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Agudo I.,Institute Astrofisica Of Andalucia | Agudo I.,Boston University | Thum C.,Institute Of Radio Astronomie Millimetrique | Wiesemeyer H.,Max Planck Institute for Radio Astronomy | And 5 more authors.
Astronomy and Astrophysics

Context. Several millimeter and submillimeter facilities with linear polarization observing capabilities have started operating during the last years. These facilities, as well as other previous millimeter telescopes and interferometers, require bright and stable linear polarization calibrators to calibrate new instruments and to monitor their instrumental polarization. The current limited number of adequate calibrators implies difficulties in the acquisition of these calibration observations. Aims. Looking for additional linear polarization calibrators in the millimeter spectral range, we started monitoring 3C 286 in mid-2006. This source is a standard and highly stable polarization calibrator for radio observations. Methods. Here we present the 3 mm and 1 mm monitoring observations obtained between September 2006 and January 2012 with the XPOL polarimeter on the IRAM 30 m Millimeter Telescope. Results. Our observations show that 3C 286 is a bright source of constant total flux with 3 mm flux density S 3 mm = (0.91 ± 0.02) Jy. The 3 mm linear polarization degree (p 3 mm = [13.5 ± 0.3] %) and polarization angle (χ 3 mm = [37.3 ± 0.8] °, expressed in the equatorial coordinate system) were also constant during the time span of our observations. Although with poorer time sampling and signal-to-noise ratio, our 1 mm observations of 3C 286 are also reproduced by a constant source of 1 mm flux density (S 1 mm = [0.30 ± 0.03] Jy), polarization fraction (p 1 mm = [14.4 ± 1.8] %), and polarization angle (χ 1 mm = [33.1 ± 5.7]°). Conclusions. This, together with the previously known compact structure of 3C 286-extended by ∼3.5′′ in the sky-allow us to propose 3C 286 as a new calibrator for both single-dish and interferometric polarization observations at 3 mm, and possibly at shorter wavelengths. © 2012 ESO. Source

Billot N.,California Institute of Technology | Billot N.,Institute Radio Astronomia Milimetrica | Morales-Calderon M.,Spitzer Science Center | Stauffer J.R.,Spitzer Science Center | And 2 more authors.
Astrophysical Journal Letters

We have obtained time series observations of the Orion Nebula Cluster at 70 μm and 160 μm from the Herschel/PACS Photometer. This represents the first wide-field far-infrared photometric monitoring of a young star-forming region. The acquired 35′ × 35′ maps show complex extended structures, with unprecedented detail, that trace the interaction between the molecular gas and the young hot stars. We detect 43 protostars, most of which are situated along the integral-shaped filament extending from the Orion nebula, through OMC2 and OMC3. We present high-reliability light curves for some of these objects using the first six epochs of our observing program spread over 6 weeks. We find amplitude variations in excess of 20% for a fraction of the detected protostars over periods as short as a few weeks. This is inconsistent with the dynamical timescales of cool far-IR emitting material that orbits at hundreds of AU from the protostar, and it suggests that the mechanism(s) responsible for the observed variability originates from the inner region of the protostars, likely driven by variable mass accretion. © 2012. The American Astronomical Society. All rights reserved.. Source

Drahus M.,University of California at Los Angeles | Jewitt D.,University of California at Los Angeles | Guilbert-Lepoutre A.,University of California at Los Angeles | Waniak W.,Jagiellonian University | Sievers A.,Institute Radio Astronomia Milimetrica
Astrophysical Journal

One of the least understood properties of comets is the compositional structure of their nuclei, which can either be homogeneous or heterogeneous. The nucleus structure can be conveniently studied at millimeter wavelengths, using velocity-resolved spectral time series of the emission lines, obtained simultaneously for multiple molecules as the body rotates. Using this technique, we investigated the sources of CH3OH and HCN in comet 103P/Hartley 2, the target of NASA's EPOXI mission, which had an exceptionally favorable apparition in late 2010. Our monitoring with the IRAM 30m telescope shows short-term variability of the spectral lines caused by nucleus rotation. The varying production rates generate changes in brightness by a factor of four for HCN and by a factor of two for CH3OH, and they are remarkably well correlated in time. With the addition of the velocity information from the line profiles, we identify the main sources of outgassing: two jets, oppositely directed in a radial sense, and icy grains, injected into the coma primarily through one of the jets. The mixing ratio of CH3OH and HCN is dramatically different in the two jets, which evidently shows large-scale chemical heterogeneity of the nucleus. We propose a network of identities linking the two jets with morphological features reported elsewhere and postulate that the chemical heterogeneity may result from thermal evolution. The model-dependent average production rates are 3.5 × 10 26moleculess-1 for CH3OH and 1.25 × 1025moleculess-1 for HCN, and their ratio of 28 is rather high but not abnormal. The rotational temperature from CH3OH varied strongly, presumably due to nucleus rotation, with the average value being 47K. © 2012. The American Astronomical Society. All rights reserved. Source

Nielbock M.,Max Planck Institute for Astronomy | Muller T.,Max Planck Institute for Extraterrestrial Physics | Klaas U.,Max Planck Institute for Astronomy | Altieri B.,European Space Agency | And 6 more authors.
Experimental Astronomy

We present a flux calibration scheme for the PACS chopped point-source photometry observing mode based on the photometry of five stellar standard sources. This mode was used for science observations only early in the mission. Later, it was only used for pointing and flux calibration measurements. Its calibration turns this type of observation into fully validated data products in the Herschel Science Archive. Systematic differences in calibration with regard to the principal photometer observation mode, the scan map, are derived and amount to 5 - 6 %. An empirical method to calibrate out an apparent response drift during the first 300 Operational Days is presented. The relative photometric calibration accuracy (repeatability) is as good as 1 % in the blue and green band and up to 5 % in the red band. Like for the scan map mode, inconsistencies among the stellar calibration models become visible and amount to 2 % for the five standard stars used. The absolute calibration accuracy is therefore mainly limited by the model uncertainty, which is 5 % for all three bands. © 2013 Springer Science+Business Media Dordrecht. Source

Moor A.,Konkoly Observatory | Muller T.G.,Max Planck Institute for Extraterrestrial Physics | Kiss C.,Konkoly Observatory | Balog Z.,Max Planck Institute for Astronomy | And 2 more authors.
Experimental Astronomy

The absolute stability of the PACS bolometer response over the entire mission lifetime without applying any corrections is about 0.5 % (standard deviation) or about 8 % peak-to-peak. This fantastic stability allows us to calibrate all scientific measurements by a fixed and time-independent response file, without using any information from the PACS internal calibration sources. However, the analysis of calibration block observations revealed clear correlations of the internal source signals with the evaporator temperature and a signal drift during the first half hour after the cooler recycling. These effects are small, but can be seen in repeated measurements of standard stars. From our analysis we established corrections for both effects which push the stability of the PACS bolometer response to about 0.2 % (stdev) or 2 % in the blue, 3 % in the green and 5 % in the red channel (peak-to-peak). After both corrections we still see a correlation of the signals with PACS FPU temperatures, possibly caused by parasitic heat influences via the Kevlar wires which connect the bolometers with the PACS Focal Plane Unit. No aging effect or degradation of the photometric system during the mission lifetime has been found. © 2013 Springer Science+Business Media Dordrecht. Source

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