84 research outputs found
Automated reduction of submillimetre single-dish heterodyne data from the James Clerk Maxwell Telescope using ORAC-DR
With the advent of modern multi-detector heterodyne instruments that can
result in observations generating thousands of spectra per minute it is no
longer feasible to reduce these data as individual spectra. We describe the
automated data reduction procedure used to generate baselined data cubes from
heterodyne data obtained at the James Clerk Maxwell Telescope. The system can
automatically detect baseline regions in spectra and automatically determine
regridding parameters, all without input from a user. Additionally it can
detect and remove spectra suffering from transient interference effects or
anomalous baselines. The pipeline is written as a set of recipes using the
ORAC-DR pipeline environment with the algorithmic code using Starlink software
packages and infrastructure. The algorithms presented here can be applied to
other heterodyne array instruments and have been applied to data from
historical JCMT heterodyne instrumentation.Comment: 18 pages, 13 figures, submitted to Monthly Notices of the Royal
Astronomical Societ
IRC+10216's Innermost Envelope -- The eSMA's View
We used the Extended Submillimeter Array (eSMA) in its most extended
configuration to investigate the innermost (within a radius of 290 R* from the
star) circumstellar envelope (CSE) of IRC+10216. We imaged the CSE using HCN
and other molecular lines with a beam size of 0."22 x 0."46, deeply into the
very inner edge (15 R*) of the envelope where the expansion velocity is only 3
km/s. The excitation mechanism of hot HCN and KCl maser lines is discussed. HCN
maser components are spatially resolved for the first time on an astronomical
object. We identified two discrete regions in the envelope: a region with a
radius of . 15 R*, where molecular species have just formed and the gas has
begun to be accelerated (region I) and a shell region (region II) with a radius
of 23 R* and a thickness of 15 R*, whose expansion velocity has reached up to
13 km/s, nearly the terminal velocity of 15 km/s. The SiS line detected
in region I shows a large expansion velocity of 16 km/s due to strong wing
components, indicating that the emission may arise from a shock region in the
innermost envelope. In region II, the P.A. of the most copious mass loss
direction was found to be 120 +/- 10 degrees, which may correspond to the
equatorial direction of the star. Region II contains a torus-like feature.
These two regions may have emerged due to significant differences in the size
distributions of the dust particles in the two regions.Comment: 26 pages, 8 figures, accepted for publication in The Astrophysical
Journal. Please find the pdf at
http://www.submm.caltech.edu/~hs/astroph/0904.0280.pdf and the ps file at
http://www.submm.caltech.edu/~hs/astroph/0904.0280.p
Resolving the inner jet structure of 1924-292 with the EVENT HORIZON TELESCOPE
We present the first 1.3 mm (230 GHz) very long baseline interferometry model
image of an AGN jet using closure phase techniques with a four-element array.
The model image of the quasar 1924-292 was obtained with four telescopes at
three observatories: the James Clerk Maxwell Telescope (JCMT) on Mauna Kea in
Hawaii, the Arizona Radio Observatory's Submillimeter Telescope (SMT) in
Arizona, and two telescopes of the Combined Array for Research in
Millimeterwave Astronomy (CARMA) in California in April 2009. With the greatly
improved resolution compared with previous observations and robust closure
phase measurement, the inner jet structure of 1924-292 was spatially resolved.
The inner jet extends to the northwest along a position angle of at
a distance of 0.38\,mas from the tentatively identified core, in agreement with
the inner jet structure inferred from lower frequencies, and making a position
angle difference of with respect to the cm-jet. The size of
the compact core is 0.15\,pc with a brightness temperature of
\,K. Compared with those measured at lower frequencies, the
low brightness temperature may argue in favor of the decelerating jet model or
particle-cascade models. The successful measurement of closure phase paves the
way for imaging and time resolving Sgr A* and nearby AGN with the Event Horizon
Telescope.Comment: 6 pages, 4 figures, accepted for publication in ApJ
The eSMA: description and first results
The eSMA ("extended SMA") combines the SMA, JCMT and CSO into a single
facility, providing enhanced sensitivity and spatial resolution owing to the
increased collecting area at the longest baselines. Until ALMA early science
observing (2011), the eSMA will be the facility capable of the highest angular
resolution observations at 345 GHz. The gain in sensitivity and resolution will
bring new insights in a variety of fields, such as protoplanetary/transition
disks, high-mass star formation, solar system bodies, nearby and high-z
galaxies. Therefore the eSMA is an important facility to prepare the grounds
for ALMA and train scientists in the techniques.
Over the last two years, and especially since November 2006, there has been
substantial progress toward making the eSMA into a working interferometer. In
particular, (i) new 345-GHz receivers, that match the capabilities of the SMA
system, were installed at the JCMT and CSO; (ii) numerous tests have been
performed for receiver, correlator and baseline calibrations in order to
determine and take into account the effects arising from the differences
between the three types of antennas; (iii) first fringes at 345 GHz were
obtained on August 30 2007, and the array has entered the science-verification
stage.
