205 research outputs found
Submillimeter CO emission from shock-heated gas in the L1157 outflow
We present the CO J=6-5, 4-3, and 3-2 spectra from the blueshifted gas of the
outflow driven by the low-mass class 0 protostar in the L1157 dark cloud.
Strong submillimeter CO emission lines with T_mb > 30 K have been detected at
63" (~0.13 pc) south from the protostar. It is remarkable that the blue wings
in the submillimeter lines are stronger by a factor of 3-4 than that of the CO
J=1-0 emission line. The CO line ratios suggest that the blueshifted lobe of
this outflow consists of moderately dense gas of n(H_2) = (1-3)x10^4 cm^-3
heated to T_kin = 50-170 K.It is also suggested that the kinetic temperature of
the outflowing gas increases from ~80 K near the protostar to ~170 K at the
shocked region in the lobe center, toward which the largest velocity dispersion
of the CO emission is observed. A remarkable correlation between the kinetic
temperature and velocity dispersion of the CO emission along the lobe provides
us with direct evidence that the molecular gas at the head of the jet-driven
bow shock is indeed heated kinematically. The lower temperature of ~80 K
measured at the other shocked region near the end of the lobe is explained if
this shock is in a later evolutionary stage, in which the gas has been cooled
mainly through radiation of the CO rotational lines.Comment: 10 pages, 4 PDF figures, APJL in pres
Revealing the environs of the remarkable southern hot core G327.3-0.6
We present a submm study of the massive hot core G327.3-0.6 that constrains
its physical parameters and environment. The APEX telescope was used to image
CO and N2H+ emission, to observe lines from other molecules toward a hot and a
cold molecular core, and to measure the continuum flux density of the hot core.
In the C18O J=3-2 line, two clumps were found, one associated with the HII
region G327.3-0.5 and the other associated with the hot core. An additional
cold clump is found 30 arcsec (0.4 pc) northeast of the hot core in bright N2H+
emission. From the the continuum data, we calculate a mass of 420 Msol and a
size of 0.1 pc for the hot core. A new, more accurate position of the hot core
is reported, which allows the association of the core with a bright
mid-infrared source. The luminosity of the hot core is estimated to be between
5 and 15 10^4 Lsol. This study revealed several different evolutionary stages
of massive star formation in the G327.3-0.6 region.Comment: APEX A&A special issue, accepte
AMI-LA radio continuum observations of Spitzer c2d small clouds and cores: Perseus region
We present deep radio continuum observations of the cores identified as
deeply embedded young stellar objects in the Perseus molecular cloud by the
Spitzer c2d programme at a wavelength of 1.8 cm with the Arcminute Microkelvin
Imager Large Array (AMI-LA). We detect 72% of Class 0 objects from this sample
and 31% of Class I objects. No starless cores are detected. We use the flux
densities measured from these data to improve constraints on the correlations
between radio luminosity and bolometric luminosity, infrared luminosity and,
where measured, outflow force. We discuss the differing behaviour of these
objects as a function of protostellar class and investigate the differences in
radio emission as a function of core mass. Two of four possible very low
luminosity objects (VeLLOs) are detected at 1.8 cm.Comment: 18 pages, 9 figures, accepted MNRA
Mid- and high-J CO observations towards UCHIIs
A study of 12 ultracompact HII regions was conducted to probe the physical
conditions and kinematics in the inner envelopes of the molecular clumps
harboring them. The APEX telescope was used to observe the sources in the CO
(4-3) and 13CO (8-7) lines. Line intensities were modeled with the RATRAN
radiative transfer code using power laws for the density and temperature to
describe the physical structure of the clumps. All sources were detected in
both lines. The optically thick CO (4-3) line shows predominantly blue skewed
profiles reminiscent of infall. Line intensities can be reproduced well using
the physical structure of the clumps taken from the literature. The optically
thick line profiles show that CO is a sensitive tracer of ongoing infall in the
outer envelopes of clumps harboring ultracompact HII regions and hot molecular
cores.Comment: APEX A&A special issue, accepte
High mass star formation in the IRAS 17233-3606 region: a new nearby and bright hot core in the southern sky
We present molecular line observations of the massive star forming region
IRAS 17233-3606 aimed at studying the molecular core associated with the
source. The observations were made using the Atacama Pathfinder Experiment
telescope in the CO (3-2) and HCO^+ (4-3) transitions, and in the CH_3OH
(6_K-5_K), (7_K-6_K) and CH_3CN (16_K-15_K) bands. For the CO(3-2) and HCO^+
(4-3) transitions, we obtained maps with a size of 70''\times 70''. The typical
angular resolution of the data is ~18''. Our observations reveal an
exceptionally rich molecular spectrum, a signpost of hot core activity.
