The Kinematics of Globular Clusters Measured with a Fabry Perot: the Inner 0.7' of M15 and 47 TUC

Details The Kinematics of Globular Clusters Measured with a Fabry Perot: the Inner 0.7' of M15 and 47 TUC The Kinematics of Globular Clusters Measured with a Fabry Perot: the Inner 0.7' of M15 and 47 TUC

Dec 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.4308g&link_type=abstract

American Astronomical Society, 181st AAS Meeting, #43.08; Bulletin of the American Astronomical Society, Vol. 24, p.1188

Astronomy and Astrophysics

Astronomy

3

Scientific paper

We are using the Rutgers Imaging Fabry Perot Interferometer on the CTIO 4m telescope to study the kinematics of globular clusters. The etalon has a resolution of 0.7 Angstroms at 5900 Angstroms (FWHM), which equals the broadening caused by a velocity dispersion of 15 \kms. We take a series of images, spaced at about 0.25 Angstroms, covering a strong absorption line (one of the Na D lines or a Ca triplet line) to produce a short spectrum at each pixel. The Fabry Perot field of view is about 4.5 square arcmin, but, due to the parabolic variation of wavelength with radius in the field, we get good coverage of the absorption line out to about 0.7' from the center with 15 exposures. If conditions are not photometric, we can normalize the images by using the stars on the edge of the field that are in the continuum. The information in these frames can be exploited in several ways. Measuring the brightness in each frame of every identifiable star yields stellar spectra and thus velocities. We use DAOPHOT II (Stetson, P.B. 1987 (Pub. A.S.P., 99, 191)) to do this. DAOPHOT can also subtract most of the light of the brighter stars and produce frames of residual cluster light, from which we can get the spectra of the integrated light. The broadening of the line in the spectrum of the diffuse light yields, in principle, the velocity dispersion of the underlying fainter stars, particularly near the cusp center. We present our results from two runs for the clusters M15 and 47 Tuc. We confirm the inward increase in the velocity dispersion of M15 previously measured by Peterson, R.C., Seitzer, P. and Cudworth, K.M. 1989 (Ap. J., 347, 251), but our dispersion estimates are smaller than theirs. Our measured dispersion for 25 stars within the 0.2' of the cluster center is 10 \kms, 5 \kms smaller than the value found by Peterson et.al..

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