The First Adaptive Optics High Resolution Mid – IR Imaging of Evolved Stars: Case Studies of RV Boo and AC Her

1. 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) 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 radius~0.2” (the largest disk that can exist without being detected). This model requires a reasonable Tb > 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. The First Adaptive Optics High Resolution Mid – IR Imaging of Evolved Stars: Case Studies of RV Boo and AC Her Fig 5 – The 9.8, 11.7, and 18QS mm images of AC Her and PSF starsm 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” (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. 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 c2values 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 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. 2000, A&A, 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 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.