While thousands of exoplanets have been confirmed, the known properties about individual discoveries remain sparse and depend on detection technique. To utilize more than a small section of the exoplanet data set, tools need to be developed to estimate missing values based on the known measurements. Here, we demonstrate the use of a neural network that models the density of planets in a space of six properties that is then used to impute a probability distribution for missing values. Our results focus on planetary mass, which neither the radial velocity nor transit techniques for planet identification can provide alone. The neural network can impute mass across the four orders of magnitude in the exoplanet archive, and return a distribution of masses for each planet that can inform us about trends in the underlying data set. The average error on this mass estimate from a radial velocity detection is a factor of 1.5 of the observed value, and 2.7 for a transit observation. The mass of Proxima Centauri b found by this method is 1.6_-0.36_^+0.46^M{Earth}, where the upper and lower bounds are derived from the root mean square deviation from the log mass probability distribution. The network can similarly impute the other potentially missing properties, and we use this to predict planet radius for radial velocity measurements, with an average error of a factor 1.4 of the observed value. The ability of neural networks to search for patterns in multidimensional data means that such techniques have the potential to greatly expand the use of the exoplanet catalog.
Data for numerical modeling of planetary atmospheres
Date:
12 Jun 2017 10:19:38
Publisher:
Instituto de Astrofisica de Andalucia-CSIC; INTA-CAB
Description:
Numerical modeling of composition and thermal balance of planetary
atmospheres requires a considerable amount of laboratory data. Among
them, the absorption cross sections in the UV range are needed both
for computing the heating in the atmosphere and the photodissociation
coefficients to initiate a rich disequilibrium chemistry. Prompted by
these needs in the community and by the sparse collection of data in
several other web pages (http://www.science-softcon.de/ or
http://satellite.mpic.de/spectral_atlas/index.html whose data depend
on some pre-processing before being ingested in these models), this
web page aims at providing the community with absorption cross
sections in the range 20 nm to 400 nm equally spaced every 0.2, 0.5
and 1.0 nm. Also, original data as appearing in the refereed journal
and the reference itself are downloadable.
The "Data Inventory of Space-Based Celestial Observations Version 1.0" (DISCO) is a directory to data contained in sixteen catalogs dealing with observations from space. (Sounding rocket, solar, and planetary observations have been excluded.) The information extracted from the catalogs includes names of objects observed, 1950 equatorial coordinates, and the name of the catalog or instrument. A second file contains full references to the source catalogs and other pertinent information. The purpose of creating DISCO is (1) to unify astronomical observations from space, which are at present scattered and hard to locate, and then (2) to provide a machine-readable index to these observations, thus enabling easy access by computer. Such a directory will permit an astronomer to find out what objects have been observed from space, which spacecraft and instruments made the observations, and where to go to find the data themselves.
We have adapted the algorithmic tools developed during the Kepler mission to vet the quality of transit-like signals for use on the K2 mission data. Using the four sets of publicly available light curves at MAST, we produced a uniformly vetted catalog of 772 transiting planet candidates from K2 as listed at the NASA Exoplanet Archive in the K2 Table of Candidates. Our analysis marks 676 of these as planet candidates and 96 as false positives. All confirmed planets pass our vetting tests. Sixty of our false positives are new identifications, effectively doubling the overall number of astrophysical signals mimicking planetary transits in K2 data. Most of the targets listed as false positives in our catalog show either prominent secondary eclipses, transit depths suggesting a stellar companion instead of a planet, or significant photocenter shifts during transit. We packaged our tools into the open-source, automated vetting pipeline Discovery and Vetting of Exoplanets (DAVE), designed to streamline follow-up efforts by reducing the time and resources wasted observing targets that are likely false positives. DAVE will also be a valuable tool for analyzing planet candidates from NASA's TESS mission, where several guest-investigator programs will provide independent light-curve sets - and likely many more from the community. We are currently testing DAVE on recently released TESS planet candidates and will present our results in a follow-up paper.
We present a method which uses colour-colour cuts on the Sloan Digital Sky Survey (SDSS) photometry to select white dwarfs with hydrogen-rich (DA) atmospheres without the recourse to spectroscopy. This method results in a sample of DA white dwarfs that is 95 per cent complete at an efficiency of returning a true DA white dwarf of 62 per cent. The approach was applied to SDSS Data Release 7 for objects with and without SDSS spectroscopy.
Spectrophotometric observations at high signal-to-noise ratio were obtained of a complete sample of 347 DA white dwarfs from the Palomar Green (PG) Survey (1986, Cat. <II/207>). Fits of observed Balmer lines to synthetic spectra calculated from pure-hydrogen model atmospheres were used to obtain robust values of T_eff_, log(g), masses, radii, and cooling ages. The luminosity function of the sample, weighted by 1/V_max_, was obtained and compared with other determinations.
We report the spectroscopic identification of close to 1000 hydrogen-rich (DA) white dwarfs discovered in the course of the Anglo-Australian 2dF QSO Redshift Survey (2QZ, Cat. <VII/223>). We measured the atmospheric parameters of a subsample of 201 stars based on good-quality Balmer line spectra and we determine the 2QZ population characteristics. Over ten per cent of the sample are potential ZZ Ceti variables. We estimate the DA white dwarf birthrate (b_DA_=0.5-1.0x10^-12^/yr/pc^3^) and the scale-height (h=220-300pc) of the population in the thin disc of the Galaxy by combining information acquired in the Palomar-Green, AAT-UVX and new 2QZ surveys. White dwarfs appear related to G and late-F progenitors. A catalogue of 201 DA white dwarfs is presented.
We present near- and mid-infrared photometry and spectroscopy from PAIRITEL, IRTF, and Spitzer of a metallicity-unbiased sample of 117 cool, hydrogen-atmosphere white dwarfs (WDs) from the Palomar-Green survey and find five with excess radiation in the infrared, translating to a 4.3^+2.7^_-1.2_% frequency of debris disks. This is slightly higher than, but consistent with the results of previous surveys. Using an initial-final mass relation, we apply this result to the progenitor stars of our sample and conclude that 1-7M_{sun}_ stars have at least a 4.3% chance of hosting planets; an indirect probe of the intermediate-mass regime eluding conventional exoplanetary detection methods. Alternatively, we interpret this result as a limit on accretion timescales as a fraction of WD cooling ages; WDs accrete debris from several generations of disks for ~10Myr. The average total mass accreted by these stars ranges from that of 200km asteroids to Ceres-sized objects, indicating that WDs accrete moons and dwarf planets as well as solar system asteroid analogs.