Documentation and Methodology

The Exoplanet Data Explorer (EDE) gives Web users access to the Exoplanet Orbit Database (EOD). Our full methodology is here and is available on astro-ph.

FAQ

Why should I use the EOD instead of one of the other lists ofexoplanets?

If you are interested in:

• The most accurate orbital ephemerides for known planets
• A carefully vetted list of confidently detected exoplanets with well measured orbital properties from the peer-reviewed literature
• Transit data, such as planet-star radius ratios and transit durations
• An elegant and powerful plotting tool for presentation or publication quality plots

then we believe you should use our site. Other sites include announced planets whose properties and existence have not been scrutinized by peer review, and lack many of the stellar and transit fields our site has. Our site has also corrected many typos appearing in the literature.

On the other hand, if you want a comprehensive list of all planet announcements that have not been disproven; or a list of real planets that lack well-measured orbits (including microlensing planets and imaged planets); or planets orbiting things other than single, "ordinary" stars (like pulsars, white dwarfs, or hot subdwarfs); or you would like to decide for yourself which planets to include in your sample, you should use another site (we list our favorite ones here). We use these sites regularly to keep up-to-date on planet discoveries, and we share information with them about literature errors. We consider these sites complementary, serving slightly different purposes from exoplanets.org.

Why isn't my favorite exoplanet/datum listed in the EOD?
Why does your site list fewer planets than site X?

There are four primary reasons:

• The EOD contains only carefully vetted, peer-reviewed data. If your favorite planet has not been published (or accepted for publication) in a peer-reviewed journal, it will not appear in this Database, with rare exceptions. Also, in a small number of cases we have made a judgement call that a peer-reviewed datum (or planet) is not up to the Database's standards, or uses an unproven method whose results we are not comfortable including. Basically, we have done a lot of work to keep an updated list of planets with "good" orbits by our own published and peer-reviewed criteria, and this database is our way to share that list with the public.
• The EOD is a database of stellar properties, transit parameters, and orbital elements of planets around "normal" stars. If an exoplanet's orbit is not well measured (because it was discovered via imaging, for instance), it is not in our database
• We are not all-seeing; sometimes we miss an ephemeris update, or even a whole planet! If you know of a better source of data than the reference in our table (or find an error!), please let us know.
• We are not fast; it can take time for us to fully digest a new planet announcement, decide that it warrants inclusion, enter the data, verify the transcription, and sync up the EOD with the EDE. Summer updates may be especially slow.

Why don't the numbers in the EDE agree with the numbers in the reference / exported file?

The EDE displays data with a conservative "significant figures" algorithm. The exported CSV files contain the data at the "full precision" stored in the database, which should be consistent with the literature values to machine precision. Thus, if the literature lists a datum as 1001 with a standard error of 100, that will appear in the CSV as such, but the EDE will display "1000 +/- 100" because it deems the trailing "1" not significant. This concession is necessary to make the online tables easily readable; the machine-readable exported files have full fidelity to the literature.

We have also made some minor modifications to data to make it conform to our database standards -- for instance we restrict the domain of little omega to [0,360).

Why doesn't FIRSTREF refer to this prior press release / posterabstract / conference proceeding?

The EOD contains only peer-reviewed references; see below. The FIRSTREF field is not a "credit" field.

How do I make the Table/Plotter do what I want?

Try the help pages. User the left-hand column to browse various help topics. These pages include videos made for the Kepler Data Explorer. Though they differ in the available planet properties, the behavior of the Exoplanets Data Explorer and the Kepler Data Explorer are identical.

Why doesn't the "Export" button export all of the data in the EOD?

The "Export" button in the EDE Table exports the table as you, the user, have currently displayed it. If you would like the entire database, it is available in a single click on the front page, or here.

Major Updates

Some recent updates as of March 2013 (these updates will also be described in details in our upcoming paper):

Kepler Objects of Interest (KOIs)

The Kepler Objects of Interst (KOIs) are stars that are suspected to host one or more exoplanets, but yet to be confirmed or validated. Although they are not counted as part of the EOD due to their candidacy status, we include them in our website so that these KOIs are put into the context of all confirmed exoplanets. The KOIs listed in our table include two past Kepler data releases and the most up-to-date release from January 2013. The original data are from the NASA Exoplanet Archive.

The most important updates from the Wright et al. 2011 documentation of the EODs are below:

RSTAR

For stars with transiting planets, we record the radius with asymmetrical error bars when it is calculated in the literature. For other stars with masses less than 0.6 Solar mass, we apply the formula of Torres et al (2010) to our recorded spectroscopic parameters, log(g), Teff, and [Fe/H]. The Torres formula has systematic errors of no more than 3%. We propagate errors from our spectroscopic parameters assuming no covariance into the field URSTAR.

