Search

The authors would like to thank the researchers and engineers who are not coauthors of this paper but who have taken part and have brought their contribution to the proposed missions to ESA successive calls: NEAT (M3), micro-NEAT (S1), and Theia (M4 and M5). An extensive list of supporters for the science objectives is given in [17]. We thank also Arianna Gallo for her contribution in our investigation of the shape of the MilkyWay dark matter halo and Krzysztof A. Rybicki who generated the plots from Fig. 14. We are grateful to the anonymous referee who helped to improve the quality of the paper with his/her remarks. Concerning the funding of our work, we would like to acknowledge the support of many agencies or programs. R.B. acknowledges support from NASA’s Virtual Planetary Laboratory lead team under cooperative agreements NNA13AA93A. A.C.M.C. acknowledges support from CFisUC strategic project (UID/FIS/04564/2019). F.C. acknowledges support by the Swiss National Science Foundation (SNSF) and by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (COSMICLENS: grant agreement No. 787886). M.F. received support from Polish National Science Centre (NCN) under Grant No. 2017/26/D/ST9/00591. M.F. gratefully acknowledge the support of the Swedish National Space Agency (DNR 65/19, 174/18). D.H. thanks the Swedish National Space Agency (SNSA/Rymdstyrelsen) for their support. A.M. thanks the Portugese Fundac¸ ˜ao para a Ciˆencia e a Tecnologia (FCT) through the Strategic Programme UID/FIS/00099/2019 for CENTRA. P.S. acknowledges support from the Australian Research Council under grant FT190100814. L.W. acknowledges support from the Polish NCN grants: Harmonia No. 2018/06M/ST9/00311 and Daina No. 2017/27/L/ST9/03221. The OATo team acknowledges partial funding by the Italian Space Agency (ASI) under contracts 2014-025-R.1.2015 and 2018-24-HH.0, and by a grant from the Italian Ministry of Foreign Affairs and International Cooperation (ASTRA). A.C. and F.M. acknowledge support by the LabEx FOCUS ANR-11-LABX-0013. The work of C.J., X.L. and J.P. was supported by the Spanish Ministry of Science, Innovation and University (MICIU/FEDER, UE) through grants RTI2018-095076-B-C21, ESP2016-80079-C2-1-R, and the Institute of Cosmos Sciences University of Barcelona (ICCUB, Unidad de Excelencia ’Mar´ıa de Maeztu’) through grants MDM-2014-0369 and CEX2019-000918-M. A.K.-M., A.A., V.C., P.G., P.G., A.M.A., A.M., M.S. were supported by Fundac¸ ˜ao para a Ciˆencia e a Tecnologia, with grants reference UIDB/00099/ 2020 and SFRH/BSAB/142940/2018 (P.G. only). A.D. and L.O. also acknowledge partial support from the Italian Ministry of Education, University and Research (MIUR) under the Departments of Excellence grant L.232/2016, and from the INFN grant InDark. G.J.W. gratefully acknowledges support of an Emeritus Fellowship from The Leverhulme Trust. EV is supported by Spanish grant PGC2018-101950-B-100. This research has made use of NASA’s Astrophysics Data System Bibliographic Services. Open access funding provided by Istituto Nazionale di Astrofisica within the CRUI-CARE Agreement., Sky survey telescopes and powerful targeted telescopes play complementary roles in astronomy. In order to investigate the nature and characteristics of the motions of very faint objects, a flexibly-pointed instrument capable of high astrometric accuracy is an ideal complement to current astrometric surveys and a unique tool for precision astrophysics. Such a space-based mission will push the frontier of precision astrometry from evidence of Earth-mass habitable worlds around the nearest stars, to distant Milky Way objects, and out to the Local Group of galaxies. As we enter the era of the JamesWebb Space Telescope and the new ground-based, adaptive-optics-enabled giant telescopes, by obtaining these high precision measurements on key objects that Gaia could not reach, a mission that focuses on high precision astrometry science can consolidate our theoretical understanding of the local Universe, enable extrapolation of physical processes to remote redshifts, and derive a much more consistent picture of cosmological evolution and the likely fate of our cosmos. Already several missions have been proposed to address the science case of faint objects in motion using high precision astrometry missions: NEAT proposed for the ESA M3 opportunity, micro-NEAT for the S1 opportunity, and Theia for the M4 and M5 opportunities. Additional new mission configurations adapted with technological innovations could be envisioned to pursue accurate measurements of these extremely small motions. The goal of this White Paper is to address the fundamental science questions that are at stake when we focus on the motions of faint sky objects and to briefly review instrumentation and mission profiles., NASA’s Virtual Planetary Laboratory NNA13AA93A, CFisUC strategic project (UID/FIS/04564/2019), Swiss National Science Foundation (SNSF), European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (COSMICLENS: grant agreement No. 787886), Polish National Science Centre (NCN) under Grant No. 2017/26/D/ST9/00591, Swedish National Space Agency (DNR 65/19, 174/18), Swedish National Space Agency (SNSA/Rymdstyrelsen), Portugese Fundacão para a Ciência e a Tecnologia (FCT) through the Strategic Programme UID/FIS/00099/2019 for CENTRA, Australian Research Council under grant FT190100814, Polish NCN grants: Harmonia No. 2018/06M/ST9/00311 and Daina No. 2017/27/L/ST9/03221, Italian Space Agency (ASI) under contracts 2014-025-R.1.2015 and 2018-24-HH.0, Italian Ministry of Foreign Affairs and International Cooperation (ASTRA), LabEx FOCUS ANR-11-LABX-0013, Spanish Ministry of Science, Innovation and University (MICIU/FEDER, UE) through grants RTI2018-095076-B-C21, ESP2016-80079-C2-1-R, Institute of Cosmos Sciences University of Barcelona (ICCUB, Unidad de Excelencia ’Mar´ıa de Maeztu’) through grants MDM-2014-0369 and CEX2019-000918-M, Fundacão para a Ciência e a Tecnologia, with grants reference UIDB/00099/ 2020 and SFRH/BSAB/142940/2018 (P.G. only), Italian Ministry of Education, University and Research (MIUR) under the Departments of Excellence grant L.232/2016, and from the INFN grant InDark, Emeritus Fellowship from The Leverhulme Trust, Spanish grant PGC2018-101950-B-100, Istituto Nazionale di Astrofisica within the CRUI-CARE Agreement

