978 research outputs found
FUSE spectroscopy of sdOB primary of the post common-envelope binary LB 3459 (AA Dor)
LB 3459 (AA Dor) is an eclipsing, close, post common-envelope binary
consisting of an sdOB primary star and an unseen secondary with an
extraordinarly low mass - formally a brown dwarf. A recent NLTE spectral
analysis shows a discrepancy with the surface gravity, which is derived from
analyses of radial-velocity and lightcurves. We aim at precisely determing of
the photospheric parameters of the primary, especially of the surface gravity,
and searching for weak metal lines in the far UV. We performed a detailed
spectral analysis of the far-UV spectrum of LB 3459 obtained with FUSE by means
of state-of-the-art NLTE model-atmosphere techniques.
A strong contamination of the far-UV spectrum of LB 3459 by interstellar line
absorption hampers a precise determination of the photospheric properties of
its primary star. Its effective temperature (42 kK) was confirmed by the
evaluation of new ionization equilibria. For the first time, phosphorus and
sulfur have been identified in the spectrum of LB 3459. Their photospheric
abundances are solar and 0.01 times solar, respectively. From the C III
1174-1177A multiplet, we can measure the rotational velocity of 35 +/- 5 km/sec
of the primary of LB 3459 and confirm that the rotation is bound. From a
re-analysis of optical and UV spectra, we determine a higher log g = 5.3 (cgs)
that reduces the discrepancy in mass determination in comparison to analyses of
radial-velocity and lightcurves. However, the problem is not completely solved.Comment: 10 pages, 15 figure
DE Canum Venaticorum : a bright, eclipsing red dwarfâwhite dwarf binary
Context. Close white dwarfâred dwarf binaries must have gone through a common-envelope phase during their evolution. DE CVn is a detached white dwarfâred dwarf binary with a relatively short (âŒ8.7 h) orbital period. Its brightness and the presence of eclipses makes this system ideal for a more detailed study.
Aims. From a study of photometric and spectroscopic observations of DE CVn we derive the system parameters that we discuss in the framework of common-envelope evolution.
Methods. Photometric observations of the eclipses are used to determine an accurate ephemeris. From a model fit to an average lowresolution spectrum of DE CVn, we constrain the temperature of the white dwarf and the spectral type of the red dwarf. The eclipse light curve is analysed and combined with the radial velocity curve of the red dwarf determined from time-resolved spectroscopy to derive constraints on the inclination and the masses of the components in the system.
Results. The derived ephemeris is HJDmin = 2 452 784.5533(1) + 0.3641394(2) Ă E. The red dwarf in DE CVn has a spectral type of M3V and the white dwarf has an effective temperature of 8 000 K. The inclination of the system is 86+3⊠â2 and the mass and radius of the red dwarf are 0.41 ± 0.06 M and 0.37+0.06 â0.007 R, respectively, and the mass and radius of the white dwarf are 0.51+0.06
â0.02 M and 0.0136+0.0008 â0.0002 R, respectively.
Conclusions. We found that the white dwarf has a hydrogen-rich atmosphere (DA-type). Given that DE CVn has experienced a common-envelope phase, we can reconstruct its evolution and we find that the progenitor of the white dwarf was a relatively lowmass star (M †1.6 M). The current age of this system is 3.3â7.3 Ă 109 years, while it will take longer than the Hubble time for DE CVn to evolve into a semi-detached system
On the Theory of Gamma Ray Bursts and Hypernovae: The Black Hole Soft X-ray Transient Sources
We show that a common evolutionary history can produce the black hole
binaries in the Galaxy in which the black holes have masses of ~ 5-10 M_sun. In
with low-mass, <~ 2.5 M_sun, ZAMS (zero age main sequence) companions, the
latter remain in main sequence during the active stage of soft X-ray transients
(SXTs), most of them being of K or M classification. In two intermediate cases,
IL Lupi and Nova Scorpii with ZAMS ~ 2.5 M_sun companions the orbits are
greatly widened because of large mass loss in the explosion forming the black
hole, and whereas these companions are in late main sequence evolution, they
are close to evolving. Binaries with companion ZAMS masses >~ 3 M_sun are
initially "silent" until the companion begins evolving across the Herzsprung
gap. We provide evidence that the narrower, shorter period binaries, with
companions now in main sequence, are fossil remnants of gamma ray bursters
(GRBs). We also show that the GRB is generally accompanied by a hypernova
