Subject: An additional science case for AVO demo From: Alberto Salama Date: Wed, 22 Oct 2003 18:23:32 +0200 To: Paolo Padovani CC: Timo Prusti , Pedro Garcia-Lario , Matteo Guainazzi Dear Paolo, It was nice to meet you in Strasbourg last week. As we discussed, Matteo and myself had fruitful discussions with Laurent Cambresy in view of the proposed AVO science case on galactic star forming regions. A collaboration with him has started. Laurent will give the input for the telecon tomorrow. In addition, I want to bring to your attention, and if you want to the SWG attention, another scientific case, suggested by Pedro Garci'a-Lario, astronomer in the ISO Data Centre. It is to my opinion a very nice case for VO usage. The text is somewhat long, because we decided appropriate to list various aspects, one (or more) of which could be further developed in case it is judged worth pursuing for the AVO demo next January. I copy this message to Timo Prusti, as ESA representative in the SWG. Ciao, Alberto P.S. As an example, a multi-wavelength plot of Henize 3-401 is attached. ----------------------------------------------------------------------- Galactic Scenario for AVO Demo ------------------------------ Milky Way Stars - Late stages of stellar evolution Science Drivers: ---------------- Study the evolution of sources in the transition phase from the Asymptotic Giant Branch (AGB) to the Planetary Nebula (PN) stage through the combination of spectroscopic data (also photometry can be used) available in various existing astronomical archives covering from the UV and X-ray wavelengths to the infrared and radio domain. 1. Introduction: why should this additional scenario be considered? - For an AVO demo it would be interesting to show that the impact is on all astrophysical fields. Thus, showing three different test cases: i) galactic/young stellar objects (star forming regions) ii) galactic/evolved stars (late stages of stellar evolution) iii) extragalactic: obscured quasars (unified model for AGNs) would cover a wide(r) variety of topics. - Objects in this transition phase show very nice spectroscopic properties to show in a demo (especially PNe) because of the presence of: i) multiple components in their SEDs (the central star + hot dust from the -sometimes- on-going mass loss (not always detected if there is no on-going mass loss) + cool dust from the circumstellar envelope ejected in the AGB, still detectable in the PN stage) ii) detection of gas phase atomic and molecular features, solid state features (coming from the dust grains) and presence of nebular emission lines (when the star becomes a PN). iii) the spectroscopic data can be complemented by spectacular images (ISO/CAM-CVF in the mid-infrared, HST-NICMOS in the near infrared, HST-WFPC2 in the optical, Chandra in X-ray, ..) which can also be shown during the demo. - Stars in the AGB-PN stage are esentially point-like sources or just slightly extended to most of the existing facilities so that putting together spectra coming from various archives do not imply performing corrections due to the use of different apertures (this could be a problem for the star forming region case!). - Stars in the transition phase from the AGB to the PN stage evolve fast and dramatic spectroscopic changes are predicted by the models (and observed) throughout the whole spectral range. Their SEDs evolve from being completely dominated by the optical/nir emission of the extremely cold central AGB star to an extremely hot central star of a PN, detected only in the UV/optical. In between the AGB and the PN stage there is a phase of total obscuration when the star can only be detected in the mid-far infrared (being the brightest sources in the sky at these wavelengths). In addition (especially PNe) objects in this late stages of the stellar evolution show strong emission at practically all wavelengths (X-ray, UV, optical, infrared . This means that in many cases it is possible to show attractive spectroscopic data for a large number of sources covering the whole spectral domain. 2. The scientific case: stars in the transition from the AGB to the PN stage - The evolution AGB - Post-AGB - PN is still poorly known and multi-wavelength analysis of a large sample of stars in this short transition phase is needed to test current models. Thus, multi-archive data is needed. - The combination of data from various archives with the AVO can be used in this specific area of research with several purposes: i) studying individual sources (see example of Henize 3-401) by the reconstruction of their SED. - scientific goals: i) identification of the different SED components above mentioned; ii) determination of the dominant chemistry in the central star and/or in the dust of the envelope iii) detailed analysis of the chemical abundances of the central star and/or the nebular gas. iv) detection of on-going mass-loss (through the detection of the hot dust component in the SED or not) v) detection of incipient ionisation in the envelope (through the detection of nebular emission lines in the inner high density core) vi) comparison with photoionisation models which include dust formation - method: just by putting together the different pieces of information available (IUE UV spectrum, ground-based optical spectroscopy and photometry, near infrared JHKL'M photometry + ISO IR data (includes PHT-S + SWS) + IRAS photometry. - advantage of AVO: fast way of putting together all the relevant pieces of information to perform a detailed multi-wavelength analysis of individual sources (at least one order of magnitude faster in time). ii) studying a well defined sample of sources selected on the basis of given MULTI-WAVELENGTH (multi-archive) scientific criteria (for instance, study of the evolutionary stage of all the sources classified as stars in the transition phase from the AGB to the PN stage by SIMBAD) in order to derive conclusions based on statistics. - scientific goals: i) determine the spectroscopic evolution of a star in this transition phase. ii) determine whether is there any connection between the observed chemistry and the mass of the progenitor star (as predicted by the models) iii) determine whether post-AGB mass loss can play a significant role in accelerating the evolution in this transition phase iv) test dredge-up models which predict the chemical evolution of stars in the AGB as a function of the stellar mass. - method: i) can be done: a) through the statistical analysis of the relative strength of the various components above identified in their SEDs (central star vs. hot dust vs. cool dust) using data coming from various archives. b) through the analysis of the spectroscopic features detected over the underlying continua (to study the physical parameters of the central star and the physical and chemical properties of the nebular gas and of the dust in the envelope) using again data from various archives. ii) can be done: by looking for correlations with other properties which can be used as distance independent mass indicators, like the different scale height of stars in the sample showing different spectroscopic properties iii) can be done: by determining the percentage of known post-AGB stars in which we detect the presence of a near infrared excess in the SED which can be attributed to hot dust (indicator of on-going mass loss). iv) can be done by establishing connections between the observed chemical abundances, evolutionary stage and overall SEDs to test the model predictions, using statistical criteria. - advantage of AVO: strong potential to apply multi-wavelength selection criteria which can lead to a better definition of samples to study a particular subject. In our case we can create a grid of sources in the transition phase from the AGB to the PN stage which consider their multi-wavelength spectroscopic properties as a whole. iii) Search for new sources in the transition AGB-PN This example is not a spectroscopic aplication of the AVO but the DEMO can be extended to show also the capability of AVO in searching for new candidate sources in this transition phase for further analysis in the future by combines existing photometric data in various infrared surveys (2MASS, MSX and IRAS). This is especially important for the study of this transition phase because the number of galactic sources is expected to be small (this is a very short-lived phase) and, in addition, new candidates are difficult to find because of the strong obscuration they experience in the optical range. New sources in the transition AGB-PN can be found among the infrared MSX sources (8-21 microns) with no previous identification in the liteature/ in SIMBAD. For this, the following procedure can be shown in the demo: i) the astrometric coordinates of all sources classified as AGB - PN stars in SIMBAD are retrieved ii) these coordinates are crossed with MSX point source catalogue coordinates of all sources well detected in A,B,C,D (and E) filters. This way it is possible to obtain the MSX photometry of these sources (already done by our group; we have found some 3000 sources including AGB stars, post-AGB stars and PNe) iii) these sources are plotted in MSX colour-colour diagrams together with other type of astronomical sources (normal stars, young stellar objects - including compact HII regions- and extragalactic sources) to show the location of sources of different astronomical class in these diagrammes. iii) Stars in the transition phase AGB - PN show colours are actually peculiar in the sense that they show only some overlap with young stellar objects/HII regions. Thus, colour criteria can be defined which identify potential new candidates among the unidentified sources in the MSX catalogue. iv) this contamination can be strongly decreased by combining the information in this catalogue with the available 2MASS data (JHK photometry) and/or by restricting the search to latitudes larger than +- 2 degrees, with the resulting sample giving a ~90-95% level of confidence that the sources satisfying the new selection criteria are in the AGB-PN stage. v) the search is extended to the sources (~30000) detected by MSX with unknown identification in the literature. vi) the resulting sample can be used for further follow up using spectroscopic techniques in the optical or in the infrared.