mountain profile Institute for Astronomy University of Hawaii

2001 REU Students' AAS Abstracts

Maintained by LG

AAS 199th meeting, Washington, DC, January 2002
[56.18] The Chemical Composition of the Globular Cluster M71 from Keck/HIRES Spectra of Turn-Off Stars
A. M. Boesgaard (U. Hawaii), A. M. Cody (Harvard U.), C. P. Deliyannis (Indiana U.), J. R. King (UNLV), A. Stephens (U. Hawaii)

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
[63.03] Rotational Studies of MUSES-C Target Asteroid (25143) 1998 SF36
J.S. Lambert, D.J. Tholen (IFA, U. Hawaii)

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
[54.01] Near-Infrared Spectroscopy of a Sample of Luminous Infrared Galaxies
R. D. Joseph (University of Hawaii), M. Pitts (Ohio State University)

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
[96.08] The Stellar Population Associated with NGC7023
A. Urban, M. R. Meyer (Steward Obs., U. of Arizona), G. H. Herbig, S. Dahm (IfA, U. of Hawaii)

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.
This research project was supported by the NSF REU program.