Kepler planets

The extraordinary precision of the Kepler instrument and detailed ground-based follow up allows planets to be detected purely photometrically, without the usual spectroscopic orbital parameter K. Since these planets' reality can be established as well as any in the EOD, and since a precise ephemeris is available, we have opted to include Kepler planets in the EOD even in those cases where the planets' radial velocity signature has not been measured. In these cases we leave the K field blank in the EDE (set to NaN in the EOD). In cases where planets' masses can be constrained dynamically, or have upper limits due to a lack of RV signature, we supply the MSINI field with the appropriate values and reference the source of those numbers, instead of calculating MSINI from K.

References

We have added references and URL fields for nearly every field in the EOD; all data in these fields are now uniquely referenced. The only fields without rigorous citations are those containing coordinates, magnitudes, and rotation/activity measurements.

Asymmetric uncertainties

We are updating asymmetric error bars throughout the database in all fields.

Summary of Methodology

The text below is subject to the updates above.

Orbital parameters:

We record the published fundamental observables of single-lined spectroscopic binaries: period, RV semiamplude, and eccentricity, argument of periastron, and time of periastron passage. In a few cases of multiple planet systems, the best orbital parameters come from dynamical fits, and in a small number of cases (e.g. GJ 876) planet-planet interactions cause these elements to detectably evolve with time. In those cases where osculating elements for the planets are reported, we have recorded those, and the epoch at which they are valid can be found in the reference cited in ORBREF.

Where uncertainties in orbital elements are not reported in the literature, they remain undefined in our table.

m sin(i)

From the orbital parameters and the mass of the host star we calculate the "minimum mass" of the planet from the mass function, as described in Butler et al. 2006. Note that we calculate this quantity separately for each planet in a multiplanet system, as though it were a singleton planet. For simplicity and consistency, we always denote this quantity "m sin(i)", though strictly speaking it is simply the minimum value for the planet's mass as calculated from the mass function.

m sini will occasionally differ from the values listed in the paper cited in ORBREF. The most common reason for this is that we have adopted a different stellar mass than that listed in ORBREF. In other cases, inclinations are known from transits, or constrained through astrometry or dynamical considerations. In a small number of cases m sin (i) was misreported in the original paper.

a

We calculate orbital semimajor axes directly from Kepler's Third Law in all cases. In cases where it differs from literature values, the usual culprit is that we have adopted a different stellar mass.

Radial velocities and orbital fit

The orbital fit parameters refer to the fit in ORBREF and the listed orbital parameters. The corresponding RV curve is displayed in the upper-left of each planet's minipage, which can be accessed by clicking on a planet's name. The radial velocities in this plot are not necessarily those of the orbital reference, but are representative velocities collected from NStED. This feature is not fully supported -- for many stars, including binaries, certain multiplanet systems, and those for which no velocities are published or otherwise available in NStED, no plot is shown.

Parallaxes

We have adopted the van Leeuwen (2008) parallaxes (from a rereduction of the Hipparcos data) for most stars.

Transiting planets

We have recorded the fundamental photometric transit parameters and some derived quantities as they appear in the literature. In some cases we calculate time of periastron passage and the argument of periastron, planetary density, planetary gravity, or the impact parameter where those elements are not listed explicitly.

Radius, density and gravity

Where available, we record the published radius, density, gravity for transiting planets from TRANSITREF, and do not attempt to recompute them from the transit parameters except where they are not otherwise available. Therefore, these values may be inconsistent with the mass derived from MSINI and the inclination because our MSINI values may have been computed from different spectroscopic orbital parameters or assuming a different stellar mass.

Uncertainties

We have recorded literature uncertainties in stellar masses, but when estimating uncertainties in msini and a we conservatively assume a minimum uncertainty in stellar mass of 5%. We do this to account for likely systematic errors in model estimates of stellar masses (limits in their accuracy) for most planet-bearing stars.

FIRSTREF

The "first reference" field cites the first peer-reviewed journal article to contain a orbital solution and/or radial velocities documenting the existence of the planet. In many cases this does not correspond to the first public announcement of a planet's existence, which may have been by press release, in conference proceedings, or by reference in another paper. A list of planet discoveries, confirmations, and discovery claims is available at http://obswww.unige.ch/~naef/who_discovered_that_planet.html.

JHK Photometry

JHK photometry is from the 2MASS point source catalog (Skrutskie et al. 2006). In most cases coordinates come from the van Leeuwen (2008) rereduction of the Hipparcos data. B and V magnitudes are heterogeneous, coming variously from the Hipparcos catalog, SIMBAD, and other literature sources, and so are not strictly all on the same scale. Chromospheric activity measurements are from various sources, usually planet discovery papers plus references cited in Butler et al. (2006).

This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France, NASA's Astrophysics Data System, the Exoplanets Encyclopedia maintained by Jean Schneider, and data products from 2MASS, which is a joint project of the University of Massachusetts and IPAC/Caltech. This research received generous funding from NASA and the NSF.