Ultralow-amplitude RR Lyrae Stars in M4

Wallace, Joshua; Hartman, J. D.; Bakos, G. Á.; Bhatti, W.

doi:10.3847/2041-8213/aaf8ac

Cited by 10 publications

(16 citation statements)

References 46 publications

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“…We noticed two cases where known low-amplitude variables-specifically, the millimagnitude RR Lyrae (mmRR) variables of Wallace et al (2019a)-were marked as blends. This was because their periods were ∼ 2 3 that of some large-amplitude-variable neighbors.…”

Section: Search For Variabilitymentioning

confidence: 98%

“…Two of the HB stars-W2015 and W2386-have been more fully examined in Wallace et al (2019a) as potential low-amplitude RRC pulsators (millimagnitude RR Lyrae variables, or mmRRs as coined in that work). W2015 is mmRR 1 from that work, W2386 is mmRR2, and W4081 is G3168 briefly mentioned in that work.…”

Section: Millimagnitude Rr Lyrae and The Other Horizontal Branch Starsmentioning

confidence: 99%

“…W2015 is mmRR 1 from that work, W2386 is mmRR2, and W4081 is G3168 briefly mentioned in that work. We define the HB in similar fashion as Wallace et al (2019a): stars with 14.3 < G BP < 13.0 and G BP − G RP < 1.5 and a >95% cluster membership probability (though the membership probabilities for all these stars are so high that a 99% cutoff could be used with no loss). Excluding the 10 stars previously identified as RR Lyrae variables (see Table 2), we have light curves for 24 HB stars, eight of which we detected as significantly variable.…”

Section: Millimagnitude Rr Lyrae and The Other Horizontal Branch Starsmentioning

confidence: 99%

“…In the inset x-axis and the listed period, "d" stands for "day." W2015 and W2386 are the mmRRs from Wallace et al (2019a). ability at other periods close to the peak period, so it is entirely possible that multiharmonic variability is to be found among many of the other 16 non-RR-Lyrae HB stars.…”

Section: Millimagnitude Rr Lyrae and The Other Horizontal Branch Starsmentioning

confidence: 99%

“…Fortunately, techniques exist to partially mitigate the effects of the blending, and given the expected richness and value of the derived light curves, the effort to work through these issues is still worthwhile. The present work uses image subtraction (Alard & Lupton 1998) among other techniques to deal with the blending, and, building off of Wallace et al (2019a), it is, as far as we are aware, the first general analysis of the K2 observations of a GC. Previous work on these images were limited in scope: Miglio et al (2016) looked at asteroseismic oscillations in K giants and Kuehn et al (2017) looked at the RR Lyrae variables, but that has been it so far.…”

Section: Introductionmentioning

confidence: 99%

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A Search for Variable Stars in the Globular Cluster M4 with K2

Wallace

Hartman

Bakos

et al. 2019

ApJS

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Section: Search For Variabilitymentioning

confidence: 98%

Section: Millimagnitude Rr Lyrae and The Other Horizontal Branch Starsmentioning

confidence: 99%

Section: Millimagnitude Rr Lyrae and The Other Horizontal Branch Starsmentioning

confidence: 99%

Section: Millimagnitude Rr Lyrae and The Other Horizontal Branch Starsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

A Search for Variable Stars in the Globular Cluster M4 with K2

Wallace

Hartman

Bakos

et al. 2019

ApJS

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Periodic variable A-F spectral type stars in the northern TESS continuous viewing zone

Skarka

Žák

Fedurco

et al. 2022

A&A

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Context. In the time of large space surveys that provide tremendous amounts of precise data, it is highly desirable to have a commonly accepted methodology and system for the classification of variable stars. This is especially important for A-F stars, which can show intrinsic brightness variations due to both rotation and pulsations. Aims. The goal of our study is to provide a reliable classification of the variability of A-F stars brighter than 11 mag located in the northern TESS continuous viewing zone. We also aim to provide a thorough discussion about issues in the classification related to data characteristics and the issues arising from the similar light-curve shape generated by different physical mechanisms. Methods. We used TESS long-and short-cadence photometric data and corresponding Fourier transform to classify the variability type of the stars. We also used spectroscopic observations to determine the projected rotational velocity of a few stars. Results. We present a clear and concise classification system that is demonstrated on many examples. We find clear signs of variability in 3025 of 5923 studied stars (51 %). For 1813 of these 3025 stars, we provide a classification; the rest cannot be unambiguously classified. Of the classified stars, 64.5 % are pulsating stars of g-mode γ Doradus (GDOR) and p-mode δ Scuti types and their hybrids. We realised that the long-and short-cadence pre-search data conditioning simple aperture photometry data can differ significantly not only in amplitude but also in the content of instrumental and data-reduction artefacts, making the long-cadence data less reliable. We identified a new group of stars that show stable light curves and characteristic frequency spectrum patterns (8.5 % of the classified stars). According to the position in the Hertzsprung-Russell diagram, these stars are likely GDOR stars but are on average about 200 K cooler than GDORs and have smaller amplitudes and longer periods. With the help of spectroscopic measurements of v sin i, we show that the variability of stars with unresolved groups of peaks located close to the positions of the harmonics in their frequency spectra (16 % of the classified stars) can be caused by rotation rather than by pulsations. We show that without spectroscopic observations it can be impossible to unambiguously distinguish between ellipsoidal variability and rotational variability. We also applied our methodology to three previous studies and find significant discrepancies in the classification. Conclusions. We demonstrate how difficult the classification of variable A-F stars can be when using only photometric data, how the residual artefacts can produce false positives, and that some types cannot actually be distinguished without spectroscopic observations. Our analysis provides collections that can be used as training samples for automatic classification.

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To grow old and peculiar: Survey of anomalous variable stars in M80 with age determinations using K2 and Gaia

Molnár,

Plachy,

Bódi

et al. 2023

A&A

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The globular cluster Messier 80 was monitored by the Kepler space telescope for 80 days during the K2 mission. Continuous, high-precision photometry of such an old, compact cluster allows us for studies of its variable star population in unprecedented detail. We used differential-image photometry to extract light curves for 27 variable stars A search for new variables in the images has led to the discovery of two new variable stars: an RR Lyrae and a variable red giant star. An analysis of the RR Lyrae population reveals multiple RRc stars with additional modes and/or peculiar modulation cycles. We have newly classified the star V28 as a spotted extreme horizontal branch variable. Despite their faintness, we were also able to clearly detect the three SX Phe stars, but we did not find new pulsation modes beyond the known ones in them. Spectra taken with the VLT and Magellan Clay telescopes, as well as absolute color-magnitude diagrams of the cluster based on Gaia and Pan-STARRS observations, confirm the classification of the peculiar modulated variables as bona fide RRc stars. We propose that they highlight a subgroup of overtone stars that may have been overlooked before. We fit MESA isochrones to the CMDs to estimate the age and metallicity of the cluster. We confirm that M80 is old and metal-poor, but we show that isochrone fitting to old populations comes with numerous uncertainties.

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Ultralow-amplitude RR Lyrae Stars in M4

Cited by 10 publications

References 46 publications

A Search for Variable Stars in the Globular Cluster M4 with K2

A Search for Variable Stars in the Globular Cluster M4 with K2

Periodic variable A-F spectral type stars in the northern TESS continuous viewing zone

To grow old and peculiar: Survey of anomalous variable stars in M80 with age determinations using K2 and Gaia

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