174 research outputs found
High resolution observations of the L1551 bipolar outflow
The nearby dark cloud Lynds 1551 contains one of the closest examples of a well-collimated bipolar molecular outflow. This source has the largest angular size of any known outflow and was the first bipolar outflow to be detected. The outflow originates from a low-luminosity young stellar object, IRS-5. Optical and radio continuum observations show the presence of a highly collimated, ionized stellar wind orginating from close to IRS-5 and aligned with the molecular outflow. However, we have little information on the actual mechanism that generates the stellar wind and collimates it into opposed jets. The Very Large Array (VLA) observations indicate that the winds originate within 10(15) cm of IRS-5, unfortunately at a size scale difficult to resolve. For these reasons, observations of the structure and dynamics of the hypersonic molecular gas may provide valuable information on the origin and evolution of these outflows. In addition, the study of the impact of the outflowing gas on the surrounding molecular material is essential to understand the consequence these outflows have on the evolution and star formation history of the entire cloud. Moriarty-Schieven et al. (1986) obtained a oversampled map of the CO emission of a portion of both the blueshifted and redshifted outflows in LI551 using Five College Radio Astronomy Observatory 14 m telescope. The oversampled maps have been reconstructed to an effective angular resolution of 20 arcsec using a maximum entropy algorithm. A continuation of the study of Moriarty-Schieven et al. is presented. The entire L1551 outflow has now been mapped at 12 arcsec sampling requiring roughly 4000 spectra. This data has been constructed to 20 arcsec resolution to provide the first high resolution picture of the entire L1551 outflow. This new data has shown that the blueshifted lobe is more extended than previously thought and has expanded downstream sufficiently to break out of the dense molecular cloud, but the redshifted outflow is still confined within the molecular cloud. Details of the structure and kinematics of the high velocity gas are used to test the various models of the origin and evolution of outflows
The young stellar population of Lynds 1340. An infrared view
We present results of an infrared study of the molecular cloud Lynds 1340,
forming three groups of low and intermediate-mass stars. Our goals are to
identify and characterise the young stellar population of the cloud, study the
relationships between the properties of the cloud and the emergent stellar
groups, and integrate L1340 into the picture of the star-forming activity of
our Galactic environment. We selected candidate young stellar objects from the
Spitzer and WISE data bases using various published color criteria, and
classified them based on the slope of the spectral energy distribution. We
identified 170 Class II, 27 Flat SED, and Class 0/I sources. High angular
resolution near-infrared observations of the RNO 7 cluster, embedded in L1340,
revealed eight new young stars of near-infrared excess. The surface density
distribution of young stellar objects shows three groups, associated with the
three major molecular clumps of L1340, each consisting of less than 100
members, including both pre-main sequence stars and embedded protostars. New
Herbig--Haro objects were identified in the Spitzer images. Our results
demonstrate that L1340 is a prolific star-forming region of our Galactic
environment in which several specific properties of the intermediate-mass mode
of star formation can be studied in detail.Comment: 73 pages, 33 figures, 15 tables. Accepted for publication in ApJ
Detection of Infall Signatures Towards Serpens SMM4
We present the detection of kinematic infall signatures towards the Class 0
protostellar system SMM4 in the Serpens cloud core. We have observed the dense
molecular gas towards the embedded source using millimeter and submillimeter
line transitions of density sensitive molecular tracers. High signal-to-noise
ratio maps obtained in HCO+ J=1-0, J=3-2, and J=4-3, and CS J=2-1 show the
blue-bulge infall signature. The blue-bulge infall signature can be observed in
the centroid velocity maps of protostellar objects when infall dominates over
rotation. The line profiles of HCO+ and CS exhibit the characteristic blue
asymmetric line profile signature consistent with infall. In addition, HCO+ and
CS optical depth profiles obtained using isotopic observations show a red
asymmetry also consistent with an infall interpretation. Using
three-dimensional radiative transfer models based on the rotating, collapse
model of Terebey, Shu and Cassen, we derive infall parameters of the source. To
determine the direction and orientation of molecular outflows in the larger
Serpens cluster, wide-field mapping of CO J=1-0 emission was also performed.Comment: 27 pages, 7 figures, to appear in Ap
The Nature of the IRAS Ring G159.6−18.5 in Perseus and Its Exciting Star HD 278942
We discuss an extended feature in the Perseus molecular cloud complex, most prominent in the IRAS database as an almost complete ring of radius 0.75 degrees, but also clearly seen in optical surveys and in radio continuum emission
The Enigmatic Radio Afterglow of GRB 991216
We present wide-band radio observations spanning from 1.4 GHz to 350 GHz of
the afterglow of GRB 991216, taken from 1 to 80 days after the burst. The
optical and X-ray afterglow of this burst were fairly typical and are explained
by a jet fireball. In contrast, the radio light curve is unusual in two
respects: (a) the radio light curve does not show the usual rise to maximum
flux on timescales of weeks and instead appears to be declining already on day
1 and (b) the power law indices show significant steepening from the radio
through the X-ray bands. We show that the standard fireball model, in which the
afterglow is from a forward shock, is unable to account for (b) and we conclude
that the bulk of the radio emission must arise from a different source. We
consider two models, neither of which can be ruled out with the existing data.
