101 research outputs found
Distances and Kinematics of Gould Belt Star-Forming Regions with Gaia DR2 results
We present an analysis of the astrometric results from Gaia second data
release (DR2) to Young Stellar Objects (YSOs) in star-forming regions related
to the Gould Belt. These regions are Barnard 59, Lupus 1 to 4, Chamaeleon I and
II, -Chamaeleontis, the Cepheus flare, IC 5146 and Corona Australis.
The mean distance to the YSOs in each region are consistent with earlier
estimations, though a significant improvement to the final errors was obtained.
The mean distances to the star-forming regions were used to fit an ellipsoid of
size pc, and centered at
pc, consistent with recently
determined parameter of the Gould Belt. The mean proper motions were combined
with radial velocities from the literature to obtain the three dimensional
motion of the star-forming regions, which are consistent with a general
expansion of the Gould Belt. We estimate that this expansion is occurring at a
velocity of km s. This is the first time that YSOs motions
are used to investigate the kinematic of the Gould Belt. As an interesting side
result, we also identified stars with large peculiar velocities.Comment: 18 pages, 14 figures, and 5 tables. Accepted for publication in The
Astrophysical Journa
Radio Proper Motions of the Nearby Ultra-cool dwarf binary VHS 12561257AB
The proper motions of a source obtained at different epochs or in different
spectral regions should in principle be consistent. However, in the case of a
binary source or a source with associated ejecta, they could be different
depending on the epochs when the observations were made and on what emission is
traced in each spectral region. In this paper we determine the radio proper
motions of the ultra-cool dwarf binary VHS 12561257AB from Very Large Array
(VLA) observations, that we find are consistent within error ()
with those reported by Gaia DR3. The comparison of the proper motions and the
analysis of the VLA data imply that, as in the optical, the radio emission is
coming in comparable amounts from both components of the unresolved binary.Comment: 8 pages, 3 figures. To appear in Revista Mexicana de Astronomia y
Astrofisic
From downtown to the outskirts: A radio survey of the Orion Nebula Cluster
© The Author(s) 2021. Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.We present a newly enlarged census of the compact radio population towards the Orion Nebula Cluster (ONC) using high-sensitivity continuum maps (3-10 μ Jy beam-1) from a total of ∼30-h centimetre-wavelength observations over an area of ∼20 × 20 arcmin2 obtained in the C-band (4-8 GHz) with the Karl G. Jansky Very Large Array (VLA) in its high-resolution A-configuration. We thus complement our previous deep survey of the innermost areas of the ONC, now covering the field of view of the Chandra Orion Ultra-deep Project (COUP). Our catalogue contains 521 compact radio sources of which 198 are new detections. Overall, we find that 17 per cent of the (mostly stellar) COUP sources have radio counterparts, while 53 per cent of the radio sources have COUP counterparts. Most notably, the radio detection fraction of X-ray sources is higher in the inner cluster and almost constant for r > 3 arcmin (0.36 pc) from θ1 Ori C, suggesting a correlation between the radio emission mechanism of these sources and their distance from the most massive stars at the centre of the cluster, e.g. due to increased photoionisation of circumstellar discs. The combination with our previous observations 4 yr prior lead to the discovery of fast proper motions of up to ∼373 km s-1 from faint radio sources associated with ejecta of the OMC1 explosion. Finally, we search for strong radio variability. We found changes in flux density by a factor of ≲5 within our observations and a few sources with changes by a factor >10 on long time-scales of a few years.Peer reviewe
Searching for compact radio sources associated to UCHII regions
Ultra-Compact (UC)HII regions represent a very early stage of massive star
formation whose structure and evolution are not yet fully understood.
Interferometric observations in recent years show that some UCHII regions have
associated compact sources of uncertain nature. Based on this, we carried out
VLA 1.3 cm observations in the A configuration of selected UCHII regions in
order to report additional cases of compact sources embedded in UCHII regions.
From the observations, we find 13 compact sources associated to 9 UCHII
regions. Although we cannot establish an unambiguous nature for the newly
detected sources, we assess some of their observational properties. According
to the results, we can distinguish between two types of compact sources. One
type corresponds to sources that probably are deeply embedded in the dense
ionized gas of the UCHII region. These sources are being photo-evaporated by
the exciting star of the region and will last for 10 yr. They may play
a crucial role in the evolution of the UCHII region as the photo-evaporated
material could replenish the expanding plasma and might provide a solution to
the so-called lifetime problem for these regions. The second type of compact
sources is not associated with the densest ionized gas of the region. A few of
these sources appear resolved and may be photo-evaporating objects such as
those of the first type but with significantly lower mass depletion rates. The
rest of sources of this second type appear unresolved and their properties are
varied. We speculate on the similarity between the sources of the second type
and those of the Orion population of radio sources.Comment: 33 pages, 6 figures, 4 tables. Accepted for publication in Ap
Internal and relative motions of the Taurus and Ophiuchus star-forming regions
We investigate the internal and relative motions of the Taurus and Ophiuchus
star-forming regions using a sample of young stars with accurately measured
radial velocities and proper motions. We find no evidence for expansion or
contraction of the Taurus complex, but a clear indication for a global
rotation, resulting in velocity gradients, this suggests a common origin,
possibly related to that of Gould's Belt.Comment: 2 figure
Multi-Epoch VLBA Observations of the Compact Wind-Collision Region in the Quadruple System Cyg OB2 #5
We present multi--epoch VLBA observations of the compact wind collision
region in the Cyg OB2 #5 system. These observation confirm the arc-shaped
morphology of the emission reported earlier. The total flux as a function of
time is roughly constant when the source is "on", but falls below the detection
limit as the wind collision region approaches periastron in its orbit around
the contact binary at the center of the system. In addition, at one of the "on"
epochs, the flux drops to about a fifth of its average value. We suggest that
this apparent variation could result from the inhomogeneity of the wind that
hides part of the flux rather than from an intrinsic variation. We measured a
trigonometrical parallax, for the most compact radio emission of 0.61
0.22 mas, corresponding to a distance of 1.65 kpc, in
agreement with recent trigonometrical parallaxes measured for objects in the
Cygnus X complex. Using constraints on the total mass of the system and orbital
parameters previously reported in the literature, we obtain two independent
indirect measurements of the distance to the Cyg OB2 #5 system, both consistent
with 1.3--1.4 kpc. Finally, we suggest that the companion star responsible for
the wind interaction, yet undetected, is of spectral type between B0.5 to O8.Comment: manuscript format, 24 pages, 5 figures, accepted for publication in
The Astrophysical Journa
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