explosion (a very energetic supernova explosion). We further show that the
binaries with evolved companions are good models for some of the ultraluminous
X-ray sources (ULXs) recently seen by Chandra in other galaxies. The great
regularity in our evolutionary history, especially the fact that most of the
companions of ZAMS mass <~ 2.5 M_sun remain in main sequences as K or M stars
can be explained by the mass loss in common envelope evolution to be Case C;
i.g., to occur only after core He burning has finished. Since our argument for
Case C mass transfer is not generally understood in the community, we add an
appendix, showing that with certain assumptions which we outline we can
reproduce the regularities in the evolution of black hole binaries by Case C
mass transfer.Comment: 59 pages, 12 figures, review articl
The system parameters of DW Ursae Majoris
We present new constraints on the system parameters of the SW Sextantis star
DW Ursae Majoris, based on ultraviolet (UV) eclipse observations with the
Hubble Space Telescope. Our data were obtained during a low state of the
system, in which the UV light was dominated by the hot white dwarf (WD)
primary. Eclipse analysis, using the full Roche lobe geometry, allows us to set
firm limits on the masses and radii of the system components and the distance
between them: 0.67 \leq M_1/M_sun \leq 1.06, 0.008 \leq R_1/R_sun \leq 0.014,
M_2/M_sun > 0.16, R_2/R_sun > 0.28 and a/R_sun > 1.05. For q = M_2/M_1 < 1.5
the inclination must satisfy i > 71 degrees. Using Smith & Dhillon's
mass-period relation for CV secondaries, our estimates for the system
parameters become M_1/M_sun = 0.77 \pm 0.07, R_1/R_sun = 0.012 \pm 0.001,
M_2/M_sun = 0.30 \pm 0.10, R_2/R_sun = 0.34 \pm 0.04, q =0.39 \pm 0.12, i = 82
\pm 4 degrees and a/R_sun = 1.14 \pm 0.06. We have also estimated the spectral
type of the secondary, M3.5 \pm 1.0, and distance to the system, d =930 \pm 160
pc, from time-resolved I- and K-band photometry. Finally, we have repeated
Knigge et al.'s WD model atmosphere fit to the low-state UV spectrum of DW UMa
in order to account for the higher surface gravity indicated by our eclipse
analysis. In this way we obtained a second estimate for the distance, d = 590
\pm 100 pc, which allows us to obtain a second estimate for the spectral type
of the secondary, M7 \pm 2.0. We conclude that the true value for the distance
and spectral type will probably be in between the values obtained by the two
methods.Comment: 23 pages including 5 figures and 3 tables. Accepted for publication
in Ap
White Dwarf - Red Dwarf Systems Resolved with the Hubble Space Telescope: I. First Results
First results are presented for a Hubble Space Telescope Advanced Camera for
Surveys snapshot study of white dwarfs with likely red dwarf companions. Of 48
targets observed and analyzed so far, 27 are totally or partially resolved into
two or more components, while an additional 15 systems are almost certainly
unresolved binaries. These results provide the first direct empirical evidence
for a bimodal distribution of orbital separations among binary systems
containing at least one white dwarf.Comment: 46 pages, 3 figures, 5 tables, accepted to ApJ. Full-resolution
images available upon request. A few table entries correcte
Versatile Coordination of Cyclopentadienyl-Arene Ligands and Its Role in Titanium-Catalyzed Ethylene Trimerization
Cationic titanium(IV) complexes with ansa-(η5-cyclopentadienyl,η6-arene) ligands were synthesized and characterized by X-ray crystallography. The strength of the metal-arene interaction in these systems was studied by variable-temperature NMR spectroscopy. Complexes with a C1 bridge between the cyclopentadienyl and arene moieties feature hemilabile coordination behavior of the ligand and consequently are active ethylene trimerization catalysts. Reaction of the titanium(IV) dimethyl cations with CO results in conversion to the analogous cationic titanium(II) dicarbonyl species. Metal-to-ligand backdonation in these formally low-valent complexes gives rise to a strongly bonded, partially reduced arene moiety. In contrast to the η6-arene coordination mode observed for titanium, the more electron-rich vanadium(V) cations [cyclopentadienyl-arene]V(NiPr2)(NC6H4-4-Me)+ feature η1-arene binding, as determined by a crystallographic study. The three different metal-arene coordination modes that we experimentally observed model intermediates in the cycle for titanium-catalyzed ethylene trimerization. The nature of the metal-arene interaction in these systems was studied by DFT calculations.
