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241. Cepheid Period-Wesenheit-Metallicity relation
ID:
ivo://CDS.VizieR/J/A+A/659/A167
Title:
Cepheid Period-Wesenheit-Metallicity relation
Short Name:
J/A+A/659/A167
Date:
23 Mar 2022 15:18:20
Publisher:
CDS
Description:
Classical Cepheids (DCEPs) represent a fundamental tool to calibrate the extragalactic distance scale. However, they are also powerful stellar population tracers, in the context of Galactic studies. The forthcoming Data Release 3 (DR3) of the Gaia mission will allow us to study with unprecedented detail the structure, the dynamics and the chemical properties of the Galactic disc, and in particular of the spiral arms, where most Galactic DCEPs reside. In this paper we aim at quantifying the metallicity dependence of the Galactic DCEPs Period-Wesenheit (PWZ) relation in the Gaia bands. We adopt a sample of 499 DCEPs with metal abundances from high-resolution spectroscopy, in conjunction with Gaia Early Data Release 3 parallaxes and photometry to calibrate a PWZ relation in the Gaia bands. We find a significant metallicity term, of the order of -0.5mag/dex, which is larger than the values measured in the NIR bands by different authors. Our best PWZ relation is W=(-5.988+/-0.018)-(3.176+/-0.044)(logP-1.0)-(0.520+/-0.090)[Fe/H]. We validate our PWZ relations by using the distance to the Large Magellanic Cloud as a benchmark, finding a very good agreement with the geometric distance provided by eclipsing binaries. As an additional test, we evaluate the metallicity gradient of the young Galactic disc, finding -0.0527+/-0.0022dex/kpc, in very good agreement with previous results.
242. Cepheid radial velocities
ID:
ivo://CDS.VizieR/J/AJ/115/635
Title:
Cepheid radial velocities
Short Name:
J/AJ/115/635
Date:
21 Oct 2021
Publisher:
CDS
Description:
A catalog of Cepheid variables is used to probe the kinematics of the Galactic disk. Radial velocities are measured for eight distant Cepheids toward l=300{deg}; these new Cepheids provide a particularly good constraint on the distance to the Galactic center, R_0_. We model the disk with both an axisymmetric rotation curve and one with a weak elliptical component, and find evidence for an ellipticity of 0.043+/-0.016 near the Sun. Using these models, we derive R_0_=7.66+/-0.32kpc and v_circ_=237+/-12km/s. The distance to the Galactic center agrees well with recent determinations from the distribution of RR Lyrae variables and disfavors most models with large ellipticities at the solar orbit.
243. Cepheid Radial Velocities (CRaV) project
ID:
ivo://CDS.VizieR/J/AJ/150/13
Title:
Cepheid Radial Velocities (CRaV) project
Short Name:
J/AJ/150/13
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have examined high accuracy radial velocities of Cepheids to determine the binary frequency. The data are largely from the CORAVEL spectrophotometer and the Moscow version, with a typical uncertainty of {<=}1km/s, and a time span from 1 to 20years. A systemic velocity was obtained by removing the pulsation component using a high order Fourier series. From this data we have developed a list of stars showing no orbital velocity larger than +/-1km/s. The binary fraction was analyzed as a function of magnitude, and yields an apparent decrease in this fraction for fainter stars. We interpret this as incompleteness at fainter magnitudes, and derive the preferred binary fraction of 29%+/-8% (20%+/-6% per decade of orbital period) from the brightest 40 stars. A comparison of this fraction in this period range (1-20years) implies a large fraction for the full period range. This is reasonable in that the high accuracy velocities are sensitive to the longer periods and smaller orbital velocity amplitudes in the period range sampled here. Thus the Cepheid velocity sample provides a sensitive detection in the period range between short period spectroscopic binaries and resolved companions. The recent identification of {delta} Cep as a binary with very low amplitude and high eccentricity underscores the fact that the binary fractions we derive are lower limits, to which other low amplitude systems will probably be added. The mass ratio (q) distribution derived from ultraviolet observations of the secondary is consistent with a flat distribution for the applicable period range (1-20years).
