The paper “CSI 2264: Simultaneous optical and X-ray variability in pre-main sequence stars. I” of M. G. Guarcello has been published in A&A
Observing how the light emitted by stars changes with the time can be an interesting hobby, but it can also be something more important: an important and powerful diagnostic for something that can be hardly studied with some other approach…
This can be particularly important for pre-main sequence stars with protoplanetary disks. In these stars, in fact, important and violent time-variable phenomena occur, which can hardly be directly observed but that can be studied in the time domain. For instance, the internal region of the disk, distant few 0.1 AU from the central star, is very important for the coupling between star and disk and the evolution of the disk itself. This region can not be observed directly. However, warps in the central part of the disk can obscure the central star, absorb part of its radiation, allowing us to study their geometry and composition. Similarly, stars with disks may accrete material from their disks. This is an energetic and variable phenomenon, important for early stellar evolution, but that can not be observed directly. Again, time domain analysis can unveil the physical properties of the accretion phenomenon on stars with disks.
The paper “CSI 2264: Simultaneous optical and X-ray variability in pre-main sequence stars. I: Time resolved spectral analysis during optical dips and accretion bursts in stars with disks” of Mario Giuseppe Guarcello, recently published on Astronomy & Astrophysics, uses the optical light curves from CoRoT (i.e. time variability of the emitted optical radiation) of stars with disks in NGC 2264 to separate time intervals during which the circumstellar material associated with the disks obscures the central stars or optical bursts due to the material accreting from the disks to the stars are observed. Then, the X-ray properties during these time intervals are obtained, in order to understand more on the nature and characteristics of the circumstellar material and accretion process. For instance, the composition and properties of the obscuring material associated to the disks of whether the accretion process is a regular or irregular phenomenon. The most important results obtained by the authors are:
- The evidence that circumstellar material can absorb both the optical and X-ray radiation, and that in the analysed stars the obscuring structure are accretion funnels connecting stars and disks.
- The evidence that during accretion bursts observed in optical also soft (0.5-1 keV) X-ray radiation is observed, and the evidence that in two stars the accretion process is unstable.
In the image (link) the comparison between the soft and hard (1-8 keV) emission observed during the accretion bursts and when bursts are not occurring, proving the presence of soft X-ray emission during the bursts.