! Proposal 6463, submission 1 ! PI: Dr. Stefan Dreizler ! Received Thu Feb 15 07:33:11 EST 1996 ! From: supas083@astrophysik.uni-kiel.d400.de ! +====================+ ! | PED OUTPUT PRODUCT | ! +====================+ ! ! /astrotmp_week/supas083/cycle6/6463.prop ! Generated by PREPROCESSOR, version 6.0e ! Date: Mon Feb 12 15:51:26 MET 1996 Proposal_Information Title: The origin of the peculiar hybrid PG 1159 stars Proposal_Category: GO Scientific_Category: HOT STARS Cycle: 6 Investigators PI_Name: Dr. Stefan Dreizler PI_Institution: Institut fuer Astronomie und Astrophysik der Universitaet CoI_Name: Dr. Ulrich Heber CoI_Institution: Astronomisches Institut der Universitaet Erlangen--Nuernberg Contact: CoI_Name: Dr. Ralf Napiwotzki CoI_Institution: Astronomisches Institut der Universitaet Erlangen--Nuernberg Contact: CoI_Name: Dr. Klaus Werner CoI_Institution: Lehrstuhl Astrophysik, Universitaet Potsdam Contact: Abstract: The PG 1159 stars form a new class of hydrogen deficient pre white dwarfs (PWD) representing the hottest stage of PWD evolution. Quantitative spectral analyses of most known PG 1159 stars have been carried out by the proposers from optical, UV (IUE, HST) and EUV (EUVE) observations. It has been shown that these stars have atmospheres dominated by C and He. In the hottest stars also a significant amount of O is present. The proposed targets, HS2324+3944, NGC7094, and Abell43 define a small group of peculiar PG 1159 stars. Unlike all other PG 1159 stars hydrogen is detected in their spectra. Stellar parameters derived by the investigators from optical spectra suggest that, as a consequence of a lower mass, they went through a less drastic mass-loss phase than the ordinary PG 1159 stars. In order to verify that hypothesis a more precise determination of the effective temperature is required. This is not possible from optical analyses alone. We demonstrate that a great improvement on the determination of the effective temperatures can be achieved by HST-GHRS spectra. The spectra will be analyzed with new highly sophisticated NLTE line blanketed model atmospheres, which allow to include many elements up to the iron group self- consistently. A precise placement of HS2324+3944, NGC7094, and Abell43 in the HR-diagram holds the key for understanding the evolutionary history of the PG 1159 class. Questions Observing_Description: We propose the following observations: Each star shall be observed with the GHRS using grating G140L in the wavelength range 1150-1437 Angstrom. NGC7094 is bright enough to expose additionally a spectrum in the wavelength range 1463-1750 Angstrom within one orbit. The primary aim is to determine the effective temperature as precise as possible as well as to determine the oxygen abundance. A simultaneous analysis of the OV 1371 Angstrom line together with OIV lines (1340 Angstrom) for NGC7094, and Abell43 and OVI lines for HS2324+3944, NGC7094 and Abell43 is the only means to determine the O abundance and will reduce the uncertainties in T(eff) considerably. Fig.15 in WHH and Fig.2 in this proposal predict an extreme temperature sensitivity of the oxygen lines. It follows that the determination of T(eff) with a precision of 2% equivalent widths can be measured to an accuracy of about 10%. The first spectral range also covers the NV, 1240 Angstrom resonance line. Due to the high effective temperature it is the only means to determine the nitrogen abundance in HS2324+3944 (no other N lines are detectable). Due to a possible contamination with interstellar NV the nitrogen abundance in HS2324+3944 can be an upper limit only. For the three cooler stars we predict the presence of several (weaker) NIV lines serving as consistency checks for the derived nitrogen abundances. Many other lines of CIV and OVI can be identified in the first wavelength range (see WHH) and will allow to determine abundances with unprecedented precision. The second wavelength range for NGC7094 additionally covers the CIV resonance line, the HeII 1640 Angstrom line, and the NIV 1718 Angstrom line. All three lines can be used to additionally constrain the carbon, helium, and nitrogen abundance. Because of the high gravity, all spectral features are relatively broad and shallow. Hence a spectral resolution of about 1 Angstrom is sufficient, which can be reached with grating G140L and the large science aperture. A high S/N ratio is necessary, however, in