7411( 12) - 02/03/98 13:18 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7411 Version: 12 Check-in Date: 03-Feb-1998 13:16:29 1.Proposal Title: Intergalactic Stars in the Virgo Cluster ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: HARRY FERGUSON SPACE TELESCOPE SCIENCE INSTITUTE CoI: Ted von Hippel University of Wisconsin N CoI: Nial Tanvir University of Cambridge N ------------------------------------------------------------------------------------ 5. Abstract Using deep star counts from WFPC2 we have shown the existence of a population of intergalactic stars in the Virgo cluster. Here we propose deep infrared and optical imaging of this diffuse component in several fields to map its spatial distribution and provide information on its metallicity. These results will provide (1) an improved estimate of the mass of stars stripped off from galaxies in encounters during the formation of the Virgo cluster; (2) a critical test of distance estimates to the Virgo cluster based on Cepheids; (3) a measure of the radial density profile of the diffuse population; (4) a measure of the symmetry of the population about M87, and (5) a sensitive search for galaxies far below the surface brightness limits of conventional surface photometry. ------------------------------------------------------------------------------------ 7411( 12) - 02/03/98 13:18 - [ 2] Observations Description ------------------------ The installation of STIS and NICMOS in HST will greatly increase the speed with which we can detect and measure intergalactic RGB tip stars in Virgo. Furthermore, using both of these instruments we will be able to measure colors for these stars. These colors will allow us to more easily remove background contaminating galaxies from our sample and to determine the metallicities, at least in a relative manner, for the RGB tip stars (see Fig. 2). We calculate that we can achieve our science goals by observing to J ~ 26.4 (S/N = 4) and to a comparable depth with STIS, depending on the metallicity of the RGB. This will require 3 orbits using STIS + 50CCD (clear) filter and 3 orbits using NIC3 + F110W, per field. (5/21/97 -- as NIC3 is out of focus, we have substituted NIC2. There will be enough stars in the field to meet our scientific goals, although NIC3 would be better if it becomes available.) Our calculations are based on detailed simulations which assume the instrument characteristics in the STIS and NICMOS Instrument Handbooks, the Padova isochrones for a 13.8 Gyr population, and a distance modulus to Virgo of 31.3 (Tanvir et al. 1995). The simulations have been carried out for three different metallicities (see Fig. 2), 0.02 * solar, 0.2 * solar, and solar. For each simulated star a realistic S/N is determined, and then that star is scattered with a gaussian random error with Sigma = S/N^-1. All simulated stars for which S/N >= 4 in both bands are plotted. The STIS magnitudes were determined by integrating stellar spectra at the appropriate temperature, as given by the Padova isochrones, over the STIS + 50CCD bandpass. Note the tremendous metallicity sensitivity for this combination of bandpasses. beginfigure plottwosim_cm_fig3land.psfieldpos.ps caption Simulation of the J versus STIS-J color--magnitude diagram expected for the intergalactic stars in the Virgo cluster, where STIS is the ``color'' from the STIS detector with the clear filter. The simulations have been carried out for three different metallicities, from left to right, 0.02 * solar, 0.2 * solar, and solar. The open circles are simulated AGB stars and the asterisk symbols are simulated RGB stars, both based on Padova isochrones for a 13.8 Gyr population. The STIS magnitudes were determined by integrating stellar spectra at the appropriate temperature, as given by the Padova isochrones, over the STIS + clear filter bandpass. The input isochrones are plotted as dashed and solid lines, respectively. For each simulated star a realistic S/N is determined, and then that star is scattered with a gaussian random error with Sigma = S/N^-1. All simulated stars for which S/N >= 4 in both bands are plotted. These simulations assume 3 orbits of exposure for the STIS and 3 orbits of exposure for the J-band. Note the tremendous metallicity sensitivity for this combination of bandpasses. Galaxies are plotted as +'s, from counts and colors extrapolated from the Hubble Deep Field using a passive-evolution model with q_0 = 0.01. caption The open square marks the position of our Cycle- 6 field in this view of the core of the Virgo cluster. The solid squares mark the positions proposed for this cycle. The field sizes are much smaller than the squares. The solid circles are scaled by