Figure 5. (above)
This color-magnitude
diagram of globular
cluster NGC 1851’s
crowded center combines
near-infrared observations
obtained using GeMS/
GSAOI at Gemini South
and optical data from the
Hubble Space Telescope.
Red dots mark the main
sequence turnoff and
the main sequence knee,
around Ks = 18 and 20.5
magnitudes, respectively.
Figure 6. (below)
This small extract from
the full 83-arcsecond
field-of-view illustrates
the quality and depth of
the images from Gemini.
The planet, orbiting at roughly the same
distance as Saturn in our Solar System, can
account for some dynamical features of
the disk, such as its warp. However, it cannot fully account for several other features.
In particular, β Pic b is not responsible for
clearing the region to the observed inner
disk edge at 23 astronomical units. Another planet could be the cause, but it would
have to be very faint to avoid detection so
far. Complete results are published in The
Astrophysical Journal; part of a press release
also appears on the following Gemini website, which provides a summary of the work,
including additional illustrations and an
animation of the data showing the planet’s
motion (viewable here).
The Deepest Ground-based
Photometry in a Crowded Field
Paolo Turri (University
of Victoria, Canada) and
colleagues have used
the Gemini Multi-conjugate adaptive optics
System (GeMS) with the
Gemini South Adaptive
Optics Imager (GSAOI)
to produce the most
accurate and deepest
near-infrared photometry from the ground of
a crowded field. Their Ks
measurements of the
Galactic globular cluster NGC 1851 reach the
precision and depth of
optical observations obtained using the Hubble
Space Telescope, and
the resulting combined
color-magnitude diagram reveals physical
characteristics of the
cluster (Figure 5).
24
GeminiFocus
Specifically, the researchers detect the double subgiant branch in the cluster’s center,
which indicates either multiple episodes of
star formation or multiple populations having distinct metal composition, rather than
a single uniform population of stars. Turri et
al. measure the main sequence well below
its turnoff, for 3.5 magnitudes. A feature
observed around KS = 20.5 is the “main sequence knee,” which may be useful to determine the cluster’s age, independent of distance and reddening estimates.
The delivered image qu