RR Lyrae Stars in the Field of Sagittarius II

Abstract

We present the detection of RR Lyrae variable stars in the field of the Sagittarius II (Sgr II) ultra-faint dwarf (UFD) galaxy. Using B, V time-series photometry obtained with the Korea Microlensing Telescope Network (KMTNet) 1.6 m telescope at CTIO and G-band data from Gaia Data Release 2 (DR2), we identified and characterized two ab-type and four c-type RR Lyrae variables. Five out of the six stars are clustered within three half-light radii (~4.8') of the galaxy indicating their association with Sgr II, while the RRab star V4 is located ~22' from the galaxy center. By excluding V4, the high c-type fraction (0.8) and the period of the only RRab star V3 (P_V3 = 0.666 days) suggest an Oosterhoff II (Oo II) classification for Sgr II. Located close to the locus of Oo II clusters in the period-amplitude diagram, V3 is similar to RRab stars in other UFDs having Oosterhoff-intermediate and Oo II properties. Sgr II is, however, more compact than usual UFDs, placed in between star clusters and dwarf galaxies in the size-luminosity plane, and therefore spectroscopic studies are eventually required to ascertain the true nature of this stellar system. We derive the metallicity ([Fe/H]_RRab = -2.1 +- 0.3) and heliocentric distance (~64 +- 3 kpc) of Sgr II from the RR Lyrae stars, and estimate its age (~12 Gyr) based on our stellar population models. The Oosterhoff properties of UFDs can be explained with the evolution effect of RR Lyrae stars in the instability strip.

arXiv commentAccepted for publication in ApJ, 6 pages, 4 figures, and 1 table

References in corpus (44)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• The Sloan Digital Sky Survey: Technical Summary
• Gaia Data Release 2. Summary of the contents and survey properties
• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• The Gaia mission
• The Dark Energy Survey: more than dark energy - an overview
• The Kinematics of the Ultra-Faint Milky Way Satellites: Solving the Missing Satellite Problem
• Gaia Data Release 2: Photometric content and validation
• The SDSS View of the Palomar-Green Bright Quasar Survey
• Variable Stars in Galactic Globular Clusters
• The Third US Naval Observatory CCD Astrograph Catalog (UCAC3)
• The Quenching of the Ultra-Faint Dwarf Galaxies in the Reionization Era
• Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
• A Complete Spectroscopic Survey of the Milky Way Satellite Segue 1: The Darkest Galaxy
• Sagittarius II, Draco II and Laevens 3: three new Milky Way satellites discovered in the Pan-STARRS 1 3pi Survey
• On a new theoretical framework for RR Lyrae stars I: the metallicity dependence
• A multi-color and Fourier study of RR Lyrae variables in the globular cluster NGC 5272 (M3)
• A Magellanic Origin of the DES Dwarfs
• Discovery of two neighboring satellites in the Carina constellation with MagLiteS
• The MACHO Project 9 Million Star Color-Magnitude Diagram of the Large Magellanic Cloud
• A Deeper Look at the New Milky Way Satellites: Sagittarius II, Reticulum II, Phoenix II, and Tucana III
• CCD Photometry of Galactic Globular Clusters. IV. The NGC 1851 RR Lyraes
• Star Formation Histories of Globular Clusters with Multiple Populations. I. ω Cen, M22, and NGC 1851
• La Silla QUEST RR Lyrae Star Survey: Region I
• The Leo IV dwarf spheroidal galaxy: color-magnitude diagram and pulsating stars
• RR Lyrae Stars in the Bootes dSph
• On the RR Lyrae stars in globulars: IV. $\omega$ Centauri Optical UBVRI Photometry
• On the newly discovered Canes Venatici II dSph galaxy
• Stellar Archaeology in the Galactic halo with the Ultra-Faint Dwarfs: VI. Ursa Major II
• BVI time series data of the Galactic Globular Cluster NGC3201. I. RR Lyrae stars
• Stellar Archaeology in the Galactic halo with Ultra-Faint Dwarfs: VII. Hercules
• Variable stars in the ultra-faint dwarf spheroidal galaxy Ursa Major I
• The Globular Cluster NGC 5286. II. Variable Stars
• Pulsating Variable Stars in the Coma Berenices dwarf spheroidal galaxy
• Stacking the Invisibles: A Guided Search for Low-Luminosity Milky Way Satellites
• HST/WFPC2 Imaging of the Dwarf Satellites And XI and And XIII : HB Morphology and RR Lyraes
• Variable stars in the field of the Hydra II ultra-faint dwarf galaxy
• A Search for RR Lyrae Stars in Segue 2 and Segue 3
• Weak Galactic Halo--Fornax dSph Connection from RR Lyrae Stars
• Mapping the Tidal Disruption of the Hercules Dwarf: A Wide-Field DECam Imaging Search for RR Lyrae Stars
• On a new method to estimate distance, reddening and metallicity of RR Lyrae stars using optical/near-infrared ($B$,$V$,$I$,$J$,$H$,$K$) mean magnitudes: $\omega$ Centauri as a first test case
• Serendipitous discovery of RR Lyrae stars in the Leo V ultra-faint galaxy
• The Early Chemical Enrichment Histories of Two Sculptor Group Dwarf Galaxies as Revealed by RR Lyrae Variables
• RR Lyrae Variable Stars in the Crater II Dwarf Galaxy

Cited by in corpus (7)

• Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST and literature data
• Search for RR Lyrae stars in DES ultra-faint systems: Grus I, Kim 2, Phoenix II, and Grus II
• Pegasus IV: Discovery and Spectroscopic Confirmation of an Ultra-Faint Dwarf Galaxy in the Constellation Pegasus
• The Pristine Dwarf-Galaxy survey - II. In-depth observational study of the faint Milky Way satellite Sagittarius II
• Gaia RR Lyrae Stars in Nearby Ultra-Faint Dwarf Satellite Galaxies
• RR Lyrae-based Distances for 39 Nearby Dwarf Galaxies Calibrated to Gaia eDR3
• DELVE Milky Way Satellite Galaxy Census I: Satellite Population and Survey Selection Function in DES, DELVE, and Pan-STARRS