TEPCat: Frequently asked questions


 

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Why does TEPCat exist?
How is TEPCat maintained and updated?
What objects are included in TEPCat?
Can I access older versions of TEPCat?
What happened to some transiting planets which are not listed in TEPCat?
What is the scope of TEPCat - what masses does it include?
What is the difference between well-studied and little-studied objects?
Why are some quantities in the individual planet pages in brackets?
Why are some quantities in physical properties table in italics and brackets?
 

Why does TEPCat exist?

I have previously worked on a series of papers in which I calculated the physical properties of known transiting planetary systems using a homogeneous approach. By Paper 4 it became clear that the results were distributed over too many papers to expect anyone else to keep track of them. I therefore decided to make my own compilation available in a way which was easy to use. It then made sense to include other information which might be helpful to other researchers, so I constructed TEPCat.
 

How is TEPCat maintained and updated?

The basic data for TEPCat are held in a set of text files. I have written a long but simple IDL procedure to convert these into the html and csv files which make up TEPCat. New results are added into TEPCat as soon as possible after they have been published.

The following journals of astrophysics are systematically inspected to find new results: A&A, AJ, ApJ, ApJS, MNRAS, Nature and PASP. I also check the arXiv preprint server on a daily basis (new submissions only; replacements and cross-lists are not checked).
 

What objects are included in TEPCat?

The aim of TEPCat is to provide a critical compilation of the properties of all known confirmed transiting planets. The following criteria must be satisfied for any object to be included in TEPCat:

  • A study of the system has been published in one of the refereed journal papers noted above.
  • The full sky position and orbital ephemerides are available, allowing people to perform follow-up observations.
  • The mass or radius of the putative planet must be within the planetary regime.
  • The physical properties of the planet must be adequately measured with a reasonable error analysis.
  • It must be orbiting a "normal" star.

Whether or not an object of a given mass and radius is a planet is a tricky question. For my upper mass limit I adopt 35-40 Mjup (see here for more discussion), and I do not impose a lower mass limit.

Quite a few objects do not have mass limits, but have radii which are too small for them not to be planets. Figures 1 and 2 of Chabrier et al. (2009AIPC.1094..102C) show theoretical models which predict the smallest radius of an object more massive that 35-40 Mjup to be about 0.75 Rjup. I therefore include objects without mass limits but with radii smaller than 0.50 Rjup (5.6 Rearth) in TEPCat. Objects with greater radii might be brown dwarfs or low-mass stars, so are not included in TEPCat unless they have a measured mass or upper limit on mass which places them in the planetary regime.
 

Can I access older versions of TEPCat?

TEPCat is continuously updated and does not include a comprehensive change-log, but older versions are systematically archived. On roughly the first day of each month I save the then-current version of the webpages in a subdirectory, and these historical versions of TEPCat are freely available for reference. To view them in your web browser, simply add the month and year (in format YYYYmmm/) to the URL. For example:

http://www.astro.keele.ac.uk/jkt/tepcat/allplanets-noerr.html

becomes

http://www.astro.keele.ac.uk/jkt/tepcat/2011dec/allplanets-noerr.html

to access the version archived on 1st December 2011. This works for all pages except those of individual planets, which are not archived for space reasons. The first month for which an archive was kept is 2011 July.
 

What happened to some transiting planets which are not listed in TEPCat?

A number of transiting planets are not listed in TEPCat. The reason why for each of them is now given on the Where is … page.

What is the scope of TEPCat - what objects does it include?

The upper mass limit for planets is widely taken to be 13 Mjup (Jupiter masses), the point above which a gaseous object is able to undergo thermonuclear fusion of deuterium (2H) in its core. The lower mass limit for stars is somewhere in the region of 80 Mjup (0.08 times the mass of the Sun) - above this limit a gaseous object can sustain thermonuclear fusion of hydrogen (H). The objects between these two limits are called "brown dwarfs", and they are rare. The problem with these definitions is that the two limits are not strict - they are must be derived theoretically and can be significantly modified by changes in physical properties such as chemical composition and magnetic field strength.

