J/ApJS/226/18 5yr radial velocity measurements of 19 Cepheids (Anderson+, 2016)
Vetting Galactic Leavitt law calibrators using radial velocities:
on the variability, binarity, and possible parallax error of 19 long-period
Cepheids.
Anderson R.I., Casertano S., Riess A.G., Melis C., Holl B., Semaan T.,
Papics P.I., Blanco-Cuaresma S., Eyer L., Mowlavi N., Palaversa L.,
Roelens M.
<Astrophys. J. Suppl. Ser., 226, 18-18 (2016)>
=2016ApJS..226...18A 2016ApJS..226...18A (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Radial velocities ; Binaries, spectroscopic
Keywords: binaries: general; binaries: spectroscopic; distance scale; parallaxes
stars: distances; stars: variables: Cepheids
Abstract:
We investigate the radial velocity (RV) variability and spectroscopic
binarity of 19 Galactic long-period (Ppuls≳10d) classical Cepheid
variable stars whose trigonometric parallaxes are being measured using
the Hubble Space Telescope and Gaia. Our primary objective is to
constrain possible parallax error due to undetected orbital motion.
Using over 1600 high-precision RVs measured between 2011 and 2016, we
find no indication of orbital motion on ≲5yr timescales for 18
Cepheids and determine upper limits on allowed configurations for a
range of input orbital periods. The results constrain the unsigned
parallax error due to orbital motion to <2% for 16 stars, and <4% for
18. We improve the orbital solution of the known binary YZ Carinae and
show that the astrometric model must take into account orbital motion
to avoid significant error (~±100µarcsec). We further investigate
long-timescale (Porb>10yr) variations in pulsation-averaged velocity
vγ via a template fitting approach using both new and
literature RVs. We discover the spectroscopic binarity of XZ Car and
CD Cyg, find first tentative evidence for AQ Car, and reveal KN Cen's
orbital signature. Further (mostly tentative) evidence of
time-variable vγ is found for SS CMa, VY Car, SZ Cyg, and X
Pup. We briefly discuss considerations regarding a vetting process of
Galactic Leavitt law calibrators and show that light contributions by
companions are insignificant for most distance scale applications.
Description:
We here present a detailed investigation of spectroscopic binarity of
the 19 Cepheids for which HST/WFC3 spatial scan parallaxes are being
recorded (Riess+ 2014ApJ...785..161R 2014ApJ...785..161R; Casertano+ 2016ApJ...825...11C 2016ApJ...825...11C).
We have secured time-series observations from three different
high-resolution echelle spectrographs: Coralie (R∼60000) at the Swiss
1.2m Euler telescope located at La Silla Observatory, Chile; Hermes
(R∼85000) at the Flemish 1.2m Mercator telescope located at the Roque
de los Muchachos Observatory on La Palma, Canary Islands, Spain;
Hamilton (R∼60000) at the 3m Shane telescope located at Lick
Observatory, California, USA.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 74 19 Basic information on the sample of Cepheids
discussed here
table2.dat 49 1630 RV data obtained for this program
table3.dat 88 19 Results from RV curve modeling for all
program Cepheids
table4.dat 80 18 *Upper limits on wsini, the maximum unsigned
projected parallax error estimated from
upper limits on spectroscopic binarity
table6.dat 62 33 Time-variable vγ of new spectroscopic binaries
based on RV template fitting
table7.dat 63 41 Time-dependent vγ based on RV template fitting
for reported binary Cepheids
table8.dat 62 19 Estimating typical photometric bias due to main
sequence companions
refs.dat 65 38 References
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Note on table4.dat: The orbital elements for the spectroscopic binary
YZ Carinae are given in table 5:
------------------------------------------------------------------------------
Porb e K Vgam T0-2.4M omega asini Fmass rms wsini
d km/s km/s deg [10+6km] Msun km/s %w
------------------------------------------------------------------------------
830.22 0.041 10.62 0.844 53422 195 117.1 0.093 0.39 26
±0.34 ±0.010 ±0.82 ±0.063 ±29 ±12 ±9.4 ±0.041
------------------------------------------------------------------------------
See section 4.2 for further explanations.
