ORCID Profile
0000-0001-6147-3360
Current Organisation
Istituto nazionale di astrofisica
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Publisher: American Astronomical Society
Date: 02-2023
Abstract: RR Lyrae variables are excellent Population II distance indicators thanks to their well-defined period–luminosity relations (PLRs) at infrared wavelengths. We present results of near-infrared (NIR) monitoring of Galactic globular clusters to empirically quantify the metallicity dependence of NIR PLRs for RR Lyrae variables. Our s le includes homogeneous, accurate, and precise photometric data for 964 RR Lyrae variables in 11 globular clusters covering a large metallicity range (Δ[Fe/H] ∼ 2 dex). We derive JHK s -band period–luminosity–metallicity (PLZ) and period–Wesenheit–metallicity (PWZ) relations anchored using 346 Milky Way field RR Lyrae stars with Gaia parallaxes, and simultaneously solved for independent distances to globular clusters. We find a significant metallicity dependence of ∼0.2 mag dex −1 in the JHK s -band PLZ and PWZ relations for RR Lyrae stars independent of the adopted metallicity scale. The metallicity coefficients and the zero-points of the empirical PLZ and PWZ relations are in excellent agreement with the predictions from the horizontal branch evolution and pulsation models. Furthermore, RR Lyrae–based distances to our s le of globular clusters are also statistically consistent with other independent measurements in the literature. Our recommended empirical JHK s -band PLZ relations for RR Lyrae stars with periods of fundamental mode pulsation ( P f ) are: M J = − 0.44 ( ± 0.03 ) − 1.83 ( ± 0.02 ) log ( P f ) + 0.20 ( ± 0.02 ) [ Fe / H ] ( σ = 0.05 mag ) M H = − 0.74 ( ± 0.02 ) − 2.29 ( ± 0.02 ) log ( P f ) + 0.19 ( ± 0.01 ) [ Fe / H ] ( σ = 0.05 mag ) M K s = − 0.80 ( ± 0.02 ) − 2.37 ( ± 0.02 ) log ( P f ) + 0.18 ( ± 0.01 ) [ Fe / H ] ( σ = 0.05 mag ) .
Publisher: American Astronomical Society
Date: 27-10-2020
Publisher: American Astronomical Society
Date: 03-2021
Abstract: We present new near-infrared, JHK s , period–luminosity relations (PLRs) for RR Lyrae variables in the Messier 53 (M53 or NGC 5024) globular cluster. Multi-epoch JHK s observations, obtained with the WIRCam instrument on the 3.6 m Canada–France–Hawaii Telescope, are used for the first time to estimate precise mean magnitudes for 63 RR Lyrae stars in M53 including 29 fundamental-mode (RRab) and 34 first-overtone mode (RRc) variables. The JHK s -band PLRs for RR Lyrae stars are best constrained for RRab types with a minimal scatter of 22, 23, and 19 mmag, respectively. The combined s le of RR Lyrae is used to derive the K s -band PLR, K s = − 2.303 ( 0.063 ) log P + 15.212 ( 0.016 ) , exhibiting a 1 σ dispersion of only 0.027 mag. Theoretical period–luminosity–metallicity (PLZ) relations are used to predict parallaxes for 400 Galactic RR Lyrae, resulting in a median parallax zero-point offset of −7 ± 3 μ as in Gaia Early Data Release 3 (EDR3), which increases to 22 ± 2 μ as if the parallax corrections are applied. We also estimate a robust distance modulus, μ M53 = 16.403 ± 0.024 (statistical) ± 0.033 (systematic) mag, to M53 based on theoretical calibrations. Homogeneous and precise mean magnitudes for RR Lyrae in M53 together with similar literature data for M3, M4, M5, and ω Cen are used to empirically calibrate a new RR Lyrae PLZ K s relation, K s = − 0.848 ( 0.007 ) − 2.320 ( 0.006 ) log P + 0.166 ( 0.011 ) [ Fe / H ] , anchored with Gaia EDR3 distances and theoretically predicted relations, and to simultaneously estimate precise RR Lyrae-based distances to these globular clusters.
Publisher: American Astronomical Society
Date: 22-12-2021
Abstract: The Transiting Exoplanet Survey Satellite (TESS) space telescope is collecting continuous, high-precision optical photometry of stars throughout the sky, including thousands of RR Lyrae stars. In this paper, we present results for an initial s le of 118 nearby RR Lyrae stars observed in TESS Sectors 1 and 2. We use differential image photometry to generate light curves and analyze their mode content and modulation properties. We combine accurate light-curve parameters from TESS with parallax and color information from the Gaia mission to create a comprehensive classification scheme. We build a clean s le, preserving RR Lyrae stars with unusual light-curve shapes, while separating other types of pulsating stars. We find that a large fraction of RR Lyrae stars exhibit various low- litude modes, but the distribution of those modes is markedly different from those of the bulge stars. This suggests that differences in physical parameters have an observable effect on the excitation of extra modes, potentially offering a way to uncover the origins of these signals. However, mode identification is hindered by uncertainties when identifying the true pulsation frequencies of the extra modes. We compare mode litude ratios in classical double-mode stars to stars with extra modes at low litudes and find that they separate into two distinct groups. Finally, we find a high percentage of modulated stars among the fundamental mode pulsators, but also find that at least 28% of them do not exhibit modulation, confirming that a significant fraction of stars lack the Blazhko effect.
Publisher: American Astronomical Society
Date: 08-10-2019
Location: Korea, Republic of
No related grants have been discovered for Anupam Bhardwaj.