Comparisons with two other prominent southern hot cores were made through
observations in the same frequency setups. We also detected a bipolar outflow
in CO (3-2) and HCO^+ (4-3) lines. Modelling reveals a hot core of size ~3''
and a temperature of 150 K in the IRAS17233-3606 region. The parameters of the
molecular outflow are derived through the analysis of the CO (3-2) emission,
and are typical of outflows driven by high-mass young stellar objects.Comment: 9 pages, 10 figures (plus 8 figures as Online material), accepted by
A&
The Rotating Molecular Structures and the Ionized Outflow Associated with IRAS 16547-4247
We present VLA 1.3 cm radio continuum and water maser observations as well as
SMA SO (226.300 GHz) and 1.3 mm dust continuum observations toward the
massive star formation region IRAS 16547-4247. We find evidence of multiple
sources in the central part of the region. There is evidence of a rotating
structure associated with the most massive of these sources, traced at small
scales (~50 AU) by the water masers. At large scales (~1000 AU) we find a
velocity gradient in the SO2 molecular emission with a barely resolved
structure that can be modeled as a rotating ring or two separate objects. The
velocity gradients of the masers and of the molecular emission have the same
sense and may trace the same structure at different size scales. The position
angles of the structures associated with the velocity gradients are roughly
perpendicular to the outflow axis observed in radio continuum and several
molecular tracers. We estimate the mass of the most massive central source to
be around 30 solar masses from the velocity gradient in the water maser
emission. The main source of error in this estimate is the radius of the
rotating structure. We also find water masers that are associated with the
large scale molecular outflow of the system, as well as water masers that are
associated with other sources in the region. Our results suggest that the
formation of this source, one of the most luminous protostars or protostellar
clusters known, is taking place with the presence of ionized jets and disk-like
structures.Comment: 26 pages, 7 figure
Detection of abundant solid methanol toward young low mass stars
We present detections of the absorption band at 3.53 micron due to solid
methanol toward three low-mass young stellar objects located in the Serpens and
Chameleon molecular cloud complexes. The sources were observed as part of a
large spectroscopic survey of ~40 protostars. This is the first detection of
solid methanol in the vicinity of low mass (M <1 Msol) young stars and shows
that the formation of methanol does not depend on the proximity of massive
young stars. The abundances of solid methanol compared to water ice for the
three sources are in the range 15-25% which is comparable to those for the most
methanol-rich massive sources known. The presence of abundant methanol in the
circumstellar environment of some low mass young stars has important
consequences for the formation scenarios of methanol and more complex organic
species near young solar-type stars.Comment: Accepted for publication in A&A letter
Evidence for a Massive Protocluster in S255N
S255N is a luminous far-infrared source that contains many indications of
active star formation but lacks a prominent near-infrared stellar cluster. We
present mid-infrared through radio observations aimed at exploring the
evolutionary state of this region. Our observations include 1.3mm continuum and
spectral line data from the Submillimeter Array, VLA 3.6cm continuum and 1.3cm
water maser data, and multicolor IRAC images from the Spitzer Space Telescope.
