Rationale and Topics
Though multiwavelength astronomy was born about fifty years ago, the full use of multiwavelength diagnostics is quite recent. Even in the last decade, astronomers still mostly relied on the optical domain. This is certainly going to change, as most current and future instruments are dedicated to the infrared, from the near- to the far-IR bands.
While this domain is a known "must" for low-mass stars, especially the very low-mass ones, the infrared emission of high-mass stars has been often neglected. Many advantages of the infrared must however be underlined, like its strong potential for circumstellar material and atmosphere diagnostics, and its insensitivity to obscuration. Its interest with regards to the first generation of stars, thought to be very massive, is also well known.
It is thus important to discuss the results obtained for massive stars from existing IR facilities (VLTs/VLTI, Spitzer, Herschel, CRIRES, GAIA, ...) as well as tools for interpreting IR data (e.g. atmosphere modeling) and observing capabilities of future facilities (ELTs, JWST, ...). To this aim, we will hold a 1.5-day special session (SpS) at the next IAU General Assembly meeting in Beijing.
Note there will also be a joint discussion on 'Very Massive Stars in the Local Universe' during the same GA. More info on this website
Topics to be presented during this special session:
Obscured and distant clusters
- Massive stars are rare objects of the stellar population (i.e. more exoplanets are known than WR stars!), so that we are generally dealing with only a few objects. To improve the knowledge of the massive star population, the IR domain is crucial as it can reveal obscured and/or distant clusters, like those close to the Galactic Center. The striking results obtained recently on the Arches and Westerlund 1 clusters, thanks to IR data, have underlined the importance of such studies. Such analyses also reveal the strong impact of massive stars on the clusters themselves, thanks to dynamical interactions and the eroding effect of their energetic radiation.
Stellar and wind parameters
- As they are rare and short-lived, important stellar and wind parameters of massive stars remain poorly constrained. IR facilities here play a key role. For example, the IR spectra can constrain the abundances and mass-loss rates while IR interferometers are a very efficient tool to study the close stellar environment, as well as the stellar multiplicity, and sometimes even (part of) the wind topology.In this context, wind diagnostics using IR data just begin to be explored, but they will certainly help to disentangle between the various wind models (incl. different clumping scenarios). Indeed, constraints on the mass-loss rates of weak-wind OB stars using the Br-Alpha line have provided promising results. Finally, pioneering metalliticy studies of massive stars in the IR have revealed the importance of accurate atomic data in this wavelength domain, which study has also begun.
Matter ejection and feedback
- Steady stellar winds are not the only mass-loss process for massive stars – one should not forget LBV eruptions and SN explosions. With the recent reduction in “observed” mass-loss rates (by a factor of about 3), the episodic matter ejections represent even more crucial keys for understanding the evolution of massive stars. Such events can be studied through the circumstellar nebulae surrounding LBVs and WRs. In addition, the exact contribution of massive stars to the dust content of the ISM is still a debated question: efficient dust formation has been seen in dense shocks, while dust in the pre-supernova circumstellar medium can sometimes be observed as an IR echo. Ground based observations limit the study of only the nearest and brightest events, while Spitzer and Herschel have greatly increased sensitivity. JWST is likely to trigger a leap forward, notably in assessing the contribution of SNe to the galactic dust budget because higher spatial resolution in the near/mid-IR is needed for crowded extragalactic fields where massive star progenitors of SNe reside. Studying both LBV eruptions and SN explosions leads to a better knowledge of the stellar feedback, hence of the Galactic ecology.