Context. We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry, radial velocities, and information on astrophysical parameters and variability, for sources brighter than magnitude 21. In addition epoch astrometry and photometry are provided for a modest sample of minor planets in the solar system. Aims: A summary of the contents of Gaia DR2 is presented, accompanied by a discussion on the differences with respect to Gaia DR1 and an overview of the main limitations which are still present in the survey. Recommendations are made on the responsible use of Gaia DR2 results. Methods: The raw data collected with the Gaia instruments during the first 22 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into this second data release, which represents a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products. Results: Gaia DR2 contains celestial positions and the apparent brightness in G for approximately 1.7 billion sources. For 1.3 billion of those sources, parallaxes and proper motions are in addition available. The sample of sources for which variability information is provided is expanded to 0.5 million stars. This data release contains four new elements: broad-band colour information in the form of the apparent brightness in the GBP (330-680 nm) and GRP (630-1050 nm) bands is available for 1.4 billion sources; median radial velocities for some 7 million sources are presented; for between 77 and 161 million sources estimates are provided of the stellar effective temperature, extinction, reddening, and radius and luminosity; and for a pre-selected list of 14 000 minor planets in the solar system epoch astrometry and photometry are presented. Finally, Gaia DR2 also represents a new materialisation of the celestial reference frame in the optical, the Gaia-CRF2, which is the first optical reference frame based solely on extragalactic sources. There are notable changes in the photometric system and the catalogue source list with respect to Gaia DR1, and we stress the need to consider the two data releases as independent. Conclusions: Gaia DR2 represents a major achievement for the Gaia mission, delivering on the long standing promise to provide parallaxes and proper motions for over 1 billion stars, and representing a first step in the availability of complementary radial velocity and source astrophysical information for a sample of stars in the Gaia survey which covers a very substantial fraction of the volume of our galaxy.

/pdf/gaia-data-release-2-summary-of-the-contents-and-survey-539viwt72y.pdf

Gaia Data Release 2. Summary of the contents and survey properties

At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7. We summarize Gaia DR1 and provide illustrations of the scientific quality of the data, followed by a discussion of the limitations due to the preliminary nature of this release. Gaia DR1 consists of: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the Hipparcos and Tycho-2 catalogues and a secondary astrometric data set containing the positions for an additional 1.1 billion sources. The second component is the photometric data set,consisting of mean G-band magnitudes for all sources. The G-band light curves and the characteristics of ~3000 Cepheid and RR Lyrae stars, observed at high cadence around the south ecliptic pole, form the third component. For the primary astrometric data set the typical uncertainty is about 0.3 mas for the positions and parallaxes, and about 1 mas/yr for the proper motions. A systematic component of ~0.3 mas should be added to the parallax uncertainties. For the subset of ~94000 Hipparcos stars in the primary data set, the proper motions are much more precise at about 0.06 mas/yr. For the secondary astrometric data set, the typical uncertainty of the positions is ~10 mas. The median uncertainties on the mean G-band magnitudes range from the mmag level to ~0.03 mag over the magnitude range 5 to 20.7. Gaia DR1 represents a major advance in the mapping of the heavens and the availability of basic stellar data that underpin observational astrophysics. Nevertheless, the very preliminary nature of this first Gaia data release does lead to a number of important limitations to the data quality which should be carefully considered before drawing conclusions from the data.

/pdf/gaia-data-release-1-summary-of-the-astrometric-photometric-2co37amcsl.pdf

Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties

Context. At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7. Aims: A summary of Gaia DR1 is presented along with illustrations of the scientific quality of the data, followed by a discussion of the limitations due to the preliminary nature of this release. Methods: The raw data collected by Gaia during the first 14 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into an astrometric and photometric catalogue. Results: Gaia DR1 consists of three components: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the Hipparcos and Tycho-2 catalogues - a realisation of the Tycho-Gaia Astrometric Solution (TGAS) - and a secondary astrometric data set containing the positions for an additional 1.1 billion sources. The second component is the photometric data set, consisting of mean G-band magnitudes for all sources. The G-band light curves and the characteristics of 3000 Cepheid and RR Lyrae stars, observed at high cadence around the south ecliptic pole, form the third component. For the primary astrometric data set the typical uncertainty is about 0.3 mas for the positions and parallaxes, and about 1 mas yr-1 for the proper motions. A systematic component of 0.3 mas should be added to the parallax uncertainties. For the subset of 94 000 Hipparcos stars in the primary data set, the proper motions are much more precise at about 0.06 mas yr-1. For the secondary astrometric data set, the typical uncertainty of the positions is 10 mas. The median uncertainties on the mean G-band magnitudes range from the mmag level to0.03 mag over the magnitude range 5 to 20.7. Conclusions: Gaia DR1 is an important milestone ahead of the next Gaia data release, which will feature five-parameter astrometry for all sources. Extensive validation shows that Gaia DR1 represents a major advance in the mapping of the heavens and the availability of basic stellar data that underpin observational astrophysics. Nevertheless, the very preliminary nature of this first Gaia data release does lead to a number of important limitations to the data quality which should be carefully considered before drawing conclusions from the data.

