490 research outputs found
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High resolution CO observations of S88-B
CO J = 2-1 and 13CO J = 2-1 and 1-0 observations have been made of the H II region S88-B, using the 15-m James Clerk Maxwell telescope in Hawaii and the 20-m telescope at Onsala. The core of the cloud is resolved into a horseshoelike structure which surrounds a diffuse reflection nebula. The central core has a mass of ≥ 1000 M⊙, with 400 M⊙ in the horseshoe structure. The gas in the horse in the horseshoe appears highly fragmented, and has a kinetic temperature of ≈ 60 K, suggesting it is closely coupled to the dust temperature. A recently formed high mass star appears to be in the process of evacuating a cavity, possibly through a large molecular outflow that is found to show an accelerated component in its blue-shifted lobe. A velocity gradient across the horseshoe structure suggest ordered motion, and could represent rotation in the parental cloud
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High signal/noise <sup>13</sup>CO observations of the bipolar outflow in L1551
New high-signal/noise 13CO observations of the bipolar outflow in the molecular cloud L1551 are reported. Contrary to earlier observations of CO J = 1-0 and 2-1, no strong spatial dependence is found for the velocity profile of these spectra. The implications of these observations are such that the model of an empty shell for this source is less likely, and a model consisting of a shell which contains significant amounts of outflowing molecular gas inside the swept-up cavity walls is suggested
Discovery of X-ray emission from the proto-stellar jet L1551 IRS5 (HH 154)
We have for the first time detected X-ray emission associated with a
proto-stellar jet, on the jet emanating from L1551 IRS5. The IRS5 proto-star is
hidden beyond a very large absorbing column density, making the direct
observation of the jet's emission possible. The observed X-ray emission is
likely associated with the shock ``working surface'', i.e. the interface
between the jet and the circumstellar medium. The X-ray luminosity emanating
from the jet is moderate, at LX ~ 3 times 10^29 erg/s, a significant fraction
of the luminosity normally associated with the coronal emission from young
stars. The spectrum of the X-ray emission is compatible with thermal emission
from a hot plasma, with T ~ 0.5 MK, fully compatible with the temperature
expected (on the basis of the jet's velocity) for the shock front produced by
the jet hitting the circumstellar medium.Comment: To appear in "Stellar Coronae in the Chandra and XMM Era", ASP
Conference Series in press, F. Favata & J. Drake ed
Towards a Molecular Inventory of Protostellar Discs
The chemical environment in circumstellar discs is a unique diagnostic of the
thermal, physical and chemical environment. In this paper we examine the
structure of star formation regions giving rise to low mass stars, and the
chemical environment inside them, and the circumstellar discs around the
developing stars.Comment: 9 page PDF, 550 kbyte
High Angular Resolution, Sensitive CS J=2-1 and J=3-2 Imaging of the Protostar L1551 NE: Evidence for Outflow-Triggered Star Formation ?
High angular resolution and sensitive aperture synthesis observations of CS
() and CS () emissions toward L1551 NE, the second brightest
protostar in the Taurus Molecular Cloud, made with the Nobeyama Millimeter
Array are presented. L1551 NE is categorized as a class 0 object deeply
embedded in the red-shifted outflow lobe of L1551 IRS 5. Previous studies of
the L1551 NE region in CS emission revealed the presence of shell-like
components open toward L1551 IRS 5, which seem to trace low-velocity shocks in
the swept-up shell driven by the outflow from L1551 IRS 5. In this study,
significant CS emission around L1551 NE was detected at the eastern tip of the
swept-up shell from = 5.3 km s to 10.1 km s, and
the total mass of the dense gas is estimated to be 0.18 0.02 .