Closer inspection of the known population of low-mass objects shows that they split naturally into two classes: planet-like and star-like. This division appears to be due to their formation mechanism, and does not depend on the two mass limits discussed above. This implies that the term "brown dwarf" is slightly redundant, as the objects naturally separate out into the two classes (planet-like and star-like). A good illustration of this is Fig.8 in Grether & Lineweaver (2006ApJ...640.1051G). It shows that there are plenty of stars and planets, but very few objects in between. This is commonly termed the "brown dwarf desert".

TEPCat currently includes all objects which are known to eclipse a star and have been shown to have a mass less than 80 Mjup. In the future it is likely that a mass limit around the 35-40 Mjup mark will be introduced, and more massive systems will be de-listed. They may alternatively be separated out, and supplemented with other transiting objects to make a "low-mass star" extension to TEPCat. The affected systems include CoRoT-15, LHS 6343 and WASP-30.
 

What is the difference between well-studied and little-studied objects?

The announcement in February 2014 that the NASA Kepler satellite had discovered 715 new planets posed a problem to the format of TEPCat. If I simply included all these objects then each table would have been a Kepler sandwich: roughly 100 CoRoT/GJ/HAT/HD planets followed by a swamp of 900 Kepler planets then another 100 or so OGLE/TrES/WASP/XO planets. This would mean a lot of scrolling up and down for people to find the information they wanted.

The many new Kepler planets were also studied in very little detail each (see Rowe et al. 2014). Their planetary nature was (mostly) confirmed by the study of transit-timing variations, with a few false positives expected. No radial velocity measurements were obtained, and no limits on the planetary masses were determined. It therefore made more sense to create a new table for little-studied planets.

The little-studied planets are defined to be those without radial-velocity constraints on their masses and which had not been the subject of a detailed study beyond the minimum required to demonstrate their planetary nature. Several planets which were already in TEPCat have been re-assigned to the "little-studied" table (e.g. Kepler-23 and Kepler-24). As above I require a radius of 0.5 Rjup or less to be a confirmed planet in the absence of an explicit constraint on the mass of an object.

Why are some quantities in the individual planet pages in brackets?

Several of the physical properties held within TEPCat are quoted in different units by different authors. In these cases the values in TEPCat have been converted to my preferred units. For some of the physical properties I give the values in several different units in the individual planet pages, for convenience. Please note that in these cases the values in TEPCat might not correspond exactly to the original measurements in published papers, due to differences in conversion factors and rounding-off. The quantities quoted in two units are:

Property TEPCat unit Alternative unit
Transit duration days hours
Stellar density ρsun g cm-3
Planetary mass Mjup Mearth
Planetary radius Rjup Rearth
Planetary surface gravity m s-2 log(c.g.s.)
Planetary density ρjup g cm-3

Why are some quantities in the physical properties table in italics and brackets?

The values of some quantities are not given in published papers, but could be calculated from other quantities which are. In these cases the missing quantities have been calculated from the available quantities and are included in the HTML versions of the table of physical properties. They are distinguished from other quantities by being italicised and bracketed. The errorbars are not given as it is difficult to reverse-engineer reliable uncertainties for these quantities.

The quantities in question are the orbital semimajor axis a (calculated from M*, Mp and Porb), stellar surface gravity logg (calculated from M* and R*), stellar density ρ* (calculated from M* and R*), planetary surface gravity gp (calculated from Mp and Rp), planetary density ρp (calculated from Mp and Rp), and planetary equilibrium temperature Teq (calculated from Teff and R*).

The quantities calculated for TEPCat are not included in the ASCII or CSV versions of the tables, as they would need to be clearly labelled as such and this would require significant format changes to the files. They are currently not included in the individual planet pages but this might be fixed in future.


 


Last modified: 2017/08/14           John Southworth   (Keele University, UK)