head 1.2; access; symbols; locks http:1.2; strict; comment @# @; expand @b@; 1.2 date 2004.11.30.15.26.38; author PaoloPadovani; state Exp; branches; next 1.1; 1.1 date 2004.11.30.14.52.07; author PaoloPadovani; state Exp; branches; next ; desc @none @ 1.2 log @none @ text @ Title: Circumstellar disks: from Pre-Main Sequence stars to stars harboring planets. by Enrique Solano et al. (LAEFF) Science Case: The study of protoplanetary disks is currently undergoing an exciting stage partly propelled by the discovery of extrasolar planetary systems following the detection of 51 PegB by Mayor & Queloz (1995, Nature 378, 355). The possible discovery of telluric planets in the near future, in addition to the jovian-like planets already detected, will pose interesting questions on the formation of extrasolar planetary systems. Knowledge of the properties of protoplanetary disks and how they evolve to debris disks around main-sequence (MS) stars is, therefore, a crucial step in such a process. Although theories of dust evolution have given the general outline on how the disks evolve from the optically thick phase around the youngest stars to the debris disks possibly harboring planets around the main sequence Vega-type stars, there are, however, still many open questions concerning to the driven-mechanisms and the factors that have influence on the disk evolution. The driving goal of this proposal for Science Reference Mission is to study a statistically significant number of stars covering a wide range of masses and evolutionary stages (HAeBes, ETTs, CTTs, PTTs, A-shell and Vega-type stars) to track and characterize from an observational point of view the evolution of protoplanetary disks. A methodological approach based on the comparison of the observed spectral energy distribution (SED) with a grid of synthetic models including both the stellar and disk contributions will allow to derive the physical parameters of the star and the disk. Theoretical modelling of SEDs has proven to constitute an invaluable tool for understanding the structure and properties of protoplanetary disks (e.g. Meri'n et al. (2004, A&A 419, 301), Chiang & Goldreich (1997,ApJ 490, 368; 1999, ApJ 519, 279), D'Alessio et al. (1998, ApJ, 500, 411; 1999, ApJ, 527, 893; 2001 ApJ, 553, 321), Dullemond et al. (2001, ApJ, 560, 957)). Requirements: - Archive Data: The building of SEDs needs to collect multiwavelength information across the electromagnetic spectrum. This will require accessing to on-line astronomical archives with absolute calibrated data (IUE, ISO) as well as astronomical catalogues (IRAS, 2MASS, Stro"mgren photometry,...) through the Vizier service and, desirably, other information taken from publications. - EXPORT Data: In addition to the archive data we will make use of the EXPORT observations (Eiroa et al. 2000, ASP Conf. Series, vol. 219, p. 3) consisting of photometry from optical to the near infrared, and optical medium and high resolution spectroscopy of a sample of 70 stars (both PMS and MS stars). The use of EXPORT data will permit to take advantage of the fact that the optical and near-IR photometry were obtained simultaneously. This observational approach is appropriate since T Tauri and HAeBe stars vary markedly in these spectral regimes and a significant part of the total luminosity of the object is radiated by the PMS stellar photosphere at these wavelengths. - Future Data: Despite the wealth of information provided by the IRAS and ISO satellites, the sensitivity of these missions did not allow to answer many key questions concerning the evolution of the disks and the possible formation of planets. For that purpose, future missions are being planned by both ESA and NASA to finally get the observational basis for a complete picture of the evolution of circumstellar disks around young stars and the possible mechanisms of planetary formation. The first mission of this series is the Spitzer Space Telescope from NASA. It is already providing an unprecedented improvement in sensitivity allowing major advances in this area of research. To make use of Spitzer data, synthetic magnitudes for the four IRAC (InfraRed Array Camera) photometers, operating at 3.6, 4.5, 5.8 and 8.0 microns, have been calculated by convolving the model fluxes with the respective filter passbands. Thus we are able to predict the magnitudes and colours of the young stars harboring planet-forming disks and interpret their physical state according to the IRAC colours (Allen et al, 2004 ApJS, 154, 363). During its lifetime, Spitzer will observe many young stars with ages spanning a wide range of evolutionary stages, from objects still embedded in their parental clouds to stars