order to perform detailed line profile fits (S/N~100 at 1350 Angstrom is aimed at). In the second wavelength range for NGC7094 a lower S/N is acceptable, since we expect strong carbon and helium lines. Exposure times and S/N have been calculated from available (or scaled) IUE fluxes, visibility periods, overhead times and the sensitivities given in the handbook. Two orbit (54 min/52 min visibility) are necessary for HS2324+3944, NGC7094, and Abell43 each. Subtracting the overhead time for guide star acquisition and re--acquisition as well as target acquisition (8 + 11 + 5 = 23min.) 84 minutes of exposure time remain for HS2324+3944, 79 minutes remain for Abell43. The 79 minutes for NGC7094 will be split in 33 minutes for the bluer and 46 minutes for the redder wavelength range. Real_Time_Justification: Calibration_Justification: Additional_Comments: Fixed_Targets Target_Number: 1 Target_Name: STAR-NGC7094 Alternate_Names: NGC7094 Description: STAR,PG1159 STAR, Position: RA=21H 36M 52.98S +/- 0.2",DEC=12D 47' 19.1" +/- 0.2",PLATE-ID=02KW Equinox: J2000 RV_or_Z: RA_PM: Dec_PM: Epoch: Annual_Parallax: Flux: V = 13.7+/-0.1 E(B-V) = 0.1+/-0.03 F(1350)=1.2+/-0.1e-12 F(1550)=7.9+/-0.1e-13 Comments: GSC Coordinates; Color_Excess from Burstein and Heiles 1982, AJ 87, 1165;Flux(1350A/1550A) from IUE spectrum; Target_Number: 2 Target_Name: STAR-2324+3944 Alternate_Names: HS2324+3944 Description: STAR,PG1159 STAR, Position: RA=23H 27M 15.88S +/- 0.2",DEC=40D 01' 24.7" +/- 0.3",PLATE-ID=02S2 Equinox: J2000 RV_or_Z: RA_PM: Dec_PM: Epoch: Annual_Parallax: Flux: V = 14.8+/-0.2 E(B-V) = 0.15+/-0.03 F(1350)=2.0+/-0.1e-13 Comments: GSC Coordinates; Color_Excess from Burstein and Heiles 1982, AJ 87, 1165;Flux(1350A) from IUE spectrum; Target_Number: 3 Target_Name: STAR-ABELL43 Alternate_Names: ABELL43 Description: STAR,PG1159 STAR, Position: RA=17H 53M 32.29S +/- 0.3",DEC=10D 37' 23.65" +/- 0.3",PLATE-ID=00JA Equinox: J2000 RV_or_Z: RA_PM: Dec_PM: Epoch: Annual_Parallax: Flux: V = 14.8+/-0.1 E(B-V) = 0.18+/-0.03 F(1350)=2.0+/-0.1e-13 Comments: DSS-phaseII Coordinates; Color_Excess from Burstein and Heiles 1982, AJ 87, 1165;Flux(1350A) from IUE spectrum; Solar_System_Targets Generic_Targets Scan_Data Visits Visit_Number: 01 Visit_Requirements: On_Hold_Comments: Visit_Comments: Exposure_Number: 1 Target_Name: STAR-NGC7094 Config: HRS Opmode: ACQ Aperture: 2.0 Sp_Element: MIRROR-N1 Wavelength: Optional_Parameters: SEARCH-SIZE=3,BRIGHT=RETURN Number_of_Iterations: 1 Time_Per_Exposure: 5.4S Special_Requirements: ONBOARD ACQ FOR 2-3 Comments: STEP-TIME=0.6s, EXPECT 400 CNTS Exposure_Number: 2 Target_Name: STAR-NGC7094 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1150-1437 Optional_Parameters: FP-SPLIT=STD,COMB=FOUR,DOPPLER=ON Number_of_Iterations: 1 Time_Per_Exposure: 1305.6S Special_Requirements: Comments: Exposure_Number: 3 Target_Name: STAR-NGC7094 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1463-1750 Optional_Parameters: FP-SPLIT=STD,COMB=FOUR,DOPPLER=ON Number_of_Iterations: 1 Time_Per_Exposure: 2828.8S Special_Requirements: Comments: Visit_Number: 02 Visit_Requirements: On_Hold_Comments: Visit_Comments: Exposure_Number: 1 Target_Name: STAR-2324+3944 Config: HRS Opmode: ACQ Aperture: 2.0 Sp_Element: MIRROR-N1 Wavelength: Optional_Parameters: SEARCH-SIZE=3,BRIGHT=RETURN Number_of_Iterations: 1 Time_Per_Exposure: 21.6S Special_Requirements: ONBOARD ACQ FOR 2 Comments: STEP-TIME=2.4s, EXPECT 400 CNTS Exposure_Number: 2 Target_Name: STAR-2324+3944 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1150-1437 Optional_Parameters: FP-SPLIT=STD,COMB=FOUR,DOPPLER=ON Number_of_Iterations: 1 Time_Per_Exposure: 4460.8S Special_Requirements: Comments: Visit_Number: 03 Visit_Requirements: On_Hold_Comments: Visit_Comments: Exposure_Number: 1 Target_Name: STAR-ABELL43 Config: HRS Opmode: ACQ Aperture: 2.0 Sp_Element: MIRROR-N1 Wavelength: Optional_Parameters: SEARCH-SIZE=3,BRIGHT=RETURN Number_of_Iterations: 1 Time_Per_Exposure: 21.6S Special_Requirements: ONBOARD ACQ FOR 2 Comments: STEP-TIME=2.4s, EXPECT 400 CNTS Exposure_Number: 2 Target_Name: STAR-ABELL43 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G140L Wavelength: 1150-1437 Optional_Parameters: FP-SPLIT=STD,COMB=FOUR,DOPPLER=ON Number_of_Iterations: 1 Time_Per_Exposure: 4243.2S Special_Requirements: Comments: Data_Distribution ! 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