Other
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21710204g&link_type=abstract
American Astronomical Society, AAS Meeting #217, #102.04; Bulletin of the American Astronomical Society, Vol. 43, 2011
Other
Scientific paper
Polaris (α UMi; F7Ib-II) is the best known star in the northern sky. It has enjoyed special standing since the Earth’s precession brought our north celestial pole to its almost exact direction. Polaris is also the nearest ( 130 pc) and brightest (V 1.97-mag) classical Cepheid. Polaris has proven to be full of surprises, displaying both a systematic decrease in light amplitude, an increase in pulsation period and a probable increase in luminosity. Presently Polaris has a light amplitude ΔV 0.045-mag, its 3.97-day period is increasing at +3.5sec/year and its mean brightness has apparently increased by 0.2-mag over the past century (Engle & Guinan 2006). Recent FUSE observations show the presence of CIII 977/1176A and OVI 1032/1038A emissions, indicative of hot 30,000-300,000 K plasmas (Engle & Guinan, 2007). A study of IUE data indicates a possible small temperature increase (which in the FUV-region is very sensitive to Teff) between 1978/79 and 1991/93, indicating an increase of 35+/-12K. Also, Polaris, along with two other Cepheids beta Dor and delta Cep, have been detected as soft-X-ray sources with log LX 29.0 ergs/sec. But Polaris has a nearby binary companion that could contribute to the observed X-ray emission. HST/COS medium-resolution 1150-2000Å spectrometry was conducted during Dec-2009. These observations were conducted to investigate possible evolutionary changes (manifested by small changes in Teff) and also to study upper atmospheric high energy emissions. Below 1400A data is essentially free of the stellar continuum of the F8-supergiant and contains important diagnostic high energy emission lines such as C III, Ly-alpha, NV, OI, CII, & Si IV. At wavelengths >1600A, the stellar photospheric flux rapidly increases. We report on analyses of the COS observations and discuss implications for Cepheid evolution and upper atmosphere heating mechanisms.
This work is supported by NASA Grant-HST-GO-11726.
No associations
LandOfFree
Mysteries of the North Star: Far Ultraviolet HST/COS Spectroscopy of the Classical Cepheid Polaris does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Mysteries of the North Star: Far Ultraviolet HST/COS Spectroscopy of the Classical Cepheid Polaris, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Mysteries of the North Star: Far Ultraviolet HST/COS Spectroscopy of the Classical Cepheid Polaris will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1393154