Cepheids In Galaxies Research Articles

Insensitivity of the distance ladder Hubble constant determination to Cepheid calibration modelling choices

Recent determination of the Hubble constant via Cepheid-calibrated supernovae by \citet{riess_2.4_2016} (R16) find $\sim 3\sigma$ tension with inferences based on cosmic microwave background temperature and polarization measurements from $Planck$. This tension could be an indication of inadequacies in the concordance $\Lambda$CDM model. Here we investigate the possibility that the discrepancy could instead be due to systematic bias or uncertainty in the Cepheid calibration step of the distance ladder measurement by R16. We consider variations in total-to-selective extinction of Cepheid flux as a function of line-of-sight, hidden structure in the period-luminosity relationship, and potentially different intrinsic color distributions of Cepheids as a function of host galaxy. Considering all potential sources of error, our final determination of $H_0 = 73.3 \pm 1.7~{\rm km/s/Mpc}$ (not including systematic errors from the treatment of geometric distances or Type Ia Supernovae) shows remarkable robustness and agreement with R16. We conclude systematics from the modeling of Cepheid photometry, including Cepheid selection criteria, cannot explain the observed tension between Cepheid-variable and CMB-based inferences of the Hubble constant. Considering a `model-independent' approach to relating Cepheids in galaxies with known distances to Cepheids in galaxies hosting a Type Ia supernova and finding agreement with the R16 result, we conclude no generalization of the model relating anchor and host Cepheid magnitude measurements can introduce significant bias in the $H_0$ inference.

A Precision Determination of the Effect of Metallicity on Cepheid Absolute Magnitudes in VIJHK Bands from Magellanic Cloud Cepheids

Abstract Using high-quality observed period–luminosity (P–L) relations in both Magellanic Clouds in the VIJHK s bands and optical and near-infrared Wesenheit indices, we determine the effect of metallicity on Cepheid P–L relations by comparing the relative distance between the LMC and SMC as determined from the Cepheids to the difference in distance between the Clouds that has been derived with very high accuracy from late-type eclipsing binary systems. Within an uncertainty of 3%, which is dominated by the uncertainty on the mean difference in metallicity between the Cepheid populations in the LMC and SMC, we find metallicity effects smaller than 2% in all bands and in the Wesenheit indices, consistent with a zero metallicity effect. This result is valid for the metallicity range from −0.35 dex to −0.75 dex corresponding to the mean [Fe/H] values for classical Cepheids in the LMC and SMC, respectively. Yet most Cepheids in galaxies beyond the Local Group and located in the less crowded outer regions of these galaxies do fall into this metallicity regime, making our result important for applications to determine the distances to spiral galaxies well beyond the Local Group. Our result supports previous findings that indicated a very small metallicity effect on the near-infrared absolute magnitudes of classical Cepheids, and resolves the dispute about the size and sign of the metallicity effect in the optical spectral range. It also resolves one of the most pressing problems in the quest toward a measurement of the Hubble constant with an accuracy of 1% from the Cepheid–supernova Ia method.

Cepheid parallaxes and the Hubble constant

Revised Hipparcos parallaxes for classical Cepheids are analysed together with 10 HST-based parallaxes (Benedict et al.). In a reddening-free V,I relation we find that the coefficient of logP is the same within the uncertainties in our Galaxy as in the LMC, contrary to some previous suggestions. Cepheids in the inner region of NGC4258 with near solar metallicities (Macri et al.) confirm this result. We obtain a zero-point for the reddening-free relation and apply it to Cepheids in galaxies used by Sandage et al. to calibrate the absolute magnitudes of SNIa and to derive the Hubble constant. We revise their result from 62 to 70+/-5 km/s/Mpc. The Freedman et al. 2001 value is revised from 72 to 76+/-8 km/s/Mpc. These results are insensitive to Cepheid metallicity corrections. The Cepheids in the inner region of NGC4258 yield a modulus of 29.22+/-0.03(int) compared with a maser-based modulus of 29.29+/-0.15. Distance moduli for the LMC, uncorrected for any metallicity effects, are; 18.52+/-0.03 from a reddening-free relation in V,I; 18.47+/-0.03 from a period-luminosity relation at K; 18.45+/-0.04 from a period-luminosity-colour relation in J,K. Adopting a metallicity correction in V,I from Marci et al. leads to a true LMC modulus of 18.39+/-0.05.

