Sign on

SAO/NASA ADS Astronomy Abstract Service

· Find Similar Abstracts (with default settings below)
· Electronic Refereed Journal Article (HTML)
· Full Refereed Journal Article (PDF/Postscript)
· On-line Data
· References in the article
· Citations to the Article (12) (Citation History)
· Refereed Citations to the Article
· SIMBAD Objects (17)
· Also-Read Articles (Reads History)
·
· Translate This Page
Title:
A Starfish Preplanetary Nebula: IRAS 19024+0044
Authors:
Sahai, Raghvendra; Sánchez Contreras, Carmen; Morris, Mark
Affiliation:
AA(Jet Propulsion Laboratory, MS 183-900, Caltech, Pasadena, CA 91109; .), AB(Astronomy Department, Caltech, MS 105-24, Pasadena, CA 91125.), AC(Division of Astronomy and Astrophysics, UCLA, Los Angeles, CA 90095.)
Publication:
The Astrophysical Journal, Volume 620, Issue 2, pp. 948-960. (ApJ Homepage)
Publication Date:
02/2005
Origin:
UCP
ApJ Keywords:
Stars: Circumstellar Matter, ISM: refection nebulae, ISM: Planetary Nebulae: General, Stars: AGB and Post-AGB, Stars: Individual: Alphanumeric: IRAS 19024+0044, Stars: Mass Loss
DOI:
10.1086/426469
Bibliographic Code:
2005ApJ...620..948S

Abstract

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"×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. A very 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 s-1), weak wings, and a narrower blueshifted absorption feature signifying the presence of a ~100 km s-1 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 s-1, 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 7.3×10-9 ergs s-1 cm-2, and the luminosity 2850 Lsolar. 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 Msolar. The lobes, which appear to be hollow structures with dense walls, have a total mass greater than or equal to about 0.02 Msolar. The dusty tori in the center have masses of a few times 10-3 Msolar. The faint halo has a power-law radial surface brightness profile with an exponent of about -3 and most likely represents the remnant spherical circumstellar envelope formed as a result of constant mass loss during the AGB phase over the past several thousand years. From the CO data we infer a molecular mass >~0.025 Msolar and an expansion age <~2870 yr, giving a mass-loss rate >~10-5 Msolar yr-1. The far-infrared fluxes of I19024 indicate the presence of a large mass of cool dust in the nebula; from a simple model we infer the presence of ``cool'' (109 K) and ``warm'' (280 K) components of dust mass 5.7×10-4 and 1.5×10-7 Msolar. We discuss our results for I19024 in the light of past and current ideas for the dramatic transformation of the morphology and kinematics of mass-ejecta as AGB stars evolve into planetary nebulae.

The phrase ``preplanetary nebula,'' which refers to an object in the evolutionary phase immediately preceding the planetary nebula phase, is used in this paper in place of the more commonly used ``proto-planetary nebula,'' because the term ``proto-planetary'' is widely used to refer to disks around pre-main-sequence stars. Since the term protoplanet is used by the planet and planet formation communities to refer to planets undergoing formation, the use of the term ``protoplanetary nebula'' to refer to a completely different kind of object is an unfortunate choice, which compounds our inconvenience of having the historically inherited misnomer ``planetary nebula.'' We believe, therefore, that it is important to replace the term ``proto-planetary nebula'' (in this work and future studies) with ``preplanetary nebula,'' which is both unique (in the planetary community, the term ``preplanet'' is not used, and never will be) and correct in its meaning.

Bibtex entry for this abstract   Preferred format for this abstract (see Preferences)
   

Find Similar Abstracts:

Use: Authors
Title
Keywords (in text query field)
Abstract Text
Return: Query Results Return    items starting with number
Query Form
Database: Astronomy
Physics
arXiv e-prints