Ulysses GAS - Interstellar Neutral Gas Experiment Bundle Ulysses Jupiter Encounter GAS Experiment Sky Maps Data Description PDS3 DATA_SET_ID = ULY-J-GAS-5-SKY-MAPS-V1.0 ORIGINAL DATA_SET_NAME = ULY JUPITER INTERSTELLAR NEUTRAL-GAS EXPERIMENT SKY MAPS START_TIME = 1991-07-22T23:17:00.000 STOP_TIME = 1992-04-10T22:42:00.000 DATA_SET_RELEASE_DATE = 1999-03-01 PRODUCER_FULL_NAME = MANFRED WITTE Data Description ================ Bundle Overview ================= The GAS-Instrument on ULYSSES provides angular distributions of count rates from interstellar helium particles (in the NG-mode) or from celestial UV-intensities (UV-mode). Therefore the data are presented in the form of maps rather than as time series (as for most other ULYSSES experiments). The intensities are mapped in an ecliptic coordinate system centered in the spacecraft. In this system, the positions of the Sun and the planets vary with time and with the position of the spacecraft along its trajectory, however, the positions of stars remain fixed. The actual positions of Sun, Earth, and Jupiter are indicated by yellow, green and white dots, respectively. The area around the Sun is excluded from observation to avoid damaging intensities from direct sunlight. The intensities obtained in the UV-mode (the housekeeping parameter HV given in the bottom line of each map, has a positive value) are color coded in the range 10...1000 counts/s, in the NG-mode (HV has a negative value) in the range 0.1...10 counts/s. File Name Conventions: [Note that the naming convention was modified from that originally provided to ISO 9660 and DOS compliant 8.3 at the PDS/PPI node. The description provided below reflects these changes.] The maps are provided in three different formats, as indicated in the extensions of the filenames yddd_NV.ext. 1.) *.ps : postscript format. 2.) *.gif : ready-to-view GIF-format. 3.) *.txt : ASCII-format to allow further computerized processing. This format is described in detail in the separate file FORMAT.TXT. These files are contained in a compressed format in the *.ZIP-files. The further information encoded in the filename is yddd : date of measurement(yy: year,ddd: day of the year). N : indicator of the telescope used, 1 = narrow field of view (NFOV), 2 = wide field of view (WFOV). V : Version indicator, 1,2, ... : Running number of measurement during that day. C : The map is composited from individual sub-images, named in the lower left corner of the map. Ix : This map contains data from more than one scan through the covered area (to improve counting statistics). Interstellar Gas (NG-mode): Most of these maps are restricted to an area around the apparent flow direction of the interstellar helium particles. It is important to note, that the locally observed, apparent flow direction deviates from the flow direction at large distances (outside the solar system) for two reasons: 1.) The local flow direction results from a deflection of the asymptotic direction due to the solar gravity (hyperbolic orbits). 2.) The observed, apparent flow direction deviates from the local flow direction due to the aberration effect, resulting from a combination of the particle velocity vector and the spacecraft velocity vector. This effect is significant (of the order of 10 degrees) as the spacecrafts velocity is of the same order as the particle velocity (several 10 km/s). The systematic variation in the flow intensity which can be observed during over extended periodes in the ULYSSES mission is a result of the variation of the relative energy of the particles in the instrument's system. The detection efficiency of helium particles is strongly energy dependent with a sharp cut-off at energy around 30 eV (equivalent to a velocity of about 30 km/s for helium particles). This threshold is only exceeded when the spacecraft velocity (in magnitude and direction) adds in a favourable way to the local particle velocity. This is the case during extended periodes of the ULYSSES mission, from launch to Jupiter fly-by (Nov. 1990 to Feb. 1992) and in periods before and after perihelion (July 1994 to July 96 and again in 1999 to 2001). Due to a residual sensitivity of the instrument to UV-photons, even in the NG-mode, also the signal from UV-stars is registered. This has been used to verify the pointing accuracy of the instrument to be of the order to a few tenths of a degree. Neutral particles from Jupiter: Close to Jupiter, in January to April 1992, the integral fluxes of low energy neutral particles can be derived from the observation of their angular distributions. Record Format ------------- The files are written in ASCII, free format. Each file consists of a - HEADER section (records 1 to 50) and the - PIXEL-DATA section (records 51 to EOF) 1.) HEADER records: 1-10: HOUSEKEEPING DATA of date: 1: date of start of measurements, source-filename 2-6: housekeeping-data (command register contents) 7: file generation date 8: ecl. longitude and latitude of Sun, as seen from ULS 9: ecl. longitude and latitude of Earth, as seen from ULS 10: ecl. longitude and latitude of Jupiter, as seen from ULS 11-17: CELESTIAL DATA of date (ecliptic system, sun-centered) 11: date(yy,doy,hh,mm); direction of spin axis (ecl.long; ecl.lat;(deg.)) 12: position + velocity of ULS(ecl.kart.coord.(AU, Km/s)) 13: position + velocity of Earth(ecl.kart.coord.(AU, Km/s)) 14: position + velocity of Jupiter(ecl.kart.coord. (AU, Km/s)) 15-17: transformation matrix, S/C-system -> ecliptic system 18: source-files for this image 19-20: TBD 21-50: Model parameter (TBD) 2.) PIXELDATA records 51-end of file(EOF): each record contains the data for one pixel in the fields: 1: measured counts/s * 100 2: total number of counts in the accumulation period 3: star flag 0 = O.K.; 1 = pixel contaminated by star light -1 = not yet determined 4: counts/sec, as calculated along the line of sight from a model (dummy value = -99.) 5-7: TBD (dummy value = -99.) 8-EOR: 5 pixel coordinates (each direction is given in longitude and latitude (deg.) of the ecl.system, ULS centered) 8: direction of the pixel center (line of sight) 9-12: 4 directions to the corners of the pixel, (9-EOR): (there can be 3 or 5 or more corners, in case the pixel intersects with the borders of the coordinate system) References: ======== Banaszkiewicz, M., M. Witte, and H. Rosenbauer, Determination of interstellar helium parameters from the ULYSSES-NEUTRALGAS experiment: Method of data analysis, Astron. Astrophys. Supp. Ser., 120, 1-16, 1996. Witte, M., H. Rosenbauer, E. Keppler, H. Fahr, P. Hemmerich, H. Lauche, A. Loidl, and R. Zwick. The Interstellar Neutral-Gas Experiment On Ulysses, Astron. Astrophys. Suppl. Ser., 333, 1992. Witte, M., H. Rosenbauer, M. Banaszkiewics, and H. Fahr, The Ulysses Neutral Gas Experiment: determination of the velocity and temperature of the interstellar neutral Helium, Adv. Space Res., 13, (6)121, 1993. (https://doi.org/10.1016/0273-1177(93)90401-V) Witte, M., M. Banaszkiewicz, and H. Rosenbauer, Recent results on the parameters of the interstellar helium from the ULYSSES/GAS experiment, Space Sci. Rev., 78, 289-296, 1996. (http://dx.doi.org/10.1007/BF00170815)