TY - JOUR
T1 - Ultraviolet Mg II emission from fast neutral ejecta around Eta Carinae
AU - Smith, Nathan
AU - Morse, Jon A.
N1 - Funding Information:
2IRAF is distributed by the National Optical Astronomy Observatories, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation. The Space Telescope Science Data Analysis System (STSDAS) is distributed by the Space Telescope Science Institute.
Funding Information:
We acknowledge helpful comments from the referee, which helped to clarify several aspects of the observations and analysis presented in this paper. We thank STScI science and technical staff members Peter McCullough and Amber Armstrong for special assistance in planning the DD time observations and Joe DePasquale for producing the colour HST image in Fig. 2 and the similar image superposed on the Chandra X-ray image in Fig. 6. We thank both Kenji Hamaguchi and Mike Corcoran for discussions over many years concerning the X-ray emission from ? Car's outer shell. JM appreciates helpful discussions with John Raymond and Pat Hartigan. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Support was provided by NASA through grants GO-15596, GO-15289, GO-14768, and AR-14586 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. NS's research on Eta Carinae also received support from NSF grants AST-1312221 and AST-1515559.
Funding Information:
Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Support was provided by NASA through grants GO-15596, GO-15289, GO-14768, and AR-14586 from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. NS’s research on Eta Carinae also received support from NSF grants AST-1312221 and AST-1515559.
Publisher Copyright:
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
PY - 2019/10/11
Y1 - 2019/10/11
N2 - We present the first images of the nebula around η Carinae obtained with the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope (HST), including an ultraviolet (UV) image in the F280N filter that traces Mg II emission, plus contemporaneous imaging in the F336W, F658N, and F126N filters that trace near-UV continuum, [N II], and [Fe II], respectively. The F336W and F658N images are consistent with previous images in these filters, and F126N shows that for the most part, [Fe II] λ12567 traces clumpy shocked gas seen in [N II]. The F280N image, however, reveals Mg II emission from structures that have not been seen in any previous line or continuum images of η Carinae. This image shows diffuse Mg II emission immediately outside the bipolar Homunculus nebula in all directions, but with the strongest emission concentrated over the poles. The diffuse structure with prominent radial streaks, plus an anticorrelation with ionized tracers of clumpy shocked gas, leads us to suggest that this is primarily Mg II resonant scattering from unshocked, neutral atomic gas. We discuss the implied structure and geometry of the Mg II emission, and its relation to the Homunculus lobes and various other complex nebular structures. An order of magnitude estimate of the neutral gas mass traced by Mg II is 0.02 M☉, with a corresponding kinetic energy around 1047 erg. This may provide important constraints on polar mass-loss in the early phases of the great eruption. We argue that the Mg II line may be an excellent tracer of significant reservoirs of freely expanding, unshocked, and otherwise invisible neutral atomic gas in a variety of stellar outflows.
AB - We present the first images of the nebula around η Carinae obtained with the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope (HST), including an ultraviolet (UV) image in the F280N filter that traces Mg II emission, plus contemporaneous imaging in the F336W, F658N, and F126N filters that trace near-UV continuum, [N II], and [Fe II], respectively. The F336W and F658N images are consistent with previous images in these filters, and F126N shows that for the most part, [Fe II] λ12567 traces clumpy shocked gas seen in [N II]. The F280N image, however, reveals Mg II emission from structures that have not been seen in any previous line or continuum images of η Carinae. This image shows diffuse Mg II emission immediately outside the bipolar Homunculus nebula in all directions, but with the strongest emission concentrated over the poles. The diffuse structure with prominent radial streaks, plus an anticorrelation with ionized tracers of clumpy shocked gas, leads us to suggest that this is primarily Mg II resonant scattering from unshocked, neutral atomic gas. We discuss the implied structure and geometry of the Mg II emission, and its relation to the Homunculus lobes and various other complex nebular structures. An order of magnitude estimate of the neutral gas mass traced by Mg II is 0.02 M☉, with a corresponding kinetic energy around 1047 erg. This may provide important constraints on polar mass-loss in the early phases of the great eruption. We argue that the Mg II line may be an excellent tracer of significant reservoirs of freely expanding, unshocked, and otherwise invisible neutral atomic gas in a variety of stellar outflows.
KW - Circumstellar matter
KW - Outflows
KW - Stars: evolution
KW - Stars: winds
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U2 - 10.1093/mnras/stz1996
DO - 10.1093/mnras/stz1996
M3 - Article
AN - SCOPUS:85079682179
VL - 489
SP - 268
EP - 281
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 1
ER -