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2481. Cepheid abund.: multiphase results & spatial gradients
ID:
ivo://CDS.VizieR/J/AJ/156/171
Title:
Cepheid abund.: multiphase results & spatial gradients
Short Name:
J/AJ/156/171
Date:
21 Oct 2021
Publisher:
CDS
Description:
Parameters and abundances have been derived for 435 Cepheids based on an analysis of 1127 spectra. Results from five or more phases are available for 52 of the program stars. The latter set of stars span periods between 1.5 and 68 days. The parameters and abundances show excellent consistency across phase. For iron, the average range in the determined abundance is 0.11 from these 52 stars. For 163 stars with more than one phase available the average range is 0.07. The variation in effective temperature tracks well with phase, as does the total broadening velocity. The gravity and microturbulent velocity follow phase, but with less variation and regularity. Abundance gradients have been derived using Gaia DR2 (Cat. I/345) parallax data, as well as Bayesian distance estimates based upon Gaia DR2 from Bailer-Jones et al. (2018, Cat. I/347). The abundance gradient derived for iron is d[Fe/H]/dR=-0.05 dex/kpc, similar to gradients derived in previous studies.
2482. 90 cepheid candidates nearby NGC 6814
ID:
ivo://CDS.VizieR/J/ApJ/885/161
Title:
90 cepheid candidates nearby NGC 6814
Short Name:
J/ApJ/885/161
Date:
08 Mar 2022
Publisher:
CDS
Description:
We present a Cepheid-based distance to the nearby Seyfert galaxy NGC6814 from Hubble Space Telescope observations. We obtained F555W and F814W imaging over the course of 12 visits with logarithmic time spacing in 2013 August-October. We detected and made photometric measurements for 16469 unique sources across all images in both filters, from which we identify 90 excellent Cepheid candidates spanning a range of periods of 13-84days. We find evidence for incompleteness in the detection of candidates at periods <21days. Based on the analysis of Cepheid candidates above the incompleteness limit, we determine a distance modulus for NGC6814 relative to the LMC of {mu}_rel,LMC_=13.200_-0.031_^+0.031^mag. Adopting the recent constraint of the distance modulus to the LMC determined by Pietrzynski et al., we find m-M=31.677_-0.041_^+0.041^ which gives a distance of 21.65{+/-}0.41Mpc to NGC6814.
2483. Cepheid period-luminosity-metallicity relation
ID:
ivo://CDS.VizieR/J/A+A/619/A8
Title:
Cepheid period-luminosity-metallicity relation
Short Name:
J/A+A/619/A8
Date:
21 Oct 2021
Publisher:
CDS
Description:
We use parallax data from the Gaia second data release (GDR2), combined with parallax data based on HIPPARCOS and HST data, to derive the period-luminosity-metallicity (PLZ) relation for Galactic classical cepheids (CCs) in the V, K, and Wesenheit WVK bands. An initial sample of 452 CCs are extracted from the literature with spectroscopically derived iron abundances. Reddening values, classifications, pulsation periods, and mean V- and K-band magnitudes are taken from the literature. Based on nine CCs with a goodness-of-fit (GOF) statistic smaller than 8 and with an accurate non-Gaia parallax ({sigma}_{pi}_ comparable to that in GDR2), a parallax zero-point offset of -0.049+/-0.018mas is derived. Selecting a GOF statistic smaller than 8 removes about 40% of the sample most likely related due to binarity. Excluding first overtone and multi-mode cepheids and applying some other criteria reduces the sample to about 200 stars. The derived PL(Z) relations depend strongly on the parallax zero-point offset. The slope of the PL relation is found to be different from the relations in the LMC at the 3{sigma} level. Fixing the slope to the value found in the LMC leads to a distance modulus (DM) to the LMC of order 18.7mag, larger than the canonical distance. The canonical DM of around 18.5 mag would require a parallax zero-point offset of order -0.1mas. Given the strong correlation between zero point, period and metallicity dependence of the PL relation, and the parallax zero-point offset there is no evidence for a metallicity term in the PLZ relation. The GDR2 release does not allow us to improve on the current distance scale based on CCs. The value of and the uncertainty on the parallax zero-point offset leads to uncertainties of order 0.15mag on the distance scale. The parallax zero-point offset will need to be known at a level of 3{mu}as or better to have a 0.01mag or smaller effect on the zero point of the PL relation and the DM to the LMC.
2484. 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.
2485. 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.
2486. 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).
2487. 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.
2488. 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.
2489. 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.
2490. 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.

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