2,863 research outputs found
A BeppoSAX observation of the supersoft source 1E 0035.4-7230
Results from a 37,000 s BeppoSAX Low-Energy Concentrator Spectrometer (LECS)
observation of the supersoft source SMC 13 (=1E 0035.4-7230) in the Small
Magellanic Cloud are reported. The BeppoSAX spectrum is fitted either with a
blackbody spectrum with an effective temperature kT = 26-58 eV, an LTE white
dwarf atmosphere spectrum with kT = 35-50 eV, or a non-LTE white dwarf
atmosphere spectrum with kT = 25-32 eV. The bolometric luminosity is < 8 10^37
erg s-1 and < 3 10^37 erg s^-1 for the LTE and the non-LTE spectrum. We also
applied a spectral fit to combined spectra obtained with BeppoSAX LECS and with
ROSAT PSPC. The kT derived for the non-LTE spectrum is 27-29 eV, the bolometric
luminosity is 1.1-1.2 10^37 erg s^-1. We can exclude any spectrally hard
component with a luminosity > 2 10^35 erg s^-1 (for a bremmstrahlung with a
temperature of 0.5 keV) at a distance of 60 kpc. The LTE temperature is
therefore in the range 5.5+/-0.2 10^5 K and the non-LTE temperature in the
range 3.25+/-0.16 10^5 K. Assuming the source is on the stability line for
atmospheric nuclear burning, we constrain the white dwarf mass from the LTE and
the non-LTE fit to ~1.1 M-solar and ~0.9 M-solar respectively. However, the
temperature and luminosity derived with the non-LTE model for 1E 0035.4-7230 is
consistent with a lower mass M~0.6-0.7 M-solar white dwarf as predicted by Sion
and Starrfield (1994). At the moment, neither of these two alternatives for the
white dwarf mass can be excluded.Comment: 6 pages, accepted by A&A March 30th 199
Isolation and characterization of two novel polyhydroxybutyrate (PHB)-producing bacteria
Bioplastics are naturally occurring biodegradable polymers made from polyhydroxyalkanoates (PHA) of which poly 3-hydroxy butyric acid (PHB) is the most common. PHB serves as an energy storage molecule and accumulates intracellularly as storage granules in microbes. This work utilized the biodiversity of bacteria to isolate various species from different environments and screen them for their ability to produce PHB. Sixteen unknown samples were collected, assayed and compared with known bioplastic producers (Ralstonia, Bacillus and Pseudomonas). These species were identified by 16S rRNA sequencing. Conditions were extensively optimized by varying the temperature, carbon, nitrogen and substrate sources for maximal PHB production. Presence of accumulation of PHB in these strains was confirmed by microscopic staining. This is the first report to experimentally demonstrate the synthesis of PHB by two novel species, Rahnella aquatilis and Stenotrophomonas maltophilia. R. aquatilis was collected from a children’s plastic toy, while S. maltophilia was collected from the sand of a local beach. The phenotypic profiles of these two species were subsequently studied using phenotype microarray panels which allowed the testing of the effect of more than 90 different carbon, nitrogen, sulfur and phosphorus sources as well as pH on the growth characteristics of these strains.Key words: Poly 3-hydroxy butyric acid (PHB), polyhydroxybutyrate, bioplastics, phenotype microarray, Rahnella, Stenotrophomonas
Luminous supersoft X-ray emission from the recurrent nova U Scorpii
BeppoSAX detected luminous 0.2-2.0 keV supersoft X-ray emission from the
recurrent nova U Sco ~19-20 days after the peak of the optical outburst in
February 1999. U Sco is the first recurrent nova to be observed during a
luminous supersoft X-ray phase. Non-LTE white dwarf atmosphere spectral models
(together with a ~0.5 keV optically thin thermal component) were fitted to the
BeppoSAX spectrum. We find that the fit is acceptable assuming enriched He and
an enhanced N/C ratio. This implies that the CNO cycle was active during the
outburst, in agreement with a thermonuclear runaway scenario. The best-fit
temperature is ~9 10^5 K and the bolometric luminosity those predicted for
steady nuclear burning on a WD close to the Chandrasekhar mass. The fact that
U~Sco was detected as a supersoft X-ray source is consistent with steady
nuclear burning continuing for at least one month after the outburst. This
means that only a fraction of the previously accreted H and He was ejected
during the outburst and that the WD can grow in mass, ultimately reaching the
Chandrasekhar limit. This makes U~Sco a candidate type Ia supernova progenitor.Comment: 4 pages, accepted by A&A Letters 15 June 199
Young stars and dust in AFGL437: NICMOS/HST polarimetric imaging of an outflow source
We present near infrared broad band and polarimetric images of the compact
star forming cluster AFGL437 obtained with the NICMOS instrument aboard HST.
