Herschel-PACS photometry of faint stars

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

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 Fülle von Beobachtungsdaten mit hoher räumlicher Auflösung, 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 Wellenlängen wie 3.8 Mikrometer nachgewiesen werden, was die Bedeutung von Beobachtungen in diesem Wellenlängenbereich noch einmal unterstreicht. Für beide Objekte finden wir, daß die Annahme einer sphärischen Symmetrie die Beobachtungen nicht konsistent erklären kann; wahrscheinlich stellen abgeflachte, axialsymmetrische Strukturen ein realistischeres Modell dar. Diese Schlußfolgerung wird durch erste einfache Strahlungstransport-Überlegungen unterstützt. Schließlich setzen wir diese Ergebnisse in einen weiteren Zusammenhang und diskutieren kurz eine größere Kandidaten-Liste für sogenannte massereiche protostellare Objekte (HMPOs), für 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

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

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

Infrared Observation of Hot Cores

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(H$_2$O), 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

The properties of the inner disk around HL Tau: Multi-wavelength modeling of the dust emission

We conducted a detailed radiative transfer modeling of the dust emission from the circumstellar disk around HL Tau. The goal of our study is to derive the surface density profile of the inner disk and its structure. In addition to the Atacama Large Millimeter/submillimeter Array images at Band 3 (2.9mm), Band 6 (1.3mm), and Band 7 (0.87mm), the most recent Karl G. Jansky Very Large Array (VLA) observations at 7mm were included in the analysis. A simulated annealing algorithm was invoked to search for the optimum model. The radiative transfer analysis demonstrates that most radial components (i.e., >6AU) of the disk become optically thin at a wavelength of 7mm, which allows us to constrain, for the first time, the dust density distribution in the inner region of the disk. We found that a homogeneous grain size distribution is not sufficient to explain the observed images at different wavelengths simultaneously, while models with a shallower grain size distribution in the inner disk work well. We found clear evidence that larger grains are trapped in the first bright ring. Our results imply that dust evolution has already taken place in the disk at a relatively young (i.e., ~1Myr) age. We compared the midplane temperature distribution, optical depth, and properties of various dust rings with those reported previously. Using the Toomre parameter, we briefly discussed the gravitational instability as a potential mechanism for the origin of the dust clump detected in the first bright ring via the VLA observations.Comment: Accepted for publication in A&A (10 pages