NGC 869 and NGC 884: The Double Cluster

A little page of information and pictures presented by Chris Mertens.

 
 
 
(This page is ideally viewed in a large sized window)
 
NGC 869 NGC 884
Right Ascension 2:19.0 (h:m) 2:22.4 (h:m)
Declination +57d 09' +57d 07'
Appearent Magnitude 4.3 4.4
Appearent Dimension 30arcmin 30arcmin
Distance 7.1 kly 7.4 kly
While star clusters are neat in themselves, this pair of open clusters, NGC 869 and NGC 884, are doubly interesting. They are also known as h and chi Persei, respectively, as well as Caldwell 14. While double clusters are extremely rare, this one is particularly special because it can be seen in a dark location with the naked eye. Although their discovery likely precedes written history, the double cluster was first cataloged by the Greek astronomer Hipparcos. The clusters are over 7000 light years away in the direction of the constellation Perseus, but are separated by only a few hundred light years.

Both clusters are very young, and found in the Perseus OB1 association. They are mostly composed of very young, hot stars. The hottest main sequence stars are of spectral type B0, thus they are both very young clusters. According to Sky Catalog 200, the ages for NGC 869 and NGC 884 are 5.6 and 3.2 million years. Both clusters are approaching earth at a rate of about 21 km/sec. The clusters are found, as mentioned above, in the constellation Perseus, where there are a number of spectacular objects to look at. This is aributed to the milky-way band "running through" the constellation. We can then see that the clusters are on the disk of our galaxy. This makes sense as they are young hot stars, as opposed to the ancient globular clusters which are found in the halo about the galaxy.
                                     NGC 869                                                          NGC 884
  

DETAILS OF MY OBSERVATIONS
Above are the pictures I took with the 16'' reflecting telescope at the Macalester Observatory using the ST -6 CCD camera, at 12:34 a.m. of November 29th, 1999. It was particularly cold and mostly clear that night, with a very small amount of moisture in the air. The air mass values were 1.17 and 1.18 for NGC 869 and NC 884, respectively. The signal to noise ratio for the two was 30.6 and 46.9, which under the given conditions and equipment, is quite good. The displayed picture is the result of combining three images taken with different colored filters, (red, green, and blue). The images were taken with 1 second exposures at high resolution, then combined into one composite image. While this comparatively short exposure only brought out a portion of the stars (to see the stars of greater magnitude, longer exposure times would be necessary), we can see the simmilarities and differences between the two clusters. NGC 869 has more stores overall than its partner, as well as fewer red stars. This is quite visible in the two side-by-side images. We can se a definitely red start in the middle of NGC 884. It should also be noted that the images that I took above are only a portion of the center of the clusters. To see the entire clusters, in one image, we can look below.
 
 


 
 
 
 
 
 
 
 

This image was processed and printed by J. Roberts. It was taken from Tolland, CT on 21 August 1993, through a 500mm F6.3 Vivitar lens. The exposure time is believed to be about four minutes.
 
 
 

For some really great color images of these two spectacular clusters, check out Andy Steere's website,  here.

If you have questions or comments about this page, feel free to e-mail me, Chris Mertens.

P.L.U.R.