288 research outputs found
Observations of extragalactic masers in bright IRAS sources
We report the first results of an ongoing survey at 22 GHz with the 100-m
Effelsberg telescope to search for water maser emission in bright IRAS sources.
We have detected water vapor emission in IC 342. The maser, associated with a
star forming region ~10-15 arcsec west of the nucleus, consists of a single 0.5
km/s wide feature and reaches an isotropic luminosity of 0.01 L(sun) (D = 1.8
Mpc). Our detection raises the detection rate among northern galaxies with IRAS
point source fluxes S(100micron) > 50 Jy to 16%.Comment: 6 pages, 3 figures. Proceeding of the conference "SRT: the impact of
large antennas on Radio Astronomy and Space Science", Cagliari, Italy, 7-10
Nov. 2001, Eds. Porceddu et al. Needs srt_style.st
Infrared variability, maser activity, and accretion of massive young stellar objects
Methanol and water masers indicate young stellar objects. They often exhibit
flares, and a fraction shows periodic activity. Several mechanisms might
explain this behavior but the lack of concurrent infrared (IR) data complicates
to identify the cause. Recently, 6.7 GHz methanol maser flares were observed,
triggered by accretion bursts of high-mass YSOs which confirmed the IR-pumping
of these masers. This suggests that regular IR changes might lead to maser
periodicity. Hence, we scrutinized space-based IR imaging of YSOs associated
with periodic methanol masers. We succeeded to extract the IR light curve from
NEOWISE data for the intermediate mass YSO G107.298+5.639. Thus, for the first
time a relationship between the maser and IR variability could be established.
While the IR light curve shows the same period of ~34.6 days as the masers, its
shape is distinct from that of the maser flares. Possible reasons for the IR
periodicity are discussed.Comment: 4 pages, 3 figures, to be published in: Proceedings IAU Symposium 336
"Astrophysical Masers: Unlocking the Mysteries of the Universe", Editors: A.
Tarchi, M.J. Reid & P. Castangia, updated version with hyperlinks adde
Milliarcsecond structure of water maser emission in two young high-mass stellar objects associated with methanol masers
The 22.2 GHz water masers are often associated with the 6.7 GHz methanol
masers but owing to the different excitation conditions they likely probe
independent spatial and kinematic regions around the powering young massive
star. We compared the emission of these two maser species on milliarcsecond
scales to determine in which structures the masers arise and to test a
disc-outflow scenario where the methanol emission arises in a circumstellar
disc while the water emission comes from an outflow. We obtained high-angular
and spectral resolution 22.2 GHz water maser observations of the two sources
G31.581+00.077 and G33.641-00.228 using the EVN. In both objects the water
maser spots form complex and filamentary structures of sizes 18-160 AU. The
emission towards the source G31.581+00.077 comes from two distinct regions of
which one is related to the methanol maser source of ring-like shape. In both
targets the main axis of methanol distribution is orthogonal to the water maser
distribution. Most of water masers appear to trace shocks on a working surface
between an outflow/jet and a dense envelope. Some spots are possibly related to
the disc-wind interface which is as close as 100-150 AU to the regions of
methanol emission.Comment: 10 pages, accepted to Astronomy and Astrophysic
Momentum-driven outflow emission from an O-type YSO: Comparing the radio jet with the molecular outflow
Aims: We want to study the physical properties of the ionized jet emission in
the vicinity of an O-type young stellar object (YSO), and estimate how
efficient is the transfer of energy and momentum from small- to large-scale
outflows. Methods: We conducted Karl G. Jansky Very Large Array (VLA)
observations, at both 22 and 45 GHz, of the compact and faint radio continuum
emission in the high-mass star-forming region G023.01-00.41, with an angular
resolution between 0.3" and 0.1", and a thermal rms of the order of 10
uJy/beam. Results: We discovered a collimated thermal (bremsstrahlung) jet
emission, with a radio luminosity (L_rad) of 24 mJy kpc^2 at 45 GHz, in the
inner 1000 AU from an O-type YSO. The radio thermal jet has an opening angle of
44 degrees and brings a momentum rate of 8 10^-3 M_sun yr^-1 km/s. By combining
the new data with previous observations of the molecular outflow and water
maser shocks, we can trace the outflow emission from its driving source through
the molecular clump, across more than two order of magnitude in length (500
AU-0.2 pc). We find that the momentum-transfer efficiency, between the inner
jet emission and the extended outflow of entrained ambient gas, is near unity.
