208 research outputs found
CCS and NH_3 Emission Associated with Low-Mass Young Stellar Objects
In this work we present a sensitive and systematic single-dish survey of CCS emission (complemented with ammonia observations) at 1 cm, toward a sample of low- and intermediate-mass young star-forming regions known to harbor water maser emission, made with NASA's 70 m antenna at Robledo de Chavela, Spain. Out of the 40 star-forming regions surveyed in the CCS (2_(1)-1_(0)) line, only six low-mass sources show CCS emission: one transitional object between the prestellar and protostellar Class 0 phase (GF9-2), three Class 0 protostars (L1448-IRS3, L1448C, and B1-IRS), a Class I source (L1251A), and a young T Tauri star (NGC 2071 North). Since CCS is considered an "early-time" (≲10^5 yr) molecule, we explain these results by either proposing a revision of the classification of the age of NGC 2071 North and L1251A, or suggesting the possibility that the particular physical conditions and processes of each source affect the destruction/production of the CCS. No statistically significant relationship was found between the presence of CCS and parameters of the molecular outflows and their driving sources. Nevertheless, we found a significant relationship between the detectability of CCS and the ammonia peak intensity (higher in regions with CCS), but not with its integrated intensity. This tendency may suggest that the narrower ammonia line widths in the less turbulent medium associated with younger cores may compensate for the differences in ammonia peak intensity, rendering differences in integrated intensity negligible. From the CCS detection rate we derive a lifetime of this molecule of ≃(0.7-3) × 10^4 yr in low-mass star-forming regions
High-Resolution Observations in B1-IRS: ammonia, CCS and water masers
We present a study of the structure and dynamics of the star forming region
B1-IRS (IRAS 03301+3057) using the properties of different molecules at high
angular resolution (~4''). We have used VLA observations of NH3, CCS, and H2O
masers at 1 cm. CCS emission shows three clumps around the central source, with
a velocity gradient from red to blueshifted velocities towards the protostar,
probably due to the interaction with outflowing material. Water maser emission
is elongated in the same direction as a reflection nebula detected at 2micron
by 2MASS, with the maser spots located in a structure of some hundreds of AU
from the central source, possibly tracing a jet. We propose a new outflow model
to explain all our observations, consisting of a molecular outflow near the
plane of the sky. Ammonia emission is extended and anticorrelated with CCS. We
have detected for the first time this anticorrelation at small scales (1400 AU)
in a star forming region.Comment: 6 pages, 3 figures. To appear in the Proceedings of the 2004 European
Workshop: "Dense Molecular Gas around Protostars and in Galactic Nuclei",
Eds. Y.Hagiwara, W.A.Baan, H.J.van Langevelde, 2004, a special issue of ApSS,
Kluwe
Statistical Studies of Giant Pulse Emission from the Crab Pulsar
We have observed the Crab pulsar with the Deep Space Network (DSN) Goldstone
70 m antenna at 1664 MHz during three observing epochs for a total of 4 hours.
Our data analysis has detected more than 2500 giant pulses, with flux densities
ranging from 0.1 kJy to 150 kJy and pulse widths from 125 ns (limited by our
bandwidth) to as long as 100 microseconds, with median power amplitudes and
widths of 1 kJy and 2 microseconds respectively. The most energetic pulses in
our sample have energy fluxes of approximately 100 kJy-microsecond. We have
used this large sample to investigate a number of giant-pulse emission
properties in the Crab pulsar, including correlations among pulse flux density,
width, energy flux, phase and time of arrival. We present a consistent
accounting of the probability distributions and threshold cuts in order to
reduce pulse-width biases. The excellent sensitivity obtained has allowed us to
probe further into the population of giant pulses. We find that a significant
portion, no less than 50%, of the overall pulsed energy flux at our observing
frequency is emitted in the form of giant pulses.Comment: 19 pages, 17 figures; to be published in Astrophysical Journa
Characterizing the transition from diffuse atomic to dense molecular clouds in the Magellanic clouds with [CII], [CI], and CO
We present and analyze deep Herschel/HIFI observations of the [CII] 158um,
[CI] 609um, and [CI] 370um lines towards 54 lines-of-sight (LOS) in the Large
and Small Magellanic clouds. These observations are used to determine the
physical conditions of the line--emitting gas, which we use to study the
transition from atomic to molecular gas and from C^+ to C^0 to CO in their low
metallicity environments. We trace gas with molecular fractions in the range
0.1<f(H2)<1, between those in the diffuse H2 gas detected by UV absorption
(f(H2)<0.2) and well shielded regions in which hydrogen is essentially
completely molecular. The C^0 and CO column densities are only measurable in
regions with molecular fractions f(H2)>0.45 in both the LMC and SMC. Ionized
carbon is the dominant gas-phase form of this element that is associated with
molecular gas, with C^0 and CO representing a small fraction, implying that
most (89% in the LMC and 77% in the SMC) of the molecular gas in our sample is
CO-dark H2. The mean X_CO conversion factors in our LMC and SMC sample are
larger than the value typically found in the Milky Way. When applying a
correction based on the filling factor of the CO emission, we find that the
values of X_CO in the LMC and SMC are closer to that in the Milky Way. The
observed [CII] intensity in our sample represents about 1% of the total
far-infrared intensity from the LOSs observed in both Magellanic Clouds.Comment: 32 pages, 21 figures, Accepted to Ap
DSS-28: a novel wide bandwidth radio telescope devoted to educational outreach
