Astronomy & Astrophysics

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Issue		A&A Volume 454, Number 2, August I 2006 APEX Special Booklet
Page(s)		L33 - L36
Section		Letters
DOI		10.1051/0004-6361:20065341

A&A 454, L33-L36 (2006)
DOI: 10.1051/0004-6361:20065341

Letter

First observations with CONDOR, a 1.5 THz heterodyne receiver

M. C. Wiedner¹, G. Wieching¹, F. Bielau¹, K. Rettenbacher¹, N. H. Volgenau¹, M. Emprechtinger¹, U. U. Graf¹, C. E. Honingh¹, K. Jacobs¹, B. Vowinkel¹, K. M. Menten², L.-Å. Nyman³, R. Güsten², S. Philipp², D. Rabanus¹, J. Stutzki¹ and F. Wyrowski²

¹ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
    e-mail: lastname@ph1.uni-koeln.de
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
    e-mail: lastname@mpifr-bonn.mpg.de
³ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago, Chile
    e-mail: initial.lastname@eso.org

(Received 31 March 2006 / Accepted 31 May 2006)

Abstract
Context.The THz atmospheric "windows", centered at roughly 1.3 and 1.5 THz, contain numerous spectral lines of astronomical importance, including three high-J CO lines, the [N II] line at 205 $\mu$ m, and the ground transition of para-H₂D⁺. The CO lines are tracers of hot (several 100 K), dense gas; [N II] is a cooling line of diffuse, ionized gas; the H₂D⁺ line is a non-depleting tracer of cold (~20 K), dense gas.
Aims.As the THz lines benefit the study of diverse phenomena (from high-mass star-forming regions to the WIM to cold prestellar cores), we have built the CO N⁺ Deuterium Observations Receiver (CONDOR) to further explore the THz windows by ground-based observations.
Methods.CONDOR was designed to be used at the Atacama Pathfinder EXperiment (APEX) and Stratospheric Observatory For Infrared Astronomy (SOFIA). CONDOR was installed at the APEX telescope and test observations were made to characterize the instrument.
Results.The combination of CONDOR on APEX successfully detected THz radiation from astronomical sources. CONDOR operated with typical $T_{\rm rec}=1600$ K and spectral Allan variance times of ~30 s. CONDOR's "first light" observations of CO 13-12 emission from the hot core Orion FIR 4 (= OMC1 South) revealed a narrow line with $T_{\rm MB}\approx 210$ K and $\Delta V\approx 5.4$ km s^-1. A search for [N II] emission from the ionization front of the Orion Bar resulted in a non-detection.
Conclusions.The successful deployment of CONDOR at APEX demonstrates the potential for making observations at THz frequencies from ground-based facilities.

Key words: instrumentation: detectors -- methods: observational -- submillimeter -- stars: formation -- HII regions -- Orion FIR4

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