- ID:
- ivo://CDS.VizieR/J/AJ/159/98
- Title:
- I-band LC of the microlensing event KMT-2016-BLG-1836
- Short Name:
- J/AJ/159/98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of a super-Jovian planet in the microlensing event KMT-2016-BLG-1836, which was found by the Korea Microlensing Telescope Network (KMTNet) high-cadence observations ({Gamma}~4/hr). The planet-host mass ratio q~0.004. A Bayesian analysis indicates that the planetary system is composed of a super-Jovian M_planet_=2.2_-1.1_^+1.9^M_J_ planet orbiting an M or K dwarf, M_host_=0.49_-0.25_^+0.38^M_{sun}_, at a distance of D_L_=7.1_-2.4_^+0.8^kpc. The projected planet-host separation is 3.5_-0.9_^+1.1^au, implying that the planet is located beyond the snow line of the host star. Future high-resolution images can potentially strongly constrain the lens brightness and thus the mass and distance of the planetary system. Without considering detailed detection efficiency, selection, or publication biases, we find a potential mass-ratio desert at -3.7<~logq<~-3.0 for the 31 published KMTNet planets.
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- ID:
- ivo://CDS.VizieR/J/AJ/162/96
- Title:
- I-band light curve of KMT-2016-BLG-2605 with KMTNet
- Short Name:
- J/AJ/162/96
- Date:
- 11 Mar 2022 14:37:06
- Publisher:
- CDS
- Description:
- With a planet-host mass ratio q=0.012{+/-}0.001, KMT-2016-BLG-2605 has the shortest Einstein timescale, tE=3.41{+/-}0.13days, of any planetary microlensing event to date. This prompts us to examine the full sample of seven short (tE<7days) planetary events with good q measurements. We find that six have clustered Einstein radii {theta}E=115{+/-}20{mu}as and lens-source relative proper motions {mu}rel~9.5{+/-}2.5mas/yr. For the seventh, these two quantities could not be measured. These distributions are consistent with a Galactic bulge population of very low mass (VLM) hosts near the hydrogen-burning limit. This conjecture could be verified by imaging at first adaptive optics light on next-generation (30m) telescopes. Based on a preliminary assessment of the sample, "planetary" companions (i.e., below the deuterium-burning limit) are divided into "genuine planets," formed in their disks by core accretion, and VLM brown dwarfs, which form like stars. We discuss techniques for expanding the sample, which include taking account of the peculiar "anomaly-dominated" morphology of the KMT-2016-BLG-2605 light curve.
- ID:
- ivo://CDS.VizieR/J/AJ/162/267
- Title:
- I-band light curve of OGLE-2019-BLG-1058 with KMTNet
- Short Name:
- J/AJ/162/267
- Date:
- 25 Mar 2022 06:06:33
- Publisher:
- CDS
- Description:
- We show that because the conditions for producing terrestrial microlens parallax (TPRX; i.e., a nearby disk lens) will also tend to produce a large lens-source relative proper motion ({mu}rel), source proper motion ({mu}S) measurements in general provide a strong test of TPRX signals, which Gould & Yee (2013) showed were an important probe of free-floating planet (FFP) candidates. As a case study, we report a single-lens/single-source microlensing event designated as OGLE-2019-BLG-1058. For this event, the short timescale (~2.5days) and very fast {mu}rel (~17.6mas/yr) suggest that this isolated lens is an FFP candidate located in the disk of our Galaxy. For this event, we find a TPRX signal consistent with a disk FFP, but at low significance. A direct measurement of the {mu}S shows that the large {mu}rel is due to an extreme {mu}S, and thus, the lens is consistent with being a very-low-mass star in the bulge and the TPRX measurement is likely spurious. By contrast, we show how a precise measurement of {mu}S with the mean properties of the bulge proper motion distribution would have given the opposite result; i.e., provided supporting evidence for an FFP in the disk and the TPRX measurement.
- ID:
- ivo://CDS.VizieR/J/AJ/159/116
- Title:
- I-band light curves of OGLE-2015-BLG-1771Lb
- Short Name:
- J/AJ/159/116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery and the analysis of the short (t_E_<5days) planetary microlensing event, OGLE-2015-BLG-1771. The event was discovered by the Optical Gravitational Lensing Experiment, and the planetary anomaly (at I~19) was captured by The Korea Microlensing Telescope Network. The event has three surviving planetary models that explain the observed light curves, with planet-host mass ratio q~5.4x10^-3^, 4.5x10^-3^ and 4.5x10^-2^, respectively. The first model is the best-fit model, while the second model is disfavored by {Delta}_{chi}^2^_~3. The last model is strongly disfavored by {Delta}_{chi}^2^_~15 but not ruled out. A Bayesian analysis using a Galactic model indicates that the first two models are probably composed of a Saturn-mass planet orbiting a late M dwarf, while the third one could consist of a super-Jovian planet and a mid-mass brown dwarf. The source-lens relative proper motion is {mu}_rel_~9mas/yr, so the source and lens could be resolved by current adaptive-optics instruments in 2020 if the lens is luminous.
