83 research outputs found
The Brightening of Re50N: Accretion Event or Dust Clearing?
The luminous Class I protostar HBC 494, embedded in the Orion A cloud, is
associated with a pair of reflection nebulae, Re50 and Re50N, which appeared
sometime between 1955 and 1979. We have found that a dramatic brightening of
Re50N has taken place sometime between 2006 and 2014. This could result if the
embedded source is undergoing a FUor eruption. However, the near-infrared
spectrum shows a featureless very red continuum, in contrast to the strong CO
bandhead absorption displayed by FUors. Such heavy veiling, and the high
luminosity of the protostar, is indicative of strong accretion but seemingly
not in the manner of typical FUors. We favor the alternative explanation that
the major brightening of Re50N and the simultaneous fading of Re50 is caused by
curtains of obscuring material that cast patterns of illumination and shadows
across the surface of the molecular cloud. This is likely occurring as an
outflow cavity surrounding the embedded protostar breaks through to the surface
of the molecular cloud. Several Herbig-Haro objects are found in the region.Comment: 8 pages, accepted by Ap
A shallow though extensive H2 2.12 micron imaging survey of Taurus-Auriga-Perseus: I. NGC1333, L1455, L1448 and B1
We discuss wide-field near-IR imaging of the NGC1333, L1448, L1455 and B1
star forming regions in Perseus. The observations have been extracted from a
much larger narrow-band imaging survey of the Taurus-Auriga-Perseus complex.
These H2 2.12 micron observations are complemented by broad-band K imaging,
mid-IR imaging and photometry from the Spitzer Space Telescope, and published
submillimetre CO J=3-2 maps of high-velocity molecular outflows. We detect and
label 85 H2 features and associate these with 26 molecular outflows. Three are
parsec-scale flows, with a mean flow lobe length exceeding 11.5 arcmin. 37
(44%) of the detected H2 features are associated with a known Herbig-Haro
object, while 72 (46%) of catalogued HH objects are detected in H2 emission.
Embedded Spitzer sources are identified for all but two of the 26 molecular
outflows. These candidate outflow sources all have high near-to-mid-IR spectral
indices (mean value of alpha ~ 1.4) as well as red IRAC 3.6-4.5 micron and
IRAC/MIPS 4.5-24.0 micron colours: 80% have [3.6]-[4.5] > 1.0 and [4.5]-[24] >
1.5. These criteria - high alpha and red [4.5]-[24] and [3.6]-[4.5] colours -
are powerful discriminants when searching for molecular outflow sources.
However, we find no correlation between alpha and flow length or opening angle,
and the outflows appear randomly orientated in each region. The more massive
clouds are associated with a greater number of outflows, which suggests that
the star formation efficiency is roughly the same in each region.Comment: 23 pages (including Appoendix); 11 main text figures, 5 colour
appendix figs uploaded as gifs; accepted by MNRAS; for higher-resolution
figures please visit http://www.jach.hawaii.edu/~cdavis
Star formation in Perseus - V. Outflows detected by HARP
Molecular outflows provide an alternative method of identifying protostellar
cores, complementary to recent mid-infrared studies. Continuing our studies of
Perseus, we investigate whether all Spitzer-identified protostars, and
particularly those with low luminosities, drive outflows, and if any new
protostellar cores (perhaps harbouring low-mass sources) can be identified via
their outflows alone. We have used the heterodyne array receiver HARP on JCMT
to make deep 12CO 3-2 maps of submm cores in Perseus, extending and deepening
our earlier study with RxB and bringing the total number of SCUBA cores studied
up to 83. Our survey includes 23/25 of the Dunham et al. (2008) Spitzer
low-luminosity objects believed to be embedded protostars, including three
VeLLOs. All but one of the cores identified as harbouring embedded YSOs have
outflows, confirming outflow detections as a good method for identifying
protostars. We detect outflows from 20 Spitzer low-luminosity objects. We do
not conclusively detect any outflows from IR-quiet cores, though confusion in
clustered regions such as NGC1333 makes it impossible to identify all the
individual driving sources. This similarity in detection rates despite the
difference in search methods and detection limits suggests either that the
sample of protostars in Perseus is now complete, or that the existence of an
outflow contributes to the Spitzer detectability, perhaps through the
contribution of shocked H2 emission in the IRAC bands. For five of the
low-luminosity sources, there is no protostellar envelope detected at 350
microns and the Spitzer emission is entirely due to shocks. Additionally, we
detect the outflow from IRAS 03282+3035 at 850 microns with SCUBA due to CO
line contamination in the continuum passband.Comment: 25 pages, 12 figures, to be published in A&
Comparison of Magnetic Field Structures on Different Scales in and around the Filamentary Dark Cloud GF 9
New visible polarization data combined with existing IR and FIR polarization
data are used to study how the magnetic field threading the filamentary
molecular cloud GF 9 connects to larger structures in its general environment.