Our high resolution images reveal a well collimated bipolar reflection
nebulosity in the cluster and allow us to identify WK34 as the illuminating
source. The scattered light in the bipolar nebulosity centered on this source
is very highly polarized (up to 79%). Such high levels of polarization implies
a distribution of dust grains lacking large grains, contrary to the usual dust
models of dark clouds. We discuss the geometry of the dust distribution giving
rise to the bipolar reflection nebulosity and make mass estimates for the
underlying scattering material. We find that the most likely inclination of the
bipolar nebulosity, south lobe inclined towards Earth, is consistent with the
inclination of the large scale CO molecular outflow associated with the
cluster, strengthening the identification of WK34 as the source powering it.Comment: 26 pages, 10 figues. Accepted for publication in the Astrophysical
Journa
SNODGRASS Procedure A Versatile Technique for Various Types of Hypospadias Repair
There are about 156 operations described forhypospadias. The sheer number of proceduresindicates that no single procedure is standardfor hypospadias. We report our series of 20patients operated for hypospadias by Snodgrassprocedure. The technical details of the proce-dure and post-operative management protocolis discussed
The EXOSAT database and archive
The EXOSAT database provides on-line access to the results and data products (spectra, images, and lightcurves) from the EXOSAT mission as well as access to data and logs from a number of other missions (such as EINSTEIN, COS-B, ROSAT, and IRAS). In addition, a number of familiar optical, infrared, and x ray catalogs, including the Hubble Space Telescope (HST) guide star catalog are available. The complete database is located at the EXOSAT observatory at ESTEC in the Netherlands and is accessible remotely via a captive account. The database management system was specifically developed to efficiently access the database and to allow the user to perform statistical studies on large samples of astronomical objects as well as to retrieve scientific and bibliographic information on single sources. The system was designed to be mission independent and includes timing, image processing, and spectral analysis packages as well as software to allow the easy transfer of analysis results and products to the user's own institute. The archive at ESTEC comprises a subset of the EXOSAT observations, stored on magnetic tape. Observations of particular interest were copied in compressed format to an optical jukebox, allowing users to retrieve and analyze selected raw data entirely from their terminals. Such analysis may be necessary if the user's needs are not accommodated by the products contained in the database (in terms of time resolution, spectral range, and the finesse of the background subtraction, for instance). Long-term archiving of the full final observation data is taking place at ESRIN in Italy as part of the ESIS program, again using optical media, and ESRIN have now assumed responsibility for distributing the data to the community. Tests showed that raw observational data (typically several tens of megabytes for a single target) can be transferred via the existing networks in reasonable time
The EXOSAT medium-energy slew survey catalog
We present a catalog of X-ray sources observed during slew maneuvers by the
Medium Energy Detector Array onboard the EXOSAT Observatory. The EXOSAT Medium
Energy slew-survey catalog (EXMS) provides a unique record of the 1--8 keV
X-ray sky between 1983 and 1986. 98% of the sky was observed, with 85%
receiving an exposure of >60 s. 1210 sources were detected. By comparing these
source positions with other catalogs, identifications are given for 992
detections (82% of the sample). These identifications consist of 250 distinct
objects, including 95 different X-ray binary systems, and 14 different AGN. A
further 58 detections have multiple candidates, while 160 detections remain
unidentified. Collimator transmission corrected 1-8 keV count rates are given
for the identified sources, together with raw count rates for the other
detections. The construction of the EXMS and the checks performed to ensure the
validity of the derived source properties are discussed. A publically available
version of this catalog is maintained on the EXOSAT database and archive system
(telnet://[email protected]).Comment: 52 pages. 22 Figures. To be published in A&AS. For more information,
see http://astro.estec.esa.nl/SA-general/Projects/Exosat/exmsintro.htm
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