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26 April 2024 |
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Polaris the Cepheid returns: 4.5 years of monitoring from ground and space | | H. Bruntt
; N. R. Evans
; D. Stello
; A. J. Penny
; J. A. Eaton
; D. L. Buzasi
; D. D. Sasselov
; H. L. Preston
; E. Miller-Ricci
; | | Date: |
23 Apr 2008 | | 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), that go back more than a century, show a decrease from 120 mmag to 30
mmag (V magnitude) around the turn of the millennium. It has been speculated
that the reason for the decrease in amplitude is the evolution of Polaris
towards the edge of the instability strip. However, our new data reveal an
increase in the amplitude by about 30% from 2003-2006. 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 datasets, and we find no
evidence for additional variation for periods in the range 3-50 days with an
upper limit of 100 m/s. However, in the WIRE data we find evidence of variation
on time-scales of 2-6 days, which we interpret as being due to granulation. | | Source: | arXiv, 0804.3593 | | Services: | Forum | Review | PDF | Favorites | |
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