4,080 research outputs found
G315.1+2.7: a new Galactic SNR from the AAO/UKST HAlpha survey
New narrow-band HAlpha imaging and subsequent optical spectra confirm
G315.1+2.7, a previously identified candidate supernova remnant (SNR), as a
bona-fide Galactic SNR. Present observations are based on independent discovery
of filamentary optical emission nebulosity on images of the AAO/UKST HAlpha
survey of the southern Galactic plane which were found to co-incide with
existing multi-frequency radio detections. Separate medium and high dispersion
spectra were taken across two locations of this 11 arcmin N-S aligned optical
filament. The resulting spectral signatures were found to strongly confirm the
SNR identification based on standard emission line ratio discriminators which
characterise emission from shock heated gas. The average observed ratios of
[SII]/HAlpha=1.13, [NII]/HAlpha=1.43 and [SII] 6717/6731=1.46, together with
the simultaneous detection of [OII] at 3727A, [OIII] 5007A and [OI] 6300A, all
point to an SNR origin of the observed optical emission. Careful scrutiny of
the low-resolution but high sensitivity SHASSA HAlpha survey also revealed a
low-level but distinct optical emission arc. This arc precisely correlates with
the large, 2.5 degree, north-south angular extent of the proposed new SNR also
seen as a fractured structure in the extant radio data. G315.1+2.7 was detected
previously at 2400 and 4800 MHz and at 408 and 1420 MHz. We also identified
associated radio emission at 843 MHz from the now publicly available SUMSS
survey. On the basis of optical imaging and spectra and radio observations at
five frequencies, we identify G315.1+2.7 as a new Galactic SNR. The large
projected angular extent of the new remnant, together with the distance
estimate of ~1.7 kpc and diameter of ~80pc, make G315.1+2.7 one of the largest
remnants known.Comment: 10 pages, 10 figures. Accepted for MNRA
Newly confirmed and high quality candidate Galactic SNRs uncovered from the AAO/UKST HAlpha survey
We present a catalogue of 18 new Galactic supernova remnants (SNRs) uncovered
in the optical regime as filamentary emissions and extended nebulosities on
images of the Anglo Australian Observatory/United Kingdom Schmidt Telescope
(AAO/UKST) HAlpha survey of the southern Galactic plane. Our follow-up spectral
observations confirmed classical optical SNR emission lines for these 18
structures via detection of very strong [SII] at 6717 and 6731A relative to
HAlpha ([SII]/HAlpha> 0.5). Morphologically, 10 of these remnants have
coherent, extended arc or shell structures, while the remaining objects are
more irregular in form but clearly filamentary in nature, typical of optically
detected SNRs.
In 11 cases there was a clear if not complete match between the optical and
radio structures with H filamentary structures registered inside and along the
presumed radio borders. Additionally, ROSAT X-ray sources were detected inside
the optical/radio borders of 11 of these new remnants and 3 may have an
associated pulsar.
The multi-wavelength imaging data and spectroscopy together present strong
evidence to confirm identification of 18 new, mostly senile Galactic SNRs. This
includes G288.7-6.3, G315.1+2.7 and G332.5-5.6, identified only as possible
remnants from preliminary radio observations. We also confirm existence of
radio quiet but optically active supernova remnants.Comment: In original form 21 pages, 29 figures Accepted for MNRA
Emission Measures and Emission-measure-weighted Temperatures of Shocked ISM and Ejecta in Supernova Remnants
A goal of supernova remnant (SNR) evolution models is to relate fundamental
parameters of a supernova (SN) explosion and progenitor star to the current
state of its SNR. The SNR hot plasma is characterized by its observed X-ray
spectrum, which yields electron temperature, emission measure and abundances.
Depending on their brightness, the properties of the plasmas heated by the SNR
forward shock, reverse shock or both can be measured. The current work utilizes
models which are spherically symmetric. One dimensional hydrodynamic
simulations are carried out for SNR evolution prior to onset of radiative
losses. From these, we derive dimensionless emission measures and
emission-measure-weighted temperatures, and we present fitting formulae for
these quantities as functions of scaled SNR time. These models allow one to
infer SNR explosion energy, circumstellar medium density, age, ejecta mass and
ejecta density profile from SNR observations. The new results are incorporated
into the SNR modelling code SNRPy. The code is demonstrated with application to
three historical SNRs: Kepler, Tycho and SN1006.Comment: 50 pages, 10 figures, 5 table
Radio-continuum detections of Galactic Planetary Nebulae I. MASH PNe detected in large-scale radio surveys
We present an updated and newly compiled radio-continuum data-base for MASH
PNe detected in the extant large scale "blind" radio-continuum surveys (NVSS,
SUMSS/MGPS-2 and PMN) and, for a small number of MASH PNe, observed and
detected in targeted radio-continuum observations. We found radio counterparts
for approximately 250 MASH PNe. In comparison with the percentage of previously
known Galactic PNe detected in the NVSS and MGPS-2 radio-continuum surveys and
according to their position on the flux density-angular diameter and the radio
brightness temperature evolutionary diagrams we conclude, unsurprisingly, that
the MASH sample presents the radio-faint end of the known Galactic PNe
population. Also, we present radio-continuum spectral properties of a small
sub-sample of MASH PNe located in the strip between declinations -30arcdeg and
-40arcdeg, that are detected in both the NVSS and MGPS-2 radio surveys.Comment: 13 figures and 7 tables, accepted for publication in MNRA
A digital video system for observing and recording occultations
Stellar occultations by asteroids and outer solar system bodies can offer
