11699( 4) - 11-Mar-2009 14:31:23 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 11699 Version: 4 Check-in Time: 11-Mar-2009 14:31:23 STScI Edit Number: 1 Title On the evolutionary status of extremely hot helium stars - are the O(He) stars successors of the R CrB stars? ------------------------------------------------------------------------------------ Type Cycle GO 17 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Thomas Rauch Universitat Tubingen, Institut fur Astronomie & Astrophysik CoI: Dr. Falk Herwig University of Keele N CoI: Dr. Lars Koesterke University of Texas at Austin N CoI: Dr. Klaus Werner Universitat Tubingen, Institut fur Y Astronomie & Astrophysik ------------------------------------------------------------------------------------ Abstract We propose UV spectroscopy of the four unique post-AGB stars of spectral type O(He) in order to understand the origin of their peculiar surface abundances. These stars are the only known amongst the hottest post-AGB stars (effective temperatures > 100, 000 K) whose atmospheres are composed of almost pure helium. This chemistry markedly differs from that of the hydrogen-deficient post-AGB evolutionary sequence with objects which have carbon dominated atmospheres (PG1159 stars and Wolf-Rayet central stars). While PG1159 and Wolf-Rayet stars are the result of a late helium-shell flash, this scenario cannot explain the O(He) stars. Instead, they are possibly double-degenerate mergers. We speculate that the four O(He) stars represent evolved RCrB stars, which also have helium-dominated atmospheres. We aim to determine the C, N, O, and Si abundances precisely, in order to proof this evolutionary link. ------------------------------------------------------------------------------------ Observations Description ------------------------ We propose to take medium-resolution high S/N spectra with COS/FUV of the four O(He) stars. With grating G140L we cover the wavelength range 1105 / 2203A including many diagnostic metal lines. A resolution of about 0.5A is sufficient for our purpose because the lines are relatively broad. We aim to achieve S/N > 50 at 1425A which is necessary from our experience with STIS/G140L observations. The respective exposure time have been determined with the COS Exposure Time Calculator using theoretical NLTE model atmospheres. For any of the four objects, the S/N can be obtained within one orbit. Real Time Justification ----------------------- Calibration Justification ------------------------- 11699( 4) - 11-Mar-2009 14:31:23 - [ 2] Additional Comments ------------------- ------------------------------------------------------------------------------------ 11699( 4) - 11-Mar-2009 14:31:23 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 K1-27-CENTRA STAR, PLANETARY NEBULA RA=05H57M2.1350S +/- 0.1", J2000 V = 16.7 +/- 0.2 FUSE: log (Flambda / L-STAR CENTRAL STAR DEC=-75D40'22.51" +/- 0.1" erg/cm**2/sec/A) = -12.5 Reference Frame: ICRS Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. ------------------------------------------------------------------------------------------------------------------------------------ 2 LOTR-4-CENTR STAR, PLANETARY NEBULA RA=11H52M29.2310S +/- 0.1", J2000 V = 16.1 +/- 0.2 FUSE: log (Flambda / AL-STAR CENTRAL STAR DEC=-42D17'38.69" +/- 0.1" erg/cm**2/sec/A) = -13.2 Reference Frame: ICRS Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 0.0001333 0.018 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 3 HS-1522+6615 STAR, POST-AGB STAR RA=15H22M56.7000S +/- 0.1", J2000 V = 16.6 +/- 0.2 FUSE: log (Flambda / DEC=+66D04'42.10" +/- 