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Last Updated 2018-05-23

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The design is the same as TIC-5, in that the columns and their format are the same, but there have been significant changes compared to TIC deliveries prior to TIC-6. TIC IDs have not been changed and all future deliveries of the TIC will use the same IDs for specific objects. New objects added to the TIC will always receive new IDs. Objects may be removed from the TIC, if they are found to be spurious, but TIC IDs will always be unique and a new TIC object will never receive the ID of an old TIC object.

Changes compared to TIC-5

This delivery contains major changes in computed quantities compared to TIC-5. It should be noted that the methods used to estimate a variety of stellar parameters are still under active development and can be affected by poor catalog photometry when there is no acceptable alternative photometry for a given star. The major changes compared to previous versions are:

1. All stars with matches between 2MASS and Gaia now have their coordinates given in the epoch 2015 Gaia system. Stars that did not have matches to the Gaia catalog have their coordinates given in the original 2MASS system. Entries where multiple Gaia stars match to one 2MASS star will have a single entry in TIC-6, but are flagged as Gaia multiples in the TIC. The position is re-computed as the flux-weighted position of the Gaia stars, and the associated Gaia magnitude is derived from the added flux of the components. The Source-ID of the brightest Gaia star is given as the matching Gaia source. 2MASS stars with multiple Gaia sources are removed from the Candidate Target List (CTL) but still appear in the TIC. 2MASS stars with multiple Gaia sources that are also in the Cool Dwarf list are not removed from the CTL. See section 2.1.2 of the full documentation for details.
2. We include new relations to transform to TESS magnitude using Gaia G magnitudes and Johnson V, 2MASS J, H or Ks magnitudes.
3. We include new relations to transform Gaia G, 2MASS Ks color to Johnson V and have changed the order of preference of observed and calculated V magnitudes.
4. The spectroscopic catalogs of APOGEE-2 (from SDSS DR-14), LAMOST DR-3, RAVE DR-5 and HERMES DR-1 have been added to our spectroscopic database increasing the number of stars with spectra from 1.5 million to 2.6 million. Please see the notes on column 64 for the updated priority scheme.
5. The proper motion catalogs of Hot Stuff for One Year and UCAC-5 have been added to the proper motion table. Please see the notes on column 17 for the updated preference scheme for proper motions.
6. An updated version of the specially curated cool dwarf list has been added to the catalog as well as curated lists for hot subdwarfs, bright stars, known planet hosts, and stars which were identified as missing in TIC-5 during Cycle 1 of the NASA Guest Investigator program.
7. Stars in the specially curated list of known exoplanet hosts (as detailed in the NASA exoplanet archive) have been included in the CTL and appropriately flagged. Due to time constraints, the specially curated list could not be fully incorporated into CTL-6. Stars which were in the CTL, prior to the list’s delivery, are listed with their full CTL-6 default stellar parameters (~800 stars). Stars which were not in the CTL prior to the list’s delivery, have no stellar parameters provided and their priority values have been set to 0 (~1600 stars). The full set of stellar parameters for these stars will be included in future versions of the CTL.
8. The CTL priority function (column 88) has been updated with the following:
   1. The radius now scales as R^1.5, rather than R (column 71).
   2. For both CTL6.1 and CTL6.2, the given star’s priority is now boosted based on the star’s ecliptic latitude (column 28) and the number of sectors the star is likely to appear in, rather than a factor of sqrt(13) if the star was in the continuous viewing zone. Generally, this boosts the priority of stars closer to a continuous viewing zone. For CTL-6.2, the gaps in priority from the expected positions of camera gaps have been removed
   3. For CTL-6.1, the priority function scaled with (sqrt(cratio+1)*phot_err) rather than sqrt(sqrt(cratio+1)*phot_err), where cratio is the contamination ratio (column 85) and phot_err is the photometric error provided by Sullivan et al. 2015 based on the TESS magnitude of the star (column 61). For CTL-6.2,the expected photometric error is now directly calculated using the same formalism from Sullivan et al. 2015, where the total noise (N) is defined as: N= sqrt(Nstar^2+Nsky^2+Ncont^2+Nread^2+Nsys^2). Nstar represents the photon error from the star; Nsky represents the photon error from the sky background; Ncont is the expected photon error from contaminants in the aperture (this replaces the contamination ratio); Nread is the readout error of the detector; and N sys is the unrecoverable 60ppm systematic error that is expected. Pepper et al. 2018 explains this new formalism in greater detail.
9. We have removed all SDSS extended sources (~120 million extended sources) that are not also in 2MASS. This is the largest set of objects that initially appeared in TIC-5 that were specifically removed from TIC-6.  Many of the brighter objects in the SDSS extended source catalog, have been shown to be ghost images created by SDSS diffraction spikes and were erroneously classified as galaxies in TIC-5 (see Full Documentation Section 2.1.3). These objects created numerous duplicate objects in the TIC and caused many unintended effects on the distribution of CTL parameters and objects (typically resembling the SDSS footprint in an all sky map). Removing these objects alleviated these effects.
10. The size of the CTL has been decreased from ~10 million stars to ~3.8 millions stars. Stars are now considered for the CTL if they are: 1) identified as RPMJ dwarfs with greater than 2-sigma confidence; and 2) meet one of the following temperature criteria: (T<12 and Teff >= 5500K) or (T<13 and Teff < 5500K) where T is the star’s TESS magnitude (column 61) and Teff is the effective temperature of the star (column 65). Additionally, any star that is a member of the bright star list (T < 6) or specially curated cool dwarf list is included in the CTL.
11. We exclude any star from the CTL that only has: 1) an effective temperature which has not been corrected for reddening; 2) falls within a tolerance strip during the dereddening process; and 3) those stars with effective temperatures which have been corrected for reddening but are cooler than 3840K. Stars within the bright star list are not subject to these stipulations.
12. Stellar characteristics are calculated for the stars in the bright star list but should not be accepted at face value. Many objects in the bright star list are giants and the stellar parameter calculations are designed for dwarfs.
13. Stars from CTL-5 that are no longer in CTL-6 are not assigned a priority but have had their stellar parameters updated with CTL-6 procedures to be consistent with the rest of TIC-6.

