Regular intrinsic brightness variations observed in many stars are caused by pulsations. These pulsations provide information on the global and structural parameters of the star. The pulsation periods range from seconds to years, depending on the compactness of the star and properties of the matter that forms its outer layers. Here, we report the discovery of more than a dozen previously unknown short-period variable stars: blue large-amplitude pulsators. These objects show very regular brightness variations with periods in the range of 20–40 min and amplitudes of 0.2–0.4 mag in the optical passbands. The phased light curves have a characteristic sawtooth shape, similar to the shape of classical Cepheids and RR Lyrae-type stars pulsating in the fundamental mode. The objects are significantly bluer than main-sequence stars observed in the same fields, which indicates that all of them are hot stars. Follow-up spectroscopy confirms a high surface temperature of about 30,000 K. Temperature and colour changes over the cycle prove the pulsational nature of the variables. However, large-amplitude pulsations at such short periods are not observed in any known type of stars, including hot objects. Long-term photometric observations show that the variable stars are very stable over time. Derived rates of period change are of the order of 10−7 per year and, in most cases, they are positive. According to pulsation theory, such large-amplitude oscillations may occur in evolved low-mass stars that have inflated helium-enriched envelopes. The evolutionary path that could lead to such stellar configurations remains unknown.
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Udalski, A., Szymański, M. K. & Szymański, G. OGLE-IV: fourth phase of the Optical Gravitational Lensing Experiment. Acta Astron. 65, 1–38 (2015).
Soszyński, I. et al. The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. XV. Long-period variables in the galactic bulge. Acta Astron. 63, 21–36 (2013).
Soszyński, I. et al. Over 38000 RR Lyrae stars in the OGLE galactic bulge fields. Acta Astron. 64, 177–196 (2014).
Soszyński, I. et al. The OGLE collection of variable stars. Classical Cepheids in the Magellanic System. Acta Astron. 65, 297–312 (2015).
Soszyński, I. et al. The OGLE collection of variable stars. Over 450000 eclipsing and ellipsoidal binary systems toward the galactic bulge. Acta Astron. 66, 405–420 (2016).
Mróz, P. et al. One thousand new dwarf novae from the OGLE survey. Acta Astron. 65, 313–328 (2015).
Pietrukowicz, P. et al. Large variety of new pulsating stars in the OGLE-III galactic disk fields. Acta Astron. 63, 379–404 (2013).
Rodríguez, E., López-González, M. J. & López de Coca, P . A revised catalogue of delta Sct stars. Astron. Astrophys. Suppl. 144, 469 (2000).
Pietrukowicz, P. et al. A low-resolution spectroscopic exploration of puzzling OGLE variable stars. Acta Astron. 63, 63–79 (2015).
Stankov, A. & Handler, G. Catalog of galactic Beta Cephei stars. Astrophys. J. Suppl. Ser. 158, 193–216 (2005).
Pigulski, A. & Pojmański, G. β Cephei stars in the ASAS-3 data. I. Long-term variations of periods and amplitudes. Astron. Astrophys. 477, 907–915 (2008).
Pigulski, A. & Pojmański, G. β Cephei stars in the ASAS-3 data. II. 103 new β Cephei stars and a discussion of low-frequency modes. Astron. Astrophys. 477, 917–929 (2008).
De Cat, P. Observational asteroseismology of slowly pulsating B stars. Commun. Astroseismol. 150, 167–174 (2007).
Heber, U. Hot subluminous stars. Publ. Astron. Soc. Pac. 128, 082001 (2016).
Woolf, V. M. & Jeffery, C. S. Temperature and gravity of the pulsating extreme helium star LSS 3184 (BX Cir) through its pulsation cycle. Astron. Astrophys. 395, 535–540 (2002).
Jeffery, C. S. et al. Subaru and Swift observations of V652 Herculis: resolving the photospheric pulsation. Mon. Not. R. Astron. Soc. 447, 2836–2851 (2015).
Christensen-Dalsgaard, J. in Proc. SOHO 14 / GONG 2004 Workshop (ESA SP-559): Helio- and Asteroseismology: Towards a Golden Future (ed. Danesy, D.) 1–33 (New Haven, 2004).
Eyer, L. & Mowlavi, N. Variable stars across the observational HR diagram. J. Phys. Conf. Ser. 118, 012010 (2008).
Catelan, M. & Smith, H. A. Pulsating Stars (Wiley, 2015).
Pamyatnykh, A. A. Pulsational instability domains in the upper main sequence. Acta Astron. 49, 119–148 (1999).
Edelmann, H. et al. Spectral analysis of sdB stars from the Hamburg Quasar Survey. Astron. Astrophys. 400, 939 (2003).