the square root of the galaxy luminosity. The central bright galaxy is M87, and the dashed circle marks a region 50 arcminutes from M87. The field positions are such that there are no bright galaxies which should contribute significantly to the star counts in excess of the intergalactic population. endfigure The major difficulty initially will be in defining completeness limits, which may depend strongly on position within the NICMOS field, and in defining an absolute calibration of the metallicity scale. The instrument calibration plans are expected to yield photometric calibrations of both STIS and NICMOS accurate to ~ 10\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ RGB colors change by more than 1 mag over 1 dex change in metallicity, this photometric accuracy is adequate for our goals. We are requesting 8 fields in this proposal but we will observe them in such a manner that parallel observations are done between STIS and NICMOS. Then roughly 6 months later the field is revisited and the positions of the two instruments are juxtaposed. This will mean that we require effectively only 3 orbits per field, rather than 6. The total orbit request is thus 24 orbits. The positions of the fields are shown in Fig. 3. LOW-SKY will be requested to avoid scattered light. Real Time Justification ----------------------- None. Calibration Justification ------------------------- Additional Comments ------------------- The ORIENT is chosen to put STIS & NICMOS along an east-west line. Subsequent visits put STIS in the NIC2 field, and vice versa. Thus the ORIENT requirement is very important. The ORIENT is based on the aperture locations in the cycle-7 call for proposals and should be updated based on the aperture locations measured on orbit. We expect this will modify the ORIENT requirement by less than 2 degrees, and hence should have no affect on scheduling windows for the LRP. LOW-SKY is desired, but is incompatible with our ORIENT requirement. Nevertheless, while we cannot control the zodiacal background, the observations would be best scheduled to avoid the bright earth limb. A minimum bright-earth avoidence angle of 30 degrees would be best if it is feasible. 7 Jan 1998: The positions of the fields and the ORIENTS have been updated to reflect the aperture positions of NIC2 and STIS 50CCD in the latest version of the SIAF file available on the web. ------------------------------------------------------------------------------------ 7411( 12) - 02/03/98 13:18 - [ 3] Data Distribution Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7411( 12) - 02/03/98 13:18 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 VIRGO-CLUS2 CLUSTER OF RA=12H 33M 51S +/- 2",DEC=12D J2000 Z = V = 28.0+/-0.5 GALAXIES,POOR 20' 44.2" +/- 2" 0.004 I = 28.0+/-0.5 CLUSTER,BLANK SKY,HALO,EXT-STAR,K III Comments: BLANK FIELD IN THE VIRGO CLUSTER Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J2000 0.0 0.0 0.0 2 VIRGO-CLUS3 CLUSTER OF RA=12H 33M 13.7S +/- 2",DEC=12D J2000 Z = V = 28.0+/-0.5 GALAXIES,POOR 20' 44.2" +/- 2" 0.004 I = 28.0+/-0.5 CLUSTER,BLANK SKY,HALO,EXT-STAR,K III Comments: BLANK FIELD IN THE VIRGO CLUSTER Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J2000 0.0 0.0 0.0 3 VIRGO-CLUS4 CLUSTER OF RA=12H 32M 36.5S +/- 2",DEC=12D J2000 Z = V = 28.0+/-0.5 GALAXIES,POOR 20' 44.2" +/- 2" 0.004 I = 28.0+/-0.5 CLUSTER,BLANK SKY,HALO,EXT-STAR,K III Comments: BLANK FIELD IN THE VIRGO CLUSTER Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J2000 0.0 0.0 0.0 7411( 12) - 02/03/98 13:18 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 280.7D TO 280.7D On Hold Comments: Additional Comments: Orientation is set to put the center of STIS 50CCD due west of the center of NIC2. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 VIRGO-CLUS2 NIC2 MULTIAC NIC2 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF PAR 12-14 WITH 10 CUM ------------------------------------------------------------------------------------------------------------------------------------ 12 VIRGO-CLUS2 NIC1 MULTIAC NIC1 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 13 VIRGO-CLUS2 NIC3 MULTIAC NIC3 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 14 VIRGO-CLUS2 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=4 1 2380 S CD Comments: This parallel is of EQUAL importance to the primary. I.e. it is essential. ------------------------------------------------------------------------------------------------------------------------------------ 20 VIRGO-CLUS2 NIC2 MULTIAC NIC2 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF PAR 22-24 WITH 20 POS CUM TARG 0.5167,0.5167 ------------------------------------------------------------------------------------------------------------------------------------ 