7394( 7) - 06/17/99 08:34 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7394 Version: 7 Check-in Date: 17-Jun-1999 08:34:14 1.Proposal Title: Mass Loss in Globular Cluster Giants: NGC 6752 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Ruth Peterson Astrophysical Advances CoI: Graeme Smith UCO/Lick Observatories N CoI: Andrea K. Dupree Smithsonian Astrophysical Observatory N ------------------------------------------------------------------------------------ 5. Abstract Uncertainty in the amount of mass lost by a low-mass, old, metal-poor star as it evolves up the giant branch for the first time is one of the most significant impediments to the interpretation of globular-cluster color-magnitude diagrams. For example, since the total amount of mass loss governs a star's position on the horizontal branch, a knowledge of the mass loss rate among bright cluster giants at various luminosities is crucial to understanding horizontal-branch morphology, which in turn is often used to indicate cluster age. For the first time, it is possible to characterize the behavior of mass loss as a function of luminosity explicitly among Population II giants of the same age and metallicity. We propose to do this by measuring the absorption in the blue wing of the Mg II\ emission line of giants spanning a range of 1.8 magnitudes near the tip of the giant branch of the globular cluster NGC6752, which is nearby, little reddened, and has many extremely blue objects whose production is encouraged by high mass loss. Many stars can be observed efficiently, since \ngc 6752 is in the CVZ and STIS is an imaging spectrograph. Using STIS in the echelle mode with a 70Angstrom\ Mg II\ filter, we will record high resolution spectra simultaneously for both giants and blue horizontal branch stars within a field 25"\ on a side. After removal of the interstellar contribution seen in the BHB stars, the mass loss indicated from the Mg II\ line profile will be examined for each giant, and its dependence on luminosity found directly. ------------------------------------------------------------------------------------ 7394( 7) - 06/17/99 08:34 - [ 2] Observations Description ------------------------ We plan to use the E230M grating for a resolution of 5 km/s/pix to resolve the Mg II\ h and k emission profile and the interstellar contribution. To reduce the overlapping of spectra from different stars, we will use the 25"\ square aperture with the Mg II\ filter, which blocks all wavelengths except for a region of 70 Angstrom\ centered on the Mg II\ lines. The IUE flux of the field BHB star \hd 74721, with V = 8.0, \bmv\ = 0.03, is 9 * 10^-13 erg/s/c m^2/Angstrom\ in the continuum at 2800Angstrom. This implies a flux of 1.5 * 10^- 15 erg/cm^2/s/Angstrom\ in the continuum at 2800Angstrom\ for a hot blue HB star with V = 15.2 if unreddened. This becomes 1.3 * 10^-15 erg/cm^2/s/Angstrom\ after correction for reddening with \ebmv\ = 0.04. The 2800Angstrom\ flux changes by only a few tens of percent across the entire blue horizontal branch because the bolometric luminosity for these stars is nearly the same. Also, for the brightest giants Dupree Etal\ recorded a flux level comparable to this near the base of the Mg II\ emission reversals, with peak fluxes factors of five to ten brighter. Allowing a transmission of 63\ filter and clear aperture sensitivities), and using the sensitivity for the E230M grating, we derive a count rate of 1.8 * 10^-3 cts/s/pix. Thus 20, 000s, or about 4 orbits, should yield spectra for the giants proposed here which have 36 cts/pix in the continuum of the BHB star or near the base of the Mg II\ emission line cores. Since one pixel = 5 km/s, this should prove adequate to measure both the stellar emission profile and the absorption due to the interstellar medium, given that multiple BHB stars will be used for the latter. Because bright giants are relatively rare, they are sparsely distributed across the field of NGC 6752, and few happen to fall within 30"\ of another giant of comparable brightness. Consequently, the 25"\ square fields to be observed with STIS must be chosen primarily with giants in mind, and the only HB stars observed will be those which happen to be close by. We list below four candidate fields and their stars, together with V and \bmv\ photometry (from Buonanno Etal\ 1986). While two fields contain extremely hot BHB stars, the more common cooler BHB stars outnumber them. Each star as bright or brighter than the HB will contribute a spectrum, which will consist of one full echelle order plus parts of two additional ones. Use of the cross-dispersion grating will offset these from the originating star. However, the spectrum of one star may overlap that of