Hubble Space TelescopeFine Guidance Sensor Parallaxes of Galactic Cepheid Variable Stars: Period-Luminosity Relations

Abstract

We present new absolute trigonometric parallaxes and relative proper motions for nine Galactic Cepheid variable stars: ℓ Car, ζ Gem, β Dor, W Sgr, X Sgr, Y Sgr, FF Aql, T Vul, and RT Aur. We obtain these results with astrometric data from Fine Guidance Sensor 1r, a white-light interferometer on Hubble Space Telescope. We find absolute parallaxes in milliseconds of arc: ℓ Car, 2.01 ± 0.20 ; ζ Gem, 2.78 ± 0.18 ; β Dor, 3.14 ± 0.16 ; W Sgr, 2.28 ± 0.20 ; X Sgr, 3.00 ± 0.18 ; Y Sgr, 2.13 ± 0.29 ; FF Aql, 2.81 ± 0.18 ; T Vul, 1.90 ± 0.23 ; and RT Aur, 2.40 ± 0.19 , an average σ π /π = 8%. Two stars (FF Aql and W Sgr) required the inclusion of binary astrometric perturbations, providing Cepheid mass estimates. With these parallaxes we compute absolute magnitudes in V, I, K, and Wesenheit W V I bandpasses corrected for interstellar extinction and Lutz-Kelker-Hanson bias. Adding our previous absolute magnitude determination for δ Cep, we construct Period-Luminosity relations for ten Galactic Cepheids.We compare our new Period-Luminosity relations with those adopted by several recent investigations, including the Freedman and Sandage H 0 projects. Adopting our Period-Luminosity relationship would tend to increase the Sandage H 0 value, but leave the Freedman H 0 unchanged. Comparing our Galactic Cepheid PLR with those derived from LMC Cepheids, we find the slopes for K and W V I identical in the two galaxies within their respective errors. Our data lead to a W V I distance modulus for the Large Magellanic Cloud, m-M = 18.50±0.03, uncorrected for any metallicity effects. Applying recently derived metalllcity corrections yields a corrected LMC distance modulus of (m-M) 0 =18.40±0.05. Comparing our Period-Luminosity relationship to solar-metallicity Cepheids in NGC 4258 results in a distance modulus, 29.28 ± 0.08, which agrees with that derived from maser studies.

Measuring the Hubble Constant With the Hubble Space Telescope

“…The Cepheid distance is 7.5 ± 0.3 Mpc (Macri et al 2006). In addition, HST trigonometric parallaxes for a sample of Cepheids have become available (Benedict et al 2007), confirming the Key Project period-luminosity calibration, as shown in Figure 25. The probability distribution for H 0 , combining the results of the secondary distance indicators and the full error budget of the Key Project is shown in Figure 26 (Freedman et al 2001).…”

Observational probes of cosmic acceleration

“…The recent determination of H 0 = 73.8 ± 2.4 km s −1 Mpc −1 by Riess et al (2011) yields a 1σ uncertainty of only 3.3%, including all identified sources of systematic uncertainty and calibration error. One important change in this analysis is a shift to Cepheid calibration based on the maser distances to NGC 4258 (Herrnstein et al, 1999;Humphreys et al, 2008Humphreys et al, , 2013 and on parallaxes to Galactic Cepheids measured with Hipparcos (van Leeuwen et al, 2007) and with the HST fine-guidance sensors (Benedict et al, 2007). These calibrations circumvent the statistical and systematic uncertainties in the LMC distance, and they directly calibrate the P − L relation in the metallicity range typical of calibrator galaxies, albeit with a sample of only ∼ 10 stars reaching an error-on-the-mean of 2.8% in the case of Milky Way parallaxes.…”

“…Monson et al (2012) calibrate the 3.6µm P − L zero-point against Galactic Cepheid samples, including the Benedict et al (2007) parallax sample, and thereby infer the distance modulus to the LMC as a test of the optical Cepheid P − L relation and its metallicity correction. Freedman et al (2012) use these Milky Way parallaxes to calibrate the optical Cepheid P − L relation and then recalibrate the Key Project data set to infer H 0 ; this determination still relies on optical, WFPC2 Cepheid data (and the associated metallicity corrections and flux and color zero-point uncertainties), and the Key Project SN Ia calibrator sample includes several SNe with photographic photometry or high extinction.…”

Pulsation Period Change & Classical Cepheids: Probing the Details of Stellar Evolution

“…Hence, we require another constraint, one provided by interferometry. For instance, assuming parallaxes from Hipparcos and HST (van Leeuwen et al 2007;Benedict et al 2007), the radius of Polaris and l Car are 43.5 ± 0.8 and 159.9 ± 16.6 R , respectively Mérand et al 2006). This permits Figure 1.…”