A slowly pulsating B-type star (SPB), formerly known as a 53 Persei variable, is a type of pulsating variable star. They may also be termed a long-period pulsating B star (LPB). As the name implies, they are main-sequence stars of spectral type B2 to B9 (3 to 9 times as massive as the Sun) that pulsate with periods between approximately half a day and five days, however within this most member stars have been found to have multiple periods of oscillations. They display variability both in their light emission and in their spectral line profile. The variations in magnitude are generally smaller than 0.1 magnitudes, making it quite hard to observe variability with the naked eye in most cases. The variability increases with decreasing wavelength, thus they are more obviously variable in ultraviolet spectrum than visible light. Their pulsations are non-radial, that is, they vary in shape rather than volume; different parts of the star are expanding and contracting simultaneously.
These stars were first identified as a group and named by astronomers Christoffel Waelkens and Fredy Rufener in 1985 while looking for and analysing variability in hot blue stars. Improvements in photometry had made finding smaller changes in magnitude easier, and they had found that a high percentage of hot stars were intrinsically variable. They referred to them as 53 Persei stars after the prototype 53 Persei. Ten had been discovered by 1993, though Waelkens was unsure if the prototype was actually a member and recommended referring to the group as slowly pulsating B (SPB) stars. The General Catalogue of Variable Stars uses the acronym LPB for "comparatively long-period pulsating B stars (periods exceeding one day)", although this terminology is rarely seen elsewhere.
The similar Beta Cephei variables have shorter periods and have p-mode pulsations, while the SPB stars show g-mode pulsations. By 2007, 51 SPB stars had been confirmed with another 65 stars possible members. Six stars, namely Iota Herculis, 53 Piscium, Nu Eridani, Gamma Pegasi, HD 13745 (V354 Persei) and 53 Arietis had been found to exhibit both Beta Cephei and SPB variability.
List The following list contains selected slowly pulsating B-type stars that are of interest to amateur or professional astronomy. Unless otherwise noted, the given magnitudes are in the V-band. Star Averagemagnitude Spectraltype Period(in days) Distance(in parsecs) Gamma Pegasi (Algenib) 2.84 B2IV Also a Beta Cephei variable 113 Zeta Pegasi (Homam) 3.41 B8V 0.96 63 Omicron Velorum 3.63 B3IV 2.80 151 Iota Herculis (Tianbang) 3.80 B3IV 3.49 139 Gamma Muscae 3.88 B3V 2.73 100 Tau Herculis (Asuusiha) 3.90 B5IV 1.25 94 Nu Eridani 3.92 B2III 207 Mu Eridani 4.00 B5IV Also an Algol variable 160 Rho Lupi 4.05 B5V 0.45 97 HD 105382 4.47 B6IIIe 1.30 134 Tau8 Eridani 4.63 B5V 0.86 116 Nu Pavonis 4.64 B7III 0.86 135 HY Velorum 4.82 B3IV 1.55 148 HD 131120 5.01 B7IIIp 1.57 151 HR 5780 5.17 B5V 1.26 122 3 Vulpeculae 5.19 B6III 1.26 120 12 Lacertae 5.23 B2III 411 WZ Columbae 5.29 B9.5V 1.38 131 V575 Persei 5.30 B5V 166 Xi Octantis 5.31 B6V 1.77 151 HD 25558 5.33 B5V 1.53 196 25 Serpentis 5.39 B8III 0.87 188 GU Eridani 5.43 B5IV 1.87 200 HR 3600 5.54 B5V 132 KL Velorum 5.56 B8 2.91 212 HD 1976 5.58 B5IV 1.06 307 V450 Carinae 5.64 B9III+B8V 1.65 151 EO Leonis 5.66 B2V 2.78 289 V539 Arae 5.71 B2/B3Vnn 303 HD 128207 5.73 B8V 0.48 147 HD 27563 5.84 B5III 3.80 242 26 Canis Majoris 5.90 B2IV/V 2.73 257 16 Monocerotis 5.92 B3V 1.94 263 V335 Velorum 5.93 B.25III 3.76 704 V869 Centauri 5.96 B9IV 1.46 251 V363 Puppis 5.97 B2.5V+B9V 0.70 278 V433 Aurigae 5.99 B2IV-V 4.64 325 V1141 Tauri 6.00 B8IV-V 0.62 170 HD 206540 6.05 B5IV 1.39 215 HR 1397 6.07 B6IV 1.26 198 V576 Persei 6.09 B7V 0.84 159 V2100 Cygni 6.11 B5III 2.61 239 HR 2517 6.15 B2.5III 2.56 2500 V492 Carinae 6.18 B3V 1.06 370 HR 1328 6.20 B9V 0.38 121 V4199 Sagittarii 6.26 B5III 1.24 240 HR 3562 6.26 B3IV 370 V4198 Sagittarii 6.28 B8V 1.19 186 V377 Lacertae 6.32 B7III 2.62 305 DY Chamaeleontis 6.32 B8IV 0.97 236 HR 2680 6.33 B3V 258 V473 Carinae 6.35 B5V 0.95 218 V405 Lacertae 6.37 B5V 1.02 170 HD 34798 6.39 B5Vs 1.28 263 HD 176582 6.40 B5V 1.58 292 V1377 Orionis 6.41 B3III 1.01 476 HR 8768 6.42 B2V 3.25 326 GY Eridani 6.42 B3V 1.33 220 QZ Velorum 6.49 B1IIIn 1.03 813 V550 Lyrae 6.49 B3V 1.69 379 HD 208727 6.50 B8V 0.32 330 HD 43317 6.61 B3IV 369 23 Sextantis 6.64 B3.2IV 769 HD 33331 6.90 B5III 1.15 296 HD 163868 7.36 B5Ve Also a shell star 588 HD 163899 8.30 B2Ib/II 23.20 HD 50209 8.36 B9Ve 0.67 694
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