Assigned ID: 585
----- Attempting Submission 1 (Fri Feb 24 19:03:19 GMT 2012) -----
HST Phase I Proposal 585 (heibal_apt) successfully submitted.
----- Attempting Submission 2 (Fri Feb 24 23:30:30 GMT 2012) ---------- Attempting Submission 1 (Tue Jul 10 14:08:06 GMT 2012) -----As explained in our observation description, we don't use all four
FP-POS for CENWAVE=3360 because their isn't sufficient time but
more importantly, lines of interest aren't covered by all FP-POS.
Target 1 (SDSS J085053.12+445122.5 has positional uncertainties
less than 0.4", so we should be safe using just ACQ/IMAGE. We do
do a search for the second target SDSS J142927.28+523849.5, which
has a DEC uncertainty of 0.41".The Nature of Partial Covering in Broad Absorption Line QuasarsEjected gas is seen as broad absorption lines in ~20% of quasars. It has been known for ~15 years that prominent lines such as CIV are usually saturated but not black because the absorbing gas only partially covers the continuum emission region. Therefore, column densities estimated from these lines are only lower limits. Accurate column densities can be obtained from rare ions that have two or more transitions from the same lower level, so that the optical depth and covering fraction can be solved for simultanously. Suitable lines are hard to find, so such measurements are rare. We have found that metastable helium is particularly useful for these measurements. Yet despite these advances, partial covering remains a just a parameter and its physical nature is not understood.
We propose a unique experiment to constrain the physical nature of partial covering. We will compare the covering fraction measured from PV (a doublet in the far UV) with that measured from metastable HeI (optical and IR). The ions creating these lines are relatively rare, and they present similar opacity over a wide range of gas parameters. But due to their wide wavelength separation, these lines probe dramatically different regions of the continuum source, the temperature-dependent accretion disk. So we expect different covering fraction behavior for different partial covering scenarios. This experiment is relevant for understanding the geometry and clumpiness of the outflow, and the results may impact our understanding of the global covering fraction, a parameter critical for determining the outflow kinetic luminosity, and thereby estimating feedback efficiency for broad absorption line outflows.We were awarded observations of two HeI* BALQSOs using HST COS with
the G230 grating. Two central wavelengths (2950 and 3360) will be
used for each object. The properties and plan for each object will be
described sequentially below.
We note that we will be applying for LBT observations of both objects
starting with the 2012B opportunity. The ground-based observations
are intended to be contemporaneous rather than simultaneous;
nevertheless, we will keep STScI informed on our progress in obtaining
the time and executing the observations.
SCIENCE SUMMARY AND STRATEGY
The UV and FUV rest-wavelength spectra of BALQSOs are full of
absorption lines. Our science involves a comparison of the HeI* broad
absorption lines (BALs) observed in the optical and IR with the BALs
from other lines in the UV. The absorption line that we are
principally interested in is PV, which falls at ~1121 Angstroms rest
frame, but approximately at 1760 Angstroms for these z~0.57 objects.
The maximum velocity of the outflow may be up to ~7000 km/s, thus
stretching the feature down to ~1720 Angstroms. This is best observed
in Segment A with CENWAVE=2950. So we allocate the larger fraction of
our time to observations using that central wavelength. These
observations are long enough that we are able to cover all four
FP-POS. We are also interested in other absorption lines including
CIV and SIV, which fall in Segment A with CENWAVE=3360. The shorter
observations don't permit efficient use of all 4 FP-POS, and in the
case of our higher redshift object SDSS-J142927.28+523849.5, CIV is
not visible for FP-POS=3 or 4.
The objects are faint enough to be observed in TIME-TAG mode, and we
will use FLASH=YES as recommended in the COS IHB section 5.2.1.
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SDSS J085053.12+445122.5
Properties:
This HeI* BALQSO has a redshift of 0.5422. Based on the SDSS
photometry, we estimate that V=17.4 and B=17.7. We estimate ~0.5 mag
uncertainty due to quasar variability. SDSS 0850+4451 was observed
four times by GALEX. The flux density inferred from the GALEX UV
results ranged from 9.1e-16 to 1.06e-15 erg/s/cm^2/A. We use the mean
9.8e-16 erg/s/cm^2/A for simulations. We plan to observed this object
using 5 of our 15 orbits.
Acquisition:
The target is in the GSC2 and therefore it has ICRS coordinates. The
positional uncertainties are 0.387 and 0.369 arc seconds. Those
values are less than the limit of 0.4 arc seconds, so we can do a
simple imaging acquisition.
The mean GALEX NUV flux density among four observations is 9.8e-16
erg/s/cm^2/A. The GALEX NUV filter response is fairly similar to the
COS NUV+Mirror A filter response. In principle, a target of this flux
density should be able to be acquired using PSA+Mirror A. However,
quasars vary, and so it is conceivable that the flux density may be
half this value (5e-16) or twice this value (2e-15). If twice the
observed flux, the object would be too bright to acquire using
PSA+Mirror A. So, to be conservative, we choose COS NUV PSA+Mirror B
and assume a low flux density of 5.0e-16 erg/s/cm^2/A. In that case,
we obtain, for SNR=40, an exposure time of 320s (COS.ta.415851).
