3 Discussion

Individual J, H, and K images were shifted and averaged to yield the combined frames shown in Fig. 1. V605 Aql is not visible on some individual J images, but can be seen in the combined images. In June $J=18.7\pm 0.3$ and in September $J=18.1\pm 0.1$. The average H and K photometry from the individual images yield $H=16.78\pm 0.15$ and $K=14.67\pm 0.04$ for the June images and $H=16.43 \pm 0.05$ and $K=14.63 \pm 0.03$ for the September images. The formal uncertainty is the standard deviation of the individual measurements. The J-H-K color temperature of V605 Aql is $\sim$1000 K but the three points are not perfectly defined by a blackbody. The June and September magnitudes agree at about the size of the uncertainty and no variation in the magnitude of V605 Aql is indicated. The observed flux is significantly less (by $\sim$1.5 mag at J; 3.7 mag at K) than that predicted by Kimeswenger et al. (2000).

Astrometry of V605 Aql in the June H and K images yields the position

19$^{\rm h}$18$^{\rm m}$20 $.\!\!^{\rm s}$5 $\pm$ 0 $.\!\!^{\rm s}$6  +1$^\circ$46$^\prime$58 $.\!\!^{\prime\prime}$$7\pm 1$ $.\!\!^{\prime\prime}$0 (2000)

relative to the HST Guide Star reference frame. As noted above, the HST and USNO A2 reference frames differ in this field by nearly 1 $^{\prime\prime}$. A shift between TYCHO2 and USNO A2 coordinate systems of a similar magnitude is mentioned by Kimeswenger et al. (2000). V605 Aql is visible on both the red and blue Digital Sky Survey 2 (DSS2) images. From the DSS2 red image we find the position for V605 Aql to be

19$^{\rm h}$18$^{\rm m}$20 $.\!\!^{\rm s}$56$\pm$0 $.\!\!^{\rm s}$17  +1$^\circ$46$^\prime$58 $.\!\!^{\prime\prime}$8$\pm$0 $.\!\!^{\prime\prime}$3 (2000)

using the HST guide star reference frame. The infrared and DSS2 positions agree to within the uncertainty. The coordinates agree nicely with those measured from the Palomar Sky Survey by Pollacco et al. (1992). However, the coordinates differ slightly from those of Kimeswenger et al. (2000) which were apparently measured from the DSS2. The disagreement in RA is within the uncertainty but the disagreement in declination is more than 2 $^{\prime\prime}$.

We confirm the Kimeswenger et al. (2000) identification of the star measured by van der Veen et al. (1989) and Harrison (1996). We measure magnitudes of J= 10.16, H= 9.48, K=9.07 with formal uncertainties of better than 0.01 magnitude. It must be emphasized that since the star measured by van der Veen et al. (1989) and Harrison (1996) was not V605 Aql, near infrared magnitudes reported for V605 Aql up to now in the literature are incorrect and must be disregarded. We have also measured, using the DSS2, the position of the van der Veen/Harrison star, 19$^{\rm h}$18$^{\rm m}$18 $.\!\!^{\rm s}$16  +1$^\circ$46$^\prime$51 $.\!\!^{\prime\prime}$9, and the 17th magnitude offset star mentioned by Herbig, 19$^{\rm h}$18$^{\rm m}$20 $.\!\!^{\rm s}$81  +1$^\circ$46$^\prime$ 51 $.\!\!^{\prime\prime}$8. The infrared magnitudes of the Herbig star are J=12.77, H=11.99, K=11.82. Observers may find these field stars useful for setting up on V605 Aql.

The spatial resolution of the infrared images reported in this paper is relatively coarse, $\sim$1 $.\!\!^{\prime\prime}$4. While these images are useful for measuring the overall infrared properties of V605 Aql, it has been pointed out by Pollacco et al. (1992) that the expanding material resulting from the final flash of V605 Aql should now have a diameter on the order of 1 $^{\prime\prime}$. Clayton & De Marco (1997) and Guerrero & Manchado (1996) have marginally resolved this shell, referred to as the central knot of A58, using optical emission lines. The infrared radiation originates in optically thick dust in the central knot (Clayton & De Marco 1997) and comparison of images of the dust with images of the emission lines would be revealing of the geometry.

Acknowledgements

We thank Dr. K. Michael Merrill for assisting with SQIID. We are indebted to Dr. Glenn Tiede for obtaining the observation on 14 September. We acknowledge Dr. George Jacoby for useful discussions and thank him for providing an observation of the V605 Aql field and for noting the image of V605 Aql on the blue DSS2. We thank the referees, Dr. F. Kerber and Dr. C. Waelkens, for comments that improved this paper. This research made use of the SIMBAD database, operated by CDS in Strasbourg, France, and NASA's Astrophysics Data System Abstract Service.