A photometric and spectroscopic study of the brightest northern Cepheids - III. A high-resolution view of Cepheid atmospheres

László L. Kiss, J. Vinkó

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29 Citations (Scopus)

Abstract

We present new high-resolution spectroscopic observations (λ/Δλ ≈ 40 000) of 18 bright northern Cepheids carried out at the David Dunlap Observatory in 1997. The measurements mainly extend those presented in Paper I of this series, adding three more stars (AW Per, SV Vul, T Mon). The spectra were obtained in the yellow-red spectral region in the interval of 5900 and 6660 Å, including strong lines of sodium D and Hα. New radial velocities determined with the cross-correlation technique and the bisector technique are presented. The new data are compared with those recently published by several groups. We found systematic differences between the spectroscopic and CORAVEL-type measurements as large as 1-3 km s-1 in certain phases. We performed Baade-Wesselink analysis for CK Cam discovered by the Hipparcos satellite. The resulting radius is 31 ± 1 R, which is in very good agreement with recent period-radius relation by Gieren, Moffett & Barnes III. It is shown that the systematic velocity differences do not affect the Baade-Wesselink radius more than 1 per cent for CK Cam. Observational pieces of evidence of possible velocity gradient affecting the individual line profiles are studied. The full-width at half minimum (FWHM) of the metallic lines, similarly to the velocity differences, shows a very characteristic phase dependence, illustrating the effect of global compression in the atmosphere. The smallest line widths always occur around the maximal radius, while the largest FWHM is associated with velocity reversal before the minimal radius. Three first overtone pulsators do not follow the general trend: the largest FWHM in SU Cas and SZ Tau occurs after the smallest radius, during the expansion, while in V1334 Cyg there are only barely visible FWHM variations. The possibility of a bright yellow companion of V1334 Cyg is briefly discussed. The observed line-profile asymmetries exceed the values predicted with a simple projection effect by a factor of 2-3. This could be associated with the velocity gradient, which is also supported by the differences between individual line velocities of different excitation potentials.

Original languageEnglish
Pages (from-to)420-432
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Volume314
Issue number2
Publication statusPublished - May 11 2000

Fingerprint

atmospheres
radii
atmosphere
high resolution
cams
Hipparcos satellite
gradients
profiles
radial velocity
cross correlation
observatories
projection
sodium
asymmetry
intervals
observatory
trends
harmonics
stars
compression

Keywords

  • Cepheids
  • Stars: atmospheres
  • Stars: fundamental parameters

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

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title = "A photometric and spectroscopic study of the brightest northern Cepheids - III. A high-resolution view of Cepheid atmospheres",
abstract = "We present new high-resolution spectroscopic observations (λ/Δλ ≈ 40 000) of 18 bright northern Cepheids carried out at the David Dunlap Observatory in 1997. The measurements mainly extend those presented in Paper I of this series, adding three more stars (AW Per, SV Vul, T Mon). The spectra were obtained in the yellow-red spectral region in the interval of 5900 and 6660 {\AA}, including strong lines of sodium D and Hα. New radial velocities determined with the cross-correlation technique and the bisector technique are presented. The new data are compared with those recently published by several groups. We found systematic differences between the spectroscopic and CORAVEL-type measurements as large as 1-3 km s-1 in certain phases. We performed Baade-Wesselink analysis for CK Cam discovered by the Hipparcos satellite. The resulting radius is 31 ± 1 R⊙, which is in very good agreement with recent period-radius relation by Gieren, Moffett & Barnes III. It is shown that the systematic velocity differences do not affect the Baade-Wesselink radius more than 1 per cent for CK Cam. Observational pieces of evidence of possible velocity gradient affecting the individual line profiles are studied. The full-width at half minimum (FWHM) of the metallic lines, similarly to the velocity differences, shows a very characteristic phase dependence, illustrating the effect of global compression in the atmosphere. The smallest line widths always occur around the maximal radius, while the largest FWHM is associated with velocity reversal before the minimal radius. Three first overtone pulsators do not follow the general trend: the largest FWHM in SU Cas and SZ Tau occurs after the smallest radius, during the expansion, while in V1334 Cyg there are only barely visible FWHM variations. The possibility of a bright yellow companion of V1334 Cyg is briefly discussed. The observed line-profile asymmetries exceed the values predicted with a simple projection effect by a factor of 2-3. This could be associated with the velocity gradient, which is also supported by the differences between individual line velocities of different excitation potentials.",
keywords = "Cepheids, Stars: atmospheres, Stars: fundamental parameters",
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year = "2000",
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journal = "Monthly Notices of the Royal Astronomical Society",
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T1 - A photometric and spectroscopic study of the brightest northern Cepheids - III. A high-resolution view of Cepheid atmospheres

AU - Kiss, László L.

