36 research outputs found
Spatial Distributions of Multiple Dust Components in the PPN/PN Dust Shells
We investigate spatial distributions of specific dust components in the
circumstellar shells of a proto-planetary nebula candidate, HD 179821, and a
planetary nebula, BD3639, by means of spectral imaging. With
high-resolution ground-based images and ISO spectra in the mid-infrared, we can
derive ``dust feature only'' maps by subtracting synthesized continuum maps
from the observed images at the feature wavelength. Such spatially detailed
information will help to develop models for the evolution of dust grains around
evolved stars.Comment: 4 pages + 7 figures, to appear in the proceedings of the conference,
"Post-AGB Objects (proto-planetary nebulae) as a Phase of Stellar Evolution",
Torun, Poland, July 5-7, 2000, eds. R. Szczerba, R. Tylenda, and S.K. Gorny.
Figures have been degraded to minimize the total file siz
Investigating the Near-Infrared Properties of Planetary Nebulae. I. Narrowband Images
We present the results of a near-infrared narrowband imaging survey of
planetary nebulae. Objects were selected in a way that complements similar
surveys done at visible and near-infrared wavelengths. No new detections of
molecular hydrogen emission were made. The H2 is frequently found to be
extended, except in young, visibly compact objects. Our results are consistent
with the already determined correlation of H2 emission with planetary nebula
morphological type. Filamentary and other kinds of structures are clearly
resolved in many nebulae.Comment: 21 pages text+tables and 38 figures, full preprint available at
http://www.cv.nrao.edu/html/library/nrao_preprints.html, report #9571 (4.4MB
gzipped file), or email [email protected]. Accepted ApJS, scheduled
Sept. 199
Infrared Array Camera (IRAC) Observations of Planetary Nebulae
We present the initial results from the Infrared Array Camera (IRAC) imaging survey of planetary nebulae (PNs). The IRAC colors of PNs are red, especially in the 8.0 μm band. Emission in this band is likely due to contributions from two strong H2 lines and a [Ar III] line in that bandpass. IRAC is sensitive to the emission in the halos as well as in the ionized regions that are optically bright. In NGC 246, we have observed an unexpected ring of emission in the 5.8 and 8.0 μm IRAC bands not seen previously at other wavelengths. In NGC 650 and NGC 3132, the 8.0 μm emission is at larger distances from the central star compared to the optical and other IRAC bands, possibly related to the H2 emission in that band and the tendency for the molecular material to exist outside of the ionized zones. In the flocculi of the outer halo of NGC 6543, however, this trend is reversed, with the 8.0 μm emission bright on the inner edges of the structures. This may be related to the emission mechanism, where the H2 is possibly excited in shocks in the NGC 6543 halo, whereas H2 emission is likely fluorescently excited in the UV fields near the central star
Mid-infrared imaging of the massive young star AFGL 2591: Probing the circumstellar environment of an outflow source
Most, if not all, stars are now believed to produce energetic outflows during
their formation. Yet, almost 20 years after the discovery of bipolar outflows
from young stars, the origins of this violent phenomenon are not well
understood. One of the difficulties of probing the outflow process,
particularly in the case of massive embedded stars, is a deficit of high
spatial resolution observations. Here, we present sub-arcsecond-resolution
mid-infrared images of one massive young stellar object, AFGL 2591, and its
immediate surroundings. Our images, at 11.7, 12.5 and 18.0 microns, reveal a
knot of emission ~6'' SW of the star, which may be evidence for a recent
ejection event or an embedded companion star. This knot is roughly coincident
with a previously seen near-infrared reflection nebula and a radio source, and
lies within the known large-scale CO outflow. We also find a new faint NW
source which may be another embedded lower-luminosity star. The IRAS
mid-infrared spectrum of AFGL 2591 shows a large silicate absorption feature at
10 microns, implying that the primary source is surrounded by an optically
thick dusty envelope. We discuss the interrelationship of these phenomena and
suggest that mid-infrared imaging and spectroscopy provide powerful tools for
probing massive star birth.Comment: 14 pages, 3 PostScript figures, accepted for publication in The
Astrophysical Journal Letter
Discovery of an Extended Dust Emission around IRAS 18576+0341 (AFGL 2298) at 10.3 and 18.0 microns: a New Luminous Blue Variable Candidate?
We report detection of an extended mid-infrared emission from \iras
18576+0341 (AFGL 2298). The object shows a dusty circumstellar shell that has
diameter of \age 7\arcsec at 10.3 and 18.0 \um. The dust nebula shows two
emission peaks concentrically elongated and symmetrically oriented on the
opposite sides of the third, central peak, which appears to be the central star
of the system. The observed mid-infrared morphology indicates that the
circumstellar dust shell has an equatorially-enhanced material distribution,
which is a common signature of stellar objects that have experienced mass loss.
Radiative transfer model calculations suggest that the central star is an
extremely bright (\lstar = 10^{6.4} \lsun) star at a distance of about 10
kpc: this object is best described as a new luminous blue variable candidate.
