J/AJ/150/13 Cepheid Radial Velocities (CRaV) project (Evans+, 2015)
Binary properties from Cepheid radial velocities (CRaV).
Evans N.R., Berdnikov L., Lauer J., Morgan D., Nichols J., Gunther H.M.,
Gorynya N., Rastorguev A., Moskalik P.
<Astron. J., 150, 13 (2015)>
=2015AJ....150...13E 2015AJ....150...13E
ADC_Keywords: Stars, variable ; Radial velocities
Keywords: binaries: general - stars: massive - stars: variables: Cepheids -
techniques: radial velocities
Abstract:
We have examined high accuracy radial velocities of Cepheids to
determine the binary frequency. The data are largely from the CORAVEL
spectrophotometer and the Moscow version, with a typical uncertainty
of ≤1km/s, and a time span from 1 to 20years. A systemic velocity
was obtained by removing the pulsation component using a high order
Fourier series. From this data we have developed a list of stars
showing no orbital velocity larger than ±1km/s. The binary fraction
was analyzed as a function of magnitude, and yields an apparent
decrease in this fraction for fainter stars. We interpret this as
incompleteness at fainter magnitudes, and derive the preferred binary
fraction of 29%±8% (20%±6% per decade of orbital period) from the
brightest 40 stars. A comparison of this fraction in this period range
(1-20years) implies a large fraction for the full period range. This
is reasonable in that the high accuracy velocities are sensitive to
the longer periods and smaller orbital velocity amplitudes in the
period range sampled here. Thus the Cepheid velocity sample provides a
sensitive detection in the period range between short period
spectroscopic binaries and resolved companions. The recent
identification of δ Cep as a binary with very low amplitude and
high eccentricity underscores the fact that the binary fractions we
derive are lower limits, to which other low amplitude systems will
probably be added. The mass ratio (q) distribution derived from
ultraviolet observations of the secondary is consistent with a flat
distribution for the applicable period range (1-20years).
Description:
While radial velocity spectrometers have produced a huge amount of
velocity data for Cepheids, the data have never been analyzed to
determine the fraction of stars which show no orbital motion over the
more than three decades they cover. That is the goal of this project,
Cepheid Radial Velocities (CRaV). We have limited the data examined to
observations with a typical accuracy of 1km/s per observation.
In this first paper, we include data from 1978 to 2000 of "northern
stars" down to -20.9°. We plan two subsequent papers on southern
stars and observations since 2000. We begin with the 38 stars in Table
2. To complete the analysis, we examine all stars brighter than 9th
magnitude (Table 6).
The data are largely from the CORAVEL spectrophotometer and the Moscow
velocities (Gorynya et al., cat. III/229). The Moscow velocities are a
large dataset for which many stars are covered annually in the 1990's.
For this reason, we are defining our "northern sample" to be stars
with decl.>-20.9°, the region they covered. On the other hand,
CORAVEL data from both Observatoire de Haute-Provence and ESO La Silla
(Bersier et al. 1994, cat. J/A+AS/108/25; Bersier, 2002ApJS..140..465B 2002ApJS..140..465B)
have been included since they were taken and analyzed with the N
hemisphere stars by the Geneva group.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 44 38 Data sources
table3.dat 22 60 Annual corrections
table4.dat 31 339 Cepheid annual mean velocities
table6.dat 34 61 Multiplicity status
table8.dat 43 24 Mass ratios
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See also:
III/229 : Radial Velocities of Cepheids (Gorynya+ 1992-98)
J/A+A/566/L10 : Cepheid radial velocity amplitude modulations (Anderson, 2014)
J/ApJS/156/227 : Radial velocities of 16 Galactic Cepheids (Barnes+, 2005)
J/A+A/415/531 : Radial velocities of 10 Galactic Cepheids (Storm+, 2004)
J/A+AS/143/211 : Galactic Cepheids BVRI photometry (Berdnikov+, 2000)
J/A+AS/140/79 : Radii of 22 galactic Cepheids (Imbert, 1999)
J/A+AS/108/25 : Cepheids fundamental parameters II. (Bersier+, 1994)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Cepheid identifier
11- 12 A2 --- Ref1 'gg' means data from Gorynya et al. 1992-98
(cat. III/229)
14- 15 A2 --- Ref2 'b9' means data from Bersier et al. 1994
(cat. J/A+AS/108/25)
17- 18 A2 --- Ref3 'im' means data from Imbert 1999
(cat. J/A+AS/140/79)
20- 21 A2 --- Ref4 'ba' means data from Barnes et al. 2005
(cat. J/ApJS/156/227)
23- 24 A2 --- Ref5 'kk' means data from Kiss and Vinko
(2000MNRAS.314..420K 2000MNRAS.314..420K)
26- 27 A2 --- Ref6 'b0' means data from Bersier
(2002ApJS..140..465B 2002ApJS..140..465B)
29- 30 A2 --- Ref7 's4' means data from Storm et al. 2004
(cat. J/A+A/415/531)
32- 36 F5.2 d Per [2.74/68.46] Period (1)
38- 41 F4.2 mag <Vmag> [3.9/9.05] Mean V-band magnitude (1)
43- 44 A2 --- Mode [o?] The flag 'o' indicates a star pulsating in
an overtone mode (2)
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Note (1): Taken from Fernie et al. (1995IBVS.4148....1F 1995IBVS.4148....1F), except for CK Cam,
which is from Berdnikov et al. 2000, cat. J/A+AS/143/211.
