65 research outputs found
YSO jets in the Galactic plane from UWISH2 – III. Jets and outflows in Cassiopeia and Auriga
We present the analysis of 35.5 deg2 of images in the 1–0 S(1) line of H2 from the UK Widefield Infrared Survey for H2 (UWISH2) towards Cassiopeia and Auriga. We have identified 98 Molecular Hydrogen emission-line Objects (MHOs) driven by Young Stellar Objects, 60 per cent of which are bipolar outflows and all are new discoveries. We estimate that the UWISH2-extended emission object catalogue contains fewer than 2 per cent false positives and is complete at the 95 per cent level for jets and outflows brighter than the UWISH2 detection limit. We identified reliable driving source candidates for three quarters of the detected outflows, 40 per cent of which are associated with groups and clusters of stars. The driving source candidates are 20 per cent protostars, the remainder are Classical T-Tauri Stars. We also identified 15 new star cluster candidates near MHOs in the survey area. We find that the typical outflow identified in the sample has the following characteristics: the position angles are randomly orientated; bipolar outflows are straight within a few degrees; the two lobes are slightly asymmetrical in length and brightness; the length and brightness of the lobes are not correlated; typical time gaps between major ejections of material are 1–3 kyr, hence FU-Ori or EX-Ori eruptions are most likely not the cause of these, but we suggest MNors as a possible source. Furthermore, we find that outflow lobe length distributions are statistically different from the widely used total length distributions. There are a larger than expected number of bright outflows indicating that the flux distribution does not follow a power law
A General Catalogue of Molecular Hydrogen Emission-Line Objects (MHOs) in Outflows from Young Stars
We present a catalogue of Molecular Hydrogen emission-line Objects (MHOs) in
outflows from young stars, most of which are embedded. All objects are
identified in the near-infrared lines of molecular hydrogen, all reside in the
Milky Way, and all are associated with jets or molecular outflows from young
stars. Objects in both low and high-mass star forming regions are included.
This catalogue complements the existing database of Herbig-Haro objects;
indeed, for completeness, HH objects that are detected in H2 emission are
included in the MHO catalogue.Comment: 8 Pages, 5 figures. Accepted for publication in A&A. Searchable
catalogue/Data tables available from http://www.jach.hawaii.edu/UKIRT/MHCat
V2494 cyg: A unique FU ori type object in the cygnus OB7 complex
A photometric and spectral study of the variable star V2494 Cyg in the L 1003 dark cloud is presented. The brightness of the star, formerly known as HH 381 IRS, increased by 2.5 mag in R (probably in the 1980s) and since then has remained nearly constant. Since the brightness increase, V2494 Cyg has illuminated a bipolar cometary nebula. The stellar spectrum has several features typical of the FU Ori (FUor) type, plus it exhibits very strong Ha and forbidden emissionlines with high-velocity components. These emission lines originate in the Herbig-Haro (HH) jet near the star. The kinematic age of the jet is consistent with it forming at the time of the outburst leading to the luminosity increase. V2494 Cyg also produces a rather extended outflow; it is the first known FUor with both an observed outburst and a parsec-sized HH flow. The nebula, illuminated by V2494 Cyg, possesses similar morphological and spectral characteristics to Hubble's variable nebula (R Monocerotis/NGC 2261). © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
CSO Bolocam 1.1 mm continuum mapping of the Braid Nebula star formation region in Cygnus OB7
