85 research outputs found
A comparison of the globular cluster luminosity functions of the inner and outer halo of the Milky Way and M31
We show that the globular cluster luminosity function (GCLF) of the inner
halo of the Milky Way is statistically different from the GCLF of the outer
halo. We also find a similar difference between the inner and outer halo
population of M31. We assert that this difference is evidence for some form of
dynamical evolution of the cluster population and/or a dependence of GCLF shape
on the environment in which the cluster population formed. We also find that
the turnover luminosity of the GCLF is unaffected by these differences and
further assert that this stability of the turnover luminosity affirms its
usefulness as an indicator of cosmic distance.Comment: 3 pages, 2 figures, submitted to MNRA
Pencil-Beam Surveys for Trans-Neptunian Objects: Novel Methods for Optimization and Characterization
Digital co-addition of astronomical images is a common technique for
increasing signal-to-noise and image depth. A modification of this simple
technique has been applied to the detection of minor bodies in the Solar
System: first stationary objects are removed through the subtraction of a
high-SN template image, then the sky motion of the Solar System bodies of
interest is predicted and compensated for by shifting pixels in software prior
to the co-addition step. This "shift-and-stack" approach has been applied with
great success in directed surveys for minor Solar System bodies. In these
surveys, the shifts have been parameterized in a variety of ways. However,
these parameterizations have not been optimized and in most cases cannot be
effectively applied to data sets with long observation arcs due to objects'
real trajectories diverging from linear tracks on the sky. This paper presents
two novel probabilistic approaches for determining a near-optimum set of
shift-vectors to apply to any image set given a desired region of orbital space
to search. The first method is designed for short observational arcs, and the
second for observational arcs long enough to require non-linear shift-vectors.
Using these techniques and other optimizations, we derive optimized grids for
previous surveys that have used "shift-and-stack" approaches to illustrate the
improvements that can be made with our method, and at the same time derive new
limits on the range of orbital parameters these surveys searched. We conclude
with a simulation of a future applications for this approach with LSST, and
show that combining multiple nights of data from such next-generation
facilities is within the realm of computational feasibility.Comment: Accepted for publication in PASP March 1, 2010
Consequences of a Distant Massive Planet on the Large Semi-major Axis Trans-Neptunian Objects
We explore the distant giant planet hypothesis by integrating the large
semi-major axis, large pericenter Trans-Neptunian Objects (TNOs) in the
presence of the giant planets and an external perturber whose orbit is
consistent with the proposed distant, eccentric, and inclined giant planet, so
called planet 9. We find that TNOs with semi-major axes greater than 250 au
experience some longitude of perihelion shepherding, but that a generic outcome
of such evolutions is that the TNOs evolve to larger pericenter orbits, and
commonly get raised to retrograde inclinations. This pericenter and inclination
evolution requires a massive disk of TNOs (tens of M_\Earth) in order to
explain the detection of the known sample today. Some of the highly inclined
orbits produced by the examined perturbers will be inside of the orbital
parameter space probed by prior surveys, implying a missing signature of the
9th planet scenario. The distant giant planet scenarios explored in this work
do not reproduce the observed signal of simultaneous clustering in argument of
pericenter, longitude of the ascending node, and longitude of perihelion in the
region of the known TNOs
The Kuiper Belt Luminosity Function from m(R)=21 to 26
We have performed an ecliptic imaging survey of the Kuiper belt with our
deepest and widest field achieving a limiting flux of m(g') = 26.4, with a sky
coverage of 3.0 square-degrees. This is the largest coverage of any other
Kuiper belt survey to this depth. We detect 72 objects, two of which have been
previously observed. We have improved the Bayesian maximum likelihood fitting
technique presented in Gladman et al. (1998) to account for calibration and sky
density variations and have used this to determine the luminosity function of
the Kuiper belt. Combining our detections with previous surveys, we find the
luminosity function is well represented by a single power-law with slope alpha
= 0.65 +/- 0.05 and an on ecliptic sky density of 1 object per square-degree
brighter than m(R)=23.42 +/- 0.13. Assuming constant albedos, this slope
suggests a differential size-distribution slope of 4.25 +/- 0.25, which is
steeper than the Dohnanyi slope of 3.5 expected if the belt is in a state of
collisional equilibrium. We find no evidence for a roll-over or knee in the
luminosity function and reject such models brightward of m(R) ~ 24.6.Comment: 50 Pages, 8 Figure
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