14 research outputs found
Disc Clearing of Young Stellar Objects: Evidence for Fast Inside-out Dispersal
The time-scale over which and the modality by which young stellar objects
(YSOs) disperse their circumstellar discs dramatically influences the eventual
formation and evolution of planetary systems. By means of extensive radiative
transfer (RT) modelling, we have developed a new set of diagnostic diagrams in
the infrared colour-colour plane (K-[24] vs. K-[8]), to aid with the
classification of the evolutionary stage of YSOs from photometric observations.
Our diagrams allow the differentiation of sources with unevolved (primordial)
discs from those evolving according to different clearing scenarios (e.g.
homologous depletion vs. inside-out dispersal), as well as from sources that
have already lost their disc. Classification of over 1500 sources in 15 nearby
star-forming regions reveals that approximately 39 % of the sources lie in the
primordial disc region, whereas between 31 % and 32 % disperse from the
inside-out and up to 22 % of the sources have already lost their disc. Less
than 2 % of the objects in our sample lie in the homogeneous draining regime.
Time-scales for the transition phase are estimated to be typically a few 10^5
years independent of stellar mass. Therefore, regardless of spectral type, we
conclude that currently available infrared photometric surveys point to fast
(of order 10 % of the global disc lifetime) inside-out clearing as the
preferred mode of disc dispersal.Comment: 31 pages, 21 figures, 6 tables, accepted for publication in MNRA
Circumstellar discs: What will be next?
This prospective chapter gives our view on the evolution of the study of
circumstellar discs within the next 20 years from both observational and
theoretical sides. We first present the expected improvements in our knowledge
of protoplanetary discs as for their masses, sizes, chemistry, the presence of
planets as well as the evolutionary processes shaping these discs. We then
explore the older debris disc stage and explain what will be learnt concerning
their birth, the intrinsic links between these discs and planets, the hot dust
and the gas detected around main sequence stars as well as discs around white
dwarfs.Comment: invited review; comments welcome (32 pages
A Census of Early Phase High-Mass Star Formation in the Central Molecular Zone
We present new observations of C-band continuum emission and masers to assess high-mass (8 ) star formation at early evolutionary phases in the inner 200 pc of the Central Molecular Zone (CMZ) of the Galaxy. The continuum observation is complete to free-free emission from stars above 10-11 in 91% of the covered area. We identify 104 compact sources in the continuum emission, among which five are confirmed ultracompact H II regions, 12 are candidates of ultra-compact H II regions, and the remaining 87 sources are mostly massive stars in clusters, field stars, evolved stars, pulsars, extragalactic sources, or of unknown nature that is to be investigated. We detect class II CHOH masers at 23 positions, among which six are new detections. We confirm six known HCO masers in two high-mass star forming regions, and detect two new HCO masers toward the Sgr C cloud, making it the ninth region in the Galaxy that contains masers of this type. In spite of these detections, we find that current high-mass star formation in the inner CMZ is only taking place in seven isolated clouds. The results suggest that star formation at early evolutionary phases in the CMZ is about 10 times less efficient than expected by the dense gas star formation relation, which is in line with previous studies that focus on more evolved phases of star formation. This means that if there will be any impending, next burst of star formation in the CMZ, it has not yet begun
Global Star-formation Properties Extracted from Synthetic Star-forming Regions | Appendix C
∼5800 realistic synthetic observations (FITS files) of a synthetic star-forming regio