[Context] Gaia Early Data Release 3 (Gaia EDR3) contains results for 1.812 billion sources in the magnitude range G = 3-21 based on observations collected by the European Space Agency Gaia satellite during the first 34 months of its operational phase. [Aims] We describe the input data, the models, and the processing used for the astrometric content of Gaia EDR3, as well as the validation of these results performed within the astrometry task. [Methods] The processing broadly followed the same procedures as for Gaia DR2, but with significant improvements to the modelling of observations. For the first time in the Gaia data processing, colour-dependent calibrations of the line- and point-spread functions have been used for sources with well-determined colours from DR2. In the astrometric processing these sources obtained five-parameter solutions, whereas other sources were processed using a special calibration that allowed a pseudocolour to be estimated as the sixth astrometric parameter. Compared with DR2, the astrometric calibration models have been extended, and the spin-related distortion model includes a self-consistent determination of basic-angle variations, improving the global parallax zero point. [Results] Gaia EDR3 gives full astrometric data (positions at epoch J2016.0, parallaxes, and proper motions) for 1.468 billion sources (585 millionwith five-parameter solutions, 882 million with six parameters), and mean positions at J2016.0 for an additional 344 million.Solutions with five parameters are generally more accurate than six-parameter solutions, and are available for 93% of the sources brighter than the 17th magnitude. The median uncertainty in parallax and annual proper motion is 0.02-0.03 mas at magnitude G = 9-14, and around 0.5 mas at G = 20. Extensive characterisation of the statistical properties of the solutions is provided, including the estimated angular power spectrum of parallax bias from the quasars., This work was financially supported by the European Space Agency (ESA) in the framework of the Gaia project; the German Aerospace Agency (Deutsches Zentrum für Luft- und Raumfahrt e.V., DLR) through grants 50QG0501, 50QG0601, 50QG0901, 50QG1401 and 50QG1402; the Spanish Ministry of Economy (MINECO/FEDER, UE) through grants ESP2016-80079-C2-1-R, RTI2018-095076-B-C21 and the Institute of Cosmos Sciences University of Barcelona (ICCUB, Unidad de Excelencia “María de Maeztu”) through grants MDM-2014-0369 and CEX2019-000918-M; the Swedish National Space Agency (SNSA/Rymdstyrelsen); and the United Kingdom Particle Physics and Astronomy Research Council (PPARC), the United Kingdom Science and Technology Facilities Council (STFC), and the United Kingdom Space Agency (UKSA) through the following grants to the University of Bristol, the University of Cambridge, the University of Edinburgh, the University of Leicester, the Mullard Space Sciences Laboratory of University College London, and the United Kingdom Rutherford Appleton Laboratory (RAL): PP/D006511/1, PP/D006546/1, PP/D006570/1, ST/I000852/1, ST/J005045/1, ST/K00056X/1, ST/K000209/1, ST/K000756/1, ST/L006561/1, ST/N000595/1, ST/N000641/1, ST/N000978/1, ST/N001117/1, ST/S000089/1, ST/S000976/1, ST/S001123/1, ST/S001948/1, ST/S002103/1, and ST/V000969/1.

