| Title | Astrometry with the Hubble Space Telescope: A Parallax of the Fundamental Distance Calibrator δ Cephei |
| Authors | Benedict, G. Fritz; McArthur, B. E.; Fredrick, L. W.; Harrison, T. E.; Slesnick, C. L.; Rhee, J.; Patterson, R. J.; Skrutskie, M. F.; Franz, O. G.; Wasserman, L. H.; Jefferys, W. H.; Nelan, E.; van Altena, W.; Shelus, P. J.; Hemenway, P. D.; Duncombe, R. L.; Story, D.; Whipple, A. L.; Bradley, A. J. |
| Bibcode | 2002AJ....124.1695B Search ADS ↗ |
| Abstract | We present an absolute parallax and relative proper motion for the fundamental distance scale calibrator δ Cep. We obtain these with astrometric data from FGS 3, a white-light interferometer on the Hubble Space Telescope (HST). Utilizing spectrophotometric estimates of the absolute parallaxes of our astrometric reference stars and constraining δ Cep and reference star HD 213307 to belong to the same association (Cep OB6), we find πabs=3.66+/-0.15 mas. The larger than typical astrometric residuals for the nearby astrometric reference star HD 213307 are found to satisfy Keplerian motion with P=1.07 +/- 0.02 yr, a perturbation and period that could be due to an F0 V companion ~7 mas distant from and ~4 mag fainter than the primary. Spectral classifications and VRIJHKT2M and DDO51 photometry of the astrometric reference frame surrounding δ Cep indicate that field extinction is high and variable along this line of sight. However the extinction suffered by the reference star nearest (in angular separation and distance) to δ Cep, HD 213307, is lower and nearly the same as for δ Cep. Correcting for color differences, we find V>=0.23+/-0.03 for δ Cep and hence an absolute magnitude MV=-3.47+/-0.10. Adopting an average V magnitude, =15.03+/-0.03, for Cepheids with logP=0.73 in the large Magellanic Cloud (LMC) from Udalski et al., we find a V-band distance modulus for the LMC, m-M=18.50+/-0.13, or 18.58+/-0.15, where the latter value results from a highly uncertain metallicity correction. These agree with our previous RR Lyr HST parallax-based determination of the distance modulus of the LMC. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. |