0.1" erg/cm**2/sec/A) = -12.8 Reference Frame: ICRS Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. ------------------------------------------------------------------------------------------------------------------------------------ 4 HS-2209+8229 STAR, POST-AGB STAR RA=22H08M25.8000S +/- 0.1", J2000 V = 16.6 +/- 0.2 FUSE: log (Flambda / DEC=+82D44'52.00" +/- 0.1" erg/cm**2/sec/A) = -13.1 Reference Frame: ICRS Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. ------------------------------------------------------------------------------------------------------------------------------------ 11699( 4) - 11-Mar-2009 14:31:23 - [ 4] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 K1-27-CENTR COS/FUV ACQ/SEA PSA G140L 1105 STEP-SIZE=1.767, 1 0.2 S AL-STAR RCH CENTER=FLUX-WT, SCAN-SIZE=3, SEGMENT=A ------------------------------------------------------------------------------------------------------------------------------------ 2 K1-27-CENTR COS/FUV ACQ/PEA PSA G140L 1105 SEGMENT=A 1 0.2 S AL-STAR KXD ------------------------------------------------------------------------------------------------------------------------------------ 3 K1-27-CENTR COS/FUV ACQ/PEA PSA G140L 1105 CENTER=DEF, NUM-POS=3, 1 0.2 S AL-STAR KD STEP-SIZE=1.2, SEGMENT=A ------------------------------------------------------------------------------------------------------------------------------------ 4 K1-27-CENTR COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=120, FP-POS=AUTO, 1 2020 S AL-STAR G FLASH=YES, SEGMENT=A ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ K1-27-CENTRAL-STAR 1 COS/FUV ACQ/SEA PSA G140L 1105 none none none none 1 N/A RCH K1-27-CENTRAL-STAR 2 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KXD K1-27-CENTRAL-STAR 3 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KD K1-27-CENTRAL-STAR 4 COS/FUV TIME-TA PSA G140L 1105 none none none 1 1 N/A G K1-27-CENTRAL-STAR 4 COS/FUV TIME-TA PSA G140L 1105 none none none 2 1 N/A G K1-27-CENTRAL-STAR 4 COS/FUV TIME-TA PSA G140L 1105 none none none 3 1 N/A G K1-27-CENTRAL-STAR 4 COS/FUV TIME-TA PSA G140L 1105 none none none 4 1 N/A G 11699( 4) - 11-Mar-2009 14:31:23 - [ 5] Visit: 02 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 LOTR-4-CENT COS/FUV ACQ/SEA PSA G140L 1105 STEP-SIZE=1.767, 1 0.9 S RAL-STAR RCH CENTER=FLUX-WT, SCAN-SIZE=3, SEGMENT=A ------------------------------------------------------------------------------------------------------------------------------------ 2 LOTR-4-CENT COS/FUV ACQ/PEA PSA G140L 1105 SEGMENT=A 1 0.9 S RAL-STAR KXD ------------------------------------------------------------------------------------------------------------------------------------ 3 LOTR-4-CENT COS/FUV ACQ/PEA PSA G140L 1105 CENTER=DEF, NUM-POS=3, 1 0.9 S RAL-STAR KD STEP-SIZE=1.2, SEGMENT=A ------------------------------------------------------------------------------------------------------------------------------------ 4 LOTR-4-CENT COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=240, FP-POS=AUTO, 1 1786 S RAL-STAR G FLASH=YES, SEGMENT=A ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ LOTR-4-CENTRAL-STAR 1 COS/FUV ACQ/SEA PSA G140L 1105 none none none none 1 N/A RCH LOTR-4-CENTRAL-STAR 2 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KXD LOTR-4-CENTRAL-STAR 3 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KD LOTR-4-CENTRAL-STAR 4 COS/FUV TIME-TA PSA G140L 1105 none none none 1 1 N/A G LOTR-4-CENTRAL-STAR 4 COS/FUV TIME-TA PSA G140L 1105 none none none 2 1 N/A G LOTR-4-CENTRAL-STAR 4 COS/FUV TIME-TA PSA G140L 1105 none none none 3 1 N/A G LOTR-4-CENTRAL-STAR 4 