7346( 5) - 07/23/98 17:31 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7346 Version: 5 Check-in Date: 23-Jul-1998 17:30:13 1.Proposal Title: The nature of the bright 'Supersoft X-ray Source' RX J 0019+21 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Klaus Beuermann Universitaets-Sternwarte Goettingen CoI: Boris T. Gaensicke Universitaets-Sternwarte Goettingen Y CoI: Klaus Reinsch Universitaets-Sternwarte Goettingen N CoI: Andre van Teeseling Universitaets-Sternwarte Goettingen N ------------------------------------------------------------------------------------ 5. Abstract RX J0019+21 is by far the brightest member of the new still small class of close- binary `Supersoft X-ray Sources' which probably contain a near-Eddington accreting and nuclear burning white dwarf. Supersoft X-ray sources radiate most of their energy in the UV and soft X-ray bands with a wealth of information contained in the UV. With V=12, RX J0019+21 is the prime candidate for an in-depth UV study. It may also be the only example of an intermittently burning white dwarf. The STIS is needed to obtain decisive information on the true nature of this unique source. We propose to use the STIS to obtain two sets of echelle spectra of RX J0019+21 at the quadrature phases of the binary orbit. We will be able to determine the UV spectral energy distribution, to separate stellar and interstellar components of e.g. IonCII, IonSiII, IonSiIII and IonOI absorption lines, to search for <~\ absorption of stellar or disk origin, measure the profile of the LineHeII1640 emission line, and search for other emission/absorpti on lines. Such information is required to determine the structure and the temperature distribution of the putative accretion disk, to model the wind component, to derive elemental abundances, to obtain an independent estimate of the distance, and to test the combined results against current models for `Supersoft Sources'. ------------------------------------------------------------------------------------ 7346( 5) - 07/23/98 17:31 - [ 2] Observations Description ------------------------ HST will be used to obtain two sets of observations of the supersoft source RX J0019+21 near orbital phases 0.25 and 0.75, each extending over two HST orbits. In the first orbit of each set, an E230M spectrum will be obtained covering the region 1720--2528 Angstrom, the second orbit of each set will be used to obtain an E140M spectrum covering the region 1150--1700Angstrom. The target (V=12.5) is well-suited for the standard acquisition with a following point-source peakup in the 0.2x0.2 echelle slit. The overheads in the first orbits are: 9 min guide star acquisition, 8 min target acquisition, ~ 8 min for the peakup and 8 min for the instrument setup/wavelength calibration. This leaves 19 min for the E230M spectrum, yielding a S/N ~ 20. During the second orbits, the overheads are 6 min for the guide star re- acquisition plus 8 min instrument setup, which leaves 38 min for the E140M spectrum, yielding a S/N ~ 10. All exposures have been run through the STIS Spectroscopic Ex posure Time Calculator using the s pectral distribution known from our IUE exposures; all expected count rates are far below the MAMA safety limits. Real Time Justification ----------------------- The observations should take place near the quadrature phases Phi = 0.75 and Phi = 0.25 according to the spectroscopic ephemeris given in Will & Barwig 1996, Beuermann. et al 1955 (see also Fig.1):, T(Phi=0) = HJD 2448864.439(14) + 0.6604721(72) * E We will organize contemporaneous optical spectroscopy which will not be a major problem for a 12 mag object. Calibration Justification ------------------------- Real_Time_Justification Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: DAT Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7346( 5) - 07/23/98 17:31 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 