4 Comparison of the ALMA and Herschel - ESO

An example is DRSP contribution 3.3.2, Line Surveys in Evolved Stars. The plan is to produce
images like those in Fig 17 for 6 objects other than IRC+10216 and also for higher frequencies.
The survey will include 6 sources, 4 ALMA receiver bands. It will use an angular resolution of
0.6” to 0.3” and a velocity resolution of 0.5 kms -1 . The rms noise in the spectral lines will be better
than 1 Kelvin in 10 minutes of integration time. The continuum rms will be better than 0.01 Jy.
The programme will require 170 hours of time.
6.9.2 Continuum Emission
Another research topic is the search for continuum radio emission from red giant and supergiant
stars. From 1.3 cm and 7 mm measurements, Reid & Menten (1997) found that such
emission has an optically thick thermal spectrum.
In DRSP 3.2.3, Thermal Emission from Red Giant and Supergiant Stars, it is proposed to measure
a number of spectral lines in the envelopes of well-known stars such as ο Ceti, R Leonis, W
Hydrae, R Aquilae, Chi Cygni and R Cassiopeiae. It is estimated that the continuum emission
from these nearby objects can be detected with ALMA in 10 seconds. In 30 minutes integration,
one reaches 7 μJy, so that one can detect G and M dwarf stars at 10 pc distance at 100 GHz. In
DRSP 3.2.6, Millimetre Survey of Stellar Disk Emission from late-type Stars, R. Osten proposes
to detect the emission from 20 stars in 3.5 hours. A repeat of these measurements would be made
more than 1 month late to search for variability. In any such programme, the highest angular
resolution is needed to eliminate confusion. In DRSP 3.2.7, Flares from Young Stellar Objects:
what we learned from the 2003 January fl are in GMR-A it is proposed to integrate for a short
time on a large number of objects in the three lowest frequency ALMA receiver bands to search
for variability caused by magnetic surface activity.
6.9.3 Solar System Objects
Studies of the outer planets are often searching for the origin of external water. The sources
might be dust from asteroids or comets, or local production. These sources can be distinguished
by measuring Deuterium/Hydrogen ratios. At present, there seems to be different
D/H ratios for comets and the outer planets, including Titan. Further studies might confirm
this result and lead to more secure models. Herschel would concentrate on measurements of
H 2
O, while ALMA would be used to determine HDO abundances; by combining these data
one would obtain reliable D/H ratios. An associated study would be the relation of water
vapour production and evolution in comets as a function of heliocentric distance.
For Herschel, water vapour excitation would be an extensive study in comets, and in
additional searches for small water abundances could be carried out for asteroids, distant
comets and Centaur objects. This would include short period comets formed in the Kuiper
Belt, and the measurements should be extended to deuterated water to determine the D/H
ratios. These may require simultaneous measurements.
Mars is another prime object of study. One could use Herschel for a spectral line survey in
the 960 to 1250 GHz range, and then use ALMA for follow-up studies and confirmations.
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