The long-lived Type IIn SN 2015da: Infrared echoes and strong interaction within an extended massive shell star star star
In this paper we report the results of the first similar to four years of spectroscopic and photometric monitoring of the Type IIn supernova SN 2015da (also known as PSN J13522411+3941286, or iPTF16tu). The supernova exploded in the nearby spiral galaxy NGC 5337 in a relatively highly extinguished environment. The transient showed prominent narrow Balmer lines in emission at all times and a slow rise to maximum in all bands. In addition, early observations performed by amateur astronomers give a very well-constrained explosion epoch. The observables are consistent with continuous interaction between the supernova ejecta and a dense and extended H-rich circumstellar medium. The presence of such an extended and dense medium is difficult to reconcile with standard stellar evolution models, since the metallicity at the position of SN 2015da seems to be slightly subsolar. Interaction is likely the mechanism powering the light curve, as confirmed by the analysis of the pseudo bolometric light curve, which gives a total radiated energy greater than or similar to 10(51) erg. Modeling the light curve in the context of a supernova shock breakout through a dense circumstellar medium allowed us to infer the mass of the prexisting gas to be similar or equal to 8 M-circle dot, with an extreme mass-loss rate for the progenitor star similar or equal to 0.6 M-circle dot yr(-1), suggesting that most of the circumstellar gas was produced during multiple eruptive events. Near- and mid-infrared observations reveal a fluxexcess in these domains, similar to those observed in SN 2010jl and other interacting transients, likely due to preexisting radiatively heated dust surrounding the supernova. By modeling the infrared excess, we infer a mass greater than or similar to 0.4 x 10(-3) M-circle dot for the dustSpanish MICINN gran
Hubble Space Telescope Ultraviolet Spectroscopy of Fourteen Low-Redshift Quasars
We present low-resolution ultraviolet spectra of 14 low redshift (z<0.8)
quasars observed with HST/STIS as part of a Snap project to understand the
relationship between quasar outflows and luminosity. By design, all
observations cover the CIV emission line. Nine of the quasars are from the
Hamburg-ESO catalog, three are from the Palomar-Green catalog, and one is from
the Parkes catalog. The sample contains a few interesting quasars including two
broad absorption line (BAL) quasars (HE0143-3535, HE0436-2614), one quasar with
a mini-BAL (HE1105-0746), and one quasar with associated narrow absorption
(HE0409-5004). These BAL quasars are among the brightest known (though not the
most luminous) since they lie at z<0.8. We compare the properties of these BAL
quasars to the z1.4 Large Bright Quasar samples. By
design, our objects sample luminosities in between these two surveys, and our
four absorbed objects are consistent with the v ~ L^0.62 relation derived by
Laor & Brandt (2002). Another quasar, HE0441-2826, contains extremely weak
emission lines and our spectrum is consistent with a simple power-law
continuum. The quasar is radio-loud, but has a steep spectral index and a
lobe-dominated morphology, which argues against it being a blazar. The unusual
spectrum of this quasar resembles the spectra of the quasars PG1407+265,
SDSSJ1136+0242, and PKS1004+13 for which several possible explanations have
been entertained.Comment: Uses aastex.cls, 21 pages in preprint mode, including 6 figures and 2
tables; accepted for publication in The Astronomical Journal (projected vol
133
Advances in mass spectrometry-based post-column bioaffinity profiling of mixtures
In the screening of complex mixtures, for example combinatorial libraries, natural extracts, and metabolic incubations, different approaches are used for integrated bioaffinity screening. Four major strategies can be used for screening of bioactive mixtures for protein targetsâpre-column and post-column off-line, at-line, and on-line strategies. The focus of this review is on recent developments in post-column on-line screening, and the role of mass spectrometry (MS) in these systems. On-line screening systems integrate separation sciences, mass spectrometry, and biochemical methodology, enabling screening for active compounds in complex mixtures. There are three main variants of on-line MS based bioassays: the mass spectrometer is used for ligand identification only; the mass spectrometer is used for both ligand identification and bioassay readout; or MS detection is conducted in parallel with at-line microfractionation with off-line bioaffinity analysis. On the basis of the different fields of application of on-line screening, the principles are explained and their usefulness in the different fields of drug research is critically evaluated. Furthermore, off-line screening is discussed briefly with the on-line and at-line approaches
A High-Velocity Narrow Absorption Line Outflow in the Quasar J212329.46-005052.9
We report on a variable high-velocity narrow absorption line outflow in the
redshift 2.3 quasar J2123-0050. Five distinct outflow systems are detected with
velocity shifts from -9710 to -14,050 km/s and CIV 1548,1551 line widths of
FWHM = 62-164 km/s. These data require five distinct outflow structures with
similar kinematics, physical conditions and characteristic sizes of order
0.01-0.02 pc. The most likely location is ~5 pc from the quasar. The
coordinated line variations in <0.63 yr (rest) are best explained by global
changes in the outflow ionization caused by changes in the quasar's ionizing
flux. The absence of strong X-ray absorption shows that radiative shielding is
not needed to maintain the moderate ionizations and therefore, apparently, it
is not needed to facilitate the radiative acceleration to high speeds. The
kinetic energy yield of this flow is at least two orders of magnitude too low
to be important for feedback to the host galaxy's evolution.Comment: 20 pages. In press with MNRA
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