Showing papers by "Oliver Krause published in 2000"
16 Nov 2000
TL;DR: In this article, the authors developed a focal plane chopper capable of operation under cryovacuum conditions, in order to meet the stringent requirements with respect to power dissipation and positional accuracy.
Abstract: The imaging photometer and spectroscopic camera PACS, one of the three scientific instruments aboard the European 3.5 m infrared space telescope FIRST, will apply a tilting mirror mechanism for optical beam switching. The development of this focal plane chopper, capable of operation under cryovacuum conditions, is reported here. In order to meet the stringent requirements with respect to power dissipation and positional accuracy, special drive coils and a new position sensor had to be developed. A simulation model including electromagnetic analysis by the 3D code MAFIA, verified by extensive cold testing of the prototype hardware, was used for the optimization of the system and led to the advanced prototype of the chopper. Closed loop control of the mirror deflection allows square wave modulation in the frequency range 0 - 15 Hz (80% duty cycle) with amplitudes of +/- 9 degree(s) with high positional accuracy of less than 30'. The power dissipation at operating temperature of 4 K is below 500 (mu) W.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
7 citations
01 Jan 2000
TL;DR: In this article, a number of very cold cores with temperature Tdust≲13 K have been found in an 11° x 8° sized region, and compared the FIR data with radio measurements, all of them have high gas column densities, N(H2) > 1021 cm-2, and 7 out of 10 have low gas temperatures.
Abstract: ISOPHOT Serendipity Survey (ISOSS) observations of the nearby interstellar medium towards Chamaeleon have revealeda number of cold cloud cores. Far-infraredcolours have been studiedusing ISOSS and IRAS data. 10 very cold cores with colour temperatures Tdust≲13 K have been foundin an 11° x 8° sized region. Comparing the FIR data with radio measurements, all of the very cold cores have high gas column densities, N(H2) > 1021 cm-2, and 7 out of 10 have low gas temperatures as indicated by Tex(C18O) ≈ 8 K.
2 citations
Journal Article•
TL;DR: In this paper, the distribution of the ISOSS/IRAS based T(I170=I100) colour temperature have been studied in a nearby low-mass star forming region.
Abstract: ISOPHOT Serendipity Survey (ISOSS) observa- tions at 170m reveal cold dust clouds in the nearby star form- ing region Chamaeleon. The distribution of the ISOSS/IRAS based T(I170=I100) colour temperature have been studied in a nearby low-mass star forming region. T(I170=I100) sepa- rates the obscured and intercloud regions as seen from a com- parison to optical extinction data. The interstellar medium in Chamaeleon-Musca appears to be cold with dust colour tem- peratures of 16:3 K for intercloud regions, and 14:5 K for obscured clouds. The cold clouds account for 3 % of the area. ISOSS found 9 very cold cores with colour temperatures as low as Tdust . 12:5 Ki n an 11 8 sized region. All C 18 O cores of the Chamaeleon main clouds which were crossed by ISOSS slews were also detected. Of these 11 (73 %) are cold with Tdust 15 K, 6 (40 %) are associated with very cold cores. The very cold cores have high gas column densities, N(H2) > 10 21 cm 2 , and 7 out of 9 have low gas kinetic temperatures as indicated by Tex(C 18 O) 8 K. The physical parameters of the very cold cores agree with the results of radia- tive transfer calculations of a spherical model cloud heated from outside by one third of the the solar neighbourhood ISRF inten- sity. A check of the photometric calibration of ISOSS against ISOPHOT AOT PHT22 maps and DIRBE interpolated 170m values showed an agreement of10 % and20 %, respectively. We expect to discover in total more than 100 very cold cores in the Galaxy by ISOSS.
1 citations