40 research outputs found
Improved VLBI astrometry of OH maser stars
Aims: Accurate distances to evolved stars with high mass loss rates are
needed for studies of many of their fundamental properties. However, as these
stars are heavily obscured and variable, optical and infrared astrometry is
unable to provide enough accuracy.
Methods: Astrometry using masers in the circumstellar envelopes can be used
to overcome this problem. We have observed the OH masers of a number of
Asymptotic Giant Branch (AGB) stars for approximately 1 year with the Very Long
Baseline Array (VLBA). We have used the technique of phase referencing with
in-beam calibrators to test the improvements this technique can provide to Very
Long Baseline Interferometry (VLBI) OH maser astrometric observations.
Results: We have significantly improved the parallax and proper motion
measurements of the Mira variable stars U Her, S CrB and RR Aql.
Conclusions: It is shown that both in-beam phase-referencing and a decrease
in solar activity during the observations significantly improves the accuracy
of the astrometric observations. The improved distances to S CrB (418 +21 -18
pc) and RR Aql (633 +214 -128 pc) are fully consistent with published P-L
relations, but the distance to U Her (266 +32 -28 pc) is significantly smaller.
We conclude that for sources that are bright and have a nearby in-beam
calibrator, VLBI OH maser astrometry can be used to determine distances to OH
masing stars of up to ~2 kpc.Comment: 15 pages, 10 figures; accepted for publication in A&A; for a version
with high-resolution figures see
http://www.astro.uni-bonn.de/~wouter/papers/astrom/astrom.shtm
Asymptotic Giant Branch Variables in the Galaxy and the Local Group
AGB variables, particularly the large amplitude Mira type, are a vital step
on the distance scale ladder. They will prove particularly important in the era
of space telescopes and extremely large ground-based telescopes with adaptive
optics, which will be optimized for infrared observing. Our current
understanding of the distances to these stars is reviewed with particular
emphasis on improvements that came from Hipparcos as well as on recent work on
Local Group galaxies. In addition to providing the essential calibration for
extragalactic distances Gaia may also provide unprecedented insight into the
poorly understood mass-loss process itself.Comment: Accepted for publication in Astrophysics and Space Science. From a
presentation at the conference "The Fundamental Cosmic Distance Scale: State
of the Art and Gaia Perspective, Naples May 2011. 8 Pages, 9 Figure
VERA Observation of the W49N H2O Maser Outburst in 2003 October
We report on a strong outburst of the W49N H2O maser observed with VERA.
Single-dish monitoring with VERA 20 m telescopes detected a strong outburst of
the maser feature at V_LSR = -30.7 km/s in 2003 October. The outburst had a
duration of ~100 days and a peak intensity of 7.9 x 10^4 Jy, being one of the
strongest outbursts in W49N observed so far. VLBI observations with the VERA
array were also carried out near to the maximum phase of the outburst, and the
outburst spot was identified in the VLBI map. While the map was in good
agreement with previous studies, showing three major concentrations of maser
spots, we found a newly formed arc-like structure in the central maser
concentration, which may be a shock front powered by a forming star or a star
cluster. The outburst spot was found to be located on the arc-like structure,
indicating a possible connection of the present outburst to a shock phenomenon.Comment: 4 pages, 2 figures included, to appear in PASJ letter (Vol.56, #3,
2004 June
Young and Intermediate-age Distance Indicators
Distance measurements beyond geometrical and semi-geometrical methods, rely
mainly on standard candles. As the name suggests, these objects have known
luminosities by virtue of their intrinsic proprieties and play a major role in
our understanding of modern cosmology. The main caveats associated with
standard candles are their absolute calibration, contamination of the sample
from other sources and systematic uncertainties. The absolute calibration
mainly depends on their chemical composition and age. To understand the impact
of these effects on the distance scale, it is essential to develop methods
based on different sample of standard candles. Here we review the fundamental
properties of young and intermediate-age distance indicators such as Cepheids,
Mira variables and Red Clump stars and the recent developments in their
application as distance indicators.Comment: Review article, 63 pages (28 figures), Accepted for publication in
Space Science Reviews (Chapter 3 of a special collection resulting from the
May 2016 ISSI-BJ workshop on Astronomical Distance Determination in the Space
Age
Event-related potential studies of post-traumatic stress disorder: a critical review and synthesis
