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Millimeter & Submillimeter Astronomy Group
at the Max-Planck-Institut für Radioastronomie
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Circumstellar Envelopes around Evolved Stars
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Carbon chains in CRL618
Astronomical observations of the carbon chain molecules HCN, HNC,
HCCCN and HC5N have been carried out employing the IRAM 30m,
Effelsberg 100m, CSO and VLA telescopes. Main target of the studies
was the object CRL 618 to obtain new observational results on the
transient protoplanetary nebula phase.
More and Stronger Submillimeter HCN Lasers
In recent years we
reported the detection of
submillimeter laser emission in the 804 GHz J=9-8
transition of HCN in the third overtone
of the vibrationally excited bending mode (0400) towards
the innermost circumstellar envelope of the high-mass-loss
carbon star IRC+10216. Apart from its remarkably high
excitation, one interesting fact
about this line is that besides the (3,3) line of
ammonia this is the only maser line found both in the
laboratory and in space. It is in fact part of a Coriolis-coupled
system between the (1110) and (0400) vibrational states, around
J=8 and 10, that was well-studied in the early days of
molecular laser spectroscopy. By analogy with the laboratory
situation, Schilke et al. also predicted laser emission
in the (1110)-(0400), J=10-9 line near 890 GHz.
This line was indeed detected using the CSO, not only in
IRC+10216 but also in another high-mass-loss carbon star, CIT 6,
and in the low-mass-loss C-star Y CVN.
Spectra taken over a two year span show pronounced
variability, as does the 804 GHz line which was reobserved in
IRC+10216 and detected in CIT 6. In both of these
stars the 890 GHz line is about an order of magnitude
stronger than the 804 GHz line.
Imaging the Radio Photospheres of Mira Stars
Recent simultaneous observations of the radio continuum and SiO masers
at 43 GHz with the VLA resolve and image the radio photosphere of a sample of oxygen-rich Miras better
than before and locate more precisely the SiO masers with respect to
the star. For example in the case of ο Ceti, where the star is resolved and a (uniform disk) diameter of
&asymp52 mas and a brightness temperature of ≈1670 K is
determined. The stellar image shows signs of elongation in the
east-west direction.
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