<=== observer ===>
"MBARLOW",\
"Barlow, M.J.",\
"Department of Physics & Astronomy",\
"University College London",\
"Gower Street",\
"",\
"WC1E 6BT",\
"London",\
"United Kingdom",\
" 44 713807160",\
" 44 713807145",\
"mjb@star.ucl.ac.uk"
<=== proposal ===>
"HIRES",1,3,\
{"circumstellar envelopes","abundances","AGB stars"},\
{"LWS consortium","Baluteau, J.","Emery, R.","Glencross, W.","Habing, H.",\
"Omont, A.","Rieu, N-Q.","Cohen, R.","Skinner, C.","van Dishoeck, E."}
<=== title ===>
High spectral resolution observations of molecules and atoms in outflows
from evolved stars
<=== abstract ===>
SCIENTIFIC ABSTRACT
We propose to carry out high spectral resolution observations of atomic and
molecular lines from the outflows around a number of cool evolved objects.
These observations will address the following questions: (a) Can direct
observational evidence be provided for the first time showing the operation of
the proposed IR radiative pump mechanism for OH maser emission? (b) What is the
abundance of H2O in O-rich winds? It has been proposed that OH originates
mainly from H2O dissociation and, further, that H2O can be an important coolant
in such winds.
OBSERVATION SUMMARY
We will use the SWS Fabry-Perot to observe the 34.6um doublet, which should be
in absorption, as it is believed to pump the observed OH maser lines in the
microwave region. The LWS Fabry-Perots will be used to observe seven OH
doublets at 48.76um, 53.31um, 79.15um, 96.34um, 98.73um, 119.34um and 163.26um
which are predicted to be part of the resulting emission cascade which leads
to the inversion of the OH ground state. The SWS and LWS observations will be
tied as closely together in time as possible for each target, due to the known
strong variability of the OH masers. LWS FP observations will also be obtained
at the wavelengths of three H2O rotational lines, at 108.07um, 136.50um and
179.53um, whose fluxes are predicted to be detectable from a number of
objects, in an effort to diagnose how important H2O is as a coolant in the
outflows.
If targets in the Orion-hole should be observable (i.e. a Spring launch), the
total amount of LWS Guaranteed (spacecraft) time allocated will be 19.86 hours,
of which 7.51 hours will be for Priority 1 targets. For an Autumn launch
(Sagittarius-hole observable), 19.38 hours of LWS Guaranteed (spacecraft) time
will be allocated, of which 7.31 hours will be for Priority 1 targets.
3.5 hours of Mission Scientist (H.J. Habing) Guaranteed time is being
used for this project, with the remainder coming from LWS Consortium
Guaranteed time.
<=== scientific_justification ===>
Two particular problems in the field of cool evolved stars will be studied with
the LWS. These are : (a) the excitation mechanism for the 18cm OH maser
emission observed from Mira and OH/IR stars; (b) the abundance of H2O in O-rich
stellar winds.
(a) OBSERVATIONS OF IR TRANSITIONS ASSOCIATED WITH THE OH MASER PUMP
Many late type stars are sources of microwave maser emission from OH, H2O
and SiO molecules. The OH sources exhbit maser emission from transitions within
the J = 3/2 2Pi(3/2) ground state. It has been proposed that the upper sublevel
of the 1612 MHz transition is inverted by 34.6um photons, emitted by dust in
the wind, which are absorbed from the ground state up to the J=5/2 2Pi(1/2)
rotational level, followed by a cascade back to the ground state, involving the
emission of 98.7um, 163.2um and 79.1um photons; 48.7um, 96.3um and 119.4um
photons; and 53.3um photons (Elitzur, Goldreich and Scoville, Ap.J., 205, 384,
1976).