Accurate and Deep Wide Field Photometry: The Stellar Perspective

We discuss how a wide field imager with very high spatial resolution on a relatively small telescope–but located in an observing site with very good seeing–might constrain the fraction of binary stars in Galactic globular clusters. We also mention the role that the new data might play in investigating advanced evolutionary phases of low-mass stars. Moreover, we discuss the role that an Extremely Large Telescope might have on the longstanding problem of cosmic distances and stellar populations. In particular, we discuss the impact that the detection of Cepheids in galaxies at the distance of the Coma cluster and of RR Lyrae stars in galaxies at the distance of the Virgo cluster might have on the calibration of secondary distance indicators.

On the light curve shape of Cepheids in IC 1613 and NGC 6822

Comparison of the Fourier parameters of fundamental mode Cepheids with period near 10 d in galaxies of the Local Group (IC 1613, NGC 6822, Milky Way, Magellanic Clouds) confirms the previous indication of the lack of a spread of $\phi_{21}$ values in some dwarf irregular galaxies. It is not yet clear whether this is a real effect or if it is just due to the low number of Cepheids in these galaxies. We suspect however that in this period range the Cepheids of IC 1613 and NGC 6822 behave differently from those in the Milky Way and the Magellanic Clouds. The main effect of the different metallicity on the Fourier parameters is confirmed to be the larger R 21 values of shorter period Cepheids in metal-poorer galaxies. However the metallicity alone should not be enough to explain the various differences among the Cepheids of the four galaxies. The difference between the spread of $\phi_{21}$ values near 10 d in Milky Way and Magellanic clouds is pointed out.

The effect of metallicity on the Cepheid Period-Luminosity relation from a Baade-Wesselink analysis of Cepheids in the Galaxy and in the Small Magellanic Cloud

(ABRIDGED) We have applied the near-IR Barnes-Evans realization of the Baade-Wesselink method as calibrated by Fouque & Gieren (1997) to five metal-poor Cepheids with periods between 13 and 17 days in the Small Magellanic Cloud as well as to a sample of 34 Galactic Cepheids to determine the effect of metallicity on the period-luminosity (P-L) relation. For ten of the Galactic Cepheids we present new accurate and well sampled radial-velocity curves. The Baade-Wesselink analysis provides accurate individual distances and luminosities to the Cepheids in the two samples, allowing us to constrain directly, in a purely differential way, the metallicity effect on the Cepheid P-L relation. For the Galactic Cepheids we provide a new set of P-L relations which have zero-points in excellent agreement with astrometric and interferometric determinations. These relations can be used directly for the determination of distances to solar-metallicity samples of Cepheids in distant galaxies, circumventing any corrections for metallicity effects on the zero-point and slope of the P-L relation. We find evidence for both such metallicity effects in our data. Comparing our two samples of Cepheids at a mean period of about 15 days, we find a weak effect of metallicity on the luminosity similar to that adopted by the HST Key Project on the Extragalactic Distance Scale.

Variable Stars in the Sextans Dwarf Spheroidal Galaxy

view Abstract Citations (87) References (70) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Variable Stars in the Sextans Dwarf Spheroidal Galaxy Mateo, Mario ; Fischer, Philippe ; Krzeminski, Wojtek Abstract We describe a survey for variable stars in the Sextans dwarf spheroidal (dSph) galaxy based on the analysis of 113 B and 48 V CCD images of four fields covering a total area of 18' x 18'. We have identified 44 variables: 36 RR Lyr star, 6 anomalous Cepheids, one long-period red variable, all probable members of Sextans, and one foreground contact binary. We have used the pulsating stars to derive a true distance modulus of 19.67 +/- 0.15 for Sextans (or D = 86 +/-6 kpc), where the error is primarily due to uncertainties in the luminosity-metallicity relation for RR Lyr stars. Based on our new data we conclude that [Fe/H]_Sex_ = -1.6 +/- 0.2, somewhat higher than the value from Suntzeff et al. (ApJ, 418,208(1993)] obtained from the analysis of fiber spectroscopy of the near-IR Calcium triplet. We present a new deep color- magnitude diagram for Sextans which reveals the presence of a metal-poor population containing stars as young as 2-4 Gyr, consistent with the presence of anomalous Cepheids in the galaxy. This young population may represent as much as 25% of the total stellar content of Sextans. We find a surprisingly strong correlation between the frequency of anomalous Cepheids in dSph galaxies and galaxian luminosity and speculate on the possible origin of this strange effect. The RR Lyr stars in Sextans do not exhibit the Oosterhoff dichotomy observed in globular clusters and in the Galactic halo field. Publication: The Astronomical Journal Pub Date: November 1995 DOI: 10.1086/117676 Bibcode: 1995AJ....110.2166M Keywords: GALAXIES: INDIVIDUAL: DSPH; GALAXIES: STELLAR CONTENT full text sources ADS | data products SIMBAD (53) NED (1) CDS (1)