J/ApJ/804/144 δ Cephei new spectroscopic observations (Anderson+, 2015)
Revealing δ Cephei's secret companion and intriguing past.
Anderson R.I., Sahlmann J., Holl B., Eyer L., Palaversa L., Mowlavi N.,
Suveges M., Roelens M.
<Astrophys. J., 804, 144 (2015)>
=2015ApJ...804..144A 2015ApJ...804..144A
ADC_Keywords: Binaries, spectroscopic ; Stars, variable ; Radial velocities
Keywords: binaries: general; binaries: spectroscopic; stars: distances;
stars: individual: del Cephei & HD 213306 & HIP 110991;
stars: oscillations; stars: variables: Cepheids
Abstract:
Classical Cepheid variable stars are crucial calibrators of the cosmic
distance scale thanks to a relation between their pulsation periods
and luminosities. Their archetype, δ Cephei, is an important
calibrator for this relation. In this paper, we show that
δCephei is a spectroscopic binary based on newly obtained
high-precision radial velocities. We combine these new data with
literature data to determine the orbit, which has period 2201 days,
semi-amplitude 1.5km/s, and high eccentricity (e=0.647). We re-analyze
Hipparcos intermediate astrometric data to measure δ Cephei's
parallax (varpri=4.09±0.16mas) and find tentative evidence for an
orbital signature, although we cannot claim detection. We estimate
that Gaia will fully determine the astrometric orbit. Using the
available information from spectroscopy, velocimetry, astrometry, and
Geneva stellar evolution models (MδCep∼5.0-5.25M☉), we
constrain the companion mass to within 0.2M☉<M2<1.2. We
discuss the potential of ongoing and previous interactions between the
companion and δ Cephei near pericenter passage, informing
reported observations of circumstellar material and bow shock. The
orbit may have undergone significant changes due to a Kozai-Lidov
mechanism driven by the outer (visual and astrometric) companion
HD213307. Our discovery of δ Cephei's nature as a spectroscopic
binary exposes a hidden companion and reveals a rich and dynamical
history of the archetype of classical Cepheid variables.
Description:
Line-of-sight (radial) velocities were measured from 136 observations
taken between 2011 September and 2014 using the fiber-fed
high-resolution (R∼85000) spectrograph Hermes at the Flemish 1.2m
Mercator Telescope located at Roque de los Muchachos Observatory, La
Palma, Canary Islands.
Objects:
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RA (ICRS) DE Designation(s)
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22 29 10.27 +58 24 54.7 HD 213306 = * del Cep
01 47 44.83 +63 51 09.0 HD 10780 = HIP 8362
05 07 27.01 +18 38 42.2 HD 32923 = * m Tau
06 13 12.50 +10 37 37.7 HD 42807 = V* V1357 Ori
09 29 54.82 +05 39 18.5 HD 82106 = BD+06 2182
16 04 56.79 +39 09 23.4 HD 144579 = BD+39 2947
18 15 32.46 +45 12 33.5 HD 168009 = BD+45 2684
20 40 45.14 +19 56 07.9 HD 197076 = HIP 102040
23 31 22.21 +59 09 55.9 HD 221354 = BD+58 2605
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 34 136 The new Hermes radial velocity data of δ Cep
table2.dat 35 237 List of radial velocity standard stars
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See also:
III/254 : 2nd Cat. of RVs with Astrometric Data (Kharchenko+, 2007)
III/252 : Pulkovo radial velocities for 35493 HIP stars (Gontcharov, 2006)
III/192 : Radial Velocities measured at PPO by FEHRENBACH (Fehrenbach+ 1996)
J/AJ/150/13 : Cepheid Radial Velocities (CRaV) project (Evans+, 2015)
J/AN/336/70 : Vel & proper motions of Galactic Cepheids (Mel'nik+, 2015)
J/A+A/566/L10 : Cepheid RV amplitude modulations (Anderson, 2014)
J/A+A/561/A126 : RV and vsini of southern stars (de Medeiros+, 2014)