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See also:
B/gcvs : General Catalogue of Variable Stars (Samus+ 2007-2013)
J/ApJ/826/56 : HST/WFC3 obs. of Cepheids in SN Ia host gal. (Riess+, 2016)
J/ApJ/824/74 : OGLE LC classification of MC Cepheids (Garcia-Varela+, 2016)
J/MNRAS/455/4231 : Coralie radial velocities for l Car (Anderson+, 2016)
J/AJ/150/13 : Cepheid Radial Velocities (CRaV) project (Evans+, 2015)
J/A+A/579/A68 : CANDID code for interferometric observations (Gallenne+, 2015)
J/ApJ/804/144 : del Cephei new spectroscopic observations (Anderson+, 2015)
J/MNRAS/446/4008 : RT Aur and SZ tau UBV light curves (Evans+, 2015)
J/A+A/566/L10 : Cepheid radial velocity amplitude modulations (Anderson, 2014)
J/MNRAS/434/2238 : Cepheids in open clusters (Anderson+, 2013)
J/A+A/553/A24 : Models for rotating stars (Georgy+, 2013)
J/AJ/144/187 : Iris photom. near southern Cepheids. V. AQ Pup (Turner+, 2012)
J/A+A/546/A61 : Radial velocities for XHIP catalogue (de Bruijne+, 2012)
J/A+A/537/A146 : Stellar models with rotation. 0.8<M<120. (Ekstrom+, 2012)
J/A+A/534/A94 : Milky Way Cepheids radial velocities (Storm+, 2011)
J/ApJ/730/119 : HST/WFC3 obs. of Cepheids in SN Ia hosts (Riess+, 2011)
J/ApJ/699/539 : Cepheids in SN-Ia host galaxies (Riess+, 2009)
J/PAZh/35/451 : Light Curves of RS Pup (Berdnikov+, 2009)
J/AcA/58/313 : LMC Cepheids in OGLE and MACHO data (Poleski+, 2008)
J/AcA/58/163 : VI light curves of LMC classical Cepheids (Soszynski+, 2008)
J/MNRAS/362/1167 : Radial velocities of 14 southern Cepheids (Petterson+, 2005)
J/A+A/399/1167 : Hipparcos Variability-Induced Movers (Pourbaix+, 2003)
J/A+AS/140/79 : Radii of 22 galactic Cepheids (Imbert, 1999)
J/A+A/314/541 : Long period Cepheids (Antonello+, 1996)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Name Cepheid name
8- 17 A10 --- Other Other name (HD or Hipparcos)
19- 20 I2 h RAh Hour of Right Ascension (J2000) (1)
22- 23 I2 min RAm Minute of Right Ascension (J2000) (1)
25- 29 F5.2 s RAs Second of Right Ascension (J2000) (1)
31 A1 --- DE- Sign of the Declination (J2000) (1)
32- 33 I2 deg DEd Degree of Declination (J2000) (1)
35- 36 I2 arcmin DEm Arcminute of Declination (J2000) (1)
38- 39 I2 arcsec DEs Arcsecond of Declination (J2000) (1)
41- 43 F3.1 mag Vmag [7.5/10] Mean V band magnitude (1)
45- 47 I3 --- Ncor [0/118] Number of Observations, Coralie
49- 50 I2 --- Nham [0/78] Number of Observations, Hamilton
52- 53 I2 --- Nher [0/45] Number of Observations, Hermes
55- 57 F3.1 yr dtObs [1/5] Total temporal baseline of new observations
59- 74 A16 --- Ref References (see refs.dat file) (2)
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Note (1): Coordinates and mean magnitudes are based on the information from the
GCVS (http://www.sai.msu.su/gcvs/gcvs/; see B/gcvs);
average magnitudes are approximate.
