Tycho Epoch Photometry Annex

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The presence of Tycho epoch photometry in the Hipparcos and Tycho

Catalogues (ESA 1997) is defined in Tycho field T50:



- a blank field indicates that epoch photometry is not provided;



- ’A’ (34,446 occurrences) means that epoch photometry is given for

  these stars in the machine-readable Tycho Epoch Photometry Annex A,

  as made available on the ASCII CD-ROMs (ESA SP-1200, disc 4);



- ’B’ (447,107 occurrences) means that epoch photometry is not given

  in the Annex A but is given in a machine-readable data set, Annex B,

  made available at CDS (I/239/epophot,

  http://cdsarc.u-strasbg.fr/ftp/cats/I/239/epophot/). Note that Tycho

  Epoch Photometry Annex B includes objects flagged ‘A’ as well as

  those flagged ‘B’, and therefore contains 34,446 + 447,107 = 481,553

  entries.



As a result of unrecoverable data loss (in some sky zones) that took

place between delivery of the epoch data to CDS and their ingestion

into the VizieR database, the actual epoch photometry that has been

served by CDS as of 2001 differs from what is documented in ESA

SP-1200 (1997). CDS provides data for 524,423 entries (although there

is only actual data for 508,578 stars):



- ’A’ (34,181 occurrences) indicates Tycho Epoch Photometry Annex A;



- ’B’ (424,331 occurrences) indicates Tycho Epoch Photometry Annex B;



- ’b’ (12,998 occurrences) indicates a class ’B’ object for which the

  data was reconstructed in 2001 albeit not with exactly the same

  result;



- ’c’ (33,769 occurrences) indicates a star originally announced

  without epoch photometry (T50 is blank) but for which epoch

  photometry could be derived in 2001;



- ’-’ (3319 occurrences) indicates a class ’B’ object for which the

  epoch photometry could not be reconstructed in 2001.



Note: ’A’ + ’B’ + ’b’ + ’c’ + ’-’ = 508,578



The data served here, through the Hipparcos and Tycho Legacy Archive,

has yet a different origin. In view of the data corruption detected in

the Tycho Epoch Photometry Annex B - confirmed by CDS/VizieR - we

have partially recovered these data. The recovered data has been

kindly provided by members of the Tycho consortium (TDAC,

C. Fabricius) in the form of 11 DVDs with just above 10,000 stars in

each file, except for the last one, that contained 10582 stars. In the

combined dataset, we have identified a total of 458,089 stars with

valid data and declared a data loss of 50,489 stars with respect to

the initial tyc_epo.dat data product for two reasons:



1. 14,881 stars lost due to truncation (TYC ID > 9209-501-1):

   - ’A’: 417

   - ’B’: 1 (TYC ID 9232-1010-1)

   - ’b’: 3502

   - ’c’: 8166

   - ’-’: 2795 stars


2. 35,608 stars lost due to data corruption in the TYC ID range

2161-16-1 to 2634-1009-1:

   - ’A’: 525

   - ’b’: 9476

   - ’c’: 25603

   - ’-’: 4 stars



The epoch photometry of a total of 12979 B/b-type sources has been

declared lost for the Tycho Epoch Photometry Annex B.



ESASky Hipparcos and Tycho Legacy Archive team

28 June 2021