We have obtained subarcsecond mid-IR images of a sample of debris disks within 100 pc. For our sample of 19 A-type debris disk candidates chosen for their IR excess, we have resolved, for the first ...time, five sources plus the previously resolved disk around HD 141569. Two other sources in our sample have been ruled out as debris disks since the time of sample selection. Three of the six resolved sources have inferred radii of 1-4 AU (HD 38678, HD 71155, and HD 181869), and one source has an inferred radius ~10-30 AU (HD 141569). Among the resolved sources with detections of excess IR emission, HD 71155 appears to be comparable in size (r ~ 2 AU) to the solar system's asteroid belt, thus joining Delta *z Lep (HD 38678, reported previously) to comprise the only two resolved sources of that class. Two additional sources (HD 95418 and HD 139006) show spatial extents that imply disk radii of ~1-3 AU, although the excess IR fluxes are not formally detected with better than 2 Delta *s significance. For the unresolved sources, the upper limits on the maximum radii of mid-IR disk emission are in the range ~1-20 AU, four of which are comparable in radius to the asteroid belt. We have compared the global color temperatures of the dust to that expected for the dust in radiative equilibrium at the distances corresponding to the observed sizes or limits on the sizes. In most cases, the temperatures estimated via these two methods are comparable, and therefore, we see a generally consistent picture of the inferred morphology and the global mid-IR emission. Finally, while our sample size is not statistically significant, we note that the older sources (>200 Myr) host much warmer dust (T 400 K) than younger sources (in the tens of Myr).
Our Spitzer IRS observation of the infrared companion Glass Ib revealed fine-structure emission with high ionization (NeIII/NeII = 2.1 and SIV/SIII = 0.6) that indicates that the gas is likely ...illuminated by hard radiation. While models suggest that extreme-ultraviolet radiation could be present in T Tauri stars, this is the first detection of SIV and such a high NeIII/NeII ratio in a young star. We also find that Glass Ib displays the molecules HCN, CO sub(2), and H sub(2)O in emission. Here we investigate the Glass I binary system and consider possible mechanisms that may have caused the high ionization, whether from an outflow or disk irradiation.We also model the spectral energy distributions of Glass Ia and Ib to test if the system is a young member of the Chameleon I star-forming region, and we consider other possible classifications for the system. We find that Glass Ib is highly variable, showing changes in continuum strength and emission features at optical, near-infrared, and mid-infrared wavelengths. The optical light curve indicates that a central stellar component in Glass Ib became entirely visible for 2.5 years beginning in mid-2002 and possibly displayed periodic variability with repeated, short-period dimming during that time. As the fine-structure emission was not detected in observations before or after our Spitzer IRS observation, we explore whether the variable nature of Glass Ib is related to the gas being highly ionized, possibly due to variable accretion or an X-ray flare.
We present findings for DoAr 24E, a binary system that includes a classical infrared companion. We observed the DoAr 24E system with the Spitzer Infrared Spectrograph (IRS), with high-resolution, ...near-infrared spectroscopy of CO vibrational transitions, and with mid-infrared imaging. The source of high extinction toward infrared companions has been an item of continuing interest. Here we investigate the disk sttucture of DoAr 24E using the column densities, temperature, and velocity profiles of two CO absorption features seen toward DoAr 24Eb. We model the special energy distributions found using T-ReCS imaging and investigate the likely sources of extinction toward DoAr 24Eb. We find the lack of silicate absorption and small CO column density toward DoAr 24Eb suggest that the mid-infrared continuum is not as extinguished as the near-infrared, possibly due to the mid-infrared originating from an extended region. This, along with the velocity profile of the CO absorption, suggests that the source of high extinction is likely due to a disk or disk wind associated with DoAr 24Eb.
Comet-like bodies of dust and ice residing in the disk can also be perturbed by the gravitational influence of larger planetary bodies and can end up near the star, resulting in sublimation of the ...smaller bodies' volatile components and the release of dust. A sharp drop in luminosity on a timescale of years might signal variability due to periodic accretion of gas onto the star or to intra-disk shadowing, in which an inner region of the disk puffs up through stellar heating and prevents light from reaching the more distant parts of the disk.
As global leaders meet to discuss climate change, AGU’s editors in chief make an appeal for urgent action based on years of accumulated climate science research.
Young stars grow up and narrow their focus Moerchen, Margaret M.
Science (American Association for the Advancement of Science),
04/2015, Letnik:
348, Številka:
6230
Journal Article
As individuals serving on the AGU Advances editorial board, we condemn racism, affirm that Black Lives Matter, and recognize that inequality is built into the systems that have allowed us to prosper. ...We aim to persistently foster discussion about racism, inequity, and the need to make our community more diverse and inclusive. This will help AGU Advances do a better job in publishing important science that inclusively reflects the ideas and contributions of all in our community.
Key Points
The editorial board wishes to enable their journal to represent the Earth and space sciences community in all its diversity
The board recognizes that inequality is part of systems that have allowed them to prosper and pledges to support diversity and inclusion
The board will commission and take contributions to an editorial series on the nature and impact of racism and other inequities in science
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