In the first (conventional) model, the early radio emission is attributed to
emission from the reverse shock as in the case of GRB 990123. We predict that
the prompt optical emission would have been as bright (or brighter) than 8th
magnitude. In the second (exotic) model, the radio emission originates from the
forward shock of an isotropically energetic fireball (10^54 erg) expanding into
a tenuous medium (10^-4 cm^-3). The resulting fireball would remain
relativistic for months and is potentially resolvable with VLBI techniques.
Finally, we note that the near-IR bump of the afterglow is similar to that seen
in GRB 971214 and no fireball model can explain this bump.Comment: ApJ, submitte
L1551NE - Discovery of a Binary Companion
L1551NE is a very young (class 0 or I) low-mass protostar located close to
the well-studied L1551 IRS5. We present here evidence, from 1.3mm continuum
interferometric observations at ~1'' resolution, for a binary companion to
L1551NE. The companion, whose 1.3mm flux density is ~1/3 that of the primary
component, is located 1.43'' (~230 A.U. at 160pc) to the southeast. The
millimeterwave emission from the primary component may have been just barely
resolved, with deconvolved size ~0.82"x0.70" (~131x112 A.U.). The companion
emission was unresolved (<100 A.U.). The pair is embedded within a flattened
circum-binary envelope of size ~5.4'' x 2.3'' (~860 x 370 A.U.). The masses of
the three components (i.e. from the cicumstellar material of the primary star
and its companion, and the envelope) are approximately 0.044, 0.014 and 0.023
Mo respectively.Comment: 8 pages, 1 figur
A Coordinated Radio Afterglow Program
We describe a ground-based effort to find and study afterglows at centimeter
and millimeter wavelengths. We have observed all well-localized gamma-ray
bursts in the Northern and Southern sky since BeppoSAX first started providing
rapid positions in early 1997. Of the 23 GRBs for which X-ray afterglows have
been detected, 10 have optical afterglows and 9 have radio afterglows. A
growing number of GRBs have both X-ray and radio afterglows but lack a
corresponding optical afterglow.Comment: To appear in Proc. of the 5th Huntsville Gamma-Ray Burst Symposium, 5
pages, LaTe
Multi-Generational Star Formation in L1551
The L1551 molecular cloud contains two small clusters of Class 0 and I
protostars, as well as a halo of more evolved Class II and III YSOs, indicating
a current and at least one past burst of star formation. We present here new,
sensitive maps of 850 and 450 um dust emission covering most of the L1551
cloud, new CO J=2-1 data of the molecular cloud, and a new, deep, optical image
of [SII] emission. No new Class 0/I YSOs were detected. Compact sub-millimetre
emitters are concentrated in two sub-clusters: IRS5 and L1551NE, and the
HL~Tauri group. Both stellar groups show significant extended emission and
outflow/jet activity. A jet, terminating at HH 265 and with a very weak
associated molecular outflow, may originate from LkHa 358, or from a binary
companion to another member of the HL Tauri group. Several Herbig Haro objects
associated with IRS5/NE were clearly detected in the sub-mm, as were faint
ridges of emission tracing outflow cavity walls. We confirm a large-scale
molecular outflow originating from NE parallel to that from IRS5, and suggest
that the "hollow shell" morphology is more likely due to two interacting
outflows. We confirm the presence of a prestellar core (L1551-MC) of mass 2-3
Mo north-west of IRS5. The next generation cluster may be forming in this core.
The L1551 cloud appears cometary in morphology, and appears to be illuminated
and eroded from the direction of Orion, perhaps explaining the multiple
episodes of star formation in this cloud. The full paper (including figures)
can be downloaded at http://www.jach.hawaii.edu/~gms/l1551/l1551-apj641.pdf, or
viewed at http://www.jach.hawaii.edu/~gms/l1551/.Comment: Accepted for publication in The Astrophysical Journal, April 2006
(vol. 641). 27 pages, 17 figure
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