Near-infrared evidence for a sudden temperature increase in Eta Carinae

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dc.contributor.authorMehner, Andrea
dc.contributor.authorIshibashi, Kazunori
dc.contributor.authorWhitelock, Patricia
dc.contributor.authorNagayama, Takahiro
dc.contributor.authorFeast, Michael
dc.contributor.authorvan Wyk, Francois
dc.contributor.authorde Wit, Willem-Jan
dc.date.accessioned2021-10-07T12:56:19Z
dc.date.available2021-10-07T12:56:19Z
dc.date.issued2014
dc.description.abstractAims. Eta Car's ultra-violet, optical, and X-ray light curves and its spectrum suggest a physical change in its stellar wind over the last decade. It was proposed that the mass-loss rate decreased by a factor of about 2 in the last 15 years. We complement these recent results by investigating the past evolution and the current state of eta Car in the near-infrared (IR). Methods. We present JHKL photometry of eta Car obtained at SAAO Sutherland from 2004-2013 with the Mk II photometer at the 0.75-m telescope and JHKs photometry with SIRIUS at the 1.4-m IRSF telescope from 2012-2013. The near-IR light curves since 1972 are analyzed. Results. The long-term brightening trends in eta Car's JHKL light curves were discontinuous around the 1998 periastron passage. After 1998, the star shows excess emission above the extrapolated trend from earlier dates, foremost in J and H, and the blueward, cyclical progression in its near-IR colors is accelerated. The near-IR color evolution is strongly correlated with the periastron passages. After correcting for the secular trend we find that the color evolution matches an apparent increase in blackbody temperature of an optically thick near-IR emitting plasma component from about 3500 to 6000 K over the last 20 years. Conclusions. We suggest that the changing near-IR emission may be caused by variability in optically thick bremsstrahlung emission. Periastron passages play a key role in the observed excess near-IR emission after 1998 and the long-term color evolution. We thus propose as a hypothesis that angular momentum transfer (via tidal acceleration) during periastron passages leads to sudden changes in eta Car's atmosphere resulting in a long-term decrease in the mass-loss rate.
dc.identifier.apacitationMehner, A., Ishibashi, K., Whitelock, P., Nagayama, T., Feast, M., van Wyk, F., & de Wit, W. (2014). Near-infrared evidence for a sudden temperature increase in Eta Carinae. <i>Astronomy and Astrophysics</i>, 564(4), A14 - 177. http://hdl.handle.net/11427/34196en_ZA
dc.identifier.chicagocitationMehner, Andrea, Kazunori Ishibashi, Patricia Whitelock, Takahiro Nagayama, Michael Feast, Francois van Wyk, and Willem-Jan de Wit "Near-infrared evidence for a sudden temperature increase in Eta Carinae." <i>Astronomy and Astrophysics</i> 564, 4. (2014): A14 - 177. http://hdl.handle.net/11427/34196en_ZA
dc.identifier.citationMehner, A., Ishibashi, K., Whitelock, P., Nagayama, T., Feast, M., van Wyk, F. & de Wit, W. 2014. Near-infrared evidence for a sudden temperature increase in Eta Carinae. <i>Astronomy and Astrophysics.</i> 564(4):A14 - 177. http://hdl.handle.net/11427/34196en_ZA
dc.identifier.issn0004-6361
dc.identifier.issn1432-0746
dc.identifier.ris TY - Journal Article AU - Mehner, Andrea AU - Ishibashi, Kazunori AU - Whitelock, Patricia AU - Nagayama, Takahiro AU - Feast, Michael AU - van Wyk, Francois AU - de Wit, Willem-Jan AB - Aims. Eta Car's ultra-violet, optical, and X-ray light curves and its spectrum suggest a physical change in its stellar wind over the last decade. It was proposed that the mass-loss rate decreased by a factor of about 2 in the last 15 years. We complement these recent results by investigating the past evolution and the current state of eta Car in the near-infrared (IR). Methods. We present JHKL photometry of eta Car obtained at SAAO Sutherland from 2004-2013 with the Mk II photometer at the 0.75-m telescope and JHKs photometry with SIRIUS at the 1.4-m IRSF telescope from 2012-2013. The near-IR light curves since 1972 are analyzed. Results. The long-term brightening trends in eta Car's JHKL light curves were discontinuous around the 1998 periastron passage. After 1998, the star shows excess emission above the extrapolated trend from earlier dates, foremost in J and H, and the blueward, cyclical progression in its near-IR colors is accelerated. The near-IR color evolution is strongly correlated with the periastron passages. After correcting for the secular trend we find that the color evolution matches an apparent increase in blackbody temperature of an optically thick near-IR emitting plasma component from about 3500 to 6000 K over the last 20 years. Conclusions. We suggest that the changing near-IR emission may be caused by variability in optically thick bremsstrahlung emission. Periastron passages play a key role in the observed excess near-IR emission after 1998 and the long-term color evolution. We thus propose as a hypothesis that angular momentum transfer (via tidal acceleration) during periastron passages leads to sudden changes in eta Car's atmosphere resulting in a long-term decrease in the mass-loss rate. DA - 2014 DB - OpenUCT DP - University of Cape Town IS - 4 J1 - Astronomy and Astrophysics LK - https://open.uct.ac.za PY - 2014 SM - 0004-6361 SM - 1432-0746 T1 - Near-infrared evidence for a sudden temperature increase in Eta Carinae TI - Near-infrared evidence for a sudden temperature increase in Eta Carinae UR - http://hdl.handle.net/11427/34196 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/34196
dc.identifier.vancouvercitationMehner A, Ishibashi K, Whitelock P, Nagayama T, Feast M, van Wyk F, et al. Near-infrared evidence for a sudden temperature increase in Eta Carinae. Astronomy and Astrophysics. 2014;564(4):A14 - 177. http://hdl.handle.net/11427/34196.en_ZA
dc.language.isoeng
dc.publisher.departmentDepartment of Astronomy
dc.publisher.facultyFaculty of Science
dc.sourceAstronomy and Astrophysics
dc.source.journalissue4
dc.source.journalvolume564
dc.source.paginationA14 - 177
dc.source.urihttps://dx.doi.org/10.1051/0004-6361/201322729
dc.subject.otherstars: massive
dc.subject.otherstars: variables: S Doradus
dc.subject.otherstars: individual: ηCarinae
dc.subject.otherstars: winds, outflows
dc.subject.otherstars: mass-loss
dc.subject.otherstars: winds
dc.subject.otheroutflows
dc.titleNear-infrared evidence for a sudden temperature increase in Eta Carinae
dc.typeJournal Article
uct.type.publicationResearch
uct.type.resourceJournal Article
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