Danuta Dobrzycka

Spectroscopic observations of the cataclysmic variable PG 0917 + 342 - an ultra short-period nova like system

We present time-resolved spectroscopic observations of the cataclysmic variable PG 0917+342 which reveal it to be a nova-like system with an orbital period of 104 minutes. The spectra show lines of H, He I, and Ca I in absorption with variable emission cores, and Hα emission always above the continuum. Orbital parameters derived from our radial velocity data indicate a system inclination of ∼ 32°, M 2 =0.2 M ⊙ , and a likely, but not well determined, mass for the white dwarf of ∼0.3 M ⊙ . PG 0917+342 appears to be the first non-magnetic nova-like star below the CV period gap

VISIR upgrade overview and status

We present an overview of the VISIR upgrade project. VISIR is the mid-infrared imager and spectrograph at ESO’s VLT. The project team is comprised of ESO staff and members of the original VISIR consortium: CEA Saclay and ASTRON. The project plan is based on input from the ESO user community with the goal of enhancing the scientific performance and efficiency of VISIR by a combination of measures: installation of improved hardware, optimization of instrument operations and software support. The cornerstone of the upgrade is the 1k by 1k Si:As AQUARIUS detector array (Raytheon) which has been carefully characterized in ESO’s IR detector test facility (modified TIMMI 2 instrument). A prism spectroscopic mode will cover the N-band in a single observation. New scientific capabilities for high resolution and high-contrast imaging will be offered by sub-aperture mask (SAM) and phase-mask coronagraphic (4QPM/AGPM) modes. In order to make optimal use of favourable atmospheric conditions a water vapour monitor has been deployed on Paranal, allowing for real-time decisions and the introduction of a user-defined constraint on water vapour. During the commissioning in 2012 it was found that the on-sky sensitivity of the AQUARIUS detector was significantly below expectations and that VISIR was not ready to go back to science operations. Extensive testing of the detector arrays in the laboratory and on-sky enabled us to diagnose the cause for the shortcoming of the detector as excess low frequency noise (ELFN). It is inherent to the design chosen for this detector and can’t be remedied by changing the detector set-up. Since this is a form of correlated noise its impact can be limited by modulating the scene recorded by the detector. We have studied several mitigation options and found that faster chopping using the secondary mirror (M2) of the VLT offers the most promising way forward. Faster M2 chopping has been tested and is scheduled for implementation before the end of 2014 after which we plan to re-commission VISIR. In addition an upgrade of the IT infrastructure related to VISIR is planned in order to support burst-mode operations. The upgraded VISIR will be a powerful instrument providing close to background limited performance for diffraction-limited observations at an 8-m telescope. It will offer synergy with facilities such as ALMA, JWST, VLTI and SOFIA, while a wealth of targets is available from survey work (e.g. VISTA, WISE). In addition it will bring confirmation of the technical readiness and scientific value of several aspects of potential mid-IR instrumentation at Extremely Large Telescopes.

CRIRES: commissioning and first science results

CRIRES is a cryogenic, pre-dispersed, infrared Echelle spectrograph designed to provide a nominal resolving power ν/Δν of 105 between 1000 and 5000 nm for a nominal slit width of 0.2. The CRIRES installation at the Nasmyth focus A of the 8-m VLT UT1 (Antu) marks the completion of the original instrumentation plan for the VLT. A curvature sensing adaptive optics system feed is used to minimize slit losses and to provide 0.2 spatial resolution along the slit. A mosaic of four Aladdin InSb-arrays packaged on custom-fabricated ceramic boards has been developed. It provides for an effective 4096 × 512 pixel focal plane array to maximize the free spectral range covered in each exposure. Insertion of gas cells is possible in order to measure radial velocities with high precision. Measurement of circular and linear polarization in Zeeman sensitive lines for magnetic Doppler imaging is foreseen but not yet fully implemented. A cryogenic Wollaston prism on a kinematic mount is already incorporated. The retarder devices will be located close to the Unit Telescope focal plane. Here we briefly recall the major design features of CRIRES and describe the commissioning of the instrument including a report of extensive testing and a preview of astronomical results.

