From December 12, 2017 13:15 until December 12, 2017 13:45
At Seminar Room
Episodic accretion is thought to be common or even universal among young stellar objects (YSOs). If so, this would solve long standing problems in stellar evolution, i.e. the observed scatter around the best fitting isochrone of HR diagrams of pre-MS clusters, and the so-called “luminosity problem”, where typical luminosities of YSOs in clusters are lower than expected for Sun-like stars that should be above the main sequence. The abrupt increase in the mass accretion rate on to the central star leads to a sudden rise of the luminosity of the object. Stars that display such variability are known as eruptive YSOs. These are usually classified according to their spectral and photometric characteristics during outburst (the so-called FUors and EXors).
The search for high amplitude infrared variable stars in 119 deg2 of the Galactic midplane with the VVV survey yields 816 variables with DeltaKs>1 mag in the 2010-2012 data. The sample is strongly concentrated toward areas of star formation and variables found in these regions have SEDs typical of Young Stellar Objects. We find 106 likely YSOs with eruptive light curves which increases the number of known eruptive variable YSOs by a factor of about 5. The majority of the YSOs are optically obscured systems at earlier stages of evolution than the known FUor and EXor types. Spectroscopic follow up confirms 19 variable stars as new additions to the broad class of eruptive YSOs. However, most members of the sample show a mixture of the spectroscopic and photometric characteristics of the known subclasses. This is in line with a small number of other recent discoveries that have already begun to blur the distinction. Since these previously atypical objects are now the majority amongst embedded members of the class, we propose a new classification for them as “MNors”. This term (pronounced “emnor”) follows V1647 Ori, the illuminating star of McNeil’s Nebula.