Emergence and Persistence of Extreme Political Systems

We investigate the dynamics of political systems in a framework where transitions are driven by reforms and revolts, and where political systems are a priori unconstrained, ranging continuously from single-man dictatorships to full-scale democracies. The dynamics are governed by the likelihood of transitions and their outcome, which are both determined endogenously. We find that reforms and revolts result in extreme political systems - reforms by enfranchising the majority of the population leading to democracies, and revolts by installing autocracies. Reinforcing this polarization, extreme political systems are persistent across time: Democracies are intrinsically stable, leading to long episodes without political change. Autocracies, in contrast, are subject to frequent regime changes. Nevertheless they are persistent, since ensuing revolts lead to autocracies comparable to their predecessors. Taken together, our results suggest that the long-run distribution of political systems is bimodal with mass concentrated on the extremes. The dynamics are consistent with cross-country data

Dynamics of Political Systems

We develop a model of regime dynamics that embeds the principal transition scenarios examined by the literature. Political systems are a priori unrestricted and dynamics emerge through the combination and interaction of transition events over time. The model attributes a key role to beliefs held by political outsiders about the vulnerability of regimes, governing the likelihood and outcome of transitions. In equilibrium, transition likelihoods are declining in a regime's maturity,generating episodes of political stability alternating with rapid successions of revolts, counter revolts, and reforms. The stationary distribution of regimes is bimodal. The model dynamics match the data remarkably well

Integer Programming Subject to Monomial Constraints

We investigate integer programs containing monomial constraints. Due to the number-theoretic nature of these constraints, standard methods based on linear algebra cannot be applied directly. Instead, we present a reformulation resulting in integer programs with linear constraints and polynomial objective functions, using prime decompositions of the right hand sides. Moreover, we show that minimizing a linear objective function with nonnegative coefficients over bivariate constraints is possible in polynomial time

Combined Spectroscopic and Photometric Analysis of Flares in the Dwarf M Star EV Lacertae

We report results of an observing campaign to study the dwarf M flare star EV Lacertae. Between October 2021 and January 2022 we obtained concurrent B band photometry and low resolution spectroscopy of EV Lac on 39 occasions during 10 of which we observed flares with amplitude greater than 0.1 magnitude. Spectra were calibrated in absolute flux using concurrent photometry and flare-only spectra obtained by subtracting mean quiescent spectra. We measured B band flare energies between Log E = 30.8 and 32.6 erg. In the brightest flares we measured temporal development of flare flux in H I and He I emission lines and in the adjacent continuum and found that flux in the continuum subsided more rapidly than in the emission lines. Although our time resolution was limited, in our brightest flare we saw flux in the continuum clearly peaking before flux in the emission lines. We observed a progressive decrease in flare energy from H\b{eta} to H{\delta}. On average we found 37% of B band flare energy appeared in the H\b{eta} to H{\epsilon} emission lines with the remainder contributing to a rise in continuum flux. We measured black-body temperatures for the brightest flares between 10,500 +- 700 K and 19,500 +- 500 K and found a linear relationship between flare temperature and continuum flux at 4170 {\AA}. Balmer lines in flare-only spectra were well fitted by Gaussian profiles with some evidence of additional short-lived blue-shifted emission at the flare peak.Comment: 12 pages, 13 figures, accepted for publication in the Journal of the AAVS

Discovery of an intermediate-luminosity red transient in M51 and its likely dust-obscured, infrared-variable progenitor

We present the discovery of an optical transient (OT) in Messier 51, designated M51 OT2019-1 (also ZTF19aadyppr, AT 2019abn, ATLAS19bzl), by the Zwicky Transient Facility (ZTF). The OT rose over 15 days to an observed luminosity of $M_r=-13$ (${\nu}L_{\nu}=9\times10^6~L_{\odot}$), in the luminosity gap between novae and typical supernovae (SNe). Spectra during the outburst show a red continuum, Balmer emission with a velocity width of $\approx400$ km s$^{-1}$, Ca II and [Ca II] emission, and absorption features characteristic of an F-type supergiant. The spectra and multiband light curves are similar to the so-called "SN impostors" and intermediate-luminosity red transients (ILRTs). We directly identify the likely progenitor in archival Spitzer Space Telescope imaging with a $4.5~\mu$m luminosity of $M_{[4.5]}\approx-12.2$ and a $[3.6]-[4.5]$ color redder than 0.74 mag, similar to those of the prototype ILRTs SN 2008S and NGC 300 OT2008-1. Intensive monitoring of M51 with Spitzer further reveals evidence for variability of the progenitor candidate at [4.5] in the years before the OT. The progenitor is not detected in pre-outburst Hubble Space Telescope optical and near-IR images. The optical colors during outburst combined with spectroscopic temperature constraints imply a higher reddening of $E(B-V)\approx0.7$ mag and higher intrinsic luminosity of $M_r\approx-14.9$ (${\nu}L_{\nu}=5.3\times10^7~L_{\odot}$) near peak than seen in previous ILRT candidates. Moreover, the extinction estimate is higher on the rise than on the plateau, suggestive of an extended phase of circumstellar dust destruction. These results, enabled by the early discovery of M51 OT2019-1 and extensive pre-outburst archival coverage, offer new clues about the debated origins of ILRTs and may challenge the hypothesis that they arise from the electron-capture induced collapse of extreme asymptotic giant branch stars.Comment: 21 pages, 5 figures, published in ApJ

