Atlas Image mosaic,
covering 10´ × 10´ on the sky of the globular star cluster
Messier 68 (M68). Salaris & Weiss (2002, A&A, 388, 492) recently
determined the age of the cluster to be 11.2 Gyr, which is slightly older
than the ~10 Gyr found by Brocato, Castellani, & Piersimoni (1997, ApJ,
491, 789). This cluster is relatively metal-poor. The light from globular
clusters in the near-infrared is dominated by old red giant stars, which
have approximately the same near-infrared colors. Thus, all the stars appear
to be about the same color, although not necessarily the same brightness.
Atlas Image mosaic,
covering 28´ × 28´ on the sky of the open cluster
IC 1590.
The cluster centers around the Trapezium-like system, HD 5005 (the bright blue
object north of image center). The cluster is associated with, and generally
embedded in, the nebula NGC 281 (Sharpless 184). Guetter & Turner (1997, AJ,
113, 2116) performed detailed optical photometry and spectroscopy, and limited
K-band photometry, of stars in the cluster and found the distance of 2.9 kpc
(9450 light years) to the optically-visible cluster, behind nearly 2
visual magnitudes of extinction. They find the cluster to be quite young,
~3.5 Myr. What is most remarkable is that, comparing an optical image of
NGC 281
with the 2MASS image, what are dark regions of dust in the optical nebula are
bright regions of dust and molecular gas emission in the near-infrared. More
importantly, deeply embedded newly-forming stars are evident, to the southwest
of the optical cluster (additional star formation appears to be occurring to
the east as well). The 2MASS color-color and
color-magnitude diagrams for both clusters show
that the age, distance, and reddening are consistent for the stars around
HD 5005 (green tracks on the diagrams), but the more embedded, probably very
young objects are behind up to ~15 visual magnitudes of extinction.
Atlas Image mosaic,
covering 25´ × 31´ on the sky of the filamentary, or
snake-like, infrared dark cloud G11.11-0.12. This is an example of
various
regions in the Milky Way Galaxy with very high visual extinction, in excess of
25 magnitudes. They were discovered by routine survey observations of the
Galactic plane by the
Infrared Space Observatory and the
Midcourse Space
Experiment. From the lack of emission
between 8 and 100 μm and high mid-infrared opacities, Egan et al. (1998,
ApJ, 494, L199) concluded that the infrared dark clouds contain cold (T<13 K)
dust and suggested that they are dense molecular cores. Carey et al. (2000,
ApJ, 543, L157) find strong submillimeter bright, compact sources in eight
dark clouds, using
SCUBA at the
JCMT, and these
authors suggest that these
highly embedded sources are potentially the sites for very early star
formation in the Galaxy. These
clouds, of course, look very dark on the near-infrared 2MASS images.
Image mosaic by S. Van Dyk (IPAC). These data are included in the Second
Incremental Data Release!
Atlas Image mosaic,
covering 15´ × 15´ on the sky of the prototypical reflection
nebula NGC 7023, aka the Iris Nebula.
The filamentary structures to the north and south are the edges of molecular
hydrogen gas clouds emitting in the near infrared. A bipolar cavity is seen to
to the east (and north) in this molecular emission (Gerin et al. 1998, ApJ,
500, 329). Rogers, Heyer, & Dewdney (1995, ApJ, 442, 694) indicate that a
bipolar outflow from the young, central Herbig Be star, HD 200775 (the bright
star toward the center of the 2MASS image), is responsible for the formation
of the cavity. Compare the Iris seen here with that in the
optical.
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