Upgrade of VISIR the mid-infrared instrument at the VLT

The European Southern Observatory (ESO) is preparing to upgrade VISIR, the mid-IR imager and spectrograph at the VLT. The project team is comprised of ESO staff and members of the original consortium that built VISIR: CEA Saclay and ASTRON. The goal is to enhance the scientific performance of VISIR and to facilitate its use by the ESO community. In order to capture the needs of the user community, we collected input from the users by means of a webbased questionnaire. In line with the results of the internal study and the input from the user community, the upgrade plan calls for a combination measures: installation of improved hardware, optimization of instrument operations and software support. The limitations of the current detector (sensitivity, cosmetics, artifacts) have been known for some time and a new 1k x 1k Si:As Aquarius array (Raytheon) will be the cornerstone of the VISIR upgrade project. A modified spectroscopic mode will allow covering the N-band in a single observation. Several new scientific modes (e.g., polarimetry, coronagraphy) will be implemented on a best effort basis. In addition, the VISIR operational scheme will be enhanced to ensure that optimal use of the observing conditions will be made. Specifically, we plan to provide a means to monitor precipitable water vapour (PWV) and enable the user to specify it as a constraint set for service mode observations. In some regions of the mid-IR domain, the amount of PWV has a fundamental effect on the quality of a given night for mid-IR astronomy. The plan also calls for full support by ESO pipelines that will deliver science-ready data products. Hence the resulting files will provide physical units and error information and all instrumental signatures will have been removed. An upgraded VISIR will be a powerful instrument providing diffraction-limited performance at an 8-m telescope. Its improved performance and efficiency as well as new science capabilities will serve the needs of the ESO community but will also offer synergy with various other facilities such as ALMA, JWST, VLTI and SOFIA. A wealth of targets for detailed study will be available from survey work done by VISTA and WISE. Finally, the upgraded VISIR will also serve as a pathfinder for potential mid-IR instrumentation at the European Extremely Large Telescope (E-ELT) in terms of technology as well as operations.

Probing the Solar Wind Acceleration Region with the Sun-grazing Comet C/2002 S2

Comet C/2002 S2, a member of the Kreutz family of Sungrazing comets, was discovered in white light images of the SOHO/LASCO coronagraph on 2002 September 18 and observed in hi, lya, emission by the SOHO/UVCS instrument at four different heights as it approached the Sun. The hi, lya, line profiles detected by UVCS are analyzed to determine the spectral parameters: line intensity, width and Doppler shift with respect to the coronal background. Two dimensional comet images of these parameters are reconstructed at the different heights. A novel aspect of the observations of this sungrazing comet data is that, whereas the emission from the most of the tail is blue--shifted, that along one edge of the tail is red--shifted. We attribute these shifts to a combination of solar wind speed and interaction with the magnetic field. In order to use the comet to probe the density, temperature and speed of the corona and solar wind through which it passes, as well as to determine the outgassing rate of the comet, we develop a Monte Carlo simulation of the hi, lya, emission of a comet moving through a coronal plasma. From the outgassing rate, we estimate a nucleus diameter of about 9 meters. This rate steadily increases as the comet approaches the Sun while the optical brightness decreases by more than a factor of ten and suddenly recovers. This indicates that the optical brightness is determined by the lifetimes of the grains, sodium atoms and molecules produced by the comet.

EVALSO, a high-bandwidth communication infrastructure to efficiently connect the ESO Paranal and the Cerro Armazones Observatories to Europe: demonstration activities and start of operations

EVALSO (Enabling Virtual Access to Latin-American Southern Observatories) is an international consortium of nine astronomical organizations, and research network operators, part-funded under the European Commission FP7, to create and exploit high-speed bandwidth connections to the observatories of Cerro Paranal and Cerro Armazones in Chile. The communication infrastructure was delivered in November 2010 and this paper reports on the initial results of the project and the demonstrations of its capabilities, including the possibilities that the new infrastructure opens up in the geographically distributed operation of the observatories.

VLT VISIR: controlling data quality and instrument performance

VISIR is the new ESO VLT instrument mounted at the Cassegrain focus of Melipal (UT3) telescope. At Paranal it is the very first instrument capable of high sensitivity imaging in the N band and Q band mid infrared atmospheric windows. In addition, it features a long-slit spectrometer with a range of spectral resolutions between 150 and 30000. VISIR had been included in the standard VLT data flow operation even before regular observing started in March/April 2005. Data products are pipeline-processed and quality checked by the Data Flow Operations Group in Garching. The calibration data are processed to create calibration products and to extract Quality Control parameters. These parameters provide health checks and monitor instruments performance. They are stored in a database, compared to earlier data, trended over time and made available on the VISIR Quality Control web pages that are updated daily. We present the parameters that were designed to assess quality of the data and to monitor performance of the MIR instrument. We also discuss the general process of data flow and data inspection.

