J/ApJS/281/61 Confirmed K2 exoplanet host stars opt. sp. (Loaiza-Tacuri+, 2025)
Stellar characterization, magnesium abundances, and chromospheric activity
analysis of stars with confirmed exoplanets from the K2 mission.
Loaiza-Tacuri V., Souto D., Quispe-Huaynasi F., Cunha K., Daflon S.,
Costa-Almeida E., Smith V.V., Ghezzi L.
<Astrophys. J. Suppl. Ser., 281, 61 (2025)>
=2025ApJS..281...61L 2025ApJS..281...61L
ADC_Keywords: Stars, double and multiple; Exoplanets; Spectra, optical;
Abundances; Stars, masses; Stars, diameters
Keywords: Stellar activity ; Fundamental parameters of stars ; Parallax ;
Exoplanet systems ; Spectroscopy ; Chemical abundances
Abstract:
We present a homogeneous spectroscopic analysis of confirmed Kepler's
extended mission (K2) exoplanet-hosting stars, comprising 301 targets
with high-resolution optical spectra from HIRES and TRES taken from
ExoFOP. We derived effective temperatures, surface gravities, and iron
and magnesium abundances in local thermodynamic equilibrium by
measuring the equivalent widths of Fe I, Fe II, and Mg I lines. Three
estimates of stellar masses and radii were obtained via the
Stefan-Boltzmann and isochrone methods using the codes PARAM and
isochrones. These were used to derive exoplanetary radii reaching
internal precisions of 2.5%, 2.6%, and 6.6%, respectively, and the
radius gap was consistently detected near 1.9R⊕. We measured
chromospheric activity from the CaII H and K and Hα lines.
Within the low-activity range (logR'HK<-4.75), stellar activity
appears to decrease with increasing planetary radius from
super-Earths, sub-Neptunes, sub-Saturns, into the Jupiter regime.
According to the [Mg/Fe] measurements, most of our K2 planet hosts
belong to the Galactic thin disk, but our sample has a population from
the thick disk (high-alpha sequence). Most stars show consistent
chemodynamical behavior. We find that the [Mg/Fe] ratios are
indistinguishable between systems containing large or small
exoplanets, as well as single- or multi-exoplanetary systems. Both the
[Fe/H] and [Mg/H] distributions reveal that stars hosting large
planets are more iron and magnesium enhanced than those having only
small planets, further confirming the link between stellar abundances
and exoplanetary size, but no significant differences are found
between the single-versus multi-exoplanetary systems.
Description:
The sample consists of stars with confirmed exoplanets observed by K2
during the C0-C8 and C10-C18 campaigns, whose high-resolution optical
spectra were obtained from the ExoFOP database (doi: 10.26134/EXOFOP2).
These spectra were acquired using two instruments: the High-Resolution
Echelle Spectrometer (HIRES) on the Keck I 10m telescope and the
Tillinghast Reflector Echelle Spectrograph (TRES) on the 1.5m
Tillinghast telescope at the Fred Lawrence Whipple Observatory on
Mount Hopkins, Arizona.
