2,440 research outputs found
1.3 mm Polarized emission in the circumstellar disk of a massive protostar
We present the first resolved observations of the 1.3 mm polarized emission from the disk-like structure surrounding the high-mass protostar Cepheus A HW2. These CARMA data partially resolve the dust polarization, suggesting a uniform morphology of polarization vectors with an average position angle of 57° ± 6° and an average polarization fraction of 2.0% ± 0.4%. The distribution of the polarization vectors can be attributed to (1) the direct emission of magnetically aligned grains of dust by a uniform magnetic field, or (2) the pattern produced by the scattering of an inclined disk. We show that both models can explain the observations, and perhaps a combination of the two mechanisms produces the polarized emission. A third model including a toroidal magnetic field does not match the observations. Assuming scattering is the polarization mechanism, these observations suggest that during the first few 104 years of high-mass star formation, grain sizes can grow from1 mm to several 10s μm.Fil: Fernandez Lopez, Manuel. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomia; ArgentinaFil: Stephens, I. W.. Harvard-Smithsonian Center for Astrophysics; Estados Unidos. Boston University; Estados Unidos. University of Illinois; Estados UnidosFil: Girart, J. M.. Harvard-Smithsonian Center for Astrophysics; Estados Unidos. Institut de Ciències de l’Espai; EspañaFil: Looney, L.. University of Illinois; Estados UnidosFil: Curiel, S.. Universidad Nacional Autónoma de México; MéxicoFil: Segura Cox, D.. University of Illinois; Estados UnidosFil: Eswaraiah, C.. National Tsing Hua University; República de ChinaFil: Lai, S. P.. National Tsing Hua University; República de Chin
A new radiative cooling curve based on an up to date plasma emission code
This work presents a new plasma cooling curve that is calculated using the
SPEX package. We compare our cooling rates to those in previous works, and
implement the new cooling function in the grid-adaptive framework `AMRVAC'.
Contributions to the cooling rate by the individual elements are given, to
allow for the creation of cooling curves tailored to specific abundance
requirements. In some situations, it is important to be able to include
radiative losses in the hydrodynamics. The enhanced compression ratio can
trigger instabilities (such as the Vishniac thin-shell instability) that would
otherwise be absent. For gas with temperatures below 10,000 K, the cooling time
becomes very long and does not affect the gas on the timescales that are
generally of interest for hydrodynamical simulations of circumstellar plasmas.
However, above this temperature, a significant fraction of the elements is
ionised, and the cooling rate increases by a factor 1000 relative to lower
temperature plasmas.Comment: 11 pages, 6 figures. Typos fixed to match version on A&A
'forthcoming' website. Tables in text format online available at
http://www.phys.uu.nl/~schure/coolin
Finding substructures in protostellar disks in Ophiuchus
High-resolution, millimeter observations of disks at the protoplanetary stage
reveal substructures such as gaps, rings, arcs, spirals, and cavities. While
many protoplanetary disks host such substructures, only a few at the younger
protostellar stage have shown similar features. We present a detailed search
for early disk substructures in ALMA 1.3 and 0.87~mm observations of ten
protostellar disks in the Ophiuchus star-forming region. Of this sample, four
disks have identified substructure, two appear to be smooth disks, and four are
considered ambiguous. The structured disks have wide Gaussian-like rings
() with low contrasts () above a
smooth disk profile, in comparison to protoplanetary disks where rings tend to
be narrow and have a wide variety of contrasts
( and ranges from ). The four
protostellar disks with the identified substructures are among the brightest
sources in the Ophiuchus sample, in agreement with trends observed for
protoplanetary disks. These observations indicate that substructures in
protostellar disks may be common in brighter disks. The presence of
substructures at the earliest stages suggests an early start for dust grain
growth and, subsequently, planet formation. The evolution of these protostellar
substructures is hypothesized in two potential pathways: (1) the rings are the
sites of early planet formation, and the later observed protoplanetary disk
ring-gap pairs are secondary features, or (2) the rings evolve over the disk
lifetime to become those observed at the protoplanetary disk stage.Comment: Accepted by ApJ, 22 pages, 10 figure
CARMA Large Area Star Formation Survey: Observational Analysis of Filaments in the Serpens South Molecular Cloud
We present the N2H+(J=1-0) map of the Serpens South molecular cloud obtained
as part of the CARMA Large Area Star Formation Survey (CLASSy). The
observations cover 250 square arcminutes and fully sample structures from 3000
AU to 3 pc with a velocity resolution of 0.16 km/s, and they can be used to
constrain the origin and evolution of molecular cloud filaments. The spatial
distribution of the N2H+ emission is characterized by long filaments that
resemble those observed in the dust continuum emission by Herschel. However,
the gas filaments are typically narrower such that, in some cases, two or three
quasi-parallel N2H+ filaments comprise a single observed dust continuum
filament. The difference between the dust and gas filament widths casts doubt
on Herschel ability to resolve the Serpens South filaments. Some molecular
