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SWEDIBLES WORKSHOP / Summary
From March 29th to April 1st, 2016, the SWEDIBLES (Snellius Workshop on the ESO Diffuse Interstellar Bands Large Exploration Survey) meeting took place as a workshop at the Snellius location of the Lorentz Center. The workshop discussed during four days the many different aspects of the collaborative efforts within the EDIBLES consortium to use an extensive VLT filler program (nearly 300 hr) to obtain diffuse interstellar band spectra towards a very large number of different targets. About 30 participants (list added) worked through a program (also added) with contributed talks and several discussion rounds. These focused on; i) an update of the observational program (what has been done and what is still in the pipeline), ii) streamlining the data reduction process (challenges), iii) new approaches to take into account telluric pollution, iv) connecting EDIBLES observations to predictions from PDR modelling, v) (varying) DIB profiles, vi) linking the observational data to the latest developments in the laboratory (specifically PAHs and fullerenes), and vii) showing how theory can help in interpreting DIB spectra. The direct outcome of the workshop will be a pilot paper (Cox et al.), putting into the literature (likely A&A) an overview of all data that have/will become available within the EDIBLES program. It will describe a large sample that allows a statistical analysis of a number of DIB properties, and extends towards objects and into wavelength domains where no consistent DIB measurement programs were performed yet. In the paper, specific data will be discussed for a few selected and typical targets only, though. The paper furthermore acts as introduction for a number of priority projects that will focus on specific topics that are addressed as soon as all analyzed data have become available to the consortium. A few examples:
► Last year 2 bands around 960 nm were identified as originating from C60+ (Campbell et al., Science, 2015). In a follow-up study two more (and rather weak) C60+ bands at somewhat shorter wavelengths were claimed as well (Walker et al., ApJL 2015). Whereas the laboratory detection is outside any discussion – actually, an independent check was presented during this workshop by Scheier – there are doubts about the astronomical detections. At least one astronomical group (not included in EDIBLES) questions the correct interpretation by Campbell et al. and the detection by Walker et al.. EDIBLES offers a unique data sample that allows to check independently for astronomical C60+ features and this will be one of the first deliverables.
► EDIBLES contains many data of smaller species (OH+, SH, NH, CH, C2, CN, …) that have much diagnostic potential. The corresponding line positions are largely known (or were presented during this workshop) and will be used to connect DIBs and DIB profiles to specific environmental conditions.
► The large sample also allows to compare DIB profiles towards different sources and to interpret eventual differences in terms of changing rotational profiles of vibrational modes showing up. These provide additional information that further constrain DIB carriers.
► Given the progress in recording and calculating optical spectra of PAHs, another topic will be a systematic comparison of (new) DIB features with the data recorded within EDIBLES.
Much time was reserved for discussions, during the workshop itself and at the workshop dinner. As the participants cover rather different backgrounds this allowed to view projects from different points of view. This has been relevant for this Snellius workshop but also will add to the overall value of the outcome of this collaborative effort to systematically study DIB features.
Additional resources were needed to take care of extra costs not covered by the ‘basic funding’ offered by the Lorentz Center. Specifically, some contribution towards travel/accommodation costs of a number of participants (PhD students, one participant from Iran, one emeritus, two of the five organizers, workshop dinner, …). Financial support – very much appreciated - has been warranted through a number of organizations. The financial report is added to this report.
On behalf of the organizers,
Harold Linnartz, Nick Cox, Jan Cami, Peter Sarre, and Pascale Ehrenfreund