Forming the Dusty Ring in HR 4796A

We describe planetesimal accretion calculations for the dusty ring observed in the nearby A0 star HR 4796A. Models with initial masses of 10-20 times the minimum mass solar nebula produce a ring of width 7-15 AU and height 0.3-0.6 AU at 70 AU in roughly 10 Myr. The ring has a radial optical depth of 1. These results agree with limits derived from infrared images and from the excess infrared luminosity.Comment: 6 pages, including 2 figures and 1 table; ApJ Letters, in pres

Interpreting Spectral Energy Distributions from Young Stellar Objects. I. A grid of 200,000 YSO model SEDs

We present a grid of radiation transfer models of axisymmetric young stellar objects (YSOs), covering a wide range of stellar masses (from 0.1Msun to 50Msun) and evolutionary stages (from the early envelope infall stage to the late disk-only stage). The grid consists of 20,000 YSO models, with spectral energy distributions (SEDs) and polarization spectra computed at ten viewing angles for each model, resulting in a total of 200,000 SEDs. [...]. These models are publicly available on a dedicated WWW server: http://www.astro.wisc.edu/protostars/ . In this paper we summarize the main features of our models, as well as the range of parameters explored. [...]. We examine the dependence of the spectral indices of the model SEDs on envelope accretion rate and disk mass. In addition, we show variations of spectral indices with stellar temperature, disk inner radius, and disk flaring power for a subset of disk-only models. We also examine how changing the wavelength range of data used to calculate spectral indices affects their values. We show sample color-color plots of the entire grid as well as simulated clusters at various distances with typical {\it Spitzer Space Telescope} sensitivities. We find that young embedded sources generally occupy a large region of color-color space due to inclination and stellar temperature effects. Disk sources occupy a smaller region of color-color space, but overlap substantially with the region occupied by embedded sources, especially in the near- and mid-IR. We identify regions in color-color space where our models indicate that only sources at a given evolutionary stage should lie. [...].Comment: 69 pages, 28 figures, Accepted for publication in ApJS. Preprint with full resolution figures available at http://www.astro.wisc.edu/protostars

Librarians\u27 Perceptions of Artificial Intelligence and Its Potential Impact on the Profession

The subject of artificial intelligence (AI) is being discussed everywhere in the media. Stephen Hawking, Elon Musk, and Bill Gates regularly sound the alarm about AI as an existential threat to humankind. Open a newspaper, turn on the television, or log on to the internet, and you will find a plethora of information and opinions on AI and its potential impact on human endeavors. In addition to being a hot topic in the media, the scholarly literature in medicine and law is replete with AI research. It acknowledges AI as a transformative, if not disruptive, game changer. AI is being used today in the practice of law—in areas of contract review, billing, and jury selection. In the field of medicine, AI’s ability to crunch massive datasets has allowed it to surpass humans in diagnostic capabilities. Educators in law and medicine have also acknowledged that AI is changing the way professionals are trained, and it will ultimately reduce the number of lawyers and doctors needed in the workforce of the future. That said, the topic of AI is not everywhere—it’s not in the library literature. Oddly, for a profession that has done more than its share of coping with disruptive technologies over the years, we librarians are not in any meaningful way discussing AI as compared to those in other professions. We have not developed any substantial research on this topic nor have our library schools acknowledged the possibility of reducing admissions. Capability for machine learning, natural language processing, and massive computing power are the three aspects of AI that impact the professions of law and medicine. These will likewise impact the profession of librarianship. We were curious: Why is there a paucity of discussion about AI in our professional literature? In order to understand this, we surveyed our colleagues on their perception of AI, specifically as it relates to the future, the potential impact on our work, and the numbers in the workforce

Why metallic surfaces with grooves a few nanometers deep and wide may strongly absorb visible light

It is theoretically shown that nanometric silver lamellar gratings present very strong visible light absorption inside the grooves, leading to electric field intensities by several orders of magnitude larger than that of the impinging light. This effect, due to the excitation of long wave vector surface plasmon polaritons with particular small penetration depth in the metal, may explain the abnormal optical absorption observed a long time ago on almost flat Ag films. Surface enhanced Raman scattering in rough metallic films could also be due to the excitation of such plasmon polaritons in the grain boundaries or notches of the films.Comment: 5 pages, 5 figure, submitted to Phys. Rev. Let

