Observing faint targets with MIDI at the VLTI -- The MIDI AGN Large Programme experience

Abstract

In order to put MIDI/VLTI observations of AGNs on a significant statistical basis, the number of objects had to be increased dramatically from the few prominent bright cases to over 20. For this, correlated fluxes as faint as ~ 150 mJy need to be observed, calibrated and their errors be estimated reliably. We have developed new data reduction methods for the coherent estimation of correlated fluxes with the Expert Work Station (EWS). They increase the signal/noise of the reduced correlated fluxes by decreasing the jitter in the group delay estimation. While correlation losses cannot be fully avoided for the weakest objects even with the improved routines, we have developed a method to simulate observations of weak targets and can now detect --- and correct for --- such losses. We have analyzed all sources of error that are relevant for the observations of weak targets. Apart from the photon-noise error, that is usually quoted, there is an additional error from the uncertainty in the calibration (i.e. the conversion factor). With the improved data reduction, calibration and error estimation, we can consistently and reproducibly observe fluxes as weak as ~ 150 mJy with an uncertainty of ~ 15 % under average conditions.

arXiv comment13 pages, 7 figures; to appear in SPIE Astronomical Telescopes and Instrumentation, SPIE Conference Series 8445

References in corpus (6)

• AGN Dusty Tori: I. Handling of Clumpy Media
• Dust Emission from Active Galactic Nuclei
• Resolving the complex structure of the dust torus in the active nucleus of the Circinus galaxy
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Cited by in corpus (16)

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• Mid-infrared interferometry of 23 AGN tori: On the significance of polar-elongated emission
• On the structure of the transition disk around TW Hya
• Revealing the large nuclear dust structures in NGC 1068 with MIDI/VLTI
• The structure of disks around intermediate-mass young stars from mid-infrared interferometry. Evidence for a population of group II disks with gaps
• Thermal imaging of dust hiding the black hole in the Active Galaxy NGC 1068
• New evidence for the dusty wind model: Polar dust and a hot core in the type-1 Seyfert ESO323-G77
• Sculpting the disk around T Cha: an interferometric view
• An interferometric study of the post-AGB binary 89 Herculis. II Radiative transfer models of the circumbinary disk
• Parsec-scale Dusty Winds in Active Galactic Nuclei: Evidence for Radiation Pressure Driving
• The twofold debris disk around HD 113766 A - Warm and cold dust as seen with VLTI/Midi and Herschel/Pacs
• A Compact Jet at the Infrared Heart of the Prototypical Low-Luminosity AGN in NGC 1052
• NGC 1068: No change in the mid-IR torus structure despite X-ray variability
• Resolving the Hot Dust Disk of ESO323-G77
• Mid-infrared interferometry of Seyfert galaxies: Challenging the Standard Model
• Embedded AGN and star formation in the central 80 pc of IC 3639