10172( 6) - 07/19/04 06:44 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 10172 Version: 6 Check-in Date: 19-Jul-2004 10:41:49 1.Proposal Title: Our Galaxy's most promising Super Star Cluster candidate, Westerlund 1: Tip of the Iceberg? ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle 4. Parallel Pointing Tolerance GO 13 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Dr. Richard de Grijs University of Sheffield CoI: Dr. Simon Portegies Zwart Universiteit van Amsterdam N CoI: Dr. Steve McMillan Drexel University N CoI: Dr. Margaret M. Hanson University of Cincinnati Main Campus N ------------------------------------------------------------------------------------ 6. Abstract Recent ground-based observations have revealed that the highly reddened Galactic cluster Westerlund 1 is the current best and by far the nearest "Young Massive Star Cluster" (YSC) candidate, i.e. a young (< 10 Myr), dense and massive (> 10, 000 Mo) object of which until recently 30 Doradus in the LMC was believed to be the nearest example. However, extrapolations of the locally derived cluster luminosity function indicate that perhaps up to a hundred similar objects should exist within the Galaxy. The close-up view of a YSC provided by Westerlund 1 allows us to obtain an unprecedented glimpse of the process of massive cluster formation, evolution and fate, which are among the very key issues in modern astrophysics. Utilising deep ACS and NICMOS imaging and sophisticated N-body and Monte Carlo simulations, we will address key questions regarding Westerlund 1's nature, formation and dynamical evolution. These include, What are the initial conditions with which Westerlund 1 was born? To what degree was mass segregation really primordial? Has the binary fraction changed during the short cluster lifetime? Do we expect the cluster to have a population of stellar-mass black holes? Does the cluster harbour an intermediate- mass black hole in its core? Is Westerlund 1 unique as a Galactic YSC? How similar is the cluster to the massive "Arches" and "Quintuplet" Galactic Centre clusters, and to 30 Doradus? With an expected life-span of > 100 Myr, it is conceivable that there should be more YSCs like Westerlund 1 in the Galactic disk. Our dynamical simulations will help us determine the ultimate fate of such clusters, allowing us to at least begin to answer the question of Westerlund 1's uniqueness in the context of the Galaxy's stellar populations. ------------------------------------------------------------------------------------ 10172( 6) - 07/19/04 06:44 - [ 2] Observations Description ------------------------ We will cover the densest cluster area entirely with our NICMOS observations, in a mosaic of 7 exposures; the ACS/WFC field of view will be covering the entire area of interest in a single F814W exposure. Exposure Time Estimates We have estimated the exposure times using the on-line ACS and NICMOS Exposure Time Calculators, and also included the unavoidable overheads (e.g., for guide star acquisition, and science overheads for the individual exposures) in our final orbit calculations. We aim to reach a minimum unextincted I-band point- source luminosity of m_I = 26 mag (Assuming that Westerlund 1 is located at a (worst-case) distance of 5 kpc, its distance modulus m-M = 13.5 mag; the I-band extinction of A_I ~ 6.5 mag will allow us to observe stars down to M_I = +6 mag. The absolute V-band magnitude of a K5 dwarf is M_V = +7.35; V-I ~ 1.5 mag (Allen's Astrophysical Quantities), so M_I, K5 < +6, i.e., well within our magnitude limit for the individual stars using ACS, and similarly, m_K = 20 mag using NICMOS. Assuming average zodiacal, air glow and earth shine background levels and CCD parameters, gain=4 and CR-SPLIT=5, we calculated the exposure times required to reach a minimum signal-to-noise (S/N) ratio for the ACS/WFC observations of S/N ~10 in a standard 0.2 arcsec circular aperture. We require a CR-SPLIT >= 5 for efficient cosmic-ray removal and to avoid saturating the brightest stars. For the lowest-mass stars that we expect to detect in this cluster, we adopt (Kurucz) spectral energy distributions of B0-B5 stars (i.e., adequate for the cluster age of ~4-8 Myr). In a single orbit or ~50 minutes of on-source exposure time, we will reach a S/N ratio of ~10 for the m_I = 26 mag stars that we target as our faintest objects. It is important that we sample several magnitudes of the CMD's main sequence, in order to obtain the relevant mass leverage to robustly analyse the mass function behaviour with radius. Similarly, for a 1-orbit (50 minute) exposure time with NICMOS camera 2, we will reach S/N ~ 10-13 in a standard circular aperture of 0.2 arcsec radius. While our ACS observations will not go as deep as our NICMOS data (due to the high extinction), they are crucial to obtain reliable estimates of the main sequence turn-off and the locus of the cluster's main sequence. The deeper NICMOS observations will allow us to follow the present-day mass function to unprecedented faint levels in a cluster a massive as Westerlund 1. We therefore require exposure times of ~1 orbit for the ACS/WFC exposure and also for the individual NICMOS/NIC2 observations. In order to avoid a situation in which the gap between the two WFC chips would be placed across the centre of the cluster, we will offset the centre of our field by 30 arcsec in N and E, and (slightly) restrict the range of ORIENTs allowed (in order to avoid a situation in which this gap crosses the cluster core directly). Thus, the total exposure time required for this programme is 8 orbits. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- 10172( 6) - 07/19/04 06:44 - [ 3] ------------------------------------------------------------------------------------ 10172( 6) - 07/19/04 06:44 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 WESTERLUND1 EXT-CLUSTER, GLOBULAR RA=16H47M6.5S +/- 0.1", DEC=- J2000 I=26 CLUSTER 45D50'12.3" +/- 0.1", PLATE- K=20 limiting magnitude at S/N~10 ID=01FR Coordinate Source: GUIDE_STAR_CATALOG 2 WESTERLUND1- EXT-CLUSTER, GLOBULAR RA=16H47M4.6S +/- 0.1", DEC=- J2000 I=26 POS2 CLUSTER 45D50'38.9" +/- 0.1", PLATE- K=20 limiting magnitude at S/N~10 ID=01FR Coordinate Source: GUIDE_STAR_CATALOG 3 WESTERLUND1- EXT-CLUSTER, GLOBULAR RA=16H47M5.83S +/- 0.1", DEC=- J2000 I=26 POS3 CLUSTER 45D50'38.9" +/- 0.1", PLATE- K=20 limiting magnitude at S/N~10 ID=01FR Coordinate Source: GUIDE_STAR_CATALOG 4 WESTERLUND1- EXT-CLUSTER, GLOBULAR RA=16H47M3.37S +/- 0.1", DEC=- J2000 I=26 POS4 CLUSTER 45D50'38.9" +/- 0.1", PLATE- K=20 limiting magnitude at S/N~10 ID=01FR Coordinate Source: GUIDE_STAR_CATALOG 5 WESTERLUND1- EXT-CLUSTER, GLOBULAR RA=16H47M5.22S +/- 0.1", DEC=- J2000 I=26 POS5 CLUSTER 45D50'20.2" +/- 0.1", PLATE- K=20 limiting magnitude at S/N~10 ID=01FR Coordinate Source: GUIDE_STAR_CATALOG 6 WESTERLUND1- EXT-CLUSTER, GLOBULAR RA=16H47M3.98S +/- 0.1", DEC=- J2000 I=26 POS6 CLUSTER 45D50'20.2" +/- 0.1", PLATE- K=20 limiting magnitude at S/N~10 ID=01FR Coordinate Source: GUIDE_STAR_CATALOG 7 WESTERLUND1- EXT-CLUSTER, GLOBULAR RA=16H47M5.22S +/- 0.1", DEC=- J2000 I=26 POS7 CLUSTER 45D50'57.5" +/- 0.1", PLATE- K=20 limiting magnitude at S/N~10 ID=01FR Coordinate Source: GUIDE_STAR_CATALOG 8 WESTERLUND1- EXT-CLUSTER, GLOBULAR RA=16H47M3.98S +/- 0.1", DEC=- J2000 I=26 POS8 CLUSTER 45D50'57.5" +/- 0.3", PLATE- K=20 limiting magnitude at S/N~10 ID=01FR Coordinate Source: GUIDE_STAR_CATALOG 10172( 6) - 07/19/04 06:44 - [ 5] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 3 Point_Spacing 3.011 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 85.28 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type NIC-SPIRAL-DITH Pattern_Purpose DITHER Number_Of_Points 3 Point_Spacing 0.525 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 0.0 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 10172( 6) - 07/19/04 06:44 - [ 6] Visit: 01 Visit Priority: Visit Requirements: PCS MODE FINE; ORIENT 161.0D TO 253.0 D; ORIENT 341.0D TO 73.0 D On Hold Comments: Additional Comments: Field offset by 30 arcsec to the N and E w.r.t. the cluster centre and orientation angle set in order to avoid the gap between the CCDs crossing the cluster if the spacecraft roll angle would happen to be disadvantageous. For reference, the U3 axis runs (approx.) N-S on the sky. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 WESTERLUND1 ACS/WFC ACCUM WFC F814W CR-SPLIT=NO,GAIN=2 1 1000 S PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Visit Id| Exp Id |Primary |Secondary |Iteration |CR-SPLIT |Orbit Num |Duration | |Pattern Pos |Pattern Pos |Num |Num | | ------------------------------------------------------------------------------------------------------------------------------------ 01 1 1 none none none 1 802.0 01 1 2 none none none 1 802.0 01 1 3 none none none 1 803.0 10172( 6) - 07/19/04 06:44 - [ 7] Visit: 02 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 WESTERLUND1 NIC2 MULTIAC NIC2 F222M NSAMP=16,SAMP-SEQ=SPARS64 1 DEF PATTERN 2 1 -POS2 CUM ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Visit Id| Exp Id |Primary |Secondary |Iteration |CR-SPLIT |Orbit Num |Duration | |Pattern