Construction of the STK Star Catalogs
The STK installation contains two star catalogs: Hipparcos 2 and Bright Star version 5. Additional catalogs, including Hipparcos 1, Tycho 1, and Tycho 2, are available on a supplementary data disc on the AGI website. Each catalog consists of a data file (binary or ASCII) and an ASCII cross-reference file, which enables you to cross-reference between the catalog-specific IDs and common names.
Common data structure
Regardless of the source of star data, STK assumes a common data structure. Not all elements of the common data structure are directly available from all source star catalogs. In the case of missing data elements, STK will do one fo the following:
- Augment with data from other catalogs
- Compute the element from available data
- Set the element to a default value
For the exact method of construction for each catalog, see the Catalogs section below.
| Data Type | Parameter | Description |
|---|---|---|
|
ID |
ID Type |
Identifier type (Example: Hip for Hipparcos ID) |
|
ID |
Identifier |
|
|
Astrometric Data |
Epoch |
Epoch of specified RA/Dec (Example: J2000) |
|
Reference Frame |
Reference frame of specified RA/Dec (Example: ICRF) |
|
|
Right Ascension |
Right ascension at specified epoch |
|
|
Declination |
Declination at specified epoch |
|
|
Proper Motion RA |
Proper motion in right ascension, |
|
|
Proper Motion Dec |
Proper motion in declination, |
|
|
Radial Velocity |
Radial velocity |
|
|
Parallax |
Trigonometric parallax |
|
|
Constellation |
Astronomical constellation |
|
|
Physical Data |
Visual Magnitude |
Johnson visual magnitude |
|
B-V |
Johnson B-V |
|
|
Effective Temperature |
Effective temperature |
|
|
Irradiance Conversion Factor |
Converts Planck function radiance to a rescaled irradiance at Earth |
Determination of astronomical constellations
None of the preprocessed catalogs contain constellation designations. However, STK considers all stars to lie within the boundaries of a constellation. STK computes constellation assignments using boundary information provided in catalog form by Davenhall and Leggett1, which is available through the CDS2, using the boundary data in the mean of 1875 reference frame. STK assigns individual stars to a constellation based on the transformation of their epoch positions from the reference frame of the catalog to the mean of 1875 reference frame.
Effective temperature
None of the preprocessed catalogs contain effective temperature. STK computes the effective temperature based on the following relationship from Sekiguchi and Fukugita3:
using the full sample coefficients from Sekiguchi and Fukugita3 and reproduced in the following table:
Parameter fit for effective temperature relation
| Parameter | Value |
|---|---|
|
c 0 |
3.939654 |
|
c 1 |
-0.395361 |
|
c 0 |
0.2082113 |
|
c 0 |
-0.0604097 |
|
f 1 |
0.027153 |
|
f 2 |
0.005036 |
|
g 1 |
0.007367 |
|
h 1 |
-0.01069 |
As of the STK 9.2.1 release, STK does not use metalicity, 
, and surface gravity, 
, in the computation, but sets them to zero. The value for 
is taken from the catalog currently in use. For a brief validation of the effective temperature computation, see Computation of Star Effective Temperature for STK.
Magnitude to Irradiance Conversion Factor
The magnitude to Irradiance Conversion Factor is not given directly in any catalog. This factor converts the Planck function radiance to a rescaled irradiance at Earth’s distance from the star. It is computed from the following relation to the effective temperature and visual magnitude,
where,
hc/k = 143 877 520.0
l = 5500 Ångstroms
T sun = 5 777.0 K
R = sun’s radius (695 508.0 km)
d = earth – sun distance (149 597 872.0 km)
Catalogs
The following are descriptions of the preprocessing steps for each star catalog, including specification of the associated reference frame and epoch. All star information was obtained through the Strasbourg Astronomical Data Center (CDS)4.
The Bright Star Catalogue, 5th Revised Edition
The Bright Star catalog5 provides a complete set of astrometric data for 9110 objects. The Harvard Revised (HR) number is the primary identifier. Astrometric data is specified at the Julian epoch 2000.0 (J2000) and referenced to the mean of J2000 reference frame.
The Hipparcos 2 catalog6 provides the second, and improved, reduction of the Hipparcos astrometric data7. Star identification is via the Hipparcos identifier, a simple count starting at 1. There are 118,218 total entries in the Hipparcos catalog, with 263 entries lacking astrometric information, resulting in an astrometric catalog of 117,955 entries. While the Hipparcos 2 catalog does not provide radial velocity, the astrometric solution is augmented with radial velocity8 for a subset of the catalog based on the work of Gontcharov9. Astrometric data is specified at the Julian epoch 1991.25 (J1991.25) and referenced to the International Celestial Reference Frame (ICRF). The visual magnitude is taken from Hipparcos 1 as it is not given directly in the Hipparcos 2 catalog.