The HIRES spectra, acquired by the California Planet Search program
after 2004 August with upgraded CCDs, cover the 3640-7990Å range
and include key activity indicators such as the CaII H and K lines and
Halpha. A total of 2320 reduced HIRES spectra corresponding to
198 stars were obtained from ExoFOP. A subsequent inspection of these
spectra revealed that 165 of them possessed signal-to-noise ratios
sufficiently high to facilitate analysis to derive stellar parameters
and metallicities (Section 3). The TRES spectra span the 3800-9100Å
range and contribute 160 spectra of 103 stars.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 83 303 Sample K2 stars
table2.dat 26 157 Line list
table3.dat 122 304 Stellar parameters
table4.dat 86 260 Stellar masses and radii
table5.dat 74 339 Planetary radii
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See also:
III/159 : Ca II H and K Measurements Made at MWO (Duncan+ 1991)
II/335 : Catalog of GALEX UV sources (GUVcat_AIS GR6+7) (Bianchi+ 2017)
IV/34 : K2 Ecliptic Plane Input Catalog (EPIC) (Huber+, 2017)
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
I/352 : Distances to 1.47 billion stars in Gaia EDR3 (Bailer-Jones+, 2021)
III/286 : APOGEE-2 DR17 final allStar catalog (Abdurro'uf+, 2022)
VII/233 : 2MASS All-Sky Extended Source Catalog (XSC) (IPAC/UMass, 2003-2006)
J/AJ/111/439 : Chromospheric emission in late-type stars. (Henry+ 1996)
J/ApJ/622/1102 : The planet-metallicity correlation. (Fischer+, 2005)
J/MNRAS/367/1329 : Elemental abundances for 176 stars (Reddy+, 2006)
J/A+A/469/309 : Activity in late-type stars (Cincunegui+, 2007)
J/MNRAS/384/1178 : 2MASS, SDSS and BVRI photometry for 825 stars (Bilir+, 2008)
J/A+A/495/959 : Radial velocity curve of HD 189733 (Boisse+, 2009)
J/ApJ/709/447 : Chemical composition of OGLE-2007-BLG-514S (Epstein+, 2010)
J/ApJ/725/875 : Chromospheric activity for CPS stars (Isaacson+, 2010)
J/A+A/511/A54 : Magnetic cycles and RVel for 8 stars (Santos+, 2010)
J/ApJ/771/40 : Main-sequence A, F, G & K stars photometry (Boyajian+, 2013)
J/A+A/562/A71 : Abundances of solar neighbourhood dwarfs (Bensby+, 2014)
J/A+A/566/A66 : Correlation of logR'HK with logIHa (Gomes da Silva+, 2014)
J/A+A/594/A100 : K2 new planetary and EB candidates (Barros+, 2016)
J/ApJS/225/32 : Extended abundance analysis of cool stars (Brewer+, 2016)
J/ApJS/226/7 : Planet cand. using K2's 1st yr (Crossfield+, 2016)
J/ApJ/829/23 : Stellar flares from Q0-Q17 Kepler LCs (Davenport, 2016)
J/ApJS/224/2 : K2 EPIC stellar properties for 138600 targets (Huber+, 2016)
J/ApJS/222/14 : Planetary cand. from 1st yr K2 mission (Vanderburg+, 2016)
J/AJ/154/109 : California-Kepler Survey (CKS). III. Radii (Fulton+, 2017)
J/ApJ/844/102 : KIC star plxs from asteroseismology vs Gaia (Huber+, 2017)
J/AJ/154/108 : California-Kepler Survey (CKS). II. (Johnson+, 2017)
J/ApJ/836/77 : High-S/N optical spectra of FGKM stars (Yee+, 2017)
J/A+A/616/A108 : Cool stars chromospheric activity cat. (Boro Saikia+, 2018)
J/ApJS/237/38 : Extended abundance analysis of KOIs (Brewer+, 2018)
J/AJ/156/264 : California-Kepler Survey. VII. Radius gap (Fulton+, 2018)
J/ApJ/860/109 : Keck HIRES sp of subgiants (retired A stars) (Ghezzi+, 2018)
J/ApJ/852/49 : Properties of metal-poor stars in APOGEE DR13 (Hayes+, 2018)
J/AJ/156/277 : Planets from K2 campaigns 5-8 (Livingston+, 2018)
J/AJ/155/136 : Planets orbiting bright stars in K2 C0-10 (Mayo+, 2018)