22 VIRGO-CLUS2 NIC1 MULTIAC NIC1 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 23 VIRGO-CLUS2 NIC3 MULTIAC NIC3 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 24 VIRGO-CLUS2 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=4 1 2380 S CD Comments: This parallel is of EQUAL importance to the primary. I.e. it is essential. ------------------------------------------------------------------------------------------------------------------------------------ 30 VIRGO-CLUS2 NIC2 MULTIAC NIC2 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF PAR 32-34 WITH 30 POS CUM TARG -0.5167,-0.5167 ------------------------------------------------------------------------------------------------------------------------------------ 32 VIRGO-CLUS2 NIC1 MULTIAC NIC1 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 33 VIRGO-CLUS2 NIC3 MULTIAC NIC3 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 34 VIRGO-CLUS2 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=4 1 2380 S CD Comments: This parallel is of EQUAL importance to the primary. I.e. it is essential. ------------------------------------------------------------------------------------------------------------------------------------ 7411( 12) - 02/03/98 13:18 - [ 6] Visit: 02 Visit Priority: Visit Requirements: ORIENT 280.7D TO 280.7D On Hold Comments: Additional Comments: Orientation is set to put the center of STIS 50CCD due west of the center of NIC2. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 VIRGO-CLUS3 NIC2 MULTIAC NIC2 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF PAR 12-14 WITH 10 CUM ------------------------------------------------------------------------------------------------------------------------------------ 12 VIRGO-CLUS3 NIC1 MULTIAC NIC1 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 13 VIRGO-CLUS3 NIC3 MULTIAC NIC3 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 14 VIRGO-CLUS3 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=4 1 2380 S CD Comments: This parallel is of EQUAL importance to the primary. I.e. it is essential. ------------------------------------------------------------------------------------------------------------------------------------ 20 VIRGO-CLUS3 NIC2 MULTIAC NIC2 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF PAR 22-24 WITH 20 POS CUM TARG 0.5167,0.5167 ------------------------------------------------------------------------------------------------------------------------------------ 22 VIRGO-CLUS3 NIC1 MULTIAC NIC1 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 23 VIRGO-CLUS3 NIC3 MULTIAC NIC3 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 24 VIRGO-CLUS3 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=4 1 2380 S CD Comments: This parallel is of EQUAL importance to the primary. I.e. it is essential. ------------------------------------------------------------------------------------------------------------------------------------ 30 VIRGO-CLUS3 NIC2 MULTIAC NIC2 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF PAR 32-34 WITH 30 POS CUM TARG -0.5167,-0.5167 ------------------------------------------------------------------------------------------------------------------------------------ 32 VIRGO-CLUS3 NIC1 MULTIAC NIC1 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 33 VIRGO-CLUS3 NIC3 MULTIAC NIC3 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 34 VIRGO-CLUS3 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=4 1 2380 S CD Comments: This parallel is of EQUAL importance to the primary. I.e. it is essential. ------------------------------------------------------------------------------------------------------------------------------------ 7411( 12) - 02/03/98 13:18 - [ 7] Visit: 03 Visit Priority: Visit Requirements: ORIENT 100.7D TO 100.7D On Hold Comments: Additional Comments: Orientation is set to put the center of STIS 50CCD due east of the center of NIC2. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 VIRGO-CLUS3 NIC2 MULTIAC NIC2 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF PAR 12-14 WITH 10 CUM ------------------------------------------------------------------------------------------------------------------------------------ 12 VIRGO-CLUS3 NIC1 MULTIAC NIC1 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 13 VIRGO-CLUS3 NIC3 MULTIAC NIC3 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 14 VIRGO-CLUS3 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=4 1 2380 S CD Comments: This parallel is of EQUAL importance to the primary. I.e. it is essential. ------------------------------------------------------------------------------------------------------------------------------------ 