The Archive is the main Gaia data distribution hub. The contents of DR1 are briefly reviewed and the data structures discussed. The system architecture, based on Virtual Observatory standards, is also presented, together with the extensions that allow e.g. authenticated access, persistent uploads and table sharing. Finally some usage examples are provided., 4 pages, 3 figures. to be published in Astrometry and Astrophysics in the Gaia Sky. Proceedings IAU Symposium No. 330, 2017

Presentation on the Gaia Archive at the NYC Gaia Sprint, 2016-10

In 1998 the EXPORT team monitored microlensing event lightcurves using a CCD camera on the IAC 0.8m telescope on Tenerife to evaluate the prospect of using northern telescopes to find microlens anomalies that reveal planets orbiting the lens stars. The high airmass and more limited time available for observations of Galactic Bulge sources makes a northern site less favourable for microlensing planet searches. However, there are potentially a large number of northern 1m class telescopes that could devote a few hours per night to monitor ongoing microlensing events. Our IAC observations indicate that accuracies sufficient to detect planets can be achieved despite the higher airmass., 8 pages, 14 figures, 1 bbl file, based on EXPORT observations, accepted by MNRAS

The impact of bright extended sources on the observation and detection of faint sources by Gaia has been studied. The effect has been characterized using the representative case of stars near the Jupiter disk and consists of three parts. First, an analytical representation of the PSF, including aberrations and electronic distortions, has been developed to produce images of Jupiter and solar type stars. Second, those images have been combined to produce fields of view including Jupiter and stellar patterns. Third, the CCD images have been fed to the VPU algorithms prototype to determine the limits until which detections are possible. This work can be useful for science cases such as GAREQ.

We have carried out a conceptual design study for a near-infrared (NIR) wide-field camera and a mid-infrared (MIR) camera-spectrograph for a 2.5 m telescope at Dome C. The main scientific drivers are the characterisation of young embedded objects, the evolution of crystalline silicates in circumstellar disks and the observation of exoplanet secondary transits. Both instrument exploit the unique features of Dome C: improved infrared transmission, reduced sky background, superb seeing, low temperature, and increased atmospheric stability. The NIR camera covers the wavelength range 0.8–5.5 μ m and is optimized for the K dark and L bands. The MIR instrument is sensitive in the range 7–40 μ m with a possible extension to the sub-mm. It is optimized for the Q window, including the Q+ extended portion (25–40 μ m) only observable from the Antarctic Plateau.

We are exploring instrumental concepts of Near and Mid InfraRed (NIR, MIR) wide field camera-spectrographs for a 2 m-class telescope at Antarctica. Scientific drivers are star formation and very low mass objects. Both concepts pretend to exploit the unique features of Dome C: superb seeing, low temperature, improved IR transmission and reduced sky background. Two preliminary concepts are presented here. The NIR instrument would cover the wavelength range 0.97–5.0 μ m and would be optimized for the K, L and M bands. The MIR instrument would observe in the range 7–30 μ m and would be specifically designed to exploit the extended portion of the Q window (20+ μ m).

The success of projects aiming at the detection of Earth-like planets orbiting nearby stars and the physical-chemical characterization of the terrestrial planet's atmospheres requires a careful selection of the target stars as well as a detailed knowledge of their properties and of the stellar environment. Both aspects have to be fulfilled with specific observations. The conditions of Dome C for astronomical observations are very much appropriate to make a significant contribution to these preparatory observations. Some examples are presented here, in particular related to high-precision photometry and high spatial resolution observations.

Context. Eris is the largest dwarf planet currently known in the solar system. Knowledge about its physical parameters is necessary to interpret the characteristics of these kinds of bodies. Aims. The goal of this work is to study Eris' short-term and long-term variability in order to determine the amplitude of the lightcurve, which can be linked to the degree of elongation of the body or to the degree of albedo heterogeneity on the surface of the dwarf planet. In addition, the rotation period can be determined. Methods. CCD photometric observations of the trans Neptunian object Eris in R band on 16 nights spanning two years were carried out using the 1.5 m telescope at Sierra Nevada Observatory (OSN), the 2.5 m Isaac Newton Telescope (INT) telescope at the Roque de los Muchachos Observatory, and the 2.2 m Telescope at Calar Alto Observatory. Results. The time-series analysis leads to indications of a short-term variability whose nature is not clear. It could be real or a result of data-reduction artifacts, such as contamination by close, faint-background stars. The most significant periodicities are 14 h or its double, but other possibilities cannot be ruled out, like a 32 h weaker peak in the periodogram. As for the amplitude of the lightcurve, we get a peak-to-peak variability of 0.01 ± 0.01 mag. The study of the long-term variability indicates that a long rotation period cannot be rejected, but the amplitude would be smaller than 0.06 mag. These results are compatible with a nearly spherical body that has a homogeneous surface.

In this contribution we describe both the teaching and popularization activities carried out at the Universidad Autonoma de Madrid (UAM, Spain) Observatory. The former are in the framework of the Physics degree at the University and the latter consists of several courses given at the University and amateur observations organised by members of our research group. We will also describe the equipment available and the state of the repairs of the Jeronimo Munoz 0.51 meter telescope.