J/MNRAS/434/2238 : Cepheids in open clusters (Anderson+, 2013)
J/MNRAS/434/870 : Radial velocity curves of 3 Cepheids (Szabados+, 2013)
J/A+A/553/A24 : Models for rotating stars (Georgy+, 2013)
J/A+A/537/A146 : Stellar models with rotation. 0.8<M<120 (Ekstrom+, 2012)
J/A+A/525/A95 : Search for brown-dwarf companions of stars (Sahlmann+, 2011)
J/AJ/142/136 : Spectroscopy of Cepheids. l=30-250° (Luck+, 2011)
J/A+A/504/959 : Amplitudes of single-mode Cepheids (Klagyivik+, 2009)
J/AN/328/889 : Mean Radial Velocities of open clusters (Kharchenko+, 2007)
J/A+A/453/155 : Extended envelopes around Gal. Cepheids II. (Merand+, 2006)
J/ApJS/156/227 : Radial velocities of 16 Galactic Cepheids (Barnes+, 2005)
J/AJ/130/1880 : Cepheids with periods between 3 & 6 days (Andrievsky+, 2005)
J/A+A/430/165 : Radial velocities for 6691 K and M giants (Famaey+, 2005)
J/A+A/415/531 : Radial velocities of 10 Galactic Cepheids (Storm+, 2004)
J/A+A/381/32 : Galactic Cepheid abundances (Andrievsky+, 2002)
J/A+AS/137/451 : Radial velocities. IX. (Grenier+, 1999)
J/A+AS/108/25 : Cepheids fundamental parameters II. (Bersier+, 1994)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 12 F12.6 d BJD Barycentric Julian Date; BJD-2400000
14- 20 F7.5 -- Phase Pulsation phase (1)
22- 28 F7.3 km/s RVel [-34.8/4] Barycentric Radial Velocity (2)
30- 34 F5.3 km/s e_RVel [0.018] Uncertainty in RVel (3)
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Note (1): With Phase = 0 at minimum radius, see paper. Pulsation phase is
defined here as 0 when vr=vγ at the steep part of
the RV curve.
Note (2): These are the newly-obtained radial velocities obtained with the
Hermes spectrograph. To bring these measurements to the
CORAVEL-ELODIE zeropoint (as was done in the paper), subtract 55m/s.
Note (3): We adopt a fixed uncertainty of 18m/s, to account for uncertainty
in the wavelength calibration and zero-point calibration, see text.
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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- 2 A2 --- --- [HD]
3- 8 I6 --- HD Standard Star Identifier (8 stars)
10- 21 F12.6 d BJD Barycentric Julian Date; BJD-2400000
23- 29 F7.3 km/s RVel [-64.7/29.9] Barycentric Radial Velocity (1)
31- 35 F5.3 km/s e_RVel [0.003/0.07] Uncertainty in RVel
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Note (1): The individual (pressure-corrected) radial velocity measurements
used to determine the relative offset in zero-point between Hermes
and CORAVEL. These measurements were used to create the average
velocities shown in Table 2 and repeated here:
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HD SpT <RVel> <RVelref> ΔRVelref RMSnc RMScorr
km/s km/s km/s m/s m/s
----------------------------------------------------------------------
10780 K0V 2.771 2.70 0.071 38.7 17.1
32923 G4V 20.627 20.50 0.127 70.1 14.8
42807 G2V 6.068 6.00 0.068 115.2 29.7
82106 K3V 29.784 29.75 0.034 45.8 20.8
144579 G8V -59.452 -59.45 -0.002 42.7 20.0
168009 G1V -64.581 -64.65 0.069 36.4 20.0
197076 G5V -35.413 -35.40 -0.013 78.3 10.9
221354 K0V -25.111 -25.20 0.089 53.8 15.5
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Spectral types from SIMBAD, Hermes RVs of standard stars from new
observations, Udry et al., 1999ASPC..185..367U 1999ASPC..185..367U,
offsets between new and reference RVs, and RMS of new observations
without ("RMSnc") and with pressure corrections applied ("RMScorr")
following Anderson, R. I. 2013, PhD thesis, Universite de Geneve
(Sec. 2.1.5).
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 27-Aug-2015