J/MNRAS/455/4231 Coralie radial velocities for l Car (Anderson+, 2016)
Investigating Cepheid l Carinae's cycle-to-cycle variations via
contemporaneous velocimetry and interferometry.
Anderson R.I., Merand A., Kervella P., Breitfelder J., Lebouquin J.-B.,
Eyer L., Gallenne A., Palaversa L., Semaan T., Saesen S., Mowlavi N.
<Mon. Not. R. Astron. Soc., 455, 4231-4248 (2016)>
=2016MNRAS.455.4231A 2016MNRAS.455.4231A (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Stars, late-type ; Radial velocities
Keywords: techniques: high angular resolution - techniques: radial velocities -
stars: individual: l Car - stars: oscillations -
stars: variables: Cepheids; distance scale
Abstract:
Baade-Wesselink-type (BW) techniques enable geometric distance
measurements of Cepheid variable stars in the Galaxy and the
Magellanic clouds. The leading uncertainties involved concern
projection factors required to translate observed radial velocities
(RVs) to pulsational velocities and recently discovered modulated
variability. We carried out an unprecedented observational campaign
involving long-baseline interferometry (VLTI/PIONIER) and spectroscopy
(Euler/Coralie) to search for modulated variability in the long-period
(P∼35.5d) Cepheid ℓ Carinae. We determine highly precise angular
diameters from squared visibilities and investigate possible
differences between two consecutive maximal diameters,
ΔmaxΘ. We characterize the modulated variability along
the line of sight using 360 high-precision RVs. Here we report
tentative evidence for modulated angular variability and confirm
cycle-to-cycle differences of ℓ Carinae's RV variability. Two
successive maxima yield ΔmaxΘ=13.1±0.7(stat.)µas
for uniform disc models and 22.5±1.4(stat.)µas (4 percent of the
total angular variation) for limb-darkened models. By comparing new
RVs with 2014 RVs, we show modulation to vary in strength. Barring
confirmation, our results suggest the optical continuum (traced by
interferometry) to be differently affected by modulation than gas
motions (traced by spectroscopy). This implies a previously unknown
time dependence of projection factors, which can vary by 5 percent
between consecutive cycles of expansion and contraction. Additional
interferometric data are required to confirm modulated angular
diameter variations. By understanding the origin of modulated
variability and monitoring its long-term behaviour, we aim to improve
the accuracy of BW distances and further the understanding of stellar
pulsations.
Description:
360 radial velocity measurements (RVs) of ℓ Carinae are made
publicly available. These RVs were measured using optical spectra
observed with the Coralie spectrograph mounted to the 1.2m Swiss Euler
telescope situated at La Silla Observatory, Chile.
Objects:
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RA (2000) DE Designation(s)
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09 45 14.81 -62 30 28.5 l Car = HD 84810
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 28 360 Coralie radial velocities of ℓ Carinae
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 12 F12.6 d BJD Barycentric Julian Date (BJD-2400000)
15- 21 F7.3 km/s RV Barycentric Radial Velocity
24- 28 F5.3 km/s e_RV Uncertainty on Barycentric Radial Velocity
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Acknowledgements:
Richard I. Anderson, ria(at)jhu.edu
(End) R. Anderson [Johns Hopkins Univ., USA], P. Vannier [CDS] 21-Jul-2016