We present a 1.1 mm map of the Braid Nebula star formation region in Cygnus OB7 taken using Bolocam on the Caltech Submillimeter Observatory. Within the 1 deg2 covered by the map, we have detected 55 cold dust clumps all of which are new detections. A number of these clumps are coincident with IRAS point sources although the majority are not. Some of the previously studied optical/near-IR sources are detected at 1.1 mm. We estimate total dust/gas masses for the 55 clumps together with peak visual extinctions. We conclude that over the whole region, approximately 20% of the clumps are associated with IRAS sources suggesting that these are protostellar objects. The remaining 80% are classed as starless clumps. In addition, both FU Orionis (FUor) like objects in the field, the Braid Star and HH 381 IRS, are associated with strong millimeter emission. This implies that FUor eruptions can occur at very early stages of pre-main-sequence life. Finally, we determine that the cumulative clump mass function for the region is very similar to that found in both the Perseus and Ï? Ophiuchus star-forming regions. © 2011. The American Astronomical Society. All rights reserved
Looking into the hearts of Bok globules: MM and submm continuum images of isolated star-forming cores
We present the results of a comprehensive infrared, submillimetre, and
millimetre continuum emission study of isolated low-mass star-forming cores in
32 Bok globules, with the aim to investigate the process of star formation in
these regions. The submillimetre and millimetre dust continuum emission maps
together with the spectral energy distributions are used to model and derive
the physical properties of the star-forming cores, such as luminosities, sizes,
masses, densities, etc. Comparisons with ground-based near-infrared and
space-based mid and far-infrared images from Spitzer are used to reveal the
stellar content of the Bok globules, association of embedded young stellar
objects with the submm dust cores, and the evolutionary stages of the
individual sources. Submm dust continuum emission was detected in 26 out of the
32 globule cores observed. For 18 globules with detected (sub)mm cores we
derive evolutionary stages and physical parameters of the embedded sources. We
identify nine starless cores, most of which are presumably prestellar, nine
Class 0 protostars, and twelve Class I YSOs. Specific source properties like
bolometric temperature, core size, and central densities are discussed as
function of evolutionary stage. We find that at least two thirds (16 out of 24)
of the star-forming globules studied here show evidence of forming multiple
stars on scales between 1,000 and 50,000 AU. However, we also find that most of
these small prototstar and star groups are comprised of sources with different
evolutionary stages, suggesting a picture of slow and sequential star formation
in isolated globulesComment: 60 pages, 28 figures, accepted by The Astrophysical Journal
Supplement Serie
YSO jets in the Galactic Plane from UWISH2: II - Outflow Luminosity and Length distributions in Serpens and Aquila
Jets and outflows accompany the mass accretion process in protostars and
young stellar objects. Using a large and unbiased sample, they can be used to
study statistically the local feedback they provide and the typical mass
accretion history. Here we analyse such a sample of Molecular Hydrogen emission
line Objects in the Serpens and Aquila part of the Galactic Plane. Distances
are measured by foreground star counts with an accuracy of 25%. The resulting
spacial distribution and outflow luminosities indicate that our objects sample
the formation of intermediate mass objects. The outflows are unable to provide
a sizeable fraction of energy and momentum to support, even locally, the
turbulence levels in their surrounding molecular clouds. The fraction of parsec
scale flows is one quarter and the typical dynamical jet age of the order of
1E4yrs. Groups of emission knots are ejected every 1E3yrs. This might indicate
that low level accretion rate fluctuations and not FU-Ori type events are
responsible for the episodic ejection of material. Better observational
estimates of the FU-Ori duty cycle are needed.Comment: 16pages, 3tables, 10figures, accepted for publication by MNRAS, a
version with higher resolution figures can be found at
http://astro.kent.ac.uk/~df
Radio continuum emission and water masers towards CB 54
We present high angular resolution observations of water masers at 1.3 cm and
radio continuum emission at 1.3, 3.6 and 6 cm towards the Bok globule CB 54
using the Very Large Array. At 1.3 cm, with subarsecond angular resolution, we
detect a radio continuum compact source located to the south-west of the
globule and spatially coincident with a mid-infrared embedded object (MIR-b).
