Examinando por Autor "Kervella P."

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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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    The Structure of Chariklo's Rings from Stellar Occultations
    (Journal, 2017-10) Bérard D.; Sicardy B.; Camargo J.I.B.; Desmars J.; Braga-Ribas F.; Ortiz J.-L.; Duffard R.; Morales N.; Meza E.; Leiva R.; Benedetti-Rossi G.; Vieira-Martins R.; Jnior, A.-R.; Gomes; Assafin M.; Colas F.; Dauvergne J.-L.; Kervella P.; Lecacheux J.; Maquet L.; Vachier F.; Renner S.; Monard B.; Sickafoose A.A.; Breytenbach H.; Genade A.; Beisker W.; Bath K.-L.; Bode H.-J.; Backes M.; Ivanov V.D.; Jehin E.; Gillon M.; Manfroid J.; Pollock J.; Tancredi G.; Roland S.; Salvo R.; Vanzi L.; Herald D.; Gault D.; Kerr S.; Pavlov H.; Hill K.M.; Bradshaw J.; Barry M.A.; Cool A.; Lade B.; Cole A.; Broughton J.; Newman J.; Horvat R.; Maybour D.; Giles D.; Davis L.; Paton R.A.; Loader B.; Pennell A.; Jaquiery P.-D.; Brillant S.; Selman F.; Dumas C.; Herrera C.; Carraro G.; Monaco L.; Maury A.; Peyrot A.; Teng-Chuen-Yu J.-P.; Richichi A.; Irawati P.; Witt, C. De; Schoenau P.; Prager R.; Colazo C.; Melia R.; Spagnotto J.; Blain A.; Alonso S.; Román A.; Santos-Sanz P.; Rizos J.-L.; Maestre J.-L.; Dunham D.
    Two narrow and dense rings (called C1R and C2R) were discovered around the Centaur object (10199) Chariklod uring a stellar occultation observed on 2013 June 3. Following this discovery, we planned observations of several occultations by Chariklos system in order to better characterize the physical properties of the ring and main body. Here, we use 12 successful occulations by Chariklo observed between 2014 and 2016. They provide ring profiles (physical width, opacity, edge structure) and constraints on the radii and pole position. Our new observations are currently consistent with the circular ring solution and pole position, to within the ±3.3 km formal uncertainty for the ring radii derived by Braga-Ribas et al. The six resolved C1R profiles reveal significant width variations from ∼5 to 7.5 km. The width of the fainter ring C2R is less constrained, and may vary between 0.1 and 1 km. The inner and outer edges of C1R are consistent with infinitely sharp boundaries, with typical upper limits of one kilometer for the transition zone between the ring and empty space. No constraint on the sharpness of C2Rs edges is available. A 1s upper limit of ∼20 m is derived for the equivalent width of narrow (physical width <4 km) rings up to distances of 12,000 km, counted in the ring plane. © 2017. The American Astronomical Society. All rights reserved.