9837( 4) - 05/20/03 14:03 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9837 Version: 4 Check-in Date: 20-May-2003 14:01:22 1.Proposal Title: Stellar Populations in the Outskirts of M33: A Unique Probe of Disk Galaxy Formation ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 12 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Dr. Annette Ferguson Max-Planck-Institut fur Astrophysik CoI: Dr. Andrew Cole Kapteyn Astronomical Institute N CoI: Dr. Rodrigo Ibata Observatoire de Strasbourg, Strasbourg N CoI: Dr. Michael Irwin University of Cambridge N CoI: Dr. Geraint Lewis University of Sydney N CoI: Dr. Tammy A. Smecker-Hane University of California - Irvine N CoI: Dr. Nial R. Tanvir University of Hertfordshire N ------------------------------------------------------------------------------------ 5. Abstract The fossil record of galaxy formation and evolution is imprinted on the structure and composition of galactic stellar populations. We have recently completed an extensive ground-based imaging survey of the low mass Local Group spiral, M33. Our analysis of the global structure of M33 suggests it is a 'pure disk' galaxy, with no discernible stellar halo. Furthermore, the disk surface brightness declines very abruptly beyond ~5 scalelengths. We propose here to obtain deep ACS imagery of two fields in the far outer disk of M33, located at 4.5 and 6 exponential scalelengths. Deep colour-magnitude diagrams reaching main sequence turn-offs of ~8 Gyr (corresponding to star formation episodes since z< 1) will be constructed and used for quantitative modelling of the star formation history. State-of-the-art cosmological simulations of galaxy formation predict stars in the outer regions of galactic disks should be predominantly young-to-intermediate age. The data we propose to obtain will directly test this idea, and provide a much-needed observational constraint on the epoch at which disk galaxies were assembled. The proposed observations will provide an excellent complement to an ongoing Cycle 11 program to study the outer disk of the more massive system, M31. ------------------------------------------------------------------------------------ 9837( 4) - 05/20/03 14:03 - [ 2] Observations Description ------------------------ Our objective is to obtain deep colour-magnitude diagrams (CMDs) at two locations in the outskirts of M33 to characterize in detail the old and intermediate-age resolved stellar populations. Based on our ground-based survey, we expect the locations chosen to be entirely dominated by disk stars. Our two fields lie at 35 and 47\arcmin along the major axis of M33, corresponding to 4.5 and 6 exponential scalelengths respectively. These radii sample regions of the disk where few, if any, young blue stars are present. We will image in the broad-V (F606W) and I (F814W) filters, the former choice being motivated by the significant throughput gains provided by the wider bandpass. Our exposure time calculations assume E(B$-$V)$=$0.04 (Schlegel \etal 1998) and a mean distance of 850~kpc. Note that if we adopt the largest distance estimate of 916~kpc derived from the TRGB (Kim \etal 2002), this translates into a magnitude difference of 0.15 and has only a small effect on our S/N estimates. Our exposures are designed to detect and study the main sequence with high S/N down to turn-off ages of $8~$Gyr (\ie mid-late F stars). For a metallicity of [Fe/H]$=-1.3$ , the main sequence turnoff of an 8~Gyr old population is V=28.2, V$-$I=0.50 (Girardi \etal 2000). Using the ACS ETC, we calculate that 4 orbits with F606W and 8 orbits with F814W are sufficient to reach a V$=$28.2 with a S/N$\approx 8-9$. This assumes $\squig 2300$s orbital visibility, after accounting for realistic overheads. For these exposures, we will dither by non-integer pixels in between exposures, to optimise S/N on faint stars. Note that we estimate reaching a limiting magnitude of V$\squig 29$, I$\squig$ 28.3 with a S/N$\squig 4-5$ which, assuming a similarily metal- poor population, corresponds to an 11~Gyr main sequence turn-off or stars formed at a z$\lesssim2$. WFPC2 parallel observations are also requested. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9837( 4) - 05/20/03 14:03 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 M33- GALAXY, DISK, SPIRAL RA=01H35M0.00S +/- 0.5", J2000 V = 22.0+/-0.5 013500+31120 DEC=+31D12'0.00" +/- 0.5", 0 PLATE-ID=00DV Coordinate Source: GSC_SURVEY_PLATE Comments: flux data refers to the brightest RGB stars expected in this field 2 M33- GALAXY, DISK, SPIRAL RA=01H35M15.0S +/- 0.5", J2000 V = 22.0+/-0.5 013515+31220 DEC=+31D22'0.00" +/- 0.5", 0 PLATE-ID=00DV Coordinate Source: GSC_SURVEY_PLATE Comments: flux data refers to the brightest RGB stars expected in this field 9837( 4) - 05/20/03 14:03 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.265 Coordinate_Frame POS-TARG Pattern_Orient 20.67 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type LINE ACS-WFC-DITHER-BOX Pattern_Purpose DITHER DITHER Number_Of_Points 2 4 Point_Spacing 0.1459 0.265 Coordinate_Frame POS-TARG POS-TARG Pattern_Orient 47.17 20.67 Center_Pattern NO NO ------------------------------------------------------------------------------------------------------------------------------------ 