J/ApJ/898/47 Fe/H & radii from blended sp. of simulated binaries (Furlan+, 2020)
Unresolved binary exoplanet host stars fit as single stars: effects on the
stellar parameters.
Furlan E., Howell S.B.
<Astrophys. J., 898, 47 (2020)>
=2020ApJ...898...47F 2020ApJ...898...47F
ADC_Keywords: Stars, double and multiple; Spectroscopy; Models;
Abundances, [Fe/H]; Stars, diameters; Optical
Keywords: Stellar spectral lines; Stellar properties;
Fundamental parameters of stars; High resolution spectroscopy;
Binary stars; Planet hosting stars
Abstract:
In this work, we quantify the effect of an unresolved companion star
on the derived stellar parameters of the primary star if a blended
spectrum is fit assuming the star is single. Fitting tools that
determine stellar parameters from spectra typically fit for a single
star, but we know that up to half of all exoplanet host stars may have
one or more companion stars. We use high- resolution spectra of planet
host stars in the Kepler field from the California-Kepler Survey to
create simulated binaries; we select eight stellar pairs and vary the
contribution of the secondary star, then determine stellar parameters
with SpecMatch-Emp and compare them to the parameters derived for the
primary star alone. We find that, in most cases, the effective
temperature, surface gravity, metallicity, and stellar radius derived
from the composite spectrum are within 2-3σ of the values
determined from the unblended spectrum, but the deviations depend on
the properties of the two stars. Relatively bright companion stars
that are similar to the primary star have the largest effect on the
derived parameters; in these cases, the stellar radii can be
overestimated by up to 60%. We find that metallicities are generally
underestimated, with values up to eight times smaller than the typical
uncertainty in [Fe/H]. Our study shows that follow-up observations are
necessary to detect or set limits on stellar companions of planetary
host stars so that stellar (and planet) parameters are as accurate as
possible.
Description:
We selected 16 stars from the California-Kepler Survey (CKS;
see Petigura+, 2017, J/AJ/154/107) to combine their spectra and create
blended systems. As part of the CKS, 1305 stars in the Kepler field
were observed with the High Resolution Echelle Spectrometer (HIRES) on
the Keck I telescope.
We used the reduced HIRES spectra of our selected 16 stars from the
CKS sample and determined their stellar parameters (Teff, logg,
[Fe/H], and R*) using SpecMatch-Emp
(http://github.com/samuelyeewl/specmatch-emp).
This fitting code is a different version of SpecMatch
(Yee+ 2017, J/ApJ/836/77).
See Section 2.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 69 16 Stellar parameters derived with SpecMatch-Emp for the
eight stellar pairs used in this work to create
simulated binaries
table2.dat 67 232 Stellar parameters derived with SpecMatch-Emp from
the blended spectra of the the simulated binaries
--------------------------------------------------------------------------------
See also:
V/133 : Kepler Input Catalog (Kepler Mission Team, 2009)
J/A+A/415/1153 : [Fe/H] for 98 extra-solar planet-host stars (Santos+, 2004)
J/ApJ/622/1102 : The planet-metallicity correlation. (Fischer+, 2005)
J/ApJS/159/141 : Spectroscopic properties of cool stars. I. (Valenti+, 2005)
J/ApJS/190/1 : A survey of stellar families (Raghavan+, 2010)
J/A+A/512/A13 : EW-Teff calibration for solar-type stars (Sousa+, 2010)
J/AJ/142/19 : Speckle observations of KOI (Howell+, 2011)
J/AJ/144/42 : Infrared photometry of 90 KOIs (Adams+, 2012)
J/other/Nat/486.375 : Stellar parameters of KOI stars (Buchhave+, 2012)
J/A+A/546/A10 : Multiplicity in planet-host stars (Lillo-Box+, 2012)
J/ApJ/750/L37 : Stellar parameters of low-mass KOIs (Muirhead+, 2012)
J/ApJ/757/161 : Spectroscopy of 56 exoplanet host stars (Torres+, 2012)
J/ApJ/771/107 : Spectroscopy of faint KOI stars (Everett+, 2013)
J/ApJ/767/127 : Asteroseismic solutions for 77 Kepler stars (Huber+, 2013)
