η Carinae's Dusty Homunculus Nebula from Near-infrared to Submillimeter Wavelengths: Mass, Composition, and Evidence for Fading Opacity

Journal Article · Tue Jun 20 04:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA71B3· OSTI ID:22876116

Morris, Patrick W. ^[1]; Gull, Theodore R. ^[2]; Hillier, D. John ^[3]; Barlow, M. J. ^[4]; Royer, Pierre ^[5]; Nielsen, Krister ^[6]; Black, John ^[7]; Swinyard, Bruce ^[8]

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1. California Institute of Technology, IPAC, M/C 100−22, Pasadena, CA 91125 (United States)
2. NASA Goddard Space Flight Center, Code 667, Greenbelt, MD 20771 (United States)
3. Department of Physics and Astronomy, University of Pittsburgh, 3941 O’Hara Street, Pittsburgh, PA 15260 (United States)
4. Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom)
5. Katholieke Universiteit Leuven, Institute of Astronomy, Celestijnenlaan 200 D, B-3001 Leuven (Belgium)
6. Department of Physics, IACS, Catholic University of America, Washington, DC 20064 (United States)
7. Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-43992 Onsala (Sweden)
8. Space Science and Technology Department, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon (United Kingdom)

Infrared observations of the dusty, massive Homunculus Nebula around the luminous blue variable η Carinae are crucial to characterize the mass-loss history and help constrain the mechanisms leading to the great eruption. We present the 2.4–670 μm spectral energy distribution, constructed from legacy Infrared Space Observatory observations and new spectroscopy obtained with the Herschel Space Observatory. Using radiative transfer modeling, we find that the two best-fit dust models yield compositions that are consistent with CNO-processed material, with iron, pyroxene and other metal-rich silicates, corundum, and magnesium-iron sulfide in common. Spherical corundum grains are supported by the good match to a narrow 20.2 μm feature. Our preferred model contains nitrides AlN and Si{sub 3}N{sub 4} in low abundances. Dust masses range from 0.25 to 0.44 M{sub ⊙}, but M{sub tot}⩾45 M{sub ⊙} in both cases, due to an expected high Fe gas-to-dust ratio. The bulk of dust is within a 5{sup ′′}×7{sup ′′} central region. An additional compact feature is detected at 390 μm. We obtain L{sub IR} = 2.96 × 10{sup 6} L{sub ⊙}, a 25% decline from an average of mid-IR photometric levels observed in 1971–1977. This indicates a reduction in circumstellar extinction in conjunction with an increase in visual brightness, allowing 25%–40% of optical and UV radiation to escape from the central source. We also present an analysis of {sup 12}CO and {sup 13}CO J = 5–4 through 9–8 lines, showing that the abundances are consistent with expectations for CNO-processed material. The [{sup 12}C ii] line is detected in absorption, which we suspect originates in foreground material at very low excitation temperatures.

• OSTI ID: 22876116
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 842; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION
ALUMINIUM NITRIDES
CARBON MONOXIDE
COMPUTERIZED SIMULATION
COSMIC DUST
ELEMENT ABUNDANCE
ENERGY SPECTRA
IRON
IRON SULFIDES
MAGNESIUM
MASS TRANSFER
NEBULAE
RADIANT HEAT TRANSFER
SILICATE MINERALS
SILICATES
SILICON NITRIDES
SPACE
STARS
STELLAR WINDS
WAVELENGTHS