MUSE Integral Field Unit Observation of the Compact Objects in the Globular Cluster NGC 6397

Globular clusters are very old groups of stars. Due to their age and the gravitational
interactions dominating the dynamics of the clusters, they are home to a significant fraction
of compact binaries. The formation and evolution of these kinds of binaries is still not
completely understood. Of special interest is the globular cluster NGC 6397 as it is the
closest core-collapsed cluster and has therefore been extensively studied with instruments
like the Chandra X-ray Observatory, the Hubble Space Telescope, and more recently in the
optical with the Multi Unit Spectroscopic Explorer (MUSE), installed on the Very Large
Telescope (VLT). Integral field spectrographs, like MUSE, have many advantages compared
to traditional long slit spectroscopic instrument, as spectra are obtained for every pixel
and thus for every object in the large field of view (1' x 1'). Here we present an analysis
of the compact binary population in NGC 6397 taken with MUSE. The goal is to further
understand the characteristics of the proposed bimodal population of cataclysmic variables
(CVs) in the cluster, which have been suggested to be of primordial and dynamically formed
origins. In this work we were able to spectrocopically confirm two new CV candidates as well
as retrieve the spectra of three previously identified CVs. Spectral analysises of the extracted
spectra allow us to estimate the mass ratio for a sample of the identified CVs. We also were
able to compare the magnitude in the R band with previous observation of NGC 6397 to
determine if any of the CVs were observed during an outburst. From the spectral emission
and absorption lines we were also able to estimate the possible type of the companion and
examine the magnetic nature of the CVs. We specifically searched for Helium II lines as
signature of magnetism, and Titanium Oxide lines from a M type companion. We show that
this shallow observation of NGC 6397 with MUSE is a good starting point to finally obtain
optical spectra of compact objects in globular clusters but that with deeper observations a
more complete study of the CVs and other compact objects can be carried out.