101 research outputs found
The spatio-kinematical structure and distance of the pre-planetary nebula IRAS 19134+2131
Using the VLBA, we have observed H2O maser emission in the pre-planetary
nebula IRAS 19134+2131(I19134), in which the H2O maser spectrum has two groups
of emission features separated in radial velocity by ~100 km/s. We also
obtained optical images of I19134 with the HST to locate the bipolar reflection
nebula in this source for the first time. The spatio-kinematical structure of
the H2O masers indicates the existence of a fast, collimated (precessing) flow
having a projected extent of ~140 mas and an expansion rate of ~1.9 mas/yr on
the sky plane, which gives a dynamical age of only ~40 yr. The two detected
optical lobes are also separated by ~150 mas in almost the same direction as
that of the collimated flow. The good agreement between the extent and
orientation of the H2O maser outflow and optical lobes suggests that the lobes
have been recently formed along the collimated fast flow. The positions of all
of the detected maser features have been measured with respect to the reference
source J1925+2106 over one year. Therefore we analyzed maser feature motions
that consist of the combination of an annual parallax, a secular motion
following Galactic rotation, and the intrinsic motions within the flow. We
obtain an annual-parallax distance to I19134 of D~8 kpc kpc and estimate its
location in the Galaxy to be (R, theta, z)=(7.4 kpc, 62 deg, 0.65 kpc). From
the mean motion of the blue-shifted and red-shifted clusters of maser features,
we estimate the 3-D secular motion of I19134 to be (V_{R}, V_{theta},
V_{z})=(3, 125, 8) [km/s]. From the height from the Galactic plane, z, and the
velocity component perpendicular to the Galactic plane, V_{z}, we estimate a
rough upper limit of ~9 M_{sun} to the stellar mass of I19134's progenitor.Comment: 17 pages, 5 figures, to appear in the Astrophysical Journal, October
20 issu
A Study of H2 Emission in Three Bipolar Proto-Planetary Nebulae: IRAS 16594-4656, Hen 3-401, and Rob 22
We have carried out a spatial-kinematical study of three proto-planetary
nebulae, IRAS 16594-4656, Hen 3-401, and Rob 22. High-resolution H2 images were
obtained with NICMOS on the HST and high-resolution spectra were obtained with
the Phoenix spectrograph on Gemini-South. IRAS 16594-4656 shows a
"peanut-shaped" bipolar structure with H2 emission from the walls and from two
pairs of more distant, point-symmetric faint blobs. The velocity structure
shows the polar axis to be in the plane of the sky, contrary to the impression
given by the more complex visual image and the visibility of the central star,
with an ellipsoidal velocity structure. Hen 3-401 shows the H2 emission coming
from the walls of the very elongated, open-ended lobes seen in visible light,
along with a possible small disk around the star. The bipolar lobes appear to
be tilted 10-15 deg with respect to the plane of the sky and their kinematics
display a Hubble-like flow. In Rob 22, the H2 appears in the form of an "S"
shape, approximately tracing out the similar pattern seen in the visible. H2 is
especially seen at the ends of the lobes and at two opposite regions close to
the unseen central star. The axis of the lobes is nearly in the plane of the
sky. Expansion ages of the lobes are calculated to be approximately 1600 yr
(IRAS 16594-4656), 1100 yr (Hen 3-401), and 640 yr (Rob 22), based upon
approximate distances
Pinpointing the Position of the Post-AGB Star at the Core of RAFGL 2688 using Polarimetric Imaging with NICMOS
We have used infrared polarimetric imaging with NICMOS to determine precisely
the position of the star that illuminates (and presumably generated) the
bipolar, pre-planetary reflection nebula RAFGL 2688 (the Egg Nebula). The
polarimetric data pinpoint the illuminating star, which is not detected
directly at wavelengths less than or equal to 2 microns, at a position well
within the dark lane that bisects the nebula, 0.55" (about 550 AU) southwest of
the infrared peak which was previously detected at the southern tip of the
northern polar lobe. The inferred position of the central star corresponds to
the geometric center of the tips of the four principle lobes of near-infrared
H2 emission; identifying the central star at this position also reveals the
strong point symmetric structure of the nebula, as seen both in the intensity
and polarization structure of the polar lobes. The polarimetric and imaging
data indicate that the infrared peak directly detected in the NICMOS images is
a self-luminous source and, therefore, is most likely a distant binary
companion to the illuminating star. Although present theory predicts that
bipolar structure in pre-planetary and planetary nebulae is a consequence of
binary star evolution, the separation between the components of the RAFGL 2688
binary system, as deduced from these observations, is much too large for the
presence of the infrared companion to have influenced the structure of the
RAFGL 2688 nebula.Comment: 15 pages, 6 figures, to appear in The Astrophysical Journa
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