filaments show velocity gradients along their major axis, and two are
characterized by a steep velocity gradient in the direction perpendicular to
the filament axis. The observed velocity gradient along one of these filaments
was previously postulated as evidence for mass infall toward the central
cluster, but these kind of gradients can be interpreted as projection of
large-scale turbulence.Comment: 12 pages, 4 figures, published in ApJL (July 2014
Are Proto-Planetary Nebulae Shaped by a Binary? Results of a Long-Term Radial Velocity Study
The shaping of the nebula is currently one of the outstanding unsolved
problems in planetary nebula (PN) research. Several mechanisms have been
proposed, most of which require a binary companion. However, direct evidence
for a binary companion is lacking in most PNs. We have addressed this problem
by obtaining precise radial velocities of seven bright proto-planetary nebulae
(PPNs), objects in transition from the asymptotic giant branch to the PN phases
of stellar evolution. These have F-G spectral types and have the advantage over
PNs of having more and sharper spectral lines, leading to better precision. Our
observations were made in two observing intervals, 1991-1995 and 2007-2010, and
we have included in our analysis some additional published and unpublished
data. Only one of the PPNs, IRAS 22272+5435, shows a long-term variation that
might tentatively be attributed to a binary companion, with P 22 years, and
from this, limiting binary parameters are calculated. Selection effects are
also discussed. These results set significant restrictions on the range of
possible physical and orbital properties of any binary companions: they have
periods greater than 25 years or masses of brown dwarfs or super-Jupiters.
While not ruling out the binary hypothesis, it seems fair to say that these
results do not support it.Comment: 14 pages, 3 figures, to appear Astrophys J, 734 (2011 June 10
Estudios interferométricos del campo magnético en regiones de formación estelar: observaciones milimétricas con CARMA
Currently, the possible role of magnetic fields in star formation processes is not clear. Despite the efforts made through single-dish observations, a stronger observational effort is required in order to broaden the sample of detections and acquire more insight into the morphology of the magnetic field at high-angular resolution scales. Here we present some results obtained from CARMA 1.25 mm continuum and spectral line polarization observations. The target of these observations were two accretion disks around a Class 0 (L1527) and a T Tauri (HL Tau) protostar and the massive star-forming region W3OH. We resolved the morphology of the magnetic field in both disks and, in W3OH, we achieved the first Zeeman detection ever made with an interferometer.Fil: Fernandez Lopez, Manuel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina. University of Illinois at Urbana; Estados UnidosFil: Stephens, Ian. University Of Boston. Departament Astronomy. Center For Space Physics; Estados UnidosFil: Segura Cox, D.. University of Illinois at Urbana; Estados UnidosFil: Crutcher, R.. University of Illinois at Urbana; Estados UnidosFil: Looney, L. W.. University of Illinois at Urbana; Estados UnidosFil: Kwon, W.. Sron Netherlands Institute For Space Research; Países BajosReunión de la Asociación Argentina de AstronomíaCórdobaArgentinaInstituto de Astronomía Teórica y ExperimentalUniversidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimenta
Flow of gas detected from beyond the filaments to protostellar scales in Barnard 5
Infall of gas from outside natal cores has proven to feed protostars after
the main accretion phase (Class 0). This changes our view of star formation to
a picture that includes asymmetric accretion (streamers), and a larger role of
the environment. However, the connection between streamers and the filaments
that prevail in star-forming regions is unknown. We investigate the flow of
material toward the filaments within Barnard 5 (B5) and the infall from the
envelope to the protostellar disk of the embedded protostar B5-IRS1. Our goal
is to follow the flow of material from the larger, dense core scale, to the
protostellar disk scale. We present new HCN line data from the NOEMA and
30m telescopes covering the coherence zone of B5, together with ALMA HCO
and CO maps toward the protostellar envelope. We fit multiple Gaussian
components to the lines so as to decompose their individual physical
components. We investigate the HCN velocity gradients to determine the
direction of chemically-fresh gas flow. At envelope scales, we use a clustering
algorithm to disentangle the different kinematic components within HCO
emission. At dense core scales, HCN traces the infall from the B5 region
toward the filaments. HCN velocity gradients are consistent with accretion
toward the filament spines plus flow along them. We found a au
streamer in HCO emission which is blueshifted with respect to the protostar
and deposits gas at outer disk scales. The strongest velocity gradients at
large scales curve toward the position of the streamer at small scales,
suggesting a connection between both flows. Our analysis suggests that the gas
can flow from the dense core to the protostar. This implies that the mass
available for a protostar is not limited to its envelope, and can receiving
chemically-unprocessed gas after the main accretion phase.Comment: 25 pages, 27 figures, accepted for publication on Astronomy and
Astrophysics. The scripts used for analysis can be seen at
https://github.com/tere-valdivia/Barnard_5_infal
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