Karen Hamm (CLAS)
and Gail Zasowski (GSAS)




Groupings of stars
Born from the same giant molecular cloud
Young, low stellar density objects
Contain up to several thousand stars
M45: The Pleiades (the “7 Sisters”)
M67



Cluster motions,
distances, chemistry,
and ages much easier
to measure than
single stars’
Very useful tracers of
Galactic structure, star
formation, and
evolution
Probe tangled regions
of Milky Way
M51, the
“Whirlpool
Galaxy”
Milky Way



Clusters in disk of the
Milky Way, along with
dust
Dust makes stars
fainter and changes
their color
Dust effects are less
severe at longer
wavelengths
Barnard 68, ESO



Clusters in disk of the
Milky Way, along with
dust
Dust makes stars
fainter and changes
their color
Dust effects are less
severe at longer
wavelengths
“Extinction”  fainter
“Reddening”  redder
Barnard 68, ESO

NASA Spitzer Space
Telescope Surveys
◦
◦
◦
◦
NASA/ JPL Caltech
GLIMPSE-360
Cygnus-X
SMOG
Vela-Carina
Sun
Spitzer Space Telescope

NASA Spitzer Space
Telescope Surveys
◦
◦
◦
◦
NASA/ JPL Caltech
GLIMPSE-360
Cygnus-X
SMOG
Vela-Carina
Vela-Carina
Cygnus-X
Sun
SMOG
GLIMPSE-360
Spitzer Space Telescope


575 deg2 of
images
Candidate Criteria:
◦ Overdensity of stars
◦ Similar size and
brightness
Sample screenshot of SAOImage DS9 program
Each
= 1/3600 deg

◦ Depends on stars’ temperature, distance, etc.
Sorted candidates based on the clarity of the Spitzer
image and the strength and disparity of the CMDs
Brightness 
“Color-magnitude diagrams” (CMDs)
Brightness 

 Temperature
Brightness 
Brightness 
 Temperature
 Temperature
 Temperature
Zasowski, Beaton,
& Hamm, in prep.

◦ Depends on stars’ temperature, distance, etc.
Sorted candidates based on the clarity of the Spitzer
image and the strength and disparity of the CMDs
Brightness 
“Color-magnitude diagrams” (CMDs)
Brightness 

 Temperature
Brightness 
Brightness 
 Temperature
 Temperature
 Temperature
Zasowski, Beaton,
& Hamm, in prep.
Reddening compared to cluster
Brightness 

Brightness 

Each cluster CMD contains the stellar sequence of
that cluster, plus foreground and background
stars
Cluster stars should share similar foreground
reddening
Fit high-quality models (“isochrones”) to the
filtered stellar populations
Number

 Temperature
 Temperature
Zasowski, Beaton, & Hamm, in prep.
Cluster
Comparison
Restrict reddening range to [0.2 – 0.45]
Cluster
Comparison
Cluster
Comparison
Restrict reddening range to [0.0 – 0.1]
Cluster
Comparison
Cluster
Comparison
• Distance = 5.12 light-years
• Fraction of heavy elements
Restrict
to [0.2 – 0.45]
~63%reddening
that ofrange
the Sun
Cluster
Comparison
Cluster
Comparison
• Distance = 4.56 light-years
• Fraction of heavy elements
Restrict
[0.0 – 0.1]
equal reddening
to that ofrange
thetoSun
Cluster
Comparison



Identified ~375 open cluster candidates in
the outer Milky Way
Derived basic cluster parameters
(reddening, chemical abundance, distance)
for objects with well-populated near-IR
CMDs
Submitting paper with coordinates &
parameters for >30 newly-discovered and
unstudied clusters






Vela-Carina survey as focus of senior
thesis (Hamm)
Obtain more observations of interesting
candidates with large telescopes to
determine cluster motions
Write software to detect clusters
automatically
R.L. Beaton (GSAS)
S.R. Majewski (Dept of Astronomy)
B.A. Whitney (University of Wisconsin-Madison)
Gemini Observatory, HI








Churchwell, E., Babler, B. L., Meade, M. R., et al. 2009, PASP, 121,
213
Whitney, B., Arendt, R., Babler, B., et al. 2008, in Spitzer Proposal ID
#60020, 60020 (GLIMPSE-360)
Carey, S., Ali, B., Berriman, B., et al. 2008, in Spitzer Proposal ID
#50398, 50398 (SMOG)
Hora, J., Adams, J., Allen, L., et al. 2007, in Spitzer Proposal ID
#40184, 40184 (Cyg-X)
Majewski, S. R., et al. 2008, in Spitzer Proposal ID #
40791,40791 (Vela-Carina)
Whitney, B., Benjamin, R., Meade, M., et al. 2011, in Bulletin of the
American Astronomical Society, Vol. 43, American Astronomical
Society Meeting Abstracts No. 217, 241.16
Majewski, S.R., Zasowski, G., & Nidever, D.L. 2011, ApJ, 739, 25
Girardi, L., Bertelli, G., Bressan, A., et al. 2002, A&A, 391, 195