6087( 0) - 07/18/95 19:54 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6087 Version: ********** Check-in Date: ********** 1.Proposal Title: The UV Flux Deficiency in Chemically Peculiar Stars: GHRS Observations of Alpha^2 CVn ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Hot Stars GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Glenn Wahlgren Computer Sciences Corporation CoI: David Leckrone NASA/GSFC N CoI: Sveneric Johansson Univ. Lund N CoI: Thierry Lanz NASA/GSFC N ------------------------------------------------------------------------------------ 6. Abstract The chemically peculiar stars of the upper main sequence display a deficiency in their ultraviolet flux relative to normal composition stars of similar UBV color. The source of this deficiency is as yet unknown, but has been speculated to arise from enhanced line and continuous opacity from overabundant elements, particularly the iron-peak and rare- earths, as well as to abnormal atmospheric structure. A high signal-to-noise, medium-resolution spectrum of the prototypical Ap star Alpha^2 CVn, covering the wavelength region from 1510 to 2640 Angstrom, will be obtained with the GHRS to determine the extent to which line and continuous opacity sources are responsible for the flux deficiency. The role of weak lines and overabundant species in the flux deficiency, in particular the rare earth elements, will be defined. This data set would represent the first substantial spectrum of an Ap star obtained with the HST and will be used as a `roadmap' by both astronomers and atomic spectroscopists for the study of rare-earth element lines in the ultraviolet. ------------------------------------------------------------------------------------ 6087( 0) - 07/18/95 19:54 - [ 2] Observations Description ------------------------ The GHRS will be used to obtain high signal-to-noise (100- 150), medium resolution (R = 20000-30000) spectra of the bright chemically peculiar Ap star Alpha^2 CVn. Three gratings (G160M, G200M, G270M) will be used to obtain spectra via WSCANs from 1510 to nearly 2640 Angstrom\ at the light-curve phase of rare-earth element line strength maximum (phase 0.0). The choice of instrument grating is driven by the stellar rotational velocity (v sin i = 24 km s^-1) which precludes usage of the echelle yet is low enough to allow detection and analysis of weak lines by normal synthetic spectrum techniques. The Small Science Aperture (SSA) will provide the maximum spectral resolution possible with these gratings and has a well defined point-spread function that we can readily incorporate into our synthetic spectrum calculations. Step- patterns of 5 and 11 will be used with the G160M, G200M and G270M gratings, respectively. Exposure times were calculated by the equation (S/N)^2 = (flux)*(sensitivity)*(exp time), as discussed in the GHRS Instrument Handbook, post-COSTAR version 5.0. Stellar fluxes were obtained from IUE low-dispersion spectra. Instrument sensitivities and the LSA to SSA conversion factor were obtained from the instrument handbook. Computed exposure times at a single grating setting range from 220 sec near 1500 Angstrom\ to 87 sec near 2700 Angstrom\ for a S/N of 150 per data point. The determination of spacecraft time is based upon experience obtained from scheduling our Cycle-2 Sirius atlas observations, which used a similar format. As a result of the memory capacity of the HST NSSC-1 on-board computer the number of observations that can be obtained with the GHRS (and other instruments) during any 8 hour command load period is limited. For the observations that we propose to make, utilizing the GHRS FPSPLIT = 2 option to aid in the removal of detector fixed pattern noise, the entire spectral region needs to be broken up into segments, or scheduling units. As only one segment can be scheduled during an eight hour period and there is no guarantee that the segments will not be interrupted by visits to other targets, each segment requires its own target acquisition procedure (or visit). Three visits are required for the complete scan. Each visit requires two orbits of HST time. The data will be analysed using several computer codes that generate synthetic spectra under either LTE (ATLAS, SYNTHE) or non-LTE (MULTI, TLUSTY) assumptions. These programs are currently in use at GSFC and to a lesser extent in Lund. The analysis will be comprised of, but not limited to: identification of atomic lines, particularly from heavy elements (Z > 28), determination of abundances for REE as well as other heavy elements/ions that are not observable in ground-based spectra of these stars, determination of atomic parameters for the REE transitions by laboratory techniques and theoretical codes to produce atomic data required for spectrum synthesis, searches for opacity edges from bound-free transitions and autoionization, such as the Si II photoionization features near 1600 A, study of the flux deficiency and uv opacity sources, both from bound-bound and bound-free sources, comparing against other CP and normal stars, and the extension of the GHRS analysis to include IUE archival data of other CP2 stars. Real Time Justification ----------------------- Our requested observations are in one sense time critical. The rotational period of 5.497 days modulates the spectrum variations. Scheduling constraints would require one or perhaps two wave scans to be the only GHRS activity during any 8-hour period defining a command load. Therefore, WSCANs can be run in only two consecutive 8 hour periods before the rotation of the star becomes a concern in terms of mixing data obtained at significantly different light-curve phases. Otherwise, to get nearly the same phase of the star, the scheduling would require that the visits be separated by 5.469 days +/- 8 hours. The ephemeris for the occurrence of rare-earth element maximum line strength (phase 0.0) is JD(Eu II maximum) = 2419869.720 + 5.46939E. Ground-based spectroscopy may be obtained in advance of the observations to accurately test the epoch of REE maximum. