J/A+A/684/A126 Field RR Lyrae stars RV and pulsation models (Bras+, 2024)
The Baade-Wesselink projection factor of RR Lyrae stars.
Calibration from OHP/SOPHIE spectroscopy and Gaia DR3 parallaxes.
Bras G., Kervella P., Trahin B., Wielgorski P., Zgirski B., Merand A.,
Nardetto N., Gallenne A., Hocde V., Breuval L., Afanasiev A.,
Prietrzynski G., Gieren W.
<Astron. Astrophys. 684, A126 (2024)>
=2024A&A...684A.126B 2024A&A...684A.126B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Radial velocities ; Models
Keywords: techniques: radial velocities - stars: distances -
stars: oscillations - stars: variables: RR Lyrae
Abstract:
The application of the Parallax of Pulsation (PoP) technique to
determine the distances of pulsating stars implies the use of a
scaling parameter, the projection factor (p-factor), that is required
to transform disk-integrated radial velocities (RVs) into photospheric
expansion velocities. The value of this parameter is poorly known and
still debated. Most present applications of the PoP technique assume a
constant p-factor. However, it may actually depend on the physical
parameters of each star, as past studies aimed at calibrating the
p-factor (usually for Cepheids) led to a broad range of individual
values. We aim at calibrating the p-factors of a sample of RR Lyrae
stars (RRLs), to compare them with classical Cepheids (CCs). Due to
their higher surface gravity, RRLs have more compact atmospheres, thus
providing a valuable comparison with their supergiant siblings. We
determine the p-factor of 17 RR Lyrae stars, by modelling their
pulsation using the SPIPS code. The models are constrained using Gaia
DR3 parallaxes, photometry and new radial velocities that we collected
with the OHP/SOPHIE spectrograph. We carefully examine the different
steps of the PoP technique, in particular the method to determine the
RV from spectra using the classical approach based on the cross-
correlation function (CCF). The method employed to extract the radial
velocity from the CCF has a strong impact on the p-factor, up to 10%.
However, this choice of method results in a global scaling of the
p-factor, and it affects only marginally the scatter of p within the
sample for a given method. Over our RRL sample, we find a mean value
of p=1.248±0.022 for RVs derived using a Gaussian fit of the CCF.
There is no evidence for a different value of the p-factors of RRLs,
although their distribution for RRLs appear significantly less
scattered (σ∼7%) than those of CCs (σ∼12%). The p-factor
does not appear to depend in a simple way on fundamental stellar
parameters (pulsation period, radius, metallicity, amplitude of the
radial velocity curve). We argue that large-amplitude dynamical
phenomena occurring in the atmosphere of RRLs (and CCs) during their
pulsation affect the relative velocity of the spectral line-forming
regions compared to the velocity of the photosphere.
Description:
Table 5 contains measurements of radial velocity from spectra with the
OHP/SOPHIE spectrograph using different cross-correlation masks and
fitting methods. Specific cross-correlation masks are given for
different spectral depths Models presented in Appendix A are given for
all 17 RR Lyrae stars.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 48 25 List of studied stars
table5.dat 240 369 Radial velocity measurements from OHP/SOPHIE
spectra
mask_a.dat 60 364 Mask all unblended lines
mask_d.dat 60 80 Mask deep unblended lines
mask_m.dat 60 155 Mask medium unblended lines
mask_w.dat 60 140 Mask all unblended lines
maskaw.dat 76 339 Weighted mask all unblended lines
fits/* . 17 Individual fits of SPIPS models
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Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- Name Star name
11- 12 I2 h RAh Simbad right ascension (J2000)
14- 15 I2 min RAm Simbad right ascension (J2000)
17- 21 F5.2 s RAs Simbad right ascension (J2000)
23 A1 --- DE- Simbad declination sign (J2000)
24- 25 I2 deg DEd Simbad declination (J2000)
27- 28 I2 arcmin DEm Simbad declination (J2000)
30- 33 F4.1 arcsec DEs Simbad declination (J2000)
35- 45 A11 --- FileName Name of the SPIPS models fits file
in subdirectory fits
47- 48 A2 --- LC [lc ] Indicates light curve data in table 5
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Object name
11- 22 F12.4 d Epoch Heliocentric Julian Day of observation
24- 53 A30 --- Spect SOPHIE spectrum name
55- 71 F17.14 --- S/N Signal-to-noise ratio for the spectrum
73- 93 F21.16 km/s RVg ? RV, gaussian fit, all unblended lines
96-113 F18.16 km/s e_RVg ? RV error, gaussian fit, all unblended lines
115-135 F21.16 km/s RV2g ? RV, bigaussian fit, all unblended lines
138-156 F19.16 km/s e_RV2g ? RV error, bigaussian fit, all unblended lines
158-178 F21.16 km/s RVd ? RV, gaussian fit, deep unblended lines
181-198 F18.16 km/s e_RVd ? RV error, gaussian fit, deep unblended lines
200-220 F21.16 km/s RVm ? RV, gaussian fit, medium unblended lines
223-240 F18.16 km/s e_RVm ? RV error, gaussian fit, medium unblended lines
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Byte-by-byte Description of file: mask_a.dat mask_d.dat mask_m.dat mask_w.dat
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Bytes Format Units Label Explanations
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1- 18 F18.14 nm wavePeak Line central wavelength
20- 37 F18.14 nm waveBase Line minimum wavelength
39- 56 F18.14 nm waveTop Line maximum wavelength
58- 60 F3.1 --- Depth Depth of the mask
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Byte-by-byte Description of file: maskaw.dat
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Bytes Format Units Label Explanations
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1- 18 F18.14 nm wavePeak Line central wavelength
20- 37 F18.14 nm waveBase Line minimum wavelength
39- 56 F18.14 nm waveTop Line maximum wavelength
58- 76 F19.17 --- Depth Depth of the line for the mask
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Acknowledgements:
Garance Bras, garance.bras(at)obspm.fr
(End) Patricia Vannier [CDS] 27-Dec-2023