2 Observations and analysis

Observations were made on 14 June 2000 UT and 14 September 2000 UT at the KPNO 2.1-m telescope using the facility imager SQIID (Ellis et al. 1992). SQIID utilizes three dichroic beamsplitters to image a field simultaneously at J, H, K, and (narrow band) L. The June observations were among the first since the SQIID detectors were upgraded from the original low quantum efficiency PtSi arrays to high quantum efficiency Aladdin InSb arrays, increasing the responsivity by factors of 10 (J) to 50 (K). The SQIID optics illuminate most of a 512 $\times$ 512 Aladdin quadrant (but not the entire $1024\times1024$ array) with a resultant pixel scale at the 2.1-m of 0 $.\!\!^{\prime\prime}$69. Large thermal background due to hot weather at the times of the observations prevented images from being recorded at L.

The June observations consisted of five coadded 2 s observations at five locations (i.e., a total exposure of 50 s) centered on V605 Aql and on a calibration star. Each observation yielded three colors, J, H, and K. The grid of images was a standard five raster set, one with the object in the middle and the other four centered on the corners of a square, with each corner 7 $^{\prime\prime}$ diagonally offset from the midpoint. Each image was analyzed separately, with the quoted mean and uncertainty being calculated from the five separate measurements. The UKIRT Faint Standards Catalog star FS28 (SA109-71) was used for photometric calibration. The observations were repeated in September with a 4 by 4 grid of 30 coadded 5 s integrations (i.e. a total exposure of 2400 s).

IRAF routines were employed in the photometric and astrometric analysis of the images. All images were flat fielded using a dark subtracted flat field derived from sky observations. To produce a sky image the sets of images for each object in each color were combined using a median filter. The sky was then subtracted from each image and photometry was carried out using the "phot'' task in the "digiphot'' package. Each image was processed separately and the values combined to produce the uncertainty.

V605 Aql appears as a very red star on the images and was too faint to detect on individual June J images. To measure the position of V605 Aql astrometry was carried out on the H and K images, using the "tfinder'' and "tastrom'' tasks in the IRAF finder package. "tfinder'' uses the Hubble Guide Star catalogue for the reference star coordinates. To compare the Guide Star coordinates with USNO A2.0 coordinates we solved for the USNO A2.0 stars in our images. There does appear to be a small (less than 1 $^{\prime\prime}$) systematic offset between the two coordinate systems, most likely reflecting the limiting precision of the Guide Star coordinates.

Figure 1: Images of the V605 Aql field. Only the $88\hbox {$^{\prime \prime }$ }\times 88\hbox {$^{\prime \prime }$ }$section centered on V605 Aql is shown. The R band image is from the DSS2. The JHK images are the September 2000 SQIID data. V605 Aql is to the right of the horizontal line near the center of each image. In the R image both the planetary nebula A58 and the central star V605 Aql can be seen. In the K image we have marked the Herbig offset star (just above and to the right of the diagonal line just below the center of the image) and the van der Veen/Harrison star (bright star just above vertical line at right edge of image)