Daniel E. Reichart

A ring system detected around the Centaur (10199) Chariklo

Hitherto, rings have been found exclusively around the four giant planets in the Solar System. Rings are natural laboratories in which to study dynamical processes analogous to those that take place during the formation of planetary systems and galaxies. Their presence also tells us about the origin and evolution of the body they encircle. Here we report observations of a multichord stellar occultation that revealed the presence of a ring system around (10199) Chariklo, which is a Centaur—that is, one of a class of small objects orbiting primarily between Jupiter and Neptune—with an equivalent radius of 124u2009u20099u2009kilometres (ref. 2). There are two dense rings, with respective widths of about 7 and 3 kilometres, optical depths of 0.4 and 0.06, and orbital radii of 391 and 405 kilometres. The present orientation of the ring is consistent with an edge-on geometry in 2008, which provides a simple explanation for the dimming of the Chariklo system between 1997 and 2008, and for the gradual disappearance of ice and other absorption features in its spectrum over the same period. This implies that the rings are partly composed of water ice. They may be the remnants of a debris disk, possibly confined by embedded, kilometre-sized satellites.

The fading of Cassiopeia A, and improved models for the absolute spectrum of primary radio calibration sources

Based on five years of observations with the 40-foot telescope at Green Bank Observatory (GBO), Reichart & Stephens (2000) found that the radio source Cassiopeia A had either faded more slowly between the mid-1970s and late 1990s than Baars et al. (1977) had found it to be fading between the late 1940s and mid-1970s, or that it had rebrightened and then resumed fading sometime between the mid-1970s and mid-1990s, in L band (1.4 GHz). Here, we present 15 additional years of observations of Cas A and Cyg A with the 40-foot in L band, and three and a half additional years of observations of Cas A, Cyg A, Tau A, and Vir A with GBOs recently refurbished 20-meter telescope in L and X (9 GHz) bands. We also present a more sophisticated analysis of the 40-foot data, and a reanalysis of the Baars et al. (1977) data, which reveals small, but non-negligible differences. We find that overall, between the late 1950s and late 2010s, Cas A faded at an average rate of

Searching for Long-Period Variables in Globular Clusters: A Demonstration on NGC 1851 Using PROMPT

0.670 pm 0.019

Robust Chauvenet Outlier Rejection

%/yr in L band, consistent with Reichart & Stephens (2000). However, we also find, at the 6.3

Orbital and physical parameters of eclipsing binaries from the ASAS catalogue - IV. A 0.61 + 0.45 M_sun binary in a multiple system

sigma

An Observing Campaign of the Mutual Events Within (617) Patroclus-Menoetius Binary Trojan System

credible level, that it did not fade at a constant rate. Rather, Cas A faded at a faster rate through at least the late 1960s, rebrightened (or at least faded at a much slower rate), and then resumed fading at a similarly fast rate by, at most, the late 1990s. Given these differences from the original Baars et al. (1977) analysis, and given the importance of their fitted spectral and temporal models for flux-density calibration in radio astronomy, we update and improve on these models for all four of these radio sources. In doing so, we additionally find that Tau A is fading at a rate of

Lightcurve Analysis of 5899 Jedicke: A New Hungaria Binary

0.102^{+0.042}_{-0.043}

Two-site photometry and spectroscopy of the rapidly pulsating sdB star EC 22221-3152

%/yr in L band.

GRB 130831A: Rise and demise of a magnetar at z = 0.5

We demonstrate how a small, robotically controlled telescope can be used to monitor bright, long- period variable stars in dense stellar systems like Galactic globular clusters. Observations of NGC 1851 gathered with the No. 5 PROMPT 0.4 m telescope in BV RI yielded quality color-magnitude diagrams to well below the horizontal branch at V ¼ 16:1 mag. We recovered many of the known RR Lyrae variables, clarified the nature of the three known bright variables in the cluster, detected two new long-period variables, and flagged seven more sus- pected variables. We describe methods that should yield good results in variable star searches and monitoring using this and other small telescopes. Online material: color figures, extended table

Pluto's atmosphere from stellar occultations in 2012 and 2013

Sigma clipping is commonly used in astronomy for outlier rejection, but the number of standard deviations beyond which one should clip data from a sample ultimately depends on the size of the sample. Chauvenet rejection is one of the oldest, and simplest, ways to account for this, but, like sigma clipping, depends on the samples mean and standard deviation, neither of which are robust quantities: Both are easily contaminated by the very outliers they are being used to reject. Many, more robust measures of central tendency, and of sample deviation, exist, but each has a tradeoff with precision. Here, we demonstrate that outlier rejection can be both very robust and very precise if decreasingly robust but increasingly precise techniques are applied in sequence. To this end, we present a variation on Chauvenet rejection that we call robust Chauvenet rejection (RCR), which uses three decreasingly robust/increasingly precise measures of central tendency, and four decreasingly robust/increasingly precise measures of sample deviation. We show this sequential approach to be very effective for a wide variety of contaminant types, even when a significant -- even dominant -- fraction of the sample is contaminated, and especially when the contaminants are strong. Furthermore, we have developed a bulk-rejection variant, to significantly decrease computing times, and RCR can be applied both to weighted data, and when fitting parameterized models to data. We present aperture photometry in a contaminated, crowded field as an example. RCR may be used by anyone at this https URL, and source code is available there as well.