27 research outputs found
Optimal spectral lines for measuring chromospheric magnetic fields
This paper identifies spectral lines from X-ray to infrared wavelengths which
are optimally suited to measuring vector magnetic fields as high as possible in
the solar atmosphere. Instrumental and Earth's atmospheric properties, as well
as solar abundances, atmospheric properties and elementary atomic physics are
considered without bias towards particular wavelengths or diagnostic
techniques. While narrowly-focused investigations of individual lines have been
reported in detail, no assessment of the comparative merits of all lines has
ever been published. Although in the UV, on balance the Mg+ h and k lines near
2800 Angstroms are optimally suited to polarimetry of plasma near the base of
the solar corona. This result was unanticipated, given that longer-wavelength
lines offer greater sensitivity to the Zeeman effect. While these lines sample
optical depths photosphere to the coronal base, we argue that cores of multiple
spectral lines provide a far more discriminating probe of magnetic structure as
a function of optical depth than the core and inner wings of a strong line.
Thus, together with many chromospheric lines of Fe+ between 2585 and the h line
at 2803 Angstrom, this UV region promises new discoveries concerning how the
magnetic fields emerge, heat, and accelerate plasma as they battle to dominate
the force and energy balance within the poorly-understood chromosphere.Comment: Accepted for publication in the Astrophysical Journal. 12 pages, 2
figures, and 1 tabl
739 observed NEAs and new 2-4m survey statistics within the EURONEAR network
We report follow-up observations of 477 program Near-Earth Asteroids (NEAs)
using nine telescopes of the EURONEAR network having apertures between 0.3 and
4.2 m. Adding these NEAs to our previous results we now count 739 program NEAs
followed-up by the EURONEAR network since 2006. The targets were selected using
EURONEAR planning tools focusing on high priority objects. Analyzing the
resulting orbital improvements suggests astrometric follow-up is most important
days to weeks after discovery, with recovery at a new opposition also valuable.
Additionally we observed 40 survey fields spanning three nights covering 11 sq.
degrees near opposition, using the Wide Field Camera on the 2.5m Isaac Newton
Telescope (INT), resulting in 104 discovered main belt asteroids (MBAs) and
another 626 unknown one-night objects. These fields, plus program NEA fields
from the INT and from the wide field MOSAIC II camera on the Blanco 4m
telescope, generated around 12,000 observations of 2,000 minor planets (mostly
MBAs) observed in 34 square degrees. We identify Near Earth Object (NEO)
candidates among the unknown (single night) objects using three selection
criteria. Testing these criteria on the (known) program NEAs shows the best
selection methods are our epsilon-miu model which checks solar elongation and
sky motion and the MPC's NEO rating tool. Our new data show that on average 0.5
NEO candidates per square degree should be observable in a 2m-class survey (in
agreement with past results), while an average of 2.7 NEO candidates per square
degree should be observable in a 4m-class survey (although our Blanco
statistics were affected by clouds). At opposition just over 100 MBAs (1.6
unknown to every 1 known) per square degree are detectable to R=22 in a 2m
survey based on the INT data, while our two best ecliptic Blanco fields away
from opposition lead to 135 MBAs (2 unknown to every 1 known) to R=23.Comment: Published in Planetary and Space Sciences (Sep 2013
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Advancing solar and heliospheric science through the ongoing development and support of atomic and laboratory plasma physics
Peer reviewed: TrueAcknowledgements: A modified version of this paper was submitted to the 2024 Solar and Space Physics Decadal Survey and is published in the associated issue of the Bulletin of the American Astronomical Society.This paper outlines the necessity for the availability, accessibility, and expansion of atomic physics data and analysis tools for the meaningful interpretation of spectroscopic and polarimetric observations. As we move towards observing the Sun at higher spatio-temporal resolutions, and near-continuously at a range of wavelengths, it becomes critical to develop the appropriate atomic data and physics tools to facilitate scientific progress. We recommend the continued improvement and expansion of current databases to support the development of optically-thick/radiative transfer models, evaluate non-thermal and non-equilibrium ionization effects, and quantify uncertainties in atomic and molecular values. A critical long-term goal will require extending and strengthening collaborations across the atomic, solar/heliospheric, and laboratory plasma physics communities through the participation and training of early career scientists. We also recommend establishing funding for a centralized atomic physics resource made up of a comprehensive and user-oriented atomic database and modeling framework