Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userConstraining Orbital Periods from Nonconsecutive Observations: Period Estimates for Long-Period Planets in Six Systems Observed by K2 During Multiple Campaigns
149
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Most planetary discoveries with the K2 and TESS missions are restricted to short periods because of the limited duration of observation. However, the re-observation of sky area allows for the detection of longer period planets. We describe new transits detected in six candidate planetary systems which were observed by multiple K2 mission campaigns. One of these systems is a multiplanet system with four candidate planets; we present new period constraints for two planets in this system. In the other five systems, only one transit is observed in each campaign, and we derive period constraints from this new data. The period distributions are highly multimodal resulting from missed potential transits in the gap between observations. Each peak in the distribution corresponds to transits at an integer harmonic of the two observed transits. We further detail a generalized procedure to constrain the period for planets with multiple observations with intervening gaps. Because long period photometrically discovered planets are rare, these systems are interesting targets for follow-up observations and confirmation. Specifically, all six systems are bright enough (V = 10.4-12.7) to be amenable to radial velocity follow-up. This work serves as a template for period constraints in a host of similar yet-to-be-discovered planets in long baseline, temporally gapped observations conducted by the TESS mission.
rate research
Read More
We have analyzed data from Campaigns 0-5 of the K2 mission and report 19 ultra-short-period candidate planets with orbital periods of less than 1 day (nine of which have not been previously reported). Planet candidates range in size from 0.7-16 Earth radii and in orbital period from 4.2 to 23.5 hours. One candidate (EPIC 203533312, Kp=12.5) is among the shortest-period planet candidates discovered to date (P=4.2 hours), and, if confirmed as a planet, must have a density of at least rho=8.9 g/cm^3 in order to not be tidally disrupted. Five candidates have nominal radius values in the sub-Jovian desert (R_P=3-11 R_E and P<=1.5 days) where theoretical models do not favor their long-term stability; the only confirmed planet in this range is in fact thought to be disintegrating (EPIC 201637175). In addition to the planet candidates, we report on four objects which may not be planetary, including one with intermittent transits (EPIC 211152484) and three initially promising candidates that are likely false positives based on characteristics of their light curves and on radial velocity follow-up. A list of 91 suspected eclipsing binaries identified at various stages in our vetting process is also provided. Based on an assessment of our surveys completeness, we estimate an occurrence rate for ultra-short period planets among K2 target stars that is about half that estimated from the Kepler sample, raising questions as to whether K2 systems are intrinsically different from Kepler systems, possibly as a result of their different galactic location.
GY Cnc is a deeply eclipsing cataclysmic variable star with an orbital period of 4.21 hours that has shown several dwarf nova outbursts. The variable was continuously observed by the K2/Kepler satellite with a short cadence in Campaign 5 (C05) for 75 days during 2015. The star was again observed in 2017/2018 for 80 consecutive days during Campaign 16 (C16). 419 well-observed eclipses were measured over C5 and 446 timings were determined in C16. A new ephemeris was calculated combining the K2 data, previously published timings, new light curves from the KELT Follow-Up Network, and additional observations in the AAVSO database. We have refined the orbital period of GY Cnc and improved its ephemeris which had accumulated an error of about 300s over 18 years. A quadratic term was not found to be significant indicating that there is currently no detectable orbital period derivative. We observed a correlation between the quiescent system brightness and the eclipse timing residuals that are as large as +/-15s in the K2 data.
We present the observational results of an L and M band Adaptive Optics (AO) imaging survey of 54 nearby, sunlike stars for extrasolar planets, carried out using the Clio camera on the MMT. We have concentrated more strongly than all other planet imaging surveys to date on very nearby F, G, and K stars, prioritizing stellar proximity higher than youth. Ours is also the first survey to include extensive observations in the M band, which supplement the primary L observations. Models predict much better planet/star flux ratios at the L and M bands than at more commonly used shorter wavelengths (i.e. the H band). We have carried out extensive blind simulations with fake planets inserted into the raw data to verify our sensitivity, and to establish a definitive relationship between source significance in $sigma$ and survey completeness. We find 97% confident-detection completeness for 10$sigma$ sources, but only 46% for 7$sigma$ sources -- raising concerns about the standard procedure of assuming high completeness at 5$sigma$, and demonstrating that blind sensitivity tests to establish the significance-completeness relation are an important analysis step for all planet-imaging surveys. We discovered a previously unknown, approximately 0.15 solar-mass stellar companion to the F9 star GJ 3876, at a projected separation of about 80 AU. Twelve additional candidate faint companions are detected around other stars. Of these, eleven are confirmed to be background stars, and one is a previously known brown dwarf. We obtained sensitivity to planetary-mass objects around almost all of our target stars, with sensitivity to objects below 3 Jupiter masses in the best cases. Constraints on planet populations based on this null result are presented in our Modeling Results paper.
We report the discovery of EPIC201702477b, a transiting brown dwarf in a long period (40.73691 +/- 0.00037 day) and eccentric (e=0.2281 +/- 0.0026) orbit. This system was initially reported as a planetary candidate based on two transit events seen in K2 Campaign 1 photometry and later validated as an exoplanet. We confirm the transit and refine the ephemeris with two subsequent ground-based detections of the transit using the LCOGT 1m telescope network. We rule out any transit timing variations above the level of 30s. Using high precision radial velocity measurements from HARPS and SOPHIE we identify the transiting companion as a brown dwarf with a mass, radius, and bulk density of 66.9 +/- 1.7 M$_J$, 0.757 +/- 0.065 R$_J$, and 191+/-51 g.cm$^{-3}$ respectively. EPIC201702477b is the smallest radius brown dwarf yet discovered, with a mass just below the H-burning limit. It has the highest density of any planet, substellar mass object or main-sequence star discovered so far. We find evidence in the set of known transiting brown dwarfs for two populations of objects - high mass brown dwarfs and low mass brown dwarfs. The higher-mass population have radii in very close agreement to theoretical models, and show a lower-mass limit around 60 M$_J$. This may be the signature of mass-dependent ejection of systems during the formation process.
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.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