The ESA Gaia mission uses two telescopes to create the most ambitious survey of the Galaxy. The angle between them must be known with exquisite precision and accuracy. An interferometer: the Basic Angle Monitoring system measures its variations. High quality data have been retrieved and analysed for more than a year. A summary of the in-orbit performance and some early results are presented, Comment: 4 pages, 3 figures. Proceedings of The Milky Way Unravelled by Gaia. GREAT Science from the Gaia Data Releases, Barcelona (Spain) 1 - 5 December 2014. EAS publication series, in press

We present the results of a high spectral resolution study of the circumstellar (CS) gas around the intermediate mass, pre-main sequence star UX Ori. The results are based on a set of 10 echelle spectra, monitoring the star on time scales of months, days and hours. A large number of transient blueshifted and redshifted absorption features are detected in the Balmer and in many metallic lines. A multigaussian fit is applied to determine for each transient absorption the velocity, v, dispersion velocity, Delta v, and the parameter R, which provides a measure of the absorption strength of the CS gas. The time evolution of those parameters is presented and discussed. A comparison of intensity ratios among the transient absorptions suggests a solar-like composition of the CS gas. This confirms previous results and excludes a very metal-rich environment as the cause of the transient features in UX Ori. The features can be grouped by their similar velocities into 24 groups, of which 17 are redshifted and 7 blueshifted. An analysis of the velocity of the groups allows us to identify them as signatures of the dynamical evolution of 7 clumps of gas, of which 4 represent accretion events and 3 outflow events. Most of the events decelerate at a rate of tenths of ms-2, while 2 events accelerate at approximately the same rate; one event is seen experiencing both an acceleration and a deceleration phase and lasts for a period of few days. This time scale seems to be the typical duration of outflowing and infalling events in UX Ori. The dispersion velocity and the relative aborption strength of the features do not show drastic changes during the lifetime of the events, which suggests they are gaseous blobs preserving their geometrical and physical identity., 14 pages, 8 figures, corrected rotation period in section 5

For a complete understanding of the physical processes causing the photometric variability of pre-main sequence systems, simultaneous optical and near-IR observations are required to disentangle the emission from the stars and that from their associated circumstellar disks. Data of this sort are extremely rare and little systematic work has been reported to date. The work presented in this paper is a systematic attempt in this direction. It presents an analysis of the simultaneous optical and near-IR photometric variability of 18 Herbig Ae/Be and T Tauri stars which were observed in October 98 by the EXPORT collaboration. The time dierence between the UBVRI and JHK measurements is less than 1 hour in50% of the data and the largest dierence is around 2 hours in only10% of the data. Twelve stars appear to show a correlation between the optical and near-IR variability trends, which suggests a common physical origin such as spots and/or variable extinction. The optical and near-IR variability is uncorrelated in the rest of the objects, which suggests it originates in distinctly dierent regions. In general, the optical variability qualitatively follows the predictions of starspots or variable extinction. As far as the near-IR is concerned, the simultaneity of the observations demonstrates that for most objects the flux is largely produced by their circumstellar disks and, consequently, in many cases the near-IR fluctuations must be attributed to structural variations of such disks producing variations of their thermal emission and/or scattered light. The observed near-IR changes of up to around 1 mag on timescales of 1{2 days provide interesting challenges for understanding the mechanisms generating such remarkable variabilities, an issue insuciently investigated until now but one which deserves further theoretical and modeling eorts.

The ESA Gaia space astrometry mission will perform an all-sky survey of stellar objects complete in the nominal magnitude range G = [6.0 - 20.0]. The stars with G lower than 6.0, i.e. those visible to the unaided human eye, would thus not be observed by Gaia. We present an algorithm configuration for the Gaia on-board autonomous object observation system that makes it possible to observe very bright stars with G = [2.0-6.0). Its performance has been tested during the in-orbit commissioning phase achieving an observation completeness of ~94% at G = 3 - 5.7 and ~75% at G = 2 - 3. Furthermore, two targeted observation techniques for data acquisition of stars brighter than G = 2.0 were tested. The capabilities of these two techniques and the results of the in-flight tests are presented. Although the astrometric performance for stars with G lower than 6.0 has yet to be established, it is clear that several science cases will benefit from the results of the work presented here., 12 pages, 5 figures. To appear in the proceedings of the SPIE 9143, 2014 Astronomical Instrumentation and Telescopes conference

