TY - JOUR
T1 - The long-period Galactic Cepheid RS Puppis
T2 - III. A geometric distance from HST polarimetric imaging of its light echoes
AU - Kervella, P.
AU - Bond, H. E.
AU - Cracraft, M.
AU - Szabados, L.
AU - Breitfelder, J.
AU - Mérand, A.
AU - Sparks, W. B.
AU - Gallenne, A.
AU - Bersier, D.
AU - Fouqué, P.
AU - Anderson, R. I.
N1 - Funding Information:
We thank Dr Daniel Rouan for fruitful discussions of the determination of the geometry of RS Pup’s nebula. We acknowledge financial support from the “Programme National de Physique Stellaire” (PNPS) of CNRS/INSU, France. Support for Program number GO-13454 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. P.K. and A.G. acknowledge support of the French-Chilean exchange program ECOS-Sud/CONICYT. L.Sz. acknowledges support from the ESTEC Contract No. 4000106398/12/NL/KML. A.G. acknowledges support from FONDECYT grant 3130361. This research received the support of PHASE, the high angular resolution partnership between ONERA, Observatoire de Paris, CNRS, and University Denis Diderot Paris 7. We used the SIMBAD and VIZIER databases at the CDS, Strasbourg (France), and NASA’s Astrophysics Data System Bibliographic Services. We used the IRAF package, distributed by the NOAO, which are operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation. Some of the data presented in this paper were obtained from the Multimission Archive at the Space Telescope Science Institute (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NAG5-7584 and by other grants and contracts.
Publisher Copyright:
© ESO, 2014.
PY - 2014/12/1
Y1 - 2014/12/1
N2 - As one of the most luminous Cepheids in the Milky Way, the 41.5-day RS Puppis is an analog of the long-period Cepheids used to measure extragalactic distances. An accurate distance to this star would therefore help anchor the zero-point of the bright end of the period-luminosity relation. But, at a distance of about 2 kpc, RS Pup is too far away for measuring a direct trigonometric parallax with a precision of a few percentage points with existing instrumentation. RS Pup is unique by being surrounded by a reflection nebula whose brightness varies as pulses of light from the Cepheid propagate outward. We present new polarimetric imaging of the nebula obtained with HST/ACS. The derived map of the degree of linear polarization pL allows us to reconstruct the three-dimensional structure of the dust distribution. To retrieve the scattering angle from the pL value, we consider two different polarization models, one based on a Milky Way dust mixture and one assuming Rayleigh scattering. Considering the derived dust distribution in the nebula, we adjust a model of the phase lag of the photometric variations over selected nebular features to retrieve the distance of RS Pup. We obtain a distance of 1910 ± 80 pc (4.2%), corresponding to a parallax of π = 0.524 ± 0.022 mas. The agreement between the two polarization models that we considered is good, but the final uncertainty is dominated by systematics in the adopted model parameters. The distance we obtain is consistent with existing measurements from the literature, but light echoes provide a distance estimate that is not subject to the same systematic uncertainties as other estimators (e.g., the Baade-Wesselink technique). RS Pup therefore provides an important fiducial for calibrating the systematic uncertainties of the long-period Cepheid distance scale.
AB - As one of the most luminous Cepheids in the Milky Way, the 41.5-day RS Puppis is an analog of the long-period Cepheids used to measure extragalactic distances. An accurate distance to this star would therefore help anchor the zero-point of the bright end of the period-luminosity relation. But, at a distance of about 2 kpc, RS Pup is too far away for measuring a direct trigonometric parallax with a precision of a few percentage points with existing instrumentation. RS Pup is unique by being surrounded by a reflection nebula whose brightness varies as pulses of light from the Cepheid propagate outward. We present new polarimetric imaging of the nebula obtained with HST/ACS. The derived map of the degree of linear polarization pL allows us to reconstruct the three-dimensional structure of the dust distribution. To retrieve the scattering angle from the pL value, we consider two different polarization models, one based on a Milky Way dust mixture and one assuming Rayleigh scattering. Considering the derived dust distribution in the nebula, we adjust a model of the phase lag of the photometric variations over selected nebular features to retrieve the distance of RS Pup. We obtain a distance of 1910 ± 80 pc (4.2%), corresponding to a parallax of π = 0.524 ± 0.022 mas. The agreement between the two polarization models that we considered is good, but the final uncertainty is dominated by systematics in the adopted model parameters. The distance we obtain is consistent with existing measurements from the literature, but light echoes provide a distance estimate that is not subject to the same systematic uncertainties as other estimators (e.g., the Baade-Wesselink technique). RS Pup therefore provides an important fiducial for calibrating the systematic uncertainties of the long-period Cepheid distance scale.
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U2 - 10.1051/0004-6361/201424395
DO - 10.1051/0004-6361/201424395
M3 - Article
AN - SCOPUS:84913584012
VL - 572
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
SN - 0004-6361
M1 - A7
ER -