8339( 4) - 06/08/00 14:47 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8339 Version: 4 Check-in Date: 08-Jun-2000 14:46:48 1.Proposal Title: Light Element Abundance Variations in the Core of 47 Tucanae ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Michael Briley University of Wisconsin - Madison CoI: Prof. Verne Smith University of Texas El Paso N ------------------------------------------------------------------------------------ 5. Abstract We propose a novel use of the F390N and F410M WFPC2 filters to explore the extent of star-to-star light element variations in the core of the Galactic globular cluster 47 Tucanae. Observations in 47 Tuc have revealed that large star-to-star differences in sodium, correlated with CN band-strength differences, exist amoung its main- sequence turn-off stars, well before any proposed mechanism for Na production and subsequent mixing could be in operation. Moreover, the range of Na abundances and CN band-strengths observed at the turn- off are consistent with those found among the evolved red giants of 47 Tuc. The simplest interpretation of this result is that the gas from which the present cluster stars formed was inhomogeneous in at least C, N, and Na. The ratio of CN- enhanced to CN-normal stars is also found to increase by a factor of 3 from a radial distance of 17' to 10'. The ratio of CN-enhanced to CN- normal stars is unknown within a radial distance of 4' due to cro wd ing. This segregation in CN distribution carries evidence of the chemical and dynamical processes which created these inhomogeneities. Probing this signature into the very core of the cluster will provide tighter constraints on possible origins of the chemical inhomogeneities and, ultimately, on the early history of the globular clusters. The superior imaging capabilities of HST will allow us to probe much closer into the dense core of 47 Tuc. ------------------------------------------------------------------------------------ 8339( 4) - 06/08/00 14:47 - [ 2] Observations Description ------------------------ We will be imaging the core of 47 Tuc, the same field as observed in datasets U2VO0101T - U2VO0109T, in the F390N and F410M filters. The F390N observations will be broken down into 6 exposures, 2 for 180s and 4 dithered exposures for 600s. The 180s sequence will allow us to obtain photometry for stars on the upper part of the RGB without saturation, while the 600s exposures will reach V = 16 (one mag above turnoff) at S/N of approximately 130. The F410 observations will be broken down into 2 20s exposures (again for the upper RGB) and 4 dithered 80s exposures for a S/N of about 130 at V = 16. Note that for the longer exposures, saturation of the brighter stars in the target area will be come an issue. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Paper Products: YES Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8339( 4) - 06/08/00 14:47 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC104 STELLAR CLUSTER, RA=0H 24M 9.45S +/- 0", DEC=-72D J2000 V=-18.7 V = 11.7 GLOBULAR CLUSTER 5' 14.93" +/- 0" B-V = 1.6 TYPE=K5I V = 16 B-V = 0.8 TYPE=G7III Coordinate Source: Comments: Same field as datasets U2VO0101T - U2VO0109T 8339( 4) - 06/08/00 14:47 - [ 4] Visit: 01 Visit Priority: Visit Requirements: ORIENT 323.9724D TO 323.9724D On Hold Comments: Additional Comments: Same field as datasets U2VO0101T - U2VO0109T Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC104 WFPC2 IMAGE PC1-FIX F390N 3889 ATD-GAIN=7 2 180 S MAX DUR 100% ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC104 WFPC2 IMAGE PC1-FIX F410M 4090 ATD-GAIN=7 2 20 S MAX DUR 100% ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC104 WFPC2 IMAGE PC1-FIX F390N 3889 ATD-GAIN=7,DITHER-TYPE=BOX 1 600 S ------------------------------------------------------------------------------------------------------------------------------------ 40 NGC104 WFPC2 IMAGE PC1-FIX F410M 4090 ATD-GAIN=7,DITHER-TYPE=BOX 1 80 S ------------------------------------------------------------------------------------------------------------------------------------ 8339( 4) - 06/08/00 14:47 - [ 5] Summary Form for Proposal 8339 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ATD-GAIN=7 DITHER-TYPE=BOX ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 323.9724D TO 323.9724D MAX DUR 100% ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F390N F410M ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC104 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 3889 4090 ------------------------------------------------------------------------------------------------------------------------------------