Consistent radial velocities of classical Cepheids from the cross-correlation technique

Kervella, P.; Nardetto, N.; Gallenne, A.; Mérand, A.; Anderson, Richard I.; Aufdenberg, J. P.; Breuval, Louise; Gieren, W.; Hocdé, V.; Lagadec, E.; Pietrzyński, G.; Trahin, Boris

doi:10.1051/0004-6361/201935622

Cited by 19 publications

(13 citation statements)

References 69 publications

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“…We gathered 1350 high-resolution (R ∼ 75 000) spectra from 24 Cepheids acquired with the red arm (∼570 to ∼940 nm wavelength range) of the UVES spectrograph (Dekker et al 2000) mounted on the UT2 telescope at the Very Large Telescope (VLT). The processing and normalization of these spectra are detailed in Borgniet et al (2019). We acquired several consecutive spectra (up to a dozen) at each observing epoch.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

Pulsating chromosphere of classical Cepheids

Hocdé

Nardetto

Lagadec

et al. 2020

A&A

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Context. It has recently been shown that the infrared (IR) emission of Cepheids, constant over the pulsation cycle, might be due to a pulsating shell of ionized gas with a radius of about 15% of that of the star radius, which could be attributed to the chromospheric activity of Cepheids. Aims. The aim of this paper is to investigate the dynamical structure of the chromosphere of Cepheids along the pulsation cycle and to quantify its size. Methods. We present Hα and calcium near-infrared triplet (Ca IR) profile variations using high-resolution spectroscopy with the UVES spectrograph of a sample of 24 Cepheids with a good period coverage from ≈3 to 60 days. After a qualitative analysis of the spectral line profiles, we quantified the Van Hoof effect (velocity gradient between the Hα and Ca IR) as a function of the period of the Cepheids. We then used the Schwarzschild mechanism (a line doubling due to a shock wave) to quantify the size of the chromosphere. Results. We find a significant Van Hoof effect for Cepheids with a period larger than P = 10 days. In particular, Hα lines are delayed with a velocity gradient up to Δv ≈ 30 km s−1 compared to Ca IR. By studying the shocks, we find that the size of the chromosphere of long-period Cepheids is of at least ≈50% of the stellar radius, which is consistent at first order with the size of the shell made of ionized gas previously found from the analysis of IR excess. Last, for most of the long-period Cepheids in the sample, we report a motionless absorption feature in the Hα line that we attribute to a circumstellar envelope that surrounds the chromosphere. Conclusions. Analyzing the Ca IR lines of Cepheids is of importance to potentially unbias the period–luminosity relation from their IR excess, particularly in the context of forthcoming observations of radial velocity measurements from the Radial Velocity Spectrometer on board Gaia, which could be sensitive to their chromosphere.

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Section: Observations and Data Reductionmentioning

confidence: 99%

Pulsating chromosphere of classical Cepheids

Hocdé

Nardetto

Lagadec

et al. 2020

A&A

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“…On the first rung, different studies (e.g., Nardetto 2018; Borgniet et al 2019;Kervella et al 2019b;Gallenne et al 2019;Anderson 2019;Hocdé et al 2020aHocdé et al , 2020bMusella et al 2021) have focused on enhancing our understanding of the different properties of Cepheid variables, and in a recent study, Breuval et al (2020) presented a new calibration of the periodluminosity (PL) relation for Milky Way (MW) Cepheids using their companion parallaxes from Gaia (Kervella et al 2019a). In addition, the high-precision measurement of the distance to the Large Magellanic Cloud (LMC) by Pietrzyński et al (2019) provides an accurate calibration of the Cepheid periodluminosity relation in this satellite galaxy of the MW.…”

Section: Introductionmentioning

confidence: 99%

Inspecting the Cepheid Distance Ladder: the Hubble Space Telescope Distance to the SN Ia Host Galaxy NGC 5584

