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SUBROUTINE sla_AOP ( RAP, DAP, DATE, DUT, ELONGM, PHIM, HM,
: XP, YP, TDK, PMB, RH, WL, TLR,
: AOB, ZOB, HOB, DOB, ROB )
*+
* - - - -
* A O P
* - - - -
*
* Apparent to observed place, for sources distant from the solar
* system.
*
* Given:
* RAP d geocentric apparent right ascension
* DAP d geocentric apparent declination
* DATE d UTC date/time (Modified Julian Date, JD-2400000.5)
* DUT d delta UT: UT1-UTC (UTC seconds)
* ELONGM d mean longitude of the observer (radians, east +ve)
* PHIM d mean geodetic latitude of the observer (radians)
* HM d observer's height above sea level (metres)
* XP d polar motion x-coordinate (radians)
* YP d polar motion y-coordinate (radians)
* TDK d local ambient temperature (K; std=273.15D0)
* PMB d local atmospheric pressure (mb; std=1013.25D0)
* RH d local relative humidity (in the range 0D0-1D0)
* WL d effective wavelength (micron, e.g. 0.55D0)
* TLR d tropospheric lapse rate (K/metre, e.g. 0.0065D0)
*
* Returned:
* AOB d observed azimuth (radians: N=0,E=90)
* ZOB d observed zenith distance (radians)
* HOB d observed Hour Angle (radians)
* DOB d observed Declination (radians)
* ROB d observed Right Ascension (radians)
*
* Notes:
*
* 1) This routine returns zenith distance rather than elevation
* in order to reflect the fact that no allowance is made for
* depression of the horizon.
*
* 2) The accuracy of the result is limited by the corrections for
* refraction. Providing the meteorological parameters are
* known accurately and there are no gross local effects, the
* predicted apparent RA,Dec should be within about 0.1 arcsec
* for a zenith distance of less than 70 degrees. Even at a
* topocentric zenith distance of 90 degrees, the accuracy in
* elevation should be better than 1 arcmin; useful results
* are available for a further 3 degrees, beyond which the
* sla_REFRO routine returns a fixed value of the refraction.
* The complementary routines sla_AOP (or sla_AOPQK) and sla_OAP
* (or sla_OAPQK) are self-consistent to better than 1 micro-
* arcsecond all over the celestial sphere.
*
* 3) It is advisable to take great care with units, as even
* unlikely values of the input parameters are accepted and
* processed in accordance with the models used.
*
* 4) "Apparent" place means the geocentric apparent right ascension
* and declination, which is obtained from a catalogue mean place
* by allowing for space motion, parallax, precession, nutation,
* annual aberration, and the Sun's gravitational lens effect. For
* star positions in the FK5 system (i.e. J2000), these effects can
* be applied by means of the sla_MAP etc routines. Starting from
* other mean place systems, additional transformations will be
* needed; for example, FK4 (i.e. B1950) mean places would first
* have to be converted to FK5, which can be done with the
* sla_FK425 etc routines.
*
* 5) "Observed" Az,El means the position that would be seen by a
* perfect theodolite located at the observer. This is obtained
* from the geocentric apparent RA,Dec by allowing for Earth
* orientation and diurnal aberration, rotating from equator
* to horizon coordinates, and then adjusting for refraction.
* The HA,Dec is obtained by rotating back into equatorial
* coordinates, using the geodetic latitude corrected for polar
* motion, and is the position that would be seen by a perfect
* equatorial located at the observer and with its polar axis
* aligned to the Earth's axis of rotation (n.b. not to the
* refracted pole). Finally, the RA is obtained by subtracting
* the HA from the local apparent ST.
*
* 6) To predict the required setting of a real telescope, the
* observed place produced by this routine would have to be
* adjusted for the tilt of the azimuth or polar axis of the
* mounting (with appropriate corrections for mount flexures),
* for non-perpendicularity between the mounting axes, for the
* position of the rotator axis and the pointing axis relative
* to it, for tube flexure, for gear and encoder errors, and
* finally for encoder zero points. Some telescopes would, of
* course, exhibit other properties which would need to be
* accounted for at the appropriate point in the sequence.