J/AJ/155/21 : Planet candidates from K2 campaigns 5-8 (Petigura+, 2018)
J/AJ/156/254 : California-Kepler Survey.VI. Multis & singles (Weiss+, 2018)
J/AJ/157/169 : Exoplanets with deep learning in K2 (Dattilo+, 2019)
J/AJ/157/100 : RVel & bisector spans for K2-287 (Jordan+, 2019)
J/ApJS/244/11 : Planet candidates and EBs in K2 campaigns 0-8 (Kruse+, 2019)
J/A+A/623/A114 : Light curve of K2-292 (HD 119130) (Luque+, 2019)
J/ApJ/875/29 : Sp. analysis of the CKS sample. I. (Martinez+, 2019)
J/AJ/159/280 : Gaia-Kepler stellar properties cat. I. (Berger+, 2020)
J/AJ/159/211 : Exoplanets parameters from Kepler and K2 (Cloutier+, 2020)
J/ApJS/247/28 : K2 stars with Gaia & LAMOST data (Hardegree-Ullman+, 2020)
J/A+A/638/A76 : StarHorse data for 5 surveys (Queiroz+, 2020)
J/A+A/635/A43 : Stellar rot. periods from K2 C0-18 (Reinhold+, 2020)
J/ApJ/895/52 : EW and abundances in 211 stars with HARPS (Spina+, 2020)
J/ApJ/920/19 : Sp. analysis of CKS. II. Metallicities (Ghezzi+, 2021)
J/A+A/646/A77 : Activity from AMBRE-HARPS (Gomes da Silva+, 2021)
J/ApJS/254/39 : Exoplanets from TESS first 2yr obs (Guerrero+, 2021)
J/AJ/161/277 : Sample of 45 HαEW outliers (Kiman+, 2021)
J/AJ/162/238 : Radial velocity follow up of Wolf 503 (Polanski+, 2021)
J/AJ/161/82 : Phot. & sp. obs. of TOI-954 and K2-329 (Sha+, 2021)
J/MNRAS/510/3449 : KOI planets and KIC stars from Kepler DR25 (Bashi+, 2022)
J/other/Sci/377.1211 : RV and LC of 8 M dwarf stars with planets (Luque+, 2022)
J/A+A/658/A57 : F-G-K stars activity indicators (Meunier+, 2022)
J/AJ/163/179 : The California-Kepler Survey. X. (Petigura+, 2022)
J/A+A/672/A37 : Activity indicators in M dwarfs (Ibanez Bustos+, 2023)
J/ApJS/265/4 : ExoClock project. III. Ephemerides (Kokori+, 2023)
J/ApJ/946/61 : Hydra sp. of K2 planet-host stars (Loaiza-Tacuri+, 2023)
J/AJ/165/262 : Scaling K2. VI. HIRES stellar param. (Zink+, 2023)
J/ApJ/961/85 : The California-Kepler Survey. XI. Activity (Isaacson+, 2024)
J/MNRAS/532/563 : Solar-type stars Halpha line (Souza dos Santos+, 2024)
J/ApJS/278/52 : Planet masses, radii & orbits from K2 (Howard+, 2025)
J/ApJ/993/233 : Stellar & planetary param. of M-dwarfs (Wanderley+ 2025)
http://exoplanetarchive.ipac.caltech.edu/ : NASA exoplanet archive homepage
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- --- [EPIC]
6- 14 I9 --- EPIC [201110617/251319382] EPIC identifier
16- 21 A6 --- Host Host name
23- 33 F11.7 deg RAdeg [8.7/356.3] Right Ascension (J2000)
35- 45 F11.7 deg DEdeg [-28.8/27.3] Declination (J2000)
47- 55 F9.6 mag Bmag [8.77/18.43] Apparent B band magnitude (1)
57- 63 F7.4 mag Vmag [8.24/17.24] Apparent V band magnitude (1)
65- 73 A9 --- Camp K2 observing campaign number(s)
75- 79 A5 --- Inst Spectrograph identifier (HIRES or TRES)
81- 83 I3 --- Nsp [1/260] Number of spectra
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Note (1): B and V magnitudes (taken from the EPIC catalog and
the NASA Exoplanet Archive).
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.3 0.1nm lambda [4571/6862] Wavelength; Angstroms
10- 13 F4.1 --- Ion [12/26.1] Species identifier (1)
15- 19 F5.3 eV ExPot [0/5.11] Excitation potential
21- 26 F6.3 [-] log(gf) [-5.63/-0.22] log oscillator strength
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Note (1): In the format XX.Y where XX is the atomic number and Y is the
ionization, e.g. 26.0 is neutral iron.