Additionally, the following new structures were successfully revealed: a
compact disklike component with a size of 1000 AU just at L1551 NE,
an arc-shaped structure around L1551 NE, open toward L1551 NE, with a size of
AU, i.e., a bow shock, and a distinct velocity gradient of the
dense gas, i.e., deceleration along the outflow axis of L1551 IRS 5. These
features suggest that the CS emission traces the post-shocked region where the
dense gas associated with L1551 NE and the swept-up shell of the outflow from
L1551 IRS 5 interact. Since the age of L1551 NE is comparable to the timescale
of the interaction, it is plausible that the formation of L1551 NE was induced
by the outflow impact. The compact structure of L1551 NE with a tiny envelope
was also revealed, suggesting that the outer envelope of L1551 NE has been
blown off by the outflow from L1551 IRS 5.Comment: 29 pages, 12 figures, Accepted for Publication in the Astrophysical
Journa
The X-ray Luminosities of HH Objects
The recent detection of X-ray emission from HH 2 and HH 154 with the Chandra
and XMM-Newton satellites (respectively) have opened up an interesting, new
observational possibility in the field of Herbig-Haro objects. In order to be
able to plan further X-ray observations of other HH objects, it is now of
interest to be able to estimate their X-ray luminosities in order to choose
which objects to observe. This paper describes a simple, analytic model for
predicting the X-ray luminosity of a bow shock from the parameters of the flow
(i.e., the size of the bow shock, its velocity, and the pre-shock density). The
accuracy of the analytic model is analyzed through a comparison with the
predictions obtained from axisymmetric, gasdynamic simulations of the leading
working surface of an HH jet. We find that our analytic model reproduces the
observed X-ray luminosities of HH 2 and HH 154, and we propose that HH~80/81 is
a good candidate for future observations with Chandra.Comment: 10 pages (8 text, 2 figures
The molecular disk surrounding the protostellar binary L1551 IRS5
The inner three arcminutes surrounding the Class 0/1 binary protostar L1551 IRS5 have been observed using the J=1→0 transitions of the HCO+, H13CO+, 12CO and 13CO molecular species. Since the line core of HCO+ is self reversed over a substantial part of our map, observations of isotopomers such as H13CO+ are required in order to estimate the mass of the molecular gas in the immediate vicinity of IRS5. Our observations demonstrate the presence of a large ( ~ 7000 AU radius) dense, possibly rotating, molecular disk with a mass of a few M⊙ oriented perpendicular to the major axis of an extended molecular outflow. The disk is surrounded by an envelope with a radius of ~ 10 000 AU that contains two massive (each ~ 1 M⊙) clumps. One of these features appears to be kinematically disconnected from both the disk and the molecular outflow
Searching for signs of triggered star formation toward IC 1848
We have carried out an in-depth study of three bright-rimmed clouds SFO 11, SFO 11NE and SFO 11E associated with the HII region IC 1848, using observations carried out at the James Clerk Maxwell Telescope (JCMT) and the Nordic Optical Telescope (NOT), plus archival data from IRAS, 2MASS and the NVSS. We show that the overall morphology of the clouds is reasonably consistent with that of radiative-driven implosion (RDI) models developed to predict the evolution of cometary globules. There is evidence for a photoevaporated flow from the surface of each cloud and, based upon the morphology and pressure balance of the clouds, it is possible that D-critical ionisation fronts are propagating into the molecular gas. The primary O star responsible for ionising the surfaces of the clouds is the 06V star HD 17505. Each cloud is associated with either recent or ongoing star formation: we have detected 8 sub-mm cores which possess the hallmarks of protostellar cores and identify YSO candidates from 2MASS data. We infer the past and future evolution of the clouds and demonstrate via a simple pressure-based argument that the UV illumination may have induced the collapse of the dense molecular cores found at the head of SFO 11 and SFO 11 E
Nulling interferometry: performance comparison between Antarctica and other ground-based sites
Detecting the presence of circumstellar dust around nearby solar-type main
sequence stars is an important pre-requisite for the design of future
life-finding space missions such as ESA's Darwin or NASA's Terrestrial Planet
Finder (TPF). The high Antarctic plateau may provide appropriate conditions to
perform such a survey from the ground. We investigate the performance of a
nulling interferometer optimised for the detection of exozodiacal discs at Dome
C, on the high Antarctic plateau, and compare it to the expected performance of
similar instruments at temperate sites. Based on the currently available
measurements of the turbulence characteristics at Dome C, we adapt the GENIEsim
software (Absil et al. 2006, A&A 448) to simulate the performance of a nulling
interferometer on the high Antarctic plateau. To feed a realistic instrumental
configuration into the simulator, we propose a conceptual design for ALADDIN,
the Antarctic L-band Astrophysics Discovery Demonstrator for Interferometric
Nulling. We assume that this instrument can be placed above the 30-m high
boundary layer, where most of the atmospheric turbulence originates. We show
that an optimised nulling interferometer operating on a pair of 1-m class
telescopes located 30 m above the ground could achieve a better sensitivity
than a similar instrument working with two 8-m class telescopes at a temperate
site such as Cerro Paranal. The detection of circumstellar discs about 20 times
as dense as our local zodiacal cloud seems within reach for typical Darwin/TPF
targets in a integration time of a few hours. Moreover, the exceptional
turbulence conditions significantly relax the requirements on real-time control
loops, which has favourable consequences on the feasibility of the nulling
instrument.Comment: 10 pages, accepted for publication in A&
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