Stability tests based on the Allan variance method have become a standard procedure for the evaluation of the quality of radio-astronomical instrumentation. They are very simple and simulate the ...situation when detecting weak signals buried in large noise fluctuations. For the special conditions during observations an outline of the basic properties of the Allan variance is given, and some guidelines how to interpret the results of the measurements are presented. Based on a rather simple mathematical treatment clear rules for observations in "Position-Switch" , "Beam-" or "Frequency-Switch" , "On-The-Fly-" and "Raster-Mapping" mode are derived. Also, a simple "rule of the thumb" for an estimate of the optimum timing for the observations is found. The analysis leads to a conclusive strategy how to plan radio-astronomical observations. Particularly for air- and space-borne observatories it is very important to determine, how the extremely precious observing time can be used with maximum efficiency. The analysis should help to increase the scientific yield in such cases significantly.
High-resolution far-infrared and sub-millimetre spectroscopy of water lines is an important tool to understand the physical and chemical properties of cometary atmospheres. We present observations of ...several rotational ortho- and para-water transitions in comet C/2008 Q3 (Garradd) performed with HIFI on Herschel. These observations have provided the first detection of the 212–101 (1669 GHz) ortho and 111–000 (1113 GHz) para transitions of water in a cometary spectrum. In addition, the ground-state transition 110–101 at 557 GHz is detected and mapped. By detecting several water lines quasi-simultaneously and mapping their emission we can constrain the excitation parameters in the coma. Synthetic line profiles are computed using excitation models which include excitation by collisions, solar infrared radiation, and radiation trapping. We obtain the gas kinetic temperature, constrain the electron density profile, and estimate the coma expansion velocity by analyzing the map and line shapes. We derive water production rates of 1.7–2.8 × 1028 s-1 over the range rh = 1.83–1.85 AU.
We present Mars zonal wind measurements by means of infrared heterodyne spectroscopy of CO2 features at 959.3917 cm−1 (10.423 μm). Observations were carried out using the Cologne Tuneable Heterodyne ...Infrared Spectrometer (THIS) from 5–8 December 2005 shortly after Mars opposition at the McMath‐Pierce Solar Telescope of the National Solar Observatory on Kitt Peak in Arizona with an unprecedented spatial resolution of ∼1.7 arcsec on a ∼16 arcsec Martian disk. Mars was observed at six different latitudes close to the west (evening) limb and zonal winds were retrieved from Doppler shifts between CO2 non‐thermal emission from the mesosphere and absorption features from low atmospheric regions. The season on Mars was late northern winter (LS ≈ 337°). We retrieved retrograde winds at latitude 45°N (−27 ± 17 m/s) that were particularly strong at the equator (up to −80 ± 13 m/s) and prograde winds at high southern latitudes (75°S) up to 51 ± 29 m/s.
Using Herschel's HIFI instrument, we observe C ii along a cut through S140, as well as high-J transitions of CO and HCO+ at two positions on the cut, corresponding to the externally irradiated ...ionization front and the embedded massive star-forming core IRS1. The HIFI data were combined with available ground-based observations and modeled using the KOSMA-τ model for photon-dominated regions (PDRs). We derive the physical conditions in S140 and in particular the origin of C ii emission around IRS1. We identify three distinct regions of C ii emission from the cut, one close to the embedded source IRS1, one associated with the ionization front, and one further into the cloud. The line emission can be understood in terms of a clumpy model of PDRs. At the position of IRS1, we identify at least two distinct components contributing to the C ii emission, one of them a small, hot component, which can possibly be identified with the irradiated outflow walls. This is consistent with the C ii peak at IRS1 coinciding with shocked H2 emission at the edges of the outflow cavity. We note that previously available observations of IRS1 can be reproduced well by a single-component KOSMA-τ model. Thus, it is HIFI's unprecedented spatial and spectral resolution, as well as its sensitivity that has allowed us to uncover an additional hot gas component in the S140 region.
High-resolution spectroscopy is a versatile tool to study planetary atmospheres. In the mid infrared wavelength regime the highest possible spectral resolution is provided by applying heterodyne ...techniques. At spectral resolution of more than
10
5
observations of fully resolved molecular features are possible allowing retrieval of many physical parameters from single lines. In addition, due to the fact that many of the observed species are abundant also in the Earth's atmosphere, high-resolution measurements allow to peak through the telluric features and lead to less ambiguity than low-resolution data. The paper will present a detailed description of the Cologne-based receiver THIS, the only tuneable heterodyne infrared spectrometer for application to astronomy offering access to the 7–
17
μ
m
wavelength region at a resolution of up to
3
×
10
7
and a bandwidth of 3
GHz. An overview of the science addressable with THIS will be given as well as a brief introduction to the theory of heterodyning in the infrared including a comparison to direct detection instrumentation.
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![[C I] 492 GHz Mapping Obser...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-637X_1538-4357/small "[C I] 492 GHz Mapping Observations of the High-Latitude Translucent Cloud MCLD 123.5+24.9")
