71 research outputs found
Multiwavelength campaign on Mrk 509. VI. HST/COS observations of the far-ultraviolet spectrum
We present medium resolution (R~20,000) HST/COS ultraviolet spectra covering
1155-1760 A of the Seyfert 1 Mrk 509 obtained simultaneously with a
Chandra/LETGS spectrum as part of a multiwavelength campaign in 2009 that
included observations with XMM-Newton, SWIFT, and Integral. Our high S/N
spectrum detects additional complexity in the absorption troughs from a variety
of sources in Mrk 509, including the outflow from the active nucleus, the ISM
and halo of the host galaxy, and infalling clouds or stripped gas from a merger
that are illuminated by the AGN. Variability between the STIS and COS
observation of the -400 km/s component allows us to set an upper limit on its
distance of < 250 pc. Similarly, variability of a component at +150 km/s
between two prior FUSE observations limits its distance to < 1.5 kpc. The UV
absorption only partially covers the emission from the AGN nucleus. Covering
fractions are lower than those previously seen with STIS, and are comparable to
those seen with FUSE. Given the larger apertures of COS and FUSE compared to
STIS, we favor scattered light from an extended region near the AGN as the
explanation for the partial covering. As observed in prior X-ray and UV
spectra, the UV absorption has velocities comparable to the X-ray absorption,
but the bulk of the ultraviolet absorption is in a lower ionization state with
lower total column density than the gas responsible for the X-ray absorption.
We conclude that the outflow from the active nucleus is a multiphase wind.Comment: 21 pages, 9 figures. Accepted for publication in Astronomy &
Astrophysics, 26 May 201
The Sloan Digital Sky Survey Reverberation Mapping Project: Rapid CIV Broad Absorption Line Variability
We report the discovery of rapid variations of a high-velocity CIV broad
absorption line trough in the quasar SDSS J141007.74+541203.3. This object was
intensively observed in 2014 as a part of the Sloan Digital Sky Survey
Reverberation Mapping Project, during which 32 epochs of spectroscopy were
obtained with the Baryon Oscillation Spectroscopic Survey spectrograph. We
observe significant (>4sigma) variability in the equivalent width of the broad
(~4000 km/s wide) CIV trough on rest-frame timescales as short as 1.20 days
(~29 hours), the shortest broad absorption line variability timescale yet
reported. The equivalent width varied by ~10% on these short timescales, and by
about a factor of two over the duration of the campaign. We evaluate several
potential causes of the variability, concluding that the most likely cause is a
rapid response to changes in the incident ionizing continuum. If the outflow is
at a radius where the recombination rate is higher than the ionization rate,
the timescale of variability places a lower limit on the density of the
absorbing gas of n_e > 3.9 x 10^5 cm^-3. The broad absorption line variability
characteristics of this quasar are consistent with those observed in previous
studies of quasars, indicating that such short-term variability may in fact be
common and thus can be used to learn about outflow characteristics and
contributions to quasar/host-galaxy feedback scenarios.Comment: 15 pages, 14 figures. Accepted for publication in the Astrophysical
Journa
Discovery of an Ultraviolet Counterpart to an Ultra-Fast X-ray Outflow in the Quasar PG1211+143
This is an author-created, un-copyedited version of an article published in The Astrophysical Journal. The Version of Record is available online at https://doi.org/10.3847/1538-4357/aaa42bWe observed the quasar PG 1211+143 using the Cosmic Origins Spectrograph on the Hubble Space Telescope in 2015 April as part of a joint campaign with the Chandra X-ray Observatory and the Jansky Very Large Array. Our ultraviolet spectra cover the wavelength range 912-2100 Å. We find a broad absorption feature () at an observed wavelength of 1240 Å. Interpreting this as H i Lyα, in the rest frame of PG 1211+143 (z = 0.0809), this corresponds to an outflow velocity of -16,980 (outflow redshift ), matching the moderate ionization X-ray absorption system detected in our Chandra observation and reported previously by Pounds et al. With a minimum H i column density of , and no absorption in other UV resonance lines, this Lyα absorber is consistent with arising in the same ultrafast outflow as the X-ray absorbing gas. The Lyα feature is weak or absent in archival ultraviolet spectra of PG 1211+143, strongly suggesting that this absorption is transient, and intrinsic to PG 1211+143. Such a simultaneous detection in two independent wavebands for the first time gives strong confirmation of the reality of an ultrafast outflow in an active galactic nucleus.Peer reviewe
Catalytic Transformations of Alkynes via Ruthenium Vinylidene and Allenylidene Intermediates
NOTICE: This is the peer reviewed version of the following book chapter: Varela J. A., González-RodrĂguez C., Saá C. (2014). Catalytic Transformations of Alkynes via Ruthenium Vinylidene and Allenylidene Intermediates. In: Dixneuf P., Bruneau C. (eds) Ruthenium in Catalysis. Topics in Organometallic Chemistry, vol 48, pp. 237-287. Springer, Cham. [doi: 10.1007/3418_2014_81]. This article may be used for non-commercial purposes in accordance with Springer Verlag Terms and Conditions for self-archiving.Vinylidenes are high-energy tautomers of terminal alkynes and they can be stabilized by coordination with transition metals. The resulting metal-vinylidene species have interesting chemical properties that make their reactivity different to that of the free and metal Ď€-coordinated alkynes: the carbon α to the metal is electrophilic whereas the β carbon is nucleophilic. Ruthenium is one of the most commonly used transition metals to stabilize vinylidenes and the resulting species can undergo a range of useful transformations. The most remarkable transformations are the regioselective anti-Markovnikov addition of different nucleophiles to catalytic ruthenium vinylidenes and the participation of the Ď€ system of catalytic ruthenium vinylidenes in pericyclic reactions. Ruthenium vinylidenes have also been employed as precatalysts in ring closing metathesis (RCM) or ring opening metathesis polymerization (ROMP).
Allenylidenes could be considered as divalent radicals derived from allenes. In a similar way to vinylidenes, allenylidenes can be stabilized by coordination with transition metals and again ruthenium is one of the most widely used metals. Metalallenylidene complexes can be easily obtained from terminal propargylic alcohols by dehydration of the initially formed metal-hydroxyvinylidenes, in which the reactivity of these metal complexes is based on the electrophilic nature of Cα and Cγ, while Cβ is nucleophilic. Catalytic processes based on nucleophilic additions and pericyclic reactions involving the π system of ruthenium allenylidenes afford interesting new structures with high selectivity and atom economy
Can axionlike particles explain the alignments of the polarizations of light from quasars?
The standard axion-like particle explanation of the observed large-scale
coherent orientations of quasar polarisation vectors is ruled out by the recent
measurements of vanishing of circular polarisation. We introduce a more general
wave-packet formalism and show that, although decoherence effects between waves
of different frequencies can reduce significantly the amount of circular
polarisation, the axion-like particle hypothesis is disfavoured given the
bandwidth with which part of the observations were performed. Finally, we show
that a more sophisticated model of extragalactic fields does not lead to an
alignment of polarisations.Comment: Submitted to Physical Review D; for high-resolution figures, see
http://hdl.handle.net/2268/9542
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