Polaris: Mass and Multiplicity
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). 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 +or- 0".002), we find a preliminary mass of 5.0 +or- 1.5 M(circle dot solar) for the Cepheid and 1.38 +or- 0.61 M(circle dot solar) 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.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 2006
- Accession Number
- ADA471047
Entities
People
- Brian Mason
- Dimitar Sasselov
- Edmund Nelan
- Edward Guinan
- Eric Schlegel
- Gail Schaefer
- Giuseppe Bono
- Howard E. Bond
- Margarita Karovska
- Nancy R. Evans
- Scott Engle
- Scott Wolk
Organizations
- United States Naval Observatory