The Gaia survey mission, operated by the European Space Agency (ESA) and launched on 19 December 2013, will survey approximately 109 stars or 1% of the galactic stellar population over a 5.5 year period. The main purpose of this mission is micro-arcsecond astrometry, that would yield important insights into the kinematics of the galaxy, its evolution, as well as provide important additional findings, including a updated coordinate reference system to that provided by the ICRS. Gaia performs its observations using two telescopes with fields of view separated by 106.5 degrees, spinning around an orthogonal axis at about 6 hours per day. The spin axis itself precesses: it is always oriented at 45 degrees from the sun, and precesses around the sun every 63 days. Thus each part of the sky is observed approximately every 63 days. The 6-hour spin, or scan-rate matches the CCD readout rate. The amount of data to process per day - 50-130 Gigabytes - corresponds to over 30 million stellar sources. To perform this processing, the Gaia Data Processing and Analysis Consortium (DPAC) have developed approximately 2 million lines of software, divided into subsystems specific to a given functional need, that are run across 6 different Data Processing Centres (DPCs). The final result being a catalog including the 109 stars observed. Most of the daily processing is performed at the DPC in ESAC, Spain (DPCE), which runs 3 main subsystems, the MOC Interface Task (MIT), the Initial Data Treatment (IDT), and First Look (FL). The MIT ingests the initial data provided by the MOC in the form of binary data and writes (amongst other things) `star packets' containing the raw stellar information needed for IDT, which provides a basic level of processing, including stellar positions, photometry, radial velocities, cross match and catalogue updates. FL determines the payload health (e.g, the health for the 106 CCDs, geometric calibration) and astrometric performance via the one day astrometric solution. This presentation provides an overview of the DPAC software as a whole, and focuses on the daily pipeline processing: the systems used, the teams involved, the challenges during development and operations, and lessons learned.

The radiation environment at L2 is of great importance to the science instruments of Gaia. Especially the non-ionising damage to the CCDs and the resulting increase in charge transfer inefficiency will ultimately limit the achievable science performance. With its launch in December 2013 for a nominal mission of 5 years Gaia is continuously collecting invaluable information of radiation effects on the 106 CCDs in the FPA from the analysis of the science data and dedicated calibration procedures. The paper shows first results and discusses the detected irradiation background with respect to predictions and reviews operational implications for the mission.

In this paper we present the first comprehensive results extracted from the spectroscopic campaigns carried out by the EXPORT (EXoPlanetary Observational Research Team) consortium. During 1998-1999, EXPORT carried out an intensive observational effort in the framework of the origin and evolution of protoplanetary systems in order to obtain clues on the evolutionary path from the early stages of the pre-main sequence to stars with planets already formed. The spectral types of 70 stars, and the projected rotational velocities, v sin i, of 45 stars, mainly Vega-type and pre-main sequence, have been determined from intermediate- and high-resolution spectroscopy, respectively. The first part of the work is of fundamental importance in order to accurately place the stars in the HR diagram and determine the evolutionary sequences; the second part provides information on the kinematics and dynamics of the stars and the evolution of their angular momentum. The advantage of using the same observational configuration and methodology for all the stars is the homogeneity of the set of parameters obtained. Results from previous work are revised, leading in some cases to completely new determinations of spectral types and projected rotational velocities; for some stars no previous studies were available.

We present near-IR J H K photometric data of sample of 58 main-sequence, mainly Vega-type, and pre-main sequence stars. The data were taken during four observation runs in the period May 1998 to January 1999 and form part of a coordinated effort with simultaneous optical spectroscopy and photo-polarimetry. The near-IR colors of the MS stars correspond in most cases tp photospheric colors, although noticealbe reddening is present towards a few objects, and these stars show no brightness variability within the observational errors. On the other hand, the PMS stars show near-IR excesses and variability consistent with previous data.

This document describes the uplink commanding system for the ESA Gaia mission. The need for commanding, the main actors, data flow and systems involved are described. The system architecture is explained in detail, including the different levels of configuration control, software systems and data models. A particular subsystem, the automatic interpreter of human-readable onboard activity templates, is also carefully described. Many lessons have been learned during the commissioning and are also reported, because they could be useful for future space survey missions., Comment: 12 pages, 13 figures. To appear in SPIE proceedings 9149-26. Observatory Operations: Strategies, Processes, and Systems V

Astronomy and Astrophysics 547 (2012): A108 reproduced with permission from Astronomy & Astrophysics, Context. Our ability to extract information from the spectra of stars depends on reliable models of stellar atmospheres and appropriate techniques for spectral synthesis. Various model codes and strategies for the analysis of stellar spectra are available today. Aims. We aim to compare the results of deriving stellar parameters using different atmosphere models and different analysis strategies. The focus is set on high-resolution spectroscopy of cool giant stars. Methods. Spectra representing four cool giant stars were made available to various groups and individuals working in the area of spectral synthesis, asking them to derive stellar parameters from the data provided. The results were discussed at a workshop in Vienna in 2010. Most of the major codes currently used in the astronomical community for analyses of stellar spectra were included in this experiment. Results. We present the results from the different groups, as well as an additional experiment comparing the synthetic spectra produced by various codes for a given set of stellar parameters. Similarities and differences of the results are discussed. Conclusions. Several valid approaches to analyze a given spectrum of a star result in quite a wide range of solutions. The main causes for the differences in parameters derived by different groups seem to lie in the physical input data and in the details of the analysis method. This clearly shows how far from a definitive abundance analysis we still are, The workshop on which this paper is based was kindly supported by the ESF through the GREAT initiative, by the Robert F.Wing Support Fund at Ohio State University, and the Department of Astronomy at the University of Vienna. Funded by the Austrian Science Fund FWF projects P20046, P21988, and P23737. U.H. Support from the Swedish National Space Board. C.A. Partial support by the Spanish grant YA2008-08013-C03-03. H.N. Financial support from the Alexander von Humboldt foundation. K.E. Support from The Swedish Research Council. C.W. Financial support of CNES, OCA and ESO. Financial support of CNES and CNRS. Support by the Austrian Science Fund FWF under project number P23006