We find that when both visible and NIR polarization data are plotted as a
function of extinction, there is no evidence for a plateau or a saturation
effect in the polarization at Av ~ 1.3 as seen in dark clouds in Taurus. This
lack of saturation effect suggests that even in the denser parts of GF 9 we are
still probing the magnetic field. The visible polarization is smooth and has a
well-defined orientation. The IR data are also well defined but with a
different direction, and the FIR data in the core region are well defined and
with yet another direction, but are randomly distributed in the filament
region. On the scale of a few times the mean radial dimension of the molecular
cloud, it is as if the magnetic field were `blind' to the spatial distribution
of the filaments while on smaller scales within the cloud, in the core region
near the IRAS point source PSC 20503+6006, polarimetry shows a rotation of the
magnetic field lines in these denser phases. Hence, in spite of the fact that
the spatial resolution is not the same in the visible/NIR and in the FIR data,
all the data put together indicate that the field direction changes with the
spatial scale. Finally, the Chandrasekhar and Fermi method is used to evaluate
the magnetic field strength, indicating that the core region is approximately
magnetically critical. A global interpretation of the results is that in the
core region an original poloidal field could have been twisted by a rotating
elongated (core+envelope) structure. There is no evidence for turbulence and
ambipolar diffusion does not seem to be effective at the present time.Comment: 33 pages, 6 tables, 8 figures, Accepted by Ap
Star formation in the vicinity of the IC 348 cluster
Aims. We present molecular line observations of the southwestern part of the
IC 348 young cluster, and we use them together with NIR and mm continuum data
to determine the distribution of dense gas, search for molecular outflows, and
analyze the ongoing star formation activity in the region. Methods. Our
molecular line data consists of C18O(1--0) and N2H+(1--0) maps obtained with
the FCRAO telescope at a resolution of about 50'' and CO(2--1) data obtained
with the IRAM 30m telescope at a resolution of 11''. Results. The dense gas
southwest of IC 348 is concentrated in two groups of dense cores, each of them
with a few solar masses of material and indications of CO depletion at high
density. One of the core groups is actively forming stars, while the other
seems starless. There is evidence for at least three bipolar molecular outflows
in the region, two of them powered by previously identified Class 0 sources,
while the other one is powered by a still not well characterized low-luminosity
object. The ongoing star formation activity is producing a small stellar
subgroup in the cluster. Using the observed core characteristics and the star
formation rate in the cluster we propose that that similar episodes of stellar
birth may have produced the subclustering observed in the halo of IC 348.Comment: 10 pages, 6 figures, A&A accepte
And in the Darkness Bind Them: Equatorial Rings, B[e] Supergiants, and the Waists of Bipolar Nebulae
We report the discovery of two new circumstellar ring nebulae in the western
Carina Nebula. The brighter object, SBW1, resembles a lidless staring eye and
encircles a B1.5 Iab supergiant. Its size is identical to the inner ring around
SN1987A, but SBW1's low N abundance indicates that the star didn't pass through
a RSG phase. The fainter object, SBW2, is a more distorted ring, is N-rich, and
has a central star that seems to be invisible. We discuss these two new nebulae
in context with rings around SN1987A, Sher25, HD168625, RY Scuti, WeBo1, SuWt2,
and others. The ring bearers fall into two groups: Five rings surround hot
supergiants, and all except for the one known binary are carbon copies of the
ring around SN1987A. We propose a link between these rings and B[e]
supergiants, where the rings derive from the same material in an earlier B[e]
phase. The remaining four rings surround evolved intermediate-mass stars; all
