Description
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Using the Hubble Space Telescope, we have imaged the OH/IR star IRAS 19024+0044 (I19024) at 0.6, 0.8, 1.1, and 1.6 µm, as part of our surveys of candidate preplanetary nebulae. The images show a multipolar nebula of size ~3."7 X 2."3, with at least six elongated lobes emanating from the center of the nebula. Two of the lobes show limb-brightened tips having point-symmetric structure with respect to the expected location of the central star. The central region shows two dark bands southwest and northeast of a central shallow maximum that may be either two inclined dusty toroidal structures or the dense parts of a single wide, inhomogeneous, toroid. Avery faint, surface brightness–limited, diffuse halo surrounds the lobes. Long-slit/echelle optical spectroscopy obtained at the Mount Palomar and Keck observatories shows a spatially compact source of Hα emission; the Hα line shows a strong, narrow, central core with very broad (±1000 km sˉ¹), weak wings, and a narrower blueshifted absorption feature signifying the presence of a ~100 km sˉ¹ outflow. The spectrum is characterized by a strong, relatively featureless, continuum and lacks the strong forbidden emission lines characteristic of planetary nebulae, confirming that IRAS 19024 is a preplanetary nebula; the spectral type for the central star, although uncertain, is most likely early G. Interferometric observations of the CO J = 1-0 line emission with the Owens Valley Radio Interferometer show a marginally resolved molecular envelope (size 5."5 ; 4."4) with an expansion velocity of 13 km sˉ¹, resulting from the asymptotic giant granch (AGB) progenitor’s dense, slow wind. We derive a kinematic distance of 3.5 kpc to I19024, based on its radial velocity. The bolometric flux is 7:3 X 10-9 ergs sˉ¹ cmˉ², and the luminosity 2850 Lө. The relatively low luminosity of I19024, in comparison with stellar evolutionary models, indicates that the initial mass of its central star was ~1–1.5 Mө. The lobes, which appear to be hollow structures with dense walls, have a total mass greater than or equal to about 0.02Mө....
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