The T-R DIAGRAM of CO gas in planet-forming regions
The figure shows the temperature-radius (T-R) diagram of carbon monoxide (CO) gas in protoplanetary disks. CO is a ubiquitous tracer of molecular gas in disks, and a sensitive thermometer of the radiation environment. The diagram above is constructed from spectroscopy surveys of rovibrational CO emission obtained with CRIRES at the Very Large Telescope, which currently provides the sharpest and most sensitive view of molecular gas in inner disks. The diagram unveils an empirical temperature profile for inner disks around solar-mass stars between 0.03 and 3 AU, by tracing the local warm dust color through infrared pumping. Between 2 and 25 AU, an inversion in the temperature profile reveals disks that have large depletions in their inner dust and gas radial structures, allowing ultraviolet pumping of CO emission at such large distances from the central stars. The T-R diagram of CO emission provides an empirical sequence of disk gap opening in protoplanetary disks, spanning the entire planet-formation region (~ 0.1-10 AU) and evolutionary stages from primordial to debris disks. In the figure above, the CO sequence is put into context of the Solar System planets and of the observed distribution of massive exoplanets that may migrate and open gaps in disks (with Msini > 0.5 Jupiter masses, from exoplanets.org).
Read here the scientific publication of this work, on the Astrophysical Journal: Banzatti & Pontoppidan 2015, ApJ, 809, 167
Read here a more poetic description on the STScI science blog: "Disk, gaps, and exoplanets - a journey on the wings of a dragonfly"
More is coming on the T-R diagram, including new data and more molecules from a larger sample of disks, so stay tuned...
Directly imaging the WATER SNOW LINE from two ALMA continuum bands
The figure illustrates a proof-of-concept method proposed in Banzatti, Pinilla, et al. 2015 to image the water snow line in protoplanetary disks, through its signature imprinted in the dust continuum spectral index as observed at millimeter wavelengths from two ALMA continuum bands. We adopt a physical disk model that includes dust coagulation, fragmentation, drift, and a change in fragmentation velocities of a factor of 10 between dry silicates and icy grains as found by laboratory work. We find that the presence of a water snow line leads to a sharp discontinuity in the radial profile of the dust emission spectral index due to replenishment of small grains through fragmentation. The cartoon to the left illustrates the key components of this effect, while the model simulation to the right shows how ALMA would image the snow line by combining two continuum bands. We propose that ALMA continuum images of disks should be found to commonly show the water snow line, when the necessary spatial resolution is achieved.
This work is now available in ApJ Letters: Banzatti, Pinilla, et al. 2015, ApJL, 815, L15
Monitoring the EFFECTS OF EPISODIC ACCRETION outbursts: UV photo-chemistry and inner disk draining
The figure shows a summary of observations and results obtained as part of monitoring studies of EX Lupi (the prototype of EXor variables) pre-, during, and post-outburst in the years 2005-2014. The lightcurve of EX Lupi is shown at the top of the figure: the strong accretion outburst in 2008 is visible in the 5 magnitude increase in the V band, while the data utilized in this work are marked with vertical lines. The Spitzer-IRS spectra were obtained before and during the ouburst, showing disappearance of organics and simultaneous increase in water and OH emission during outburst. This dataset provides first direct evidence that UV photo-chemistry (dissociation of molecules, e.g. water into OH) is triggered in inner disk surfaces during accretion flares. The increase in water emission is consistent with a larger amount of water vapor as released by icy bodies evaporated through a recession of the snow line at larger disk radii during outburst. The CRIRES data showed a strong decrease in water, OH and CO emission after outburst, and allowed to measure the amount (> 1 order of magnitude) and region (< 0.3 AU) of disk material drained during the outburst, which left the inner disk largely depleted of gas. Now the system is again in an "accumulation" phase (cartoon at the bottom), during which disk gas is piling up beyond the corotation radius until the next outburst will be triggered. Observations of EX Lupi give now the opportunity to study the timescales of organic chemistry in inner disks, through monitoring their infrared features while organics may re-form after UV photo-dissociation.
Read here the scientific publications of this study, on the Astrophysical Journal Letters: Banzatti et al. 2015, ApJL, 798, 16 , and on the Astrophysical Journal: Banzatti et al. 2012, ApJ, 745, 90
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