3,652 research outputs found
Sub-au imaging of water vapour clouds around four Asymptotic Giant Branch stars
We present MERLIN maps of the 22-GHz H2O masers around four low-mass
late-type stars (IK Tau U Ori, RT Vir and U Her), made with an angular
resolution of ~ 15 milliarcsec and a velocity resolution of 0.1 km s-1. The H2O
masers are found in thick expanding shells with inner radii ~ 6 to 16 au and
outer radii four times larger. The expansion velocity increases radially
through the H2O maser regions, with logarithmic velocity gradients of 0.5--0.9.
IK Tau and RT Vir have well-filled H2O maser shells with a spatial offset
between the near and far sides of the shell, which suggests that the masers are
distributed in oblate spheroids inclined to the line of sight. U Ori and U Her
have elongated poorly-filled shells with indications that the masers at the
inner edge have been compressed by shocks; these stars also show OH maser
flares. MERLIN resolves individual maser clouds, which have diameters of 2 -- 4
au and filling factors of only ~ 0.01 with respect to the whole H2O maser
shells. The CSE velocity structure gives additional evidence the maser clouds
are density bounded. Masing clouds can be identified over a similar timescale
to their sound crossing time (~2 yr) but not longer. The sizes and observed
lifetimes of these clouds are an order of magnitude smaller than those around
red supergiants, similar to the ratio of low-mass:high-mass stellar masses and
sizes. This suggests that cloud size is determined by stellar properties, not
local physical phenomena in the wind.Comment: 21 pages, including 14 figures and 8 tables. Accepted for publication
in MNRA
Moans, Palpable Groin, and Entrapment of Bone: A Case of Malignant Peripheral Nerve Sheath Tumor in an otherwise Healthy Hispanic Male
Background: Malignant peripheral nerve sheath tumors (MPNTs) are rare malignant soft tissue sarcomas that have an incidence of about 0.001 %. MPNTs typically occur in individuals who have neurofibromatosis or secondary to radiation therapy and rarely occur sporadically. We present a case of a previously healthy 56-year-old gentleman who was diagnosed with MPNTs.
Case: A healthy 56-year-old gentleman presented with worsening LLQ abdominal pain for 6 months. Associated symptoms included bloating, LLE swelling, early satiety for the past 2 months, and a 5-10lb unintentional weight loss. Patient denied recent cough, night sweats, dyspnea, fever, chills, melena or hematochezia. Vitals were WNL. Physical examination revealed a palpable mass on LLQ extending into the groin and edema of the left leg with diminished strength 3/5. CBC and CMP were unremarkable. CT abdomen showed a large necrotic mass in the left retroperitoneum infiltrating along the iliopsoas musculature, extending into the left hip and into the left side of L3, L4, L5 vertebral bodies and through L4 transverse process measuring up to 24.6 x 11.5 x 13 cm. Pathology revealed spindle cell sarcoma composed of moderately atypical, elongated spindle cells positive for vimentin, with loss of H3/K27me3, and negative for SMA, S-100 consistent with MPNSTs.
Conclusions: The is a rare case of a sporadic presentation of MPNTs. Treatment depends on the extent of tumor burden and metastatic disease is typically treated with chemotherapy. CT chest showed innumerable pulmonary nodules. Patient is currently being treated with Doxorubicin and Ifosfamide with minimal response
Galactic Extinction from Colors and Counts of Field Galaxies in WFPC2 Frames: An Application to GRB 970228
We develop the ``simulated extinction method'' to measure average foreground
Galactic extinction from field galaxy number-counts and colors. The method
comprises simulating extinction in suitable reference fields by changing the
isophotal detection limit. This procedure takes into account selection effects,
in particular, the change in isophotal detection limit (and hence in isophotal
magnitude completeness limit) with extinction, and the galaxy color--magnitude
relation.
We present a first application of the method to the HST WFPC2 images of the
gamma-ray burster GRB 970228. Four different WFPC2 high-latitude fields,
including the HDF, are used as reference to measure the average extinction
towards the GRB in the F606W passband. From the counts, we derive an average
extinction of A_V = 0.5 mag, but the dispersion of 0.4 mag between the
estimates from the different reference fields is significantly larger than can
be accounted by Poisson plus clustering uncertainties. Although the counts
differ, the average colors of the field galaxies agree well. The extinction
implied by the average color difference between the GRB field and the reference
galaxies is A_V = 0.6 mag, with a dispersion in the estimated extinction from
the four reference fields of only 0.1 mag. All our estimates are in good
agreement with the value of 0.81\pm0.27 mag obtained by Burstein & Heiles, and
with the extinction of 0.78\pm0.12 measured by Schlegel et al. from maps of
dust IR emission. However, the discrepancy between the widely varying counts
and the very stable colors in these high-latitude fields is worth
investigating.Comment: 14 pages, 2 figures; submitted to the Astrophysical Journa
The Nuclear and Circum-nuclear Stellar Population in Seyfert 2 Galaxies: Implications for the Starburst-AGN Connection
We report the results of a spectroscopic investigation of a sample of 20 of
the brightest type 2 Seyfert nuclei. Our goal is to search for the direct
spectroscopic signature of massive stars, and thereby probe the role of
circumnuclear starbursts in the Seyfert phenomenon. The method used is based on
the detection of the higher order Balmer lines and HeI lines in absorption and
the Wolf-Rayet feature at 4680 \AA in emission. These lines are strong
indicators of the presence of young (a few Myrs) and intermediate-age (a few
100 Myrs) stellar populations. In over half the sample, we have detected HeI
and/or strong stellar absorption features in the high-order (near-UV) Balmer
series together with relatively weak lines from an old stellar population. In
three others we detect a broad emission feature near 4680 \AA that is most
plausibly ascribed to a population of Wolf-Rayet stars (the evolved descendants
of the most massive stars). We therefore conclude that the blue and near-UV
light of over half of the sample is dominated by young and/or intermediate age
stars. The ``young'' Seyfert 2's have have larger far-IR luminosities, cooler
mid/far-IR colors, and smaller [OIII]/H flux ratios than the ``old''
ones. These differences are consistent with a starburst playing a significant
energetic role in the former class. We consider the possibility that there may
be two distinct sub-classes of Seyfert 2 nuclei (``starbursts'' and ``hidden
BLR''). However, the fact that hidden BLRs have been found in three of the
``young'' nuclei argues against this, and suggests that nuclear starbursts may
be a more general part of the Seyfert phenomenon.Comment: To be published in ApJ, 546, Jan 10, 200
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