794 research outputs found
Lunar penetrometer Patent
Development and characteristics of pentrometer for measuring physical properties of lunar surfac
Deep MERLIN 5GHz Radio Imaging of Supernova Remnants in the M82 Starburst
The results of an extremely deep, 8-day long observation of the central kpc
of the nearby starburst galaxy M82 using MERLIN (Multi-Element Radio Linked
Interferometer Network) at 5 GHz are presented. The 17E-06 Jy/beam, rms noise
level in the naturally weighted image make it the most sensitive high
resolution radio image of M82 made to date. Over 50 discrete sources are
detected, the majority of which are supernova remnants, but with 13 identified
as HII regions. Sizes, flux densities and radio brightnesses are given for all
of the detected sources, which are all well resolved with a majority showing
shell or partial shell structures. Those sources within the sample which are
supernova remnants have diameters ranging from 0.3 to 6.7 pc, with a mean size
of 2.9 pc.
From a comparison with previous MERLIN 5 GHz observations made in July 1992,
which gives a 9.75 year timeline, it has been possible to measure the expansion
velocities of ten of the more compact sources, eight of which have not been
measured before. These derived expansion velocities range between 2200 and
10500 km/s.Comment: 34 pages, 10 figures. Accepted by MNRA
ALMA observations of 99 GHz free-free and H40 line emission from star formation in the centre of NGC 253
We present Atacama Large Millimeter/submillimeter Array observations of 99.02
GHz free-free and H40 emission from the centre of the nearby starburst
galaxy NGC 253. We calculate electron temperatures of 3700-4500 K for the
photoionized gas, which agrees with previous measurements. We measure a
photoionizing photon production rate of s and
a star formation rate of M yr within the central
2010 arcsec, which fall within the broad range of measurements from
previous millimetre and radio observations but which are better constrained. We
also demonstrate that the dust opacities are ~3 dex higher than inferred from
previous near-infrared data, which illustrates the benefits of using millimetre
star formation tracers in very dusty sources.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
Second Epoch Global VLBI Observations of Compact Radio Sources in the M82 Starburst Galaxy
We have presented the results of a second epoch of global Very Long Baseline
Interferometry observations, taken on 23 February 2001 at a wavelength of 18
cm, of the central kiloparsec of the nearby starburst galaxy Messier 82. These
observations were aimed at studying the structural and flux evolution of some
of the compact radio sources in the central region that have been identified as
supernova remnants. The objects 41.95+575 and 43.31+592 have been studied,
expansion velocities of 2500 +/- 1200 km/s and 7350 +/- 2100 km/s respectively
have been derived. Flux densities of 31.1 +/- 0.3 mJy and 17.4 +/- 0.3 mJy have
been measured for the two objects. These results are consistent with
measurements and predictions from previous epochs.Comment: 5 pages, 3 figures. To be published on the accompanying CD of the
Proceedings of IAU Colloquium 192: Supernova
Multi-source self-calibration: Unveiling the microJy population of compact radio sources
Context. Very Long Baseline Interferometry (VLBI) data are extremely
sensitive to the phase stability of the VLBI array. This is especially
important when we reach {\mu}Jy r.m.s. sensitivities. Calibration using
standard phase referencing techniques is often used to improve the phase
stability of VLBI data but the results are often not optimal. This is evident
in blank fields that do not have in-beam calibrators. Aims. We present a
calibration algorithm termed Multi-Source Self-Calibration (MSSC) which can be
used after standard phase referencing on wide-field VLBI observations. This is
tested on a 1.6 GHz wide-field VLBI data set of the Hubble Deep Field-North and
the Hubble Flanking Fields. Methods. MSSC uses multiple target sources detected
in the field via standard phase referencing techniques and modifies the
visibili- ties so that each data set approximates to a point source. These are
combined to increase the signal to noise and permit self-calibration. In
principle, this should allow residual phase changes caused by the troposphere
and ionosphere to be corrected. By means of faceting, the technique can also be
used for direction dependent calibration. Results. Phase corrections, derived
using MSSC, were applied to a wide-field VLBI data set of the HDF-N comprising
of 699 phase centres. MSSC was found to perform considerably better than
standard phase referencing and single source self-calibration. All detected
sources exhibited dramatic improvements in dynamic range. Using MSSC, one
source reached the detection threshold taking the total detected sources to
twenty. 60% of these sources can now be imaged with uniform weighting compared
to just 45% with standard phase referencing. The Parseltongue code which
implements MSSC has been released and made publicly available to the
astronomical community (https://github.com/jradcliffe5/multi_self_cal).Comment: 7 pages, 4 figures, accepted to A&
Resolving the masers in M82
Despite first being detected in the 1970s, surprisingly little is known about
the OH main line maser population in the nearby starburst galaxy M82. Sometimes
referred to as 'kilomasers', they have isotropic luminosities intermediate
between Galactic masers and those found in more distant megamasers. Several
observations have been carried by this group over the last ten years in an
attempt to get a better handle on their nature. High velocity resolution VLA
observations in 2006 showed that almost all of the maser spots, distributed
across the central arcminute of the galaxy, were apparently coincident with
background continuum features, and a handful displayed multiple velocity
components. The majority of those with velocity structure are located on a
blue-shifted arc in the pv-plane, spatially located on an arc northward of the
peculiar source known as B41.95+57.5. Now, new results from high spatial and
spectral resolution observations with the EVN have resolved several of these
masers into multiple spatial components for the first time. The maser emission
is compared with known continuum sources in the galaxy, and we conclude that at
least some of the maser emission is from high-gain maser action.Comment: Six pages, one table, one figure. To appear in proceedings of the
11th EVN Symposium (Bordeaux, 9-12 October 2012
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