# I can't find Rigel on Tycho 2 catalogue

I'm trying to develop a planetarium using Tycho 2 catalogue.

To read it I use the WCSTools. But I have a problem.

On Wikipedia I have found that Rigel star has RA: 05h 14min 32,3s and Dec: -08º 12’ 06’’. I have translate them to decimal degrees (78.6375, -8.2017). I've used that to find it on Tycho 2 catalogue (file catalog.dat) but I can't find it.

To search into the catalogue I have used the function TY2READ from ty2read.c file.

And this is how I search the star:

void ReadTy2Catalog()
{
double raCenter = 84.5;
double decCenter = -1.2;
double decDistance = 10.;

int nMaxStars = 20000;

char* filePath = "D:\\Fuentes\\Repos\\Planetarium\\StarsCataloguesLib\\Resources\\";

filePath,
TYCHO2,         /* Catalog code from wcscat.h */
raCenter,       /* Search center J2000 right ascension in degrees */
decCenter,      /* Search center J2000 declination in degrees */
raDistance,     /* Search half width in right ascension in degrees */
decDistance,    /* Search half-width in declination in degrees */
0,              /* Limiting separation in degrees (ignore if 0) */
0,              /* Inner edge of annulus in degrees (ignore if 0) */
1,              /* 1 to sort stars by distance from center */
WCS_J2000,      /* Search coordinate system */
2000.0,         /* Search coordinate equinox */
0.0,            /* Proper motion epoch (0.0 for no proper motion) */
-20.0,          /* Limiting magnitudes (none if equal) */
30.0,           /* Limiting magnitudes (none if equal) */
1,              /* Magnitude by which to sort (1 or 2) */
nMaxStars,      /* Maximum number of stars to be returned */
1);             /* Verbose*/
}


I have checked all the stars returned and none has Rigel's RA and DEC.

What am I doing wrong?

This frustrated me as well when I first used the Tycho-2 catalog. Not finding a well known bright star can be disconcerting. Quoting from http://heasarc.nasa.gov/W3Browse/all/tycho2.html

Supplement-1 (not part of this HEASARC database but available at ftp://cdsarc.u-strasbg.fr/cats/I/259/suppl_1.dat.gz) lists stars from the Hipparcos and Tycho-1 Catalogues which are not in Tycho-2.

I only skimmed that file, but I think this might be the line you're looking for:

5331 01752 1|H|078.63446353|-08.20163919|    1.9|   -0.6|  0.6|  0.5|  0.7|  0.5| | 0.312|0.012| 0.283|0.010|999|T| 24436


(the "-0.6" is the U-B color index, not the magntiude)

• Thanks. How do you read this file? Is there a library to read it? – VansFannel Nov 2 '15 at 15:30
• I don't know about a library, but tdc-www.harvard.edu/catalogs/tycho2.format.html describes the format. – user21 Nov 2 '15 at 16:14