Transcript The First Adaptive Optics High Resolution Mid

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 (0.98+0.03) MidIR 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.
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.
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
o
disk at a position angle of 120 . 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
o
mass disk at an inclination of 15 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 radius~0.2” (the largest disk that can exist without being
detected). This model requires a reasonable Tb > 165K.
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. 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” (FWHM~0.8”; Jura et al. (2000)) is also plotted. Note
that AC Her’s morphology appears much more consistent with that of
the PSF stars at 9.8 and 11.7 mm than an extended FWHM~0.8” disk.
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. 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. 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 FWHM~0.16” (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.
Fig. 7 – The 11.7 mm PSF of AC Her before (left) and after
(right) PSF subtraction (using a Her as the PSF) with
DAOPHOT’s ALLSTAR task. The residual flux after PSF
subtraction is <0.5% of AC Her’s 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.
257
2000, A&A, 353,
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.