This result suggests that the large-scale flow is swept-up by the mechanical
force of the radio jet emission, which originates in the inner 1000 AU from the
high-mass YSO.Comment: 5 pages, 2 figures, 2 tables, accepted by Astronomy & Astrophysic
Unveiling the gas kinematics at 10 AU scales in high-mass star-forming regions (Milliarcsecond structure of 6.7 GHz methanol masers)
This work presents a study of the milliarcsecond structure of the 6.7 GHz
methanol masers at high-velocity resolution (0.09 km s^(-1)) in four high-mass
star-forming regions: G16.59-0.05, G23.01-0.41, IRAS20126+4104, and AFGL5142.
We studied these sources by means of multi-epoch VLBI observations in the 22
GHz water and 6.7 GHz methanol masers, to determine the 3-D gas kinematics
within a few thousand AU from the (proto)star. The present work exploits the
6.7 GHz maser data collected so far to investigate the milliarcsecond structure
of this maser emission at high-velocity resolution. Most of the detected 6.7
GHz maser features present an ordered (linear, or arc-like) distribution of
maser spots on the plane of the sky, together with a regular variation in the
spot LSR velocity (V_LSR) with position. Typical values for the amplitude of
the V_LSR gradients (defined in terms of the derivative of the spot V_LSR with
position) are found to be 0.1-0.2 km s^(-1) mas^(-1). In each of the four
target sources, the orientation and the amplitude of most of the feature V_LSR
gradients remain remarkably stable in time, on timescales of (at least) several
years. We also find that the data are consistent with having the V_LSR
gradients and proper motion vectors in the same direction on the sky,
considered the measurement uncertainties. The time persistency, the ordered
angular and spatial distribution, and the orientation generally similar to the
proper motions, altogether suggest a kinematical interpretation for the origin
of the 6.7 GHz maser V_LSR gradients. This work shows that the organized
motions (outflow, infall, and rotation) revealed by the (22 GHz water and 6.7
GHz methanol) masers on large scales (~100-1000 AU) also persist to very small
(~10 AU) scales.Comment: 14 pages, 7 figures, accepted for publication in Astronomy and
Astrophysics Journa
Infall and outflow within 400 AU from a high-mass protostar. 3-D velocity fields from methanol and water masers in AFLG 5142
Observational signatures of infalling envelopes and outflowing material in
early stages of protostellar evolution, and at small radii from the protostar,
are essential to progress in the understanding of the mass-accretion process in
star formation. In this letter, we report a detailed study of the accretion and
outflow structure around a protostar in the well-known high-mass star-forming
region AFGL 5142. We focus on the mm source MM-1, which exhibits hot-core
chemistry, radio continuum emission, and strong water and methanol masers.
