AIPS HELP file for STARS in 31DEC24
As of Fri Apr 19 7:12:12 2024
STARS: Task to generate an ST ext. file with star positions
INPUTS
INNAME Image name(name).
INCLASS Image name(class).
INSEQ 0.0 9999.0 Image name(seq. #). 0=>high
INDISK Disk drive #. 0=>any
STVERS 0.0 46655.0 STar file version number.
INTEXT File with star positions
DECIMAL -1.0 2.0 1->RA Dec in decimal degrees,
2->RA DEC in arc seconds from
reference
<= 0 RA DEC sexagesimal
X Input Star Coordinate epoch
1: 1900; 2: B1950; 3: J2000
4: Galactic; 5: OHLSSON Gal.
6: VAN TULDER Galactic
7: Super Galactic; 0=> 3
Y Output Star Coordinate epoch
HELP SECTION
STARS
Type: Task
Use: STARS reads a text file containing "star" positions and makes an
ST extension file. Plot programs can then use this file to plot
symbols at the indicated positions. See EXPLAIN STARS for the
required format of the text file.
Adverbs:
INNAME......Image name (name). Standard defaults.
INCLASS.....Image name (class). Standard defaults.
INSEQ.......Image name (seq. #). 0 => highest.
INDISK......Disk unit #. 0 => any.
STVERS......Version number of ST (star position) file to be
created. 0 => highest+1.
INTEXT......Name of file containing star positions; name should be
of the form: myarea:filename.ext
DECIMAL.....= 1 => Right ascensions and declinations are in
decimal degrees
= 2 => Right ascensions and Declinations are given as
RASHIFT and DECSHIFT values in arc seconds
<= 0 => Right ascensions and declinations are in
sexagesimal
X...........Input Star Coordinate epoch
1: 1900; 2: B1950; 3: J2000; 4: Galactic
5: OHLSSON Gal.; 6: VAN TULDER Galactic
7: Super Galactic; if > 1000 then year assumed
0:=> 3 (J2000)
Y...........Output Star Coordinate epoch.
If X = Y then no transformation is performed
EXPLAIN SECTION
STARS: Task to create an ST (star position) extension file
RELATED PROGRAMS: CNTR, PCNTR, GREYS, PROFL, REGRD
PURPOSE
STARS creates an ST extension file for the specified image. This
file contains a list of positions and "sizes" for stars or whatever
else one wishes marked on images. The output file is a standard table
extension file and hence can be reviewed with PRTAB and handled by a
number of tasks including FITTP and IMLOD. The star "sizes" can be
used to indicate, for example, Gaussian component widths and position
angle or position uncertainty or magnitudes and are used as scale
factors in plotting plus signs or other symbols on contour or
grey-scale images.
COMMENTS
INTEXT:
The user must create a table from which STARS reads star
positions and uncertainties. The name of the input file must be in
the "standard" DIRECTORY:FILE format and the file name must be in
UPPER CASE LETTERS (unless you leave off the close quote mark).
Example:
INTEXT='myarea:MYSTARS.DAT'
where MYAREA is an environment variable set
before starting AIPS:
percentsetenv MYAREA /mnt/username
The AIPS area $RUNFIL is often used for STARS inputs.
The text file contains one line per star and each line has
up to 7 logical columns containing, in order:
1. X position (Right Ascension HH MM SS.SS if DECIMAL <= 0)
2. Y position (Declination +/-DD MM SS.S if DECIMAL <= 0)
RA/DEC in degrees if 0 < DECIMAL < 1.5
RA/DEC as offsets in arc sec if DECIMAL > 1.5 so that
RA = RA_0 + Value1 / cos (DEC_0)
DEC = DEC_0 + Value2
3. Major axis (Full width in arc seconds on sky)
4. Minor axis (Full width in arc seconds on sky)
5. Position Angle (E of N, degrees)
6. Star Type (-1 to 20, integer )
7. Star label (up to 24 character string)
If X and Y are not RA-DEC or DEC-RA, then the logical columns
are also 7 actual columns and the units are in AIPS standard
units (e.g. degrees, m/s etc. ). In this case the position
angle should be given as 0.0, the major axis is the width in the
Y coordinate and the minor axis is the width in the X
coordinate. For RA and DEC positions, the sexagesimal notation
is used (e.g. HH MM SS.SSS -DD MM SS.S) for the positions and
arc seconds on the sky are used for the Deltas.
The last 5 columns are not required. If the last 5 columns are
not given, a value of 1 cell is assumed for the deltas.
If the position angle is not included, the default is 0 degrees.
If the star type is not included, the default type is a cross.