The ESA Gaia spacecraft has two Shack-Hartmann wavefront sensors (WFS) on its focal plane. They are required to refocus the telescope in-orbit due to launch settings and gravity release. They require bright stars to provide good signal to noise patterns. The centroiding precision achievable poses a limit on the minimum stellar brightness required and, ultimately, on the observing time required to reconstruct the wavefront. Maximum likelihood algorithms have been developed at the Gaia SOC. They provide optimum performance according to the Cr\'amer-Rao lower bound. Detailed wavefront reconstruction procedures, dealing with partial telescope pupil sampling and partial microlens illumination have also been developed. In this work, a brief overview of the WFS and an in depth description of the centroiding and wavefront reconstruction algorithms is provided., Comment: 14 pages, 6 figures, 2 tables, proceedings of SPIE Astronomical Telescopes + Instrumentation 2012 Conference 8442 (1-6 July 2012)

Astronomy and Astrophysics 541 (2012): A40 reproduced with permission from Astronomy & Astrophysics, Context. Around 16% of the solar-like stars in our neighbourhood show IR-excesses due to dusty debris discs and a fraction of them are known to host planets. Determining whether these stars follow any special trend in their properties is important to understand debris disc and planet formation. Aims. We aim to determine in a homogeneous way the metallicity of a sample of stars with known debris discs and planets. We attempt to identify trends related to debris discs and planets around solar-type stars. Methods. Our analysis includes the calculation of the fundamental stellar parameters Teff, logg, microturbulent velocity, and metallicity by applying the iron ionisation equilibrium conditions to several isolated Fe i and Fe ii lines. High-resolution échelle spectra (R ∼ 57 000) from 2, 3 m class telescopes are used. Our derived metallicities are compared with other results in the literature, which finally allows us to extend the stellar samples in a consistent way. Results. The metallicity distributions of the different stellar samples suggest that there is a transition toward higher metallicities from stars with neither debris discs nor planets to stars hosting giant planets. Stars with debris discs and stars with neither debris nor planets follow a similar metallicity distribution, although the distribution of the first ones might be shifted towards higher metallicities. Stars with debris discs and planets have the same metallicity behaviour as stars hosting planets, irrespective of whether the planets are low-mass or gas giants. In the case of debris discs and giant planets, the planets are usually cool, – semimajor axis larger than 0.1 AU (20 out of 22 planets), even ≈65% have semimajor axis larger than 0.5 AU. The data also suggest that stars with debris discs and cool giant planets tend to have a low dust luminosity, and are among the less luminous debris discs known. We also find evidence of an anticorrelation between the luminosity of the dust and the planet eccentricity. Conclusions. Our data show that the presence of planets, not the debris disc, correlates with the stellar metallicity. The results confirm that core-accretion models represent suitable scenarios for debris disc and planet formation. These conclusions are based on a numberof stars with discs and planets considerably larger than in previous works, in particular stars hosting low-mass planets and debris discs. Dynamical instabilities produced by eccentric giant planets could explain the suggested dust luminosity trends observed for stars with debris discs and planets, This work was supported by the Spanish Ministerio de Ciencia e Innovación (MICINN), Plan Nacional de Astronomía y Astrofísica, under grant AYA2008-01727

The question of the origin and evolution of planetary systems is of fundamental importance for astrophysics. Dusty debris discs are signatures of planetary systems and, therefore, constitute valuable tools to provide new light in our understanding of how planetary systems form and evolve. We present the first results of a spectroscopic programme of a sample of stars with debris discs. High-resolution echelle spectra are used to determine metallicities and abundances. Properties of stars with debris discs, are compared with those of stars hosting planets, as well as 'normal' stars, This work was supported by the Spanish Ministerio de Ciencia e Innovación (MICINN), Plan Nacional de Astronomía y Astrofísica, under grant AYA2008-01727

Context. Circumstellar discs are ubiquitous around young stars, but rapidly dissipate their gas and dust on timescales of a few Myr. The Herschel Space Observatory allows for the study of the warm disc atmosphere, using far-infrared spectroscopy to measure gas content and excitation conditions, and far-IR photometry to constrain the dust distribution.Aims. We aim to detect and characterize the gas content of circumstellar discs in four targets as part of the Herschel science demonstration phase.Methods. We carried out sensitive medium resolution spectroscopy and high sensitivity photometry at gimel similar to 60-190 mu m using the Photodetector Array Camera and Spectrometer instrument on the Herschel Space Observatory.Results. We detect [OI] 63 mu m emission from the young stars HD 169142, TW Hydrae, and RECX 15, but not HD 181327. No other lines, including [CII] 158 and [OI] 145, are significantly detected. All four stars are detected in photometry at 70 and 160 mu m. Extensive models are presented in associated papers.

