TY - JOUR
T1 - On the he II emission in η carinae and the origin of its spectroscopic events
AU - Martin, John C.
AU - Davidson, K.
AU - Humphreys, Roberta M.
AU - Hillier, D. J.
AU - Ishibashi, K.
PY - 2006/3/20
Y1 - 2006/3/20
N2 - We describe and analyze Hubble Space Telescope (HST) observations of transient emission near 4680 Å in η Car, reported earlier by Steiner & Damineli. If, as seems probable, this is He II λ4687, then it is a unique clue to η Car's 5.5 yr cycle. According to our analysis, several aspects of this feature support a mass-ejection model of the observed spectroscopic events, and not an eclipse model. The He II emission appeared in early 2003, grew to a brief maximum during the 2003.5 spectroscopic event, and then abruptly disappeared. It did not appear in any other HST spectra before or after the event. The peak brightness was larger than previously reported and is difficult to explain even if one allows for an uncertainty factor of order 3. The stellar wind must provide a temporary larger-than-normal energy supply, and we describe a special form of radiative amplification that may also be needed. These characteristics are consistent with a class of mass-ejection or wind-disturbance scenarios, which have implications for the physical structure and stability of η Car.
AB - We describe and analyze Hubble Space Telescope (HST) observations of transient emission near 4680 Å in η Car, reported earlier by Steiner & Damineli. If, as seems probable, this is He II λ4687, then it is a unique clue to η Car's 5.5 yr cycle. According to our analysis, several aspects of this feature support a mass-ejection model of the observed spectroscopic events, and not an eclipse model. The He II emission appeared in early 2003, grew to a brief maximum during the 2003.5 spectroscopic event, and then abruptly disappeared. It did not appear in any other HST spectra before or after the event. The peak brightness was larger than previously reported and is difficult to explain even if one allows for an uncertainty factor of order 3. The stellar wind must provide a temporary larger-than-normal energy supply, and we describe a special form of radiative amplification that may also be needed. These characteristics are consistent with a class of mass-ejection or wind-disturbance scenarios, which have implications for the physical structure and stability of η Car.
KW - Binaries: general
KW - Line: profiles
KW - Stars: individual (η Car)
KW - Stars: variables: other
KW - Stars: winds, outflows
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U2 - 10.1086/500038
DO - 10.1086/500038
M3 - Article
AN - SCOPUS:33645523258
SN - 0004-637X
VL - 640
SP - 474
EP - 490
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1 I
ER -