ground based observers with modest telescopes and camera equipment the
opportunity to probe the shape, size, atmosphere and attendant moons or rings
of these distant objects. The essential requirements of the camera and
recording equipment are: good quantum efficiency and low noise, minimal dead
time between images, good horological faithfulness of the image time stamps,
robustness of the recording to unexpected failure, and low cost. We describe
the Astronomical Digital Video occultation observing and recording System
(ADVS) which attempts to fulfil these requirements and compare the system with
other reported camera and recorder systems. Five systems have been built,
deployed and tested over the past three years, and we report on three
representative occultation observations: one being a 9 +/-1.5 second
occultation of the trans-Neptunian object 28978 Ixion (mv=15.2) at 3 seconds
per frame, one being a 1.51 +/-0.017 second occultation of Deimos, the 12~km
diameter satellite of Mars, at 30 frames per second, and one being a 11.04
+/-0.4 second occultation, recorded at 7.5 frames per second, of the main belt
asteroid, 361 Havnia, representing a low magnitude drop (Dmv = 0.4)
occultation.Comment: 9 pages, 5 figures, 3 tables, accepted to Publications of the
Astronomical Society of Australia (PASA
An XMM-Newton view of Planetary Nebulae in the Small Magellanic Cloud. The X-ray luminous central star of SMP SMC 22
During an X-ray survey of the Small Magellanic Cloud, carried out with the
XMM-Newton satellite, we detected significant soft X-ray emission from the
central star of the high-excitation planetary nebula SMP SMC 22. Its very soft
spectrum is well fit with a non local thermodynamical equilibrium model
atmosphere composed of H, He, C, N, and O, with abundances equal to those
inferred from studies of its nebular lines. The derived effective temperature
of 1.5x10^5 K is in good agreement with that found from the optical/UV data.
The unabsorbed flux in the 0.1-0.5 keV range is about 3x10^{-11} erg cm^-2
s^-1, corresponding to a luminosity of 1.2x10^37 erg/s at the distance of 60
kpc. We also searched for X-ray emission from a large number of SMC planetary
nebulae, confirming the previous detection of SMP SMC 25 with a luminosity of
(0.2-6)x10^35 erg/s (0.1-1 keV). For the remaining objects that were not
detected, we derived flux upper limits corresponding to luminosity values from
several tens to hundreds times smaller than that of SMP SMC 22. The
exceptionally high X-ray luminosity of SMP SMC 22 is probably due to the high
mass of its central star, quickly evolving toward the white dwarf's cooling
branch, and to a small intrinsic absorption in the nebula itself.Comment: Accepted for publication on Astronomy and Astrophysic
The Strongest 100 Point Radio Sources in the LMC at 1.4 GHz
We present the 100 strongest 1.4 GHz point sources from a new mosaic image in
the direction of the Large Magellanic Cloud (LMC). The observations making up
the mosaic were made over a ten year period and were combined with Parkes
single dish data at 1.4 GHz to complete the image for short spacing. An initial
list of co-identifications within 10" at 0.843, 4.8 and 8.6 GHz consisted of
2682 sources. Elimination of extended objects and artifact noise allowed the
creation of a refined list containing 1988 point sources. Most of these are
presumed to be background objects seen through the LMC; a small portion may
represent compact H II regions, young SNRs and radio planetary nebulae. For the
1988 point sources we find a preliminary average spectral index of -0.53 and
present a 1.4 GHz image showing source location in the direction of the LMC.Comment: 8 pages, 2 figure
Multiwavelength appearance of Vela Jr.: Is it up to expectations?
Vela Jr. is one of the youngest and likely nearest among the known galactic
supernova remnants (SNRs). Discovered in 1997 it has been studied since then at
quite a few wavelengths, that spread over almost 20 decades in energy. Here we
present and discuss Vela Jr. properties revealed by these multiwavelength
observations, and confront them with the SNR model expectations. Questions that
remained unanswered at the time of publication of the paper of Iyudin et al.
(2005), e.g. what is the nature of the SNR's proposed central compact source
CXOU J085201.4-461753, and why is the ISM absorption column density apparently
associated with RX J0852.0-4622 much greater than the typical column of the
Vela SNR, can be addressed using the latest radio and X-ray observations of
Vela Jr.. These, and other related questions are addressed in the following.Comment: 8 pages, 7 figures. Accepted for publication in ESA SP-622,
Proceedings of the 6th INTEGRAL Workshop held in Moscow, Russia, July 02-08,
200
Verifying timestamps of occultation observation systems
We describe an image timestamp verification system to determine the exposure
timing characteristics and continuity of images made by an imaging camera and
recorder, with reference to Coordinated Universal Time (UTC). The original use
was to verify the timestamps of stellar occultation recording systems, but the
system is applicable to lunar flashes, planetary transits, sprite recording, or
any area where reliable timestamps are required. The system offers good
temporal resolution (down to 2 msec, referred to UTC) and provides exposure
duration and interframe dead time information. The system uses inexpensive,
off-the- shelf components, requires minimal assembly and requires no
high-voltage components or connections. We also describe an application to load
FITS (and other format) image files, which can decode the verification image
timestamp. Source code, wiring diagrams and built applications are provided to
aid the construction and use of the device.Comment: 10 pages, 7 figures, accepted to Publications of the Astronomical
Society of Australia (PASA
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