We have started a conceptual design study for both a near-infrared (NIR) wide-field camera and a mid-infrared (MIR) camera-spectrograph for a 2m-class telescope at Dome C, Antarctica. The main scientific drivers are the characterization of young embedded objects, the evolution of crystalline silicates in circumstellar disks and the observation of exoplanet secondary transits. Both instrument would exploit the unique features of Dome C: superb seeing, low temperature, improved infrared transmission, reduced sky background and increased atmospheric stability. Two preliminary concepts are presented here. The NIR instrument would cover the wavelength range 0.9–5.5μm and would be optimized for the K, L and M bands. The MIR instrument would observe in the range 7–40μm and would be optimized for the Q window, including the extended portion (25–40μm) only observable from Antarctica.

Planets are formed in disks around young stars. With an age of ~10 Myr, TW Hya is one of the nearest T Tauri stars that is still surrounded by a relatively massive disk. In addition a large number of molecules has been found in the TW Hya disk, making TW Hya the perfect test case in a large survey of disks with Herschel-PACS to directly study their gaseous component. We aim to constrain the gas and dust mass of the circumstellar disk around TW Hya. We observed the fine-structure lines of [OI] and [CII] as part of the Open-time large program GASPS. We complement this with continuum data and ground-based 12CO 3-2 and 13CO 3-2 observations. We simultaneously model the continuum and the line fluxes with the 3D Monte-Carlo code MCFOST and the thermo-chemical code ProDiMo to derive the gas and dust masses. We detect the [OI] line at 63 micron. The other lines that were observed, [OI] at 145 micron and [CII] at 157 micron, are not detected. No extended emission has been found. Preliminary modeling of the photometric and line data assuming [12CO]/[13CO]=69 suggests a dust mass for grains with radius < 1 mm of ~1.9 times 10^-4 Msun (total solid mass of 3 times 10^-3 Msun) and a gas mass of (0.5--5) times 10^-3 Msun. The gas-to-dust mass may be lower than the standard interstellar value of 100., 6 pages, 6 figures, accepted for publication in the A&A Herschel special issue

The Herschel GASPS Key Program is a survey of the gas phase of protoplanetary discs, targeting 240 objects which cover a large range of ages, spectral types, and disc properties. To interpret this large quantity of data and initiate self-consistent analyses of the gas and dust properties of protoplanetary discs, we have combined the capabilities of the radiative transfer code MCFOST with the gas thermal balance and chemistry code ProDiMo to compute a grid of 300 000 disc models (DENT). We present a comparison of the first Herschel/GASPS line and continuum data with the predictions from the DENT grid of models. Our objective is to test some of the main trends already identified in the DENT grid, as well as to define better empirical diagnostics to estimate the total gas mass of protoplanetary discs. Photospheric UV radiation appears to be the dominant gas-heating mechanism for Herbig stars, whereas UV excess and/or X-rays emission dominates for T Tauri stars. The DENT grid reveals the complexity in the analysis of far-IR lines and the difficulty to invert these observations into physical quantities. The combination of Herschel line observations with continuum data and/or with rotational lines in the (sub-)millimetre regime, in particular CO lines, is required for a detailed characterisation of the physical and chemical properties of circumstellar discs., Comment: 5 pages, 4 figures, accepted for publication in the A&A Herschel special issue

The EXPORT consortium carried out in 1998–1999 photo-polarimetric and spectroscopic monitoring over 74 Pre-Main Sequence (PMS) and Main Sequence (MS) stars with infrared excesses, 43 of them showing the Hα line in emission. We have measured the equivalent widths (EWs) of the Hα, [OI]6300, HeI5876 and NaID lines in 370 intermediate resolution optical spectra, obtained along four different observing campaigns, of those 43 objects. In this contribution we focus on the simultaneous spectroscopic and photometric behaviour of 12 UX-Ori type variable stars included in the sample. The main results indicate that the EW(Hα)−V correlation is a main feature of UXOrs. This correlation is also found in the [OI]6300 line in most of the objects. The variability in EW(HeI5876)–but not in the flux (F) in several cases–does not depend on the V -behaviour, as well as the complex patterns displayed in the NaI D lines. We interpret these results according to the dusty obscuration effect generated by the disks surrounding these stars, and propose that different accretion mechanisms could operate in different objects, depending on their F(HeI5876) – V behaviour.

