Anchors for the Cosmic Distance Scale: the Cepheids U Sgr, CF Cas and CEab Cas (original) (raw)
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Astronomy & Astrophysics, 2013
New and existing X-ray, UBV JHK s W (1−4) , and spectroscopic observations were analyzed to constrain fundamental parameters for M 25, NGC 7790, and dust along their sight-lines. The star clusters are of particular importance because they host the classical Cepheids U Sgr, CF Cas, and the visual binary Cepheids CEa and CEb Cas. Precise results from the multiband analysis, in tandem with a comprehensive determination of the Cepheids' period evolution (dP/dt) from ∼140 years of observations, helped to resolve concerns raised regarding the clusters and their key Cepheid constituents. Specifically, the distances derived for members of M 25 and NGC 7790 are 630 ± 25 pc and 3.40 ± 0.15 kpc, respectively.
The Cepheid Distance to NGC 0247
The Astrophysical Journal, 2009
We report VRI CCD observations of nine Cepheids in the South Polar (Sculptor) Group spiral galaxy NGC 0247. Periods of these Cepheids range from 20 to 70 days. Over the past 20 years the very brightest Cepheid in our sample, NGC 0247:[MF09] C1, has decreased its period by 6%, faded by 0.8 mag in the V band, and become bluer by 0.23 mag in (V-I). A multi-wavelength analysis of the Cepheid data yields a true distance modulus of µ o = 27.81±0.10 mag (3.36±0.16 Mpc) with a total line-of-sight reddening of E(V-I) = 0.07±0.04 mag, after adopting an LMC true distance modulus of 18.5 mag and reddening of E(B-V) = 0.10 mag. These results are in excellent agreement with other very recently published (Cepheid and TRGB) distances to NGC 0247. Combining both Cepheid datasets gives µ o = 27.85 ± 0.09 mag (3.72±0.15 Mpc) with E(V-I) = 0.11±0.03 mag.
A Revised Cepheid Distance to NGC 4258 and a Test of the Distance Scale
The Astrophysical Journal, 2001
In a previous paper (Maoz et al. 1999), we reported a Hubble Space Telescope (HST) Cepheid distance to the galaxy NGC 4258 obtained using the calibrations and methods then standard for the Key Project on the Extragalactic Distance Scale. Here, we reevaluate the Cepheid distance using the revised Key Project procedures described in Freedman et al. (2001). These revisions alter the zero points and slopes of the Cepheid Period-Luminosity (P-L) relations derived at the Large Magellanic Cloud (LMC), the calibration of the HST WFPC2 camera, and the treatment of metallicity differences. We also provide herein full information on the Cepheids described in Maoz et al. 1999. Using the refined Key Project techniques and calibrations, we determine the distance modulus of NGC 4258 to be 29.47 ± 0.09 mag (unique to this determination) ±0.15 mag (systematic uncertainties in Key Project distances), corresponding to a metric distance of 7.8±0.3±0.5 Mpc and 1.2σ from the maser distance of 7.2±0.5 Mpc. We also test the alternative Cepheid P-L relations of Feast (1999), which yield more discrepant results. Additionally, we place weak limits upon the distance to the LMC and upon the effect of metallicity in Cepheid distance determinations.
ANCHORING THE DISTANCE SCALE VIA X-RAY/INFRARED DATA FOR CEPHEID CLUSTERS: SU Cas
The Astrophysical Journal, 2012
New X-ray (XMM-Newton) and JHK s (Observatoire du Mont-Mégantic) observations for members of the star cluster Alessi 95, which Turner et al. discovered hosts the classical Cepheid SU Cas, were used in tandem with UCAC3 (proper motion) and Two Micron All Sky Survey observations to determine precise cluster parameters: E(J − H) = 0.08 ± 0.02 and d = 405 ± 15 pc. The ensuing consensus among cluster, pulsation, and trigonometric distances (d = 414 ± 5(σx) ± 10(σ) pc) places SU Cas in a select group of nearby fundamental Cepheid calibrators (δ Cep, ζ Gem). High-resolution X-ray observations may be employed to expand that sample as the data proved pertinent for identifying numerous stars associated with SU Cas. Acquiring X-ray observations of additional fields may foster efforts to refine Cepheid calibrations used to constrain H 0 .