COS/FUV TIME-TA PSA G140L 1105 none none none 4 1 N/A G 11699( 4) - 11-Mar-2009 14:31:23 - [ 6] Visit: 03 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 HS-1522+661 COS/FUV ACQ/SEA PSA G140L 1105 STEP-SIZE=1.767, 1 0.4 S 5 RCH CENTER=FLUX-WT, SCAN-SIZE=3, SEGMENT=A ------------------------------------------------------------------------------------------------------------------------------------ 2 HS-1522+661 COS/FUV ACQ/PEA PSA G140L 1105 SEGMENT=A 1 0.4 S 5 KXD ------------------------------------------------------------------------------------------------------------------------------------ 3 HS-1522+661 COS/FUV ACQ/PEA PSA G140L 1105 CENTER=DEF, NUM-POS=3, 1 0.4 S 5 KD STEP-SIZE=1.2, SEGMENT=A ------------------------------------------------------------------------------------------------------------------------------------ 4 HS-1522+661 COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=240, FP-POS=AUTO, 1 1998 S 5 G FLASH=YES, SEGMENT=A ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ HS-1522+6615 1 COS/FUV ACQ/SEA PSA G140L 1105 none none none none 1 N/A RCH HS-1522+6615 2 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KXD HS-1522+6615 3 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KD HS-1522+6615 4 COS/FUV TIME-TA PSA G140L 1105 none none none 1 1 N/A G HS-1522+6615 4 COS/FUV TIME-TA PSA G140L 1105 none none none 2 1 N/A G HS-1522+6615 4 COS/FUV TIME-TA PSA G140L 1105 none none none 3 1 N/A G HS-1522+6615 4 COS/FUV TIME-TA PSA G140L 1105 none none none 4 1 N/A G 11699( 4) - 11-Mar-2009 14:31:23 - [ 7] Visit: 04 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 HS-2209+822 COS/FUV ACQ/SEA PSA G140L 1105 STEP-SIZE=1.767, 1 0.8 S 9 RCH CENTER=FLUX-WT, SCAN-SIZE=3, SEGMENT=A ------------------------------------------------------------------------------------------------------------------------------------ 2 HS-2209+822 COS/FUV ACQ/PEA PSA G140L 1105 SEGMENT=A 1 0.8 S 9 KXD ------------------------------------------------------------------------------------------------------------------------------------ 3 HS-2209+822 COS/FUV ACQ/PEA PSA G140L 1105 CENTER=DEF, NUM-POS=3, 1 0.8 S 9 KD STEP-SIZE=1.2, SEGMENT=A ------------------------------------------------------------------------------------------------------------------------------------ 4 HS-2209+822 COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=250, FP-POS=AUTO, 1 2042 S 9 G FLASH=YES, SEGMENT=A ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ HS-2209+8229 1 COS/FUV ACQ/SEA PSA G140L 1105 none none none none 1 N/A RCH HS-2209+8229 2 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KXD HS-2209+8229 3 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KD HS-2209+8229 4 COS/FUV TIME-TA PSA G140L 1105 none none none 1 1 N/A G HS-2209+8229 4 COS/FUV TIME-TA PSA G140L 1105 none none none 2 1 N/A G HS-2209+8229 4 COS/FUV TIME-TA PSA G140L 1105 none none none 3 1 N/A G HS-2209+8229 4 COS/FUV TIME-TA PSA G140L 1105 none none none 4 1 N/A G 11699( 4) - 11-Mar-2009 14:31:23 - [ 8] Summary Form for Proposal 11699 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/PEAKD, ACQ/PEAKXD, ACQ/SEARCH, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=120, BUFFER-TIME=240, BUFFER-TIME=250, CENTER=DEF, CENTER=FLUX-WT, FLASH=YES, FP-POS=AUTO, NUM-POS=3, SCAN-SIZE=3, SEGMENT=A, STEP-SIZE=1.2, STEP-SIZE=1.767 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names HS-1522+6615, HS-2209+8229, K1-27-CENTRAL-STAR, LOTR-4-CENTRAL-STAR ------------------------------------------------------------------------------------------------------------------------------------