Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCharacterizing K2 Candidate Planetary Systems Orbiting Low-Mass Stars IV: Updated Properties for 86 Cool Dwarfs Observed During Campaigns 1-17
179
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present revised stellar properties for 172 K2 target stars that were identified as possible hosts of transiting planets during Campaigns 1-17. Using medium-resolution near-infrared spectra acquired with the NASA Infrared Telescope Facility/SpeX and Palomar/TripleSpec, we found that 86 of our targets were bona fide cool dwarfs, 74 were hotter dwarfs, and 12 were giants. Combining our spectroscopic metallicities with Gaia parallaxes and archival photometry, we derived photometric stellar parameters and compared them to our spectroscopic estimates. Although our spectroscopic and photometric radius and temperature estimates are consistent, our photometric mass estimates are systematically 0.11 solar masses (34%) higher than our spectroscopic mass estimates for the least massive stars (photometric mass estimates < 0.4 solar masses). Adopting the photometric parameters and comparing our results to parameters reported in the Ecliptic Plane Input Catalog, our revised stellar radii are 0.15 solar radii (40%) larger and our revised stellar effective temperatures are roughly 65K cooler. Correctly determining the properties of K2 target stars is essential for characterizing any associated planet candidates, estimating the planet search sensitivity, and calculating planet occurrence rates. Even though Gaia parallaxes have increased the power of photometric surveys, spectroscopic characterization remains essential for determining stellar metallicities and investigating correlations between stellar metallicity and planetary properties.
rate research
Read More
We present near-infrared spectra for 144 candidate planetary systems identified during Campaigns 1-7 of the NASA K2 Mission. The goal of the survey was to characterize planets orbiting low-mass stars, but our IRTF/SpeX and Palomar/TripleSpec spectroscopic observations revealed that 49% of our targets were actually giant stars or hotter dwarfs reddened by interstellar extinction. For the 72 stars with spectra consistent with classification as cool dwarfs (spectral types K3 - M4), we refined their stellar properties by applying empirical relations based on stars with interferometric radius measurements. Although our revised temperatures are generally consistent with those reported in the Ecliptic Plane Input Catalog (EPIC), our revised stellar radii are typically 0.13 solar radii (39%) larger than the EPIC values, which were based on model isochrones that have been shown to underestimate the radii of cool dwarfs. Our improved stellar characterizations will enable more efficient prioritization of K2 targets for follow-up studies.
We recently used near-infrared spectroscopy to improve the characterization of 76 low-mass stars around which K2 had detected 79 candidate transiting planets. Thirty of these worlds were new discoveries that have not previously been published. We calculate the false positive probabilities that the transit-like signals are actually caused by non-planetary astrophysical phenomena and reject five new transit-like events and three previously reported events as false positives. We also statistically validate 18 planets (eight of which were previously unpublished), confirm the earlier validation of 21 planets, and announce 17 newly discovered planet candidates. Revising the properties of the associated planet candidates based on the updated host star characteristics and refitting the transit photometry, we find that our sample contains 20 planets or planet candidates with radii smaller than 1.25 Earth radii, 20 super-Earths (1.25-2 Earth radii), 20 small Neptunes (2-4 Earth radii), three large Neptunes (4-6 Earth radii), and eight giant planets (> 6 Earth radii). Most of these planets are highly irradiated, but EPIC 206209135.04 (K2-72e, Rp = 1.29 (-0.13/+0.14) Earth radii), EPIC 211988320.01 (Rp = 2.86 (-0.15/+0.16) Earth radii), and EPIC 212690867.01 (Rp = 2.20 (-0.18/+0.19) Earth radii) orbit within optimistic habitable zone boundaries set by the recent Venus inner limit and the early Mars outer limit. In total, our planet sample includes eight moderately-irradiated 1.5-3 Earth radius planet candidates (Fp < 20 F_Earth) orbiting brighter stars (Ks < 11) that are well-suited for atmospheric investigations with Hubble, Spitzer, and/or the James Webb Space Telescope. Five validated planets orbit relatively bright stars (Kp < 12.5) and are expected to yield radial velocity semi-amplitudes of at least 2 m/s.