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6087( 0) - 07/18/95 19:54 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: GHRS TEAM WILL*PICK UP Ship Via: UPS Email: HRSJENN@HRS.GSFC.NASA.GOV , ------------------------------------------------------------------------------------ 6087( 0) - 07/18/95 19:54 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD112413 STAR, AP RA=12H 56M 01.664S +/- 0.02S, J2000 V = -3.0 V = 2.90 +/- 0.05 DEC=+38D 19' 06.21" +/- 0.02" B-V = -0.10 +/- 0.05 TYPE = A0P F-CONT(1500) = 7.2 +/- 0.5 E-10 F-CONT(1800) = 7.0 +/- 0.5 E-10 F-CONT(2100) = 7.8 +/- 0.5 E-10 F-CONT(2500) = 4.5 +/- 0.5 E-10 F-CONT(2700) = 5.3 +/- 0.5 E-10 Comments: CONTINUUM FLUXES FROM IUE SPECTRUM Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J2000 -0.020 0.057 0.027 6087( 0) - 07/18/95 19:54 - [ 5] Visit: 01 Visit Requirements: PERIOD 5.469D AND ZERO-PHASE JD2449749.0 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 HD112413 HRS ACQ 2.0 MIRROR-A2 1 1.8S ONBOARD ACQ FOR 2 PHASE 0.95 TO 0.10 Comments: STEP-TIME = 0.2S ------------------------------------------------------------------------------------------------------------------------------------ 2 HD112413 HRS ACQ/PEA 0.25 MIRROR-A2 1 5S ONBOARD ACQ FOR 3-4 KUP Comments: STEP-TIME=0.2S ------------------------------------------------------------------------------------------------------------------------------------ 3 HD112413 HRS WSCAN 0.25 G160M 1575- STEP-PATT=5, FP 1 1325S 1767 -SPLIT=TWO, WAVE-STEP=32 Comments: SIX WAVELENGTH SETTINGS IN WSCAN ------------------------------------------------------------------------------------------------------------------------------------ 4 HD112413 HRS WSCAN 0.25 G200M 2083- STEP-PATT=5, FP 1 670S 2227 -SPLIT=TWO, WAVE-STEP=36 Comments: FOUR WAVELENGTH SETTINGS IN WSCAN ------------------------------------------------------------------------------------------------------------------------------------ 6087( 0) - 07/18/95 19:54 - [ 6] Visit: 02 Visit Requirements: AFTER 1 PERIOD 5.469D AND ZERO-PHASE JD2449749.0 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 ------------------------------------------------------------------------------------------------------------------------------------ 5 HD112413 HRS ACQ 2.0 MIRROR-A2 1 1.8S ONBOARD ACQ FOR 6 PHASE 0.95 TO 0.10 Comments: STEP-TIME=0.2S ------------------------------------------------------------------------------------------------------------------------------------ 6 HD112413 HRS ACQ/PEA 0.25 MIRROR-A2 1 5S ONBOARD ACQ FOR 7 KUP Comments: STEP-TIME=0.2 ------------------------------------------------------------------------------------------------------------------------------------ 7 HD112413 HRS WSCAN 0.25 G160M 1765- STEP-PATT=5, FP 1 2210S 2085 -SPLIT=TWO, WAVE-STEP=32 Comments: TEN WAVELENGTH SETTINGS IN WSCAN ------------------------------------------------------------------------------------------------------------------------------------ 6087( 0) - 07/18/95 19:54 - [ 7] Visit: 03 Visit Requirements: AFTER 2 PERIOD 5.469D AND ZERO-PHASE JD2449749.0 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 ------------------------------------------------------------------------------------------------------------------------------------ 8 HD112413 HRS ACQ 2.0 MIRROR-A2 1 1.8S ONBOARD ACQ FOR 9 PHASE 0.95 TO 0.10 Comments: STEP-TIME=0.2S ------------------------------------------------------------------------------------------------------------------------------------ 9 HD112413 HRS ACQ/PEA 0.25 MIRROR-A2 1 5S ONBOARD ACQ FOR 10-12 KUP Comments: STEP-TIME=0.2S ------------------------------------------------------------------------------------------------------------------------------------ 10 HD112413 HRS WSCAN 0.25 G270M 2225- STEP-PATT=5, FP 1 670S 2477 -SPLIT=TWO, WAVE-STEP=42 Comments: SIX WAVELENGTH SETTINGS IN WSCAN ------------------------------------------------------------------------------------------------------------------------------------ 11 HD112413 HRS WSCAN 0.25 G270M 2475- STEP-PATT=11, 1 354S 2643 FP-SPLIT=TWO, WAVE-STEP=42 Comments: FOUR WAVELENGTH SETTINGS IN WSCAN ------------------------------------------------------------------------------------------------------------------------------------ 12 HD112413 HRS WSCAN 0.25 G160M 1513- STEP-PATT=5, FP 1 445S 1577 -SPLIT=TWO, WAVE-STEP=32 Comments: TWO WAVELENGTH SETTINGS IN WSCAN ------------------------------------------------------------------------------------------------------------------------------------ 6087( 0) - 07/18/95 19:54 - [ 8] Summary Form for Proposal 6087 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAKUP WSCAN ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters STEP-PATT=5 FP-SPLIT=TWO WAVE-STEP=32 WAVE-STEP=36 WAVE-STEP=42 STEP-PATT=11 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Hot Stars ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PERIOD 5.469D AND ZERO-PHASE JD2449749.0 ONBOARD ACQ FOR 2 PHASE 0.95 TO 0.10 ONBOARD ACQ FOR 3-4 AFTER 1 PERIOD 5.469D AND ZERO-PHASE JD2449749.0 ONBOARD ACQ FOR 6 PHASE 0.95 TO 0.10 ONBOARD ACQ FOR 7 AFTER 2 PERIOD 5.469D AND ZERO-PHASE JD2449749.0 ONBOARD ACQ FOR 9 PHASE 0.95 TO 0.10 ONBOARD ACQ FOR 10-12 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-A2 G160M G200M G270M ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD112413 ------------------------------------------------------------------------------------------------------------------------------------