- ID:
- ivo://CDS.VizieR/J/AJ/157/169
- Title:
- Identifying exoplanets with deep learning in K2
- Short Name:
- J/AJ/157/169
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- For years, scientists have used data from NASA's Kepler Space Telescope to look for and discover thousands of transiting exoplanets. In its extended K2 mission, Kepler observed stars in various regions of the sky all across the ecliptic plane, and therefore in different galactic environments. Astronomers want to learn how the populations of exoplanets are different in these different environments. However, this requires an automatic and unbiased way to identify exoplanets in these regions and rule out false-positive signals that mimic transiting planet signals. We present a method for classifying these exoplanet signals using deep learning, a class of machine learning algorithms that have become popular in fields ranging from medical science to linguistics. We modified a neural network previously used to identify exoplanets in the Kepler field to be able to identify exoplanets in different K2 campaigns that exist in a range of galactic environments. We train a convolutional neural network, called AstroNet-K2, to predict whether a given possible exoplanet signal is really caused by an exoplanet or a false positive. AstroNet-K2 is highly successful at classifying exoplanets and false positives, with accuracy of 98% on our test set. It is especially efficient at identifying and culling false positives, but for now, it still needs human supervision to create a complete and reliable planet candidate sample. We use AstroNet-K2 to identify and validate two previously unknown exoplanets. Our method is a step toward automatically identifying new exoplanets in K2 data and learning how exoplanet populations depend on their galactic birthplace.
- ID:
- ivo://CDS.VizieR/J/MNRAS/474/2094
- Title:
- Inferring probabilistic stellar rotation periods
- Short Name:
- J/MNRAS/474/2094
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Variability in the light curves of spotted, rotating stars is often non-sinusoidal and quasi-periodic - spots move on the stellar surface and have finite lifetimes, causing stellar flux variations to slowly shift in phase. A strictly periodic sinusoid therefore cannot accurately model a rotationally modulated stellar light curve. Physical models of stellar surfaces have many drawbacks preventing effective inference, such as highly degenerate or high-dimensional parameter spaces. In this work, we test an appropriate effective model: a Gaussian Process with a quasi-periodic covariance kernel function. This highly flexible model allows sampling of the posterior probability density function of the periodic parameter, marginalizing over the other kernel hyperparameters using a Markov Chain Monte Carlo approach. To test the effectiveness of this method, we infer rotation periods from 333 simulated stellar light curves, demonstrating that the Gaussian process method produces periods that are more accurate than both a sine-fitting periodogram and an autocorrelation function method. We also demonstrate that it works well on real data, by inferring rotation periods for 275 Kepler stars with previously measured periods. We provide a table of rotation periods for these and many more, altogether 1102 Kepler objects of interest, and their posterior probability density function samples. Because this method delivers posterior probability density functions, it will enable hierarchical studies involving stellar rotation, particularly those involving population modelling, such as inferring stellar ages, obliquities in exoplanet systems, or characterizing star-planet interactions. The code used to implement this method is available online (https://github.com/RuthAngus/GProtation/).
- ID:
- ivo://CDS.VizieR/J/AJ/160/253
- Title:
- Infrared photometry of late-type dwarfs in Kepler Field
- Short Name:
- J/AJ/160/253
- Date:
- 08 Dec 2021
- Publisher:
- CDS
- Description:
- While it is well-established that giant-planet occurrence rises rapidly with host star metallicity, it is not yet clear if small-planet occurrence around late-type dwarf stars depends on host star metallicity. Using the Kepler Data Release 25 planet candidate list and its completeness data products, we explore planet occurrence as a function of metallicity in the Kepler field's late-type dwarf stellar population. We find that planet occurrence increases with metallicity for all planet radii Rp down to at least Rp~2R{Earth}, and that in the range 2R{Earth}<~Rp<~5R{Earth}, planet occurrence scales linearly with metallicity Z. Extrapolating our results, we predict that short-period planets with Rp<~2R{Earth} should be rare around early-M dwarf stars with [M/H]<~-0.5 or late-M dwarf stars with [M/H]<~+0.0. This dependence of planet occurrence on metallicity observed in the Kepler field emphasizes the need to control for metallicity in estimates of planet occurrence for late-type dwarf stars like those targeted by Kepler's K2 extension and the Transiting Exoplanet Survey Satellite. We confirm the theoretical expectation that the small-planet occurrence-host star metallicity relation is stronger for low-mass stars than for solar-type stars. We establish that the expected solid mass in planets around late-type dwarfs in the Kepler field is comparable to the total amount of planet-making solids in their protoplanetary disks. We argue that this high efficiency of planet formation favors planetesimal accretion over pebble accretion as the origin of the small planets observed by Kepler around late-type dwarf stars.
