One-Armed Spiral Waves in Galaxy Simulations with Counter-Rotating Stars

Motivated by observations of disk galaxies with counter-rotating stars, we have run two-dimensional, collisionless N-body simulations of disk galaxies with significant counter-rotating components. For all our simulations the initial value of Toomre's stability parameter was Q = 1.1. The percentage of counter-rotating particles ranges from 25% to 50%. A stationary one-arm spiral wave is observed to form in each run, persisting from a few to five rotation periods, measured at the half-mass radius. In one run, the spiral wave was initially a leading arm which subsequently transformed into a trailing arm. We also observed a change in spiral direction in the run initially containing equal numbers of particles orbiting in both directions. The results of our simulations support an interpretation of the one armed waves as due to the two stream instability.Comment: 13 pages, 4 figure

Photometry of the Young Open Cluster Trumpler 37

Photoelectric UBV observations of 120 stars in the young open cluster Trumpler 37 are presented, primarily in the magnitude range 10.0\u3c

Sloshing in High Speed Galaxy Interactions

Observations of lopsided spiral galaxies motivated us to explore whether the rapid passage of a companion galaxy could cause them. We examine whether the center of mass of the visible matter becomes displaced from the center of mass of the dark halo during the intruder's passage, thereby causing an asymmetric response and asymmetric structure. Two dimensional $N$-body simulations indicate that this can happen. We also explore some consequences of this offset. These include the center of mass of the visible disk following a decaying orbit around the halo center of mass and the development of transient one-armed spirals that persist for up to six rotation periods. We then study the results of a variety of initial conditions based on such offsets. We report on the results of several runs in which we initially offset a disk from its halo's center of mass by an amount typical of the above interaction. In some runs the halo is free to move, while in others it is held fixed. We used three different mass distributions for the halo in these runs. We find that the disk's center of mass spiraled inward creating a variety of observed or observable phenomena including one-armed spirals, massive clumps of particles, and counter-rotating waves. The systems settle into relatively axisymmetric configurations. Whether or not the end states included a bar depended on a variety of initial conditions.Comment: 20 text pages, 3 tables, 24 figures. A gzipped postscripped version with higher resolution figures can be downloaded from http://butch.umephy.maine.edu/kickers/Research/Sloshing/ . Accepted for publication in The Astrophysical Journa

Discovering the Essential Universe

Discovering the Universe confronts the challenges of the one-term astronomy course by heightening student curiosities about the cosmos, by using the context of astronomy to teach the process of science, and by highlighting common misconceptions and showing students how to think their way past them.With its signature combination of vivid writing and spectacular images, the new edition offers new findings, new study help, and an expanded new media/supplements package centered on W.H. Freeman’s breakthrough online course space, LaunchPad.https://digitalcommons.library.umaine.edu/fac_monographs/1263/thumbnail.jp

Discovering the Essential Universe

https://digitalcommons.library.umaine.edu/fac_monographs/1176/thumbnail.jp

Discovering the Essential Universe

Based on the most recent edition of Discovering the Universe (©2006), this text is the most concise, option for introductory astronomy courses.https://digitalcommons.library.umaine.edu/fac_monographs/1084/thumbnail.jp

Heavenly Errors: Misconceptions About the Real Nature of the Universe

One of the great paradoxes of modern times is that the more scientists understand the natural world, the more we discover that our everyday beliefs about it are wrong. Astronomy, in particular, is one of the most misunderstood scientific disciplines. With the participation of thousands of undergraduate students, Neil F. Comins has identified and classified, by origin and topic, over 1,700 commonly held misconceptions. Heavenly Errors provides access to all of them and explores many, including: • Black holes suck in everything around them.• The Sun shines by burning gas.• Comets have tails trailing behind them.• The Moon alone causes tides.• Mercury, the closest planet to the Sun, is the hottest planet. In the course of correcting these errors, he explains that some occur through the prevalence of pseudosciences such as astrology and UFO-logy and some enter the public conscience through the bad astronomy of Star Trek, Star Wars, and other science-fiction movies.. Perhaps most important, Professor Comins presents the reader with the methods for identifying and replacing incorrect ideas -- tools with which to probe erroneous notions so that we can begin to question for ourselves... and to think more like scientists.https://digitalcommons.library.umaine.edu/fac_monographs/1179/thumbnail.jp