515 research outputs found
Possible magnetic field variability during the 6.7 GHz methanol maser flares of G09.62+0.20
(Abridged) Recently, the magnetic field induced Zeeman splitting was measured
for the strongest known 6.7 GHz methanol maser, which arises in the massive
star forming region G09.62+0.20. This maser is one of a handful of periodically
flaring methanol masers. The 100-m Effelsberg telescope was used to monitor the
6.7 GHz methanol masers of G09.62+0.20. With the exception of a two week period
during the peak of the maser flare, we measure a constant magnetic field of
B_||~11+-2 mG in the two strongest maser components of G09.62+0.20 that are
separated by over 200 AU. In the two week period that coincides exactly with
the peak of the maser flare of the strongest maser feature, we measure a sharp
decrease and possible reversal of the Zeeman splitting. The exact cause of both
maser and polarization variability is still unclear, but it could be related to
either background amplification of polarized emission or the presence of a
massive protostar with a close-by companion. Alternatively, the polarization
variability could be caused by non-Zeeman effects related to the radiative
transfer of polarized maser emission.Comment: 4 pages, 3 figures, accepted for publication Astronomy and
Astrophysic
KAT-7 Science Verification: Using HI Observations of NGC 3109 to Understand its Kinematics and Mass Distribution
HI observations of the Magellanic-type spiral NGC 3109, obtained with the
seven dish Karoo Array Telescope (KAT-7), are used to analyze its mass
distribution. Our results are compared to what is obtained using VLA data.
KAT-7 is the precursor of the SKA pathfinder MeerKAT, which is under
construction. The short baselines and low system temperature of the telescope
make it sensitive to large scale low surface brightness emission. The new
observations with KAT-7 allow the measurement of the rotation curve of NGC 3109
out to 32', doubling the angular extent of existing measurements. A total HI
mass of 4.6 x 10^8 Msol is derived, 40% more than what was detected by the VLA
observations.
The observationally motivated pseudo-isothermal dark matter (DM) halo model
can reproduce very well the observed rotation curve but the cosmologically
motivated NFW DM model gives a much poorer fit to the data. While having a more
accurate gas distribution has reduced the discrepancy between the observed RC
and the MOdified Newtonian Dynamics (MOND) models, this is done at the expense
of having to use unrealistic mass-to-light ratios for the stellar disk and/or
very large values for the MOND universal constant a0. Different distances or HI
contents cannot reconcile MOND with the observed kinematics, in view of the
small errors on those two quantities. As for many slowly rotating gas-rich
galaxies studied recently, the present result for NGC 3109 continues to pose a
serious challenge to the MOND theory.Comment: 25 pages, 20 figures, accepted for publication in Astronomical
Journa
VLBA imaging of a periodic 12.2 GHz methanol maser flare in G9.62+0.20E
The class II methanol maser source G9.62+0.20E undergoes periodic flares at
both 6.7 and 12.2 GHz. The flare starting in 2001 October was observed at seven
epochs over three months using the VLBA at 12.2 GHz. High angular resolution
images (beam size 1.7 x 0.6 mas) were obtained, enabling us to observe
changes in 16 individual maser components. It was found that while existing
maser spots increased in flux density, no new spots developed and no changes in
morphology were observed. This rules out any mechanism which disturbs the
masing region itself, implying that the flares are caused by a change in either
the seed or pump photon levels. A time delay of 1--2 weeks was observed between
groups of maser features. These delays can be explained by light travel time
between maser groups. The regularity of the flares can possibly be explained by
a binary system.Comment: 11 pages, accepted for publication in MNRA
Periodic class II methanol masers in G9.62+0.20E
We present the light curves of the 6.7 and 12.2 GHz methanol masers in the
star forming region G9.62+0.20E for a time span of more than 2600 days. The
earlier reported period of 244 days is confirmed. The results of monitoring the
107 GHz methanol maser for two flares are also presented. The results show that
flaring occurs in all three masing transitions. It is shown that the average
flare profiles of the three masing transitions are similar. The 12.2 GHz masers
are the most variable of the three masers with the largest relative amplitude
having a value of 2.4. The flux densities for the different masing transitions
are found to return to the same level during the low phase of the masers,
suggesting that the source of the periodic flaring is situated outside the
masing region, and that the physical conditions in the masing region are
relatively stable. On the basis of the shape of the light curve we excluded
stellar pulsations as the underlying mechanism for the periodicity. It is
argued that a colliding wind binary can account for the observed periodicity
and provide a mechanism to qualitatively explain periodicity in the seed photon
flux and/or the pumping radiation field. It is also argued that the dust
cooling time is too short to explain the decay time of about 100 days of the
maser flare. A further analysis has shown that for the intervals from days 48
to 66 and from days 67 to 135 the decay of the maser light curve can be
interpreted as due to the recombination of a thermal hydrogen plasma with
densities of approximately and respectively.Comment: 11 pages, 9 figuer
Forensic investigation of microtraces on an item of Dutch eighteenth century clothing in the Rijksmuseum collection
Most garments in museum collections have belonged to people of high societal status. Clothing of the common people, however, has rarely been preserved. Because of this, the conservation of such rare items is of special importance. The current study focuses on such an object from the Rijksmuseum collection; a pair of eighteenth century breeches that were retrieved from an anonymous grave on Spitsbergen. As these breeches contain several unidentified materials, it is unclear how best to conduct the conservation of the object. The identification of trace material plays a key role within criminal law and therefore, it is hypothesized that a forensic approach could provide a suitable framework within this case of cultural heritage as well. After forensic examination, trace material was analyzed using a microscopy-based approach and was found to be mainly of biological origin. Energy-dispersive X-ray (EDX) and Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy indicated the presence of human skin remains. It was concluded that a modern forensic approach can successfully be applied to a historical object within cultural heritage and can assist decision-making regarding possible future conservation of the object. The systematic application of the forensic methodology was found to be appropriate with little to no modification to classify and identify trace materials, but further improvements could be made. The current work should be seen as a starting point that allows for more questions regarding museum objects to be answered in a forensic manner, including aspects such as authenticity, the chain of custody, the context, original use and object conservation
New Periodic 6.7 GHz Class II Methanol Maser Associated with G358.460-0.391
Eight new class II methanol masers selected from the 6.7 GHz Methanol
Multibeam survey catalogues I and II were monitored at 6.7 GHz with the 26m
Hartebeesthoek Radio Astronomy Observatory (HartRAO) radio telescope for three
years and seven months, from February 2011 to September 2014. The sources were
also observed at 12.2 GHz and two were sufficiently bright to permit
monitoring. One of the eight sources, namely G358.460-0.391, was found to show
periodic variations at 6.7 GHz. The period was determined and tested for
significance using the Lomb-Scargle, epoch-folding and Jurkevich methods, and
by fitting a simple analytic function. The best estimate for the period of the
6.7 GHz class II methanol maser line associated with G358.460-0.391 is 220.0
0.2 day.Comment: 8 pages, 11 figures, accepted for publication in MNRAS. The appendix
of 4 pages (with 16 figures) will be published as online versio
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