- ID:
- ivo://CDS.VizieR/J/AJ/160/201
- Title:
- Infrared transmission spectrum for Kepler-79d
- Short Name:
- J/AJ/160/201
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Extremely low-density planets ("super-puffs") are a small but intriguing subset of the transiting planet population. With masses in the super-Earth range (1-10M{Earth}) and radii akin to those of giant planets (>4R{Earth}), their large envelopes may have been accreted beyond the water snow line and many appear to be susceptible to catastrophic mass loss. Both the presence of water and the importance of mass loss can be explored using transmission spectroscopy. Here, we present new Hubble space telescope WFC3 spectroscopy and updated Kepler transit depth measurements for the super-puff Kepler-79d. We do not detect any molecular absorption features in the 1.1-1.7{mu}m WFC3 bandpass, and the combined Kepler and WFC3 data are consistent with a flat-line model, indicating the presence of aerosols in the atmosphere. We compare the shape of Kepler-79d transmission spectrum to predictions from a microphysical haze model that incorporates an outward particle flux due to ongoing mass loss. We find that photochemical hazes offer an attractive explanation for the observed properties of super-puffs like Kepler-79d, as they simultaneously render the near-infrared spectrum featureless and reduce the inferred envelope mass-loss rate by moving the measured radius (optical depth unity surface during transit) to lower pressures. We revisit the broader question of mass-loss rates for super-puffs and find that the age estimates and mass-loss rates for the majority of super-puffs can be reconciled if hazes move the photosphere from the typically assumed pressure of ~10mbar to ~10{mu}bar.
- ID:
- ivo://CDS.VizieR/J/AJ/162/82
- Title:
- IRD and HPF spectra of TRAPPIST-1b,e and f
- Short Name:
- J/AJ/162/82
- Date:
- 11 Mar 2022
- Publisher:
- CDS
- Description:
- We obtained high-resolution spectra of the ultracool M-dwarf TRAPPIST-1 during the transit of its planet "b" using two high-dispersion near-infrared spectrographs, the Infrared Doppler (IRD) instrument on the Subaru 8.2m telescope, and the Habitable Zone Planet Finder (HPF) instrument on the 10m Hobby-Eberly Telescope. These spectroscopic observations are complemented by a photometric transit observation for planet "b" using the APO/ARCTIC, which assisted us in capturing the correct transit times for our transit spectroscopy. Using the data obtained by the new IRD and HPF observations, as well as the prior transit observations of planets "b," "e" and "f" from IRD, we attempt to constrain the atmospheric escape of the planet using the Hei triplet 10830{AA} absorption line. We do not detect evidence for any primordial extended H-He atmospheres in all three planets. To limit any planet-related absorption, we place an upper limit on the equivalent widths of <7.754m{AA} for planet "b," <10.458m{AA} for planet "e," <4.143m{AA} for planet "f" at 95% confidence from the IRD data, and <3.467m{AA} for planet "b" at 95% confidence from HPF data. Using these limits along with a solar- like composition isothermal Parker wind model, we attempt to constrain the mass-loss rates for the three planets. For TRAPPIST-1b, our models exclude the highest possible energy-limited rate for a wind temperature <5000K. This nondetection of extended atmospheres with low mean-molecular weights in all three planets aids in further constraining their atmospheric composition by steering the focus toward the search of high-molecular-weight species in their atmospheres.
- ID:
- ivo://CDS.VizieR/J/AJ/159/18
- Title:
- Jovian-type planets around M dwarfs with MIRI/JWST
- Short Name:
- J/AJ/159/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The upcoming launch of the James Webb Space Telescope (JWST) will dramatically increase our understanding of exoplanets, particularly through direct imaging. Microlensing and radial velocity surveys indicate that some M dwarfs host long-period giant planets. Some of these planets will likely be just a few parsecs away and a few astronomical units from their host stars, a parameter space that cannot be probed by existing high-contrast imagers. We studied whether the coronagraphs on the Mid-infrared Instrument on JWST can detect Jovian-type planets around nearby M dwarfs. For a sample of 27 very nearby M dwarfs, we simulated a sample of Saturn-Jupiter-mass planets with three atmospheric configurations and three orbital separations, observed in three different filters. We found that the f1550c 15.5 {mu}m filter is best suited for detecting Jupiter-like planets. Jupiter-like planets with patchy cloud cover, 2 au from their star, are detectable at 15.5 {mu}m around 14 stars in our sample, while Jupiters with clearer atmospheres are detectable around all stars in the sample. Saturns were most detectable at 10.65 and 11.4 {mu}m (f1065c and f1140c filters), but only with cloud-free atmospheres and within 3 pc (six stars). Surveying all 27 stars would take <170 hr of JWST integration time, or just a few hours for a shorter survey of the most favorable targets. There is one potentially detectable known planet in our sample: GJ 832 b. Observations aimed at detecting this planet should occur in 2024-2026, when the planet is maximally separated from the star.
