Bp and Ap stars

Bp and Ap stars is a group of B-type or A-type stars where some lines of one or several elements are abnormally enhanced. One can distinguish 3 subgroups:

1. Silicon stars. The enhanced lines are from the Si II at wavelenght 3856 A, 3862 A, 3954 A, 4128 A, 4130 A, 4200 A, 5041 A and 5056 A.

2. HgMn stars. The enhanced lines are from the Mn II at 4206 A and 4136 A and Hg II at 6149 A.

3. Late Ap-type stars. This subgroup contain stars in wich elements like Sr, Cr and Eu are enhanced (Sr II lines: 4077 and 4215 A, Cr II lines: 4111 A, 4171 A and 4233 A, Eu lines: 3919 A, 3930 A, 4129 A and 4205 A).

Many of this stars exhibit spectral variability. All the Ap stars have a strong magnetic field, except the manganese stars (Mn stars) where the field is very weak or non-existent. Because the magnetic field, Ap stars are good candidate for Doppler imagery of star surface (spots across the visible disk can produce changes in intensity and shapes of the spectral profiles). For this it is necessary to observe magnetically sensitive lines (Zeeman effect) like Fe II lines at 4924, 5018, and the couple ( 6147.7 - 6149.2 A)  for example.

A bright Ap/Bp stars list:

     HD         Star           R.A.        Dec.       Spec.       Mv

   358     Alpha And      00 h 08.4    29° 05     B9 HgMn      2.07
  1280     Theta And      00 h 17.1    38° 41     A2 SiSr      4.62
 10221     43 Cas         01 h 42.3    68° 03     A0 SiCr      5.57
 11502     Gamma Ari      01 h 53.5    19° 18     A1 SiCrSr    4.64
 12447                    02 h 02.0    02° 46     A2 SiSrCr    4.22
 14392     63 And         02 h 21.0    50° 09     B9 Si        5.57
 15089     Iota Cas       02 h 29.1    67° 24     A4 Sr        4.63
 19832     56 Ari         03 h 12.6    27° 15     B8 Si        5.78
 32549                    05 h 04.6    15° 24     B9 SiCr      4.68
 40312A    Theta Aur      05 h 59.7    37° 13     A0 Si        2.67
 51418     Nu Aur         05 h 51.5    39° 09     A0 HoDy      3.97
 62140     49 Cam         07 h 46.4    62° 50     A8 SrEu      6.47
 65339     53 Cam         08 h 01.7    60° 20     A3 SrEuCr    6.02
 74521     49 Cnc         08 h 44.7    10° 05     A1 SiEuCr    5.63
 89822                    10 h 24.1    65° 34     A0 SiHgSr    4.94
112185     Epsi Uma       12 h 54.0    55° 57     A1 CrEuMn    1.76
112413     Alpha Cvn      12 h 56.0    38° 19     A0 EuSiCr    2.89
118022                    13 h 34.1    03° 40     A2 CrEuSr    4.93
129174                    14 h 40.7    16° 25     B9 MnHg      4.94
137909A    Beta CrB       15 h 27.8    29° 06     A9 SrEuCr    3.90
143807                    16 h 01.4    29° 51     A0 MnHg      4.98
145389     Phi Her        16 h 08.7    44° 56     B9 MnHg      4.22
148112                    16 h 25.4    14° 02     A0 CrEu      4.57
152107A                   16 h 49.3    45° 59     A3 SrCrEu    4.83
17000A     Phi Dra        18 h 20.7    71° 20     A0 Si        4.42
176232     10 Aql         18 h 58.8    13° 54     A6 Sr        5.91
183056     4 Cyg          19 h 26.1    36° 19     B9 Si        5.18
201601     Gamma Equ      21 h 10.4    10° 07     A9 SrEu      4.70
220825                    23 h 26.9    01° 15     A1 CrSrEu    4.94