The Hipparcos 1 catalog10 provides the original reduction of the Hipparcos astrometric data11. Star identification is via the Hipparcos identifier, a simple count starting at 1. There are 118,218 total entries in the Hipparcos catalog with 263 entries lacking astrometric information resulting in an astrometric catalog of 117,955 entries. While the Hipparcos 1 catalog does not provide radial velocity, the astrometric solution is augmented with radial velocity8 for a subset of the catalog based on the work of Gontcharov9. Astrometric data is specified at the Julian epoch 1991.25 (J1991.25) and referenced to the International Celestial Reference Frame (ICRF).
The Tycho 1 catalog10 provides the original reduction of the Tycho astrometric data for slightly over a million stars11. Star identification is via the Tycho identifier. The Tycho identifier consists of three distinct parts: the Guide Star Catalog region number, the count within the region, and component of the star system. While the Tycho 1 catalog does not provide radial velocity, the astrometric solution is augmented with radial velocity8 for a subset of the catalog based on the work of Gontcharov9. Astrometric data is specified at the Julian epoch 1991.25 (J1991.25) and referenced to the International Celestial Reference Frame (ICRF).
The Tycho 2 catalog12 provides a second, expanded reduction of the Tycho astrometric data for slightly over 2.5 million stars13. Star identification is via the Tycho identifier. The Tycho identifier consists of three distinct parts: the Guide Star Catalog region number, the count within the region, and component of the star system. Identifiers are consistent between Tycho 1 and Tycho 2. While the Tycho 2 catalog does not provide radial velocity, the astrometric solution is augmented with radial velocity8 for a subset of the catalog based on the work of Gontcharov9. Astrometric data is specified at the Julian epoch 2000.0 (J2000) and referenced to the International Celestial Reference Frame (ICRF). The Tycho 2 catalog also does not provide parallax; the astrometric solution is augmented with parallax information from the Hipparcos 2 catalog. The Johnson visual magnitude is computed from the Tycho B T and V T magnitudes11:
.
The Johnson (B-V) magnitude is computed as11
.
Finally, the Tycho 2 catalog does not natively contain the brightest stars (Vmag < 1.9). Data for these brightest stars has been added from the Hipparcos 2 catalog.
References
1 Davenhall, A.C., Leggett, S.K., “Catalogue of Constellation Boundary Data”, Royal Observatory of Edinburgh, 1989.
2ftp://cdsarc.u-strasbg.fr/pub/cats/VI/49
3 Sekiguchi, M. and Fukugita, M., “A Study of the B-V Color-Temperature Relation”, The Astronomical Journal, No. 120, pp 1072-1084, August 2000.
4http://cdsarc.u-strasbg.fr/cats/Cats.htx
5ftp://cdsarc.u-strasbg.fr/pub/cats/V%2F50
6ftp://cdsarc.u-strasbg.fr/pub/cats/I/311
7 Van Leeuwen, F., Fantino, E., “A New Reduction of the Raw Hipparcos Data”, Astronomy & Astrophysics, manuscript 3193, February 2008.
8ftp://cdsarc.u-strasbg.fr/pub/cats/III%2F252
9 Gontcharov, G.A., “Radial velocities of 35 495 Hipparcos stars in a common system”, Astronomical & Astrophysical Transactions, Volume 25, Issue 2&3, April 2006 , pages 145 – 148.
10ftp://cdsarc.u-strasbg.fr/pub/cats/I%2F239
11 Perryman, M.A.C., ESA, “The Hipparcos and Tycho catalogues. Astrometric and photometric star catalogues derived from the ESA Hipparcos Space Astrometry Mission”, Publisher: Noordwijk, Netherlands: ESA Publications Division, 1997, Series: ESA SP Series vol no: 1200, ISBN: 9290923997.
12ftp://cdsarc.u-strasbg.fr/pub/cats/I%2F259
13 Høg, E., Fabricius, C., Makarov, V.V., Urban, S., Corbin, T., Wycoff, G., Bastian, U., Schwekendiek, P., and Wicenec A., “ The Tycho-2 Catalogue of the 2.5 million brightest stars”, Astronomy and Astrophysics, 355, L27-L30, 2000.