Paper Session II-C - Commercial Space Initiatives

Traditionally, space technology has been developed and used primarily to meet the needs of civil and military government initiatives. In the future, it will be increasingly featured in two emerging trends: new space enterprises and the national drive to achieve a more competitive global economic position. To realize this potential, private sector initiatives and investment must adapt space technology and access to space to economically attractive, competitive ventures. While commercial development of space must be carried out in the private sector, it is clear that the Government has an important enabling role. NASA has established the Commercial Programs Advisory Committee (CPAC), to advise ftlASA on this and other aspects of the commercial development of space. CPAC, which is a standing committee of the NASA Advisory Council, is comprised of senior private sector executives and their university counterparts. The results of the first year of CPAC\u27s work has been published in the report Charting the Course: U.S. Space Enterprise and Space Industrial Competitiveness. This paper summarizes the CPAC report and examines promising space business sectors. Additionally, NASA\u27s initiatives which are supportive of commercial space are reviewed. Finally, an up-to-date look at the role of international cooperation in a highly competitive world is offered

Paper Session I-C - Commercial Space Infrastructure: Giving Industry a Lift

Historically, the private sector\u27s involvement in space-related commercial activities has been primarily in the fields of communications and, to a lesser degree, remote sensing and launch systems. But today there are other opportunities for space-oriented, profit-making activities. The provision of commercial infrastructure -- hardware and related integration services to support industrial research and product development activities -- is a potential revenue-producing industry. The National Space Council defines five principal areas of commercial space activity satellite communications, space transportation, remote sensing, materials processing, and commercial infrastructure. This paper, in discussing commercial infrastructure, also addresses commercial space transportation (launch services). Discussed are private sector initiatives directed toward establishing a commercial space sector in the fields of commercial space transportation, upper stages, payload processing, launch facilities, and other facilities and equipment. Not discussed, but recognized as important elements of commercial space infrastructure, are the legal, financial, and insurance industries. Also not included in this paper are private-sector initiatives for financing projects primarily for government use where the government controls the design, development, and management of the project and repays the private sector entity for its initial financial investment

2-D and 3-D Radiation Transfer Models of High-Mass Star Formation

2-D and 3-D radiation transfer models of forming stars generally produce bluer 1-10 micron colors than 1-D models of the same evolutionary state and envelope mass. Therefore, 1-D models of the shortwave radiation will generally estimate a lower envelope mass and later evolutionary state than multidimensional models. 1-D models are probably reasonable for very young sources, or longwave analysis (wavelengths > 100 microns). In our 3-D models of high-mass stars in clumpy molecular clouds, we find no correlation between the depth of the 10 micron silicate feature and the longwave (> 100 micron) SED (which sets the envelope mass), even when the average optical extinction of the envelope is >100 magnitudes. This is in agreement with the observations of Faison et al. (1998) of several UltraCompact HII (UCHII) regions, suggesting that many of these sources are more evolved than embedded protostars. We have calculated a large grid of 2-D models and find substantial overlap between different evolutionary states in the mid-IR color-color diagrams. We have developed a model fitter to work in conjunction with the grid to analyze large datasets. This grid and fitter will be expanded and tested in 2005 and released to the public in 2006.Comment: 10 pages, 8 figures, to appear in the proceedings of IAU Symp 227, Massive Star Birth: A Crossroads of Astrophysics, (Cesaroni R., Churchwell E., Felli M., Walmsley C. editors

2-D Radiative Transfer in Protostellar Envelopes: II. An Evolutionary Sequence

We present model spectral energy distributions, colors, polarization, and images for an evolutionary sequence of a low-mass protostar from the early collapse stage (Class 0) to the remnant disk stage (Class III). We find a substantial overlap in colors and SEDs between protostars embedded in envelopes (Class 0-I) and T Tauri disks (Class II), especially at mid-IR wavelengths. Edge-on Class I-II sources show double-peaked spectral energy distributions, with a short-wavelength hump due to scattered light and the long-wavelength hump due to thermal emission. These are the bluest sources in mid-IR color-color diagrams. Since Class 0 and I sources are diffuse, the size of the aperture over which fluxes are integrated has a substantial effect on the computed colors, with larger aperture results showing significantly bluer colors. This causes overlap in color-color diagrams between all evolutionary states, especially in the mid-IR. However the near-IR polarization of the Class 0 sources is much higher than the Class I-II sources, providing a means to separate these evolutionary states. We varied the grain properties in the circumstellar envelope, allowing for larger grains in the disk midplane and smaller in the envelope. We find that grain growth in disks of Class I sources can be detected at wavelengths greater than 100 $\mu$m. Our image calculations predict that the diffuse emission from edge-on Class I and II sources should be detectable in the mid-IR with the Space Infrared Telescope Facility (SIRTF) in nearby star forming regions (out to several hundred parsecs).Comment: A version with high-resolution images is available at http://www.astro.wisc.edu/glimpse/glimpsepubs.htm