VISIR upgrade overview: all's well that ends well

We present an overview of the VISIR instrument after its upgrade and return to science operations. VISIR is the midinfrared imager and spectrograph at ESO’s VLT. The project team is comprised of ESO staff and members of the original VISIR consortium: CEA Saclay and ASTRON. The project plan was based on input from the ESO user community with the goal of enhancing the scientific performance and efficiency of VISIR by a combination of measures: installation of improved hardware, optimization of instrument operations and software support. The cornerstone of the upgrade is the 1k by 1k Si:As AQUARIUS detector array manufactured by Raytheon. In addition, a new prism spectroscopic mode covers the whole N-band in a single observation. Finally, new scientific capabilities for high resolution and high-contrast imaging are offered by sub-aperture mask and coronagraphic modes. In order to make optimal use of favourable atmospheric conditions, a water vapour monitor has been deployed on Paranal, allowing for real-time decisions and the introduction of a user-defined constraint on water vapour. During the commissioning in 2012, it was found that the on-sky sensitivity of the AQUARIUS detector was significantly below expectations. Extensive testing of the detector arrays in the laboratory and on-sky enabled us to diagnose the cause for the shortcoming of the detector as excess low frequency noise. It is inherent to the design chosen for this detector and cannot be remedied by changing the detector set-up. Since this is a form of correlated noise, its impact can be limited by modulating the scene recorded by the detector. After careful analysis, we have implemented fast (up to 4 Hz) chopping with field stabilization using the secondary mirror of the VLT. During commissioning, the upgraded VISIR has been confirmed to be more sensitive than the old instrument, and in particular for low-resolution spectroscopy in the N-band, a gain of a factor 6 is realized in observing efficiency. After overcoming several additional technical problems, VISIR is back in Science Operations since April 2015. In addition an upgrade of the IT infrastructure related to VISIR has been conducted in order to support burst-mode operations. Science Verification of the new modes was performed in Feb 2016. The upgraded VISIR is a powerful instrument providing close to background limited performance for diffraction-limited observations at an 8-m telescope. It offers synergies with facilities such as ALMA, JWST, VLTI and SOFIA, while a wealth of targets is available from survey works like WISE. In addition, it will bring confirmation of the technical readiness and scientific value of several aspects for future mid-IR instrumentation at Extremely Large Telescopes. We also present several lessons learned during the project.

Regaining the FORS: making optical ground-based transmission spectroscopy of exoplanets with VLT+FORS2 possible again

Transmission spectroscopy facilitates the detection of molecules and/or clouds in the atmospheres of exoplanets. Such studies rely heavily on space-based or large ground-based observatories, as one needs to perform time-resolved, high signal-to-noise spectroscopy. The FORS2 instrument at ESOs Very Large Telescope is the obvious choice for performing such studies, and was indeed pioneering the field in 2010. After that, however, it was shown to suffer from systematic errors caused by the Longitudinal Atmospheric Dispersion Corrector (LADC). This was successfully addressed, leading to a renewed interest for this instrument as shown by the number of proposals submitted to perform transmission spectroscopy of exoplanets. We present here the context, the problem and how we solved it, as well as the recent results obtained. We finish by providing tips for an optimum strategy to do transmission spectroscopy with FORS2, in the hope that FORS2 may become the instrument of choice for ground-based transmission spectroscopy of exoplanets.

New Measures in Controlling Quality of VLT VISIR

The ESOs VISIR instrument at Paranal is dedicated to observations in two mid-infrared (MIR) atmospheric windows: N-band (8-13 micron) and Q-band (16.5-24.5 micron). It is equipped with two DRS (formerly Boeing) 256 × 256 BIB detectors operating at temperatures of about 5 K. As in case of other Paranal instruments VISIR data are regularly transferred to ESO Garching within the standard data flow operation. There, they are classified and pipeline-processed. The products of VISIR technical data are analyzed in order to trend instrument performance, while calibrations and science data are checked for quality and later distributed to the users. Over the three years of VISIR operations we have been constantly gaining more experience in methods of assessing health of the instrument. In particular, we found that dark frames are particularly useful for monitoring the VISIR detectors. We also discuss performance of the OCLI silicate filters recently mounted in the instrument.