Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21914504b&link_type=abstract
American Astronomical Society, AAS Meeting #219, #145.04
Astronomy and Astrophysics
Astronomy
Scientific paper
The Lick index system of standard stars is crucial for determining ages and metallicities of unresolved stellar populations. This project involves a calibration of the Gemini Multi-Object Spectrographs (GMOS) onto the Lick Standard index system. By comparing the well-defined spectral absorption features of the Lick stars to GMOS spectral absorption observations, we can accurately calibrate GMOS. Differences between these GMOS observations and Lick features, once determined, will result in correction factors that can be used for the calibration. This calibration of GMOS is useful because it allows for more accurate observations of unresolved stellar populations using the GMOS instrument. Although the observations and data reduction of the GMOS spectra was largely complete, we needed to insure the accuracy of the GMOS observations. We previously noticed unphysical errors in the shapes of some of the original GMOS spectra, so we carefully analyzed the data reduction process in order to find the source of these errors and ultimately correct them. The preliminary part of this process involved experimentation with various methods in order to narrow down the potential sources of the errors. Ultimately, we hypothesized that the unphysical errors may have been due to the presence of scattered light in the un-extracted spectra, which the original reduction program did not eliminate. We re-reduced some GMOS spectra, including the IRAF task apscatter in the reduction script to subtract the scattered light, and found that many unphysical errors were corrected. Deciding that the subtraction of the scattered light was effective, we re-reduced all GMOS Lick spectra, including the new apscatter step. The results were mixed, as the elimination of the scattered light corrected many of the poorly shaped spectra, but some errors remained. Further analysis of the spectral reduction process will hopefully determine the source of these remaining errors.
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