! Hubble Space Telescope Cycle 5 (1995) Phase II Proposal Template ! Id: 6091 ! ! For help call your Program Coordinator: Max Mutchler ! Phone: 410 338-1321 , E-mail: mutchler@stsci.edu Proposal_Information Title: Determining the Ionization Equilibrium and Abundances in BALQSOs Proposal_Category: GO Scientific_Category: Quasars Cycle: 5 Investigators PI_name: Nahum Arav PI_Institution: California Institute of Technology CoI_Name: Kirk Korista CoI_Institution: University of Kentucky Contact: Y CoI_Name: Mitchell Begelman CoI_Institution: University of Colorado Contact: CoI_Name: Martijn de Kool CoI_Institution: Max-Planck Institute Contact: Abstract: ! Free format text (please update) About 10\% of all quasars show broad absorption lines (BALs) associated with resonance lines from abundant ions. Two important issues in the study of these objects are the determination of the ionization equilibrium and the determination of the chemical abundances that give rise to the observed BALs. Ground-based spectra by themselves are of limited value here. The main problem is that only about four BALs are typically observed from the ground, and each arises from a different element. Therefore, the effects of ionization levels and abundances cannot be separated. However, UV spectroscopy with the HST combined with ground-based spectra can cover BALs from more than one ion for some elements, in particular BALs from four ions of oxygen can be observed. This situation allows us to separate the two effects and hence to improve dramatically our understanding of both. Existing HST/FOS observations can contribute toward these goals, but the targets and exposures were never chosen with attempt to obtain optimized data to answer these questions. We propose to observe an object, for which the combination of brightness, structure of the absorption trough, length of exposure and spectral coverage, will give such optimized data. We will then use a carefully planned approach to determine the ionization equilibrium and abundances from these observations. Questions ! Free format text (please update) Observing_Description: There are about a hundred known BALQSOs. To obtain a high enough signal-to-noise spectrum with the desired rest wavelength coverage, we must choose a bright (V\ltorder 17) high redshift BALQSO (z>2). We would also like the absorption trough of the observed object (represented by the C IV Lambda1550 BAL) to be well suited for ionization studies. Two main trough shapes are desired: a) a relatively narrow (10,000 km s^-1>Delta v> 3000 km s^-1), smooth, well defined trough; b) a trough with a well resolved structure. The first shape will help us to separate most BALs, especially in crowded spectral regimes (for example, between 760 Angstrom--790 Angstrom there are at least four BALs, see Fig. 3). It will therefore make the task of determining Tau_l(v) simpler. The second shape has the potential to reveal whether the absorption components are associated with different physical flows. This can be done by checking for different Tau_l(v) changes in each of the components for BALs from different ions of the same atom. Our two final candidates represent both trough choices. 0842+3431 has the simpler trough and thus is more desirable for ionization studies. Q1524+5147 has a wider and more complicated trough, but its higher redshift shifts all the important oxygen BALs into the wavelength region of grarting G270H on FOS. This allows us to concentrate all our observing time into this one grating, which will result in a substential improvement of the signal to noise. Since none of these objects was observed below 3200 Angstrom, there is a chance that an intervening Lyman limit system will strongly absorb the spectrum below some wavelength shortward of 3200 Angstrom. In order not to waste a lot of observing time, we propose to observe each object for one orbit with the G160L (Q0842+3431) or G270H (Q1524+5147). These pilot observations will determine if there is a enough flux in these objects to justify the much longer followup observation. After examining the results of these observations, we will be able to make a better decision as to which of the two objects we want to observe with the FOS. Our request for exposure times is based on a careful comparison between the ground-based spectra of the above objects with that of 0226-1024, on the FOS spectra for this object, and on the information in the FOS Instrument Handbook. We find that all three objects have the same flux to within 30% at 3200 Angstrom. Between 3200 Angstrom-- 2200 Angstrom 0226-1024 shows a decline in flux as steep as F_Lambda\propto lambda^3. The observation taken with G190H shows that the spectrum flattens out between 2200 Angstrom- 1800 Angstrom. We can only hope that this is the worst case scenario for our objects. Therefore, based on the UV spectra of 0226-1024 and compensating for the changes due to the addition of COSTAR, we estimate that for Q0842+3431 we will need about four times the exposure used for 0226 with G270H (2000 s) and with G190H (3000 s). This is a total of 8000 s with G270H and 12000 s with G190H. According to the FOS work sheets these goals can be achieved in nine consecutive orbits. In Q1524+5147 the absorption trough is wider and more complex. Therefore, we will probably need 20,000 s -- 25,000 s of exposure with G270H in order to obtain the same scientific results. We would like to stress that all this is very uncertain due to the unknown shape of the UV continuum in these objects (we might encounter higher fluxes than in 0226). The pilot observations we are planning, would show whether the scientific goals of this program are achievable in the amount of orbits we were allocated. Real_Time_Justification: The G160L pilot observations must precede the longer FOS observation, since the choice of object for the FOS observation and the exact exposures lengh will be determined on the basis of the G160L observation. none Calibration_Justification: ! Move appropriate text from Real_Time_Justification Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: 0842+3431 Alternate_Names: CSO203 Description: GALAXY, QSO Position: RA=08H 45M 38.66S +/- 0.5S, DEC=+34D 20' 43.3" +/- 0.5", PLATE-ID=02D5 Equinox: 2000 RV_or_Z: Z = 2.131 RA_PM: Dec_PM: Epoch: 1983.132 Annual_Parallax: Flux: V=17.21 +/- 0.08 F-CONT(1120)= 7.0 E-16 ! Include at least V and B-V Comments: A broad absorption line QSO. Spectral energy distribution is unknown below 3100 Angstroms observed frame. Fixed_Targets Target_Number: 2 Target_Name: 1524+5147 Alternate_Names: CSO755 Description: GALAXY, QSO Position: RA=15H 25M 53.83S +/- 0.5S, DEC=+51D 36' 49.5" +/- 0.5", PLATE-ID=01RT Equinox: 2000 RV_or_Z: Z = 2.873 RA_PM: Dec_PM: Epoch: 1983.207 Annual_Parallax: Flux: V=17.15 +/- 0.05 F-CONT(1110)= 6.0 E-16 ! Include at least V and B-V Comments: A broad absorption line QSO. Spectral energy distribution is unknown below 3100 Angstroms observed frame. ! This is a template for a single visit containing a single exposure ! Repeat exposure and visit blocks as needed Visits ! Section 6 Visit_Number: 1 Visit_Requirements: ! Section 7.1 ! Uncomment or copy visit level special requirements needed ! Most of these requirements (including ORIENT) will limit scheduling ! PCS MODE [Fine | Gyro] ! GUIDing TOLerance ! ORIENTation TO ! ORIENTation TO FROM ! ORIENTation TO FROM NOMINAL ! SAME ORIENTation AS ! CVZ ! PARallel ! AFTER [BY [TO ]] ! AFTER ! BEFORE ! BETWEEN AND ! GROUP WITHIN