There are three OH maser lines detected in circumstellar envelopes. The
`mainlines' (1665 and 1667 MHz) are dominant in optically thin envelopes,
whereas the 1612 MHz satellite line dominates in optically thick envelopes. To
obtain 1612 MHz masing, the expected pathway is as follows: the ground
2Pi(3/2) J=3/2 state is excited to the 2Pi(1/2) J=5/2 state by 34.6um line
absorption - the preferred decay from there is to the 2Pi(1/2) J=3/2 state,
with emission at 98.7um. The next preferred stage is decay to the 2Pi(1/2)
J=1/2 state, with emission at 163.2um, and finally there is a decay back to the
2Pi(3/2) J=3/2 ground state, with emission at 79.1um. This scheme, with
sufficient 34.6um flux available, causes an inversion of the F=2/F=1 levels of
the ground state, leading to 1612 MHz maser action. Under slightly different
conditions, much the same scheme can lead to inversion between the
lambda-doubled F=2 and F=1 levels in the ground state, which are separated by
transitions at 1665 and 1667 MHz (the `main-lines'), which can thus also mase.
Observations of the far-IR transitions represent the obvious way to test the
radiative pumping scheme, since the line strengths will reveal the number of
photons making each transition and thus enable a trivial check on the degree of
inversion of the ground state F levels of the OH molecules (some other decay
pathways can be followed after absorption of 34.6um photons - the degree of
inversion of each masing transition will depend on the number of molecules
which follow each pathway. All the decay pathways are observable using the
LWS). Elitzur et al. estimated that, for a typical red giant maser, about four
34.6um photons will be absorbed for every one 1612 MHz maser photon emitted.
The upward 34.6um absorption can be observed by the SWS, while all the
resulting cascade photons can be observed by the LWS. Thus ISO observations can
critically test theory and will certainly throw light on the excitation
properties of the OH radical.
OH TARGETS:
COOL STARS
IRAS (Jy)
Name Sp. Type RA(1950) DEC(1950) 12 25 60 100
IK Tau M6-M10e 03 50 46.0 +11 15 42 4634 2377 332 103
VY Cma M5Ia 07 20 54.8 -25 40 12 9919 6651 1453 331
W Hya M8IIIe 13 46 12.2 -28 07 05 4200 1189 195 72.2
VX Sgr M4-9Ia 18 05 03.0 -22 13 56 2738 1385 263 82.3
IRC+10420 F8Ia 19 24 27.0 +11 15 11 1346 2314 718 186
OH/IR STARS
IRAS (Jy)
Name Sp. Type RA(1950) DEC(1950) 12 25 60 100
WX Psc OH/IR 01 03 48.0 +12 19 45 1155 967 215 72
OH127.8+0.0 OH/IR 01 30 27.7 +62 11 30 289 456 194 50
AFGL 5379 OH/IR 17 41 08.2 -31 54 33 1262 2723 1365 406
OH26.5+0.6 OH/IR 18 34 51.6 -05 27 24 360 634 463 <310
OH104.9+2.4 OH/IR 22 17 43.1 +59 36 16 123 229 91 35
POST-AGB OBJECT
IRAS (Jy)
Name Sp. Type RA(1950) DEC(1950) 12 25 60 100
OH231.8+4.2 OH/IR/PPN 07 39 58.9 -14 35 44 19.0 226 548 294
Our sample is chosen to include objects with mass loss rates at the low end of
the range, with the 1665 and 1667 MHz mainlines dominant (e.g. W Hya) and
optically thick objects (higher mass loss rates) with the 1612 MHz maser
dominant. We propose to observe with the LWS FP's the OH transitions listed
below, and to observe with the SWS FP the 34.6um OH pumping transition.
Wavelengths of the OH doublets to be observed with the LWS:
48.704, 48.817um
53.262, 53.351um
79.117, 79.182um
96.312, 96.367um
98.725, 98.737um
119.234, 119.441um
163.121, 163.396um
Wavelengths of the OH pumping doublet to be observed with the SWS:
34.6035, 34.6294um
AOT's:
The LWS High Resolution Line Spectrum AOT, LWS04, will be used with four
sample points per FP resolution element, scanned +-4 resolution elements on
either side of the central wavelength of each doublet component (except for the
98.7um doublet, where the components are so close to each other that a scan
centred at their mean wavelength of 98.731um will suffice). An integration time
of 5 seconds per sample point will be used, which will yield, per resolution
element, 5sigma line flux detection limits of 1.7x10(-15), 1.05x10(-15),
6.4x10(-16) and 8.1x10(-16) W m-2 at 48um, 98um, 119um and 163um, respectively.
