Welcome to the Homepage of Dejan Vinković   

Dejan Vinković

Science and Society Synergy Institute
Bana Jospia Jelacica 22B
40000 Cakovec, Croatia
e-mail: dejan_at_iszd.hr
Modeling of circumstellar environment of young stars
Active Project
Latest update: December 01, 2006
SEE ALSO "Protoplanetary Disks"
SEE ALSO "Modeling dust dynamics "

Animation of the imaging at different wavelengths (MPEG format, click on the image, 1.8Mb)
See also the figure below.
Planet formation is believed to occur in dense disks of gas and dust surrounding young pre-main-sequence (PMS) stars, but the current understanding of this process is very limited.

My work on young PMS stars initially started with addressing the problem of some observations showing large scale halos around protoplanetary disks. This halo had been traditionally ignored in the analysis of observed spectra and images, which often resulted in seemingly conflicting results. My collaborators and I were the first to recognize that this halo can be the dominant component in observations. This was demonstrated for several observed massive pre-main-sequence stars (Miroshnichenko et al. 1999, ApJL, 520, L115) where this resolves all the conflicts in a most natural way. Such a halo has far-reaching consequences for the disk structure and evolution because it provides additional disk heating and consequently influences the disk stability and dust grain growth.

Theoretical disk-in-halo model images at 30 microns and various inclination angles. In general, the observed images depend on the observational wavelength, telescope resolution, camera sensitivity and intrinsic ratio between the disk and halo surface brightness.
We also showed that the measured flux can not discriminate between the surface of a flared disk and an optically thin halo; only imaging at various wavelengths can do that (Vinkovic et al. 2003, MNRAS, 346, 1151). Since comparisons between theoretical and observational imaging are rarely performed for individual objects, it is not clear how much of the current understanding of the protoplanetary disk evolution is undermined by this degeneracy.

Theoretical model images of the close environment of a young star. Upper row: disk without halo; Lower row: disk + halo
Especially interesting, and still poorly understood, is the environment within several astronomical units (AU = distance between the Earth and the Sun) of these stars. This region comprises the inner protoplanetary disk where dust evolves from submicron particles to terrestrial planets, bipolar jets are launched, disks accrete onto the star and disk winds form. Understanding the protoplanetary disk structure is prerequisite for investigating these phenomena.

Comparisons of inner disk models with observations suggest that disk alone may not always explain the data unless an additional dusty component in a form of dusty wind is added to the models (Vinkovic et al. 2006, ApJ, 636, 348; Vinkovic & Jurkic 2007, ApJ, 658, 462). This wind surrounds the disk and creates a tenuous dusty halo around the inner disk regions. The exact process of supplying the wind with dust is not known, but observations can shed a light on this if we can reconstruct the halo properties.

In recent years, the near-infrared interferometry has emerged as a powerful observational method for exploring the inner disk regions. One of the major results is that the configuration of inner disk region differs dramatically between young PMS stars of luminosity smaller than about 1000 solar luminosities (low-L objects) and those with luminosity larger than 1000 solar (high-L). The structural differences in circumstellar environment between these two groups are sketched in the figure below.

Vinkovic, D., & Jurkic, T. 2007, ApJ, 658, 462 (PDF)
Vinkovic, D., Ivezic, Z., Jurkic, T., & Elitzur, M. 2006, ApJ, 636, 348 (ADS, PDF)
Vinkovic, D., Ivezic, Z., Miroshnichenko, A.S., & Elitzur, M. 2003, MNRAS, 346, 1151 (ADS, PDF)
Miroshnichenko, A., Ivezic, Z., Vinkovic, D., & Elitzur, M. 1999, ApJL, 520, L115 (ADS, PDF)

The emerging picture of the inner protoplanetary disk structure based on observed properties of high-L and low-L young PMS stars (Vinkovic & Jurkic 2007, ApJ, accepted).
Left: Low-L objects (luminosity smaller than 1000 solar luminosities) have two competing models explaining their near-infrared (NIR) visibilities and anomalously high NIR excess: (A) puffed-up inner disk rim and (B) dusty outflow creating a halo around the inner disk. Detected variability due to dust obscuration events suggests that either (C) the height of puffed-up rim is variable and temporarily blocks the view toward the star or (D) clumps of dust appear in the dusty outflow and occasionally intercept the line of sight. The disk inside the zone of dust sublimation (E) is optically thin, while the rest is optically thick (G) due to dust. Gaseous stellar and disk wind (F) are also present.
Right: High-L (luminosity larger than 1000 solar luminosities) YSOs have a simpler structure. The star is surrounded by optically thick gaseous accretion disk (A), which extends much closer to the star than the dust sublimation distance. But dust still may survive within the optically thick disk interior (B). Intense gaseous stellar and disk wind (C), combined with the stellar radiation pressure, are efficiently dispersing the surrounding environment.
(S) marks the star.