A Cepheid distance to NGC 4258
1999
Distances measured using Cepheid variable stars have been essential for establishing the cosmological distance scale and the value of the Hubble constant. These stars have remained the primary extragalactic distance indicator since 1929 because of the small observed scatter in the relationship between their pulsation period and luminosity, their large numbers, which allow many independent measures of the distance to a galaxy, and the simplicity of the basic physics underlying their variability. Poten-This measurement is subject to a number of potential sources of systematic error that also affect Key Project distance determinations, as described in Table 1; their possible contributions have been
The Astrophysical Journal, 1998
The distance to NGC 7331 has been derived from Cepheid variables observed with HST/WFPC2, as part of the Extragalactic Distance Scale Key Project. Multi-epoch exposures in F555W (∼ V ) and F814W (∼ I), with photometry derived independently from DoPHOT and DAOPHOT/ALLFRAME programs, were used to detect a total of 13 reliable Cepheids, with periods between 11 and 42 days. The relative distance moduli between NGC 7331 and the LMC, derived from the V and I magnitudes, imply an extinction to NGC 7331 of A V = 0.47 ± 0.15 mag, and an extinction-corrected distance modulus to NGC 7331 of 30.89 ± 0.14(random) mag, equivalent to a distance of 15.1 +1.0 −0.9 Mpc. There are additional systematic uncertainties in the distance modulus of ±0.12 mag due to the calibration of the Cepheid Period-Luminosity relation, and a systematic offset of +0.05 ± 0.04 mag if we applied the metallicity correction inferred from the M101 results of Kennicutt et al 1998. 22 With the exception that here we have corrected for the photometric distortions of the corrective optics by the multiplication of the pixel area map.
DOAJ: Directory of Open Access Journals - DOAJ, 2010
The Galactic calibration of the period-luminosity (PL) relation for classical Cepheids is examined using trigonometric, open cluster, and pulsation parallaxes, which help establish independent versions of the relationship. The calibration is important for the continued use of classical Cepheids in constraining cosmological models (by refining estimates for H 0), for defining zero-points for the SNe Ia and population II (Type II Cepheids/RR Lyrae variables) distance scales, for clarifying properties of the Milky Way's spiral structure, and for characterizing dust extinction affecting Cepheids in the Milky Way and other galaxies. Described is a program to extend and refine the Galactic Cepheid PL relation by obtaining UBVRIJHK s photometry and spectra for stars in open clusters suspected of hosting classical Cepheids, using the the facilities of the OAMM, DAO, AAVSO, and ARO.
The Discovery of Cepheids and a Distance to NGC 5128
The Astrophysical Journal, 2007
We discuss a new distance to NGC 5128 (Centaurus A) based on Cepheid variables observed with the Hubble Space Telescope. Twelve F555W (V) and six F814W (I) epochs of cosmic-ray-split Wide Field Planetary Camera 2 observations were obtained. A total of 56 bona-fide Cepheids were discovered, with periods ranging from 5 to ∼ 50 days; five of these are likely Population II Cepheids of the W Virginis class, associated with the bulge or halo of NGC 5128. Based on the period and V and I−band luminosities of a sub-sample of 42 classical (Pop I) Cepheids, and adopting a Large Magellanic Cloud distance modulus and extinction of 18.50 ± 0.10 mag and E(B − V)=0.10 mag, respectively, the true reddening-corrected distance modulus to NGC 5128 is µ • = 27.67 ± 0.12 (random) ± 0.16 (systematic) mag, corresponding to a distance of 3.42 ± 0.18 (random) ± 0.25 (systematic) Mpc. The random uncertainty in the distance is dominated by the error on the assumed value for the ratio of total to selective absorption, R V , in NGC 5128, and by the possible metallicity dependence of the Cepheid Period-Luminosity relation at V and I. This represent the first determination of a Cepheid distance to an early-type galaxy.
Some Characteristics of Galactic Cepheids Relevant to the Calibration of the Distance Scale
arXiv: Astrophysics, 1998
An analysis of the observed characteristics of the Galactic Cepheid variables is carried out in the framework of their period-luminosity relation being used as a standard candle for distance measurement. The variation of the observed number density of Galactic Cepheids as function of their period and amplitude along with stellar pulsation characteristics is used to divide the population into two groups: one with low periods, probably multi-mode or higher mode oscillators, and another of high period variables which should be dominantly fundamental mode radial pulsators. Methods to obtain extinction-corrected colors from multi-wavelength observations of the second group of variables are described and templates of the (V-I) light curves are obtained from the V light curves. Colors computed from the model atmospheres are compared with the extinction-corrected colors to determine the Cepheid instability strip in the mean surface gravity--effective temperature diagram, and relations are d...