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Polaris: Mass and Multiplicity | | Nancy Remage Evans
; Gail Schaefer
; Howard E. Bond
; Edmund Nelan
; Giuseppe Bono
; Margarita Karovska
; Scott Wolk
; Dimitar Sasselov
; Edward Guinan
; Scott Engle
; Eric Schlegel
; Brian Mason
; | | Date: |
27 Sep 2006 | | Abstract: | Polaris, the nearest and brightest classical Cepheid, is a member of at least a triple system. It has a wide ($18’’$) physical companion, the F-type dwarf Polaris B. Polaris itself is a single-lined spectroscopic binary with an orbital period of 30 years (Kamper, 1996, JRASC, 90, 140). By combining {it Hipparcos} measurements of the instantaneous proper motion with long-term measurements and the Kamper radial-velocity orbit, Wielen et al. (2000, A&A, 360, 399) have predicted the astrometric orbit of the close companion. Using the {it Hubble Space Telescope} and the Advanced Camera for Surveys’ High-Resolution Channel with an ultraviolet (F220W) filter, we have now directly detected the close companion. Based on the Wielen et al. orbit, the {it Hipparcos} parallax, and our measurement of the separation ($0.176’’$ $pm$ $0.002’’$), we find a preliminary mass of 5.0 $pm$ 1.5 M$_{odot}$ for the Cepheid and 1.38 $pm$ 0.61 M$_{odot}$ for the close companion. These values will be refined by additional {it HST} observations scheduled for the next 3 years.
We have also obtained a {it Chandra} ACIS-I image of the Polaris field. Two distant companions C and D are not X-rays sources and hence are not young enough to be physical companions of the Cepheid. There is one additional stellar X-ray source in the field, located $253’’$ from Polaris A, which is a possible companion. Further investigation of such a distant companion is valuable to confirm the full extent of the system. | | Source: | arXiv, astro-ph/0609759 | | Services: | Forum | Review | PDF | Favorites | |
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