J/MNRAS/463/1707 l Car radial velocity curves (Anderson, 2016)
Discovery of cycle-to-cycle modulated spectral line variability and velocity
gradients in long-period Cepheids.
Anderson R.I.
<Mon. Not. R. Astron. Soc., 463, 1707-1739 (2016)>
=2016MNRAS.463.1707A 2016MNRAS.463.1707A (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Radial velocities
Keywords: line: profiles - techniques: radial velocities -
stars: individual: l Carinae = HD 84810 = HIP 47854 -
stars: oscillations - stars: variables: Cepheids - distance scale
Abstract:
This work reports the discovery of cycle-to-cycle modulated spectral
line and atmospheric velocity gradient variability in long-period
Cepheids based on 925 high-resolution optical spectra of l Carinae
(P∼35.5d) recorded during three heavy duty-cycle monitoring campaigns
(in 2014, 2015, and 2016). Spectral line variability is investigated
via cross-correlation functions (CCFs) computed using three sets of
spectral lines (weak, solar, strong). A metallic line velocity
gradient, δvr(t), is computed as the difference between weak
and strong-line RVs. CCF shape indicators BIS (asymmetry), FWHM, and
depth all exhibit clear phase-dependent variability patterns that
differ from one pulsation cycle to the next. Weak-line CCFs exhibit
these effects more clearly than strong-line CCFs. BIS exhibits the
most peculiar modulated variability and can be used to identify the
presence of cycle-to-cycle modulated line profile variations.
δvr(t) clearly exhibits cycle-to-cycle differences that
correlate very closely with modulated BIS variability, suggesting
perturbations of the atmospheric velocity field as the cause for
modulated spectral line variability. These perturbations are most
significant during contraction and are not in phase with the
pulsation, transmitting information between consecutive pulsation
cycles. This work shows RV curve modulation to be a consequence of
atmospheric velocity gradient perturbations. Possible origins of these
perturbations and their impact on Cepheid RV measurements as well as
the projection factor used in Baade-Wesselink-type distance
determinations are discussed.
Description:
Line-of-sight (radial) velocities of the long-period classical Cepheid
l Carinae were measured from 925 high-quality optical spectra
recorded using the fiber-fed high-resolution (R∼60,000) Coralie
spectrograph located at the Euler telescope at La Silla Observatory,
Chile. The data were taken between 2014 and 2016. This is the full
version of Tab. 2 presented partially in the paper. Line shape
parameters (depth, width, asymmetry) are listed for the computed
cross-correlation profiles (CCFs). Radial velocities were determined
using different techniques (Gaussian, bi-Gaussian) and measured on
CCFs computed using three different numerical masks (G2, weak lines,
strong lines).
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
table2.dat 93 925 Coralie radial velocities of l Carinae
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See also:
J/ApJ/824/1 : Timing data for the classical Cepheid l Car (Neilson+, 2016)
J/MNRAS/455/4231 : Coralie radial velocities for l Car (Anderson+, 2016)
Byte-by-byte Description of file: table2.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)
14- 17 F4.1 km/s FWHM FWHM of Gaussian fitted to CCF for G2 mask
19- 24 F6.3 km/s BIS CCF asymmetry parameter for G2 mask
26- 29 F4.1 % depth CCF contrast in percent for G2 mask
31- 37 F7.3 km/s RV Barycentric Gaussian RV for G2 mask
39- 43 F5.3 km/s e_RV Uncertainty on Gaussian RV for G2 mask
45- 51 F7.3 km/s RVbiG Barycentric bi-Gaussian RV for G2 mask
53- 59 F7.3 km/s RVw Barycentric Gaussian RV for weak lines
61- 65 F5.3 km/s e_RVw Uncertainty on Gaussian RV for weak lines
67- 72 F6.3 km/s BISw CCF asymmetry for weak lines
74- 80 F7.3 km/s RVs Barycentric Gaussian RV for strong lines
82- 86 F5.3 km/s e_RVs Uncertainty on Gaussian RV for strong lines
88- 93 F6.3 km/s BISs CCF asymmetry for strong lines
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Acknowledgements:
The assistance of many observers is acknowledged. RIA is grateful to the
entire Euler team, the Geneva stellar variability group, and the Geneva
exoplanet group for their assistance and support. The friendly and
competent assistance by all ESO and non-ESO staff at La Silla Observatory
was greatly appreciated. The Swiss Euler telescope is funded by the Swiss
National Science Foundation. The ability to operate such long-term
campaigns on a small telescope with high-quality instrumentation was
crucial to this work's ability to illustrate the complex behaviour of
Cepheid pulsations in this amount of detail.
Richard I. Anderson, randerso(at)eso.org
(End) R. Anderson [Johns Hopkins Univ., USA], P. Vannier [CDS] 05-Feb-2018