Randall, S. K. et al. Pulsating hot O subdwarfs in ω Centauri: mapping a unique instability strip on the extreme horizontal branch. Astron. Astrophys. 589, A1 (2016).
Pietrinferni, A., Cassisi, S., Salaris, M. & Castelli, F. A large stellar evolution database for population synthesis studies. II. Stellar models and isochrones for an α-enhanced metal distribution. Astron. Astrophys. 642, 797–812 (2006).
Charpinet, S. et al. A driving mechanism for the newly discovered class of pulsating subdwarf B stars. Astrophys. J. 483, L123–L126 (1997).
Jeffery, C. S. & Saio, H. Radial pulsation as a function of hydrogen abundance. Mon. Not. R. Astron. Soc. 458, 1352–1373 (2016).
Nataf, D. M. et al. Reddening and extinction toward the Galactic Bulge from OGLE-III: the inner Milky Way’s RV ∼ 2.5 extinction curve. Astrophys. J. 769, 88 (2013)
Udalski, A. The Optical Gravitational Lensing Experiment: is interstellar extinction toward the galactic center anomalous? Astrophys. J. 590, 284–290 (2003)
Kieffer, T. F. & Bogdanović, T. Can star–disk collisions explain the missing red giants problem in the Galactic Center? Astrophys. J. 823, 155 (2016)
Han, Z., Podsiadlowski, P., Maxted, P. F. L., Marsh, T. R. & Ivanova, N. The origin of subdwarf B stars — I. The formation channels. Mon. Not. R. Astron. Soc. 336, 449 (2002)
Hall, P. D. & Jeffery, C. S. Hydrogen in hot subdwarfs formed by double helium white dwarf mergers. Mon. Not. R. Astron. Soc. 463, 2756 (2016)
Udalski, A., Szymański, M. K., Soszyński, I. & Poleski, R. The Optical Gravitational Lensing Experiment. Final reductions of the OGLE-III data. Acta Astron. 58, 69–87 (2008).
Woźniak, P. R. Difference image analysis of the OGLE-II bulge data. I. The method Acta Astron. 50, 421–450 (2000).
Soszyński, I. et al. Ultra-short-period binary systems in the OGLE fields toward the galactic bulge. Acta Astron. 65, 39–62 (2015).
Schwarzenberg-Czerny, A. Fast and statistically optimal period search in uneven sampled observations. Astrophys. J. 460, L107–L110 (1996).
Stetson, P. B. DAOPHOT — a computer program for crowded-field stellar photometry. Publ. Astron. Soc. Pac. 99, 191–222 (1987).
Lanz, T. & Hubeny, I. Non-LTE line-blanketed model atmospheres of hot stars. 2: Hot, metal-rich white dwarfs. Astrophys. J. 439, 905–916 (1995).
Blanchette, J.-P. et al. FUSE determination of abundances in long-period pulsating V1093 Her (PG 1716+426) Stars. Astrophys. J. 678, 1329–1341 (2008).
Saffer, R. A., Bergeron, P., Koester, D. & Liebert, J. Atmospheric parameters of field subdwarf B stars. Astrophys. J. 432, 351–366 (1993).
Latour, M., Fontaine, G., Green, E. M., Brassard, P. & Chayer, P. Improved determination of the atmospheric parameters of the pulsating sdB star Feige 48. Astrophys. J. 788, 65 (2014).
Paczyński, B. Envelopes of red supergiants. Acta Astron. 19, 1–22 (1969).
Iglesias, C. A. & Rogers, F. J. Updated OPAL opacities. Astron. Astrophys. 464, 943–953 (1996).
Dziembowski, W. Oscillations of giants and supergiants. Acta Astron. 27, 95–126 (1977).
We thank M. Kubiak and G. Pietrzyński, former members of the OGLE team, for their contribution to the collection of the OGLE photometric data over the past years. The OGLE project has received funding from the National Science Centre, Poland (grant number MAESTRO 2014/14/A/ST9/00121 to A.U.). M.L. acknowledges support from the Alexander von Humboldt Foundation. The Las Campanas Observatory, which hosts the Warsaw Telescope, Swope Telescope and Magellan Telescopes, is operated by the Carnegie Institution for Science. The Gemini Observatory is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the National Science Foundation (NSF) on behalf of the Gemini partnership: the NSF (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil).
The authors declare no competing financial interests.
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Pietrukowicz, P., Dziembowski, W., Latour, M. et al. Blue large-amplitude pulsators as a new class of variable stars. Nat Astron 1, 0166 (2017). https://doi.org/10.1038/s41550-017-0166
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