46 research outputs found
Pickup ion measurements by MAVEN: A diagnostic of photochemical oxygen escape from Mars
A key process populating the oxygen exosphere at Mars is the dissociative recombination of ionospheric O 2 + , which produces fast oxygen atoms, some of which have speeds exceeding the escape speed and thus contribute to atmospheric loss. Theoretical studies of this escape process have been carried out and predictions made of the loss rate; however, directly measuring the escaping neutral oxygen is difficult but essential. This paper describes how energetic pickup ion measurements to be made near Mars by the SEP (Solar Energetic Particle) instrument on board the MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft can be used to constrain models of photochemical oxygen escape. In certain solar wind conditions, neutral oxygen atoms in the distant Martian exosphere that are ionized and picked up by the solar wind can reach energies high enough to be detected near Mars by SEP. Key Points Photochemical hot oxygen escape rate at Mars is predicted Martian exospheric neutral oxygen model is constructed Pickup ion fluxes measured by SEP will constrain neutral oxygen escape from MarsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108375/1/grl51888.pd
Rosetta-Alice Observations of Exospheric Hydrogen and Oxygen on Mars
The European Space Agency's Rosetta spacecraft, en route to a 2014 encounter
with comet 67P/Churyumov-Gerasimenko, made a gravity assist swing-by of Mars on
25 February 2007, closest approach being at 01:54UT. The Alice instrument on
board Rosetta, a lightweight far-ultraviolet imaging spectrograph optimized for
in situ cometary spectroscopy in the 750-2000 A spectral band, was used to
study the daytime Mars upper atmosphere including emissions from exospheric
hydrogen and oxygen. Offset pointing, obtained five hours before closest
approach, enabled us to detect and map the HI Lyman-alpha and Lyman-beta
emissions from exospheric hydrogen out beyond 30,000 km from the planet's
center. These data are fit with a Chamberlain exospheric model from which we
derive the hydrogen density at the 200 km exobase and the H escape flux. The
results are comparable to those found from the the Ultraviolet Spectrometer
experiment on the Mariner 6 and 7 fly-bys of Mars in 1969. Atomic oxygen
emission at 1304 A is detected at altitudes of 400 to 1000 km above the limb
during limb scans shortly after closest approach. However, the derived oxygen
scale height is not consistent with recent models of oxygen escape based on the
production of suprathermal oxygen atoms by the dissociative recombination of
O2+.Comment: 17 pages, 8 figures, accepted for publication in Icaru
Solar cycle variability of Mars dayside exospheric temperatures: Model evaluation of underlying thermal balances
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95086/1/grl25450.pd
ALMA-IMF IX: Catalog and Physical Properties of 315 SiO Outflow Candidates in 15 Massive Protoclusters