Science Exposures:
We allocate the remainder of the first orbit and 3 more orbits (of 5
total for this target) for the observation with CENWAVE=2950. We use
FP-POS=1 through 4 sequentially. All lines of interest should be
visible in all four FP-POS. The first orbit allows 2071s of science
exposure, and subsequent orbits allow 3084s. According to the ETC,
the buffer time for these exposure times, assuming a flat spectrum and
mean flux density, is 2439s (COS.sp.414030, COS.sp.414032). To
account for variability, we multiply this value by 0.5, and again by
2/3 (as recommended), yielding a buffer time of 813s. The final orbit
is allocated to observing the object using CENWAVE=3360. This setting
has a nearly flat response curve, so in principle we could observe at
any FP-POS. However, depending on the maximum velocity of the
outflow, SiIV may not be completely observed for FP-POS=1. So we
observe at FP-POS=2 and FP-POS=3, and split the orbit between these
two FP-POS. The exposures are 1474s. The COS ETC gives a buffer time
of 2,428s (COS.sp.414258) and so we again used 0.5*(2/3) of that
value, which is 809 seconds for these final two exposures.
****************************************************************
SDSS J142927.28+523849.5
Properties:
This HeI* BALQSO has a redshift of 0.5839. Based on the SDSS
photometry, we estimate that V=17.5 and B=17.7. We estimate ~0.5 mag
uncertainty due to quasar variability. SDSS 1429+5238 was observed
twice by GALEX. The flux density inferred from the GALEX NUV
results ranged from 4.6e-16 to 5.0e-15 erg/s/cm^2/A. We use the mean
4.8e-16 erg/s/cm^2/A for simulations.
Acquisition:
The target is in the GSC2 and therefore it has ICRS coordinates. The
positional uncertainties are 0.375 and 0.406 arc seconds. The DEC
uncertainty exceeds the limit of 0.4 arc seconds, so we must do an
ACQ/SEARCH with SCAN-SIZE=2, and CENTER=FLUX-WT (COS IHB Table 8.2).
Because the positional uncertainty is on the lower edge of the range
given in Table 8.2, we use a STEP-SIZE=1.5.
The mean GALEX NUV flux among two observations is 4.8e-16
erg/s/cm^2/A. So it is safely faint enough to use the COS NUV+Mirror
A. The GALEX NUV filter response is fairly similar to the COS
NUV+Mirror A filter response. We assume a flat spectrum, and to
account for variability, assume a flux of 2.4e-16 erg/s/cm^2/A (i.e.,
50% decrease in flux). That yields an exposure of 32.7 seconds
required to obtain a S/N=40 (COS.ta.414268). We increase that to 50
seconds. We then perform an ACQ/IMAGE with the same exposure time.
Science Exposures:
We have 10 orbits total on this target using CENWAVE=2950 and
CENWAVE=3360. This will require two visits of 5 orbits each. All
FP-POS will cover the PV line for CENWAVE=2950. In addition, we will
be able to observe SIV in this higher redshift object at FP-POS=3 and
4. For CENWAVE=3360, we only cover CIV for FP-POS 1 and 2. So, for
the first visit, we allocate the remainder of the first orbit to
CENWAVE=2950 FP-POS=1. Orbits 2,3,4 are devoted to the other three
FP-POS. For the final orbit, we move to CENWAVE=3360 and observe in
FP-POS=1. The second visit is identical to the first except that we
will observe CENWAVE=3360 in FP-POS=2.
For CENWAVE=2950, the exposure times of 2343s (first orbit) and 3181s,
and for the estimated flux density of 4.8e-16 erg/s/cm^2/A and a flat
spectrum, the required buffer time is 2483s (COS.sp.414587). To
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For CENWAVE=3360, the exposure times of 2343 and 3181s, and estimated
flux density of 4e-16 erg/s/cm^2/A and a flat spectrum, the required
buffer time is 2477s (COS.sp.414589). As before, to accommodate
variability, we multiply that value by 0.5*2/3 yielding 826s.AGN/QUASARS12false0.00.0falsefalsefalsefalseSUPPORTEDGALAXYQSOJ2000J2000B=17.7, Flambda(2267 Angstroms)=9.8e-16 erg/s/cm^2/AGALAXYQSOJ2000J2000B=17.7, F_lambda(2267 Angstroms)=4.8e-16 erg/s/cm^2/ACOS/NUVSpectroscopicNoNoG230L2950COS/NUVSpectroscopicNoNoG230L3360COS/NUVSpectroscopicNoNoG230L2950COS/NUVSpectroscopicNoNoG230L3360/Users/leighly/Dropbox/proposals/hst/2012/heibal/OP-cache/HST_phase2_heibal_apt_v2-v01.xmlThe scheduling data was generated by CASM 20.2.CASM was run in Phase II mode.(Tic-Visit
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