244. Cepheid radial velocity amplitude modulations
ID:
ivo://CDS.VizieR/J/A+A/566/L10
Title:
Cepheid radial velocity amplitude modulations
Short Name:
J/A+A/566/L10
Date:
21 Oct 2021
Publisher:
CDS
Description:
Classical Cepheids are crucial calibrators of the extragalactic distance scale. The Baade-Wesselink technique can be used to calibrate Cepheid distances using Cepheids in the Galaxy and the Magellanic Clouds. To report the discovery of modulations in radial velocity (RV) curves of four Galactic classical Cepheids and to investigate their impact as a systematic uncertainty for Baade-Wesselink distances. Highly precise Doppler measurements were obtained using the Coralie high-resolution spectrograph since 2011. Particular care was taken to sample all phase points in order to very accurately trace the RV curve during multiple epochs and to search for differences in linear radius variations derived from observations obtained at different epochs. Different timescales are sampled, ranging from cycle-to-cycle to months and years. The unprecedented combination of excellent phase coverage obtained during multiple epochs and high precision enabled the discovery of significant modulation in the RV curves of the short-period s-Cepheids QZ Normae and V335 Puppis, as well as the long-period fundamental mode Cepheids l Carinae and RS Puppis. The modulations manifest as shape and amplitude variations that vary smoothly over timescales of years for short-period Cepheids, and from one pulsation cycle to the next in the long-period Cepheids. The order of magnitude of the effect ranges from several hundred m/s to a few km/s. The resulting difference among linear radius variations derived using data from different epochs can lead to systematic errors of up to 15% for Baade-Wesselink-type distances, if the employed angular and linear radius variations are not determined contemporaneously. The different nature of the Cepheids exhibiting modulation in their RV curves suggests that this phenomenon is common. The observational baseline is not yet sufficient to conclude whether these modulations are periodic. In order to ensure the accuracy of Baade-Wesselink distances, angular and linear radius variations should always be determined contemporaneously.
245. Cepheid radii
ID:
ivo://CDS.VizieR/J/A+A/318/797
Title:
Cepheid radii
Short Name:
J/A+A/318/797
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have refined the CORS method, introduced in 1980 for the computation of the Cepheid radii, in order to extend its applicability to recent and extensive sets of observations. The refinement is based on the computation, from observational data only, of one of the terms of the solving equation, previously based only on precise calibrations of photometric colors. A limited number of assumptions, generally accepted in the literature, is used. New radii are computed for about 70 Cepheids, and the resulting P-R relation is discussed.
246. Cepheid radii
ID:
ivo://CDS.VizieR/J/PAZh/24/443
Title:
Cepheid radii
Short Name:
J/PAZh/24/443
Date:
21 Oct 2021
Publisher:
CDS
Description:
Based on dense series of photoelectric observations and on our radial-velocity measurements, the radii of 62 northern Cepheids are calculated by Balona's method. For each star there are five radius calculations. Two color indices, (B-V) and (V-R), were used as the effective temperature indicators. All light curves in V, B-V and V-R magnitudes together with the descending part light curves were used to exclude shock-wave influence. For calculations of radii of spectroscopic binaries (=sb) were used pulsational radial velocity curves.
247. Cepheids and companions in M33 from HST images
ID:
ivo://CDS.VizieR/J/AJ/144/113
Title:
Cepheids and companions in M33 from HST images
Short Name:
J/AJ/144/113
Date:
21 Oct 2021
Publisher:
CDS
Description:
A precise and accurate determination of the Hubble constant based on Cepheid variables requires proper characterization of many sources of systematic error. One of these is stellar blending, which biases the measured fluxes of Cepheids and the resulting distance estimates. We study the blending of 149 Cepheid variables in M33 by matching archival Hubble Space Telescope data with images obtained at the Wisconsin-Indiana-Yale-NOAO (WIYN) 3.5m telescope, which differ by a factor of 10 in angular resolution. We find that 55%+/-4% of the Cepheids have no detectable nearby companions that could bias the WIYN V-band photometry, while the fraction of Cepheids affected below the 10% level is 73%+/-4%. The corresponding values for the I band are 60%+/-4% and 72%+/-4%, respectively. We find no statistically significant difference in blending statistics as a function of period or surface brightness. Additionally, we report all the detected companions within 2" of the Cepheids (equivalent to 9pc at the distance of M33) which may be used to derive empirical blending corrections for Cepheids at larger distances.
