A search for variable stars in the globular clusters

Kadla, Z. I.; Gerashchenko, A. N.; Malakhova, Yu. N.

doi:10.1080/10556799808201759

Cited by 4 publications

(8 citation statements)

References 5 publications

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“…Finally, for the variable star candidates S1–S9 and R1–R7 from Kadla et al (1995), we do not detect any variability above the ∼8–35 mmag light‐curve noise level for the stars S1, S2, S4, S6, R1, R2, R5, R6 and R7, and therefore we have dropped these stars from the variables listed in Table 2. The remaining variable star candidates are RR Lyrae stars (see ).…”

Section: Variable Stars In Ngc 6981mentioning

confidence: 85%

“…Stars V43–V56 are newly detected variables. Of these, V43‐V49 were discovered by inspection of the light curves of the variable star candidates from Kadla et al (1995), and V50–V53 were identified in the sequence of difference images as clearly varying sources. By converting each difference image D kij to an image of absolute deviations in units of sigma D ′ kij = | D kij |/σ kij (see ) and then constructing the sum of all such images for each filter, one can identify candidate variable sources as PSF‐like peaks in the image S ij .…”

Section: Variable Stars In Ngc 6981mentioning

confidence: 99%

“…In a brief paper by Kadla et al (1995), the authors use the cluster colour magnitude diagram to identify 16 stars in the RR Lyrae instability strip that are not already claimed to be variable in previous publications. The stars, labelled S1-S9 and R1-R7, are put forwards as "suspected" and "possible" variables, respectively.…”

Section: Variable Stars In Ngc 6981mentioning

confidence: 99%

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CCD time-series photometry of the globular cluster NGC 6981: variable star census and physical parameter estimates

Bramich¹,

Jaimes²,

Giridhar³

et al. 2011

Monthly Notices of the Royal Astronomical Society

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We present the results from 10 nights of observations of the globular cluster NGC 6981 (M72) in the V, R and I Johnson wavebands. We employed the technique of difference image analysis to perform precision differential photometry on the time‐series images, which enabled us to carry out a census of the understudied variable star population of the cluster. We show that 20 suspected variables in the literature are actually non‐variable, and we confirm the variable nature of another 29 variables while refining their ephemerides. We also detect 11 new RR Lyrae variables and three new SX Phe variables, bringing the total confirmed variable star count in NGC 6981 to 43. We performed Fourier decomposition of the light curves for a subset of RR Lyrae stars and used the Fourier parameters to estimate the fundamental physical parameters of the stars using relations available in the literature. Mean values of these physical parameters have allowed us to estimate the physical parameters of the parent cluster. We derive a metallicity of [Fe/H]ZW≈−1.48 ± 0.03 on the Zinn & West scale (or [Fe/H]UVES≈−1.38 ± 0.03 on the new Carretta et al. scale) for NGC 6981, and distances of ∼16.73 ± 0.36 and ∼16.68 ± 0.36 kpc from analysis of the RR0 and RR1 stars separately. We also confirm the Oosterhoff type I classification for the cluster, and show that our colour–magnitude data are consistent with the age of ∼12.75 ± 0.75 Gyr derived by Dotter et al.

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Section: Variable Stars In Ngc 6981mentioning

confidence: 85%

Section: Variable Stars In Ngc 6981mentioning

confidence: 99%

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CCD time-series photometry of the globular cluster NGC 6981: variable star census and physical parameter estimates

Bramich¹,

Jaimes²,

Giridhar³

et al. 2011

Monthly Notices of the Royal Astronomical Society

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“…Kadla et al (1996) reported several RR Lyrae candidates based on the position of the stars in the instability strip of the horizontal branch but none of them matched the position of the only variable star found in the field of view covered by our reference image, which is the new variable V6 explained in the next section.…”

Section: Known Variablesmentioning

confidence: 99%

Exploring the crowded central region of ten Galactic globular clusters using EMCCDs

Jaimes¹,

Bramich²,

Skottfelt³

et al. 2016

A&A

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Aims. We aim to obtain time-series photometry of the very crowded central regions of Galactic globular clusters; to obtain better angular resolution than has been previously achieved with conventional CCDs on ground-based telescopes; and to complete, or improve, the census of the variable star population in those stellar systems. Methods. Images were taken using the Danish 1.54-m Telescope at the ESO observatory at La Silla in Chile. The telescope was equipped with an electron-multiplying CCD, and the short-exposure-time images obtained (ten images per second) were stacked using the shift-and-add technique to produce the normal-exposure-time images (minutes). Photometry was performed via difference image analysis. Automatic detection of variable stars in the field was attempted. Results. The light curves of 12 541 stars in the cores of ten globular clusters were statistically analysed to automatically extract the variable stars. We obtained light curves for 31 previously known variable stars (3 long-period irregular, 2 semi-regular, 20 RR Lyrae, 1 SX Phoenicis, 3 cataclysmic variables, 1 W Ursae Majoris-type and 1 unclassified) and we discovered 30 new variables (16 long-period irregular, 7 semi-regular, 4 RR Lyrae, 1 SX Phoenicis and 2 unclassified). Fluxes and photometric measurements for these stars are available in electronic form through the Strasbourg astronomical Data Center.

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“…Surprisingly, almost half of the observed suspected variables did not show any evidence of variability. Only one out of the 11 candidate RR Lyrae variables of Kadla et al (1983) appeared to be variable. Moreover, variable v7, until now classified as an RR Lyrae star with a period of about 0.515 d, turned out to be of the BL Herculis type, with the period approximately twice that long.…”

mentioning

confidence: 99%