VI Africa

Walraven, Klaas van

doi:10.1177/016934419401200211

Cited by 6 publications

(6 citation statements)

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“…No attempt was made to refine the periods for the known variables given the short time span of the observations. Some SX Phe variables are known to pulsate in more than one mode, generating amplitude variations (Eggen 1952;Walraven 1953). Multiple periods in our SX Phe candidates were searched using the standard Lomb-Scargle technique (Scargle 1982).…”

Section: Known and Newly Found Variablesmentioning

confidence: 99%

An Ao-Assisted Variability Study of Four Globular Clusters*

Salinas

Ramos

Strader

et al. 2016

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The image subtraction technique applied to study variable stars in globular clusters represented a leap in the number of new detections, with the drawback that many of these new light curves could not be transformed to magnitudes due to the severe crowding. In this paper we present observations of four Galactic globular clusters, M 2 (NGC 7089), M 10 (NGC 6254), M 80 (NGC 6093) and NGC 1261, taken with the ground-layer adaptive optics module at the SOAR Telescope, SAM. We show that the higher image quality provided by SAM allows the calibration of the light curves of the great majority of the variables near the cores of these clusters as well as the detection of new variables even in clusters where image-subtraction searches were already conducted. We report the discovery of 15 new variables in M 2 (12 RR Lyrae stars and 3 SX Phe stars), 12 new variables in M 10 (11 SX Phe and one long-period variable) and one new W UMa-type variable in NGC 1261. No new detections are found in M 80, but previous uncertain detections are confirmed and the corresponding light curves are calibrated into magnitudes. Additionally, based on the number of detected variables and new HST /UVIS photometry, we revisit a previous suggestion that M 80 may be the globular cluster with the richest population of blue stragglers in our Galaxy.

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Section: Known and Newly Found Variablesmentioning

confidence: 99%

An Ao-Assisted Variability Study of Four Globular Clusters*

Salinas

Ramos

Strader

et al. 2016

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“…The Washington system was designed to provide metallicity and temperature estimates for G and K giants (Wallerstein & Helfer 1966). The Walraven system was designed for studies of early-type stars (Walraven & Walraven 1960). We convert the Walraven data from their default log 10 scale to magnitudes by multiplying the data by a factor of 2.5.…”

Section: Priorsmentioning

confidence: 99%

A Global Physical Model for Cepheids

Pejcha

Kochanek

2012

ApJ

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We perform a global fit to ∼5, 000 radial velocity and ∼177, 000 magnitude measurements in 29 photometric bands covering 0.3 µm to 8.0 µm distributed among 287 Galactic, LMC, and SMC Cepheids with P > 10 days. We assume that the Cepheid light curves and radial velocities are fully characterized by distance, reddening, and time-dependent radius and temperature variations. We construct phase curves of radius and temperature for periods between 10 and 100 days, which yield light curve templates for all our photometric bands and can be easily generalized to any additional band. With only 4 to 6 parameters per Cepheid, depending on the existence of velocity data and the amount of freedom in the distance, the models have typical rms light and velocity curve residuals of 0.05 mag and 3.5 km s −1 . The model derives the mean Cepheid spectral energy distribution and its derivative with respect to temperature, which deviate from a black body in agreement with metal-line and molecular opacity effects. We determine a mean reddening law towards the Cepheids in our sample, which is not consistent with standard assumptions in either the optical or near-IR. Based on stellar atmosphere models we predict the biases in distance, reddening, and temperature determinations due to the metallicity and we quantify the metallicity signature expected for our fit residuals. The observed residuals as a function of wavelength show clear differences between the individual galaxies, which are compatible with these predictions. In particular, we find that metal-poor Cepheids appear hotter. Finally, we provide a framework for optimally selecting filters that yield the smallest overall errors in Cepheid parameter determination, or filter combinations for suppressing or enhancing the metallicity effects on distance determinations. We make our templates publicly available.

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“…The realization that light-curve shapes and physical parameters are related, traces back to the paper of Walraven (1953). The relation between the pulsation of RR Lyrae variables and their physical parameters is obtained from hydrodynamic pulsation models of defined physical parameters, which are used to generate theoretical light curves.…”

Section: F O U R I E R L I G H T-c U Rv E D E C O M P O S I T I O N Amentioning

confidence: 99%

CCD photometry of the globular cluster M2: RR Lyrae physical parameters and new variables

Lázaro

Ferro

Arévalo

et al. 2006

Monthly Notices of the Royal Astronomical Society

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We report the results of CCD V and R photometry of the RR Lyrae stars in M2. The periodicities of most variables are revised and new ephemerides are calculated. Light‐curve decomposition of the RR Lyrae stars was carried out and the corresponding mean physical parameters [Fe/H]=−1.47, Teff= 6276 K, log L= 1.63 L⊙ and MV= 0.71 from nine RRab and [Fe/H]=−1.61, M= 0.54 M⊙, Teff= 7215 K, log L= 1.74 L⊙ and MV= 0.71 from two RRc stars were calculated. A comparison of the radii obtained from the above luminosity and temperature with predicted radii from non‐linear convective models is discussed. The estimated mean distance to the cluster is 10.49 ± 0.15 kpc. These results place M2 correctly in the general globular cluster sequences for Oosterhoff type, mass, luminosity and temperature, all as a function of the metallicity. Mean relationships for M, log L/L⊙, Teff and MV as a function of [Fe/H] for a family of globular clusters are offered. These trends are consistent with evolutionary and structural notions on the horizontal branch. Eight new variables are reported.

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VI Africa

Cited by 6 publications

References 0 publications

An Ao-Assisted Variability Study of Four Globular Clusters*

An Ao-Assisted Variability Study of Four Globular Clusters*

A Global Physical Model for Cepheids

CCD photometry of the globular cluster M2: RR Lyrae physical parameters and new variables

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