TY - JOUR
T1 - Mid-cycle changes in eta Carinae
AU - Martin, John C.
AU - Davidson, Kris
AU - Humphreys, Roberta M
AU - Mehner, Andrea
PY - 2010
Y1 - 2010
N2 - In late 2006, ground-based photometry of η Car plus the Homunculus showed an unexpected decrease in its integrated apparent brightness, an apparent reversal of its long-term brightening. Subsequent Hubble Space Telescope (HST)/WFPC2 photometry of the central star in the near-UV showed that this was not a simple reversal. This multi-wavelength photometry did not support increased extinction by dust as the explanation for the decrease in brightness. A spectrum obtained with the Gemini Multi-Object Spectrograph on the Gemini-South telescope revealed subtle changes mid-way in η Car's 5.5 yr spectroscopic cycle when compared with HST/Space Telescope Imaging Spectrograph (STIS) spectra at the same phase in the cycle. At mid-cycle the secondary star is 20-30 AU from the primary. We suggest that the spectroscopic changes are consistent with fluctuations in the density and velocity of the primary star's wind, unrelated to the 5.5 yr cycle but possibly related to its latitude-dependent morphology. We also discuss subtle effects that must be taken into account when comparing ground-based and HST/STIS spectra.
AB - In late 2006, ground-based photometry of η Car plus the Homunculus showed an unexpected decrease in its integrated apparent brightness, an apparent reversal of its long-term brightening. Subsequent Hubble Space Telescope (HST)/WFPC2 photometry of the central star in the near-UV showed that this was not a simple reversal. This multi-wavelength photometry did not support increased extinction by dust as the explanation for the decrease in brightness. A spectrum obtained with the Gemini Multi-Object Spectrograph on the Gemini-South telescope revealed subtle changes mid-way in η Car's 5.5 yr spectroscopic cycle when compared with HST/Space Telescope Imaging Spectrograph (STIS) spectra at the same phase in the cycle. At mid-cycle the secondary star is 20-30 AU from the primary. We suggest that the spectroscopic changes are consistent with fluctuations in the density and velocity of the primary star's wind, unrelated to the 5.5 yr cycle but possibly related to its latitude-dependent morphology. We also discuss subtle effects that must be taken into account when comparing ground-based and HST/STIS spectra.
KW - Line: profiles
KW - Stars: individual (eta Carinae)
KW - Stars: variables: general
KW - Stars: winds, outflows
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U2 - 10.1088/0004-6256/139/5/2056
DO - 10.1088/0004-6256/139/5/2056
M3 - Article
AN - SCOPUS:77950981826
SN - 0004-6256
VL - 139
SP - 2056
EP - 2065
JO - Astronomical Journal
JF - Astronomical Journal
IS - 5
ER -