Pos |Pattern Pos |Num |Num | | ------------------------------------------------------------------------------------------------------------------------------------ 02 1 1 none none none 1 tbd 02 1 2 none none none 1 tbd 02 1 3 none none none 1 tbd 10172( 6) - 07/19/04 06:44 - [ 8] Visit: 03 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 WESTERLUND1 NIC2 MULTIAC NIC2 F222M NSAMP=16,SAMP-SEQ=SPARS64 1 DEF PATTERN 2 1 -POS3 CUM ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Visit Id| Exp Id |Primary |Secondary |Iteration |CR-SPLIT |Orbit Num |Duration | |Pattern Pos |Pattern Pos |Num |Num | | ------------------------------------------------------------------------------------------------------------------------------------ 03 1 1 none none none 1 tbd 03 1 2 none none none 1 tbd 03 1 3 none none none 1 tbd 10172( 6) - 07/19/04 06:44 - [ 9] Visit: 04 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 WESTERLUND1 NIC2 MULTIAC NIC2 F222M NSAMP=16,SAMP-SEQ=SPARS64 1 DEF PATTERN 2 1 -POS4 CUM ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Visit Id| Exp Id |Primary |Secondary |Iteration |CR-SPLIT |Orbit Num |Duration | |Pattern Pos |Pattern Pos |Num |Num | | ------------------------------------------------------------------------------------------------------------------------------------ 04 1 1 none none none 1 tbd 04 1 2 none none none 1 tbd 04 1 3 none none none 1 tbd 10172( 6) - 07/19/04 06:44 - [ 10] Visit: 05 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 WESTERLUND1 NIC2 MULTIAC NIC2 F222M NSAMP=16,SAMP-SEQ=SPARS64 1 DEF PATTERN 2 1 -POS5 CUM ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Visit Id| Exp Id |Primary |Secondary |Iteration |CR-SPLIT |Orbit Num |Duration | |Pattern Pos |Pattern Pos |Num |Num | | ------------------------------------------------------------------------------------------------------------------------------------ 05 1 1 none none none 1 tbd 05 1 2 none none none 1 tbd 05 1 3 none none none 1 tbd 10172( 6) - 07/19/04 06:44 - [ 11] Visit: 06 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 WESTERLUND1 NIC2 MULTIAC NIC2 F222M NSAMP=16,SAMP-SEQ=SPARS64 1 DEF PATTERN 2 1 -POS6 CUM ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Visit Id| Exp Id |Primary |Secondary |Iteration |CR-SPLIT |Orbit Num |Duration | |Pattern Pos |Pattern Pos |Num |Num | | ------------------------------------------------------------------------------------------------------------------------------------ 06 1 1 none none none 1 tbd 06 1 2 none none none 1 tbd 06 1 3 none none none 1 tbd 10172( 6) - 07/19/04 06:44 - [ 12] Visit: 07 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 WESTERLUND1 NIC2 MULTIAC NIC2 F222M NSAMP=16,SAMP-SEQ=SPARS64 1 DEF PATTERN 2 1 -POS7 CUM ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Visit Id| Exp Id |Primary |Secondary |Iteration |CR-SPLIT |Orbit Num |Duration | |Pattern Pos |Pattern Pos |Num |Num | | ------------------------------------------------------------------------------------------------------------------------------------ 07 1 1 none none none 1 tbd 07 1 2 none none none 1 tbd 07 1 3 none none none 1 tbd 10172( 6) - 07/19/04 06:44 - [ 13] Visit: 08 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 WESTERLUND1 NIC2 MULTIAC NIC2 F222M NSAMP=16,SAMP-SEQ=SPARS64 1 DEF PATTERN 2 1 -POS8 CUM ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Visit Id| Exp Id |Primary |Secondary |Iteration |CR-SPLIT |Orbit Num |Duration | |Pattern Pos |Pattern Pos |Num |Num | | ------------------------------------------------------------------------------------------------------------------------------------ 08 1 1 none none none 1 tbd 08 1 2 none none none 1 tbd 08 1 3 none none none 1 tbd 10172( 6) - 07/19/04 06:44 - [ 14] Summary Form for Proposal 10172 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC NIC2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC NIC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO GAIN=2 SAMP-SEQ=SPARS64 NSAMP=16 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE FINE; ORIENT 161.0D TO 253.0 D; ORIENT 341.0D TO 73.0 D PATTERN 1 1 PATTERN 2 1 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W F222M ------------------------------------------------------------------------------------------------------------------------------------ Target Names WESTERLUND1 WESTERLUND1-POS2 WESTERLUND1-POS3 WESTERLUND1-POS4 WESTERLUND1-POS5 WESTERLUND1-POS6 WESTERLUND1-POS7 WESTERLUND1-POS8 ------------------------------------------------------------------------------------------------------------------------------------