Atlas Image mosaic, covering
5.0´ × 5.0´ on the sky, of the planetary nebula
NGC 6369. The nebula,
noted for its peculiar fishtail-like outer loop morphology in
the light of optical emission lines (also seen faintly in this near-infrared
image, outside the bright ring of the nebula). This planetary nebula
is associated with fast low-ionization
emission regions, or FLIERs, which are thought to be discrete, collimated,
and highly supersonic ejection events from the very hot central star
(Hajian 1997, ApJ, 487, 304), which can be seen at the center of the ring.
Planetary nebulae are formed as low-mass stars, like our Sun, reach the end of
their lives and lose their outer envelopes to the interstellar medium.
The pinkish color in the bright ring of the nebula may arise from emission by
atomic and molecular hydrogen primarily in the 2.17 µm wavelength
(Ks) band, or dust scattering in a combination of all three bands.
These data are included in the Second Incremental Release!
Atlas Image mosaic, covering
6.7´ × 6.7´ on the sky, of comet 52P/Harrington-Abell,
which was serendipitously observed by 2MASS on 1998 Oct 8 UT
and is among twenty comets included in the
2MASS Second Incremental Data Release. Comets, of course, are within our
Solar System and orbit the Sun, and therefore do not move sidereally (that is,
as the stars do). Astronomers, however, have determined the
ephemerides, or orbital parameters, for large numbers of known comets, so
their positions in the sky along their orbits can be accurately predicted.
Occasionally, comets, asteroids, and even planets can "accidentally" wander
into the Survey. Comets reflect sunlight, yet near-infrared photometry can
provide useful compositional and structural information about these objects.
This comet was seen optically to experience a significant outburst in 1998
July (IAUC 6975) and became unusually bright by August (IAUC 6994), exceeding
visual magnitude 11 by 1999 February (IAUC 7113). Its coma diameter was
1-2´ and tail length of about 2´ in 1998 (IAUC 6975). In 2001
December the comet was seen to have split into two (IAUC 7769), following
a brightening by more than two magnitudes between 2001 August and September
(IAUC 7773).
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12 billion years. Tavarez & Friel find a reddening to
the cluster of E(B-V)=0.73; here we show
the 2MASS color-color diagram for the cluster. It is difficult to exactly
determine the reddening from this diagram, but it does appear to be modest.
Here we show the 2MASS color-magnitude diagram,
with Padua theoretical isochrones (Bertelli et al. 1994, A&AS, 106, 275)
overlaid. An age of ~12 billion years (green line) is consistent with
the near-infrared data, however, with a lower reddening, E(B-V)~0.60.
(The diagram also shows that ages of 10 billion years [red line]
and 14.5 billion years [blue line] are also consistent with the data,
since these age tracks become somewhat degenerate in the near-infrared colors;
scatter in the datapoints, due to crowding, is also present;
the other bluer stars on the diagram are foreground stellar contamination.)
At least one likely dust-enshrouded AGB star, the reddish star
(Ks=8.03, J-Ks=4.55, not shown on the diagram) is
evident in the cluster (the other reddish
"star" just south of the brightest star in the image is a known artifact).
Lyngå 7 represents an important
link between the oldest open clusters and the youngest globular clusters in
the Galaxy. Image mosaic by S. Van Dyk (IPAC). These data are included in
the Second Incremental Release!
