107 research outputs found

    Herschel-PACS photometry of faint stars

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    Our aims are to determine flux densities and their photometric accuracy for a set of seventeen stars that range in flux from intermediately bright (<2.5 Jy) to faint (>5 mJy) in the far-infrared (FIR). We also aim to derive signal-to-noise dependence with flux and time, and compare the results with predictions from the Herschel exposure-time calculation tool. The PACS faint star sample has allowed a comprehensive sensitivity assessment of the PACS photometer. Accurate photometry allows us to establish a set of five FIR primary standard candidates, namely alpha Ari, epsilon Lep, omega,Cap, HD41047 and 42Dra, which are 2 -- 20 times fainter than the faintest PACS fiducial standard (gamma Dra) with absolute accuracy of <6%. For three of these primary standard candidates, essential stellar parameters are known, meaning that a dedicated flux model code may be run.Comment: 42 pages, 12 figure

    Regions of massive star formation: structure and stellar populations

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    Viele Details der Entstehung massereicher Sterne (Sterne mit Massen > 8...10 Sonnenmassen) stellen die Theoretiker wie auch die beobachtenden Astronomen immernoch vor Probleme. Diese Dissertation untersucht dieses Forschungsgebiet vom Blickwinkel des Beobachters aus. Unter Einbeziehung einer F√ľlle von Beobachtungsdaten mit hoher r√§umlicher Aufl√∂sung, vom nahen und thermischen Infrarot bis hin zu VLA 7-mm Interferometrie, haben wir zwei prominente massereiche Sternentstehungsgebiete ausgiebig untersucht: G9.62+0.19-F und GGD27. Die massereichen Zentralobjekte beider Regionen konnten erstmals bei so kurzen Wellenl√§ngen wie 3.8 Mikrometer nachgewiesen werden, was die Bedeutung von Beobachtungen in diesem Wellenl√§ngenbereich noch einmal unterstreicht. F√ľr beide Objekte finden wir, da√ü die Annahme einer sph√§rischen Symmetrie die Beobachtungen nicht konsistent erkl√§ren kann; wahrscheinlich stellen abgeflachte, axialsymmetrische Strukturen ein realistischeres Modell dar. Diese Schlu√üfolgerung wird durch erste einfache Strahlungstransport-√úberlegungen unterst√ľtzt. Schlie√ülich setzen wir diese Ergebnisse in einen weiteren Zusammenhang und diskutieren kurz eine gr√∂√üere Kandidaten-Liste f√ľr sogenannte massereiche protostellare Objekte (HMPOs), f√ľr die VLA 7-mm Beobachtungen und Infrarot-Nachfolgebeobachtungen geplant sind. Many details of the formation of high-mass stars (stars with masses > 8...10 solar masses) still pose problems for the theoreticians as well as for the observers. This thesis tries to approach the topic from the observational side. By means of a broad range of data, from near- and thermal infrared imaging to VLA 7-mm interferometry, all comprising high spatial resolution we scrutinised two prominent regions of massive star formation: G9.62+0.19-F and GGD27. The central massive objects of both regions could be detected for the first time at wavelengths as short as 3.8 micron, further highlighting the importance of observations in this wavelength range. For both objects, we find that the assumption of spherical symmetry cannot coherently explain the observations; probably flattened axial-symmetric structures are a more realistic model. This conclusion is further supported by first simple radiative transfer considerations. Finally, the results are set into context regarding a larger sample of candidates for so-called high-mass proto-stellar objects (HMPOs), for which VLA 7-mm observations and infrared follow-up measurements are envisaged

    On the massive young stellar object AFGL4176: High-spatial-resolution multi-wavelength observations and modeling

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    Deeply embedded and at distances of several kiloparsecs, massive young stellar objects (MYSOs) present numerous challenges for observation and study. In this work, we present spatially-resolved observations of one MYSO, AFGL 4176, together with survey and literature data, ranging from interferometric observations with VLTI/MIDI in the mid-infrared, to single-dish Herschel measurements in the far-infrared, and sub-millimeter data from APEX. We consider this spatially-resolved, multi-wavelength data set in terms of both radiative transfer and geometric models. We find that the observations are well described by one-dimensional models overall, but there are also substantial deviations from spherical symmetry at scales of tens to hundreds of astronomical units, which are revealed by the mid-infrared interferometric measurements. We use a multiple-component, geometric modeling approach to explain the mid-infrared emission on scales of tens to hundreds of astronomical units, and find the MIDI measurements are well described by a model consisting of a one-dimensional Gaussian halo and an inclined (\theta=60 deg) circumstellar disk extending out to several hundred astronomical units along a position angle of 160 deg. Finally, we compare our results both with previous models of this source, and with those of other MYSOs, and discuss the present situation with mid-infrared interferometric observations of massive stars.Comment: 15 pages, 14 figures. Accepted to Astronomy and Astrophysic

    The Herschel PACS photometer calibration - A time dependent flux calibration for the PACS chopped point-source photometry AOT mode

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    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.Comment: 20 pages, 7 pages of appendix, 11 figures, accepted to appear in Experimental Astronomy, Special Issue for Herschel Calibrations based on the "Herschel Calibration Workshop: Only the Best Data Products for the Legacy Archive", held at ESAC, 25 - 27 March 2013, http://herschel.esac.esa.int/CalibrationWorkshop5.shtm

    Arecibo Observations of Formaldehyde in L1551

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    We report observations of the formaldehyde (H2CO) 6 cm (4.8 GHz) line toward L1551. The observations were conducted with the Arecibo Telescope (beam FWHP ~ 1') to verify the tentative detection of H2CO thermal emission reported by Duncan and collaborators in 1987. The H2CO emission lines were expected to be present with a signal-to-noise ratio of 10 in our spectra. However, we did not detect H2CO emission; i.e., our data rule out their tentative detection. The absence of H2CO emission is also confirmed by the fact that the H2CO line profiles at the two positions of expected emission are well fitted by a single absorption component (accounting for the hyperfine structure of the line) in one of the positions and by a single absorption line plus a red-wing absorption component in the second position. The Orion BN/KL region remains the only H2CO 6 cm thermal emitter known. Our observations also demonstrate that the H2CO 6 cm absorption line traces not only the quiescent molecular cloud but also the kinematics associated with the star formation process in L1551-IRS 5

    Infrared Observation of Hot Cores

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    We report on mid-infrared imaging of hot cores performed with SpectroCam-10 and TIMMI2. The observations aimed at the detection of thermal emission presumably associated with the hot cores. Mid-infrared flux measurements are required to improve the luminosity and optical depth estimates for these sources. Results are presented for W3(H2_2O), G9.62+0.19, G10.47+0.03, and the possible hot core candidate G232.620+0.996. They illustrate that the morphology of these sources cannot be described by simple geometries. Therefore, line-of-sight effects and considerable extinction even at mid-infrared wavelengths must not be neglected.Comment: 6 pages, 4 figures, Conference proceeding "Origins of stars and planets: The VLT view", ESO, Garching, April 24-27 200
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