Period Variations for the Cepheid VZ Cyg

Abstract

The Cepheid Period-Luminosity law is a key rung on the extragalactic distance ladder. However, numerous Cepheids are known to undergo period variations. Monitoring, refining, and understanding these period variations allows us to better determine the parameters of the Cepheids themselves and of the instability strip in which they reside, and to test models of stellar evolution. VZ Cyg, a classical Cepheid pulsating at $\sim$4.864 days, has been observed for over 100 years. Combining data from literature observations, the Kilodegree Extremely Little Telescope (KELT) transit survey, and new targeted observations with the Robotically Controlled Telescope (RCT) at Kitt Peak, we find a period change rate of $dP/dt=-0.0642\pm 0.0018$ sec yr${}^{-1}$. However, when only the recent observations are examined, we find a much higher period change rate of $dP/dt=-0.0923\pm 0.0110$ sec yr${}^{-1}$. This higher rate could be due to an apparent long-term (P $\approx$ 26.5 yr) cyclic period variation. The possible interpretations of this single Cepheid's complex period variations underscore both the need to regularly monitor pulsating variables, and the important benefits that photometric surveys such as KELT can have on the field. Further monitoring of this interesting example of Cepheid variability is recommended to confirm and better understand the possible cyclic period variations. Further, Cepheid timing analyses are necessary to fully understand their current behaviors and parameters, as well as their evolutionary histories.

10 pages including 8 figures, accepted for publication in AJ

References in corpus (36)

• The SIMBAD astronomical database
• A 2.4% Determination of the Local Value of the Hubble Constant
• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• The VizieR database of Astronomical Catalogues
• Gaia Data Release 1: Astrometry - one billion positions, two million proper motions and parallaxes
• The Kilodegree Extremely Little Telescope (KELT): A Small Robotic Telescope for Large-Area Synoptic Surveys
• New Period-Luminosity and Period-Color Relations of Classical Cepheids: I. Cepheids in the Galaxy
• Eclipsing Binary Stars as Benchmarks for Trigonometric Parallaxes in the Gaia Era
• Classical Cepheid Pulsation Models. X. The Period-Age Relation
• The KELT-South Telescope
• Estimating distances from parallaxes. III. Distances of two million stars in the Gaia DR1 catalogue
• Rate of Period Change as a Diagnostic of Cepheid Properties
• Populations of rotating stars. - I. Models from 1.7 to 15 Msun at Z = 0.014, 0.006, and 0.002 with Ω/Ωcrit between 0 and 1
• Evidence for a systematic offset of $-$0.25 mas in the Gaia DR1 parallaxes
• On the Enhancement of Mass Loss in Cepheids Due to Radial Pulsation
• On the effect of rotation on populations of classical Cepheids I. Predictions at solar metallicity
• Observational studies of Cepheid amplitudes. I - Period-amplitude relationships for Galactic Cepheids and interrelation of amplitudes
• Baade-Wesselink distances to Galactic and Magellanic Cloud Cepheids and the effect of metallicity
• On the evolutionary and pulsation mass of Classical Cepheids: III. the case of the eclipsing binary Cepheid CEP0227 in the Large Magellanic Cloud
• A test of Gaia Data Release 1 parallaxes: implications for the local distance scale
• Observations of Cepheids with the MOST satellite: Contrast between Pulsation Modes
• Investigating Cepheid $\ell$ Carinae's Cycle-to-cycle Variations via Contemporaneous Velocimetry and Interferometry
• Discovery of Cycle-to-cycle Modulated Spectral Line Variability and Velocity Gradients in Long-period Cepheids
• The Kepler Cepheid V1154 Cyg revisited: light curve modulation and detection of granulation
• Binary Properties from Cepheid Radial Velocities (CRaV)
• The Secret Lives of Cepheids: $\delta$ Cep -- the Prototype of a New Class of Pulsating X-ray Variable Stars
• The Secret Lives of Cepheids: Evolutionary Changes and Pulsation-Induced Shock Heating in the Prototype Classical Cepheid δ Cep
• CoRoT space photometry of seven Cepheids
• VEGA/CHARA interferometric observations of Cepheids. I. A resolved structure around the prototype classical Cepheid delta Cep in the visible spectral range
• The Secret Lives of Cepheids: Evolution, Mass Loss, and Ultraviolet Emission of the Long-Period Classical Cepheid $l$ Carinae
• Resolved Companions of Cepheids: Testing the Candidates with X-Ray Observations
• TGAS Error Renormalization from the RR Lyrae Period-Luminosity Relation
• The RCT 1.3-meter Robotic Telescope: Broad-band Color Transformation and Extinction Calibration
• A Search for Mass Loss on the Cepheid Instability Strip using HI 21-cm Line Observations
• BRITE observations of classical Cepheids
• The Secret Lives of Cepheids: A Multi-Wavelength Study of the Atmospheres and Real-Time Evolution of Classical Cepheids