The open star cluster NGC 6649 in Scutum, shown in a color-composite CCD image from the 2.1m telescope of Kitt Peak National Observatory. The three-color data were taken by Bill Keel and Lisa Frattare in June 2003, in the teeth of the same high south wind that made fighting the nearby Catalina wildfire so difficult. The field is 4.6 by 4.7 arcminutes, with north at the top and east to the left.
NGC 6649 is young enough (with an age of about 50 million years) to have supergiants. Most interesting is the Cepheid variable star V367 Scuti, the bright yellowish star at the southwestern (lower left) edge of the cluster. Cepheid variables are supergiant stars that are unstable to pulsation, and whose period of pulsation correlates closely with the star's luminosity (making them the distance tracer of choice for galaxies that are not too far away). Cepheids in clusters offer a way to calibrate the zero point of the distance scale extending all the way to the Virgo cluster of galaxies, since we can use the properties of all the stars in the cluster to estimate the Cepheid's distance. For NGC 6649, the distance is estimated from colors and magnitudes of the member stars at 1600 parsecs or 5200 light-years. In this direction, looking inward toward the Galactic Center, the starlight is heavily reddened by intervening dust particles.
Last changes: 3/2005 © 2005