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

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

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.