8312( 3) - 02/18/99 08:48 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8312 Version: 3 Check-in Date: 18-Feb-1999 08:48:16 1.Proposal Title: Low Column Density Ly-Alpha Absorbers at z=1.2: High SNR Echelle Spectroscopy of PG 1634+706 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Buell Jannuzi National Optical Astronomy Observatories CoI: Prof. Jill Bechtold University of Arizona N CoI: Dr. Ray Weymann The Observatories of the Carnegie N Institution of Washington CoI: Prof. John Bahcall Institute for Advanced Study N CoI: Dr. Sofia Kirhakos Institute for Advanced Study N CoI: Prof. Donald Schneider The Pennsylvania State University N CoI: Prof. David Weinberg Ohio State University N ------------------------------------------------------------------------------------ 5. Abstract We propose to produce the highest signal-to-noise ratio (SNR) Echelle resolution spectrum yet obtained of Ly-Alpha absorbers between z=0.9 and 1.2 by augmenting the planned cycle 7 observations of the luminous quasar PG 1634+706 with five orbits of CVZ observing time with the E230M grating. Our choice of a different central wavelength for our observations will allow the construction of a combined high SNR spectrum covering from 1865 to 3100 Angstroms. Recent theoretical work has shown that the neutral hydrogen column density N_HI of an absorber is tightly correlated with its overdensity, and hence with its dynamical and physical state. However, the mapping between overdensity and N_HI changes as the universe expands. If we wish to study absorbers at z~1 that are physically similar to absorbers at z~3 we must probe a factor ~20-50 lower in column density (Dave et al. 1998). The high SNR spectrum obtained from our observations of PG 1634+706 will allow the accurate measurement of the neutral column densities and line profiles of lines with N_HI as low as 3* 10^12 cm^-2. For the first time it will be possible to study at z~1 the mildly overdense regions of the intergalactic medium that have been observed so successfully at high redshift (z~3) with HIRES and the Keck I telescope. ------------------------------------------------------------------------------------ 8312( 3) - 02/18/99 08:48 - [ 2] Observations Description ------------------------ We propose to use a single visit and 5 CVZ orbits to obtain a total of approximately 440 minutes of exposure time using STIS, the NUV MAMA, the 0.2x0.2 apt., in ACCUM mode, and using the E230M grating with the primary tilt that yields a central wavelength of 2707 Angstroms. After combining our spectrum with that being obtained in an approved cycle 7 program (E230M observation with a central wavelength of 2269) our final spectrum will have a range of SNR, from sections as low as SNR=8 per resolution element to as high as 47. Acquisition time was determined using the V-band magnitude of the quasar. Real Time Justification ----------------------- By observing PG 1634+706 in the continuous viewing zone we will obtain as high a signal-to-noise ratio spectrum at high resolution of Ly-alpha absorption at z~1.2 as it is possible to obtain in only 5 orbits. This extremely luminous quasar is fortuitously placed at a declination that will allow us to obtain 5 consecutive orbits of exposure time during one of two available windows in the CVZ. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Paper Products: NO Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8312( 3) - 02/18/99 08:48 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PG1634+706 GALAXY, QSO, EXT- RA=16H 34M 28.9S +/- 0.2", J2000 Z = F(2700)=1.5+/-0.5e-14 MEDIUM, ABSORPTION LINE DEC=70D 31' 33" +/- 0.2", PLATE- 1.334 F(2850)=4.e-14 SYSTEM - EXTRAGALACTIC ID=01L7 V = 14.7+/-.1 Comments: The flux quoted at 2850 angstroms is the flux at the peak of the quasar's Lyman alpha emission. The uncertainty in the flux measurement quoted at 2700 angstroms is much smaller than 0.5e-14. The uncertainty listed just reflects what we feel is the possible change in quasar brightness due to intrinsic variability. 8312( 3) - 02/18/99 08:48 - [ 4] Visit: 01 Visit Priority: Visit Requirements: CVZ 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 PG1634+706 STIS/C ACQ F28X50L MIRROR 1 2 S ONBOARD ACQ FOR 30 CD P ------------------------------------------------------------------------------------------------------------------------------------ 30 PG1634+706 STIS/N ACCUM 0.2X0.2 E230M 2707 5 80 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 40 PG1634+706 STIS/N ACCUM 0.2X0.2 E230M 2707 1 2425 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8312( 3) - 02/18/99 08:48 - [ 5] Summary Form for Proposal 8312 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 0.2X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ ONBOARD ACQ FOR 30 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR E230M ------------------------------------------------------------------------------------------------------------------------------------ Target Names PG1634+706 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 2707 ------------------------------------------------------------------------------------------------------------------------------------