with ages around 10 Myrs, the so-called Vega-type stars. This collection of observations will represent a big step towards an unbiased statistical study of the early evolution of stars and disks. The possibility to apply the expertise gained with these studies to other missions (e.g. PACS (Photodetector Array Camera and Spectrometer) onboard Herschel and operating between 60 and 210 microns or MIRI, the Mid InfraRed Instrument planned for the James Webb Space Telescope, operating between 5 and 28 microns) will allow to achieve a good theoretical framework for a better scientific exploitation of the new data. - Models: The models from D'Alesio et al. (e.g., 2001, ApJ, 553, 321) represent one of the best approaches for studying the physics of illuminated accretion disks around PMS stars. An on-line library of models covering the whole relevant physical parameter space for the central star and the disk has been built and will be used in the analysis. VO aspects: - Need of VO: SEDs building, model fitting and the associated detailed analysis require to devote a tremendous amount of work and time which makes it quite inefficient for large datasets. This was clearly demonstrated in Meri'n et al. (2004) even if it was focused on ONLY two stars. This situation can be alleviated if all the analysis is performed under the VO framework. - Suitability of the Science case: SEDs building requires accessing to a variety of services (e.g. name resolver at CDS) , astronomical catalogues and archives both local and remote. The data transfer protocols already defined in the VO framework (SIAP, ConeSearch, SSA, VOTable) have demonstrated how efficient they are to handle all this heterogeneous and dispersed information. - Expanding the VO view (VO-science without the "official" VO-tool): The Spanish Virtual Observatory is developing a general-purpose facility that will be implemented as a web service to build spectral energy distributions. The user's interface is a HTML page where the user enters the object identification or coordinates and chooses the archives where the search has to be made. It is also possible to enter his/her own data. After this, the system asks CDS to resolve the name of the object. This request is made via the SOAP protocol to one of the web services currently running at CDS. The service returns the object information (including its coordinates) in XML format. Having the coordinates of the object, a request is made to each of the data centres (INES, ISO, VIZIER,...) using the VO SIAP protocol. Each one of the data centres returns the data in VOTable format. The data will be interpreted by the web application using its VOTable interpreter module. Once the data retrieved by each of the data centres have been interpreted correctly, it can be combined, processed, or passed to the data mining layer (see "Data mining" section) to perform the model fitting. After this, the user will be able to visualize the result using the visualization tools that will be implemented in the web application. - Implementation of analysis tools: We strongly feel that, in the VO framework, a deeper involvement of the astronomical data centres in the development of analysis tools is required. Accordingly, the system incorporates a set of tools to estimate the stellar physical parameters. In order to fit the best model to the observations it is necessary to have a first estimation of the stellar physical parameters (effective temperature, surface gravity and metallicity) as well as the interstellar reddening. In all cases, the parameter estimation will follow a pre-defined hierarchy in which the values provided by the user are on the top. Significant differences between the input values and the values obtained after the iterative process by the data mining tools may indicate either a non-adequate set of input values (due, for instance, to variable reddening and lack of simultaneity between the Stro"mgren and 2MASS photometry) or the presence of peculiarities in the spectral energy distribution that might deserve further and more detailed analysis. - Data mining: Data mining is a key aspect in the VO framework. The system includes a tool to estimate the model parameters following a Bayesian method. The main aim is to help users to quantitatively analyze the data in terms of evidence favoring one or several sets of parameters, what other alternative models can compete with the most a posteriori probable one, and what are the most discriminant observations to discard alternatives. These functionalities will be linked with the capacity of the server to query other archives in search of values for the discriminant observables. @ 1.1 log @none @ text @d3 2 @