K2-HERMES II. Planet-candidate properties from K2 Campaigns 1-13

Wittenmyer, Robert A.; Clark, Jake T.; Sharma, Sanjib; Stello, Dennis; Horner, Jonathan; Kane, Stephen R.; Stevens, Catherine; Wright, D. E.; Spina, L.; Čotar, Klemen; Asplund, Martin; Bland‐Hawthorn, J.; Buder, Sven; Casey, Andrew R.; Silva, Gayandhi M. De; D’Orazi, V.; Freeman, K. C.; Kos, Janez; Lewis, Geraint F.; Lin, Jane; Lind, Karin; Martell, Sarah L.; Simpson, Jeffrey D.; Zucker, D. B.; Zwitter, T.

doi:10.1093/mnras/staa1528

“…Analysis of asteroseismic and spectroscopic data together is key for GALAH+ DR3, and enables in-depth exploration of the structure and history of the Milky Way (e.g., Sharma et al 2016Sharma et al , 2019. The spectroscopic data also provide essential insights for the planet hosting stars identified in K2 data (Wittenmyer et al 2018(Wittenmyer et al , 2020.…”

Section: Target Selectionmentioning

confidence: 99%

The GALAH Survey: second data release

Buder

¹

,

Asplund

²

,

Duong

³

et al. 2018

Monthly Notices of the Royal Astronomical Society

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The Galactic Archaeology with HERMES (GALAH) survey is a large-scale stellar spectroscopic survey of the Milky Way and designed to deliver chemical information complementary to a large number of stars covered by the Gaia mission. We present the GALAH second public data release (GALAH DR2) containing 342,682 stars. For these stars, the GALAH collaboration provides stellar parameters and abundances for up to 23 elements to the community. Here we present the target selection, observation, data reduction and detailed explanation of how the spectra were analysed to estimate stellar parameters and element abundances. For the stellar analysis, we have used a multi-step approach. We use the physics-driven spectrum synthesis of Spectroscopy Made Easy (SME) to derive stellar labels (T eff , log g, [Fe/H], [X/Fe], v mic , v sin i, A K S ) for a representative training set of stars. This information is then propagated to the whole survey with the data-driven method of The Cannon. Special care has been exercised in the spectral synthesis to only consider spectral lines that have reliable atomic input data and are little affected by blending lines. Departures from local thermodynamic equilibrium (LTE) are considered for several key elements, including Li, O, Na, Mg, Al, Si, and Fe, using 1D stellar atmosphere models. Validation tests including repeat observations, Gaia benchmark stars, open and globular clusters, and K2 asteroseismic targets lend confidence to our methods and results. Combining the GALAH DR2 catalogue with the kinematic information from Gaia will enable a wide range of Galactic Archaeology studies, with unprecedented detail, dimensionality, and scope.

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“…There are 18 K2 candidates that have problematic radii with 13 having been found to be false positives in previous work (Wittenmyer et al 2018(Wittenmyer et al , 2020…”

Section: R E F I N I N G P L a N E Ta Ry S Y S T E M Smentioning

confidence: 96%

The GALAH Survey: improving our understanding of confirmed and candidate planetary systems with large stellar surveys

Clark

¹

,

Wright

²

,

Wittenmyer

³

et al. 2021

Monthly Notices of the Royal Astronomical Society

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Pioneering photometric, astrometric, and spectroscopic surveys are helping exoplanetary scientists better constrain the fundamental properties of stars within our galaxy, and the planets these stars host. In this study, we use the third data release from the stellar spectroscopic GALAH Survey, coupled with astrometric data of eDR3 from the Gaia satellite, and other data from NASA’s Exoplanet Archive, to refine our understanding of 279 confirmed and candidate exoplanet host stars and their exoplanets. This homogenously analysed data set comprises 105 confirmed exoplanets, along with 146 K2 candidates, 95 TESS Objects of Interest (TOIs) and 52 Community TOIs (CTOIs). Our analysis significantly shifts several previously (unknown) planet parameters while decreasing the uncertainties for others; Our radius estimates suggest that 35 planet candidates are more likely brown dwarfs or stellar companions due to their new radius values. We are able to refine the radii and masses of WASP-47 e, K2-106 b, and CoRoT-7 b to their most precise values yet, to less than 2.3% and 8.5% respectively. We also use stellar rotational values from GALAH to show that most planet candidates will have mass measurements that will be tough to obtain with current ground-based spectrographs. With GALAH’s chemical abundances, we show through chemo-kinematics that there are five planet-hosts that are associated with the galaxy’s thick disc, including NGTS-4, K2-183 and K2-337. Finally, we show there is no statistical difference between the chemical properties of hot Neptune and hot rocky exoplanet hosts, with the possibility that short-period rocky worlds might be the remnant cores of hotter, gaseous worlds.

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“…Crossfield et al (2018) then independently identified K2-199 b and c as planet candidates in the C17 photometry. Recently, Wittenmyer et al (2020) reported updated semimajor axis and radius measurements for the three planets using stellar properties from observations with the High Efficiency and Resolution Multi-Element Spectrograph on the Anglo-Australian Telescope (Simpson et al 2016). In Section 2.5, we highlight the improvement to the precision of the planet orbital periods and mid-transit times by including both campaigns of photometry in our analysis.…”

Section: K2-182 and K2-199 Photometrymentioning

confidence: 99%

Another Superdense Sub-Neptune in K2-182 b and Refined Mass Measurements for K2-199 b and c*

Murphy

¹

,

Kosiarek

²

,

Batalha

³

et al. 2021

AJ

9

0

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We combine multiple campaigns of K2 photometry with precision radial velocity measurements from Keck-HIRES to measure the masses of three sub-Neptune-sized planets. We confirm the planetary nature of the massive sub-Neptune K2-182 b (P b = 4.7 days, R b = 2.69 R ⊕) and derive refined parameters for K2-199 b and c (P b = 3.2 days, R b = 1.73 R ⊕ and P c = 7.4 days, R c = 2.85 R ⊕). These planets provide valuable data points in the mass–radius plane, especially as TESS continues to reveal an increasingly diverse sample of sub-Neptunes. The moderately bright (V = 12.0 mag) early K dwarf K2-182 (EPIC 211359660) was observed during K2 campaigns 5 and 18. We find that K2-182 b is potentially one of the densest sub-Neptunes known to date (20 ± 5 M ⊕ and 5.6 ± 1.4 g cm−3). The K5V dwarf K2-199 (EPIC 212779596; V = 12.3 mag), observed in K2 campaigns 6 and 17, hosts two recently confirmed planets. We refine the orbital and planetary parameters for K2-199 b and c by modeling both campaigns of K2 photometry and adding 12 Keck-HIRES measurements to the existing radial velocity data set (N = 33). We find that K2-199 b is likely rocky, at 6.9 ± 1.8 M ⊕ and 7.2 − 2.0 + 2.1 g cm−3, and that K2-199 c has an intermediate density at 12.4 ± 2.3 M ⊕ and 2.9 − 0.6 + 0.7 g cm−3. We contextualize these planets on the mass–radius plane, discuss a small but intriguing population of “superdense” sub-Neptunes (R p < 3 R ⊕, M p >20 M ⊕), and consider our prospects for the planets’ atmospheric characterization.

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K2-HERMES II. Planet-candidate properties from K2 Campaigns 1-13

Cited by 11 publications

References 97 publications

The GALAH Survey: second data release

The GALAH Survey: second data release

The GALAH Survey: improving our understanding of confirmed and candidate planetary systems with large stellar surveys

Another Superdense Sub-Neptune in K2-182 b and Refined Mass Measurements for K2-199 b and c*

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