We report on the characteristics of the eSMA and its measured performance at
230 GHz and that expected at 345 GHz. We also present the results of the
commissioning and some initial science-verification observations, including the
first absorption measurement of the C/CO ratio in a galaxy at z=0.89, located
along the line of sight to the lensed quasar PKS1830-211, and on the imaging of
the vibrationally excited HCN line towards IRC+10216.Comment: 12 pages, 7 figures, paper number 7012-12, to appear in Proceedings
of SPIE vol. 7012: "Ground-based and Airborne Telescopes II", SPIE conference
on Astronomical Instrumentation, Marseille, 23-28 June 200
A new era of wide-field submillimetre imaging: on-sky performance of SCUBA-2
SCUBA-2 is the largest submillimetre wide-field bolometric camera ever built.
This 43 square arc-minute field-of-view instrument operates at two wavelengths
(850 and 450 microns) and has been installed on the James Clerk Maxwell
Telescope on Mauna Kea, Hawaii. SCUBA-2 has been successfully commissioned and
operational for general science since October 2011. This paper presents an
overview of the on-sky performance of the instrument during and since
commissioning in mid-2011. The on-sky noise characteristics and NEPs of the 450
and 850 micron arrays, with average yields of approximately 3400 bolometers at
each wavelength, will be shown. The observing modes of the instrument and the
on-sky calibration techniques are described. The culmination of these efforts
has resulted in a scientifically powerful mapping camera with sensitivities
that allow a square degree of sky to be mapped to 10 mJy/beam rms at 850 micron
in 2 hours and 60 mJy/beam rms at 450 micron in 5 hours in the best weather.Comment: 18 pages, 15 figures.SPIE Conference series 8452, Millimetre,
Submillimetre and Far-infrared Detectors and Instrumentation for Astronomy VI
201
Detection of CI in absorption towards PKS 1830-211 with the eSMA
We report the first science observations and results obtained with the
"extended" SMA (eSMA), which is composed of the SMA (Submillimeter Array), JCMT
(James Clerk Maxwell Telescope) and CSO (Caltech Submillimeter Observatory).
Redshifted absorptions at z=0.886 of CI (^3P_1 - ^3P_0) were observed with the
eSMA with an angular resolution of 0.55"x0.22" at 1.1 mm toward the
southwestern image of the remarkable lensed quasar PKS 1830-211, but not toward
the northeastern component at a separation of ~1". Additionally, SMA
observations of CO, 13CO and C18O (all J=4-3) were obtained toward this object:
CO was also detected toward the SW component, but none of the isotopologues
were. This is the first time [CI] is detected in this object, allowing the
first direct determination of relative abundances of neutral atomic carbon to
CO in the molecular clouds of a spiral galaxy at z>0.1. The [CI] and CO
profiles can be decomposed into two and three velocity components respectively.
We derive C/CO column density ratios ranging from <0.5 (representative of dense
cores) to ~2.5 (close to translucent clouds values). This could indicate that
we are seeing environments with different physical conditions or that we are
witnessing chemical evolution of regions where C has not completely been
converted into CO.Comment: 6 pages using emulateapj, 3 tables, 2 figures ; accepted for
publication in ApJ
Vigorous star formation hidden by dust in a galaxy at
Near-infrared surveys have revealed a substantial population of enigmatic
faint galaxies with extremely red optical-to-near-infrared colours and with a
sky surface density comparable to that of faint quasars. There are two
scenarios for these extreme colours: (i) these distant galaxies have formed
virtually all their stars at very high redshifts and, due to the absence of
recently formed stars, the colours are extremely red and (ii) these distant
galaxies contain large amounts of dust, severely reddening the rest-frame
UV--optical spectrum. HR10 () is considered the archetype of the
extremely red galaxies. Here we report the detection of the continuum emission
from HR10 at 850m and at 1250m, demonstrating that HR10 is a very
dusty galaxy undergoing a major episode of star formation. Our result provides
a clear example of a high-redshift galaxy where the star formation rate
inferred from the ultraviolet luminosity would be underestimated by a factor up
to 1000, and shows that great caution should be used to infer the global star
formation history of the Universe from optical observations only.Comment: 12 pages, 1 figure, Nature, in press (30 April 1998
1.3 mm Wavelength VLBI of Sagittarius A*: Detection of Time-Variable Emission on Event Horizon Scales
Sagittarius A*, the ~4 x 10^6 solar mass black hole candidate at the Galactic
Center, can be studied on Schwarzschild radius scales with (sub)millimeter
wavelength Very Long Baseline Interferometry (VLBI). We report on 1.3 mm
wavelength observations of Sgr A* using a VLBI array consisting of the JCMT on
Mauna Kea, the ARO/SMT on Mt. Graham in Arizona, and two telescopes of the
CARMA array at Cedar Flat in California. Both Sgr A* and the quasar calibrator
1924-292 were observed over three consecutive nights, and both sources were
clearly detected on all baselines. For the first time, we are able to extract
1.3 mm VLBI interferometer phase information on Sgr A* through measurement of
closure phase on the triangle of baselines. On the third night of observing,
the correlated flux density of Sgr A* on all VLBI baselines increased relative
to the first two nights, providing strong evidence for time-variable change on
scales of a few Schwarzschild radii. These results suggest that future VLBI
observations with greater sensitivity and additional baselines will play a
valuable role in determining the structure of emission near the event horizon
of Sgr A*.Comment: 8 pages, submitted to ApJ
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