K2-55b is a Neptune-sized planet orbiting a K7 dwarf with a radius of $0.715^{+0.043}_{-0.040}R_odot$, a mass of $0.688pm0.069 M_odot$, and an effective temperature of $4300^{+107}_{-100}$K. Having characterized the host star using near-infrared spectra obtained at IRTF/SpeX, we observed a transit of K2-55b with Spitzer/IRAC and confirmed the accuracy of the original K2 ephemeris for future follow-up transit observations. Performing a joint fit to the Spitzer/IRAC and K2 photometry, we found a planet radius of $4.41^{+0.32}_{-0.28} R_oplus$, an orbital period of $2.84927265_{-6.42times10^{-6}}^{+6.87times10^{-6}}$ days, and an equilibrium temperature of roughly 900K. We then measured the planet mass by acquiring twelve radial velocity (RV) measurements of the system using HIRES on the 10m Keck I Telescope. Our RV data set precisely constrains the mass of K2-55b to $43.13^{+5.98}_{-5.80} M_oplus$, indicating that K2-55b has a bulk density of $2.8_{-0.6}^{+0.8}$ g cm$^{-3}$ and can be modeled as a rocky planet capped by a modest H/He envelope ($M_{rm envelope} = 12pm3% M_p$). K2-55b is denser than most similarly sized planets, raising the question of whether the high planetary bulk density of K2-55b could be attributed to the high metallicity of K2-55. The absence of a substantial volatile envelope despite the large mass of K2-55b poses a challenge to current theories of gas giant formation. We posit that K2-55b may have escaped runaway accretion by migration, late formation, or inefficient core accretion or that K2-55b was stripped of its envelope by a late giant impact.
We have created a catalogue of variable stars found from a search of the publicly available K2 mission data from Campaigns 1 and 0. This catalogue provides the identifiers of 8395 variable stars, including 199 candidate eclipsing binaries with periods up to 60d and 3871 periodic or quasi-periodic objects, with periods up to 20d for Campaign 1 and 15d for Campaign 0. Lightcurves are extracted and detrended from the available data. These are searched using a combination of algorithmic and human classification, leading to a classifier for each object as an eclipsing binary, sinusoidal periodic, quasi periodic, or aperiodic variable. The source of the variability is not identified, but could arise in the non-eclipsing binary cases from pulsation or stellar activity. Each object is cross-matched against variable star related guest observer proposals to the K2 mission, which specifies the variable type in some cases. The detrended lightcurves are also compared to lightcurves currently publicly available. The resulting catalogue is made available online via the MAST archive at https://archive.stsci.edu/prepds/k2varcat/, and gives the ID, type, period, semi-amplitude and range of the variation seen. We also make available the detrended lightcurves for each object.
We analyzed the photometry of 20038 cool stars from campaigns 12, 13, 14 and 15 of the K2 mission in order to detect, characterize and validate new planetary candidates transiting low-mass stars. We present a catalogue of 25 new periodic transit-like signals in 22 stars, of which we computed the parameters of the stellar host for 19 stars and the planetary parameters for 21 signals. We acquired speckle and AO images, and also inspected archival Pan-STARRS1 images and Gaia DR2 to discard the presence of close stellar companions and to check possible transit dilutions due to nearby stars. False positive probability (FPP) was computed for 22 signals, obtaining FPP < $1%$ for 17. We consider 12 of them as statistically validated planets. One signal is a false positive and the remaining 12 signals are considered as planet candidates. 20 signals have orbital period P$_{rm orb} < 10$ $d$, 2 have $10$ $d < $ P$_{rm orb} < 20$ $d$ and 3 have P$_{rm orb} > 20$ $d$. Regarding radii, 11 candidates and validated planets have computed radius R $<2 R_{oplus}$, 9 have $2 R_{oplus} <$ R $< 4 R_{oplus}$, and 1 has R $>4 R_{oplus}$. 2 validated planets and 2 candidates are located in moderately bright stars ($m_{kep}<13$) and 2 validated planets and 3 candidates have derived orbital radius within the habitable zone according to optimistic models. Of special interest is the validated warm super-Earth EPIC 248616368b (T$rm_{eq} = 318^{+24}_{-43} , K$, S$_{rm p} = 1.7pm 0.2 , S_{oplus}$, R$_{rm p} = 2.1pm 0.1 , R_{oplus} $), located in a m$rm_{kep}$ = 14.13 star.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