*
* 7) This routine takes time to execute, due mainly to the
* rigorous integration used to evaluate the refraction.
* For processing multiple stars for one location and time,
* call sla_AOPPA once followed by one call per star to sla_AOPQK.
* Where a range of times within a limited period of a few hours
* is involved, and the highest precision is not required, call
* sla_AOPPA once, followed by a call to sla_AOPPAT each time the
* time changes, followed by one call per star to sla_AOPQK.
*
* 8) The DATE argument is UTC expressed as an MJD. This is,
* strictly speaking, wrong, because of leap seconds. However,
* as long as the delta UT and the UTC are consistent there
* are no difficulties, except during a leap second. In this
* case, the start of the 61st second of the final minute should
* begin a new MJD day and the old pre-leap delta UT should
* continue to be used. As the 61st second completes, the MJD
* should revert to the start of the day as, simultaneously,
* the delta UTC changes by one second to its post-leap new value.
*
* 9) The delta UT (UT1-UTC) is tabulated in IERS circulars and
* elsewhere. It increases by exactly one second at the end of
* each UTC leap second, introduced in order to keep delta UT
* within +/- 0.9 seconds.
*
* 10) IMPORTANT -- TAKE CARE WITH THE LONGITUDE SIGN CONVENTION.
* The longitude required by the present routine is east-positive,
* in accordance with geographical convention (and right-handed).
* In particular, note that the longitudes returned by the
* sla_OBS routine are west-positive, following astronomical
* usage, and must be reversed in sign before use in the present
* routine.
*
* 11) The polar coordinates XP,YP can be obtained from IERS
* circulars and equivalent publications. The maximum amplitude
* is about 0.3 arcseconds. If XP,YP values are unavailable,
* use XP=YP=0D0. See page B60 of the 1988 Astronomical Almanac
* for a definition of the two angles.
*
* 12) The height above sea level of the observing station, HM,
* can be obtained from the Astronomical Almanac (Section J
* in the 1988 edition), or via the routine sla_OBS. If P,
* the pressure in millibars, is available, an adequate
* estimate of HM can be obtained from the expression
*
* HM ~ -29.3D0*TSL*LOG(P/1013.25D0).
*
* where TSL is the approximate sea-level air temperature in K
* (see Astrophysical Quantities, C.W.Allen, 3rd edition,
* section 52). Similarly, if the pressure P is not known,
* it can be estimated from the height of the observing
* station, HM, as follows:
*
* P ~ 1013.25D0*EXP(-HM/(29.3D0*TSL)).
*
* Note, however, that the refraction is nearly proportional to the
* pressure and that an accurate P value is important for precise
* work.
*
* 13) The azimuths etc produced by the present routine are with
* respect to the celestial pole. Corrections to the terrestrial
* pole can be computed using sla_POLMO.
*
* Called: sla_AOPPA, sla_AOPQK
*
* Last revision: 2 December 2005
*
* Copyright P.T.Wallace. All rights reserved.
*
* License:
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program (see SLA_CONDITIONS); if not, write to the
* Free Software Foundation, Inc., 59 Temple Place, Suite 330,
* Boston, MA 02111-1307 USA
*
*-
IMPLICIT NONE
DOUBLE PRECISION RAP,DAP,DATE,DUT,ELONGM,PHIM,HM,
: XP,YP,TDK,PMB,RH,WL,TLR,AOB,ZOB,HOB,DOB,ROB
DOUBLE PRECISION AOPRMS(14)
CALL sla_AOPPA(DATE,DUT,ELONGM,PHIM,HM,XP,YP,TDK,PMB,RH,WL,TLR,
: AOPRMS)
CALL sla_AOPQK(RAP,DAP,AOPRMS,AOB,ZOB,HOB,DOB,ROB)
END