# HD 25558

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**HD 25558**, also known as **V1133 Tauri** and by its [Flamsteed designation](/source/Flamsteed_designation) **40 Tauri**, is a star located about 700 [light years](/source/Light_year) from the Earth, in the constellation [Taurus](/source/Taurus_(constellation)).[1] Its [apparent magnitude](/source/Apparent_magnitude) is about 5.3,[2] making it faintly visible to the [naked eye](/source/Naked_eye) of an observer far from [city lights](/source/Light_pollution). It is a variable star, ranging in brightness from *[Hipparcos](/source/Hipparcos)* magnitude 5.28 to 5.32 over a period of 1.53232423 days.[3]

In 1998, HD 25558 was discovered to be a variable star by Christoffel Waelkens *et al.* who analyzed the *Hipparcos* photometric data for hundreds of stars, and classified HD 25558 as a [slowly pulsating B star](/source/Slowly_pulsating_B_star) with a period of 1.53 days.[4]

Beginning in 2008, HD 25558 was the subject of an observing campaign by Ádám Sódor *et al.* who gathered data collected from 17 observatories on the ground and in space. This star was chosen for the project because it is relatively bright, located near the [celestial equator](/source/Celestial_equator) (and thus observable from almost anywhere on Earth), and the slow rotation indicated in earlier studies would simplify the interpretation of [spectra](/source/Astronomical_spectroscopy#Optical_spectroscopy). The investigators concluded that HD 25558 is a [spectroscopic binary](/source/Spectroscopic_binary) with a period of about 8.9 years, but not enough data was available to derive a full description of the orbit. Both components of the binary show detectable stellar pulsations. The primary star rotates with a period of about 6 days, and the secondary rotates in just 1.2 days. The primary has no detectable magnetic field, but the secondary's field strength is at least a few hundred [gauss](/source/Gauss_(unit)). The dominant 1.53 day pulsation period arises from the primary star and those pulsations were coherent over the 20 year period spanned by the data used in the study.[5]

## References

1. Ducati, J. R. (2002). ["VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system"](https://cdsarc.cds.unistra.fr/viz-bin/cat/II/237#/browse). *Vizier Online Data Catalog*. **2237**. Strasbourg astronomical Data Center. [Bibcode:2002yCat.2237....0D](https://ui.adsabs.harvard.edu/abs/2002yCat.2237....0D). Retrieved 17 January 2023.

1. ["V1133 Tau"](https://www.aavso.org/vsx/index.php?view=detail.top&oid=36150). *International Variable Star Index*. AAVSO. Retrieved 17 January 2023.

1. Waelkens, C.; Aerts, C.; Kestens, E.; Grenon, M.; Eyer, L. (February 1998). "Study of an unbiased sample of B stars observed with Hipparcos: the discovery of a large amount of new slowly pulsating B stars". *Astronomy and Astrophysics*. **330**: 215–221. [Bibcode:1998A&A...330..215W](https://ui.adsabs.harvard.edu/abs/1998A%26A...330..215W)

1. Sódor, Á.; De Cat, P.; Wright, D. J.; Neiner, C.; Briquet, M.; Lampens, P.; Dukes, R. J.; Henry, G. W.; Williamson, M. H.; Brunsden, E.; Pollard, K. R.; Cottrell, P. L.; Maisonneuve, F.; Kilmartin, P. M.; Matthews, J.; Kallinger, T.; Beck, P. G.; Kambe, E.; Engelbrecht, C. A.; Czanik, R. J.; Yang, S.; Hashimoto, O.; Honda, S.; Fu, J. N.; Castanheira, B.; Lehmann, H.; Bognár, Zs.; Behara, N.; Scaringi, S.; Van Winckel, H.; Menu, J.; Lobel, A.; Mathias, P.; Saesen, S.; Vučković, M.; the MiMeS collaboration (March 2014). "Extensive study of HD 25558, a long-period double-lined binary with two SPB components". *Monthly Notices of the Royal Astronomical Society*. **438** (4): 3535–3556. [arXiv:1312.6307](https://arxiv.org/abs/1312.6307). [Bibcode:2014MNRAS.438.3535S](https://ui.adsabs.harvard.edu/abs/2014MNRAS.438.3535S). [doi:10.1093/mnras/stt2466](https://doi.org/10.1093/mnras/stt2466)

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