A Universal Stellar Initial Mass Function? A Critical Look at Variations

Few topics in astronomy initiate such vigorous discussion as whether or not the initial mass function (IMF) of stars is universal, or instead sensitive to the initial conditions of star formation. The distinction is of critical importance: the IMF influences most of the observable properties of stellar populations and galaxies, and detecting variations in the IMF could provide deep insights into the process by which stars form. In this review, we take a critical look at the case for IMF variations, with a view towards whether other explanations are sufficient given the evidence. Studies of the field, local young clusters and associations, and old globular clusters suggest that the vast majority were drawn from a "universal" IMF: a power-law of Salpeter index ($\Gamma=1.35$) above a few solar masses, and a log normal or shallower power-law ($\Gamma \sim 0-0.25$) between a few tenths and a few solar masses (ignoring the effects of unresolved binaries). The shape and universality of the IMF at the stellar-substellar boundary is still under investigation and uncertainties remain large, but most observations are consistent with a IMF that declines ($\Gamma < -0.5$) well below the hydrogen burning limit. Observations of resolved stellar populations and the integrated properties of most galaxies are also consistent with a "universal IMF", suggesting no gross variations in the IMF over much of cosmic time. There are indications of "non-standard" IMFs in specific local and extragalactic environments, which clearly warrant further study. Nonetheless, there is no clear evidence that the IMF varies strongly and systematically as a function of initial conditions after the first few generations of stars.Comment: 49 pages, 5 figures, to appear in Annual Reviews of Astronomy and Astrophysics (2010, volume 48

Riskometer—Voting with Your Feet

As Extension professionals, we are faced with the need to educate youth and adults about risk and to assess their preference for risk; however, many find the concepts difficult to illustrate. This article lays out a simple technique that can be used to illustrate how personal attitudes toward risk change with changes in situations. Youth and adults who participate in the exercise will have a better understanding of risk and their attitudes about risk, which will lead them to make personal choices that are right for them

Search for Nanosecond Near-infrared Transients around 1280 Celestial Objects

Stars and planetary system

A Young Super Star Cluster in the Nuclear Region of NGC 253

We present observations of a massive star cluster near the nuclear region of the nearby starburst galaxy NGC 253. The peak of near-infrared emission, which is spatially separated by 4" from the kinematic center of the galaxy, is coincident with a super star cluster whose properties we examine with low-resolution (R ~ 1,200) infrared CTIO spectroscopy and optical/near-infrared HST imaging. Extinction, measured from [FeII] lines, is estimated at Av = 17.7 +/- 2.6. The age of the cluster is estimated at 5.7 Myr, based on Bry equivalent width for an instantaneous burst using Starburst99 modeling. However, a complex star formation history is inferred from the presence of both recombination emission and photospheric CO absorption. The ionizing photon flux has a lower limit of 7.3 +/- 2.5 x 10^53 inverse seconds, corrected for extinction. Assuming a Kroupa IMF, we estimate a cluster mass of 1.4 +/- 0.4 x 10^7 solar masses. We observe a strong Wolf-Rayet signature at 2.06 microns and report a weak feature at 2.19 microns which may be due to a massive stellar population, consistent with the derived mass and age of this cluster.Comment: 8 pages, 5 figures, accepted for publication in Ap

The Crowdsourced Replication Initiative: Investigating Immigration and Social Policy Preferences. Executive Report.

In an era of mass migration, social scientists, populist parties and social movements raise concerns over the future of immigration-destination societies. What impacts does this have on policy and social solidarity? Comparative cross-national research, relying mostly on secondary data, has findings in different directions. There is a threat of selective model reporting and lack of replicability. The heterogeneity of countries obscures attempts to clearly define data-generating models. P-hacking and HARKing lurk among standard research practices in this area.This project employs crowdsourcing to address these issues. It draws on replication, deliberation, meta-analysis and harnessing the power of many minds at once. The Crowdsourced Replication Initiative carries two main goals, (a) to better investigate the linkage between immigration and social policy preferences across countries, and (b) to develop crowdsourcing as a social science method. The Executive Report provides short reviews of the area of social policy preferences and immigration, and the methods and impetus behind crowdsourcing plus a description of the entire project. Three main areas of findings will appear in three papers, that are registered as PAPs or in process

Qualitative Analysis of Bluff Erosion and Changes in the Le Sueur River

Over time, the Le Sueur River has been undergoing channel changes and creating bluff erosion in Southern Minnesota. The bluff erosion has become a threat to homes near the river causing them to be in danger of destruction. While other researchers have mapped river changes using two years of imagery, we analyzed five sets of aerial photos, ranging from 1939 to the present, of a study area southeast of Mankato to determine the extent of bluff erosion, channel changes and threats to residents. This series of images allowed us to see whether the stream changes have been steady or increasing at a more rapid rate than in the past. We interpreted the photos using Stereo Analyst in ERDAS Imagine and created anaglyphs to interpret erosion processes in stereo. We also digitized the river’s course in ArcGIS to map the changes in course and erosion over time. Spatial Analyst allowed us to produce a detailed 3-D shaded relief model of the river channel to illustrate the geomorphic changes occurring in the area over time. Our conclusion determines whether bluff erosion on the Le Sueur River is increasing as time goes on. This research could affect future development and zoning restrictions in the area