The total spacecraft time required to obtain the LWS FP scans at the thirteen
separate wavelengths settings will be 75.43 minutes per star.
We will observe the OH 34.6um doublet, expected to be in absorption, with the
SWS FP at R = 30,000, using the SWS07 AOT. The velocity separation of the
doublet components is 225 km/s, so we will scan +-200 km/s on either side of
the mean wavelength of the doublet of 34.6165um. The total spacecraft time
needed for the SWS observations of each target is listed in Table 2 below,
along with the continuum S/N ratios that are expected for these integration
times. As the SWS time estimates include the spacecraft slew-time overhead of
180 seconds, this overhead has not been included in the spacecraft time
estimates for the LWS observations.
** The LWS and SWS FP observations must be obtained as close together in
time as possible, due to the known strong variability of the OH masers.**
(b) SPECTRAL LINE OBSERVATIONS OF H2O
The photodissociation of H2O by the interstellar or chromospheric radiation
fields is thought to be the main production mechanism for OH in late-type
stellar winds. In addition, H2O can act as a heat source in the inner dense
regions (via collisional de-excitation following absorption of trapped IR line
photons), while acting as a coolant in the outer lower-density regions. The
goal of our observations is to determine the abundance of H2O in late-type
stellar winds, via LWS FP observations of a selected number of diagnostic
lines. Deguchi and Rieu (Ap.J., 360, L27, 1990) have predicted the fluxes in
various ortho and para H2O lines, based on a thermal excitation model and we
have used these predictions to select the lines to be observed.
S/N estimates for the stars listed in Table 1 (below) were based upon H2O line
fluxes predicted by N-Q-Rieu, based on the thermal excitation model of Deguchi
and Rieu (Ap.J., 360, L27, 1990). The line fluxes have been derived by
performing radiative transfer calculations based on the most recent collisional
cross sections. The line flux depends on the mass loss rate, the shell
expansion velocity, and the distance of the source. A fractional H2O abundance
(relative to molecular hydrogen) of 4x10(-4) was assumed. The
characteristics of the envelopes were taken from Knapp (Ap.J., 293, 273,
1985), Knapp and Morris (Ap.J., 292, 640, 1985) and Knapp et al. (Ap.J., 336,
822, 1989).
AOT's:
The LWS High Resolution Line Spectrum AOT, LWS04, will be used, with 4 sample
elements per resolution element, and a total scan range of +-4 resolution
elements about line centre, giving 32 sample elements per line. An integration
time of 10 seconds per point will be used. Table 1 lists the H2O lines that
will be observed towards each star. For five of the targets, the 414-303
line at 113.538um is being observed as part of the Mission Scientist proposal
mharwit_mharwit, and so will not be observed here.
For the two sources not in the OH target list, O Ceti and Alpha Ori, the
spacecraft slew time overhead of 180 seconds per target is included in
the total observing time estimates given in Table 2.
