6529( 5) - 05/14/97 11:34 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6529 Version: 5 Check-in Date: 14-May-1997 11:00:33 1.Proposal Title: Direct Imaging of Betelgeuse ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle COOL STARS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: ANDREA K. DUPREE SMITHSONIAN ASTROPHYSICAL OBS CoI: Ronald L. Gilliland Space Telescope Science Institute Y CoI: Han Uitenbroek Smithsonian Astrophysical Observatory N ------------------------------------------------------------------------------------ 6. Abstract We obtained an image of Alpha Orionis ( Betelgeuse; M2 Iab) using the FOC on HST. This is the first direct image of the surface of a star other than the Sun, and its appearance is dramatically different from the solar disk. The FOC image reveals a greatly extended atmosphere in the ultraviolet, with a diameter about twice that in the visible. Additionally, a bright unresolved spot appears to dominate the ultraviolet continuum flux. The Mg II lines, obtained by tomographic reconstruction with the HRS also show enhanced emission in the spot. We are proposing for long-term status to acquire two observations per year for the next three cycles of HST to determine the position, flux, and evolution of the spot, in order to identify its origin: convection, pulsation, or magnetic activity, and to attempt a direct measurement of a change in radius due to pulsation. ------------------------------------------------------------------------------------ 6529( 5) - 05/14/97 11:34 - [ 2] Observations Description ------------------------ The observing program will image Betelgeuse twice per year: March and September. In Cycle 6 we will use the FOC to obtain F253M images, and the near- UV objective prism to provide a low dispersion spectrum to calibrate the flux measured through the filter, and also to observe the distribution of flux across the disk and spot. One pixel corresponds to 14 mas; the ultraviolet disk of Betelgeuse will cover ~7 pixels perpendicular to the dispersion; the bright spot should be apparent through the asymmetry in the spectrum. Each of the Cycle 6 FOC visits will require an interactive acquisition, therefore 3 orbits each visit. In outlying years we will request that the observations be scheduled at similar times (+/- 1 week) enabling the same guide stars to be used. We will have evaluated the respective guide star errors and can accomplish each FOC image with just one orbit in Cycles 7 and 8. Beginning in Cycle 7 STIS will provide the requisite spectroscopic measurements, but is expected to still fall short of the FOC in terms of limiting, high quality spatial resolution. However, a long slit on STIS in conjunction with an intermediate resolution grating can be scanned across Betelgeuse to provide a spectrally well resolved image near the Mg II emission lines. We estimate that two orbits each visit should suffice to provide both target acquisition and a scanned, spectrally resolved image. Cycle 6: (Sept. 1996 3 orbits; March 1997 3 orbits) Each visit consists of - Interactive target acquisition - 128x128 mode image with F253M+F220W+F4ND filters - 256x1024 mode objective prism spectrum: PRISM2+F165W+F175W Cycle 7: (Sept. 1997 3 orbits; March 1998 3 orbits) Each visit consists of - FOC 128x128 mode image with F253M+F220W+F4ND filters - STIS target acquisition + photometric low-res spectrum: G230LB + CCD - STIS + spatial scan of 0.05'' long-slit over central 0.15'' region of Alpha Ori. G230M+Band2 MAMA Cycle 8: (Sept. 1998 3 orbits; March 1999 3 orbits) These will be repeats of the Cycle 7 visits. HST/FOC is the only instrument capable of imaging with high spatial resolution in the ultraviolet spectral region. The ultraviolet region of the spectrum is the most sensitive to wind structure and chromospheric activity. In stars with extended atmospheres like Alpha Ori, the Ca II and Mg II transitions are not formed in the same region of the atmosphere; thus, ground- based observations of Ca II can not be used to infer the behavior of Mg II. sectionData reduction and analysis RLG will have full responsibility for data reduction, image modeling, deconvolution, the tomographic reconstructions, and will participate