Note (2): Based on the discussion of Evans et al. (2015MNRAS.446.4008E 2015MNRAS.446.4008E).
IR Cep is also classified as an overtone (Groenewegen & Oudmaijer,
2000A&A...356..849G 2000A&A...356..849G).
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- Ref Code of reference source (G1)
4- 7 I4 yr Year [1977/1998] Year of the observation
9- 13 F5.2 km/s [-3.27/5.33] Mean radial velocity (1)
14 A1 --- f_ [*] Indicates correction added in Table4 (2)
16- 19 F4.2 km/s e_ [0.01/5.05]? The 1σ error in
21- 22 I2 --- o_ [1/91] Number of observation in
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Note (1): To test for small instrumental zero point variations, we have formed
the mean and standard deviation (σ) of all stars observed in each
season for each instrument. From this we have created a small instrumental
annual correction for each instrument for each season using all Cepheids.
See Section 3.4 for more details about these annual corrections.
Note (2): Corrections >0.3km/s (absolute value) from at least 4 stars. Using
corrections derived from a smaller number of stars puts too large a weight
on individual stars, i.e., corrects a possible orbital variation to 0.0.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Cepheid identifier
11- 12 A2 --- Ref Code of reference source (G1)
14- 17 I4 yr Year [1977/1998] Year of the observation
19- 23 F5.2 km/s [-3.27/5.33] Annual mean radial velocity (from
the data and the Fourier curves) (1)
25- 28 F4.2 km/s e_ [0.01/5.05]? The 1σ error in
30- 31 I2 --- o_ [1/91] Number of observation in
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Note (1): The purpose of Cepheid Radial Velocities (CRaV) is to investigate the
annual mean systemic velocities of Cepheids with accurate velocities. The
observed Cepheid velocity, of course, is a combination of the systemic
velocity of the star and the pulsation velocity curve. To correct for the
pulsation velocity, we use a Fourier representation of the curve with up to
20 terms. The velocity curves have to be aligned over decades by means of a
pulsation period. Both these steps are discussed in Sections 3.1 and 3.2.
The next step is to compare data from each season with the Fourier curve.
The average difference between the data and the curve is computed, creating
the annual mean velocity. A small instrumental correction was computed for
each instrument for each season using all Cepheids (see Table 3).
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Cepheid identifier
11- 15 F5.3 mag <Vmag> [1.982/9.053] Mean V-band magnitude (1)
17- 22 F6.3 d Per [1.949/68.464] Pulsation period
24- 26 A3 --- Mult Multiplicity status (x=single or bin=binary)
28- 29 A2 --- l_Porb [≥] Lower limit flag on Porb
31- 34 F4.1 yr Porb [1/90]? Orbital period (from Table 8)
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Note (1): We have ordered the Cepheids from the brightest to the faintest.
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Byte-by-byte Description of file: table8.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Name of the binary (1)
11 A1 --- l_M2+ [<] Upper limit flag on M2
12- 15 F4.2 Msun M2+ [1.26/5.3]? Mass of the companion (or upper value
in case of mass range)
16 A1 --- --- [-]
17- 19 F3.1 Msun M2- [1.4/2.2]? Lower value for companion mass range
21- 23 F3.1 Msun M1 [4.7/7.7]? Mass of the primary (Cepheid) (2)
25 A1 --- l_M2/M1 [<] Upper limit flag on M2/M1
26- 29 F4.2 --- M2/M1 [0.27/0.96]? Companion to Cepheid mass ratio (3)
31- 36 F6.3 d Per [3.768/18.166] Pulsation period
38 I1 --- r_M2- [1/4]? Reference for the mass of companion (4)
40- 43 F4.1 yr Porb [1/40] Orbital period
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Note (1): MU Cep, MW Cyg, VZ Cyg, and FN Vel were not observed by the
International Ultraviolet Explorer (IUE) because they are fainter than the
survey limit, so they lack mass ratio information, and are listed at the
bottom of the table.
Note (2): Derived as in Evans et al. (2013AJ....146...93E 2013AJ....146...93E), using the Leavitt
law (period-luminosity relation) from Benedict et al. (2007AJ....133.1810B 2007AJ....133.1810B)
and the mass-luminosity relation based on the models of Prada Moroni et al.
(2012ApJ...749..108P 2012ApJ...749..108P) with moderate convective overshoot.
Note (3): When a companion mass has a range, a mass from the center of the range
was used.
Note (4): The companion mass is taken from one of the following references:
1 = Evans et al. (2013AJ....146...93E 2013AJ....146...93E);
2 = The International Ultraviolet Explorer (IUE) survey (Evans,
1995ApJ...445..393E 1995ApJ...445..393E) + MCep;
3 = The HST measurement of Polaris (Evans et al., 2008AJ....136.1137E 2008AJ....136.1137E);
4 = Evans (1992ApJ...384..220E 1992ApJ...384..220E) + MCep.
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Global Notes:
Note (G1): The codes for the data sources are:
gg = Gorynya et al. (cat. III/229);
b9 = Bersier et al. 1994 (cat. J/A+AS/108/25);
im = Imbert 1999 (cat. J/A+AS/140/79);
ba = Barnes et al. 2005 (cat. J/ApJS/156/227);
kk = Kiss and Vinko (2000MNRAS.314..420K 2000MNRAS.314..420K);
b0 = Bersier (2002ApJS..140..465B 2002ApJS..140..465B);
s4 = Storm et al. 2004 (cat. J/A+A/415/531).
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 27-Jul-2015