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RR Lyrae stars and the instability strip of 4 globular clusters: A survey at Behlen Observatory
Abstract
This investigation reports on observations taken for 4 globular clusters (NGC 5466, NGC 6934, NGC 6426, and NGC 7006) with the 30-inch reflecting telescope at Behlen Observatory. These globular clusters had few previous observations collected using CCD photometry, the IRAF/DAOPHOT algorithms, and no observations through Cousins R and I filters. This was the first globular cluster investigation for Behlen Observatory. Observations concentrated on the central $2.8\sp\prime\times4.6\sp\prime$ region (dictated by the size of the CCD chip) of each globular cluster. Behlen Observatory performed admirably with some limitations: a limiting magnitude of 17.5 in R for 300 second exposures; a mechanical error in the tracking of the telescope that prevented exposures much longer than 6 minutes; and a location and night sky that usually offered a seeing value not much better than 2 arcseconds. For the data reduction of the crowded fields, the IRAF/DAOPHOT algorithms displayed an inability to reduce the extremely crowded core of a globular cluster or stars located near bad pixels on the CCD chip. This inability often produced subtle photometric errors throughout the results that were difficult to recognize. For NGC 5466, this investigation determined a horizontal branch magnitude of 16.3 in R and confirmed an external reddening of approximately zero. Eleven of twelve previous variables within the field were detected with four period corrections, and one additional variable was found. One variable, V25, showed evidence of being another anomalous Cepheid for the cluster. For NGC 6934, this investigation determined a horizontal branch magnitude of 16.5 in R and recommends an external reddening of 0.06. Thirteen of thirty-nine previous variables within the field were detected with 2 period corrections, and 5 additional variables were found. NGC 6426 and NGC 7006 both produced unreliable results due to the proximity of the limiting magnitude to their horizontal branch magnitudes. Possible improvements for future globular cluster investigations are proposed and discussed.
Subject Area
Astronomy|Astrophysics|Physics|Remote sensing
Recommended Citation
Young, Todd Scott, "RR Lyrae stars and the instability strip of 4 globular clusters: A survey at Behlen Observatory" (1998). ETD collection for University of Nebraska-Lincoln. AAI9908491.
https://digitalcommons.unl.edu/dissertations/AAI9908491