439 research outputs found
On Measuring Accurate 21-cm Line Profiles with the Robert C. Byrd Green Bank Telescope
We use observational data to show that 21 cm line profiles measured with the
Green Bank Telescope (GBT) are subject to significant inaccuracy. These include
~10% errors in the calibrated gain and significant contribution from distant
sidelobes. In addition, there are ~60% variations between the GBT and
Leiden/Argentine/Bonn 21 cm line profile intensities, which probably occur
because of the high main-beam efficiency of the GBT. Stokes V profiles from the
GBT contain inaccuracies that are related to the distant sidelobes.
We illustrate these problems, define physically motivated components for the
sidelobes, and provide numerical results showing the inaccuracies. We provide a
correction scheme for Stokes I 21 cm line profiles that is fairly successful
and provide some rule-of-thumb comments concerning the accuracy of Stokes V
profiles.Comment: 39 pages, 20 figures, accepted for publication in PAS
Recommended from our members
Reducing the Odds: an Educational Board Game for the Repatriation of Cambodian Refugees
HI Imaging of LGS 3 and an Apparently Interacting High-Velocity Cloud
We present a 93' by 93' map of the area near the Local Group dwarf galaxy LGS
3, centered on an HI cloud 30' away from the galaxy. Previous authors
associated this cloud with LGS 3 but relied on observations made with a 36'
beam. Our high-resolution (3.4'), wide-field Arecibo observations of the region
reveal that the HI cloud is distinct from the galaxy and suggest an interaction
between the two. We point out faint emission features in the map that may be
gas that has been tidally removed from the HI cloud by LGS 3. We also derive
the rotation curve of the cloud and find that it is in solid-body rotation out
to a radius of 10', beyond which the rotation velocity begins to decline.
Assuming a spherical geometry for the cloud, the implied mass is 2.8 x 10^7
(d/Mpc) M_{Sun}, where d is the distance in Mpc. The observed HI mass is 5.5 x
10^6 (d/Mpc)^2 M_{Sun}, implying that the cloud is dark-matter dominated unless
its distance is at least 1.9 Mpc. We propose that the cloud is a high-velocity
cloud that is undergoing a tidal interaction with LGS 3 and therefore is
located roughly 700 kpc away from the Milky Way. The cloud then contains a
total mass of ~2.0 x 10^7 M_{Sun}, 82% of which consists of dark matter.Comment: 5 pages, 2 color figures. Accepted for publication in ApJ Letter
Introduction to Open Scholarship (Library Workshop)
Learning objectives: What is open science? Background/context for emerging open landscape Funder mandates Review “Open” concepts Significance for Rowan University Challenges for open scholarship Available resources at Rowan Examples of open practice
Parsec-scale magnetic fields in Arp 220
We present the first very-long-baseline interferometry (VLBI) detections of
Zeeman splitting in another galaxy. We used Arecibo Observatory, the Green Bank
Telescope, and the Very Long Baseline Array to perform dual-polarization
observations of OH maser lines in the merging galaxy Arp 220. We measured
magnetic fields of 1-5 mG associated with three roughly parsec-sized
clouds in the nuclear regions of Arp 220. Our measured magnetic fields have
comparable strengths and the same direction as features at the same velocity
identified in previous Zeeman observations with Arecibo alone. The agreement
between single dish and VLBI results provides critical validation of previous
Zeeman splitting observations of OH megamasers that used a single large dish.
The measured magnetic field strengths indicate that magnetic energy densities
are comparable to gravitational energy in OH maser clouds. We also compare our
total intensity results to previously published VLBI observations of OH
megamasers in Arp 220. We find evidence for changes in both structure and
amplitude of the OH maser lines that are most easily explained by variability
intrinsic to the masing region, rather than variability produced by
interstellar scintillation. Our results demonstrate the potential for using
high-sensitivity VLBI to study magnetic fields on small spatial scales in
extragalactic systems.Comment: 9 pages, accepted to MNRA
G protein beta gamma subunits synthesized in Sf9 cells. Functional characterization and the significance of prenylation of gamma
Heterotrimeric guanine nucleotide-binding regulatory proteins (G proteins) consist of a nucleotide-binding alpha subunit and a high- affinity complex of beta and gamma subunits. There is molecular heterogeneity of beta and gamma, but the significance of this diversity is poorly understood. Different G protein beta and gamma subunits have been expressed both singly and in combinations in Sf9 cells. Although expression of individual subunits is achieved in all cases, beta gamma subunit activity (support of pertussis toxin-catalyzed ADP-ribosylation of rGi alpha 1) is detected only when beta and gamma are expressed concurrently. Of the six combinations of beta gamma tested (beta 1 or beta 2 with gamma 1, gamma 2, or gamma 3), only one, beta 2 gamma 1, failed to generate a functional complex. Each of the other five complexes has been purified by subunit exchange chromatography using Go alpha-agarose as the chromatographic matrix. We have detected differences in the abilities of the purified proteins to support ADP- ribosylation of Gi alpha 1; these differences are attributable to the gamma component of the complex. When assayed for their ability to inhibit calmodulin-stimulated type-I adenylylcyclase activity or to potentiate Gs alpha-stimulated type-II adenylylcyclase, recombinant beta 1 gamma 1 and transducin beta gamma are approximately 10 and 20 times less potent, respectively, than the other complexes examined. Prenylation and/or further carboxyl-terminal processing of gamma are not required for assembly of the beta gamma subunit complex but are indispensable for high affinity interactions of beta gamma with either G protein alpha subunits or adenylylcyclases
- …