MPIRE - The MPIfR/SRON 800 GHz heterodyne spectrometer
Figure 1: The integrated MPIfR/SRON 800 GHz system in the Cassegrain focus cabin
of the JCMT.
Introduction
The MPIfR/SRON heterodyne spectrometer (MPIRE) for the 350 mm atmospheric window (E-band) has
been successfully installed and commissioned at the JCMT in April 2000. Figure 1 shows the integrated
system in the Cassegrain cabin. The spectrometer consists of a single-channel fixed-tuned waveguide mixer
with an SIS NbTiN junction fabricated at the University of Groningen. Figure 2 shows the atmospheric
transmission of the E-band window for 0.5mm pwv together with the frequency range covered by MPIRE
and the location of some spectral lines. Among the most important lines are the transitions of CO J=7-6
[807 GHz], [CI] 3P2-3P1 [809 GHz], HCO+ J=9-8 [802 GHz], and HCN J=9-8 [797 GHz].
Figure 2: Atmospheric transmission of the 800 GHz window and the coverage of MPIRE.
First scientific results
In collaboration with the Leiden Astrochemistry group we measured a few high mass YSOs in the HCN
J=9-8 line at 797 GHz. Figure 3 shows the spectra of HCN J=9-8 and CO J=7-6 toward the high-
mass starforming region GL 2591. These spectra were obtained in beamswitch mode. The system
was found to be stable and sensitive. The spectra have only been binned, no baseline was subtracted.
The baselines are extremely flat and the offsets from the zero-levels are real and due to the dust continuum
heated by the YSO.
Figure 3: Spectra of the CO J=7-6 and HCN J=9-8 rotational transition toward the high-mass
starforming region GL 2591. The vibrational transition u 2=1 is also detected.
The HCN J = 9 level has a high critical density (~ 109 cm-3 ) and high excitation temperature (~ 200 K).
These heterodyne observations provide the missing link between the extended envelope traced by
low-level HCN observations and the small region of hot (Tex> 300 K) abundant HCN as observed in
ro-vibrational IR absorption studies with ISO. Because of the low spectral resolving power of ISO
(R~1500) the latter spectra reveal no kinematic information of this hot gas, instead the new heterodyne
spectra (R~106 ) will help to tell where hot gas is located. In addition the vibrational transition u 2=1 is
detected (3-sigma integrated emission), and provides independent information on the level populations.
A paper on the HCN detection is in preparation (Boonman, Stark, van der Tak et al. ).
Availability for semester 01A
The system is currently on loan from MPIfR and available in semester 01A for use by the JCMT
community on a collaborative basis. Astronomers interested in using it must contact Ronald Stark
(stark@mpifr-bonn.mpg.de) to arrange collaborative efforts. The instrument will stay at JCMT for
an extended time during which a continuous improvement of its performance is planned.
Current specifications of MPIRE
MPIRE is a single channel waveguide SIS heterodyne spectrometer with an RF tuning range
790 - 840 GHz. The double-sideband (DSB) receiver temperature is in the range 500 - 800 K,
the highest sensitivity is around 800 - 810 GHz. Only DSB operation is possible. The maximum
available bandwidth for the DAS is currently 920 MHz. The measured single-sideband system
temperatures at the JCMT are around 10,000 K or less under good submillimetre weather
conditions (t225 GHz<0.05). Preliminary analysis yields a main beam efficiency hmb~0.15.
Page created by Ronald Stark. Last updated: 1 September 2000