Mérand

Kervella²,

Breuval³

et al. 2021

ApJ

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The current tension between the direct and the early-universe measurements of the Hubble constant, H 0 , requires detailed scrutiny of all the data and methods used in the studies on both sides of the debate. The Cepheids in the Type Ia supernova (SN Ia) host galaxy NGC 5584 played a key role in the local measurement of H 0 . The SH0ES project used the observations of this galaxy to derive a relation between the Cepheids' periods and ratios of their amplitudes in different optical bands of the Hubble Space Telescope and used these relations to analyze the light curves of the Cepheids in around half of the current sample of local SN Ia host galaxies. In this work, we present an independent detailed analysis of the Cepheids in NGC 5584. We employ different tools for our photometric analysis and a completely different method for our light-curve analysis, and we do not find a systematic difference between our period and mean magnitude measurements compared to those reported by SH0ES. By adopting a period-luminosity relation calibrated by the Cepheids in the Milky Way, we measure a distance modulus μ = 31.810 ± 0.047 (mag), which is in agreement with μ = 31.786 ± 0.046 (mag) measured by SH0ES. In addition, the relations we find between the periods and amplitude ratios of the Cepheids in NGC 5584 are significantly tighter than those of SH0ES, and their potential impact on the direct H 0 measurement will be investigated in future studies.

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“…With many data points at different phases this linear relation can be trivially solved for the stellar radius and distance. The radius at a given phase is obtained by integrating the pulsational velocity curve for the star where the pulsational velocity is determined from the observed radial velocity by applying a suitable projection factor, p. The p-factor is largely a geometrical factor but depends also on limb darkening, the exact method used to derive the radial velocity (see Borgniet et al 2019), and other technicalities. Storm et al (2011a) calibrated the p-factor empirically and provide a detailed discussion and references on this issue.…”

Section: Stellar Parameters Labels From the Irsb Techniquementioning

confidence: 99%

Atmospheric parameters of Cepheids from flux ratios with ATHOS

Lemasle

Hanke

Storm

et al. 2020

A&A

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Context. The effective temperature is a key parameter governing the properties of a star. For stellar chemistry, it has the strongest impact on the accuracy of the abundances derived. Since Cepheids are pulsating stars, determining their effective temperature is more complicated than in the case of nonvariable stars. Aims. We want to provide a new temperature scale for classical Cepheids, with a high precision and full control of the systematics. Methods. Using a data-driven machine learning technique employing observed spectra, and in taking great care to accurately phase single-epoch observations, we tied flux ratios to (label) temperatures derived using the infrared surface brightness method. Results. We identified 143 flux ratios, which allow us to determine the effective temperature with a precision of a few Kelvin and an accuracy better than 150 K, which is in line with the most accurate temperature measures available to date. The method does not require a normalization of the input spectra and provides homogeneous temperatures for low- and high-resolution spectra, even at the lowest signal-to-noise ratios. Due to the lack of a dataset with a sufficient sample size for Small Magellanic Cloud Cepheids, the temperature scale does not extend to Cepheids with [Fe/H] < −0.6 dex. However, it nevertheless provides an exquisite, homogeneous means of characterizing Galactic and Large Magellanic Cloud Cepheids. Conclusions. The temperature scale will be extremely useful in the context of spectroscopic surveys for Milky Way archaeology with the WEAVE and 4MOST spectrographs. It paves the way for highly accurate and precise metallicity estimates, which will allow us to assess the possible metallicity dependence of Cepheids’ period-luminosity relations and, in turn, to improve our measurement of the Hubble constant H0.

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Consistent radial velocities of classical Cepheids from the cross-correlation technique

Cited by 19 publications

References 69 publications

Pulsating chromosphere of classical Cepheids

Pulsating chromosphere of classical Cepheids

Inspecting the Cepheid Distance Ladder: the Hubble Space Telescope Distance to the SN Ia Host Galaxy NGC 5584

Atmospheric parameters of Cepheids from flux ratios with ATHOS

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