Note (2): References for work previously discussing the binarity or cluster
membership of these objects are as follows (see also the binary
Cepheids database by Szabados (2003IBVS.5394....1S 2003IBVS.5394....1S)). Sections
discussing individual Cepheids in more detail are indicated in the
column Ref.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Name Cepheid name
8- 19 F12.6 d BJD [55652.8/57536.9] Observation time, BJD-2400000
21- 26 F6.4 --- Phi Pulsation Phase (φpuls) (1)
28- 34 F7.3 km/s RVel [-84.7/98.4] Barycentric radial velocity
36- 40 F5.3 km/s e_RVel [0.005/0.2] Uncertainty in RVel
42- 49 A8 --- Inst Instrument used (2)
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Note (1): Pulsation phase is defined such that Phi=0 at minimal RV and
is computed using ephemerides listed in Table 3.
Note (2): Instrument used as follows:
Hamilton = Hamilton (R∼60000) at the 3m Shane telescope located at
Lick Observatory, California, USA;
Hermes = Hermes (R∼85000) at the Flemish 1.2m Mercator telescope
located at the Roque de los Muchachos Observatory on La Palma,
Canary Islands, Spain;
Coralie = Coralie (R∼60000) at the Swiss 1.2m Euler telescope located
at La Silla Observatory, Chile.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Name Cepheid name
10- 18 F9.6 d Ppuls [9/69.7] Pulsation Period
20- 31 F12.6 d Epoch Epoch of minimal RV, BJD-2400000
33- 34 I2 --- Nfs [5/13] Number of harmonics used in
fit Fourier series
36- 42 F7.3 km/s Vgam [-69.5/77.1] Systemic mean velocity (νγ)
44- 49 F6.3 km/s Ap2p [19.2/59.6] Peak-to-peak amplitude
51- 56 F6.3 km/s A1 [9/26.1] First harmonic amplitude
58- 61 F4.2 --- R21 [0.03/0.5] Fourier amplitude ratio: 2,1
63- 66 F4.2 --- phi21 [2.9/5.3] Fourier phase ratio: 2,1
68- 71 F4.2 --- R31 [0.01/0.3] Fourier amplitude ratio: 3,1
73- 76 F4.2 --- phi31 [1.6/7.5] Fourier phase ratio: 3,1
78- 82 F5.3 km/s rms [0.03/0.9] Fit Fourier rms
84- 88 F5.3 km/s e_Vgam [0.03/0.6] Standard mean error on Vgam
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Name Cepheid name
8- 11 F4.2 yr dt [1.3/5.1] Temporal baseline of new observations
13- 15 I3 --- dof [33/111] Degrees of freedom after the fit
17- 20 F4.2 yr Porb1 [0.7/4] Derived orbital period (3)
22- 26 F5.3 km/s K1 [0.07/2] Orbital semi-amplitude (3)
28- 32 F5.3 km/s e_K1 [0.001/1.2] Uncertainty in K1 (3)(4)
34- 37 F4.2 AU asini1 [0.2/6.4] Projected semi-major axis (3)(7)(5)
39- 41 F3.1 AU wsini1 [0/7] Projected parallax error (3)(7)(6)
43- 47 I5 --- chisq1 [32/20618] Fit χ square value (3)
49- 52 F4.2 yr Porb2 [0.6/2.5] Derived orbital period (3)
54- 58 F5.3 km/s K2 [0.1/1.2] Orbital semi-amplitude (3)
60- 64 F5.3 km/s e_K2 [0.001/0.8] Uncertainty in K1 (3)(4)
66- 69 F4.2 AU asini2 [0.2/5.8] Projected semi-major axis (3)(5)(7)
71- 73 F3.1 AU wsini2 [0/4] Projected parallax error (3)(6)(7)
75- 80 I6 --- chisq2 [27/20207] Fit χ square value (3)
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Note (3): For each star, best-fit results (Porb#, K#, asini#, wsini#, chisq#),
with eccentricity e=0, are given for:
1 = that orbital solution leading to the maximum unsigned projected parallax
error (typically near 1 year orbital period);
2 = that orbital solution with overall minimal χ^2.