We present a catalog of 315 protostellar outflow candidates detected in SiO
J=5-4 in the ALMA-IMF Large Program, observed with ~2000 au spatial resolution,
0.339 km/s velocity resolution, and 2-12 mJy/beam (0.18-0.8 K) sensitivity. We
find median outflow masses, momenta, and kinetic energies of ~0.3 M,
4 M km/s, and 10 erg, respectively. Median outflow lifetimes
are 6,000 years, yielding median mass, momentum, and energy rates of
= 10 M yr, = 10 M km/s
yr, and = 1 L. We analyze these outflow properties
in the aggregate in each field. We find correlations between field-aggregated
SiO outflow properties and total mass in cores (~35), and no
correlations above 3 with clump mass, clump luminosity, or clump
luminosity-to-mass ratio. We perform a linear regression analysis and find that
the correlation between field-aggregated outflow mass and total clump mass -
which has been previously described in the literature - may actually be
mediated by the relationship between outflow mass and total mass in cores. We
also find that the most massive SiO outflow in each field is typically
responsible for only 15-30% of the total outflow mass (60% upper limit). Our
data agree well with the established mechanical force-bolometric luminosity
relationship in the literature, and our data extend this relationship up to L
10 L and 1 M km/s yr.
Our lack of correlation with clump L/M is inconsistent with models of
protocluster formation in which all protostars start forming at the same time.Comment: 46 pages, 14 figures, 10 tables. This publication has an associated
Zenodo entry, which can be found here: https://zenodo.org/records/835059
ALMA-IMF. VII. First release of the full spectral line cubes: Core kinematics traced by DCN J=(3-2)
ALMA-IMF is an Atacama Large Millimeter/submillimeter Array (ALMA) Large
Program designed to measure the core mass function (CMF) of 15 protoclusters
chosen to span their early evolutionary stages. It further aims to understand
their kinematics, chemistry, and the impact of gas inflow, accretion, and
dynamics on the CMF. We present here the first release of the ALMA-IMF line
data cubes (DR1), produced from the combination of two ALMA 12m-array
configurations. The data include 12 spectral windows, with eight at 1.3mm and
four at 3mm. The broad spectral coverage of ALMA-IMF (~6.7 GHz bandwidth
coverage per field) hosts a wealth of simple atomic, molecular, ionised, and
complex organic molecular lines. We describe the line cube calibration done by
ALMA and the subsequent calibration and imaging we performed. We discuss our
choice of calibration parameters and optimisation of the cleaning parameters,
and we demonstrate the utility and necessity of additional processing compared
to the ALMA archive pipeline. As a demonstration of the scientific potential of
these data, we present a first analysis of the DCN (3-2) line. We find that DCN
traces a diversity of morphologies and complex velocity structures, which tend
to be more filamentary and widespread in evolved regions and are more compact
in the young and intermediate-stage protoclusters. Furthermore, we used the DCN
(3-2) emission as a tracer of the gas associated with 595 continuum cores
across the 15 protoclusters, providing the first estimates of the core systemic
velocities and linewidths within the sample. We find that DCN (3-2) is detected
towards a higher percentage of cores in evolved regions than the young and
intermediate-stage protoclusters and is likely a more complete tracer of the
core population in more evolved protoclusters. The full ALMA 12m-array cubes
for the ALMA-IMF Large Program are provided with this DR1 release.Comment: 75 pages (21 main body; 54 appendix), 37 figures. The ALMA-IMF DR1
line release is hosted at https://dataverse.harvard.edu/dataverse/alma-im
ALMA-IMF. IX. Catalog and physical properties of 315 SiO outflow candidates in 15 massive protoclusters
We present a catalog of 315 protostellar outflow candidates detected in SiO J = 5 − 4 in the ALMA-IMF Large Program, observed with ∼2000 au spatial resolution, 0.339 km s−1 velocity resolution, and 2–12 mJy beam−1 (0.18–0.8 K) sensitivity. We find median outflow masses, momenta, and kinetic energies of ∼0.3 M ⊙, 4 M ⊙ km s−1, and 1045 erg, respectively. Median outflow lifetimes are 6000 yr, yielding median mass, momentum, and energy rates of Ṁ = 10−4.4 M ⊙ yr−1, Ṗ = 10−3.2 M ⊙ km s−1 yr−1, and Ė = 1 L ⊙. We analyze these outflow properties in the aggregate in each field. We find correlations between field-aggregated SiO outflow properties and total mass in cores (∼3σ–5σ), and no correlations above 3σ with clump mass, clump luminosity, or clump luminosity-to-mass ratio. We perform a linear regression analysis and find that the correlation between field-aggregated outflow mass and total clump mass—which has been previously described in the literature—may actually be mediated by the relationship between outflow mass and total mass in cores. We also find that the most massive SiO outflow in each field is typically responsible for only 15%–30% of the total outflow mass (60% upper limit). Our data agree well with the established mechanical force−bolometric luminosity relationship in the literature, and our data extend this relationship up to L ≥ 106 L ⊙ and Ṗ ≥ 1 M ⊙ km s−1 yr−1. Our lack of correlation with clump L/M is inconsistent with models of protocluster formation in which all protostars start forming at the same time
ALMA-IMF XII. Point-process mapping of 15 massive protoclusters⋆
Context. A crucial aspect in addressing the challenge of measuring the core mass function (CMF), that is pivotal for comprehending the origin of the initial mass function (IMF), lies in constraining the temperatures of the cores.
Aims. We aim to measure the luminosity, mass, column density and dust temperature of star-forming regions imaged by the ALMA-IMF large program. These fields were chosen to encompass early evolutionary stages of massive protoclusters. High angular resolution mapping is required to capture the properties of protostellar and pre-stellar cores within these regions, and to effectively separate them from larger features, such as dusty filaments.
Methods. We employed the point process mapping (PPMAP) technique, enabling us to perform spectral energy distribution fitting of far-infrared and submillimeter observations across the 15 ALMA-IMF fields, at an unmatched 2.5″ angular resolution. By combining the modified blackbody model with near-infrared data, we derived bolometric luminosity maps. We estimated the errors impacting values of each pixel in the temperature, column density, and luminosity maps. Subsequently, we employed the extraction algorithm getsf on the luminosity maps in order to detect luminosity peaks and measure their associated masses.
Results. We obtained high-resolution constraints on the luminosity, dust temperature, and mass of protoclusters, that are in agreement with previously reported measurements made at a coarser angular resolution. We find that the luminosity-to-mass ratio correlates with the evolutionary stage of the studied regions, albeit with intra-region variability. We compiled a PPMAP source catalog of 313 luminosity peaks using getsf on the derived bolometric luminosity maps. The PPMAP source catalog provides constraints on the mass and luminosity of protostars and cores, although one source may encompass several objects. Finally, we compare the estimated luminosity-to-mass ratio of PPMAP sources with evolutionary tracks and discuss the limitations imposed by the 2.5″ beam