PILOT (the Pathfinder for an International Large Optical Telescope is a proposed 2.5 m optical/infrared telescope to be located at DomeC on the Antarctic plateau. The atmospheric conditions at Dome C deliver a high sensitivity, high photometric precision, wide-field, high spatial resolution, and high-cadence imaging capability to the PILOT telescope. These capabilities enable a unique scientific potential for PILOT, which is addressed in this series of papers. The current paper presents a series of projects dealing with the nearby Universe that have been identified as key science drivers for the PILOT facility. Several projects are proposed that examine stellar populations in nearby galaxies and stellar clusters in order to gain insight into the formation and evolution processes of galaxies and stars. A series of projects will investigate the molecular phase of the Galaxy and explore the ecology of star formation, and investigate the formation processes of stellar and planetary systems. Three projects in the field of exoplanet science are proposed: a search for free-floating low-mass planets and dwarfs, a program of follow-up observations of gravitational microlensing events, and a study of infrared light-curves for previously discovered exoplanets. Three projects are also proposed in the field of planetary and space science: optical and near-infrared studies aimed at characterising planetary atmospheres, a study of coronal mass ejections from the Sun, and a monitoring program searching for small-scale Low Earth Orbit satellite debris items., Comment: 27 pages, 16 figures (degraded quality), accepted for publication in PASA

PILOT (the Pathfinder for an International Large Optical Telescope) is a proposed Australian/European optical/infrared telescope for Dome C on the Antarctic Plateau, with target first light in 2012. The proposed telescope is 2.4m diameter, with overall focal ratio f/10, and a 1 degree field-of-view. In median seeing conditions, it delivers 0.3" FWHM wide-field image quality, from 0.7-2.5 microns. In the best quartile of conditions, it delivers diffraction-limited imaging down to 1 micron, or even less with lucky imaging. The areas where PILOT offers the greatest advantages are (a) very high resolution optical imaging, (b) high resolution wide-field optical imaging, and (c) all wide-field thermal infrared imaging. The proposed first generation instrumentation consists of (a) a fast, low-noise camera for diffraction-limited optical lucky imaging; (b) a gigapixel optical camera for seeing-limited imaging over a 1 degree field; (c) a 4K x 4K near-infrared (1-5 micron) camera with both wide-field and diffraction-limited modes; and (d) a double-beamed midinfrared (7-40 micron) camera.

This work presents the determination of the effective temperature, gravity, metallicity, mass, luminosity and age of 27 young early-type stars, most of them in the age range 1-10 Myr, and three -suspected- hot companions of post-T Tauri stars belonging to the Lindroos binary sample. Most of these objects show IR excesses in their spectral energy distributions, which are indicative of the presence of disks. The work is relevant in the fields of stellar physics, physics of disks and formation of planetary systems. Spectral energy distributions and mid-resolution spectra were used to estimate the effective temperature. The comparison of the profiles of the Balmer lines with synthetic profiles provides the value of the stellar gravity. High-resolution optical observations and synthetic spectra are used to estimate the metallicity, [M/H]. Once these three parameters are known for each star, evolutionary tracks and isochrones provide estimations of the mass, luminosity, age and distance (or upper limits in some cases). The method is original in the sense that it is distance-independent, i.e. the estimation of the stellar parameters does not require, as it happens in other works, the knowledge of the distance to the object. A detailed discussion on some individual objects, in particular VV Ser, RR Tau, 49 Cet and the three suspected hot companions of post-T Tauris, is presented. The paper also shows the difficulty posed by the morphology and behaviour of the system star+disk in the computation of the stellar parameters., Comment: 18 pages, 11 figures

This article reviews the situation for robotization of telescopes and instruments at the Antarctic station Concordia on Dome C. A brain-storming meeting was held in Tenerife in March 2007 from which this review emerged.We describe and summarize the challenges for night-time operations of various astronomical experiments at conditions “between Earth and Space” and conclude that robotization is likely a prerequisite for continuous astronomical data taking during the 2000-hour night at Dome C. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present high resolution (lambda / Delta_lambda = 49000) echelle spectra of the intermediate mass, pre-main sequence stars BF Ori, SV Cep, WW Wul and XY Per. The spectra cover the range 3800-5900 angstroms and monitor the stars on time scales of months and days. All spectra show a large number of Balmer and metallic lines with variable blueshifted and redshifted absorption features superimposed to the photospheric stellar spectra. Synthetic Kurucz models are used to estimate rotational velocities, effective temperatures and gravities of the stars. The best photospheric models are subtracted from each observed spectrum to determine the variable absorption features due to the circumstellar gas; those features are characterized in terms of their velocity, v, dispersion velocity, Delta v, and residual absorption, R_max. The absorption components detected in each spectrum can be grouped by their similar radial velocities and are interpreted as the signature of the dynamical evolution of gaseous clumps with, in most cases, solar-like chemical composition. This infalling and outflowing gas has similar properties to the circumstellar gas observed in UX Ori, emphasizing the need for detailed theoretical models, probably in the framework of the magnetospheric accretion scenario, to understand the complex environment in Herbig Ae (HAe) stars. WW Vul is unusual because, in addition to infalling and outflowing gas with properties similar to those observed in the other stars, it shows also transient absorption features in metallic lines with no obvious counterparts in the hydrogen lines. This could, in principle, suggest the presence of CS gas clouds with enhanced metallicity around WW Vul. The existence of such a metal-rich gas component, however, needs to be confirmed by further observations and a more quantitative analysis., 21 pages, 13 figures. Accepted for publication by Astronomy & Astrophysics