The default is no label string.
Blank lines and lines beginning with # in column 1 are ignored.
There are currently 24 different types of star marks.
<0: No Mark, only the star label is printed
=0: value changed to -1 if a label is present, else changed to +1
1: Plus sign (default) 12: Five pointed star
2: Cross (X) 13: Star of David
3: Circle 14: Seven-pointed star
4: Box 15: Eight-pointed star
5: Triangle 16: Nine-pointed star
6: Diamond 17: Ten-pointed star
7: Pentagon 18: 11-pointed star
8: Hexagon 19: 12-pointed star
9: Septagon 20: 13-pointed star
10: Octagon 21: 14-pointed star
11: Nine-gon 22: Plus with gap
23: Vertical line
24: Cross (X) with gap
The Box (type=4) is different from the diamond in that the
star size is the half height and width of the box dimensions.
The Box and the Null (<0) are labeled at RA and Dec plus Delta
RA and Delta Dec. The other marks are labeled at the right
edge of the of the Rotated RA axis. The CROSS WITH GAP
(type=24) has the inner third of the cross removed so the
marked object is not over written.
You can view the contents of the ST file with PRTAB.
Coordinate transformation
The input and output epochs of the coordinates is specified by
X and Y. Currently indexes are:
1: 1900;
2: B1950;
3: J2000;
4: Galactic
5: OHLSSON Gal.;
6: VAN TULDER Galactic
7: Super Galactic
if > 1000 then year assumed (ie if X = 1975, input epoch
is 1975)
0:=> 3 (J2000)
The coordinate transformation performed by STARS is an
approximation to the exact transformation from B1950 to J2000.
As it currently stands, the year of observation of the B1950
coordinate can not be incorperated into the J2000 trans.
Accuraccy of the B1950 to J2000 transformation is on the
order of 1" over most of the sky if the date of observation
is not included. Also see the EXPLAIN file for REGRD.
Algorithm:
The Euler angles for the transformation from a variety of
coordinate systems to Equatorial B1950.0 are stored or
computed. To obtain the Euler angles to go from system X to
system Y, those from X to B1950.0 are combined with the
inverse of those from Y to B1950.0.
References:
Smith, C.A., et al, 1989. Astron. J., 97, 265.
Yallop, B.D., et al, 1989. Astron. J., 97, 274.
Notes:
1) A failing of the IAU1976 system was not to give simple and
unambiguous names to the systems of constants and
coordinates. For example, the equatorial coordinate system
loosely described as "J2000.0" usually means "the position at
epoch J2000.0 on the mean equator and equinox of J2000.0 in
the IAU1976 system of coordinates". However, the J prefix
only indicates the new convention for computing epochs, there
is no formal reason to disassociate it from the old Bessel-
Newcomb system.
Nevertheless, one is left to assume that any coordinate
system associated with a Julian epoch refers to the IAU1976
system, and that Besselian epochs indicate Bessel-Newcomb
precession. An epoch prefix of 'b' is interpreted as
Bessel-Newcomb without E-terms.
2) References here to "equatorial B1950.0" or "ecliptic J2000.0"
etc. refer strictly to space-fixed coordinate systems. These
are defined by the mean equator (or ecliptic) and equinox
specified by the Bessel-Newcomb precession formulae for
Besselian epochs, or the IAU1976 system for Julian epochs.
In transforming star catalogue positions it should be noted
that coordinates in the "FK4" system include the E-terms of
aberration (less than 1 arcsec), whereas the "FK5" system
excludes them. The exact transformation between these two
systems is therefore not a simple rotation.
3) The angles for transforming from J2000.0 to B1950.0 were
computed from the matrix coefficients Mij in the SLALIB
routine FK524 according to the following
PHI0 = ATAN2(-M31,M32)
THETA = ATAN2(STH,M33)
PHI = ATAN2(M13,-M23)
where STH is an average
STH = (M31/SIN(PHI0) - M13/SIN(PHI))/2D0
4) Formulae for the precession angles are conventionally given
for precession from epoch E1 to epoch E2, referenced to the
basic epoch E0 (J2000.0 or B1900.0). This is avoided here,
since it results in precession coefficients which are not
independent of one another. Instead, only precession from
the basic epoch E0 to arbitrary epoch E is used. Precession
between any two arbitrary epochs is then given by the inverse
of precession from E0 to E1 followed by precession from E0 to
E2.
5) If the Euler angles for a rotation are (PHI0, THETA, PHI)
then for the inverse rotation they are (PHI, -THETA, PHI0).
Author of coordinate transformations:
Mark Calabretta, Australia Telescope.