TABLE 1: H2O Line Observations
Line 221-110 212-101 330-321 414-303 616-505
108.073um 179.527um 136.496um 113.538um 82.030um
NAME
IK Tau X X X X X
VY CMa X X X X
W Hya X X X X
VX Sgr X X X X X
IRC+10420 X X X X X
O Ceti X X X X
Alf Ori X X X X X
WX Psc X X X X
OH127.8+0.0 X X X X
AFGL 5379 X X X X X
OH26.5+0.6 X X X X X
OH104.9+2.4 X X X X X
OH231.8+4.2 X X X X
Table 2: Summary of OH and H2O observations
SWS OH LWS OH LWS H2O Total
Prior. Hole NAME S/C Time S/C Time S/C Time S/C Time
(secs) (secs) (secs) (hours)
3 IK Tau 967 4526 2464 2.210
1 O VY CMa 967 4526 1948 2.067
1 W Hya 1956 4526 1948 2.342
1 S VX Sgr 1956 4526 2464 2.485
2 IRC+10420 967 4526 2464 2.210
2 WX Psc 1956 4526 1948 2.342
3 O OH127.8+0.0 1956 4526 2464 2.485
3 S GL 5379 967 4526 2464 2.210
1 S OH26.5+0.6 1956 4526 2464 2.485
3 OH104.9+2.4 1956 4526 2464 2.485
1 O OH231.8+4.2 1956 4526 1948 2.342
3 O Cet 2230 0.619
1 O Alf Ori 2746 0.763
SPACECRAFT TIME SUMMARY:
Orion-hole observable (Spring launch) Sgr-hole observable (Autumn launch)
Priority 1 time = 7.51 hrs (37.8%) Priority 1 time = 7.31 hrs (37.7%)
Priority 2 time = 6.76 hrs (34.0%) Priority 2 time = 6.76 hrs (34.9%)
Priority 3 time = 5.59 hrs (28.2%) Priority 3 time = 5.31 hrs (27.4%)
Total S/C time = 19.86 hrs Total S/C time = 19.38 hrs
Time distribution for autumn launch targets:
Team top 40% second 30% last 30%
LWS : 21282 20564 15353
HJH : 5040 3780 3780
total : 26322 24344 19133
Time distribution for spring launch targets:
Team top 40% second 30% last 30%
LWS : 22007 20564 16342
HJH : 5040 3780 3780
total : 27047 24344 20122
<=== autumn_launch_targets ===>
1, "LWS04", 3.0, "N", "O Ceti", 2.28028, -3.20333, 1950, 0.,0.,2230,0
2, "LWS04", 2.0, "N", "IK Tau", 3.84611, +11.26167, 1950, 0.,0.,1764,3
3, "LWS04", 2.0, "N", "IK Tau", 3.84611, +11.26167, 1950, 0.,0.,5226,4
4, "SWS07", 2.0, "N", "IK Tau", 3.84611, +11.26167, 1950, 0.,0.,967,0
5, "LWS04", 1.0, "N", "W Hya", 13.77006, -28.11806, 1950, 0.,0.,1248,6
6, "LWS04", 1.0, "N", "W Hya", 13.77006, -28.11806, 1950, 0.,0.,5226,7
7, "SWS07", 1.0, "N", "W Hya", 13.77006, -28.11806, 1950, 0.,0.,1956,0
8, "LWS04", 1.0, "N", "VX Sgr", 18.08417, -22.23222, 1950, 0.,0.,1764,9
9, "LWS04", 1.0, "N", "VX Sgr", 18.08417, -22.23222, 1950, 0.,0.,5226,10
10, "SWS07", 1.0, "N", "VX Sgr", 18.08417, -22.23222, 1950, 0.,0.,1956,0
11, "LWS04", 2.0, "N", "IRC+10420",19.40750, +11.25306, 1950, 0.,0.,1764,12
12, "LWS04", 2.0, "N", "IRC+10420",19.40750, +11.25306, 1950, 0.,0.,5226,13
13, "SWS07", 2.0, "N", "IRC+10420",19.40750, +11.25306, 1950, 0.,0.,967,0
14, "LWS04", 3.0, "N", "AFGL 5379",17.68561, -31.90917, 1950, 0.,0.,1764,15
15, "LWS04", 3.0, "N", "AFGL 5379",17.68561, -31.90917, 1950, 0.,0.,5226,16