another if the projected distance between the two is small enough. Because most targets are several arcsec apart or more, this will not happen often, but may rule out the use of one or more of the fields which are listed below. Consequently these targets are preliminary; final decision of fields will be made after the time is scheduled and the orientation is known. Field 1: 2421, 11.72, 1.17; 2387, 11.59, 1.23 Field 2: 2196, 11.74, 1.21; 2245, 12.28, 1.08; 2205, 16.67, 0.06. Field 3: 2113, 11.23, 1.41; 2479, 17.65, -0.28; 2428, 17.04, -0.22. Field 4: 3169, 11.55, 1.21; 3299, 12.54, 0.97; 3251, 14.92, -0.01; 3291, 14.53, -0.01. Real Time Justification ----------------------- The CVZ is requested to reduce orbit allocation: 90min of viewing is possible instead of 50min or less. \ngc 6752 falls well within the heart of the CVZ. We will make every effort to obtain contemporaneous spectra of HAlpha and \caii\ for the giants scheduled for HST observation. This will provide an in-depth look at the wind, and will help calibrate the optical indicators commonly used to evaluate mass loss. The rapid time variability of winds in luminous giants means that such observations must be obtained within about a week of one another; we will enlist the aid of colleagues in the Southern Hemisphere where necessary. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 7394( 7) - 06/17/99 08:34 - [ 3] Data Distribution Paper Products: Media: DAT Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7394( 7) - 06/17/99 08:34 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6752-1754 STAR;SDO;Horizontal RA=19H 11M 8.80S +/- .1S, DEC=- 2000 V=-30 V = 15.99 Branch Star 59D 52' 20.90" +/- 1", PLATE- B-V = -0.24 ID=03D3 E(B-V) = 0.04 2 NGC6752-2113 STAR;K III-I RA=19H 11M 3.100S +/- .1S, DEC=- 2000 V=-30 V = 11.23 60D 1' 48.30" +/- 1", PLATE- B-V = 1.41 ID=03D3 E(B-V) = 0.04 3 NGC6752-F22 STAR;K III-I RA=19H 11M 0.5S +/- .1S, DEC=- 2000 V=-30 V = 11.84 59D 57' 50" +/- 1", PLATE- B-V = 1.19 ID=03D3 E(B-V) = 0.04 4 NGC6752-2206 STAR;Horizontal Branch RA=19H 11M 1.06S +/- .1S, DEC=- 2000 V=-30 V = 14.30 Star 59D 57' 40.90" +/- 1", PLATE- B-V = -0.05 ID=03D3 E(B-V) = 0.04 5 NGC6752-2245 STAR;K III-I RA=19H 11M 0.300S +/- .1S, DEC=- 2000 V=-30 V = 12.28 59D 57' 20.80" +/- 1", PLATE- B-V = 1.08 ID=03D3 E(B-V) = 0.04 7394( 7) - 06/17/99 08:34 - [ 5] Visit: 01 Visit Priority: Visit Requirements: CVZ 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 NGC6752-211 STIS/C ACQ 50CCD MIRROR 1 0.3 S ONBOARD ACQ FOR 4 3 CD ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6752-211 STIS/N ACCUM 0.2X0.2 E230M 2707 2 6480 S 3 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6752-175 STIS/C ACQ 50CCD MIRROR 1 0.3 S ONBOARD ACQ FOR 8 4 CD ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC6752-175 STIS/N ACCUM 0.2X0.2 E230M 2707 2 6160 S 4 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 7394( 7) - 06/17/99 08:34 - [ 6] Visit: 02 Visit Priority: Visit Requirements: CVZ 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 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6752-F22 STIS/N ACCUM F25MGII E230M 2707 4 6480 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 7394( 7) - 06/17/99 08:34 - [ 7] Visit: 03 Visit Priority: Visit Requirements: CVZ 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 NGC6752-224 STIS/C ACQ 50CCD MIRROR 1 0.3 S ONBOARD ACQ FOR 4 5 CD ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6752-224 STIS/N ACCUM 0.2X0.2 E230M 2707 2 6553.5 5 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6752-220 STIS/C ACQ 50CCD MIRROR 1 0.3 S ONBOARD ACQ FOR 8 6 CD ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC6752-220 STIS/N ACCUM 0.2X0.2 E230M 2707 2 6553.5 6 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 7394( 7) - 06/17/99 08:34 - [ 8] Visit: 04 Visit Priority: Visit Requirements: CVZ 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 NGC6752-211 STIS/C ACQ 50CCD MIRROR 1 0.3 S ONBOARD ACQ FOR 4 3 CD ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6752-211 STIS/N ACCUM 0.2X0.2 E230M 2707 1 4350 S 3 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 7394( 7) - 06/17/99 08:34 - [ 9] Summary Form for Proposal 7394 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 50CCD 0.2X0.2 F25MGII ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ ONBOARD ACQ FOR 4 ONBOARD ACQ FOR 8 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR E230M ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC6752-2113 NGC6752-1754 NGC6752-F22 NGC6752-2245 NGC6752-2206 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 2707 ------------------------------------------------------------------------------------------------------------------------------------