AU - Vinkó, J.

PY - 2000/5/11

Y1 - 2000/5/11

N2 - We present new high-resolution spectroscopic observations (λ/Δλ ≈ 40 000) of 18 bright northern Cepheids carried out at the David Dunlap Observatory in 1997. The measurements mainly extend those presented in Paper I of this series, adding three more stars (AW Per, SV Vul, T Mon). The spectra were obtained in the yellow-red spectral region in the interval of 5900 and 6660 Å, including strong lines of sodium D and Hα. New radial velocities determined with the cross-correlation technique and the bisector technique are presented. The new data are compared with those recently published by several groups. We found systematic differences between the spectroscopic and CORAVEL-type measurements as large as 1-3 km s-1 in certain phases. We performed Baade-Wesselink analysis for CK Cam discovered by the Hipparcos satellite. The resulting radius is 31 ± 1 R⊙, which is in very good agreement with recent period-radius relation by Gieren, Moffett & Barnes III. It is shown that the systematic velocity differences do not affect the Baade-Wesselink radius more than 1 per cent for CK Cam. Observational pieces of evidence of possible velocity gradient affecting the individual line profiles are studied. The full-width at half minimum (FWHM) of the metallic lines, similarly to the velocity differences, shows a very characteristic phase dependence, illustrating the effect of global compression in the atmosphere. The smallest line widths always occur around the maximal radius, while the largest FWHM is associated with velocity reversal before the minimal radius. Three first overtone pulsators do not follow the general trend: the largest FWHM in SU Cas and SZ Tau occurs after the smallest radius, during the expansion, while in V1334 Cyg there are only barely visible FWHM variations. The possibility of a bright yellow companion of V1334 Cyg is briefly discussed. The observed line-profile asymmetries exceed the values predicted with a simple projection effect by a factor of 2-3. This could be associated with the velocity gradient, which is also supported by the differences between individual line velocities of different excitation potentials.

AB - We present new high-resolution spectroscopic observations (λ/Δλ ≈ 40 000) of 18 bright northern Cepheids carried out at the David Dunlap Observatory in 1997. The measurements mainly extend those presented in Paper I of this series, adding three more stars (AW Per, SV Vul, T Mon). The spectra were obtained in the yellow-red spectral region in the interval of 5900 and 6660 Å, including strong lines of sodium D and Hα. New radial velocities determined with the cross-correlation technique and the bisector technique are presented. The new data are compared with those recently published by several groups. We found systematic differences between the spectroscopic and CORAVEL-type measurements as large as 1-3 km s-1 in certain phases. We performed Baade-Wesselink analysis for CK Cam discovered by the Hipparcos satellite. The resulting radius is 31 ± 1 R⊙, which is in very good agreement with recent period-radius relation by Gieren, Moffett & Barnes III. It is shown that the systematic velocity differences do not affect the Baade-Wesselink radius more than 1 per cent for CK Cam. Observational pieces of evidence of possible velocity gradient affecting the individual line profiles are studied. The full-width at half minimum (FWHM) of the metallic lines, similarly to the velocity differences, shows a very characteristic phase dependence, illustrating the effect of global compression in the atmosphere. The smallest line widths always occur around the maximal radius, while the largest FWHM is associated with velocity reversal before the minimal radius. Three first overtone pulsators do not follow the general trend: the largest FWHM in SU Cas and SZ Tau occurs after the smallest radius, during the expansion, while in V1334 Cyg there are only barely visible FWHM variations. The possibility of a bright yellow companion of V1334 Cyg is briefly discussed. The observed line-profile asymmetries exceed the values predicted with a simple projection effect by a factor of 2-3. This could be associated with the velocity gradient, which is also supported by the differences between individual line velocities of different excitation potentials.

KW - Cepheids

KW - Stars: atmospheres

KW - Stars: fundamental parameters

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