248. Cepheids BVRIJHK dereddened magnitudes
ID:
ivo://CDS.VizieR/J/A+A/428/587
Title:
Cepheids BVRIJHK dereddened magnitudes
Short Name:
J/A+A/428/587
Date:
21 Oct 2021
Publisher:
CDS
Description:
The recent VINCI/VLTI observations presented in Paper I (Kervalla et al., 2004A&A...416..941K) have nearly doubled the total number of available angular diameter measurements of Cepheids. Taking advantage of the significantly larger color range covered by these observations, we derive in the present paper high precision calibrations of the surface brightness-color relations using exclusively Cepheid observations. These empirical laws allow to determine the distance to Cepheids through a Baade-Wesselink type technique. The least dispersed relations are based on visible-infrared colors, for instance FV(V-K)=-0.1336+/-0.0008(V-K)+3.9530+/-0.0006. The convergence of the Cepheid (this work) and dwarf stars (Kervella et al. 2004) visible-infrared surface brightness-color relations is strikingly good. The astrophysical dispersion of these relations appears to be very small, and below the present detection sensitivity.
249. Cepheids flux weighted gravity-luminosity
ID:
ivo://CDS.VizieR/J/A+A/640/A113
Title:
Cepheids flux weighted gravity-luminosity
Short Name:
J/A+A/640/A113
Date:
21 Oct 2021
Publisher:
CDS
Description:
The flux-weighted gravity-luminosity relation (FWGLR) is investigated for a sample of 477 classical Cepheids (CCs), including stars that have been classified in the literature as such but are probably not. The luminosities are taken from the literature, based on the fitting of the spectral energy distributions (SEDs) assuming a certain distance and reddening. The flux-weighted gravity (FWG) is taken from gravity and effective temperature determinations in the literature based on high-resolution spectroscopy. There is a very good agreement between the theoretically predicted and observed FWG versus pulsation period relation that could serve in estimating the FWG (and logg) in spectroscopic studies with a precision of 0.1dex. As was known in the literature, the theoretically predicted FWGLR relation for CCs is very tight and not very sensitive to metallicity (at least for LMC and Solar values), rotation rate and crossing of the instability strip. The observed relation has a slightly different slope and shows more scatter (0.54dex). This is due both to uncertainties in the distances and the pulsation phase averaged FWG values. Data from future Gaia data releases should reduce these errors, and then the FWGLR could serve as a powerful tool in Cepheid studies.
250. Cepheids from VVV in the southern Galactic midplane
ID:
ivo://CDS.VizieR/J/ApJ/883/58
Title:
Cepheids from VVV in the southern Galactic midplane
Short Name:
J/ApJ/883/58
Date:
21 Oct 2021
Publisher:
CDS
Description:
The far side of the Milky Way's disk is one of the most concealed parts of the known universe due to extremely high interstellar extinction and point-source density toward low Galactic latitudes. Large time-domain photometric surveys operating in the near-infrared hold great potential for the exploration of these vast uncharted areas of our Galaxy. We conducted a census of distant classical and type II Cepheids along the southern Galactic midplane using near-infrared photometry from the VISTA Variables in the Via Lactea survey. We performed a machine-learned classification of the Cepheids based on their infrared light curves using a convolutional neural network. We have discovered 640 distant classical Cepheids with up to ~40mag of visual extinction and over 500 type II Cepheids, most of them located in the inner bulge. Intrinsic color indices of individual Cepheids were predicted from sparse photometric data using a neural network, allowing their use as accurate reddening tracers. They revealed a steep, spatially varying near-infrared extinction curve toward the inner bulge. Type II Cepheids in the Galactic bulge were also employed to measure robust mean selective-to-absolute extinction ratios. They trace a centrally concentrated spatial distribution of the old bulge population with a slight elongation, consistent with earlier results from RR Lyrae stars. Likewise, the classical Cepheids were utilized to trace the Galactic warp and various substructures of the Galactic disk and uncover significant vertical and radial age gradients of the thin disk population at the far side of the Milky Way.