J/A+A/593/A45 delta Cep VEGA/CHARA observing log (Nardetto+, 2016)
VEGA/CHARA interferometric observations of Cepheids.
I. A resolved structure around the prototype classical Cepheid delta Cep in the
visible spectral range.
Nardetto N., Merand A., Mourard D., Storm J., Gieren W., Fouque P.,
Gallenne A., Graczyk D., Kervella P., Neilson H., Pietrzynski G.,
Pilecki B., Breitfelder J., Berio P., Challouf M., Clausse J.-M., Ligi R.,
Mathias P., Meilland A., Perraut K., Poretti E., Rainer M., Spang A.,
Stee P., Tallon-Bosc I., ten Brummelaar T.
<Astron. Astrophys. 593, A45 (2016)>
=2016A&A...593A..45N 2016A&A...593A..45N (SIMBAD/NED BibCode)
ADC_Keywords: Interferometry ; Stars, variable
Keywords: techniques: interferometry - stars: circumstellar matter -
stars: oscillations
Abstract:
The B-W method is used to determine the distance of Cepheids and
consists in combining the angular size variations of the star, as
derived from infrared surface-brightness relations or interferometry,
with its linear size variation, as deduced from visible spectroscopy
using the projection factor. The underlying assumption is that the
photospheres probed in the infrared and in the visible are located at
the same layer in the star whatever the pulsation phase. While many
Cepheids have been intensively observed by infrared beam combiners,
only a few have been observed in the visible.
This paper is part of a project to observe Cepheids in the visible
with interferometry as a counterpart to infrared observations already
in hand. Methods. Observations of Delta Cep itself were secured with
the VEGA/CHARA instrument over the full pulsation cycle of the star.
These visible interferometric data are consistent in first
approximation with a quasi-hydrostatic model of pulsation surrounded
by a static circumstellar environment (CSE) with a size of
θCSE=8.9±3.0mas and a relative flux contribution of
fCSE=0.07±0.01. A model of visible nebula (a background source
filling the field of view of the interferometer) with the same
relative flux contribution is also consistent with our data at small
spatial frequencies. However, in both cases, we find discrepancies in
the squared visibilities at high spatial frequencies (maximum
2σ) with two different regimes over the pulsation cycle of the
star, φ=0.0-0.8 and φ=0.8-1.0. We provide several hypotheses
to explain these discrepancies, but more observations and theoretical
investigations are necessary before a firm conclusion can be drawn.
For the first time we have been able to detect in the visible domain a
resolved structure around delta Cep. We have also shown that a simple
model cannot explain the observations, and more work will be necessary
in the future, both on observations and modelling.
Description:
The columns give, respectively, the date, the RJD, the hour angle
(HA), the minimum and maximum wavelengths over which the squared
visibility is calculated, the projected baseline length Bp and its
orientation PA, the signal-to-noise ratio on the fringe peak; the last
column provides the calibrated squared visibility V2 together with
the statistic error on V2, and the systematic error on V2 (see
text for details). The data are available on the Jean-Marie Mariotti
Center OiDB service (Available at http://oidb.jmmc.fr).
Objects:
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RA (2000) DE Designation(s)
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22 29 10.27 +58 24 54.7 delta Cep = HD 213306
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 93 175 Observing log of VEGA/CHARA observations
of delta Cep
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 5 F5.3 --- phi Pulsation phase
8- 12 F5.3 --- e_phi Error on the pulsation phase
15- 24 A10 --- Date Date of observation (YYYY.MM.DD)
27- 35 F9.3 d RJD Reduced Julian Date
38- 42 F5.2 h HA Hour Angle
45- 47 I3 nm lambdamin Minimum wavelength
50- 52 I3 nm lambdamax Maximum wavelength
55- 59 F5.2 m Bp Projected Baseline
62- 68 F7.2 deg PA [] Orientation of the projected baseline
71- 72 I2 --- S/N Signal-to-Noise ratio
75- 79 F5.3 --- V2 Squared visibility
82- 86 F5.3 --- e_V2 Statistical error associated to V2
89- 93 F5.3 --- s_V2 Systematical error associated to V2
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Acknowledgements:
Nicolas Nardetto, Nicolas.Nardetto(at)oca.eu
(End) Nicolas Nardetto [Nice, France], Patricia Vannier [CDS] 25-Jul-2016