16, "SWS07", 3.0, "N", "AFGL 5379",17.68561, -31.90917, 1950, 0.,0.,967,0
17, "LWS04", 1.0, "N", "26.5+0.6", 18.58100, -5.45667, 1950, 0.,0.,1764,18
18, "LWS04", 1.0, "N", "26.5+0.6", 18.58100, -5.45667, 1950, 0.,0.,5226,19
19, "SWS07", 1.0, "N", "26.5+0.6", 18.58100, -5.45667, 1950, 0.,0.,1956,0
20, "LWS04", 2.0, "N", "WX Psc", 1.06333, +12.32917, 1950, 0.,0.,1248,21
21, "LWS04", 2.0, "N", "WX Psc", 1.06333, +12.32917, 1950, 0.,0.,5226,22
22, "SWS07", 2.0, "N", "WX Psc", 1.06333, +12.32917, 1950, 0.,0.,1956,0
23, "LWS04", 3.0, "N", "104.9+2.4",22.29531, +59.60444, 1950, 0.,0.,1764,24
24, "LWS04", 3.0, "N", "104.9+2.4",22.29531, +59.60444, 1950, 0.,0.,5226,25
25, "SWS07", 3.0, "N", "104.9+2.4",22.29531, +59.60444, 1950, 0.,0.,1956,0
<=== spring_launch_targets ===>
1, "LWS04", 3.0, "N", "O Ceti", 2.28028, -3.20333, 1950, 0.,0.,2230,0
2, "LWS04", 2.0, "N", "IK Tau", 3.84611, +11.26167, 1950, 0.,0.,1764,3
3, "LWS04", 2.0, "N", "IK Tau", 3.84611, +11.26167, 1950, 0.,0.,5226,4
4, "SWS07", 2.0, "N", "IK Tau", 3.84611, +11.26167, 1950, 0.,0.,967,0
5, "LWS04", 1.0, "N", "Alf Ori", 5.87436, +7.39889, 1950, 0.,0.,2746,0
6, "LWS04", 1.0, "N", "VY CMa", 7.34856, -25.67000, 1950, 0.,0.,1248,7
7, "LWS04", 1.0, "N", "VY CMa", 7.34856, -25.67000, 1950, 0.,0.,5226,8
8, "SWS07", 1.0, "N", "VY CMa", 7.34856, -25.67000, 1950, 0.,0.,967,0
9, "LWS04", 1.0, "N", "W Hya", 13.77006, -28.11806, 1950, 0.,0.,1248,10
10, "LWS04", 1.0, "N", "W Hya", 13.77006, -28.11806, 1950, 0.,0.,5226,11
11, "SWS07", 1.0, "N", "W Hya", 13.77006, -28.11806, 1950, 0.,0.,1956,0
12, "LWS04", 2.0, "N", "IRC+10420",19.40750, +11.25306, 1950, 0.,0.,1764,13
13, "LWS04", 2.0, "N", "IRC+10420",19.40750, +11.25306, 1950, 0.,0.,5226,14
14, "SWS07", 2.0, "N", "IRC+10420",19.40750, +11.25306, 1950, 0.,0.,967,0
15, "LWS04", 1.0, "N", "231.8+4.2", 7.66636, -14.59556, 1950, 0.,0.,1248,16
16, "LWS04", 1.0, "N", "231.8+4.2", 7.66636, -14.59556, 1950, 0.,0.,5226,17
17, "SWS07", 1.0, "N", "231.8+4.2", 7.66636, -14.59556, 1950, 0.,0.,1956,0
18, "LWS04", 2.0, "N", "WX Psc", 1.06333, +12.32917, 1950, 0.,0.,1248,19
19, "LWS04", 2.0, "N", "WX Psc", 1.06333, +12.32917, 1950, 0.,0.,5226,20
20, "SWS07", 2.0, "N", "WX Psc", 1.06333, +12.32917, 1950, 0.,0.,1956,0
21, "LWS04", 3.0, "N", "104.9+2.4",22.29531, +59.60444, 1950, 0.,0.,1764,22
22, "LWS04", 3.0, "N", "104.9+2.4",22.29531, +59.60444, 1950, 0.,0.,5226,23
23, "SWS07", 3.0, "N", "104.9+2.4",22.29531, +59.60444, 1950, 0.,0.,1956,0
24, "LWS04", 3.0, "N", "127.8+0.0", 1.50769, +62.19167, 1950, 0.,0.,1764,25
25, "LWS04", 3.0, "N", "127.8+0.0", 1.50769, +62.19167, 1950, 0.,0.,5226,26
26, "SWS07", 3.0, "N", "127.8+0.0", 1.50769, +62.19167, 1950, 0.,0.,1956,0