D. Silva

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Publications (2)0 Total impact

  • Source
    Article: Observations towards early-type stars in the ESO-POP survey: II -- searches for intermediate and high velocity clouds
    J. V. Smoker, I. Hunter, P. M. W. Kalberla, F. P. Keenan, R. Morras, R. Hanuschik, H. M. A. Thompson, D. Silva, E. Bajaja, W. G. L. Poppel, M. Arnal
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    ABSTRACT: We present CaII K and TiII optical spectra of early-type stars taken mainly from the UVES Paranal Observatory Project, plus HI 21-cm spectra from the Vila-Elisa and Leiden-Dwingeloo surveys, which are employed to obtain distances to intermediate and high velocity clouds. HI emission at a velocity of -117 km/s towards the sightline HD 30677 with NHI=1.7x10^19 cm-2 has no corresponding CaII K absorption, which has a signal-to-noise (S/N) ratio of 610. The star has a spectroscopically determined distance of 2.7-kpc, and hence sets this as a firm lower distance limit towards Anti-Centre cloud ACII. Towards another sightline (HD 46185), HI at +122 km/s and NHI=1.2x10^19 cm-2 is seen. The CaII K spectrum has a S/N = 780, although no absorption is observed at the cloud velocity. This similarly places a firm lower distance limit of 2.9-kpc towards this parcel of gas that may be an intermediate velocity cloud. The lack of intermediate velocity (IV) CaII K absorption towards HD 196426 at a S/N = 500 reinforces a lower distance limit of 700-pc towards this part of Complex gp, where NHI is 1.1x10^19 cm-2 and velocity is +78 km/s. Additionally, no IV CaII K is seen in absorption in the spectrum of HD 19445, which is strong in HI with NHI=8x10^19 cm-2 at -42 km/s, placing a firm although uninteresting lower distance limit of 39-pc to this part of IV South. Finally, no HV CaII K absorption is seen towards HD 115363 at a S/N = 410, placing a lower distance of 3.2-kpc towards the HVC gas at velocity of +224 km/s and NHI=5.2x10^19 cm-2. This gas is in the same region of the sky as complex WE (Wakker 2001), but at higher velocities. The non-detection of CaII K absorption sets a lower distance of 3.2-kpc towards the HVC, which is unsurprising if this feature is indeed related to the Magellanic System. Comment: Accepted by MNRAS
    04/2007;
  • Source
    Article: VLT quality control and trending services
    R. Hanuschik, D. Silva
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    ABSTRACT: Any observatory worldwide has staff who permanently look into the performance of the instruments and check the quality of the data. ESO's Very Large Telescope has the operational model of a data product facility. This means that it goes beyond the day-to-day performance checks and promises to deliver data of a defined and certified quality. The Data Flow Operations Group in Garching (DFO, also frequently called QC Garching), provides many aspects of data management and quality control of the VLT data stream. One of the main responsibilities is to assess and control the quality of the calibration data taken, with the goal to know and control the performance of the VLT instruments. Information about the results of this process is fed back to Paranal Science Operations and to the ESO User Community via QC reports and web pages.
    The Messenger. 05/2002; 108:4-9.

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