The cometary morphology of the previously-known UCHII region G192.584-0.041 is
clearly revealed in our sensitive, multi-configuration 3.6cm images. The 1.3mm
continuum emission has been resolved into three compact cores, all of which are
dominated by dust emission and have radii < 7000AU. The mass estimates for
these cores range from 6 to 35 Msun. The centroid of the brightest dust core
(SMA1) is offset by 1.1'' (2800 AU) from the peak of the cometary UCHII region
and exhibits the strongest HC3N, CN, and DCN line emission in the region. SMA1
also exhibits compact CH3OH, SiO, and H2CO emission and likely contains a young
hot core. We find spatial and kinematic evidence that SMA1 may contain further
multiplicity, with one of the components coincident with a newly-detected H2O
maser. There are no mid-infrared point source counterparts to any of the dust
cores, further suggesting an early evolutionary phase for these objects. The
dominant mid-infrared emission is a diffuse, broadband component that traces
the surface of the cometary UCHII region but is obscured by foreground material
on its southern edge. An additional 4.5 micron linear feature emanating to the
northeast of SMA1 is aligned with a cluster of methanol masers and likely
traces a outflow from a protostar within SMA1. Our observations provide direct
evidence that S255N is forming a cluster of intermediate to high-mass stars.Comment: 34 pages, 11 figures, accepted for publication in The Astronomical
Journa
Interferometric multi-wavelength (sub)millimeter continuum study of the young high-mass protocluster IRAS05358+3543
The young massive star-forming region IRAS05358+3543 was observed at
high-spatial resolution in the continuum emission at 3.1 and 1.2mm with the
Plateau de Bure Interferometer, and at 875 and 438mum with the Submillimeter
Array. We resolve at least four continuum sub-sources that are likely of
protostellar nature. Two of them are potentially part of a proto-binary system
with a projected separation of 1700AU. Additional (sub)mm continuum peaks are
not necessarily harboring protostars but maybe caused by the multiple molecular
outflows. The spectral energy distributions (SEDs) of the sub-sources show
several features. The main power house mm1, which is associated with CH3OH
maser emission, a hypercompact HII region and a mid-infrared source, exhibits a
typical SED with a free-free emission component at cm and long mm wavelengths
and a cold dust component in the (sub)mm part of the spectrum (spectral index
between 1.2mm and 438mum alpha~3.6). The free-free emission corresponds to a
Lyman continuum flux of an embedded 13Msun B1 star. The coldest source of the
region, mm3, has alpha~3.7 between 1.2mm and 875mum, but has lower than
expected fluxes in the shorter wavelength 438mum band. This turnover of the
Planck-function sets an upper limit on the dust temperature of mm3 of
approximately 20K. The uv-data analysis of the density structure of individual
sub-cores reveals distributions with power-law indices between 1.5 and 2. This
resembles the density distributions of the larger-scale cluster-forming clump
as well as those from typical low-mass cores.Comment: 13 pages, 7 figures, accepted for Astronomy and Astrophysics, a
high-resolution version of the paper is also available at
http://www.mpia.de/homes/beuther/papers.htm
The Luminosities of Protostars in the Spitzer c2d and Gould Belt Legacy Clouds
Motivated by the long-standing "luminosity problem" in low-mass star
formation whereby protostars are underluminous compared to theoretical
expectations, we identify 230 protostars in 18 molecular clouds observed by two
Spitzer Space Telescope Legacy surveys of nearby star-forming regions. We
compile complete spectral energy distributions, calculate Lbol for each source,
and study the protostellar luminosity distribution. This distribution extends
over three orders of magnitude, from 0.01 Lsun - 69 Lsun, and has a mean and
median of 4.3 Lsun and 1.3 Lsun, respectively. The distributions are very
similar for Class 0 and Class I sources except for an excess of low luminosity
(Lbol < 0.5 Lsun) Class I sources compared to Class 0. 100 out of the 230
protostars (43%) lack any available data in the far-infrared and submillimeter
(70 um < wavelength < 850 um) and have Lbol underestimated by factors of 2.5 on
average, and up to factors of 8-10 in extreme cases. Correcting these
underestimates for each source individually once additional data becomes
available will likely increase both the mean and median of the sample by 35% -
40%. We discuss and compare our results to several recent theoretical studies
of protostellar luminosities and show that our new results do not invalidate
the conclusions of any of these studies. As these studies demonstrate that
there is more than one plausible accretion scenario that can match
observations, future attention is clearly needed. The better statistics
provided by our increased dataset should aid such future work.Comment: Accepted for publication in AJ. 21 pages, 10 figures, 4 table
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