Examinando por Autor "Gallenne A."

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    Circumstellar emission of Cepheids across the instability strip: Mid-infrared observations with VLTI/MATISSE
    (EDP Sciences, 0025) Hocdé V.; Matter A.; Nardetto N.; Gallenne A.; Kervella P.; Mérand A; Pietrzyń Ski G; Gieren W.; Leftley J; Robbe-Dubois S; Lopez B.; Bailleul M.C.; Bras G; Smolec R; Wielgórski P.; Hajdu G.; Afanasiev A
    Context. The circumstellar envelopes (CSE) of Cepheids are still only poorly characterized despite their potential impact on the distance determination via both the period-luminosity relation and the parallax-of-pulsation method. Aims. This paper aims to investigate Galactic Cepheids across the instability strip in the mid-infrared with MATISSE/VLTI in order to constrain the geometry and physical nature (gas and/or dust) of their CSEs. Methods. We secured observations of eight Galactic Cepheids with short- and up to long-period pulsations with MATISSE/VLTI in the L, M, and N bands. For each star, we calibrated the flux measurements to potentially detect the spectral dust signature in the spectral energy distribution (SED). We then analyzed the closure phase and the visibilities in L, M, and N bands. The parallax-of-pulsation code SPIPS was used in order to derive the infrared excess and the expected angular stellar diameter at the date of the MATISSE observations. We also computed test cases of a radiative transfer model of dusty envelopes with DUSTY to compare them with the visibilities in the N band. Results. The SED analysis in the mid-IR confirmed the absence of a spectral dust signature for the entire star sample. For each star, we observed closure phases in the L, M, and N bands that are consistent with a centro-symmetric geometry for the different targets. Finally, the visibilities in the L, M, and N bands agree with the expected angular stellar diameter. Although we did not resolve any circumstellar emission, the observations are compatible with the presence of compact CSEs within the uncertainties. We provide 2 σ upper limits on the CSE flux contribution based on model residuals for several CSE radii, which exclude models that are simultaneously large and bright (RCSE ≈ 10 R∗ and fCSE ≈ 10%) for all the stars of the sample. Last, the visibilities in the N band rule out CSE models with optical depth τV ≳ 0.001 for different types of dust. Conclusions. The MATISSE observations of eight Cepheids with different pulsation periods (from 7 to 38 days) and evolution stages provide a comprehensive picture of Cepheids from mid-infrared interferometry for the first time. We present additional evidence that circumstellar dust emission is negligible or absent around Cepheids for a wide range of stellar parameters in the instability strip. Further interferometric observations in the visible and near-infrared are required to separate the star and CSE, which is crucial for constraining the CSE contribution and its possible gaseous nature. © The Authors 2025.
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    Multiplicity of Galactic Cepheids from long-baseline interferometry V. High-accuracy orbital parallax and mass of SU Cygni
    (Astronomy and Astrophysics, Volume 6931 January 2025 Article number A111, 2025) Gallenne A.; Evans N.R.; Kervella P.; Monnier J.D.; Proffitt C.R.; Schaefer G.H.; Winston E.M.; Kuraszkiewicz J.; Mérand A.; Pietrzynski G.; Gieren W. k; Pilecki B.; Kraus S. l;; Le Bouquin J.-B.; Anugu N.; Brummelaar T.; Chhabra S.; Codron I.; Davies C.L.; Ennis J.; Gardner T.; Gutierrez M.; Ibrahim N.; Lanthermann C.; Mortimer D.; Setterholm B.R.
    Aims. We aim to accurately measure the dynamical mass and distance of Cepheids by combining radial velocity measurements with interferometric observations. Cepheid mass measurements are particularly necessary for solving the Cepheid mass discrepancy, while independent distance determinations provide a crucial test of the period–luminosity relation and Gaia parallaxes. Methods. We used the multi-telescope interferometric combiner, the Michigan InfraRed Combiner (MIRC) of the Center for High Angular Resolution Astronomy (CHARA) Array, to detect and measure the astrometric positions of the high-contrast companion orbiting the Galactic Cepheid SU Cygni. We also present new radial velocity measurements from ultraviolet spectra taken with the Hubble Space Telescope. The combination of interferometric astrometry with optical and ultraviolet spectroscopy provided the full orbital elements of the system, in addition to component masses and the distance to the Cepheid system. Results. We measured the mass of the Cepheid, MA = 4.859 ± 0.058 M , and its two companions, MBa = 3.595 ± 0.033 M and MBb = 1.546 ± 0.009 M . This is the most accurate existing measurement of the mass of a Galactic Cepheid (1.2%). Comparing with stellar evolution models, we show that the mass predicted by the tracks is higher than the measured mass of the Cepheid, which is similar to the conclusions of our previous work. We also measured the distance to the system to be 926.3 ± 5.0 pc, obtaining an unprecedented parallax precision of 6 µas (0.5%), which is the most precise and accurate distance for a Cepheid. This precision is similar to what is expected by Gaia for its last data release (DR5 in ∼2030) for single stars fainter than G = 13, but is not guaranteed for stars as bright as SU Cyg. Conclusions. We demonstrate that evolutionary models remain incapable of accurately reproducing the measured mass of Cepheids, often predicting higher masses for the expected metallicity, even when factors such as rotation or convective core overshooting are taken into account. Our precise distance measurement allowed us to compare predictions from some period–luminosity relations. We find a disagreement of 0.2–0.5 mag with relations calibrated from photometry, while relations calibrated from a direct distance measurement are in better agreement. © The Authors 2025
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    Surface brightness-colour relations of dwarf stars from detached eclipsing binaries: II. Extension of the calibrating sample
    (EDP Sciences, 0025-12) Graczyk D.; Pietrzyński G.; Galan C; Miller N; Gieren W.; Zgirski B; Hajdu G.; Kałuszyński M.; Chini R.; Gallenne A.; Górski M; Karczmarek P.
    Aims. Surface brightness-colour relations (SBCRs) are useful tools for predicting the angular diameters of stars. They offer the possibility to calculate precise spectrophotometric distances based on the eclipsing binary method or the Baade- Wesselink method. Double-lined detached eclipsing binary stars (SB2 DEBs), with precisely known trigonometric parallaxes, allow us to calibrate SBCRs with a high level of precision. To improve such calibrations, it is important to supplement the sample of suitable eclipsing binaries with precisely determined physical parameters. Methods. We selected ten SB2 DEBs within 0.8 kpc of the Sun, which feature components of spectral types ranging from B9 to K3. We analysed their TESS and Kepler K2 space-based photometry simultaneously with the radial velocities derived from HARPS spectra using the Wilson- Devinney code. The disentangled spectra of DEBs were used to derive atmospheric parameters of their components by applying the GSSP code. The direct effective temperatures were also calculated using spectral energy distribution analysis. The O-C diagrams of the minima times were investigated to detect long-term period changes or apsidal motions. Results. Most of the systems are composed of significantly unequal components, with mass ratios as low as ∼0.5. We derived precise masses, radii, and surface temperatures for them, along with their metallicities. The average precision of mass and radii determinations is 0.3% and 1.4%, respectively, for the surface temperature. The spectroscopic and photometric temperatures of the components are usually consistent to within 100 K, but in some systems, the difference is much larger. The components of HD 149946 show the highest difference (up to 400 K), while the atmospheric models favour different surface metallicities. We also provide an updated calibration of the equivalent width of the interstellar sodium D1 line and the reddening E(B-V). © The Authors 2025.