Polaris the Cepheid Returns: 4.5 Years of Monitoring from Ground and Space

Citations Over TimeTop 19% of 2008 papers

Abstract

We present the analysis of 4.5 years of nearly continuous observations of the classical Cepheid Polaris, which comprise the most precise data available for this star. We have made spectroscopic measurements from ground and photometric measurements from the WIRE star tracker and the SMEI instrument on the Coriolis satellite. Measurements of the amplitude of the dominant oscillation (P 4 days), which go back more than a century, show a decrease from AV 120 to 30 mmag around the turn of the millennium. It has been speculated that the reason for the decrease in amplitude is the evolution of Polaris toward the edge of the instability strip. However, our new data reveal an increase in the amplitude by 30 % from 2003 to 2006. It now appears that the amplitude change is cyclic rather than monotonic and most likely the result of a pulsation phenomenon. In addition, previous radial velocity campaigns have claimed the detection of long-period variation in Polaris (P> 40 days). Our radial velocity data are more precise than previous data sets, and we find no evidence for additional variation for periods in the range 3Y50 days with an upper limit of 100 m s 1. However, in the WIRE data we find evidence of variation on timescales of 2Y6 days, which we interpret as being due to granulation.

Related Papers

• → Search for Evolutionary Changes in the Periods of Cepheids: V1033 Cyg, a Classical Cepheid at the First Crossing of the Instability Strip(2019)5 cited
• → Pulsation Constants and Densities for Double-Mode Variables in the Cepheid Instability Strip(1970)23 cited
• → The Cepheid instability strip(1980)21 cited
• Non-Pulsating Stars in the R R Lyrae and Cepheid Instability Strips.(1973)