members of this ring fellowship are close binaries, hinting that binary
interactions govern the forging of such rings. We estimate that there may be
several thousand more dark rings in the Galaxy, but we are scarcely aware of
their existence due to selection effects. The lower-mass objects might be the
equatorial density enhancements often invoked to bind the waists of bipolar
PNe.Comment: AJ accepted, 27 page
Turbulent Driving Scales in Molecular Clouds
Supersonic turbulence in molecular clouds is a dominant agent that strongly
affects the clouds' evolution and star formation activity. Turbulence may be
initiated and maintained by a number of processes, acting at a wide range of
physical scales. By examining the dynamical state of molecular clouds, it is
possible to assess the primary candidates for how the turbulent energy is
injected. The aim of this paper is to constrain the scales at which turbulence
is driven in the molecular interstellar medium, by comparing simulated
molecular spectral line observations of numerical magnetohydrodynamic (MHD)
models and molecular spectral line observations of real molecular clouds. We
use principal component analysis, applied to both models and observational
data, to extract a quantitative measure of the driving scale of turbulence. We
find that only models driven at large scales (comparable to, or exceeding, the
size of the cloud) are consistent with observations. This result applies also
to clouds with little or no internal star formation activity. Astrophysical
processes acting on large scales, including supernova-driven turbulence,
magnetorotational instability, or spiral shock forcing, are viable candidates
for the generation and maintenance of molecular cloud turbulence. Small scale
driving by sources internal to molecular clouds, such as outflows, can be
important on small scales, but cannot replicate the observed large-scale
velocity fluctuations in the molecular interstellar medium.Comment: 8 pages, 7 figures, accepted for publication in A&
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
The Bolocam Galactic Plane Survey: Survey Description and Data Reduction
We present the Bolocam Galactic Plane Survey (BGPS), a 1.1 mm continuum
survey at 33" effective resolution of 170 square degrees of the Galactic Plane
visible from the northern hemisphere. The survey is contiguous over the range
-10.5 < l < 90.5, |b| < 0.5 and encompasses 133 square degrees, including some
extended regions |b| < 1.5. In addition to the contiguous region, four targeted
regions in the outer Galaxy were observed: IC1396, a region towards the Perseus
Arm, W3/4/5, and Gem OB1. The BGPS has detected approximately 8400 clumps over
the entire area to a limiting non-uniform 1-sigma noise level in the range 11
to 53 mJy/beam in the inner Galaxy. The BGPS source catalog is presented in a
companion paper (Rosolowsky et al. 2010). This paper details the survey
observations and data reduction methods for the images. We discuss in detail
the determination of astrometric and flux density calibration uncertainties and
compare our results to the literature. Data processing algorithms that separate
astronomical signals from time-variable atmospheric fluctuations in the data
time-stream are presented. These algorithms reproduce the structure of the
astronomical sky over a limited range of angular scales and produce artifacts
in the vicinity of bright sources. Based on simulations, we find that extended
emission on scales larger than about 5.9' is nearly completely attenuated (>
90%) and the linear scale at which the attenuation reaches 50% is 3.8'.
Comparison with other millimeter-wave data sets implies a possible systematic
offset in flux calibration, for which no cause has been discovered. This
presentation serves as a companion and guide to the public data release through
NASA's Infrared Processing and Analysis Center (IPAC) Infrared Science Archive
(IRSA). New data releases will be provided through IPAC IRSA with any future
improvements in the reduction.Comment: Accepted for publication in Astrophysical Journal Supplemen
- …