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Polaris: Mass and Multiplicity

Published online by Cambridge University Press:  12 July 2007

Nancy Remage Evans ,
Gail Schaefer ,
Howard E. Bond ,
Edmund Nelan ,
Giuseppe Bono ,
Margarita Karovska ,
Scott Wolk ,
Dimitar Sasselov ,
Edward Guinan  and
Scott Engle
...Show all authors
Nancy Remage Evans
Affiliation:
SAO, 60 Garden St., Cambridge MA 02138, USA email: nevans@cfa.harvard.edu
Gail Schaefer
Affiliation:
STScI, 3700 San Martin Dr., MD 21218, USA
Howard E. Bond
Affiliation:
STScI, 3700 San Martin Dr., MD 21218, USA
Edmund Nelan
Affiliation:
STScI, 3700 San Martin Dr., MD 21218, USA
Giuseppe Bono
Affiliation:
Univ. Roma, Rome, Italy
Margarita Karovska
Affiliation:
SAO, 60 Garden St., Cambridge MA 02138, USA email: nevans@cfa.harvard.edu
Scott Wolk
Affiliation:
SAO, 60 Garden St., Cambridge MA 02138, USA email: nevans@cfa.harvard.edu
Dimitar Sasselov
Affiliation:
Harvard University, 60 Garden St., Cambridge MA 02138, USA
Edward Guinan
Affiliation:
Villanova Univ., Dept. of Astronomy, Villanova, PA 19085USA
Scott Engle
Affiliation:
Villanova Univ., Dept. of Astronomy, Villanova, PA 19085USA
Eric Schlegel
Affiliation:
University of Texas, San Antonio, Dept. of Physics and Astronomy, 6900 N. Loop 1604 West, San Antonio TX 78249-0697USA
Brian Mason
Affiliation:
US Naval Observatory, 3450 Massachusetts Ave., NW, Washington, D.C. 20392-5420, USA
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Abstract

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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). By combining Hipparcos measurements of the instantaneous proper motion with long-term measurements and the Kamper radial-velocity orbit, Wielen et al (2000) have predicted the astrometric orbit of the close companion. Using the 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 Hipparcos parallax, and our measurement of the separation (0″.176 ± 0″.002), we find a preliminary mass of 5.0 ± 1.5 M⊙ for the Cepheid and 1.38 ± 0.61 M⊙ for the close companion. These values will be refined by additional HST observations scheduled for the next 3 years.

We have also obtained a 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.

Keywords

CepheidsmassesmultiplicityChandraHST
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 2 , Symposium S240: Binary Stars as Critical Tools & Tests in Contemporary Astrophysics , August 2006 , pp. 102 - 104
Copyright
Copyright © International Astronomical Union 2007

References

Evans, N.R., Schaefer, G., Bond, H.E., Nelan, E., Karovska, M., Bono, G., & Sasselov, D. 2007, in preparationGoogle Scholar
Feast, M.W., & Catchpole, R.M. 1997, MNRAS, 286, L1 CrossRefGoogle Scholar
Kamper, K.W. 1996, JRASC, 90, 140 Google Scholar
Randich, S., Schmitt, J.H.M.M., Prosser, C.F., & Stauffer, J.R. 1996, A&A, 305, 785 Google Scholar
Wielen, R., Jahreiss, H., Dettbarn, C., Lenhardt, H. & Schwan, H. 2000, A&A, 360, 399 Google Scholar