Zwicky Transient Facility and Globular Clusters: the gr-Band Period-Luminosity Relations for Mira Variables at Maximum Light and Their Applications to Local Galaxies

TL;DR

This study establishes the first gr-band period-luminosity relations for Mira variables at maximum light using ZTF data, enabling accurate distance measurements to nearby galaxies with short-period Miras.

Contribution

It derives and validates new gr-band PL relations for short-period Miras at maximum light, applicable to local galaxies and useful for future large surveys.

Findings

PL relations are accurate for short-period (<300 days) Miras.

Long-period Miras do not follow the derived PL relations.

PL relations can determine distances even with partial light-curve data.

Abstract

Based on 14 Miras located in 7 globular clusters, we derived the first gr-band period-luminosity (PL) at maximum light for the large-amplitude Mira variables using the multi-year light-curve data collected from the Zwicky Transient Facility (ZTF). Since Miras are red variables, we applied a color-term correction to subsets of ZTF light curves, and found that such corrections do not have a large impact on period determinations. We applied our derived PL relations to the known extragalactic Miras in five local galaxies (Sextans, Leo I, Leo II, NGC6822 and IC1613), and determined their Mira-based distances. We demonstrated that our PL relations can be applied to short-period (<300 days) Miras, including those in the two most distant galaxies (NGC6822 and IC1613) in our sample even when only a portion of the light-curves around maximum light have detections. We have also shown that the long-period extragalactic Miras do not follow the PL relations extrapolated to longer periods. Hence, our derived PL relations are only applicable to the short-period Miras, which will be discovered in abundance in local galaxies within the era of Vera C. Rubin Observatory's Legacy Survey of Space and Time.