225 research outputs found
SECONDARY HYPERAMMONAEMIA: A POSSIBLE MECHANISM FOR VALPROATE ENCEPHALOPATHY
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23221/1/0000150.pd
Kearns-sayre syndrome with reduced plasma and cerebrospinal fluid folate
A young woman with Kearns-Sayre syndrome and progressive central nervous system deterioration over 15 years had decreased plasma and cerebrospinal fluid folate levels while receiving phenytoin for a seizure disorder. A muscle biopsy showed a “ragged red fiber” myopathy with reduced muscle carnitine and mitochondrial enzymes. Computed tomographic brain scans showed cerebral white matter hypodensities and bilateral calcification of the basal ganglia. The mechanism for the folate deficiency and altered ratio of plasma to cerebrospinal fluid folate is unknown, but the deficiency may be responsive to replacement therapy.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50301/1/410130620_ftp.pd
Using AVIRIS In The NASA BAA Project To Evaluate The Impact Of Natural Acid Drainage On Colorado Watersheds
The Colorado Geological Survey and the co-authors of this paper were awarded one of 15 NASA Broad Agency Announcement (BAA) grants in 2001. The project focuses on the use of hyperspectral remote sensing to map acid-generating minerals that affect water quality within a watershed, and to identify the relative contributions of natural and anthropogenic sources to that drainage. A further objective is to define the most cost-effective remote sensing instrument configuration for this application
A Neutron Star Binary Merger Model for GW170817/GRB170817a/SSS17a
The merging neutron star gravitational wave event GW170817 has been observed
throughout the entire electromagnetic spectrum from radio waves to
-rays. The resulting energetics, variability, and light curves are
shown to be consistent with GW170817 originating from the merger of two neutron
stars, in all likelihood followed by the prompt gravitational collapse of the
massive remnant. The available -ray, X-ray and radio data provide a
clear probe for the nature of the relativistic ejecta and the non-thermal
processes occurring within, while the ultraviolet, optical and infrared
emission are shown to probe material torn during the merger and subsequently
heated by the decay of freshly synthesized -process material. The simplest
hypothesis that the non-thermal emission is due to a low-luminosity short
-ray burst (sGRB) seems to agree with the present data. While low
luminosity sGRBs might be common, we show here that the collective prompt and
multi-wavelength observations are also consistent with a typical, powerful sGRB
seen off-axis. Detailed follow-up observations are thus essential before we can
place stringent constraints on the nature of the relativistic ejecta in
GW170817.Comment: 9 pages, 5 figures, accepted to ApJ Letter
Electromagnetic Evidence that SSS17a is the Result of a Binary Neutron Star Merger
11 hours after the detection of gravitational wave source GW170817 by the
Laser Interferometer Gravitational-Wave Observatory and Virgo Interferometers,
an associated optical transient SSS17a was discovered in the galaxy NGC 4993.
While the gravitational wave data indicate GW170817 is consistent with the
merger of two compact objects, the electromagnetic observations provide
independent constraints of the nature of that system. Here we synthesize all
optical and near-infrared photometry and spectroscopy of SSS17a collected by
the One-Meter Two-Hemisphere collaboration. We find that SSS17a is unlike other
known transients. The source is best described by theoretical models of a
kilonova consisting of radioactive elements produced by rapid neutron capture
(the r-process). We find that SSS17a was the result of a binary neutron star
merger, reinforcing the gravitational wave result.Comment: 21 pages, 4 figures, accepted to Scienc
Connecting the progenitors, pre-explosion variability and giant outbursts of luminous blue variables with Gaia16cfr
We present multi-epoch, multicolour pre-outburst photometry and post-outburst light curves and spectra of the luminous blue variable (LBV) outburst Gaia16cfr discovered by the Gaia satellite on 2016 December 1 UT. We detect Gaia16cfr in 13 epochs of Hubble Space Telescope imaging spanning phases of 10 yr to 8 months before the outburst and in Spitzer Space Telescope imaging 13 yr before outburst. Pre-outburst optical photometry is consistent with an 18 M⊙ F8 I star, although the star was likely reddened and closer to 30 M⊙. The pre-outburst source exhibited a significant near-infrared excess consistent with a 120 au shell with 4 × 10−6 M⊙ of dust. We infer that the source was enshrouded by an optically thick and compact shell of circumstellar material from an LBV wind, which formed a pseudo-photosphere consistent with S Dor-like variables in their ‘maximum’ phase. Within a year of outburst, the source was highly variable on 10–30 d time-scales. The outburst light curve closely matches that of the 2012 outburst of SN 2009ip, although the observed velocities are significantly slower than in that event. In H α, the outburst had an excess of blueshifted emission at late times centred around −1500 km s−1, similar to that of double-peaked Type IIn supernovae and the LBV outburst SN 2015bh. From the pre-outburst and post-outburst photometry, we infer that the outburst ejecta are evolving into a dense, highly structured circumstellar environment from precursor outbursts within years of the 2016 December event.The work of
AVF was conducted in part at the Aspen Center for Physics, which
is supported by NSF grant PHY-1607611; the author thanks the
Center for its hospitality during the neutron stars workshop in 2017
June and July. AVF is grateful for financial assistance from the
TABASGO Foundation, the Christopher R. Redlich Fund, the Miller
Institute for Basic Research in Science (U.C. Berkeley) and HST
grants GO-13646 and AR-14295 from the Space Telescope Science
Institute (STScI), which is operated by AURA under NASA contract
NAS 5-26555
Double-Peaked Balmer Emission Indicating Prompt Accretion Disk Formation in an X-Ray Faint Tidal Disruption Event
We present the multi-wavelength analysis of the tidal disruption event (TDE)
AT~2018hyz (ASASSN-18zj). From follow-up optical spectroscopy, we detect the
first unambiguous case of resolved double-peaked Balmer emission in a TDE. The
distinct line profile can be well-modelled by a low eccentricity
() accretion disk extending out to 100 and a
Gaussian component originating from non-disk clouds, though a bipolar outflow
origin cannot be completely ruled out. Our analysis indicates that in
AT~2018hyz, disk formation took place promptly after the most-bound debris
returned to pericenter, which we estimate to be roughly tens of days before the
first detection. Redistribution of angular momentum and mass transport,
possibly through shocks, must occur on the observed timescale of about a month
to create the large \Ha-emitting disk that comprises 5\% of the
initial stellar mass. With these new insights from AT~2018hyz, we infer that
circularization is efficient in at least some, if not all optically-bright,
X-ray faint TDEs. In these efficiently circularized TDEs, the detection of
double-peaked emission depends on the disk inclination angle and the relative
strength of the disk contribution to the non-disk component, possibly
explaining the diversity seen in the current sample.Comment: 24 pages, 8 figures, 6 tables. Accepted for publication in Ap
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