in studying the sources of nonradiative heating based on stellar structure and evolution considerations (Gilliland 1985, 1986). AKD and HU will have primary responsibility for interpretation of the results in the context of chromospheric and wind models of cool extended atmospheres. At the Center for Astrophysics semi-empirical models of the atmosphere of Alpha Orionis (cf. Hartmann & Avrett, 1984) have been constructed with the PANDORA code developed by Avrett & Loeser (1992). PANDORA can consistently treat line formation in a spherical symmetric, expanding atmosphere accounting for non-LTE radiative transfer in calculating source functions as well as the emergent intensities. We will initially use the PANDORA code to compute not only MgII h&k profiles and fluxes that will be compared with the observed ones, but also other relevant spectroscopic features, such as the hydrogen HAlpha line and CaII H&K resonance lines in the optical, and ultraviolet molecular features obtained with IUE and HST. However, PANDORA treats partial frequency redistribution (PRD) in a very approximate way not suitable for direct comparison of line profiles, but sufficiently accurate for energy balance considerations. Currently, Uitenbroek is developing a radiative transfer code for Non-LTE radiative transfer calculations in two- dimensional geometry including accurately the effects of partial frequency redistribution (PRD), and allowing for transitions that overlap in wavelength; both are important for a realistic representation of MgII h&k line formation. The new code employs Rybicki and Hummer's (1992) accelerated lambda iteration (ALI) scheme combined with Ng's (1974) convergence acceleration technique. Uitenbroek will extend this code to spherical symmetric geometry for this project. From the HST observations we have obtained so far it is clear that the atmosphere of Alpha Orionis is not spherically symmetric, but almost rotationally symmetric due to the presence of a bright spot. If the size of this spot is of similar dimensions as the thickness of the Alpha Orionis atmosphere, as it appears to be, single component modeling (ie. purely spherical symmetric) will not suffice, as radiation exchange between the spot and its surroundings will then affect the emergent spectrum of both and any derived properties. If necessary we will consider writing a rotational symmetric code (where the atmosphere is allowed to vary in radial and longitudinal directions) and investigate the extent of radiative exchange to verify the validity of our spectral analysis. Real Time Justification ----------------------- The orbit allocation should be reevaluated once STIS is installed. We have a program accepted for the last year of IUE that will continue the monitoring of Alpha Ori from October 1995 through April 1996. The IUE program includes monitoring in optical light, radial velocity measures, and polarization measures. We anticipate that optical light monitoring and radial velocity measures will be continued beyond the lifetime of IUE. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6529( 5) - 05/14/97 11:34 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: ------------------------------------------------------------------------------------ 6529( 5) - 05/14/97 11:34 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD39801 STAR, M III-I RA=05H 52M 27.809S +/- 1950.0 V = 0.8+/-0.5 0.1",DEC=07D 23' 57.92" +/- 0.1" TYPE=M2IAB B-V = 1.86 E(B-V) = 0.21 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1950.0 0.001667 0.0100 0.0 6529( 5) - 05/14/97 11:34 - [ 5] Visit: 01 Visit Requirements: BETWEEN 01-Sep-1996 AND 15-Oct-1996 On Hold Comments: Additional Comments: fall visit Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 HD39801 FOC/96 ACQ 512X102 F253M, PIXEL=50X25,CHECK-FILTER=YES 1 100 S INT ACQ FOR 20-60 4 F220W, F4ND Comments: HD39801 was observed in the same imaging configurations in cycle 4. Expect count rate peak of 1.6 cts/px. INT ACQ should place target at position 48,86 of final 128x128 format, i.e., slightly off-center. ------------------------------------------------------------------------------------------------------------------------------------ 20 HD39801 FOC/96 IMAGE 