The spectral index derived between 6 and 1.3 cm (alpha=0.3+/-0.4) is flat,
consistent with optically thin free-free emission from ionized gas. We propose
the shock-ionization scenario as a viable mechanism to produce the radio
continuum emission observed at cm frequencies. Water masers are detected at two
different positions separated by 2.3'', and coincide spatially with two
mid-infrared sources: MIR-b and MIR-c. The association of these mid-IR sources
with water masers confirms that they are likely protostars undergoing
mass-loss, and they are the best candidate as driving sources of the molecular
outflows in the region.Comment: 17 pages, 3 figures. Accepted for publication in A
UWISH2 -- The UKIRT Widefield Infrared Survey for H2
We present the goals and preliminary results of an unbiased, near-infrared,
narrow-band imaging survey of the First Galactic Quadrant (10deg<l<65deg ;
-1.3deg<b<+1.3deg). This area includes most of the Giant Molecular Clouds and
massive star forming regions in the northern hemisphere. The survey is centred
on the 1-0S(1) ro-vibrational line of H2, a proven tracer of hot, dense
molecular gas in star-forming regions, around evolved stars, and in supernova
remnants. The observations complement existing and upcoming photometric surveys
(Spitzer-GLIMPSE, UKIDSS-GPS, JCMT-JPS, AKARI, Herschel Hi-GAL, etc.), though
we probe a dynamically active component of star formation not covered by these
broad-band surveys. Our narrow-band survey is currently more than 60% complete.
The median seeing in our images is 0.73arcsec. The images have a 5sigma
detection limit of point sources of K=18mag and the surface brightness limit is
10^-19Wm^-2arcsec^-2 when averaged over our typical seeing. Jets and outflows
from both low and high mass Young Stellar Objects are revealed, as are new
Planetary Nebulae and - via a comparison with earlier K-band observations
acquired as part of the UKIDSS GPS - numerous variable stars. With their
superior spatial resolution, the UWISH2 data also have the potential to reveal
the true nature of many of the Extended Green Objects found in the GLIMPSE
survey.Comment: 14pages, 8figures, 2tables, accepted for publication by MNRAS, a
version with higher resolution figures can be found at
http://astro.kent.ac.uk/~df
GM 2-4 - a signpost for low and intermediate mass star formation
We present a multi-wavelength study of the region towards the GM 2-4 nebula
and the nearby source IRAS 05373+2340. Our near-infrared H2 1-0 S(1) line
observations reveal various shock-excited features which are part of several
bipolar outflows. We identify candidates for the driving sources of the
outflows from a comparison of the multi-waveband archival data-sets and SED
modelling. The SED spectral slope (\alpha(IRAC)) for all the protostars in the
field was then compared with the visual extinction map. This comparison
suggests that star formation is progressing from NE to SW across this region
A near IR imaging survey of intermediate and high-mass young stellar outflow candidates
We have carried out a near-infrared imaging survey of luminous young stellar
outflow candidates using the United Kingdom Infrared Telescope. Observations
were obtained in the broad band K (2.2 mu) and through narrow band filters at
the wavelengths of H_2 v=1--0 S(1) (2.1218 mu) and Br gamma (2.166 mu) lines.
Fifty regions were imaged with a field of view of 2.2 X 2.2 arcmin^2. Several
young embedded clusters are unveiled in our near-infrared images. 76% of the
objects exhibit H_2 emission and 50% or more of the objects exhibit aligned H_2
emission features suggesting collimated outflows, many of which are new
detections. These observations suggest that disk accretion is probably the
leading mechanism in the formation of stars, at least up to late O spectral
types. The young stellar objects responsible for many of these outflows are
positively identified in our images based on their locations with respect to
the outflow lobes, 2MASS colours and association with MSX, IRAS, millimetre and
radio sources. The close association of molecular outflows detected in CO with
the H_2 emission features produced by shock excitation by jets from the young
stellar objects suggests that the outflows from these objects are jet-driven.
Towards strong radio emitting sources, H_2 jets were either not detected or
were weak when detected, implying that most of the accretion happens in the
pre-UCHII phase; accretion and outflows are probably weak when the YSO has
advanced to its UCHII stage.Comment: 64 pages, 53 figures, Accepted for publication in the MNRA
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