RXJ0019.8+21 STAR, INTERACTING RA=00H 19M 49.90S +/- 0S, J2000 V = 12.0+/-0.5 56 BINARY DEC=21D 56' 52.0" +/- 0", PLATE- B-V = 0.15+/-0.05 ID=0384 E(B-V) = 0.1+/-0.03 F(1400)=2.0+/-0.5e-13 Comments: RXJ0019.8+2156 is an HST Guide Star (Star ID 1428, Plate 0384, 02BE, 021J) 7346( 5) - 07/23/98 17:31 - [ 4] Visit: 01 Visit Priority: Visit Requirements: GROUP 1-2 WITHIN 10 D PERIOD 0.6604795 D AND ZERO-PHASE JD2450002.271300 On Hold Comments: Additional Comments: Phi=0.0, max. redshift Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 RXJ0019.8+2 STIS/C ACQ F28X50L MIRROR 1 0.5 S ONBOARD ACQ FOR 2-3 SEQ 156 CD P 1-2 NON-INT PHASE 0.9 TO 1.0 Comments: For BB=15000K, V=11.5, E(B-V)=0.1, Filter=Longpass, gain=4, Texp=0.5 sec the STIS ETC yields S/N=450 and reaches 30% of the CCD fullwell limit. ------------------------------------------------------------------------------------------------------------------------------------ 2 RXJ0019.8+2 STIS/N TIME-TA 0.2X0.2 E230M 2124 BUFFER-TIME=250 1 31 M SEQ 1-2 NON-INT 156 UV-MAM G A Comments: The known IUE spectrum yields in the ETC ~1500 integrated cts/s. Conservative BUFFER-TIME based on ~8000 cts/s ------------------------------------------------------------------------------------------------------------------------------------ 3 RXJ0019.8+2 STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=450 1 39.5 M NO SPLIT 156 UV-MAM G A Comments: The known IUE spectrum yields in the ETC ~800 integrated cts/s. Conservative BUFFER-TIME based on ~4000 cts/s ------------------------------------------------------------------------------------------------------------------------------------ 7346( 5) - 07/23/98 17:31 - [ 5] Visit: 02 Visit Priority: Visit Requirements: GROUP 1-2 WITHIN 10 D PERIOD 0.6604795 D AND ZERO-PHASE JD2450002.271300 On Hold Comments: Additional Comments: Phi=0.50, max blueshift Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 4 RXJ0019.8+2 STIS/C ACQ F28X50L MIRROR 1 0.5 S PHASE 0.4 TO 0.5 ONBOARD 156 CD P ACQ FOR 5-6 SEQ 4-5 NON-INT Comments: For BB=15000K, V=11.5, Filter=Longpass, gain=4, 0.5 sec STIS ETC yields S/N=450, 30% of the CCD fullwell limit ------------------------------------------------------------------------------------------------------------------------------------ 5 RXJ0019.8+2 STIS/N TIME-TA 0.2X0.2 E230M 2124 BUFFER-TIME=250 1 31 M SEQ 4-5 NON-INT 156 UV-MAM G A Comments: The known IUE spectrum yields in the ETC ~1500 integrated cts/s. Conservative BUFFER-TIME based on ~8000 cts/s ------------------------------------------------------------------------------------------------------------------------------------ 6 RXJ0019.8+2 STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=450 1 39.5 M NO SPLIT 156 UV-MAM G A Comments: The known IUE spectrum yields in the ETC ~800 integrated cts/s. Conservative BUFFER-TIME based on ~4000 cts/s ------------------------------------------------------------------------------------------------------------------------------------ 7346( 5) - 07/23/98 17:31 - [ 6] Summary Form for Proposal 7346 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 0.2X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=250 BUFFER-TIME=450 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GROUP 1-2 WITHIN 10 D PERIOD 0.6604795 D AND ZERO-PHASE JD2450002.271300 ONBOARD ACQ FOR 2-3 SEQ 1-2 NON-INT PHASE 0.9 TO 1.0 SEQ 1-2 NON-INT NO SPLIT PHASE 0.4 TO 0.5 ONBOARD ACQ FOR 5-6 SEQ 4-5 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR E230M E140M ------------------------------------------------------------------------------------------------------------------------------------ Target Names RXJ0019.8+2156 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 2124 1425 ------------------------------------------------------------------------------------------------------------------------------------