128X128 F253M, PIXEL=25X25,CHECK-FILTER=YES 1 490 S NO SPLIT F220W, F4ND ------------------------------------------------------------------------------------------------------------------------------------ 30 HD39801 FOC/96 IMAGE 128X128 F253M, PIXEL=25X25,CHECK-FILTER=YES 1 1200 S POS TARG 0.007,0.007 F220W, F4ND Comments: POS TARGS provide half-pixel dithering. ------------------------------------------------------------------------------------------------------------------------------------ 40 HD39801 FOC/96 IMAGE 128X128 F253M, PIXEL=25X25,CHECK-FILTER=YES 1 1200 S NO SPLIT POS TARG 0.007, F220W, 0.000 F4ND ------------------------------------------------------------------------------------------------------------------------------------ 50 HD39801 FOC/96 IMAGE 128X128 F253M, PIXEL=25X25,CHECK-FILTER=YES 1 1080 S POS TARG 0.000,0.007 F220W, F4ND ------------------------------------------------------------------------------------------------------------------------------------ 60 HD39801 FOC/96 IMAGE 256X102 PRISM2, PIXEL=25X25,CHECK-FILTER=YES 1 1250 S NO SPLIT POS TARG 0.24, 4 F165W, -1.400 F175W Comments: highest count rate of 2.3 cts/s at long wavelength 0.5 cts/s at Mg II peak (but source resolved by 3 px) 0.2 cts/s at 2500A, 0.1 at 2000 A, 0.05 at 1700A. ------------------------------------------------------------------------------------------------------------------------------------ 6529( 5) - 05/14/97 11:34 - [ 6] Visit: 02 Visit Requirements: BETWEEN 1-SEP-1997 AND 30-SEP-1997 On Hold Comments: Additional Comments: Originally spring visit, copy of original fall visit, but was bumped to the next fall by SM2 SMOV period. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 100 HD39801 FOC/96 ACQ 512X102 F253M, PIXEL=50X25,CHECK-FILTER=YES 1 100 S INT ACQ FOR 110-150 4 F220W, F4ND Comments: HD39801 was observed in the same imaging configurations in cycle 4. Expect count rate peak of 1.6 cts/px. INT ACQ should place target at position 48,86 of final 128x128 format, i.e., slightly off-center. ------------------------------------------------------------------------------------------------------------------------------------ 110 HD39801 FOC/96 IMAGE 128X128 F253M, PIXEL=25X25,CHECK-FILTER=YES 1 490 S NO SPLIT F220W, F4ND ------------------------------------------------------------------------------------------------------------------------------------ 120 HD39801 FOC/96 IMAGE 128X128 F253M, PIXEL=25X25,CHECK-FILTER=YES 1 1200 S POS TARG 0.007,0.007 F220W, F4ND ------------------------------------------------------------------------------------------------------------------------------------ 130 HD39801 FOC/96 IMAGE 128X128 F253M, PIXEL=25X25,CHECK-FILTER=YES 1 1200 S NO SPLIT POS TARG 0.007, F220W, 0.000 F4ND ------------------------------------------------------------------------------------------------------------------------------------ 140 HD39801 FOC/96 IMAGE 128X128 F253M, PIXEL=25X25,CHECK-FILTER=YES 1 1080 S POS TARG 0.000,0.007 F220W, F4ND ------------------------------------------------------------------------------------------------------------------------------------ 150 HD39801 FOC/96 IMAGE 256X102 PRISM2, PIXEL=25X25,CHECK-FILTER=YES 1 1250 S NO SPLIT POS TARG 0.24, 4 F165W, -1.400 F175W ------------------------------------------------------------------------------------------------------------------------------------ 6529( 5) - 05/14/97 11:34 - [ 7] Summary Form for Proposal 6529 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOC/96 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters PIXEL=50X25 CHECK-FILTER=YES PIXEL=25X25 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category COOL STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 01-Sep-1996 AND 15-Oct-1996 INT ACQ FOR 20-60 NO SPLIT POS TARG 0.007,0.007 NO SPLIT POS TARG 0.007,0.000 POS TARG 0.000,0.007 NO SPLIT POS TARG 0.24,-1.400 BETWEEN 1-SEP-1997 AND 30-SEP-1997 INT ACQ FOR 110-150 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F253M,F220W,F4ND PRISM2,F165W,F175W ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD39801 ------------------------------------------------------------------------------------------------------------------------------------