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1. Some stars may have reported stellar parameter errors that are larger than the parameter quantity. Users are cautioned against using these parameters in calculations for publications.
2. Users are reminded that stars that have ecliptic latitudes between -6 and 6 degrees have their priorities set to zero. This “gap” in priority is meant to mimic the expected gap in camera coverage for the two year primary TESS mission.
3. Some stars in the hot subdwarf list do not have errors for their stellar parameters. These were adopted ‘as-is’ for consistency.
4. The disposition column identifies objects that are included in the TIC, but are likely spurious, or related to other TIC objects in a non-trivial, non-astrophysical way. Currently, this column is populated as a NULL, DUPLICATE (6), ARTIFACT (7), or SPLIT (8). When a single star in a previous TIC is found to be two or more actual sources due to the enhanced resolution of Gaia DR-2, the original TICID gets the disposition SPLIT. New TICIDs are assigned to the objects and the original TICID is in column DUP_ID (column 87). The original star “SPLIT” star will have NULL in the dup_id. The DUPLICATE flag means the star is listed twice (or more) in the TIC due to prior cross-matching difficulties. In this case, DUP_ID contains the TICID of the real star.
5. Users should note the metallicity (column 69) has been adopted when available from a spectroscopic catalog, but it is not directly used in any calculation. This may result in physical parameters that are not strictly consistent with the reported metallicity.
6. The listed RA (column 14) and Dec (column 15) are not measured positions, but positions which have been propagated to EPOCH J2000.0. Users should not try to propagate forward the TIC coordinates using the proper motions listed. Instead, users should use the original catalog position (column 119 & 120), proper motions (columns 17 & 19), and corresponding errors for propagation.
7. If a star is identified as a subgiant, and a mass and log(g) are provided, users should not consider these parameters to be reliable, because the empirical relations designed to calculate the mass are valid for dwarf stars. However the luminosity and effective temperature should be accurate.
8. Asymmetric errors are computed using a Monte Carlo method and are only provided for CTL stars which are not in a specially curated list. There are borderline cases where the peak of the property-distribution was too close to the validity-limit of the property-relation in order to compute reliable errors. These stars will have no or asymmetric errors for just some properties.
9. Negative errors for some Bmag and Vmag uncertainties: there are 40354 stars with negative Vmag uncertainties and 4395461 stars with negative Bmag uncertainties.  The negative error values are all for stars from APASS DR9, and are magnitudes for which only one observation is used, and therefore are Poisson errors rather than standard deviation.  When constructing the TIC, these negative values were not caught and converted into positive values, and thus are recorded as negative values in TIC8.  Users should feel free to convert them to positive values and use them as a valid estimate of the uncertainty.
10. Neagive E(B-V) values: there are two different origins for negative uncertainties in the "eneg_EBV" and "epos_EBV" columns.  In the first case, if "EBVFlag" = 'schlegel' they are simple numerical and conversion errors between double and single precision values. These uncertainty values actually should be assumed to be 0.0. There are approximately 2.5 million stars in this group. If "EBVFlag" = 'panstarrs' the negative values originate from former CTL targets that got a negative value from the Monte Carlo method that was not restored properly. In these cases the value is assumed to be NULL, e.g., the negative value does not have any useful meaning. There are 34 total targets with this problem, the complete list is given below (one's in bold and underlined are CTL stars).

2500669, 6380774, 59886010, 66689089, 95953951, 96290610, 102780462, 106545533, 106925979, 106968320, 106995912, 150847797, 152213395, 202173923, 203817705, 256283293, 268080493, 284238301, 284706155, 321910060, 348470096, 352516090, 365424002, 381458401, 391991123, 399107554, 416800445, 427104893, 432892646, 1654554857, 1498525, 1500006, 1501102, 2652592

Joins

All stars affected are stars originating from TIC7 which did not get matched up with a Gaia DR2 star in TIC8. In all these cases, it turned out that there is a valid match between the TIC7 star and a Gaia DR2 star, and thus it is possible to update the older TIC7 values that eneded up in TIC8 with improved, Gaia-derived values, unless it is a star from a specially curated list, in which case the parameters are taken from those curated lists.

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