We have recently equipped the 34-meter DSS-28 radio telescope at the Goldstone Deep Space Communications Complex with a novel wide bandwidth radiometer and digital signal processor as part of the Goldstone Apple Valley Radio Telescope (GAVRT) educational outreach program operated by the Jet Propulsion Laboratory and the Lewis Center for Educational Research. The system employs a cryogenically cooled wide bandwidth quad-ridge feed and InP low noise amplifiers to achieve excellent noise performance from 2.7 to 14 GHz; a fractional bandwidth better than 4:1. Four independently tunable dual-polarization receivers each down-convert a 2 GHz block to baseband, providing access to 8 GHz of instantaneous bandwidth. A flexible FPGA-based signal processor has been constructed using CASPER FPGA hardware and tools to take advantage of this enormous bandwidth. This system demonstrates many of the enabling wide bandwidth technologies that will be crucial to maximizing the utility of future large centimeter-wavelength arrays, in particular the Square Kilometer Array. The GAVRT program has previously used narrow bandwidth total power radiometers to study flux variability of quasars and the outer planets. The versatility of DSS-28 will enable other projects including spectroscopy and SETI. Finally, the wide instantaneous bandwidth available makes this system uniquely suited for studying transient radio pulses. A configuration of the digital signal processor has been developed which provides the capability of recording a burst of raw baseband voltage data triggered by a real-time incoherent dedispersion system which is very sensitive to pulses from a known source, such as the Crab Nebula pulsar
Probing ISM Structure in Trumpler 14 & Carina I Using The Stratospheric Terahertz Observatory 2
We present observations of the Trumpler 14/Carina I region carried out using
the Stratospheric Terahertz Observatory 2 (STO2). The Trumpler 14/Carina I
region is in the west part of the Carina Nebula Complex, which is one of the
most extreme star-forming regions in the Milky Way. We observed Trumpler
14/Carina I in the 158 m transition of [C\,{\sc ii}] with a spatial
resolution of 48 and a velocity resolution of 0.17 km s. The
observations cover a 0.25 by 0.28 area with central position
{\it l} = 297.34, {\it b} = -0.60. The kinematics show that
bright [C\,{\sc ii}] structures are spatially and spectrally correlated with
the surfaces of CO clouds, tracing the photodissociation region and ionization
front of each molecular cloud. Along 7 lines of sight that traverse Tr 14 into
the dark ridge to the southwest, we find that the [C\,{\sc ii}] luminosity from
the HII region is 3.7 times that from the PDR. In same los we find in the PDRs
an average ratio of 1:4.1:5.6 for the mass in atomic gas:dark-CO gas: molecular
gas traced by CO. Comparing multiple gas tracers including HI 21cm, [C\,{\sc
ii}], CO, and radio recombination lines, we find that the HII regions of the
Carina Nebula Complex are well-described as HII regions with one-side freely
expanding towards us, consistent with the champagne model of ionized gas
evolution. The dispersal of the GMC in this region is dominated by EUV
photoevaporation; the dispersal timescale is 20-30 Myr.Comment: ApJ accepte
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
High-Resolution Molecular Line Observations of the Environment of the Class 0 Source B1-IRS
In this work we present VLA observations of the NH3, CCS, and H2O maser
emission at 1 cm from the star forming region B1-IRS (IRAS 03301+3057) with ~
5" (=1750 AU) of angular resolution. CCS emission is distributed in three
clumps around the central source. These clumps exhibit a velocity gradient from
red- to blueshifted velocities toward B1-IRS, probably due to an interaction
with the outflow from an embedded protostar. The outflow and its powering
source are traced by a reflection nebula and an associated infrared point
source detected in a 2MASS K-band image. We find that this infrared point
source is associated with water maser emission distributed in an elongated
structure (~ 450 AU size) along the major axis of the reflection nebula and
tracing the base of the outflow of the region. Ammonia emission is extended and
spatially anticorrelated with CCS. This is the first time that this kind of
anticorrelation is observed in a star forming region with such a high angular
resolution, and illustrates the importance of time-dependent chemistry on small
spatial scales. The relatively large abundance of CCS with respect to ammonia,
compared with other star forming regions, suggests an extreme youth for the
B1-IRS object (<10E+5 yr). We suggest the possibility that CCS abundance is
enhanced via shock-induced chemistry.Comment: 31 pages, 9 figures. Accepted by The Astrophysical Journa
H-alpha emitters in z~2 proto-clusters: evidence for faster evolution in dense environments
This is a study of H-alpha emitters in two dense galaxy proto-clusters
surrounding radio galaxies at z~2. We show that the proto-cluster surrounding
MRC 1138-262 contains 14+/-2 times more H-alpha candidates than the average
field (9 sigma significance), and the z=2.35 radio galaxy 4C+10.48 is
surrounded by 12+/-2 times more emitters than the field (5 sigma), so it is
also likely to reside in a dense proto-cluster environment. We compared these
H-alpha emitters, situated in dense environments, to a control field sample
selected from 3 separate fields forming a total area of 172 arcmin^2. We
constructed and compared H-alpha and rest-frame R continuum luminosity
functions of the emitters in both environments. The star formation density is
on average 13 times greater in the proto-clusters than the field at z~2, so the
total star formation rate within the central 1.5Mpc of the proto-clusters
exceeds 3000Msun/yr. However, we found no significant difference in the shape
of the H-alpha luminosity functions, implying that environment does not
substantially affect the strength of the H-alpha line from strongly star
forming galaxies. The proto-cluster emitters are typically 0.8mag brighter in
rest-frame R continuum than field emitters, implying they are twice as massive
as their field counterparts at the same redshift. We also show the
proto-cluster galaxies have lower specific star formation rates than field
galaxies, meaning the emitters in the dense environments formed more of their
stars earlier than the field galaxies. We conclude that galaxy growth in the
early Universe was accelerated in dense environments, and that cluster galaxies
differed from field galaxies even before the cluster had fully formed.Comment: Accepted for publication in MNRA
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