20 VIRGO-CLUS3 NIC2 MULTIAC NIC2 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF PAR 22-24 WITH 20 POS CUM TARG 0.5167,0.5167 ------------------------------------------------------------------------------------------------------------------------------------ 22 VIRGO-CLUS3 NIC1 MULTIAC NIC1 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 23 VIRGO-CLUS3 NIC3 MULTIAC NIC3 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 24 VIRGO-CLUS3 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=4 1 2380 S CD Comments: This parallel is of EQUAL importance to the primary. I.e. it is essential. ------------------------------------------------------------------------------------------------------------------------------------ 30 VIRGO-CLUS3 NIC2 MULTIAC NIC2 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF PAR 32-34 WITH 30 POS CUM TARG -0.5167,-0.5167 ------------------------------------------------------------------------------------------------------------------------------------ 32 VIRGO-CLUS3 NIC1 MULTIAC NIC1 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 33 VIRGO-CLUS3 NIC3 MULTIAC NIC3 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 34 VIRGO-CLUS3 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=4 1 2380 S CD Comments: This parallel is of EQUAL importance to the primary. I.e. it is essential. ------------------------------------------------------------------------------------------------------------------------------------ 7411( 12) - 02/03/98 13:18 - [ 8] Visit: 04 Visit Priority: Visit Requirements: ORIENT 100.7D TO 100.7D On Hold Comments: Additional Comments: Orientation is set to put the center of STIS 50CCD due east of the center of NIC2. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 VIRGO-CLUS4 NIC2 MULTIAC NIC2 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF PAR 12-14 WITH 10 CUM ------------------------------------------------------------------------------------------------------------------------------------ 12 VIRGO-CLUS4 NIC1 MULTIAC NIC1 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 13 VIRGO-CLUS4 NIC3 MULTIAC NIC3 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 14 VIRGO-CLUS4 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=4 1 2380 S CD Comments: This parallel is of EQUAL importance to the primary. I.e. it is essential. ------------------------------------------------------------------------------------------------------------------------------------ 20 VIRGO-CLUS4 NIC2 MULTIAC NIC2 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF PAR 22-24 WITH 20 POS CUM TARG 0.5167,0.5167 ------------------------------------------------------------------------------------------------------------------------------------ 22 VIRGO-CLUS4 NIC1 MULTIAC NIC1 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 23 VIRGO-CLUS4 NIC3 MULTIAC NIC3 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 24 VIRGO-CLUS4 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=4 1 2380 S CD Comments: This parallel is of EQUAL importance to the primary. I.e. it is essential. ------------------------------------------------------------------------------------------------------------------------------------ 30 VIRGO-CLUS4 NIC2 MULTIAC NIC2 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF PAR 32-34 WITH 30 POS CUM TARG -0.5167,-0.5167 ------------------------------------------------------------------------------------------------------------------------------------ 32 VIRGO-CLUS4 NIC1 MULTIAC NIC1 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 33 VIRGO-CLUS4 NIC3 MULTIAC NIC3 F110W SAMP-SEQ=SPARS256,NSAMP=12 1 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 34 VIRGO-CLUS4 STIS/C ACCUM 50CCD MIRROR CR-SPLIT=4 1 2380 S CD Comments: This parallel is of EQUAL importance to the primary. I.e. it is essential. ------------------------------------------------------------------------------------------------------------------------------------ 7411( 12) - 02/03/98 13:18 - [ 9] Summary Form for Proposal 7411 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations NIC2 NIC1 NIC3 STIS/CCD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SAMP-SEQ=SPARS256 NSAMP=12 CR-SPLIT=4 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 280.7D TO 280.7D PAR 12-14 WITH 10 PAR 22-24 WITH 20 POS TARG 0.5167,0.5167 PAR 32-34 WITH 30 POS TARG -0.5167,-0.5167 ORIENT 100.7D TO 100.7D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F110W MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names VIRGO-CLUS2 VIRGO-CLUS3 VIRGO-CLUS4 ------------------------------------------------------------------------------------------------------------------------------------