FSR 1716: A New Milky Way Globular Cluster Confirmed Using VVV RR Lyrae Stars

<jats:title>Abstract</jats:title>
<jats:p>We use deep multi-epoch near-IR images of the VISTA Variables in the Vía Láctea (VVV) Survey to search for RR Lyrae stars toward the Southern Galactic plane. Here, we report the discovery of a group of RR Lyrae stars close together in VVV tile d025. Inspection of the VVV images and PSF photometry reveals that most of these stars are likely to belong to a globular cluster that matches the position of the previously known star cluster FSR 1716. The stellar density map of the field yields a >100σ detection for this candidate globular cluster that is centered at equatorial coordinates R.A.<jats:sub>
<jats:italic>J</jats:italic>2000</jats:sub> = 16:10:30.0, decl.<jats:sub>
<jats:italic>J</jats:italic>2000</jats:sub> = −53:44:56 and galactic coordinates <jats:italic>l</jats:italic> = 329.77812, <jats:italic>b</jats:italic> = −1.59227. The color–magnitude diagram of this object reveals a well-populated red giant branch, with a prominent red clump at <jats:italic>K</jats:italic>
<jats:sub>
<jats:italic>s</jats:italic>
</jats:sub> = 13.35 ± 0.05, and <jats:italic>J</jats:italic> − <jats:italic>K</jats:italic>
<jats:sub>
<jats:italic>s</jats:italic>
</jats:sub> = 1.30 ± 0.05. We present the cluster RR Lyrae positions, magnitudes, colors, periods, and amplitudes. The presence of RR Lyrae indicates an old globular cluster, with an age >10 Gyr. We classify this object as an Oosterhoff type I globular cluster, based on the mean period of its RR Lyrae type ab, <jats:inline-formula>
<jats:tex-math>

</jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlaa5881ieqn1.gif" xlink:type="simple"/>
</jats:inline-formula> days, and argue that this is a relatively metal-poor cluster with [Fe/H] = −1.5 ± 0.4 dex. The mean extinction and reddening for this cluster are <jats:inline-formula>
<jats:tex-math>

</jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlaa5881ieqn2.gif" xlink:type="simple"/>
</jats:inline-formula> and <jats:italic>E</jats:italic>(<jats:italic>J</jats:italic> − <jats:italic>K</jats:italic>
<jats:sub>
<jats:italic>s</jats:italic>
</jats:sub>) = 0.72 ± 0.02 mag, respectively, as measured from the RR Lyrae colors and the near-IR color–magnitude diagram. We also measure the cluster distance using the RR Lyrae type ab stars. The cluster mean distance modulus is (<jats:italic>m</jats:italic> − <jats:italic>M</jats:italic>)<jats:sub>0</jats:sub> = 14.38 ± 0.03 mag, implying a distance <jats:italic>D</jats:italic> = 7.5 ± 0.2 kpc and a Galactocentric distance <jats:italic>R</jats:italic>
<jats:sub>
<jats:italic>G</jats:italic>
</jats:sub> = 4.3 kpc.</jats:p>