The First Adaptive Optics High Resolution Mid

1
The First Adaptive Optics High Resolution Mid
IR Imaging of Evolved Stars Case Studies of RV
Boo and AC Her
B.A. Biller, L.M.Close, D. Potter, J. Bieging, W.
Hoffman, P. Hinz, B.D. Oppenheimer, Steward
Observatory, University of Arizona

• We present high resolution very high strehl ratio
  (0.980.03) Mid-IR images of RV Boo and AC Her.
  These images were obtained with the unique MMT
  deformable secondary mirror adaptive optics
  system. At such high strehls, we achieve
  super-resolutions of 0.1 by deconvolving our
  images with those of a PSF star.
• RV
  Boo
• Appears slightly extended (5 eccentricity)
  relative to PSF stars in the raw data. See Figs.
  1 and 2.
• After deconvolution, we resolve RV Boo into a
  0.16 FWHM disk at a position angle of 120o. See
  Fig. 4. Bergman et al. (2000) observed a larger
  4 diameter disk in CO at a similar position
  angle.
• During the observation, the measured position
  angle of the deconvolved disk tracked the
  parallactic angle of the sky. (See Fig. 3). We
  conclude that the disk is real if the disk was
  an artifact of deconvolution, position angles
  should be distributed randomly with time.
• At a distance of 390 pc, the disk has a major
  axis FWHM of 60 pc. We measure a total disk
  flux of 145 Jy at 9.8 mm.
• We calculated single-scattering two-dimensional
  thermal emission models of the disk. The
  illuminating star was modeled as a 3000 K
  blackbody. The model which best fit the
  measured SED for RV Boo (our 9.8 mm flux IRAS
  fluxes) is a 5x10-7 solar mass disk at an
  inclination of 15o from edge-on. See Fig. 4 for
  a comparison between data and model images.
• AC
  Her
• No extended structure on scales greater than
  0.2 this result conflicts with previous
  (seeing-limited) 11.7 and 18 mm images which
  suggested the presence of a resolved 0.6
  edge-on circumbinary disk (Jura et al. 2000).
  See Figs. 5-7.
• We can put a lower limit on the temperature of
  emitting material by considering a toy model of
  an optically thick face on disk with radius0.2
  (the largest disk that can exist without being
  detected). This model requires a reasonable Tb gt
  165K.
• Generalized Interacting Stellar Winds (GISW)
  models of planetary nebulae invoke some initial
  structure which can collimate and shape the fast
  winds produced by these objects into a bipolar
  morphology. The Mid-IR disk observed around RV
  Boo may be an example of the early stages in the
  formation of such initial structure. AC Her is
  2-3 times more distant than RV Boo a similar
  but unresolved disk may exist around AC Her.

Fig 5 The 9.8, 11.7, and 18QS mm images of AC
Her and PSF stars m Uma and a Her as observed at
the MMT. In the upper right, we have inserted
the published 18 mm Keck image of AC Her (in
false color Jura et al. (2000)). The scale of
the MMT images is 1.5x1.0, the scale of the Keck
image is similar with a size of 0.7x1.0. Note
how there is no sign of any extended structure in
the MMT AC Her images in any of the filters. The
faint point source in the lower left of each MMT
image is a MIRAC3 ghost.
Fig. 1 AO Images of RV Boo, m UMa, a Her, and
AC Her at 9.8 mm. The vertical axis is telescope
altitude while the horizontal axis is telescope
azimuth. Images have been unsharp masked. All
images are shown on a logarithmic scale the
bright ring around the images is the first Airy
ring. Note that RV Boo appears nominally
extended relative to the other stars. The field
of view for each image is 1.
Fig. 2 Eccentricity vs. PSF FWHM for
undeconvolved 9.8 mm RV Boo, m UMa, a Her, and AC
Her images and RV Boo models. FWHM is measured
by 3 methods for each star by enclosed flux
(triangles), Gaussian fit (10 point stars), and
directly (4 point stars). The scatter between
the methods gives an estimate of the error.
Since it is slightly saturated, only the Gaussian
FWHM is shown for a Her. RV Boo appears slightly
extended and thus has a significantly higher
eccentricity and FWHM than the other stars.
Fig. 6 The 9.8 and 11.7 mm FWHM and
eccentricity of AC Her and the PSF stars m UMa
and a Her (the Gaussian fit FWHM are the upper
star symbols and the enclosed FWHM are
represented by the slightly lower circles AC Her
is the middle dataset in the 9.8 and 11.7 mm
clusters). The location of the previously imaged
disk morphology (FWHM0.8 Jura et al. (2000))
is also plotted. Note that AC Hers morphology
appears much more consistent with that of the PSF
stars at 9.8 and 11.7 mm than an extended
FWHM0.8 disk.
Fig. 3 Position angle of the semi-major axis
vs. time (after first observation) for
deconvolved RV Boo and m UMa nod images. Note
that the DPAs measured for RV Boo track the
parallactic angle much more closely than those
measured for m UMa, with reduced c2 values of
1.03 and 0.37 for RV Boo deconvolved with a Her
and m UMa respectively, versus a reduced c2 value
of 11.3 for m UMa deconvolved with a Her. This
implies that the elongation observed was really
associated with RV Boo and is not a PSF artifact.
Fig. 7 The 11.7 mm PSF of AC Her before (left)
and after (right) PSF subtraction (using a Her as
the PSF) with DAOPHOTs ALLSTAR task. The
residual flux after PSF subtraction is lt0.5 of
AC Hers original flux. Similar residuals
resulted from PSF subtractions at 9.8 mm and 18
mm. Based on these excellent subtractions it
appears that AC Her is not detectably extended.
Note that the small ghost image to the lower left
in each frame is not subtracted to show that the
vertical scales are the same for both images.

REFERENCES Bergman, P., Kerschbaum, F.,
Oloffson, H. 2000, AA, 353, 257 Biller, B.A.,
Close, L.M., Potter, D., Bieging, J., Hoffman,
W., Hinz, P., Oppenheimer, B.D. 2003, ApJ,
submitted Close, L.M., Biller, B.A., Hoffmann,
W., Hinz, P., Bieging, J., Wildi, F., Lloyd-Hart,
M., Brusa, G., Fisher, D., Miller, D., Angel,
R. 2003, ApJ, submitted Jura, M., Chen, C.,
Werner, M.W. 2000, ApJ, 521, 302
ACKNOWLEDGEMENTS We
acknowledge support from NASA Origins grant
NAG5-12086 and NSF SAA grant AST 0206351.
Fig. 4 -- Comparison of RV Boo to 15o
Inclination Model. For the sake of comparison
with the raw RV Boo image, the model image in the
lower right has been convolved with the m UMa PSF
(see upper right). The observed disk around RV
Boo has a major axis FWHM0.16 (60 AU at 390 pc)
and an inclination angle of 120o. For the
models, the central star was modeled as a 3000 K
blackbody. Models were fit to the measured SED
(IRAS fluxes at 12, 25, 60, and 100 mm our 9.8
mm flux). The best fit model had a disk
inclination angle from edge on of 15o and a
Mid-IR disk mass of 5x10-7 solar masses.
Particle sizes ranged from 50 to 150 mm and were
distributed at radii between 10 and 150 AU from
the star.