TU Tau B: The Peculiar 'Eclipse' of a possible proto-Barium Giant

TU Tau (= HD 38218 = HIP 27135) is a binary system consisting of a C-N carbon star primary and an A-type secondary. We report on new photometry and spectroscopy which tracked the recent disappearance of the A-star secondary. The dimming of the A-star was gradual and irregular, with one or more brief brightenings, implying the presence of nonhomogeneities in the carbon star outflow. We also present evidence that the A-star is actively accreting s-process enriched material from the carbon star and suggest that it will therefore eventually evolve into a Barium giant. This is an important system as well because the A-type star can serve as a probe of the outer atmosphere of the carbon star.Comment: 9 pages, 9 figures, 4 tables, a number of amateur observatories made significant contributions to this research. Paper accepted for publication in The Astronomical Journa

Discovery of an Intermediate-luminosity Red Transient in M51 and Its Likely Dust-obscured, Infrared-variable Progenitor

We present the discovery of an optical transient (OT) in Messier 51, designated M51 OT2019-1 (also ZTF 19aadyppr, AT 2019abn, ATLAS19bzl), by the Zwicky Transient Facility (ZTF). The OT rose over 15 days to an observed luminosity of M_r = −13 (νL ν = 9 × 10^6 L_⊙), in the luminosity gap between novae and typical supernovae (SNe). Spectra during the outburst show a red continuum, Balmer emission with a velocity width of ≈400 km s^(−1), Ca II and [Ca II] emission, and absorption features characteristic of an F-type supergiant. The spectra and multiband light curves are similar to the so-called "SN impostors" and intermediate-luminosity red transients (ILRTs). We directly identify the likely progenitor in archival Spitzer Space Telescope imaging with a 4.5 μm luminosity of M_([4.5]) ≈ −12.2 mag and a [3.6]–[4.5] color redder than 0.74 mag, similar to those of the prototype ILRTs SN 2008S and NGC 300 OT2008-1. Intensive monitoring of M51 with Spitzer further reveals evidence for variability of the progenitor candidate at [4.5] in the years before the OT. The progenitor is not detected in pre-outburst Hubble Space Telescope optical and near-IR images. The optical colors during outburst combined with spectroscopic temperature constraints imply a higher reddening of E(B − V) ≈ 0.7 mag and higher intrinsic luminosity of M_r ≈ −14.9 mag (νL_ν = 5.3 × 10^7 L⊙) near peak than seen in previous ILRT candidates. Moreover, the extinction estimate is higher on the rise than on the plateau, suggestive of an extended phase of circumstellar dust destruction. These results, enabled by the early discovery of M51 OT2019-1 and extensive pre-outburst archival coverage, offer new clues about the debated origins of ILRTs and may challenge the hypothesis that they arise from the electron-capture induced collapse of extreme asymptotic giant branch stars

The sky is your laboratory: advanced astronomy projects for amateurs

For the experienced amateur astronomer who is wondering if there is something useful, valuable, and permanent that can be done with his or her observational skills, the answer is, "Yes, you can!" This is the book for the experienced amateur astronomer who is ready to take a new step in his or her astronomical journey. Unfortunately, there is no modern text that points curious amateur astronomers to the research possibilities that are open to them. At the 2006 meeting of the Society for Astronomical Sciences, quite a few participants agreed that the lack of such a text was a serious gap in the astronomical book market, and that this gap is impeding their efforts to encourage more amateur astronomers to get involved in research collaborations. This book will fill that gap, and enable more amateur astronomers to add research-type studies to their pursuit of the hobby. Written by an astronomer who is well known amongst the amateur and professional community for the skill and quality of his work, this book describes a wide range of research areas where amateurs are gathering new scientific data that is utilized by professional astronomers. For each research area, the book provides a concise explanation of the purpose and value of the amateurs’ observations, a description of the equipment that is needed, specific observing procedures, complete data reduction instructions, and an explanation of how, and where, to submit results so that they will be available to the professional users