/pdf/gaia-data-release-1-summary-of-the-astrometric-photometric-3vnhozldyc.pdf

Gaia Data Release 1 Summary of the astrometric, photometric, and survey properties

Context. Gaia Data Release 2 (Gaia DR2) contains results for 1693 million sources in the magnitude range 3 to 21 based on observations collected by the European Space Agency Gaia satellite during the first 22 months of its operational phase.Aims. We describe the input data, models, and processing used for the astrometric content of Gaia DR2, and the validation of these resultsperformed within the astrometry task.Methods. Some 320 billion centroid positions from the pre-processed astrometric CCD observations were used to estimate the five astrometric parameters (positions, parallaxes, and proper motions) for 1332 million sources, and approximate positions at the reference epoch J2015.5 for an additional 361 million mostly faint sources. These data were calculated in two steps. First, the satellite attitude and the astrometric calibration parameters of the CCDs were obtained in an astrometric global iterative solution for 16 million selected sources, using about 1% of the input data. This primary solution was tied to the extragalactic International Celestial Reference System (ICRS) by means of quasars. The resulting attitude and calibration were then used to calculate the astrometric parameters of all the sources. Special validation solutions were used to characterise the random and systematic errors in parallax and proper motion.Results. For the sources with five-parameter astrometric solutions, the median uncertainty in parallax and position at the reference epoch J2015.5 is about 0.04 mas for bright (G = 17 mag, and 0.7 masat G = 20 mag. In the proper motion components the corresponding uncertainties are 0.05, 0.2, and 1.2 mas yr−1 , respectively.The optical reference frame defined by Gaia DR2 is aligned with ICRS and is non-rotating with respect to the quasars to within 0.15 mas yr−1 . From the quasars and validation solutions we estimate that systematics in the parallaxes depending on position, magnitude, and colour are generally below 0.1 mas, but the parallaxes are on the whole too small by about 0.03 mas. Significant spatial correlations of up to 0.04 mas in parallax and 0.07 mas yr−1 in proper motion are seen on small ( DR2 astrometry are given in the appendices.

/pdf/gaia-data-release-2-the-astrometric-solution-3fhsbjb2fz.pdf

Gaia Data Release 2: The astrometric solution

We present an analysis of the intrinsic colors and temperatures of 5-30 Myr old pre-main sequence (pre-MS) stars using the F0 through M9 type members of nearby, negligibly reddened groups: η Cha cluster, TW Hydra Association, β Pic Moving Group, and Tucana-Horologium Association. To check the consistency of spectral types from the literature, we estimate new spectral types for 52 nearby pre-MS stars with spectral types F3 through M4 using optical spectra taken with the SMARTS 1.5m telescope. Combining these new types with published spectral types, and photometry from the literature (Johnson-Cousins BV IC, 2MASS JHKS and WISE W1, W2, W3, and W4), we derive a new empirical spectral type-color sequence for 5-30 Myr old pre-MS stars. Colors for pre-MS stars match dwarf colors for some spectral types and colors, but for other spectral types and colors, deviations can exceed 0.3 mag. We estimate effective temperatures (Teff) and bolometric corrections (BCs) for our pre-MS star sample through comparing their photometry to synthetic photometry generated using the BT-Settl grid of model atmosphere spectra. We derive a new Teff and BC scale for pre-MS stars, which should be a more appropriate match for T Tauri stars than often-adopted dwarf star scales. While our new Teff scale for pre-MS stars is within ≃100 K of dwarfs at a given spectral type for stars <G5, for G5 through K6, the pre-MS stars are ∼250 K cooler than their main sequence counterparts. Lastly, we present (1) a modern Teff, optical/IR color, and bolometric correction sequence for O9V-M9V MS stars based on an extensive literature survey, (2) a revised Qmethod relation for dereddening UBV photometry of OB-type stars, and (3) introduce two candidate spectral standard stars as representatives of spectral types K8V and K9V. Subject headings: open clusters and associations: individual(η Cha cluster, TW Hydra Association, β Pic Moving Group, Tucana-Horologium Association); — stars: pre-main sequence — stars: fundamental parameters (colors, temperatures)

