorly understood.  For example; the mechanism for the formation of the decretion disk is not as simple as centrifugal force, as the rapid rotation might immediately suggest.  To add to the mix; a third of all known Be stars are binary systems.

80mm f/6 APO refractor, a Star Analyser 100 transmission grating, an Imaging Source DMK41 monochrome digital video camera or Atik ATK16 CCD camera, and, RSpec spectral recording / analysis software.

The Star Analyser 100 is a 100 line/mm transmission grating sandwiched between optical quality glass windows and mounted in a standard 1 1/4" screw-in filter housing.  The grating is mounted in a 5 position filter wheel ahead of the camera.  With the grating and camera placed in the focuser of the telescope, the entire system becomes a slit'less low resolution spectrograph, easily capable of resolving the prominent absorption and emission spectral lines of stars down to 11th magnitude or fainter.

HD45542 spectra plot
HD45542, Nu Gem, B6IIIe, 4.15 magnitude, spectra normalized and annotated, 80mm f/6, SA100

HD45995 spectra plot
HD45995, B2Vne, 6.14 magnitude, spectra normalized and annotated, 80mm f/6, SA100

Alcyone spectre plot
Alcyone spectra plot, normalized and annotated

Beta Lyrae spectra plot
Beta Lyrae spectra plot, normalized and annotated

HD29866 spectra plot
HD29866 spectra plot, normalized and annotated

HD32188 spectra plot
HD32188 spectra plot, normalized and annotated

P-Cygni spectra plot
P Cygni spectra plot, normalized and annotated

2 Per & phi And
2 Persei and Phi Andromedae plotted spectre

10 Cas
10 Cas plotted spectre

12 Aur spectre
12 Aur plotted spectre

48 Per spectra plot
48 Persei plotted spectra and expanded raw spectra

B-A type star spectre comparison
HD27742, 53 Tau, 56 Tau plotted spectre

gamma Cas spectrum
Gamma Cas plotted spectra

omi Cas spectrum
Omi Cas plotted spectra

phi Per spectrum
Phi Per plotted spectra with expanded raw spectra

Pleiades spectra
Pleiades cluster expanded raw spectre of 6 stars, annotated

Pleiades spectre plots
Pleiades cluster spectre plotted - note that Alcyone shows slight H-alpha line emission

psi Per spectra plot
Psi Persei plotted spectre with expanded raw spectra

psi Per raw spectrum annotated
Psi Persei raw spectra with zero order

Beta-2 Cyg, 20 Oct. 2013
Beta 2 Cygni spectra

9 Cygni, 20 Oct. 2013
9 Cygni, AO V spectra

BD+56 727 Per, 23 Oct. 2013
BD+56 727, a B5e type star

V2139 Cyg, 21 Oct. 2013
V2139 Cygni spectra

Beta Lyrae, 21 Oct. 2013
Beta Lyrae spectra, Ha emission line along with prominent He lines

V2144 Cyg, 21 Oct. 2013
V2144 Cygni spectra

P Cygni, 06 Oct. 2013
P Cygni spectrra