Close Encounter with the Ring Nebula

T. Jarrett, IPAC


Ring Nebula in the K band


The Ring Nebula is one of the most spectacular planetary nebula in the night sky. It is easily detected with the 2MASS arrays and thus should be detected by GALWORKS as either one big extended object or several extended objects. The results are given here.

First we would like to know what effect, if any, the ring nebular (size ~ 2 arc min) has on the background determination. The image below shows the raw K-band coadd and the star-subtracted coadd. Notice that several sources within the nebula have been detected and blanked accordingly. A couple of the sources are real stars, while the remaining detections are simply bright knots of nebular emission. The background solution image is shown in the last panel.

A gradient in the diffuse background light can be seen extending north-south, with the norther and southern ends of the coadd with the brightest background. The solution image reflects this general trend. Note that the Ring Nebula does not appear in the background solution -- which is reasonable given the relative small size of the object (the background determination is sensitive to objects larger than 3 arcmin is size).

The bright star in the lower right end of the coadd does affect the background solution (in the sense that the pixel information is blanked in this region), but is it localized to the area encompassing the star (which is blanked from the coadd and the area is excluded from further action by GALWORKS).

Extended Sources

As expected, GALWORKS "breaks" the object into two major pieces with a third piece comprising diffuse emission from the nebula.

Two of the "detections" appear as very large extended sources (radii > 1 arcmin) which we be easily identified in the database as something to follow up. The third detection arises from incomplete blanking of the first two detections (which "eat" most of the nebula), particularly at H band. There is enough diffuse light from the nebula to "bump" up the flux of the faint little block just north of the ring feature.

The scan from which we extract the ring nebula was only one degree in length, so only 1/6 of a sq. degree was covered in total. Consequently, there are only three additional "extended source" candidates in the scan besides the Ring Nebula pieces.

The three sources shown here are all rather faint, K > 13.6. The first object, id=40, is clearly a double star with a bright star next to the pair. It looks most extended in the K-band where some "fuzz" can be seen around this star. Most likely this is simply noise. The second object, id=1555, looks to be a faint star. Again, it appears to be extended only in K band (note that J and H scores are stellar). The final object is too faint to call, but it might be a double/triple system. We may conclude from this finding is that our reliability is starting to decline at K > 13.5 or so. The J and H limits may still be holding. This conclusion is very preliminary of course. This scan is not ideal for computing reliability numbers.