Notes on the individual columns

No.      Name      Notes

1          TICID       A unique identifier for every object in the TIC. The ID is unique and permanent. If an object is removed from the TIC in later versions, a new object will never inherit an old ID.

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c. Stars with absolute ecliptic latitudes (column 28) less than ~6 are not expected to be observed as part of the main mission due to a gap in camera coverage between the Southern and Northern observations. Therefore, their Ns values are 0 and thus the priority is 0.

Known Issues and Quirks:

There are a number of minor issues which have been identified by the TSWG. We expect to address these issues in a future version of the TIC. The issues include:

1. All coordinates are for the epoch of observation (often 2MASS or SDSS for extended objects). Epochs are not currently supplied.

2. Because some stars have poor quality 2MASS photometry flags (such as ‘D’, ‘U’), offsets where applied to G, V, J, H, or Ks magnitudes to provide a more realistic TESS magnitude but may be different from the true value by a magnitude or more.  

3. ‘allen’ is a deprecated flag that should be replaced by the spline flag.

4. Some stars will show an error in the stellar density which is larger than the density itself. In these cases, the error should be interpreted as equal to the density.

5. The error in the luminosity currently only reflects the effect of the radius error but should also include the effects of temperature.

6. The following 13 stars do not have a TESS magnitude and should be ignored in TIC-6.

1. TIC-IDS: 75834098, 144190256, 158983365, 101677906, 122564545, 147784016, 180764901, 6059840, 459225192, 229259238, 247903820, 590866, 54776047

7. Due to the preference of proper motion catalogs which are based on PPMXL, there is structure in the distribution of high priority candidates mainly above declinations larger than -30 deg.

8. Stars which have ecliptic latitudes between -6 and 6 degree have priorities set to 0, unless they are in the bright star list. This “gap” in priority is meant to mimic the expected gap in camera coverage for the 2 year primary TESS mission.

9. Some bright stars may have nearby impostor stars with similar magnitudes that lie along diffraction spikes from 2MASS photometry. Users can identify these impostors by checking 2MASS quality flags for very poor photometry (such as ‘D’, ‘E’, ‘F’, ‘U’). These objects should be removed in future versions of the TIC.

Column Number, Column Name, Column Data Type and Brief Description:

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