https://iopscience.iop.org/article/10.1088/0067-0049/208/1/9/pdf

Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-Main Sequence Stars

The GAPS project is running since 2012 with the goal to optimize the science return of the HARPS-N instrument mounted at Telescopio Nazionale Galileo. A large number of astronomers is working together to allow the Italian community to gain an international position adequate to the HARPS-N capabilities in the exoplanetary researches. Relevant scientific results are being obtained on both the main guidelines of the collaboration, i.e., the discovery surveys and the characterization studies. The planetary system discovered around the southern component of the binary XO-2 and its characterization together with that of the system orbiting the northern component are a good example of the completeness of the topics matched by the GAPS project. The dynamics of some planetary systems are investigated by studying the Rossiter-McLaughlin effect, while host stars are characterized by means of asteroseismology and star-planet interaction.

Global Architecture of Planetary Systems (GAPS), a project for the whole Italian Community

The World Space Observatory (WSO) concept was originally proposed at the 7th UN/ESA Workshop and formulated in the context of the needs of Basic Space Science in the developing countries. It was defined as a mutually beneficial and valid scientific mission for all scientists in the world and not confined only to the developing world. In the context of the Long Range Planning of the ESA, an Assessment Study was made, evaluating a WSO Mission for the ultraviolet domain (WSO/UV). The study was based on the characteristics defined during a meeting held in November 1999 between scientists who had expressed interest in a WSO/UV. The WSO/UV mission studied has the following characteristics: 1) Telescope: 1.7 m (T-170 Russian model; Boyarchuk et al. 1998, ESA SP-413, 809), PSF (550 nm): 0.2″; 2) Spectrograph for the UV only: primary 110–340 nm. (HIRDES German model; Kappelmann 1998, ESA SP-413, 831) with spectral resolution 5–6 × 104; as well as a low resolution capability (500–1000); 3) Imaging: 115–340 nm with quality ≈ 0.1–0.3″ (MCP based Israelian model; Brosch 1998, ESA SP-413, 789); two UV Imagers: one for maximum spatial resolution, one for maximum sensitivity, and one Imager for visual domain; 4) High Earth Orbit. Further overall properties of the mission as a whole as described in the Report of the 8th UN/ESA Workshop The WSO/UV is an Astrophysical Observatory rather than a targeted mission for a single science goal, and it could be launched optimally in 2006/7. It fills an important gap in the capabilities available to the astronomical community (Wamsteker 1999, ASP. Conf. Ser., 164, 261; Panel Discussion WSO 1998, ESA SP-413, 849). Further information can be obtained from the author or at http://www.seas.columbia.edu/~ah297/um-esa/wso.html.

/pdf/wso-uv-world-space-observatory-ultraviolet-582xep9rht.pdf

WSO/UV: World Space Observatory/Ultraviolet

The World Space Observatory UltraViolet (WSO-UV) project is an international space observatory designed for observations in the ultraviolet domain where some of the most important astrophysical processes can be efficiently studied with unprecedented sensitivity.

World Space Observatory-UltraViolet: International Space Mission for the Nearest Future

PLATO is an exoplanet hunting mission of the European Space Agency. It is a medium-class mission, with a launch foreseen in 2026. Its prime objective is to uncover Earth-sized planets residing in their habitable zone. The payload consists of 26 cameras with a very wide field of view. These cameras consist of a Telescope Optical Unit (TOU), aligned at ambient and characterized at the operational temperature, and a Focal Plane Array bearing the detectors and delivered after coupling with the Front End Electronics. In this contribution, we report on the methods used at TOU level to characterize Focal Plane using a Hartmann Mask, i.e. we illustrate the analysis pipeline after data collection in the cryo-vacuum chamber at Leonardo (LDO), the implementation of new algorithms, and an extended uncertainties study for the Hartmann analysis.

Hartmann data analysis for PLATO TOU EM

The epochs of the primary and secondary minima of AR Lac between 1900 and 1989 are analysed with two non- parametric methods of searching for periodicity in a weighted time point series. An analytical model for transforming the O C data of eclipsing binaries into the period domain is pre- sented and is applied to AR Lac. The abrupt period changes of AR Lac reported in several previous studies are most prob- ably a consequence of an oversimplied interpretation of the O C data, since these changes are as likely to be continuous, and even the possibility of a 36 y cycle in the period cannot be denitely ruled out.

http://aa.springer.de/papers/7326002/2300698.pdf

Isabella Pagano

Papers

Global Architecture of Planetary Systems (GAPS), a project for the whole Italian Community

WSO/UV: World Space Observatory/Ultraviolet

World Space Observatory-UltraViolet: International Space Mission for the Nearest Future

Hartmann data analysis for PLATO TOU EM

Period changes of AR Lacertae between 1900 and 1989