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Maintained by LG |
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2001 REU Students' AAS AbstractsAAS
199th
meeting,
Washington,
DC, January
2002 It is important to determine the composition of unevolved stars in globular clusters in order to learn the original composition of the cluster and to learn about stellar evolution and the chemical history of the Galactic halo. We have made observations of five stars at the turn-off in M 71 with the Keck I 10-m telescope and HIRES at a spectral resolution of 45,000. Such stars have not undergone any mixing with the interior layers and can provide benchmark abundances to interpret the abundance results found in red giants and other evolved stars. These stars have V = 17.7 and integration times of 2.5-5 hours were needed to obtain signal-to-noise ratios of 50-60. We have determined abundances of Li, Na, the Fe-peak elements: Fe, Cr, Ni, alpha-fusion elements: Mg, Si, Ca, Ti, and neutron capture elements: Y and Ba. Except for Li, we have found no star-to-star abundance variations and derive [Fe/H] = -0.80 ±0.02. The alpha elements are enhanced with [<\alpha>/Fe] = 0.24. Both Y and Ba are enhanced relative to Fe also. We compare our results with those from giant stars in M71, with turn-off stars in the globular clusters M13 and M92, and with halo field stars. This work has been supported by the National Science Foundation. AAS
199th
meeting,
Washington,
DC, January
2002 The Apollo-type near-Earth asteroid (25143) 1998 SF36 has been selected as the target for the Japanese MUSES-C sample return mission. To assist with mission planning, we participated in a world-wide effort to acquire physical observations of this asteroid during its close approach to the Earth in 2001. The work being presented here deals with observations to determine the rotational state and shape of the asteroid. The 2001 apparition was particularly well-suited for the determination of the orientation of the spin axis, because the asteroid swung through 180 degrees of geocentric ecliptic longitude, though our observations will need to be combined with similar ones from other observatories made at different times during the apparition to realize the full potential of the data. Our observations do show a 12-hour rotation period, which is slower than average for asteroids. The brightness variation exceeds 0.7 mag, indicating an elongated shape with an axial ratio of at least 2 to 1. This research was conducted through a Research Experience for Undergraduates (REU) position at the University of Hawaii's Institute for Astronomy. AAS
199th
meeting,
Washington,
DC, January
2002 We have obtained spectra from 0.95 to 2.35 micron at a spectral resolution of ~1,200 for a sample of luminous infrared-bright galaxies. The spectra were measured with SpeX, the new cross-dispersed medium-resolution infrared spectrometer at the NASA Infrared Telescope Facility. Since our goal was to investigate putative AGN or starburst activity in the centers of these galaxies, with as little dilution from the surrounding galaxy as possible, the spectra were taken with a 0.5 x 2 arcsec2 slit. We use these data: a) to search for broad hydrogen lines indicative of an underlying AGN, and b) to determine the stellar populations of underlying starbursts using stellar evolutionary synthesis models. These results will be compared with those found from previously-published 2 micron spectra for these galaxies obtained with a 3 x 9 arcsec2 slit. This work was supported by NSF Grant AST 99-87896 and NASA Grants NAG 5-3370 and JPL 961566. AAS
199th
meeting,
Washington,
DC, January
2002 What
is the
richness
of the
stellar
aggregate
associated
with the
reflection
nebula,
NGC7023
and what
is its
star formation
history?
NGC7023
is located
in the
Cepheus
Flare Region
and numerous
studies
have been
conducted
on the
properties
of its
nebulosity.
However,
there has
been little
investigation
into the
properties
of its
stars.
HD200775
is the
brightest
star in
NGC7023
and it
is classified
as a Herbig
Be star,
an intermediate
mass analogue
of solar-type
pre-main
sequence
T Tauri
stars.
By sampling
the full
stellar
population,
the sequence
of star
formation
and distribution
of stellar
masses
can be
investigated.
To understand
these properties,
regions
in and
around
NGC7023
were sampled
for stars
with H
alpha emission,
a reliable
method
of identifying
active
young stars.
For five
fields
around
NGC7023,
7.5 square
arcminutes
each, photometry
was obtained
in BVRI.
Point spread
function
fitting
was used
in order
to look
for blended
or binary
stars.
Color-magnitude
diagrams
were created
and compared
with pre-main
sequence
tracks
to determine
the age
of the
aggregate.
With the
knowledge
of the
distance,
extinction,
and age,
the distribution
of the
H alpha
emission
stars can
be compared
with the
distribution
of the
other members
in the
aggregate
associated
with NGC7023. |
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