We present near-IR and far-UV observations of the pre-transitional (gapped) disk in HD 169142 using NASAs Infrared Telescope Facility and Hubble Space Telescope. The combination of our data along with existing data sets into the broadband spectral en
ergy distribution reveals variability of up to 45% between ~1.5-10 {mu}m over a maximum timescale of 10 years. All observations known to us separate into two distinct states corresponding to a high near-IR state in the pre-2000 epoch and a low state in the post-2000 epoch, indicating activity within the <1 AU region of the disk. Through analysis of the Pa {beta} and Br {gamma} lines in our data we derive a mass accretion rate in May 2013 of (1.5 - 2.7) x 10^-9 Msun/yr. We present a theoretical modeling analysis of the disk in HD 169142 using Monte-Carlo radiative transfer simulation software to explore the conditions and perhaps signs of planetary formation in our collection of 24 years of observations. We find that shifting the outer edge (r = 0.3 AU) of the inner disk by 0.05 AU toward the star (in simulation of accretion and/or sculpting by forming planets) successfully reproduces the shift in NIR flux. We establish that the ~40-70 AU dark ring imaged in the NIR by Quanz et al. (2013) and Momose et al. (2013) and at 7 mm by Osorio et al. (2014) may be reproduced with a 30% scaled density profile throughout the region, strengthening the link to this structure being dynamically cleared by one or more planetary mass bodies.
Pre-transitional disks are protoplanetary disks with a gapped disk structure, potentially indicating the presence of young planets in these systems. In order to explore the structure of these objects and their gap-opening mechanism, we observed the p
re-transitional disk V1247 Orionis using the Very Large Telescope Interferometer, the Keck Interferometer, Keck-II, Gemini South, and IRTF. This allows us spatially resolve the AU-scale disk structure from near- to mid-infrared wavelengths (1.5 to 13 {mu}m), tracing material at different temperatures and over a wide range of stellocentric radii. Our observations reveal a narrow, optically-thick inner-disk component (located at 0.18 AU from the star) that is separated from the optically thick outer disk (radii >46 AU), providing unambiguous evidence for the existence of a gap in this pre-transitional disk. Surprisingly, we find that the gap region is filled with significant amounts of optically thin material with a carbon-dominated dust mineralogy. The presence of this optically thin gap material cannot be deduced solely from the spectral energy distribution, yet it is the dominant contributor at mid-infrared wavelengths. Furthermore, using Keck/NIRC2 aperture masking observations in the H, K, and L band, we detect asymmetries in the brightness distribution on scales of about 15-40 AU, i.e. within the gap region. The detected asymmetries are highly significant, yet their amplitude and direction changes with wavelength, which is not consistent with a companion interpretation but indicates an inhomogeneous distribution of the gap material. We interpret this as strong evidence for the presence of complex density structures, possibly reflecting the dynamical interaction of the disk material with sub-stellar mass bodies that are responsible for the gap clearing.
We present thirteen epochs of near-infrared (0.8-5 micron) spectroscopic observations of the pre-transitional, gapped disk system in SAO 206462 (=HD 135344B). In all, six gas emission lines (including Br gamma, Pa beta, and the 0.8446 micron line of
O I) along with continuum measurements made near the standard J, H, K, and L photometric bands were measured. A mass accretion rate of approximately 2 x 10^-8 solar masses per year was derived from the Br gamma and Pa beta lines. However, the fluxes of these lines varied by a factor of over two during the course of a few months. The continuum also varied, but by only ~30%, and even decreased at a time when the gas emission was increasing. The H I line at 1.083 microns was also found to vary in a manner inconsistent with that of either the hydrogen lines or the dust. Both the gas and dust variabilities indicate significant changes in the region of the inner gas and the inner dust belt that may be common to many young disk systems. If planets are responsible for defining the inner edge of the gap, they could interact with the material on time scales commensurate with what is observed for the variations in the dust, while other disk instabilities (thermal, magnetorotational) would operate there on longer time scales than we observe for the inner dust belt. For SAO 206462, the orbital period would likely be 1-3 years. If the changes are being induced in the disk material closer to the star than the gap, a variety of mechanisms (disk instabilities, interactions via planets) might be responsible for the changes seen. The He I feature is most likely due to a wind whose orientation changes with respect to the observer on time scales of a day or less. To further constrain the origin of the gas and dust emission will require multiple spectroscopic and interferometric observations on both shorter and longer time scales that have been sampled so far.
We have used the Spitzer Space Telescope Infrared Spectrograph (IRS) to observe the 5-37 micron thermal emission of comet 73P/Schwassmann-Wachmann 3 (SW3), components B and C. We obtained low spectral resolution (R ~ 100) data over the entire wavelen
gth interval, along with images at 16 and 22 micron. These observations provided an unprecedented opportunity to study nearly pristine material from the surface and what was until recently the interior of an ecliptic comet - cometary surface having experienced only two prior perihelion passages, and including material that was totally fresh. The spectra were modeled using a variety of mineral types including both amorphous and crystalline components. We find that the degree of silicate crystallinity, ~ 35%, is somewhat lower than most other comets with strong emission features, while its abundance of amorphous carbon is higher. Both suggest that SW3 is among the most chemically primitive solar system objects yet studied in detail, and that it formed earlier or farther from the sun than the bulk of the comets studied so far. The similar dust compositions of the two fragments suggests that these are not mineralogically heterogeneous, but rather uniform throughout their volumes. Atomic abundances derived from the spectral models indicates a depletion of O compared to solar photospheric values, despite the inclusion of water ice and gas in the models. Atomic C may be solar or slightly sub-solar, but its abundance is complicated by the potential contribution of spectrally featureless mineral species to the portion of the spectra most sensitive to the derication of the C abundance. We find a relatively high bolometric albedo, ~ 0.13 for the dust, considering the large amount of dark carbonaceous material, but consistent with the presence of abundant small particles and strong emission features.
We have re-analyzed the ultraviolet spectrum of HD 44179, the central star(s) of the Red Rectangle nebula, providing improved estimates of the column density, rotational, and vibrational temperatures of the 4th Positive A-X system of CO in absorption
. The flux shortward of 2200 A is a complex blend of CO features with no discernible stellar photosphere, making the identification of other molecular species difficult, and the direct derivation of the dust extinction curve impossible. We confirm that the spin-forbidden CO (a-X) Cameron bands are likely produced by either collisional excitation or a chemical reaction, not photoexcitation, but with a higher internal vibrational excitation than previously determined. We also detect the spin-forbidden CO a-X, d-X, and e-X absorption features. The hot CO (A-X) bands exhibit a blue-shift of ~300 km/s, likely occurring close to the white dwarf star(s) suspected as the original source of the ultraviolet flux in the system, and forming the base of the outflow of material in the Red Rectangle. The OH comet-band system near 3000 A is also analyzed, and estimates of its rovibrational temperatures determined. The source of the molecules studied in this system is still unknown, but may be a combination of gaseous material associated with the star(s), or processed material from the surrounding dust torus.
