Mercury-manganese star

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A mercury-manganese star is a type of chemically peculiar star with a prominent spectral line at 398.4 nm, due to absorption from ionized mercury.[1] These stars are of spectral type B8, B9, or A0, corresponding to surface temperatures between about 10,000 and 15,000 K, with two distinctive characteristics:

Their rotation is relatively slow, and as a consequence their atmosphere is relatively calm. It is thought, but has not been proven, that some types of atoms sink under the force of gravity, while others are lifted towards the exterior of the star by radiation pressure, making an heterogeneous atmosphere.[2]

The following table includes the brightest stars in this group.

Name[3] Bayer or Flamsteed designation Spectral type[3] Apparent visual magnitude[3]
Alpheratz α Andromedae B8IVmnp 2.06
Gienah Corvi γ Corvi B8III 2.59
Maia 20 Tauri B8III 3.87
χ Lupi B9IV 3.96
Muliphein[4] γ Canis Majoris B8II 4.10
φ Herculis B9mnp 4.23
π1 Bootis B9p 4.91
ι Coronae Borealis A0p 4.98
κ Cancri A B8IIImnp 5.24
Dabih Minor[5] β Capricorni B B9.5III/IV 6.10


  1. ^ Mercury-manganese star. The Internet Encyclopedia of Science, David Darling. Accessed on line August 14, 2008.
  2. ^ Michaud, Georges (May 1970). "Diffusion Processes in Peculiar A Stars". Astrophysical Journal 160: 641–658. Bibcode:1970ApJ...160..641M. doi:10.1086/150459. 
  3. ^ a b c Names, spectral types and apparent magnitudes taken from SIMBAD, except as noted.
  4. ^ Muliphein, Stars, Jim Kaler. Accessed on line August 14, 2008.
  5. ^ Dabih, Stars, Jim Kaler. Accessed on line August 14, 2008.