ASpitzerStudy of the Mass-Loss Histories of Three Bipolar Preplanetary Nebulae

Abstract

We present the results of far-infrared imaging of extended regions around three bipolar preplanetary nebulae, AFGL 2688, OH 231.8+4.2, and IRAS 16342À3814, at 70 and 160 m with the MIPS instrument on the Spitzer Space Telescope. After a careful subtraction of the point-spread function of the central star from these images, we place constraints on the existence of extended shells and thus on the mass outflow rates as a function of radial distance from these stars. We find no apparent extended emission in AFGL 2688 and OH 231.8+4.2 beyond 100 00 from the central source. In the case of AFGL 2688, this result is inconsistent with a previous report of two extended dust shells made on the basis of ISO observations. We derive upper limits of 2:1 ; 10 À7 and 1:0 ; 10 À7 M yr À1 for the dust mass-loss rates of AFGL 2688 and OH 231.8, respectively, at 200 00 from each source. In contrast to these two sources, IRAS 16342À3814 does show extended emission at both wavelengths, which can be interpreted as a very large dust shell with a radius of $400 00 and a thickness of $100 00 , corresponding to 4 and 1 pc, respectively, at a distance of 2 kpc. However, this enhanced emission may also be Galactic cirrus; better azimuthal coverage is necessary for confirmation of a shell. If the extended emission is a shell, it can be modeled, with some assumptions about its dust properties, as enhanced mass outflow at a dust mass outflow rate of 1:5 ; 10 À6 M yr À1 superimposed on a steady outflow with a dust mass outflow rate of 1:5 ; 10 À7 M yr À1. Because of the size of the possible shell, it is likely that this shell has swept up a substantial mass of interstellar gas during its expansion, so these estimates are upper limits to the stellar mass-loss rate. We find a constant color temperature of 32 K throughout the circumstellar envelope of IRAS 16342À3814, which is consistent with heating by the interstellar radiation field.

Far-Infrared Imaging of Post-Asymptotic Giant Branch Stars and (Proto)-Planetary Nebulae With the Akari Far-Infrared Surveyor

“…Recent Spitzer/MIPS observations by Do et al (2007) have not revealed circumstellar dust shells around CRL 2688, as reported with ISO. The latter were reported by Speck et al (2000) who identified dust shells of about 2-3 pc in two post-AGB stars.…”

The Astrosphere of the Asymptotic Giant Branch Star Cit 6

“…For example, in the case of Y CVn, an extended dust -10shell is clearly seen in ISO maps (Izumiura et al 1996) with about the same size as inferred by Yetal95, but only very faintly in the Cetal12 study. However, for CRL2688, where Speck et al (2000) reported the presence of two dust shells from ISO scan data, Spitzer imaging by Do et al (2007) showed no such shells at a level well below the intensities expected from the ISO results. We believe that a detailed re-investigation is needed to resolve such discrepancies in results related to the presence of extended dust shells as derived from IRAS and ISO, and from the more recent Spitzer and Herschel missions (utilizing modern large-format detector arrays).…”

First detection of CO lines in a water fountain star

“…However, the formula of Baud & Habing (1983) applied to an OH 1612 MHz maser peak flux of 9 Jy (Likkel & Morris 1988) yields a much higher mass loss rate of Ṁ(OH) = 1.7 ∼ 4.9 × 10 −5 M ⊙ yr −1 (with V exp = 46 km s −1 from our 12 CO line). Do et al (2007) fitted the Spitzer MIPS 70µ images with a two shell model, and obtained Ṁ(70µ) = 0.4 ∼ 3 × 10 −5 M ⊙ yr −1 for an inner smooth CSE and Ṁ(shell) = 0.4 ∼ 3 × 10 −4 M ⊙ yr −1 for an outer extended dust shell (assuming a gas-to-dust mass ratio of 200 and V exp = 15 km s −1 . Here we note that our measured 12 CO expansion velocity of 46 km s −1 may not be that of the dusty CSE, see the discussion in § 4.2).…”