Despite the sparseness of the currently available data, there is accumulating evidence of information processing impairment in post-traumatic stress disorder (PTSD). Studies of event-related potentials (ERPs) are the main tool in real time examination of information processing. In this paper, we sought to critically review the ERP evidence of information processing abnormalities in patients with PTSD. We also examined the evidence supporting the existence of a relationship between ERP abnormalities and symptom profiles or severity in PTSD patients. An extensive Medline search was performed. Keywords included PTSD or post-traumatic stress disorder, electrophysiology or EEG, electrophysiology, P50, P100, N100, P2, P200, P3, P300, sensory gating, CNV (contingent negative variation) and MMN (mismatch negativity). We limited the review to ERP adult human studies with control groups which were reported in the English language. After applying our inclusion-exclusion review criteria, 36 studies were included. Subjects exposed to wide ranges of military and civilian traumas were studied in these reports. Presented stimuli were both auditory and visual. The most widely studied components included P300, P50 gating, N100 and P200. Most of the studies reported increased P300 response to trauma-related stimuli in PTSD patients. A smaller group of studies reported dampening of responses or no change in responses to trauma-related and/or unrelated stimuli. P50 studies were strongly suggestive of impaired gating in patients with PTSD. In conclusion, the majority of reports support evidence of information processing abnormalities in patients with PTSD diagnosis. The predominance of evidence suggests presence of mid-latency and late ERP components differences in PTSD patients in comparison to healthy controls. Heterogeneity of assessment methods used contributes to difficulties in reaching firm conclusions regarding the nature of these differences. We suggest that future ERP-PTSD studies utilize standardized assessment scales that provide detailed information regarding the symptom clusters and the degree of symptom severity. This would allow assessment of electrophysiological indices-clinical symptoms relationships. Based on the available data, we suggest that ERP abnormalities in PTSD are possibly affected by the level of illness severity. If supported by future research, ERP studies may be used for both initial assessment and treatment follow-up
Inhibition of mTOR delayed but could not prevent experimental collapsing focal segmental glomerulosclerosis
Contains fulltext :
220207.pdf (publisher's version ) (Open Access
ATLASGAL-selected massive clumps in the inner Galaxy III. Dust Continuum Characterization of an Evolutionary Sample
Context: Massive-star formation and the processes involved are still poorly understood. The ATLASGAL survey provides an ideal basis for detailed studies of large numbers of massive-star forming clumps covering the whole range of evolutionary stages. The ATLASGAL Top100 is a sample of clumps selected by their infrared and radio properties to be representative for the whole range of evolutionary stages.
Aims: The ATLASGAL Top100 sources are the focus of a number of detailed follow-up studies that will be presented in a series of papers. In the present work we use the dust continuum emission to constrain the physical properties of this sample and identify trends as a function of source evolution.
Methods: We determine flux densities from mid-infrared to submillimeter wavelength (8–870 μm) images and use these values to fit their spectral energy distributions and determine their dust temperature and flux. Combining these with recent distances from the literature including maser parallax measurements we determine clump masses, luminosities and column densities.
Results: We define four distinct source classes from the available continuum data and arrange these into an evolutionary sequence. This begins with sources found to be dark at 70 μm, followed by 24 μm weak sources with an embedded 70 μm source, continues through mid-infrared bright sources and ends with infrared bright sources associated with radio emission (i.e., H ii regions). We find trends for increasing temperature, luminosity, and column density with the proposed evolution sequence, confirming that this sample is representative of different evolutionary stages of massive star formation. Our sources span temperatures from approximately 11 to 41 K, with bolometric luminosities in the range 57 L⊙−3.8 × 106L⊙. The highest masses reach 4.3 × 104M⊙ and peak column densities up to 1.1 × 1024 cm-1, and therefore have the potential to form the most massive O-type stars. We show that at least 93 sources (85%) of this sample have the ability to form massive stars and that most are gravitationally unstable and hence likely to be collapsing.
Conclusions: The highest column density ATLASGAL sources cover the whole range of evolutionary stages from the youngest to the most evolved high-mass-star forming clumps. Study of these clumps provides a unique starting point for more in-depth research on massive-star formation in four distinct evolutionary stages whose well defined physical parameters afford more detailed studies. As most of the sample is closer than 5 kpc, these sources are also ideal for follow-up observations with high spatial resolution