The Rotation and Other Properties of Comet 49P/Arend–Rigaux, 1984–2012
The Astronomical Journal, Volume 154, Number 5
Abstract:
We analyzed images of comet 49P/Arend–Rigaux on 33 nights between 2012 January and May and obtained R-band lightcurves of the nucleus. Through usual phasing of the data, we found a double-peaked lightcurve having a synodic rotation period of 13.450 ± 0.005 hr. Similarly, phase dispersion minimization and the Lomb–Scargle method both revealed rotation periods of 13.452 hr. Throughout the 2011/2012 apparition, the rotation period was found to increase by a small amount, consistent with a retrograde rotation of the nucleus. We also reanalyzed the publicly available data from the 1984/1985 apparition by applying the same techniques, finding a rotation period of 13.45 ± 0.01 hr. Based on these findings, we show that the change in rotation period is less than 14 s per apparition. Furthermore, the amplitudes of the lightcurves from the two apparitions are comparable, to within reasonable errors, even though the viewing geometries differ, implying that we are seeing the comet at a similar sub-Earth latitude. We detected the presence of a short-term jet-like feature in 2012 March, which appears to have been created by a short-duration burst of activity on March 15. Production rates obtained in 2004/2005, along with reanalysis of the previous results from 1984/1985, imply a strong seasonal effect and a very steep fall-off after perihelion. This, in turn, implies that a single source region, rather than leakage from the entire nucleus, dominates activity.
Interstellar medium conditions in z similar to 0.2 Lyman-break analogs
ASTRONOMY & ASTROPHYSICS 606 (2017) ARTN A86
The Rotation and Other Properties of Comet 49P/Arend-Rigaux, 1984 - 2012
ArXiv 1709.06089 (2017)
Galaxy Zoo and SpArcFiRe: Constraints on spiral arm formation mechanisms from spiral arm number and pitch angles
Monthly Notices of the Royal Astronomical Society Oxford University Press 472:2 (2017) 2263-2279
Abstract:
In this paper we study the morphological properties of spiral galaxies, including measurements of spiral arm number and pitch angle. Using Galaxy Zoo 2, a stellar mass-complete sample of 6,222 SDSS spiral galaxies is selected. We use the machine vision algorithm SpArcFiRe to identify spiral arm features and measure their associated geometries. A support vector machine classifier is employed to identify reliable spiral features, with which we are able to estimate pitch angles for half of our sample. We use these machine measurements to calibrate visual estimates of arm tightness, and hence estimate pitch angles for our entire sample. The properties of spiral arms are compared with respect to various galaxy properties. The star formation properties of galaxies vary significantly with arm number, but not pitch angle. We find that galaxies hosting strong bars have spiral arms substantially (4-6) looser than unbarred galaxies. Accounting for this, spiral arms associated with many-arm structures are looser (by 2) than those in two-arm galaxies. In contrast to this average trend, galaxies with greater bulge-to-total stellar mass ratios display both fewer and looser spiral arms. This effect is primarily driven by the galaxy disc, such that galaxies with more massive discs contain more spiral arms with tighter pitch angles. This implies that galaxy central mass concentration is not the dominant cause of pitch angle and arm number variations between galaxies, which in turn suggests that not all spiral arms are governed by classical density waves or modal theories.Galaxy Zoo: Major Galaxy Mergers Are Not a Significant Quenching Pathway
ASTROPHYSICAL JOURNAL 845:2 (2017) ARTN 145