High-resolution optical imaging of the core of the globular cluster M15 with FastCam

TL;DR

This paper demonstrates high-resolution optical imaging of the M15 globular cluster core using lucky imaging with FastCam, revealing detailed stellar populations and new Blue Straggler candidates.

Contribution

The study provides the deepest I-band imaging of M15's core at high spatial resolution using lucky imaging, enabling detailed photometry and identification of stellar populations.

Findings

Achieved ~0.1 arcsecond resolution imaging of M15 core.

Catalogued 1181 stars with I=19.5 limit, including new Blue Straggler candidates.

Compared results with HST data, confirming and expanding stellar population analysis.

Abstract

We present high-resolution I-band imaging of the core of the globular cluster M15 obtained at the 2.5 m Nordic Optical Telescope with FastCam, a low readout noise L3CCD based instrument. Short exposure times (30 ms) were used to record 200000 images (512 x 512 pixels each) over a period of 2 hours 43 min. The lucky imaging technique was then applied to generate a final image of the cluster centre with FWHM ~ 0".1 and 13" x 13" FoV. We obtained a catalogue of objects in this region with a limiting magnitude of I=19.5. I-band photometry and astrometry are reported for 1181 stars. This is the deepest I-band observation of the M15 core at this spatial resolution. Simulations show that crowding is limiting the completeness of the catalogue. At shorter wavelengths, a similar number of objects has been reported using HST/WFPC observations of the same field. The cross-match with the available HST catalogues allowed us to produce colour-magnitude diagrams where we identify new Blue Straggler star candidates and previously known stars of this class.