Classical Cepheid and RR Lyrae variables are radially pulsating stars that trace young and old-age stellar populations, respectively. These classical pulsating stars are the most sensitive probes for ...the precision stellar astrophysics and the extragalactic distance measurements. Despite their extensive use as standard candles thanks to their well-defined Period–Luminosity relations, distance measurements based on these objects suffer from their absolute primary calibrations, metallicity effects, and other systematic uncertainties. Here, I present a review of classical Cepheid, RR Lyrae and type II Cepheid variables starting with a historical introduction and describing their basic evolutionary and pulsational properties. I will focus on recent theoretical and observational efforts to establish absolute scale for these standard candles at multiple wavelengths. The application of these classical pulsating stars to high-precision cosmic distance scale will be discussed along with observational systematics. I will summarize with an outlook for futher improvements in our understanding of these classical pulsators in the upcoming era of extremely large telescopes.
Globular clusters are both primary fossils of galactic evolution and formation and are ideal laboratories for constraining the evolution of low-mass and metal-poor stars. RR Lyrae and type II Cepheid ...variables are low-mass, radially pulsating stars that trace old-age stellar populations. These stellar standard candles in globular clusters are crucial for measuring their precise distances and, in turn, absolute ages, and for the calibration of the extragalactic distance scale. Herein, the evolutionary stages of RR Lyrae and type II Cepheids are discussed, and their pulsation properties, including the light curves, color–magnitude and period–amplitude diagrams, and period–luminosity relations in globular clusters at optical and infrared wavelengths are presented. The RR Lyrae visual magnitude–metallicity relation and the multiband period–luminosity–metallicity relations in globular clusters covering a wide metallicity range are also discussed in detail for their application to the RR Lyrae-based distance scale.
Abstract Virgo III is a newly discovered ultra-faint-dwarf (UFD) candidate, and finding RR Lyrae associated with this galaxy is important to constrain its distance. In this work, we present a search ...of RR Lyrae in the vicinity of Virgo III based on the time-series r -band images taken from the Lulin One-meter Telescope (LOT). We have identified three RR Lyrae from our LOT data, including two fundamental mode (ab-type) and a first-overtone (c-type) RR Lyrae. Assuming these three RR Lyrae are members of Virgo III, we derived the distance to this UFD as 154 ± 25 kpc, fully consistent with the independent measurements given in the literature. We have also revisited the relation between absolute V -band magnitude ( M V ) and the number of RR Lyrae (of all types, N RRL ) found in local galaxies, demonstrating that the M V - N RRL relation is better described with the specific RR Lyrae frequency.
Abstract
Multiband light curves of two RR Lyrae variables in Segue II and Ursa Major II ultrafaint dwarf galaxies were collected from near simultaneous observations using the Lulin One-meter ...Telescope in
Vgri
bands. Together with Gaia
G
-band light curves, we determined photometric metallicities using empirical relations involving pulsation period and Fourier parameter as dependent parameters. We demonstrated that the RR Lyrae photometric metallicity can be determined accurately when these empirical relations were employed at multiple wavelengths, which can potentially improve the distance determination based on RR Lyrae stars. The photometric metallicities based on our approach were found to be −2.27 ± 0.13 dex and −1.87 ± 0.16 dex for the RR Lyrae in Segue II and Ursa Major II UFD, respectively, with corresponding distance moduli of 17.69 ± 0.15 mag and 17.58 ± 0.15 mag, in agreement with previous literature determinations. This approach of photometric metallicity of RR Lyrae based on multiband optical light curves will be particularly relevant for distance measurements in the era of the Vera C Rubin’s Legacy Survey of Space and Time.
The dense clusters within the Serpens Molecular Cloud are among the most active regions of nearby star formation. In this paper, we use Gaia DR2 parallaxes and proper motions to statistically measure ...∼1167 kinematic members of Serpens, few of which have been previously identified, to evaluate the star formation history of the complex. The optical members of Serpens are concentrated in three distinct groups located at 380-480 pc; the densest clusters are still highly obscured by optically thick dust and have few optical members. The total population of young stars and protostars in Serpens is at least 2000 stars, including past surveys that were most sensitive to protostars and disks, and may be much higher. Distances to dark clouds measured from deficits in star counts are consistent with the distances to the optical star clusters. The Serpens Molecular Cloud is seen in the foreground of the Aquila Rift, dark clouds located at 600-700 pc, and behind patchy extinction, here called the Serpens Cirrus, located at ∼250 pc. Based on the lack of a distributed population of older stars, the star formation rate throughout the Serpens Molecular Cloud increased by at least a factor of 20 within the past ∼5 Myr. The optically bright stars in Serpens Northeast are visible because their natal molecular cloud has been eroded, not because they were flung outwards from a central factory of star formation. The separation between subclusters of 20-100 pc and the absence of an older population together lead to speculation that an external forcing was needed to trigger the active star formation.
