102 research outputs found
No timing variations observed in third transit of snow-line exoplanet Kepler-421b
We observed Kepler-421 during the anticipated third transit of the snow-line exoplanet Kepler-421b in order to constrain the existence and extent of transit timing variations (TTVs). Previously, the Kepler Spacecraft only observed two transits of Kepler-421b leaving the planet's transit ephemeris unconstrained. Our visible light, time-series observations from the 4.3-meter Discovery Channel Telescope were designed to capture pre-transit baseline and the partial transit of Kepler-421b barring significant TTVs. We use the light curves to assess the probabilities of various transit models using both the posterior odds ratio and the Bayesian Information Criterion (BIC) and find that a transit model with no TTVs is favored to 3.6-sigma confidence. These observations suggest that Kepler-421b is either alone in its system or is only experiencing minor dynamic interactions with an unseen companion. With the Kepler-421b ephemeris constrained, we calculate future transit times and discuss the opportunity to characterize the atmosphere of this cold, long-period exoplanet via transmission spectroscopy. Our investigation emphasizes the difficulties associated with observing long-period exoplanet transits and the consequences that arise from failing to refine transit ephemerides
Kepler Transit Depths Contaminated by a Phantom Star
We present ground-based observations from the Discovery Channel Telescope
(DCT) of three transits of Kepler-445c---a supposed super-Earth exoplanet with
properties resembling GJ 1214b---and demonstrate that the transit depth is
approximately 50 percent shallower than the depth previously inferred from
Kepler Spacecraft data. The resulting decrease in planetary radius
significantly alters the interpretation of the exoplanet's bulk composition.
Despite the faintness of the M4 dwarf host star, our ground-based photometry
clearly recovers each transit and achieves repeatable 1-sigma precision of
approximately 0.2 percent (2 millimags). The transit parameters estimated from
the DCT data are discrepant with those inferred from the Kepler data to at
least 17-sigma confidence. This inconsistency is due to a subtle miscalculation
of the stellar crowding metric during the Kepler pre-search data conditioning
(PDC). The crowding metric, or CROWDSAP, is contaminated by a non-existent
"phantom star" originating in the USNO-B1 catalog and inherited by the Kepler
Input Catalog (KIC). Phantom stars in the KIC are likely rare, but they have
the potential to affect statistical studies of Kepler targets that use the PDC
transit depths for a large number of exoplanets where individual follow-up
observation of each is not possible. The miscalculation of Kepler-445c's
transit depth emphasizes the importance of stellar crowding in the Kepler data,
and provides a cautionary tale for the analysis of data from the Transiting
Exoplanet Survey Satellite (TESS), which will have even larger pixels than
Kepler.Comment: 11 pages, 10 figures, 5 tables. Accepted for publication in AJ.
Transit light curves will be available from AJ as Db
TESS Observations of Kepler systems with Transit Timing Variations
We identify targets in the Kepler field that may be characterized by transit
timing variations (TTVs) and are detectable by the Transiting Exoplanet Survey
Satellite (TESS). Despite the reduced signal-to-noise ratio of TESS transits
compared to Kepler, we recover 48 transits from 13 systems in Sectors 14, 15,
26, 40 and 41. We find strong evidence of a nontransiting perturber orbiting
Kepler-396 (KOI-2672) and explore two possible cases of a third planet in that
system that could explain the measured transit times. We update the ephemerides
and mass constraints where possible at KOI-70 (Kepler-20), KOI-82 (Kepler-102),
KOI-94 (Kepler-89), KOI-137 (Kepler-18), KOI-244 (Kepler-25), KOI-245
(Kepler-37), KOI-282 (Kepler-130), KOI-377 (Kepler-9), KOI-620 (Kepler-51),
KOI-806 (Kepler-30), KOI-1353 (Kepler-289) and KOI-1783 (Kepler-1662).Comment: 26 pages, 9 figure
Multiwavelength transit observations of the candidate disintegrating planetesimals orbiting WD 1145+017
We present multiwavelength, ground-based follow-up photometry of the white dwarf WD 1145+017, which has recently been suggested to be orbited by up to six or more short-period, low-mass, disintegrating planetesimals. We detect nine significant dips in flux of between 10% and 30% of the stellar flux in our ~32 hr of photometry, suggesting that WD 1145+017 is indeed being orbited by multiple, short-period objects. Through fits to the asymmetric transits that we observe, we confirm that the transit egress is usually longer than the ingress, and that the transit duration is longer than expected for a solid body at these short periods, all suggesting that these objects have cometary tails streaming behind them. The precise orbital periods of the planetesimals are unclear, but at least one object, and likely more, have orbital periods of ~4.5 hr. We are otherwise unable to confirm the specific periods that have been reported, bringing into question the long-term stability of these periods. Our high-precision photometry also displays low-amplitude variations, suggesting that dusty material is consistently passing in front of the white dwarf, either from discarded material from these disintegrating planetesimals or from the detected dusty debris disk. We compare the transit depths in the V- and R-bands of our multiwavelength photometry, and find no significant difference; therefore, for likely compositions, the radius of single-size particles in the cometary tails streaming behind the planetesimals must be ~0.15 μm or larger, or ~0.06 μm or smaller, with 2σ confidence
Multiple Explanations for the Single Transit of KIC 5951458 Based on Radial Velocity Measurements Extracted with a Novel Matched-template Technique
Planetary systems that show single-transit events are a critical pathway to increasing the yield of long-period exoplanets from transit surveys. From the primary Kepler mission, KIC 5951458 b (Kepler-456b) was thought to be a single-transit giant planet with an orbital period of 1310 days. However, radial velocity (RV) observations of KIC 5951458 from the HIRES instrument on the Keck telescope suggest that the system is far more complicated. To extract precise RVs for this V ≈ 13 star, we develop a novel matched-template technique that takes advantage of a broad library of template spectra acquired with HIRES. We validate this technique and measure its noise floor to be 4–8 m s⁻¹ (in addition to internal RV error) for most stars that would be targeted for precision RVs. For KIC 5951458, we detect a long-term RV trend that suggests the existence of a stellar companion with an orbital period greater than a few thousand days. We also detect an additional signal in the RVs that is possibly caused by a planetary or brown dwarf companion with mass in the range of 0.6–82 M_(Jup) and orbital period below a few thousand days. Curiously, from just the data on hand, it is not possible to determine which object caused the single "transit" event. We demonstrate how a modest set of RVs allows us to update the properties of this unusual system and predict the optimal timing for future observations
