Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Investigating Cepheid $\ell$ Carinae's Cycle-to-cycle Variations via
  Contemporaneous Velocimetry and Interferometry   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
$\sim$ 35.5 d) Cepheid Carinae. We determine highly precise angular diameters
from squared visibilities and investigate possible differences between two
consecutive maximal diameters, $\Delta_{\rm{max}} \Theta$. 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 $\ell$ Carinae's RV variability. Two successive
maxima yield $\Delta_{\rm{max}} \Theta$ = 13.1 $\pm$ 0.7 (stat.) {\mu}as for
uniform disk models and 22.5 $\pm$ 1.4 (stat.) {\mu}as (4% 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% 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
behavior, we aim to improve the accuracy of BW distances and further the
understanding of stellar pulsations.

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The categories of this paper are: q-alg
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The categories of this paper are: econ
24
The categories of this paper are: dg-ga
2
The categories of this paper are: math
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The categories of this paper are: patt-sol
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The categories of this paper are: chao-dyn
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The categories of this paper are: gr-qc
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The categories of this paper are: nlin
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The categories of this paper are: cs
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-th
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The categories of this paper are: acc-phys
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The categories of this paper are: atom-ph
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The categories of this paper are: math-ph
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The categories of this paper are: funct-an
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The categories of this paper are: comp-gas