Remarkably, our Very Long Baseline Interferometry (VLBI) observations of
molecular masers over six years provided us with the 3-D velocity field of
circumstellar molecular gas with a resolution of 0.001-0.005 arcseconds and at
radii <0.23 arcseconds (or 400 AU) from the protostar. In particular, our
measurements of methanol maser emission enabled, for the first time, a direct
measurement of infall of a molecular envelope (radius of 300 AU and velocity of
5 km/s) onto an intermediate- to high-mass protostar. We estimate an infall
rate of 0.0006 n_8 Msun/year, where n_8 is the ambient volume density in units
of 10^8 cm-3 (required for maser excitation). In addition, our measurements of
water maser (and radio continuum) emission identify a collimated bipolar
molecular outflow (and ionized jet) from MM-1. The evidence of simultaneous
accretion and outflow at small spatial scales, makes AFGL 5142 an extremely
compelling target for high-angular resolution studies of high-mass star
formation.Comment: 6 pages, 4 figures, 1 table, accepted for publication in A&A Letter
Trigonometric Parallaxes of Massive Star Forming Regions: VIII. G12.89+0.49, G15.03-0.68 (M17) and G27.36-0.16
We report trigonometric parallaxes for three massive star forming regions,
corresponding to distances of kpc for G12.89+0.49 (also
known as IRAS 18089-1732), kpc for G15.03-0.68 (in the
M17 region), and kpc for G27.36-0.16. Both G12.89+0.49 and
G15.03-0.68 are located in the Carina-Sagittarius spiral arm
Trigonometric Parallaxes of Massive Star Forming Regions: II. Cep A & NGC 7538
We report trigonometric parallaxes for the sources NGC 7538 and Cep A,
corresponding to distances of 2.65 [+0.12/-0.11] kpc and 0.70 [+0.04/-0.04]
kpc, respectively. The distance to NGC 7538 is considerably smaller than its
kinematic distance and places it in the Perseus spiral arm. The distance to Cep
A is also smaller than its kinematic distance and places it in the Local arm or
spur. Combining the distance and proper motions with observed radial velocities
gives the location and full space motion of the star forming regions. We find
significant deviations from circular Galactic orbits for these sources: both
sources show large peculiar motions (> 10 km/s) counter to Galactic rotation
and NGC 7538 has a comparable peculiar motion toward the Galactic center.Comment: 21 pages, 8 figures; to appear in the Astrophysical Journa
The nature of the methanol maser ring G23.657-00.127
Methanol masers are associated with young high-mass stars and are an
important tool for investigating the process of massive star formation. The
recently discovered methanol maser ring in G23.657-00.127 provides an excellent
``laboratory'' for a detailed study of the nature and physical origin of
methanol maser emission, as well as parallax and proper motion measurements.
Multi-epoch observations of the 12.2 GHz methanol maser line from the ring were
conducted using the Very Long Baseline Array. Interferometric observations with
milliarcsecond resolution enabled us to track single maser spots in great
detail over a period of 2 years. We have determined the trigonometric parallax
of G23.657-00.127 to be 0.313+/-0.039 mas, giving a distance of
3.19{+0.46}{-0.35} kpc. The proper motion of the source indicates that it is
moving with the same circular velocity as the LSR, but it shows a large
peculiar motion of about 35 km/s toward the Galactic center.Comment: 6 pages, 3 figures, accepted for publication in A&
A study on subarcsecond scales of the ammonia and continuum emission toward the G16.59-0.05 high-mass star-forming region
We wish to investigate the structure, velocity field, and stellar content of
the G16.59-0.05 high-mass star-forming region, where previous studies have
established the presence of two almost perpendicular (NE-SW and SE-NW), massive
outflows, and a rotating disk traced by methanol maser emission. We performed
Very Large Array observations of the radio continuum and ammonia line emission,
complemented by COMICS/Subaru and Hi-GAL/Herschel images in the mid- and
far-infrared (IR). Our centimeter continuum maps reveal a collimated radio jet
that is oriented E-W and centered on the methanol maser disk, placed at the SE
border of a compact molecular core. The spectral index of the jet is negative,
indicating non-thermal emission over most of the jet, except the peak close to
the maser disk, where thermal free-free emission is observed. We find that the
ammonia emission presents a bipolar structure consistent (on a smaller scale)
in direction and velocity with that of the NE-SW bipolar outflow detected in
previous CO observations. After analyzing our previous N2H+(1-0) observations
again, we conclude that two scenarios are possible. In one case both the radio
jet and the ammonia emission would trace the root of the large-scale CO bipolar
outflow. The different orientation of the jet and the ammonia flow could be
explained by precession and/or a non-isotropic density distribution around the
star. In the other case, the N2H+(1-0) and ammonia bipolarity is interpreted as
two overlapping clumps moving with different velocities along the line of
sight. The ammonia gas also seems to undergo rotation consistent with the maser
disk. Our IR images complemented by archival data allow us to derive a
bolometric luminosity of about 10^4 L_sun and to conclude that most of the
luminosity is due to the young stellar object associated with the maser disk.Comment: 11 pages, 12 figures, published in Astronomy and Astrophysic
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