RR Lyrae Stars in the Field of Sagittarius II

Seok Joo Joo; Jaemann Kyeong; Soung Chul Yang; Sang Il Han; Eon Chang Sung; Soo Chang Rey; Helmut Jerjen; Hak Sub Kim; Dongwon Kim; Hyunjin Jeong; Chang H. Ree; Sang Mok Cha; Yongseok Lee

doi:10.3847/1538-4357/ab11ca

RR Lyrae Stars in the Field of Sagittarius II

Seok Joo Joo, Jaemann Kyeong, Soung Chul Yang, Sang Il Han, Eon Chang Sung, Soo Chang Rey, Helmut Jerjen, Hak Sub Kim, Dongwon Kim, Hyunjin Jeong, Chang H. Ree, Sang Mok Cha, Yongseok Lee

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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.

Original language	English
Article number	120
Journal	Astrophysical Journal
Volume	875
Issue number	2
DOIs	https://doi.org/10.3847/1538-4357/ab11ca
Publication status	Published - 20 Apr 2019

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@article{4dba392743d5429f9c821f054780bd43,

title = "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.",

keywords = "Local Group, galaxies: dwarf, galaxies: individual (Sagittarius II), stars: variables: RR Lyrae",

author = "Joo, {Seok Joo} and Jaemann Kyeong and Yang, {Soung Chul} and Han, {Sang Il} and Sung, {Eon Chang} and Rey, {Soo Chang} and Helmut Jerjen and Kim, {Hak Sub} and Dongwon Kim and Hyunjin Jeong and Ree, {Chang H.} and Cha, {Sang Mok} and Yongseok Lee",

year = "2019",

month = apr,

day = "20",

doi = "10.3847/1538-4357/ab11ca",

language = "English",

volume = "875",

journal = "Astrophysical Journal",

issn = "0004-637X",

publisher = "American Astronomical Society",

number = "2",

}

TY - JOUR

T1 - RR Lyrae Stars in the Field of Sagittarius II

AU - Joo, Seok Joo

AU - Kyeong, Jaemann

AU - Yang, Soung Chul

AU - Han, Sang Il

AU - Sung, Eon Chang

AU - Rey, Soo Chang

AU - Jerjen, Helmut

AU - Kim, Hak Sub

AU - Kim, Dongwon

AU - Jeong, Hyunjin

AU - Ree, Chang H.

AU - Cha, Sang Mok

AU - Lee, Yongseok

PY - 2019/4/20

Y1 - 2019/4/20

N2 - 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.

AB - 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.

KW - Local Group

KW - galaxies: dwarf

KW - galaxies: individual (Sagittarius II)

KW - stars: variables: RR Lyrae

UR - http://www.scopus.com/inward/record.url?scp=85067201565&partnerID=8YFLogxK

U2 - 10.3847/1538-4357/ab11ca

DO - 10.3847/1538-4357/ab11ca

M3 - Article

SN - 0004-637X

VL - 875

JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 2

M1 - 120

ER -

RR Lyrae Stars in the Field of Sagittarius II

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