ALFA crowded star field observations: experiences, data reduction, and future strategies

David James Butler; Richard I. Davies; Markus Feldt

doi:10.1117/12.390386

7 July 2000 ALFA crowded star field observations: experiences, data reduction, and future strategies

David James Butler, Richard I. Davies, Markus Feldt

Proceedings Volume 4007, Adaptive Optical Systems Technology; (2000) https://doi.org/10.1117/12.390386
Event: Astronomical Telescopes and Instrumentation, 2000, Munich, Germany

Abstract

In objects like the Galactic center and star clusters, including Globular Clusters, the aim is to achieve the highest possible Strehl in order to separate objects with large luminosity differences. Although crowded star fields can be considered as prime targets for adaptive optics assisted NIR imaging, a number of challenges exist at both the observing and data reduction stages. While preparing for an observation, it may be useful to consider the effect of close guide star neighbors on centroiding and a sensible total integration time to achieve the desired S/N in the point spread function (PSF) halo. The centroiding issue is important because jittering of guide star neighbors in and out of the ALFA Shack-Hartmann wavefront sensor, as a result of a high stellar number density, can reduce the achievable Strehl. Total exposure time considerations may allow an empirical PSF determination with the desired PSF halo signal. In this contribution, we present our observational experiences, with ALFA, of a complicated region of stars in a Globular Cluster in both natural and a laser guide star observing mode as well as some relevant future plans. In particular, we concentrate on natural guide stars and consider the following: the use of a constrained centroiding algorithm, the change in the mean PSF halo pixel flux versus Strehl; and the use of 'a priori' astrometry and photometry in a deconvolution assisted profile fitting approach to crowded field photometry. This method reduced photometry errors and the systematic magnitude offset produced by a competing technique.

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David James Butler, Richard I. Davies, and Markus Feldt "ALFA crowded star field observations: experiences, data reduction, and future strategies", Proc. SPIE 4007, Adaptive Optical Systems Technology, (7 July 2000); https://doi.org/10.1117/12.390386

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KEYWORDS

Stars

Point spread functions

Photometry

Adaptive optics

Deconvolution

Wavefront sensors

K band

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