The Molecular and Dust Envelope of HD 56126

Abstract

We present millimeter interferometry images of the CO J=1-0 line emission arising in the circumstellar envelope of HD 56126 (a.k.a. IRAS 07134+1005), which is one of the best studied 21-micron proto-planetary nebulae (PPNs). The CO emission extends from 1.2" to 7" in radius from the central star and appears consistent with a simple expanding envelope, as expected for a post-AGB star. We quantitatively model the molecular envelope using a radiative transfer code that we have modified for detached shells. Our best fit model reveals that two sequential winds created the circumstellar envelope of HD 56126: an AGB wind that lasted 6500 years with a mass-loss rate of 5.1x10^{-6} M_odot yr^{-1} and a more intense superwind that lasted 840 years with a mass-loss rate of 3x10^{-5} M_odot yr^{-1} and that ended the star's life on the AGB 1240 years ago. The total mass of this envelope is 0.059 M_odot which indicates a lower limit progenitor mass for the system of 0.66 M_odot, quite reasonable for this low-metallicity star which probably resides in the thick disk of the Galaxy. Comparison with images of the dust emission reveal a similar structure with the gas in the inner regions. Using 2-DUST, we model the dust emission of this source so that the model is consistent with the CO emission model and find an average gas-to-dust mass ratio of 75.Comment: 23 pages, 6 figures, 3 tables, accepted for publication in 10/2004 issue of Ap

ASPITZER/INFRARED SPECTROGRAPH SPECTRAL STUDY OF A SAMPLE OF GALACTIC CARBON-RICH PROTO-PLANETARY NEBULAE

“…Some PPNs have been found to exhibit equatorial tori. For example, the dust continuum and CO map of the 21 µm source IRAS 07134+1005 suggests the presence of torus (Kwok, Volk, & Hrivnak 2002;Meixner et al 2004;Nakashima et al 2009). Tables 1 and Table 2 also give the fitting uncertainties of the feature strengths, which are estimated using the full covariance matrix of the least-squares parameters.…”

A 1.2 mm MAMBO survey of post-AGB stars

“…As a consequence, the dust mass reported in Table 3 could be underestimated because the assumed dust opacity is derived from an approximated grain model with an average grain size of 0.1 µm Ref. 1, 2, 3, 4 5, 6, 7, 18, 19, 20 3, 8, 9, 10, 18, 19, 21 11, 12, 13, 19, 22 14, 15, 18, 19, 20 13, 16, 17, 18 References -(1) Meixner et al (2004); (2) …”

ON MAGNESIUM SULFIDE AS THE CARRIER OF THE 30 μm EMISSION FEATURE IN EVOLVED STARS

“…Their detailed radiative transfer model derived a circumstellar envelope mass of M H ∼ 0.16-0.44 M ⊙ , depending on the assumed gas-to-dust ratio (∼ 220-600). Meixner et al (2004) found a more extended envelope (with radius between 1.2 ′′ -7 ′′ ) based on their CO J = 1-0 line emission images. They derived a much smaller mass for the envelope (M H ∼ 0.059 M ⊙ ).…”