J/A+A/489/1255 HARPS observations of eight galactic Cepheids (Nardetto+, 2008)
High resolution spectroscopy for Cepheids distance determination.
III. A relation between γ-velocities and γ-asymmetries.
Nardetto N., Stoekl A., Bersier D., Barnes, T.G.
<Astron. Astrophys. 489, 1255 (2008)>
=2008A&A...489.1255N 2008A&A...489.1255N
ADC_Keywords: Stars, variable ; Spectroscopy ; Radial velocities
Keywords: techniques: spectroscopic - stars: atmospheres - stars: oscillations -
stars: variables: Cepheids - stars: distances
Abstract:
We show that residual γ-velocities (compared to a axisymmetric
rotation model of the milky Way) are an intrinsic property of
Cepheids.
We observed eight galactic Cepheids with the HARPS spectroscope,
focusing specifically on 17 spectral lines. For each spectral line of
each star, we computed the γ-velocity (resp. γ-asymmetry)
as an average value of the interpolated radial velocity (resp. line
asymmetry) curve.
For each Cepheid in our sample, a linear relation is found between the
γ-velocities of the various spectral lines and their corresponding
γ-asymmetries, showing that residual γ-velocities stem from
the intrinsic properties of Cepheids. We also provide a physical
reference to the stellar γ-velocity: it should be zero when the
γ-asymmetry is zero. Following this definition, we provide very
precise and physically calibrated estimates of the γ-velocities
for all stars of our sample.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 62 8 Observed sample of Cepheids sorted by increasing
period and main results
table2.dat 45 136 Gamma-velocities and γ-asymmetries
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See also:
J/A+A/453/309 : HARPS observations of nine galactic Cepheids (Nardetto+, 2006)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Star name
10- 15 I6 --- HD HD number
17- 24 F8.5 d Per Pulsation period (1)
26- 30 F5.1 km/s VgGCD GCD γ-velocities (2)
32- 36 F5.2 --- a0 Slope of the relation (3)
38- 41 F4.2 --- e_a0 Uncertainty on a0
43- 45 F3.1 km/s b0 Zero-Point of the relation (3)
47- 49 F3.1 km/s e_b0 Uncertainty on b0
51- 52 I2 --- Chi2 Reduced Chi^2 of the fit
54- 58 F5.1 km/s VgStar Physically calibrated γ-velocity of
the star (4)
60- 62 F3.1 km/s e_VgStar Uncertainty on VgStar
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Note (1): The corresponding Julian dates (T0) can be found
in Nardetto et al., 2007A&A...471..661N 2007A&A...471..661N (Paper II)
Note (2): gGCD is the γ-velocity of the Galactic Cepheid Database :
http://www.astro.utoronto.ca/DDO/research/cepheids/
Note (3): a0 and b0 are respectively the slope and the zero-point of the
relation Vg(i)-gGCD=a0*Ag(i)+b0, where i correspond to the metallic
line considered. Vg(i) and Ag(i) can be found in table2.dat
Note (4): VgStar is defined as VgGCD+b0
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Star name
10- 13 A4 --- Ion Species metallic spectral line
15- 22 F8.3 0.1nm Line Wavelength of the spectral line
24- 28 F5.2 % Ag Gamma-asymmetry in % of the FWHM (1)
30- 34 F5.2 % e_Ag Uncertainty on Ag
36- 40 F5.2 km/s Vg Gamma-velocity
42- 45 F4.2 km/s e_Vg Uncertainty on Vg
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Note (1): Quantity derived from a bi-Gaussian fit. See paper for more detail.
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Acknowledgements: N. Nardetto, nardetto(at)mpifr-bonn.mpg.de
References:
Nardetto et al., Paper I 2006A&A...453..309N 2006A&A...453..309N, Cat. J/A+A/453/309
Nardetto et al., Paper II 2007A&A...471..661N 2007A&A...471..661N
Nardetto et al., Paper III 2008A&A...489.1263N 2008A&A...489.1263N
(End) Patricia Vannier [CDS] 19-May-2008