Multiple Explanations for the Single Transit of KIC 5951458 based on Radial Velocity Measurements Extracted with a Novel Matched-template Technique
Planetary systems that show single-transit events are a critical pathway to
increasing the yield of long-period exoplanets from transit surveys. From the
primary Kepler mission, KIC 5951458b (Kepler-456b) was thought to be a
single-transit giant planet with an orbital period of 1310 days. However,
radial velocity (RV) observations of KIC 5951458 from the HIRES instrument on
the Keck telescope suggest that the system is far more complicated. To extract
precise RVs for this star, we develop a novel matched-template
technique that takes advantage of a broad library of template spectra acquired
with HIRES. We validate this technique and measure its noise floor to be 4 - 8
m s (in addition to internal RV error) for most stars that would be
targeted for precision RVs. For KIC 5951458, we detect a long-term RV trend
that suggests the existence of a stellar companion with an orbital period
greater than a few thousand days. We also detect an additional signal in the
RVs that is possibly caused by a planetary or brown dwarf companion with mass
in the range of 0.6 - 82 and orbital period below a few thousand
days. Curiously, from just the data on hand, it is not possible to determine
which object caused the single "transit" event. We demonstrate how a modest set
of RVs allows us to update the properties of this unusual system and predict
the optimal timing for future observations.Comment: 20 pages, 14 figures, accepted for publication in the Astronomical
Journa
New Dynamical State and Habitability of the HD 45364 Planetary System
Planetary systems with multiple giant planets provide important opportunities
to study planetary formation and evolution. The HD 45364 system hosts two giant
planets that reside within the Habitable Zone (HZ) of their host star and was
the first system discovered with a 3:2 mean motion resonance (MMR). Several
competing migration theories with different predictions have previously
provided explanations regarding the observed resonance through dynamical
simulations that utilized limited data. Here, over ten years since the original
discovery, we revisit the system with a substantially increased radial velocity
(RV) sample from HARPS and HIRES that significantly extend the observational
baseline. We present the revised orbital solutions for the two planets using
both Keplerian and dynamical models. Our RV models suggest orbits that are more
circular and separated than those previously reported. As a result, predicted
strong planet-planet interactions were not detected. The system dynamics were
reanalyzed, and the planet pair was found to exhibit apsidal behavior of both
libration and circulation, indicating a quasi-resonance state rather than being
truly in MMR. The new orbital solution and dynamical state of the system
confirm migration models that predicted near circular orbits as the preferred
scenario. We also study the habitability prospects of this system and found
that an additional Earth-mass planet and exomoons in the HZ are possible. This
work showcases the importance of continued RV observation and its impact on our
knowledge of the system's dynamical history. HD 45364 continues to be an
interesting target for both planetary formation and habitability studies.Comment: 16 pages, 10 figures, accepted for publication in the Astronomical
Journa
The gold standard: accurate stellar and planetary parameters for eight Kepler M dwarf systems enabled by parallaxes
We report parallaxes and proper motions from the Hawaii Infrared Parallax Program for eight nearby M dwarf stars with transiting exoplanets discovered by Kepler. We combine our directly measured distances with mass-luminosity and radius–luminosity relationships to significantly improve constraints on the host stars’ properties. Our astrometry enables the identification of wide stellar companions to the planet hosts. Within our limited sample, all the multi-transiting planet hosts (three of three) appear to be single stars, while nearly all (four of five) of the systems with a single detected planet have wide stellar companions. By applying strict priors on average stellar density from our updated radius and mass in our transit fitting analysis, we measure the eccentricity probability distributions for each transiting planet. Planets in single-star systems tend to have smaller eccentricities than those in binaries, although this difference is not significant in our small sample. In the case of Kepler-42bcd, where the eccentricities are known to be ≃0, we demonstrate that such systems can serve as powerful tests of M dwarf evolutionary models by working in L⋆ − ρ⋆ space. The transit-fit density for Kepler- 42bcd is inconsistent with model predictions at 2.1σ (22%), but matches more empirical estimates at 0.2σ (2%), consistent with earlier results showing model radii of M dwarfs are underinflated. Gaia will provide high-precision parallaxes for the entire Kepler M dwarf sample, and TESS will identify more planets transiting nearby, late-type stars, enabling significant improvements in our understanding of the eccentricity distribution of small planets and the parameters of late-type dwarfs.Support for Program number HST-HF2-51364.001-A was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts. This paper includes data collected by the Kepler mission. Funding for the Kepler mission is provided by the NASA Science Mission directorate. The authors acknowledge the Texas Advanced Computing Center (TACC) at The University of Texas at Austin for providing HPC resources that have contributed to the research results reported within this paper. URL: http://www.tacc.utexas.edu. (HST-HF2-51364.001-A - NASA through Space Telescope Science Institute; NAS5-26555 - NASA; NNX09AF08G - NASA Office of Space Science; NASA Science Mission directorate
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