16,464 research outputs found
A Hidden Broad-Line Region in the Weak Seyfert 2 Galaxy NGC 788
We have detected a broad H alpha emission line in the polarized flux spectrum
of the Seyfert 2 galaxy NGC 788, indicating that it contains an obscured
Seyfert 1 nucleus. While such features have been observed in ~15 other Seyfert
2s, this example is unusual because it has a higher fraction of galaxy
starlight in its spectrum, a lower average measured polarization, and a
significantly lower radio luminosity than other hidden Seyfert 1s discovered to
date. This demonstrates that polarized broad-line regions can be detected in
relatively weak classical Seyfert 2s, and illustrates why well-defined,
reasonably complete spectropolarimetric surveys at H alpha are necessary in
order to assess whether or not all Seyfert 2s are obscured Seyfert 1s.Comment: 10 pages using (AASTEX) aaspp4.sty and 4 postscript figures.
Publications of the Astronomical Society of the Pacific, Research Notes, in
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Estudios de acoplamiento molecular de nuevos anĂĄlogos de quinolonas a la ADN girasa de Escherichia coli
IndexaciĂłn: Scopus.Chemicals and CAS Registry Numbers:
amino acid, 65072-01-7; ciprofloxacin, 85721-33-1; DNA topoisomerase (ATP hydrolysing); gatifloxacin, 112811-59-3, 180200-66-2; levofloxacin, 100986-85-4, 138199-71-0; lomefloxacin, 98079-51-7; moxifloxacin, 151096-09-2; nalidixic acid, 389-08-2; oxolinic acid, 14698-29-4; pipemidic acid, 51940-44-4; rufloxacin, 101363-10-4; sitafloxacin, 127254-12-0, 163253-35-8Context: Bacterial resistance to antibiotics is the inevitable consequence of the use of antimicrobial agents. Thus, quinolones are an important class of antibacterials; these agents generally consist of a 1-subtituted-1,4-dihydro-4-oxopyridine-3-carboxylic acid moiety combined with an aromatic or heteroaromatic ring fused at the 5- and 6-position. Aims: To determine the binding of quinolones to DNA gyrase of Escherichia coli. Methods: An analysis was performed using an in silico approach to determine, by docking calculations and energy descriptors, the conformer of 4âoxoâ1,4âdihydroquinoline skeleton that forms the most stable complex with DNA gyrase of E. coli. Results: The complex shows that the pose of the quinolones coincides with the amino acid residues Asp87, Thr88, Arg91 and Met92, which is expected to be critical in the binding of quinolones to DNA gyrase of E. coli. A series of quinolones were computationally designed, and the interactions between the quinolones and the amino acid residues of the DNA gyrase were calculated. Conclusions: Among the designed compounds, compounds 105 and 115 exhibit higher binding energy values and interact with amino acids Asp87, Thr88, Arg91 and Met92. © 2018 Journal of Pharmacy & Pharmacognosy Research.http://jppres.com/jppres/pdf/vol6/jppres18.368_6.5.386.pd
The mass ratio distribution of short period double degenerate stars
Short period double degenerates (DDs) are close white dwarf - white dwarf
binary stars which are the result of the evolution of interacting binary stars.
We present the first definitive measurements of the mass ratio for two DDs,
WD0136+768 and WD1204+450, and an improved measurement of the mass ratio for
WD0957-666. We compare the properties of the 6 known DDs with measured mass
ratios to the predictions of various theoretical models. We confirm the result
that standard models for the formation of DDs do not predict sufficient DDs
with mass ratios near 1. We also show that the observed difference in cooling
ages between white dwarfs in DDs is a useful constraint on the initial mass
ratio of the binary. A more careful analysis of the properties of the white
dwarf pair WD1704+481.2 leads us to conclude that the brighter white dwarf is
older than its fainter companion. This is the opposite of the usual case for
DDs and is caused by the more massive white dwarf being smaller and cooling
faster. The mass ratio in the sense (mass of younger star)/(mass of older star)
is then 1.43+-0.06 rather than the value 0.70+-0.03 given previously.Comment: Accepted for publication in MNRA
DSP-based ionospheric radiolink using DS-CDMA and on-line channel estimation
In this paper, a new blind multiuser detection algorithm is presented. It can both cancel multiuser interference and estimate the multipath channel response in a blind way. The method has been specially conceived for low coherence bandwidth channels such as the ionospheric channel and exhibits very low computational requirements. Real-time measurements from a fully digital HF radio-link are presented that confirm the reliability of the method for the ionospheric channel.Peer ReviewedPostprint (published version
The triple degenerate star WD1704+481
WD1704+481 is a visual binary in which both components are white dwarfs. We
present spectra of the H-alpha line of both stars which show that one component
(WD1704+481.2 = Sanduleak B = GR 577) is a close binary with two white dwarf
components. Thus, WD1704+481 is the first known triple degenerate star. From
radial velocity measurements of the close binary we find an orbital period of
0.1448d, a mass ratio, q=Mbright/Mfaint of q=0.70+-0.03 and a difference in the
gravitational redshifts of 11.5+-2.3km/s. The masses of the close pair of white
dwarfs predicted by the mass ratio and gravitational redshift difference
combined with theoretical cooling curves are 0.39+-0.05 solar mass and
0.56+-0.07 solar masses. WD1704+481 is therefore also likely to be the first
example of a double degenerate in which the less massive white dwarf is
composed of helium and the other white dwarf is composed of carbon and oxygen.Comment: 5 pages, 4 figure
Orbital periods of the binary sdB stars PG0940+068 and PG1247+554
We have used the radial velocity variations of two sdB stars previously
reported to be binaries to establish their orbital periods. They are
PG0940+068, (P=8.33d) and PG1247+554 (P=0.599d). The minimum masses of the
unseen companions, assuming a mass of 0.5 solar masses for the sdB stars, are
0.090 +/- 0.003 solar masses for PG1247+554 and 0.63 +/- 0.02 solar masses for
PG0940+068. The nature of the companions is not constrained further by our
data.Comment: 5 pages, 2 figure
The mass and radius of the M dwarf companion to GD 448
We present spectroscopy and photometry of GD 448, a detached white dwarf - M
dwarf binary with a period of 2.47h. We find that the NaI 8200A feature is
composed of narrow emission lines due to irradiation of the M dwarf by the
white dwarf within broad absorption lines that are essentially unaffected by
heating. Combined with an improved spectroscopic orbit and gravitational red
shift measurement from spectra of the H-alpha line, we are able to derive
masses for the white dwarf and M dwarf directly (0.41 +/- 0.01 solar masses and
0.096 +/- 0.004 solar masses, respectively). We use a simple model of the CaII
emission lines to establish the radius of the M dwarf assuming the emission
from its surface to be proportional to the incident flux per unit area from the
white dwarf. The radius derived is 0.125 +/- 0.020 solar radii. The M dwarf
appears to be a normal main-sequence star in terms of its mass and radius and
is less than half the size of its Roche lobe. The thermal timescale of the M
dwarf is much longer than the cooling age of the white dwarf so we conclude
that the M dwarf was unaffected by the common-envelope phase. The anomalous
width of the H-alpha emission from the M dwarf remains to be explained, but the
strengh of the line may be due to X-ray heating of the M dwarf due to accretion
onto the white dwarf from the M dwarf wind.Comment: 8 pages, 8 figure
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