Note (4): Uncertainties on K are based on the fit covariance matrix.
Note (5): asini is calculated using K and the corresponding fixed Porb.
Note (6): wsini is estimated as described in Section 4.1 and can have positive
or negative sign.
Note (7): wsini and asini are given in [AU], which is equivalent to percent
of the parallax.
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Byte-by-byte Description of file: table[67].dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Name Cepheid name
8- 14 F7.4 d Ppuls [9.7/34.1] Pulsation Period (1)
16- 25 F10.4 d Epoch [25787.5/57509.5] Epoch of minimal RV,
BJD-2400000 (1)
27- 30 F4.2 yr dt [0.02/7.5] Timespan of the measurements (Δt)
32- 33 I2 --- Nrv [5/98] Number of RVel measurements fitted
35- 40 F6.2 km/s Vgam [-42.4/77.2] Systemic mean velocity
(νγ) (1)
42- 45 F4.2 km/s stdmer [0.05/2.6] Standard mean error based on residual
scatter
47 A1 --- l_sigV Limit flag on sigV
48- 53 F6.3 km/s sigV [0.001/20.2] Uncertainty from the fit covariance
matrix (σ(νγ))
55- 63 A9 --- Ref References (see refs.dat file)
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Note (1): Ppuls, Epoch, and vγ are based on RV template fitting.
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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- 6 A6 --- Name Cepheid name
9- 11 A3 --- SpT Companion MK spectral type estimate (B2V or B4V)
14 I1 --- Xing [0/3] Instability crossing (8)
16- 17 I2 Myr Age [24/82] Estimated Age (9)
19- 22 F4.2 [yr] logAge [7.3/8] Log Estimated Age (9)
24- 27 F4.1 Msun m1 [6/10.2] Cepheid mass (10)
29- 32 F4.2 Msun m2 [4/7.2] Cepheid companion mass (11)
34- 38 F5.2 mag dMV [-4.6/-3.2] Magnitude contrast, V band (12)
40- 44 F5.2 mag dMI [-5.8/-3.9] Magnitude contrast, I band (12)
46- 50 F5.2 mag dMH [-7.1/-4.6] Magnitude contrast, H band (12)
52- 56 F5.2 mag dWVI [-7.7/-5] Magnitude contrast,
Wesenheit index WVI=I-1.55*(V-I) (12)
58- 62 F5.2 mag dWHVI [-7.6/-4.9] Magnitude contrast,
Wesenheit index WHVI=H-0.4*(V-I) (12)
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Note (8): Instability strip crossing based on positive (assumed to be third
crossings) and negative (second crossings) observed period changes
(Turner et al. 2006PASP..118..410T 2006PASP..118..410T).
"0" denotes crossing number not known.
Note (9): Ages are estimated using period-age relations for the appropriate
crossing assuming average initial rotation rates
(Anderson et al. 2016A&A...591A...8A 2016A&A...591A...8A).
Note (10): Cepheid masses m1 are estimated using isochrones of Solar metallicity
and average ZAMS rotation (Ekstrom et al. 2012, J/A+A/537/A146;
Georgy et al. 2013, J/A+A/553/A24) for a fixed adopted mean color
V-I=0.5 during the blue loop phase;
Note (11): m2 is the mass of a hypothetical companion with m2/m1=0.7 unless a
spectral type is known (DD Cas, KN Cen).
Note (12): Magnitude contrasts between Cepheid and hypothetical companion based
on the isochrones.
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Byte-by-byte Description of file: refs.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- Ref Reference code
6- 24 A19 --- BibCode Bibcode
26- 43 A18 --- Auth First author's name(s)
45- 65 A21 --- Comm Comment
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 09-Nov-2016