On Spectral Line Formation and Measurement in Cepheids: Implications to Distance Determination

Sabbey, C. N.; Sasselov, Dimitar; Fieldus, M. S.; Lester, John B.; Venn, Kim A.; Butler, R. P.

doi:10.1086/175783

Cited by 66 publications

(101 citation statements)

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“…At short period, shocks generated by pulsation are stronger and more frequent than at longer period, furthermore, X-ray and UV observations of short-period Cepheids suggest the presence of very hot >10 5 K plasma in the envelope that may be related to chromospheres (Engle et al 2009). This simple test suggests that chromospheric effects may affect the Pp relation, for instance, Sabbey et al (1995) did find a value p = 1.6 from hydrodynamic models suggesting the possibility of limb-brightening in spectral lines as a function of pulsation phase. A third possible resolution is related to uncertainties of Cepheid parameters, in particular gravity.…”

Section: Why Do Theory and Observations Disagree?mentioning

confidence: 96%

“…Hindsley & Bell (1986) used a similar method to measure how the p-factor varies as a function of pulsation period p = −0.03 log P + 1.39. Similarly, Sabbey et al (1995) using hydrodynamic models to measure the p-factor as a function of pulsation phase, found p = 1.3 to p = 1.6. Recent theoretical measurements based on spectral line profiles from hydrodynamical spherically-symmetric model stellar atmospheres, with HARPS spectroscopic measurements, Nardetto et al (2004Nardetto et al ( , 2007 yielded both a geometric (their Eq.…”

Section: Introductionmentioning

confidence: 94%

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Cepheid limb darkening, angular diameter corrections, and projection factor from static spherical model stellar atmospheres

Neilson

Nardetto

Ngeow

et al. 2012

A&A

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Context. One challenge for measuring the Hubble constant using classical Cepheids is the calibration of the Leavitt law or periodluminosity relationship. The Baade-Wesselink method for distance determination to Cepheids relies on the ratio of the measured radial velocity and pulsation velocity, the so-called projection factor and the ability to measure the stellar angular diameters. Aims. We use spherically-symmetric model stellar atmospheres to explore the dependence of the p-factor and angular diameter corrections as a function of pulsation period. Methods. Intensity profiles are computed from a grid of plane-parallel and spherically-symmetric model stellar atmospheres using the SAtlas code. Projection factors and angular diameter corrections are determined from these intensity profiles and compared to previous results. Results. Our predicted geometric period-projection factor relation including previously published state-of-the-art hydrodynamical predictions is not with recent observational constraints. We suggest a number of potential resolutions to this discrepancy. The model atmosphere geometry also affects predictions for angular diameter corrections used to interpret interferometric observations, suggesting corrections used in the past underestimated Cepheid angular diameters by 3-5%. Conclusions. While spherically-symmetric hydrostatic model atmospheres cannot resolve differences between projection factors from theory and observations, they do help constrain underlying physics that must be included, including chromospheres and mass loss. The models also predict more physically-based limb-darkening corrections for interferometric observations.

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Section: Why Do Theory and Observations Disagree?mentioning

confidence: 96%

Section: Introductionmentioning

confidence: 94%

Cepheid limb darkening, angular diameter corrections, and projection factor from static spherical model stellar atmospheres

Neilson

Nardetto

Ngeow

et al. 2012

A&A

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“…The exact phase dependence of the p-factor is beyond the scope of this paper. However, for Aql and Gem, the net effect of a variable p-factor can be approximated by using a 6% larger constant p-factor (Sabbey et al 1995). Thus, for both Cepheids we use an effective p-factor of 1:43 AE 0:06, constant for all pulsational phases.…”

Section: Distances and Radiimentioning

confidence: 99%

“…Because of the limited number of observations available (e.g., only three H-band measurements of Aql), we used the shape of the radial velocity curve derived from the fit to the optical data (i.e., by using the same Fourier coefficients); the IR data were only used to determine an overall amplitude of the velocity curve. For the IR points we used an effective p-factor of 1:41 AE 0:03, as recommended by D. Sasselov (2001, private communication) and based on an analysis by Sabbey et al (1995), taking into account both the use of a constant p-factor and the use of parabolic line fitting. The resulting best-fit parameters are very similar to those based on optical radial velocities (i.e., Table 5 (top) and Gem (bottom) as a function of pulsational phase, together with a model based on radial velocity data, but fitting for distance, mean radius, and phase shift.…”

Section: Distances and Radiimentioning

confidence: 99%

Long‐Baseline Interferometric Observations of Cepheids

Lane

Creech‐Eakman

Nordgren

2002

ApJ

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We present observations of the Galactic Cepheids Aql and Gem. Our observations are able to resolve the diameter changes associated with pulsation. This allows us to determine the distance to the Cepheids independent of photometric observations. We determine a distance to Aql of 320 AE 32 pc and a distance to Gem of 362 AE 38 pc. These observations allow us to calibrate surface brightness relations for use in extragalactic distance determination. They also provide a measurement of the mean diameter of these Cepheids, which is useful in constructing structural models of this class of star.

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“…[10,11,12,13,14] and references therein for a discussion of those non-trivial questions on the projection factor and other problems related to BW method in Cepheids. In reality, one can measure directly only the matter velocity vm on the photospheric level.…”

Section: Classical Baade-wesselink and Kirshner-kwan Methodsmentioning

confidence: 99%

Direct determination of the hubble parameter using type IIn supernovae

et al. 2012

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We introduce a novel approach, a Dense Shell Method (DSM), for measuring distances for cosmology. It is based on original Baade idea to relate absolute difference of photospheric radii with photospheric velocity. We demonstrate that this idea works: the new method does not rely on the Cosmic Distance Ladder and gives satisfactory results for the most luminous Type IIn Supernovae. This allows one to make them good primary distance indicators for cosmology. Fixing correction factors for illustration, we obtain with this method the median distance of ≈ 68

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On Spectral Line Formation and Measurement in Cepheids: Implications to Distance Determination

Cited by 66 publications

References 0 publications

Cepheid limb darkening, angular diameter corrections, and projection factor from static spherical model stellar atmospheres

Cepheid limb darkening, angular diameter corrections, and projection factor from static spherical model stellar atmospheres

Long‐Baseline Interferometric Observations of Cepheids

Direct determination of the hubble parameter using type IIn supernovae

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