Abstract The Draco Dwarf spheroidal (dSph) galaxy is one of the nearest and the most dark-matter-dominated satellites of the Milky Way. We obtained multiepoch near-infrared (NIR, JHK s ) observations ...of the central region of Draco dSph covering a sky area of ∼21′ × 21′ using the WIRCam instrument at the 3.6 m Canada–France–Hawaii Telescope. Homogeneous JHK s time-series photometry for 212 RR Lyrae (173 fundamental-mode, 24 first-overtone, and 15 mixed-mode variables) and five Anomalous Cepheids in Draco dSph are presented and used to derive their period–luminosity relations at NIR wavelengths for the first-time. The small scatter of ∼0.05 mag in these empirical relations for RR Lyrae stars is consistent with those in globular clusters and suggests a very small metallicity spread, up to ∼0.2 dex, among these centrally located variables. Based on empirically calibrated NIR period–luminosity–metallicity relations for RR Lyrae in globular clusters, we determined a distance modulus to Draco dSph of μ RRL = 19.557 ± 0.026 mag. The calibrated K s -band period–luminosity relations for Anomalous Cepheids in the Draco dSph and the Large Magellanic Cloud exhibit statistically consistent slopes but systematically different zero points, hinting at possible metallicity dependence of ∼ − 0.3 mag dex −1 . Finally, the apparent magnitudes of the tip of the red-giant branch in I and J bands also agree well with their absolute calibrations with the adopted RR Lyrae distance to Draco. Our recommended ∼1.5% precise RR Lyrae distance, D Draco = 81.55 ± 0.98(statistical) ± 1.17(systematic) kpc, is the most accurate and precise distance to Draco dSph galaxy.
We present time-series observations of Population II Cepheids in the Large Magellanic Cloud at near-infrared (JHKs) wavelengths. Our sample consists of 81 variables with accurate periods and optical ...(VI) magnitudes from the OGLE survey, covering various subtypes of pulsators (BL Herculis, W Virginis, and RV Tauri). We generate light-curve templates using high-quality I-band data in the LMC from OGLE and Ks-band data in the Galactic bulge from VISTA Variables in Via Láctea survey and use them to obtain robust mean magnitudes. We derive period-luminosity (P-L) relations in the near-infrared and Period-Wesenheit (P-W) relations by combining optical and near-infrared data. Our P-L and P-W relations are consistent with published work when excluding long-period RV Tauris. We find that Pop II Cepheids and RR Lyraes follow the same P-L relations in the LMC. Therefore, we use trigonometric parallax from the Gaia DR1 for VY Pyx and the Hubble Space Telescope parallaxes for k Pav and 5 RR Lyrae variables to obtain an absolute calibration of the Galactic Ks-band P-L relation, resulting in a distance modulus to the LMC of mag. We update the mean magnitudes of Pop II Cepheids in Galactic globular clusters using our light-curve templates and obtain distance estimates to those systems, anchored to a precise late-type eclipsing binary distance to the LMC. We find that the distances to these globular clusters based on Pop II Cepheids are consistent (within ) with estimates based on the relation for horizontal branch stars.
Abstract
We present a systematic analysis to determine and improve the pulsation periods of 1637 known long-period Mira variables in M33 using
gri
-band light curves spanning ∼18 yr from several ...surveys, including the M33 variability survey, Panoramic Survey Telescope and Rapid Response System, Palomar Transient Factory (PTF), intermediate PTF, and Zwicky Transient Facility. Based on these collections of light curves, we found that optical-band light curves that are as complete as possible are crucial to determine the periods of distant Miras. We demonstrated that the machine-learning techniques can be used to classify Miras into O-rich and C-rich based on the (
J
−
K
s
) period–color plane. Finally, We derived the distance modulus to M33 using O-rich Miras at maximum light together with our improved periods as 24.67 ± 0.06 mag, which is in good agreement with the recommended value given in the literature.
Abstract
SX Phoenicis (SXP) variables are short-period pulsating stars that exhibit a period–luminosity (PL) relation. We derived the
gri
-band PL and extinction-free period–Wesenheit (PW) relations, ...as well as the period-color and reddening-free period-Q-index relations for 47 SXP stars located in 21 globular clusters, using the optical light curves taken from Zwicky Transient Facility. These empirical relations were derived for the first time in the
gri
filters except for the
g
-band PL relation. We used our
gi
-band PL and PW relations to derive a distance modulus to Crater II dwarf spheroidal which hosts one SXP variable. Assuming that the fundamental and first-overtone pulsation mode for the SXP variable in Crater II, we found distance moduli of 20.03 ± 0.23 mag and 20.37 ± 0.24 mag, respectively, using the PW relation, where the latter is in excellent agreement with independent RR Lyrae based distance to Crater II dwarf galaxy.
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