The circumstellar dust shell seems to have been generated by an
equatorially-enhanced mass loss process with {\dot M} \ge 6.8 \times 10^{-6}
\msun yr and .Comment: 21 pages, 4 figures, to appear in Ap
Infrared Array Camera (IRAC) Observations of Planetary Nebulae
We present the initial results from the Infrared Array Camera (IRAC) imaging survey of planetary nebulae (PNs). The IRAC colors of PNs are red, especially in the 8.0 μm band. Emission in this band is likely due to contributions from two strong H2 lines and a [Ar III] line in that bandpass. IRAC is sensitive to the emission in the halos as well as in the ionized regions that are optically bright. In NGC 246, we have observed an unexpected ring of emission in the 5.8 and 8.0 μm IRAC bands not seen previously at other wavelengths. In NGC 650 and NGC 3132, the 8.0 μm emission is at larger distances from the central star compared to the optical and other IRAC bands, possibly related to the H2 emission in that band and the tendency for the molecular material to exist outside of the ionized zones. In the flocculi of the outer halo of NGC 6543, however, this trend is reversed, with the 8.0 μm emission bright on the inner edges of the structures. This may be related to the emission mechanism, where the H2 is possibly excited in shocks in the NGC 6543 halo, whereas H2 emission is likely fluorescently excited in the UV fields near the central star
Mid-IR Observations of Mira Circumstellar Environment
This paper presents results from high-angular resolution mid-IR imaging of
the Mira AB circumbinary environment using the MIRAC3 camera at the NASA
Infrared Telescope Facility (IRTF). We resolved the dusty circumstellar
envelope at 9.8, 11.7 and 18 micron around Mira A (o Ceti), and measured the
size of the extended emission. Strong deviations from spherical symmetry are
detected in the images of Mira AB system, including possible dust clumps in the
direction of the companion (Mira B). These observations suggest that Mira B
plays an active role in shaping the morphology of the circumstellar environment
of Mira A as it evolves toward the Planetary Nebula phase.Comment: 11 pages, 2 PostScript figures, accepted for publication in the
Astrophysical Journal Letter
A Mid-Infrared Imaging Survey of Proto-Planetary Nebula Candidates
We present the data from a mid-infrared imaging survey of 66 proto-planetary
nebula candidates using two mid-IR cameras (MIRAC2 and Berkcam) at the NASA
Infrared Telescope Facility and the United Kingdom Infrared Telescope. The goal
of this survey is to determine the size, flux, and morphology of the mid-IR
emission regions, which sample the inner regions of the circumstellar dust
shells of proto-planetary nebulae. We imaged these proto-planetary nebulae with
narrow-band filters () at wavelengths of
notable dust features. With our typical angular resolution of 1\arcsec, we
resolve 17 sources, find 48 objects unresolved, and do not detect 1 source. For
several sources, we checked optical and infrared associations and positions of
the sources. In table format, we list the size and flux measurements for all
the detected objects and show figures of all the resolved sources. Images for
all the detected objects are available on line in FITS format from the
Astronomy Digital Image Library at the National Center for Supercomputing
Application. The proto-planetary nebula candidate sample includes, in addition
to the predominant proto-planetary nebulae, extreme asymptotic giant branch
stars, young planetary nebulae, a supergiant, and a luminous blue variable. We
find that dust shells which are cooler ( K) and brighter in the
infrared are more easily resolved. Eleven of the seventeen resolved sources are
extended and fall into one of two types of mid-IR morphological classes:
core/elliptical or toroidal. Core/elliptical structures show unresolved cores
with lower surface brightness elliptical nebulae. Toroidal structures show
limb-brightened peaks suggesting equatorial density enhancements. We argue that
core/ellipticals have denser dust shells than toroidals.Comment: 32 pages, 5 tables, 2 e/ps figures (fig3 is available through ADIL
[see text]), to be published in ApJS May 1999 issu
Investigating the Near-Infrared Properties of Planetary Nebula II. Medium Resolution Spectra
We present medium-resolution (R~700) near-infrared (lambda = 1 - 2.5 micron)
spectra of a sample of planetary nebulae (PNe). A narrow slit was used which
sampled discrete locations within the nebulae; observations were obtained at
one or more positions in the 41 objects included in the survey. The PN spectra
fall into one of four general categories: H I emission line-dominated PNe, H I
and H_2 emission line PNe, H_2-dominated PNe, and continuum-dominated PNe.
These categories correlate with morphological type, with the elliptical PNe
falling into the first group, and the bipolar PNe primarily in the H_2 and
continuum emission groups. Other spectral features were observed in all
categories, such as continuum emission from the central star, C_2, CN, and CO
emission, and warm dust continuum emission.
Molecular hydrogen was detected for the first time in four PNe. An excitation
analysis was performed using the H_2 line ratios for all of the PN spectra in
the survey where a sufficient number of lines were observed. One unexpected
result from this analysis is that the H_2 is excited by absorption of
ultraviolet photons in most of the PNe surveyed, although for several PNe in
our survey collisional excitation in moderate velocity shocks plays an
important role. The correlation between bipolar morphology and H_2 emission has
been strengthened with the new detections of H_2 in this survey.Comment: 13 pages, 8 tables, 33 figure