280 research outputs found
AKARI Mission Program: Excavating Mass Loss History in Extended Dust Shells of Evolved Stars (MLHES) I. Far-IR Photometry
We performed a far-IR imaging survey of the circumstellar dust shells of 144
evolved stars as a mission programme of the AKARI infrared astronomical
satellite using the Far-Infrared Surveyor (FIS) instrument. With this survey,
we deliver far-IR surface brightness distributions of roughly 10' x 40' or 10'
x 20' areas of the sky around the target evolved stars in the four FIS bands at
65, 90, 140, and 160 microns. Our objectives are to characterize the far-IR
surface brightness distributions of the cold dust component in the
circumstellar dust shells, from which we derive the amount of cold dust grains
as low as 20 K and empirically establish the history of the early mass loss
history. In this first installment of the series, we introduce the project and
its aims, describe the observations, data reduction, and surface brightness
correction process, and present the entire data set along with the results of
integrated photometry measurements (i.e., the central source and circumstellar
dust shell altogether). We find that (1) far-IR emission is detected from all
but one object at the spatial resolution about 30" - 50" in the corresponding
bands, (2) roughly 60 - 70 % of the target sources show some extension, (3)
previously unresolved nearby objects in the far-IR are now resolved around 28
target sources, (4) the results of photometry measurements are reasonable with
respect to the entries in the AKARI/FIS Bright Source Catalogue, despite the
fact that the targets are assumed to be point-sources when catalogue flux
densities were computed, and (5) an IR two-color diagram would place the target
sources in a roughly linear distribution that may correlate with the age of the
circumstellar dust shell and can potentially be used to identify which targets
are more extended than others.Comment: To be published in PASJ AKARI Special Issue: 25 pages, 5 figures, 5
tables (and 28 supplementary figures available only in PASJ on-line
A Spitzer Study of the Mass Loss Histories of Three Bipolar Pre-Planetary Nebulae
We present the results of far-infrared imaging of extended regions around
three bipolar pre-planetary nebulae, AFGL 2688, OH 231.8+4.2, and IRAS
163423814, 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 arcseconds 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 an upper limit of
M yr and M
yr for the dust mass loss rate of AFGL 2688 and OH 231.8, respectively,
at 200 arcseconds from each source. In contrast to these two sources, IRAS
163423814 does show extended emission at both wavelengths, which can be
interpreted as a very large dust shell with a radius of 400 arcseconds
and a thickness of 100 arcseconds, corresponding to 4 pc 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 as enhanced
mass outflow at a dust mass outflow rate of M
yr superimposed on a steady outflow with a dust mass outflow rate of
M yr. 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.Comment: 31 pages, 12 figures, accepted to A
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