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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- 13 A13 --- ID Identifier (Host name or EPIC)
15- 19 F5.3 --- SHK [0.097/3.8]? Mount Wilson CaII H & K S-index
21- 25 F5.3 --- e_SHK [0.001/0.3]? Uncertainty in SHK
27- 32 F6.3 [-] logRHK [-6.25/-3.89]? log R'HK activity index
34- 38 F5.3 [-] e_logRHK [0.006/0.3]? Uncertainty in logR'HK
40- 44 F5.3 --- Ha [0.026/0.17]? The Hα index
46- 50 F5.3 --- e_Ha [0/0.003]? Uncertainty in Ha
52- 57 F6.3 [-] logIHa [-1.62/-0.77]? The log IHα index
59- 63 F5.3 [-] e_logIHa [0/0.03]? Uncertainty in logIHa
65- 68 I4 K Teff [4474/6539]? Effective temperature
70- 72 I3 K e_Teff [4/190]? Uncertainty in Teff
74- 78 F5.3 [cm/s2] log(g) [2.54/4.94]? log surface gravity
80- 84 F5.3 [cm/s2] e_log(g) [0.01/0.6]? Uncertainty in log(g)
86- 90 F5.3 [-] A(Fe) [6.5/8.11]? log final iron abundance
92- 96 F5.3 [-] e_A(Fe) [0.004/0.2]? Uncertainty in A(Fe)
98-103 F6.3 km/s VTurb [0.15/16.5]? Microtrubulent velocity
105-110 F6.3 km/s e_VTurb [0.02/35]? Uncertainty in VTurb
112-116 F5.3 [-] A(Mg) [6.57/8.3]? log final magnesium abundance
118-122 F5.3 [-] e_A(Mg) [0/0.14]? Uncertainty in A(Mg)
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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- 13 A13 --- ID Identifier (Host name or EPIC)
15- 19 F5.3 Rsun RsSB [0.5/8.4] Stefan-Boltzmann law derived
stellar radius
21- 25 F5.3 Rsun e_RsSB [0.005/1.7] Uncertainty in RsSB
27- 31 F5.3 Rsun RsPARAM [0.39/3.7]? PARAM code derived stellar radius
33- 37 F5.3 Rsun e_RsPARAM [0/0.3]? Uncertainty in RsPARAM
39- 43 F5.3 Msun MsPARAM [0.45/1.5]? PARAM code derived stellar mass
45- 49 F5.3 Msun e_MsPARAM [0/0.06]? Uncertainty in MsPARAM
51- 56 F6.3 Rsun Rsiso [0.53/10.5] Isochrones code derived stellar
radius
58- 62 F5.3 Rsun E_Rsiso [0.007/3.5] Upper uncertainty in Rsiso
64- 68 F5.3 Rsun e_Rsiso [0.007/4.7] Lower uncertainty in Rsiso
70- 74 F5.3 Msun Msiso [0.56/3.1] Isochrones code derived stellar
mass
76- 80 F5.3 Msun E_Msiso [0.004/0.7] Upper uncertainty in Msiso
82- 86 F5.3 Msun e_Msiso [0.006/0.9] Lower uncertainty in Msiso
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 16 A16 --- Planet Planet identifier
18- 26 F9.3 ppm DeltaF [73/28460] Transit depth in parts per million
28- 33 F6.3 Rgeo RpSB [0.7/79] Stefan-Boltzmann law derived
planetary radius
35- 40 F6.3 Rgeo e_RpSB [0.009/16]? Uncertainty in SB-Rp
42- 47 F6.3 Rgeo RpPARAM [0.7/23]? PARAM code derived planetary radius
49- 53 F5.3 Rgeo e_RpPARAM [0.001/2.4]? Uncertainty in PARAM-Rp
55- 60 F6.3 Rgeo Rpiso [0.7/99]? Isochrones code derived planetary
radius
62- 67 F6.3 Rgeo E_Rpiso [0.015/33]? Upper uncertainty in iso-Rp
69- 74 F6.3 Rgeo e_Rpiso [0.014/44]? Lower uncertainty in iso-Rp
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History:
From electronic version of the journal
License: CC-BY-4.0
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 29-Jun-2026