! +====================+ ! | PED OUTPUT PRODUCT | ! +====================+ ! ! /spectre/data1/aroman/proposals/6450.prop ! Generated by PREPROCESSOR, version 6.0m ! Date: Tue Feb 20 18:03:43 EST 1996 Proposal_Information Title: Hydrogen and metal abundances in the cool helium-rich white dwarf Ross640 Proposal_Category: GO Scientific_Category: HOT STARS Cycle: 6 Investigators PI_Name: Detlev Koester PI_Institution: Institut fuer Astronomie und Astrophysik CoI_Name: Nicole Allard CoI_Institution: Observatoire Paris-Meudon Contact: Abstract: The metal traces found in a few cool helium-rich white dwarfs (spectral type DZ) cannot be primordial, but must have been accreted from the interstellar matter, since their lifetimes in the atmospheres is limited to about a million years (diffusion timescales). We want to obtain high S/N UV spectra of Ross640, which is one of the brightest DZ, and only one of two objects at low Teff showing both metals and H. Abundances will be determined with model atmosphere techniques and compared with the predictions of the two-phase accretion scenario proposed by the Montreal group. This is the most advanced explanation today; however, comparisons between observation and theory are currently severely limited by the lack of reliable and accurate abundance determinations in these faint objects. HST observations of the second object with similar characteristics (L745-46A), which have recently been analyzed by us, demonstrate the huge progress that can be made with FOS now. Questions Observing_Description: Because of the requirement of high S/N and good calibration we plan to use the 4.3 aperture and an elaborate (4-stage- peakup) target acquisition to an accuracy of 0."04. We estimate that this will take about 1.5 orbits. The remainder of the second orbit will be used for a low resolution (G160L) spectrum of the range 1600 - 2300 Angstrom. From the IUE spectrum and model calculations, which we have used to estimate exposure times, we know that the flux will decrease steeply towards shorter wavelengths below 2300 Angstrom. The S/N will correspondingly fall from about 100 to 10, which is good enough to define the shape of the Lyman alpha far wing and show the stronger line features. The third orbit will, after target reacquisition, be used for a high resolution ( 2 Angstrom, G270H) high S/N spectrum of the most important region from 2300 to 3000 Angstrom. The S/N for 50 min exposure will be >= 100 over the whole region, ideal for line identifications and detailed model atmosphere analysis. The total request is thus 3 orbits. begintabularlll Cycle 6 & Primary Orbits:3 & Exposures:2, endtabular Real_Time_Justification: none none Calibration_Justification: Additional_Comments: Fixed_Targets Target_Number: 1 Target_Name: WD1626+368 Alternate_Names: ROSS640 Description: STAR,LATE-TYPE DEGENERATE,DZ Position: RA=16H 28M 25.72S +/- 0.3",DEC=36D 46' 2.6" +/- 0.3",PLATE-ID=01RW Equinox: J2000 RV_or_Z: RA_PM: -0.04087 Dec_PM: 0.7476 Epoch: B1982.39 Annual_Parallax: 0.061 Flux: V = 13.84+/-0.03 B-V = 0.18+/-0.03 Comments: Solar_System_Targets Generic_Targets Scan_Data Visits Visit_Number: 01 Visit_Requirements: On_Hold_Comments: Visit_Comments: Exposure_Number: 1 Target_Name: WD1626+368 Config: FOS/RD Opmode: ACQ/BINARY Aperture: 4.3 Sp_Element: MIRROR Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 0.82S Special_Requirements: ONBOARD ACQ FOR 2 Comments: Exposure_Number: 2 Target_Name: WD1626+368 Config: FOS/RD Opmode: ACQ/PEAK Aperture: 0.5 Sp_Element: MIRROR Wavelength: Optional_Parameters: SCAN-STEP-X=0.29,SCAN-STEP-Y=0.29,SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3 Number_of_Iterations: 1 Time_Per_Exposure: 1.0S Special_Requirements: ONBOARD ACQ FOR 3 Comments: STAGE 1 of 3 STAGE PEAKUP Exposure_Number: 3 Target_Name: WD1626+368 Config: FOS/RD Opmode: ACQ/PEAK Aperture: 0.3 Sp_Element: MIRROR Wavelength: Optional_Parameters: SCAN-STEP-X=0.17,SCAN-STEP-Y=0.17,SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3 Number_of_Iterations: 1 Time_Per_Exposure: 1.0S Special_Requirements: ONBOARD ACQ FOR 4 Comments: STAGE 2 of 3 STAGE PEAKUP Exposure_Number: 4 Target_Name: WD1626+368 Config: FOS/RD Opmode: ACQ/PEAK Aperture: 0.3 Sp_Element: MIRROR Wavelength: Optional_Parameters: SCAN-STEP-X=0.052,SCAN-STEP-Y=0.052,SEARCH-SIZE-X=5,SEARCH-SIZE-Y=5 Number_of_Iterations: 1 Time_Per_Exposure: 3.0S Special_Requirements: ONBOARD ACQ FOR 5 Comments: STAGE 3 of 3 STAGE PEAKUP Exposure_Number: 5 Target_Name: WD1626+368 Config: FOS/RD Opmode: ACCUM Aperture: 4.3 Sp_Element: G270H Wavelength: 2800 Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 39.5M Special_Requirements: MAX DUR 39.5M NO SPLIT Comments: Exposure_Number: 6 Target_Name: WD1626+368 Config: FOS/RD Opmode: ACCUM Aperture: 4.3 Sp_Element: G270H Wavelength: 2800 Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 1330S Special_Requirements: NO SPLIT Comments: Exposure_Number: 7 Target_Name: WD1626+368 Config: FOS/RD Opmode: ACCUM Aperture: 4.3 Sp_Element: G160L Wavelength: 1700-2400 Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 15.0M Special_Requirements: NO SPLIT MAX DUR 15M Comments: Data_Distribution ! 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