9837( 4) - 05/20/03 14:03 - [ 5] Visit: 01 Visit Priority: Visit Requirements: PCS MODE FINE ORIENT 0.0D TO 82.0 D ORIENT 112.0D TO 360.0 D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 M33-013500+ ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 1225 S POS TARG 0.1736, 0.1873 311200 C COMPRESSION=NONE PAR 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFPC2 IMAGE WFALL F814W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 3 M33-013500+ ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 1250 S POS TARG -0.1736,-0.1873 311200 C COMPRESSION=NONE PAR 4 WITH 3 ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFPC2 IMAGE WFALL F814W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 5 M33-013500+ ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 1310 S PAR 6 WITH 5 PATTERN 2 311200 C COMPRESSION=NONE 5-6 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY WFPC2 IMAGE WFALL F814W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 9837( 4) - 05/20/03 14:03 - [ 6] Visit: 02 Visit Priority: Visit Requirements: PCS MODE FINE SAME ORIENT AS 01 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 M33-013500+ ACS/WF ACCUM WFC F606W CR-SPLIT=NO,GAIN=2, 1 1240 S POS TARG 0.1736, 0.1873 311200 C COMPRESSION=NONE PAR 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFPC2 IMAGE WFALL F606W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 3 M33-013500+ ACS/WF ACCUM WFC F606W CR-SPLIT=NO,GAIN=2, 1 1235 S POS TARG -0.1736,-0.1873 311200 C COMPRESSION=NONE PAR 4 WITH 3 ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFPC2 IMAGE WFALL F606W CR-SPLIT=NO,ATD-GAIN=7 1 1030 S ------------------------------------------------------------------------------------------------------------------------------------ 5 M33-013500+ ACS/WF ACCUM WFC F606W CR-SPLIT=NO,GAIN=2, 1 1320 S POS TARG 0.1736,-0.1607 311200 C COMPRESSION=NONE PAR 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY WFPC2 IMAGE WFALL F606W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 7 M33-013500+ ACS/WF ACCUM WFC F606W CR-SPLIT=NO,GAIN=2, 1 1300 S POS TARG -0.1736, 0.1607 311200 C COMPRESSION=NONE PAR 8 WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY WFPC2 IMAGE WFALL F606W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 9 M33-013500+ ACS/WF ACCUM WFC F606W CR-SPLIT=NO,GAIN=2, 1 1310 S PAR 10 WITH 9 PATTERN 1 311200 C COMPRESSION=NONE 9-10 ------------------------------------------------------------------------------------------------------------------------------------ 10 ANY WFPC2 IMAGE WFALL F606W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 9837( 4) - 05/20/03 14:03 - [ 7] Visit: 03 Visit Priority: Visit Requirements: PCS MODE FINE SAME ORIENT AS 01 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 M33-013500+ ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 1225 S POS TARG -0.1736, 0.1607 311200 C COMPRESSION=NONE PAR 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFPC2 IMAGE WFALL F814W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 3 M33-013500+ ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 1250 S POS TARG 0.1736,-0.1607 311200 C COMPRESSION=NONE PAR 4 WITH 3 ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFPC2 IMAGE WFALL F814W CR-SPLIT=NO,ATD-GAIN=7 1 1100 S ------------------------------------------------------------------------------------------------------------------------------------ 5 M33-013500+ ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 1300 S POS TARG 0.273, 0.294 PAR 311200 C COMPRESSION=NONE 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY WFPC2 IMAGE WFALL F814W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 7 M33-013500+ ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 1320 S POS TARG -0.273,-0.294 311200 C COMPRESSION=NONE PAR 8 WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY WFPC2 IMAGE WFALL F814W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 9 M33-013500+ ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 1300 S POS TARG -0.273, 0.252 311200 C COMPRESSION=NONE PAR 10 WITH 9 ------------------------------------------------------------------------------------------------------------------------------------ 10 ANY WFPC2 IMAGE WFALL F814W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 11 M33-013500+ ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 1320 S POS TARG 0.273,-0.252 PAR 311200 C COMPRESSION=NONE 12 WITH 11 ------------------------------------------------------------------------------------------------------------------------------------ 12 ANY WFPC2 IMAGE WFALL F814W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 9837( 4) - 05/20/03 14:03 - [ 8] Visit: 04 Visit Priority: Visit Requirements: PCS MODE FINE ORIENT 0.0D TO 83.0 D ORIENT 118.0D TO 360.0 D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 M33-013515+ ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 1225 S POS TARG 0.1736, 0.1873 312200 C COMPRESSION=NONE PAR 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFPC2 IMAGE WFALL F814W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 3 M33-013515+ ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 1250 S POS TARG -0.1736,-0.1873 312200 C COMPRESSION=NONE PAR 4 WITH 3 ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFPC2 IMAGE WFALL F814W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 5 M33-013515+ ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 1310 S PAR 6 WITH 5 PATTERN 2 312200 C COMPRESSION=NONE 5-6 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY WFPC2 IMAGE WFALL F814W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 9837( 4) - 05/20/03 14:03 - [ 9] Visit: 05 Visit Priority: Visit Requirements: PCS MODE FINE SAME ORIENT AS 04 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 M33-013515+ ACS/WF ACCUM WFC F606W CR-SPLIT=NO,GAIN=2, 1 1240 S POS TARG 0.1736, 0.1873 312200 C COMPRESSION=NONE PAR 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFPC2 IMAGE WFALL F606W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 3 M33-013515+ ACS/WF ACCUM WFC F606W CR-SPLIT=NO,GAIN=2, 1 1235 S POS TARG -0.1736,-0.1873 312200 C COMPRESSION=NONE PAR 4 WITH 3 ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFPC2 IMAGE WFALL F606W CR-SPLIT=NO,ATD-GAIN=7 1 1030 S ------------------------------------------------------------------------------------------------------------------------------------ 5 M33-013515+ ACS/WF ACCUM WFC F606W CR-SPLIT=NO,GAIN=2, 1 1320 S POS TARG 0.1736,-0.1607 312200 C COMPRESSION=NONE PAR 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY WFPC2 IMAGE WFALL F606W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 7 M33-013515+ ACS/WF ACCUM WFC F606W CR-SPLIT=NO,GAIN=2, 1 1300 S POS TARG -0.1736, 0.1607 312200 C COMPRESSION=NONE PAR 8 WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY WFPC2 IMAGE WFALL F606W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 9 M33-013515+ ACS/WF ACCUM WFC F606W CR-SPLIT=NO,GAIN=2, 1 1310 S PAR 10 WITH 9 PATTERN 1 312200 C COMPRESSION=NONE 9-10 ------------------------------------------------------------------------------------------------------------------------------------ 10 ANY WFPC2 IMAGE WFALL F606W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 9837( 4) - 05/20/03 14:03 - [ 10] Visit: 06 Visit Priority: Visit Requirements: PCS MODE FINE SAME ORIENT AS 04 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 M33-013515+ ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 1225 S POS TARG -0.1736, 0.1607 312200 C COMPRESSION=NONE PAR 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY WFPC2 IMAGE WFALL F814W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 3 M33-013515+ ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 1250 S POS TARG 0.1736,-0.1607 312200 C COMPRESSION=NONE PAR 4 WITH 3 ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY WFPC2 IMAGE WFALL F814W CR-SPLIT=NO,ATD-GAIN=7 1 1100 S ------------------------------------------------------------------------------------------------------------------------------------ 5 M33-013515+ ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 1300 S POS TARG 0.273, 0.294 PAR 312200 C COMPRESSION=NONE 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY WFPC2 IMAGE WFALL F814W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 7 M33-013515+ ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 1320 S POS TARG -0.273,-0.294 312200 C COMPRESSION=NONE PAR 8 WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY WFPC2 IMAGE WFALL F814W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 9 M33-013515+ ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 1300 S POS TARG -0.273, 0.252 312200 C COMPRESSION=NONE PAR 10 WITH 9 ------------------------------------------------------------------------------------------------------------------------------------ 10 ANY WFPC2 IMAGE WFALL F814W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 11 M33-013515+ ACS/WF ACCUM WFC F814W CR-SPLIT=NO,GAIN=2, 1 1320 S POS TARG 0.273,-0.252 PAR 312200 C COMPRESSION=NONE 12 WITH 11 ------------------------------------------------------------------------------------------------------------------------------------ 12 ANY WFPC2 IMAGE WFALL F814W CR-SPLIT=NO,ATD-GAIN=7 1 1190 S ------------------------------------------------------------------------------------------------------------------------------------ 9837( 4) - 05/20/03 14:03 - [ 11] Summary Form for Proposal 9837 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC WFALL ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO GAIN=2 COMPRESSION=NONE ATD-GAIN=7 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE FINE ORIENT 0.0D TO 82.0 D ORIENT 112.0D TO 360.0 D POS TARG 0.1736, 0.1873 PAR 2 WITH 1 POS TARG -0.1736,-0.1873 PAR 4 WITH 3 PAR 6 WITH 5 PATTERN 2 5-6 PCS MODE FINE SAME ORIENT AS 01 POS TARG 0.1736,-0.1607 PAR 6 WITH 5 POS TARG -0.1736, 0.1607 PAR 8 WITH 7 PAR 10 WITH 9 PATTERN 1 9-10 POS TARG -0.1736, 0.1607 PAR 2 WITH 1 POS TARG 0.1736,-0.1607 PAR 4 WITH 3 POS TARG 0.273, 0.294 PAR 6 WITH 5 POS TARG -0.273,-0.294 PAR 8 WITH 7 POS TARG -0.273, 0.252 PAR 10 WITH 9 POS TARG 0.273,-0.252 PAR 12 WITH 11 PCS MODE FINE ORIENT 0.0D TO 83.0 D ORIENT 118.0D TO 360.0 D PCS MODE FINE SAME ORIENT AS 04 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names M33-013500+311200 ANY M33-013515+312200 ------------------------------------------------------------------------------------------------------------------------------------