Society of Physics Students at NMSU
SPS Undergraduate Speaker Series
Tuesday October 1st
Waves in Solids: How to Use Math and Physics to Travel the World
Stephen Hernandez (Graduate Student, UC Santa Cruz)
Seismology is the study of the propagation of longitudinal and transverse waves through a solid medium, namely, planet Earth. How do scientists know the earth has a liquid outer core? Was that earthquake in North Korea an earthquake or a clandestine nuclear explosion? How will the next great oil reserve be discovered? These and other questions are part of the realm of problems relevant to seismological interrogation. As a relatively young science, seismology uses a mixture of physics, applied mathematics, and digital signal processing to answer questions about earthquakes, the structure of planetary bodies, and other processes. As an example of ongoing applied research in seismology, I will discuss the phenomenon of slow earthquakes off the coast of the Nicoya Peninsula, in northwestern Costa Rica. Slow earthquakes have recently been implicated as potential precursors to large destructive events. Please visit as I discuss exciting career and travel opportunities (e.g., Africa, the South Pole) in geophysics.
Wednesday, September 18th
Shock Precursors in the Northeast limb of the Cygnus Loop Supernova Remnant
We present an observational study using high-resolution echelle spectroscopy of non-radiative collisionless shocks in a northeast filament of the Cygnus Loop supernova remnant. The shocks produce faint H-alpha; emission. The Balmer emission line profile is characterized by a narrow and a broad component. The narrow component is representative of the pre-shock conditions, while the broad component is produced after charge transfer between neutrals entering the shock and protons in the post-shock gas, thus reflecting the properties of the post-shock gas. We observe a diffuse H-alpha; region extending ~2.5 arcmin ahead of the shock with line width ~29 km/s, while the H-alpha; profile of the shock itself consists of a broader than expected narrow ~36 km/s and a broad ~250$ km/s component. The diffuse emission represents a photoionization precursor heated to ~18,000 K by He I and He II emission. Broad to narrow intensity ratios Ib/In of ~1.0 imply full electron-proton temperature equilibration. Broad component line widths indicate shock velocities of ~400 km/s. Comparison with shock velocities computed using proper motions and distance, suggests the distance to the Cygnus Loop is greater than the upper limit of 637 pc, implying an actual distance of ~890 pc.
Wednesday, September 4th
Rotational Synchronization May Enhance Habitability for Circumbinary Planets: Kepler Binary Case Study
We report a mechanism capable of reducing (or increasing) stellar activity in binary stars, thereby potentially enhancing (or destroying) circumbinary habitability. In single stars, stellar aggression towards planetary atmospheres causes mass-loss, which is especially detrimental for late-type stars, because habitable zones are very close and activity is long lasting. In binaries, tidal rotational breaking reduces magnetic activity, thus reducing harmful levels of XUV radiation and stellar mass-loss that are able to erode planetary atmospheres. We study this mechanism for all cofirmed circumbinary (p-type) planets. We find that main sequence twins provide minimal ux variation and in some cases improved environments, if the stars rotationally synchronize within the first Gyr. Solar-like twins, like Kepler 34 and Kepler 35, provide low habitable zone XUV fluxes and stellar wind pressures. These wide, moist, habitable zones may potentially support multiple habitable planets. Solartype stars with lower mass companions, like Kepler 47, allow for protected planets over a wide range of secondary masses and binary periods. Kepler 38 and related binaries are marginal cases. Kepler 64 and analogues have dramatically reduced stellar aggression due to synchronization of the primary, but are limited by the short lifetime. Kepler 16 appears to be inhospitable to planets due to extreme XUV flux. These results have important implications for estimates of the number of stellar systems containing habitable planets in the Galaxy and allow for the selection of binaries suitable for follow-up searches for habitable planets.