Current cluster binary studies are carried out using one of two
methods, two-band photometry, and
time-baseline radial velocity studies,
each of which experience issues which
limit their effectiveness in answering
the above science questions. However,
to deeply understand the binary
populations of open clusters, we have
created a new method which can
determine accurate masses for all
members of a cluster within a
reasonable amount of telescope
time. This new binary detection method
is nicknamed binocs: Binary INformation from Open Clusters using
SEDs. By imaging a star using multiple
filters across the spectrum (e.g., UBV
RIJHKS[3.6][4.5][5.8][8.0]), one
should be able to “re- build” spectral
energy distribution (SED) of a star
given its parameters: age,
metallicity, mass. Similarly, a binary
system could not be accurately
modelled by a single SED curve, but
instead by two SEDs added together. By
matching stars to these models, mass
can be determined, similar to how
temperature could be determined in the
idealized black- body case. Since the
star is a member of a cluster with
known parameters, so age and
metallicity are given. By matching
stars to models of a library of
synthetic single stars SEDs, mass can
be determined.
This research
formed the core of the Ph.D. Thesis of Dr. Ben
Thompson and continues with Taylor Spoo.
A majority of stars are formed in open clusters, and then ejected
into the Galactic field population
through tidal effects from external
masses, as well as internal gravitational
interactions. Therefore, understanding
the internal dynamics of open clusters,
through N-Body simulations, will inform
the growth of the Galactic stellar
population. A major input into these
N-Body simulations is the frequency and
mass distribution of binary star systems,
which are currently based on statistics
derived from the field population, but
the distributions of binaries in clusters
may be different. Current binary
detection techniques, such as radial
velocity surveys, have drawbacks which
limit their usefulness for detailed
studies over large mass ranges. As
presented in the literature, different
mass ranges may produce different
interpretations of the observed binary
population, e.g, as published recently
for NGC 1818. A clearer picture of the
binary population, covering a wide mass
range, is needed to improve the
understanding of cluster binary
populations, which will inform cluster
simulations. We introduce a new binary
detection method, Binary INformation from
Open Clusters Using SEDs (BINOCS). Using
newly-observed multi-wavelength
photometric catalogs (0.3 - 8 micron) of
the key open clusters M35, M36, M37, M67
and NGC 2420, the BINOCS method is able
to determine accurate component masses
for unresolved cluster binaries. We
showed how binary fraction decrease as a
function of cluster age.
This part of the
OCCAM project is
led by Dr. Ben Thompson and
Dr. Peter Frinchaboy.
The BINOCS code can be obtained from the Github Repository
Completing an analysis large scale binary analysis using only RV surveys could take centuries to build up enough analysis clusters to produce any useful insights. Two-band analysis, though fast, is dominated by degeneracies, and is limited to small magnitude ranges across the main sequence. For this project, we will create a unprecedented systematic cluster binary stars survey that will provide significant empirical constraints, key for verifying and improving
the input physics for cluster N-body codes. Analyzing hundreds of star
clusters, in a uniform way allows us to
yield significant insights into the true
distribution of cluster binary
fractions.
We will create a new multi-wavelength (optical, near infrared, and mid-infrared) photometric catalog and analysis of over 100 star clusters to answer three primary questions about open clusters and their stellar/binary populations:
1) How do binary population properties change as a function of time in the cluster environment? 2) What is the binary fraction of cluster stars and how does it vary as a function of primary
star mass? 3) Does the evolution and impact of the binary population vary with the cluster mass, concentration, location, and/or chemical composition?
As an integral component in addressing the above questions, we will produce a membership cleaned catalog of single and binary stars, including component masses, which will be combined with upcoming Gaia kinematic data and chemical data from other studies (SDSS/APOGEE, GaiaESO, Hermes/Galah) to create a statistically significant sample to test the overall dynamical
evolution of cluster in detail. In addition to providing a definitive answer on the effects of metallicity and Galactic location, this expanded dataset will allow detailed analysis in a number of axes including mass and central concentration.
This part of the
OCCAM project is
being led by Taylor Spoo and Dr. Peter Frinchaboy.