J/A+A/558/A106 : Chemical abundances for 83 transit hosts (Mortier+, 2013)
J/ApJS/211/2 : Revised properties of Q1-16 Kepler targets (Huber+, 2014)
J/ApJ/791/35 : Detection of Kepler planet candidates host stars (Law+, 2014)
J/A+A/566/A103 : Kepler planet host candidates imaging (Lillo-Box+, 2014)
J/ApJS/210/20 : Small Kepler planets radial velocities (Marcy+, 2014)
J/AJ/147/86 : From binaries to multiples. I. FG-67 sample (Tokovinin, 2014)
J/ApJ/806/248 : AO imaging of KOIs with gas giant planets (Wang+, 2015)
J/ApJ/813/130 : Kepler multiple transiting planet systems (Wang+, 2015)
J/AJ/152/18 : Robo-AO Kepler planetary cand. survey. II. (Baranec+, 2016)
J/AJ/152/8 : Stellar multiplicity impact on planets I. (Kraus+, 2016)
J/AJ/154/109 : California-Kepler Survey. III. Planet radii (Fulton+, 2017)
J/AJ/153/71 : Kepler follow-up obs. program. I. Imaging (Furlan+, 2017)
J/AJ/153/117 : KOIs companions from high-resolution imaging (Hirsch+, 2017)
J/AJ/154/108 : California-Kepler Survey (CKS). II. (Johnson+, 2017)
J/ApJS/229/30 : Revised properties of Q1-17 Kepler targets (Mathur+, 2017)
J/AJ/154/107 : California-Kepler Survey (CKS). I. (Petigura+, 2017)
J/ApJ/836/77 : A library of high-S/N opt. spectra of FGKM stars (Yee+, 2017)
J/AJ/153/66 : Robo-AO Kepler Planetary Cand. Survey. III. (Ziegler+, 2017)
J/ApJ/866/99 : Radii of KIC stars & planets using Gaia DR2 (Berger+, 2018)
J/ApJS/237/38 : Extended abundance analysis of KOIs (Brewer+, 2018)
J/AJ/156/264 : CKS. VII. Planet radius gap (Fulton+, 2018)
J/ApJ/861/149 : Kepler Follow-up Obs. Program. II. Spectro. (Furlan+, 2018)
J/AJ/155/89 : California-Kepler Survey (CKS). IV. Planets (Petigura+, 2018)
J/AJ/156/292 : Effect of close companions on exoplanet radii (Teske+, 2018)
J/ApJS/235/6 : Updated Mult. Star Catalog (MSC): Sept 2021 (Tokovinin, 2018)
J/AJ/155/48 : CKS. V. Masses and radii (Weiss+, 2018)
J/AJ/155/161 : Stars nearby Robo-AO Kepler planetary cand. (Ziegler+, 2018)
J/AJ/158/113 : Kepler-13AB aperture photometry (Howell+, 2019)
J/ApJ/888/34 : AO Kepler asteroseismic survey. II. (Schonhut-Stasik+, 2020)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 A2 --- Bin Simulated binary number
4- 7 I4 K dTeff [32/1404] ΔTeff of binaries
9- 12 F4.2 --- dL [0.15/0.84] Lsec/Lprim ratio
14- 17 I04 --- KOI [116/5622] KOI star identifier
(<KOI-NNNNN> in Simbad)
19- 22 I4 K Teff [4446/5892] Effective temperature
24- 26 I3 K e_Teff [70/110] Teff uncertainty
28- 31 F4.2 [cm/s2] logg [4.22/4.62] Log of surface gravity
33- 36 F4.2 [cm/s2] e_logg [0.12/0.12] Logg uncertainty
38- 42 F5.2 [Sun] [Fe/H] [-0.11/0.2] [Fe/H] abundance
44- 47 F4.2 [Sun] e_[Fe/H] [0.09/0.09] [Fe/H] uncertainty
49- 52 F4.2 Rsun Rad [0.7/1.2] Radius
54- 57 F4.2 Rsun e_Rad [0.1/0.18] Rad uncertainty
59- 63 F5.2 --- Chi2 [0.43/13.04] Median χ2 value (G1)
65- 69 F5.1 --- S/N [20.9/135.3] Signal-to-noise ratio of
the spectrum
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [KOI]
4- 7 I04 --- Star1 KOI star identifier, primary
9- 11 A3 --- --- [KOI]
12- 15 I04 --- Star2 KOI star identifier, secondary
17- 20 I4 km/s RVshift [-500/500] RV shift applied to the
scaled spectrum of secondary star
22- 25 I4 K Teff [4861/6154] Effective temperature, primary
27- 29 I3 K e_Teff [110] Uncertainty in Teff
31- 34 F4.2 [cm/s2] logg [4/4.56] Log surface gravity, primary
36- 39 F4.2 [cm/s2] e_logg [0.12] Uncertainty in logg
41- 45 F5.2 [Sun] FeH [-0.6/0.16] Metallicity, primary
47- 50 F4.2 [Sun] e_FeH [0.09] Uncertainty in FeH
52- 55 F4.2 Rsun Rad [0.7/1.83] Radius, primary
57- 60 F4.2 Rsun e_Rad [0.1/0.18] Uncertainty in Radius
62- 67 F6.3 --- chi2 [0.9/38] Median χ2 value of the fit (G1)
--------------------------------------------------------------------------------
Global notes:
Note (G1): The χ2 value is the median of the χ2 values returned by
SpecMatch-Emp (Petigura 2015PhDT........82P 2015PhDT........82P) for each 100Å segment of
the 5000-5800Å spectrum.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 16-Nov-2021