451 research outputs found
The polarization properties of Broad Absorption Line QSOs: observational results
Correlations between BAL QSO intrinsic properties and polarization have been
searched for. Some results are summarized here, providing possible constraints
on BAL outflow models.Comment: 4 pages, 5 figures; to appear in ``Mass Outflow in Active Galactic
Nuclei: New Perspectives'' ASP Conference Series, eds. D.M. Crenshaw, S.B.
Kraemer, and I.M. Georg
VLT Observations of Two Unusual BAL Quasars
Among the unusual broad absorption line quasars being found by the Sloan
Digital Sky Survey (SDSS) are objects with much stronger absorption in Fe III
than Fe II. These unusual line ratios require a high density in the outflow
(n_H >= 3 x 10^{10} cm^{-3}). They should also appear for only a limited range
of outflow column densities, which explains their rarity. Previously we
suggested that the Fe III line ratios were also affected by a resonance; we now
believe this is an artifact of structure in the underlying Fe II + Fe III
pseudocontinuum. The SDSS is also discovering objects with absorption in rarely
seen transitions such as He I. VLT+UVES high-resolution spectra of one such
object, the mini-BAL quasar SDSS 1453+0029, show that it has two He I
absorption systems with considerably different properties separated by only 350
km/s.Comment: 4 pages, 3 figures; to appear in "Active Galactic Nuclei, from
Central Engine to Host Galaxy", eds. Collin, Combes & Shlosman, PASP
Conference Series, in pres
Large-scale coherent orientations of quasar polarisation vectors: interpretation in terms of axion-like particles
The observation of redshift-dependent coherent orientations of quasar
polarisation vectors over cosmological distances in some regions of the sky is
reviewed. Based on a good-quality sample of 355 measured quasars, this
observation seems to infer the existence of a new effect acting on light
propagation on such huge distances. A solution in terms of nearly massless
axion-like particles has been proposed in the literature and its current status
is discussed.Comment: Replaced because of a previously badly displayed caption. Contributed
to "Axions 2010", Gainesville (FL), January 15-17 2010. To be published in
AIP conference series. 6 page
The orientation within the Galaxy and the Large Magellanic Cloud of nebulae ejected by massive stars
The orientation of nebulae ejected by massive stars (Luminous Blue Variables, WR stars, SN1987A) is investigated with respect to the structure of the galaxy to which they belong. In the Galaxy, we find that the projected long axes of the nebulae most often align with the galactic plane, and then also with the galactic magnetic field. This alignment is statistically significant. In addition, a few nebulae are apparently oriented perpendicular to the galactic plane. In the Large Magellanic Cloud, the nebular axes are found to closely follow the spiral magnetic field. With different inclinations, the Galaxy and the Large Magellanic Cloud probably offer complementary views of the same phenomenon. Although the sample studied thus far is small and the statistics limited, these results suggest that the orientation of massive star ejecta depends on galactic magnetic fields. Since the nebular axes are apparently correlated to the symmetry axes of the stars themselves, and since, in the early evolutionary stages, alignments of accretion disk axes with the interstellar magnetic field have been reported, it is argued that the observed alignment effect results from the star formation process. Based in part on observations collected at the European Southern Observatory (ESO, La Silla
Large scale correlations of quasar polarisation vectors: Hints of extreme scale structures?
A survey measuring quasar polarization vectors has been started in two
regions towards the North and South Galactic Poles. Here, We review the
discovery of significant correlations of orientations of polarization vectors
over huge angular distances. We report new results including a larger sample of
the quasars confirming the existence of coherent orientations at redshifts z>1.Comment: Proc. of Astronomical Polarimetry - Current Status and Future
Directions March 15-19, 2004. Waikoloa Beach Marriott, Hawaii. 5 pages, 3
figure
On the nature of the Herbig B[e] star binary system V921 Scorpii: Discovery of a close companion and relation to the large-scale bipolar nebula
Belonging to the group of B[e] stars, V921 Scorpii is associated with a
strong infrared excess and permitted and forbidden line emission, indicating
the presence of low- and high-density circumstellar gas and dust. Many aspects
of V921 Sco and other B[e] stars still remain mysterious, including their
evolutionary state and the physical conditions resulting in the class-defining
characteristics. In this paper, we employ VLTI/AMBER spectro-interferometry in
order to reconstruct high-resolution (lambda/2B=0.0013") model-independent
interferometric images for three wavelength bands around 1.65, 2.0, and 2.3
micrometer. In our images, we discover a close (25.0+/-0.8 milliarcsecond,
corresponding to 29+/-0.9 AU at 1.15 kpc) companion around V921 Sco. Between
two epochs in 2008 and 2009, we measure orbital motion of 7 degrees, implying
an orbital period of about 35 years (for a circular orbit). Around the primary
star, we detect a disk-like structure with indications for a radial temperature
gradient. The polar axis of this AU-scale disk is aligned with the
arcminute-scale bipolar nebula in which V921 Sco is embedded. Using
Magellan/IMACS imaging, we detect multi-layered arc-shaped sub-structure in the
nebula, suggesting episodic outflow activity from the system with a period of
about 25 years, roughly matching the estimated orbital period of the companion.
Our study supports the hypothesis that the B[e] phenomenon is related to
dynamical interaction in a close binary system.Comment: 7 pages, 2 figures, accepted by The Astrophysical Journal Letter
The optical polarization of radio-loud and radio-intermediate broad absorption line quasi-stellar objects
On the basis of a sample of approximately 50 broad absorption line quasi-stellar objects (BAL QSOs), we investigate possible correlations between BAL QSO radio properties and other spectral characteristics, including polarization. For this purpose new polarization data have been obtained. The main result of our statistical study is the absence of significant correlations between the radio-to-optical flux ratio R[SUP]star [/SUP] and all other quantities: the polarization p_0 of the continuum, the slope of the continuum, the balnicity and detachment indices which characterize the BAL profiles, and the terminal velocity of the flow v_max. The claimed anticorrelation between R[SUP]star [/SUP] and v_max is therefore not confirmed, as well as the correlation between R[SUP]star [/SUP] and p_0 predicted by some models. Although marginally significant, the only possible correlations occur for the BAL QSOs with low-ionization troughs. Based on observations collected at the European Southern Observatory (ESO, La Silla
Sub-arcsecond imaging and spectroscopy of the radio-loud highly polarized quasar PKS 1610-771
We report on imaging and spectroscopic observations of the radio-loud, highly
polarized quasar PKS 1610-771 (z = 1.71). Our long-slit spectroscopy of the
companion 4.55 arcseconds NW of the quasar confirms the stellar nature of this
object, so ruling out the previously suspected gravitationally lensed nature of
this system. PKS 1610-771 looks fuzzy on our sub-arcsecond R and I images and
appears located in a rich environment of faint galaxies. Possible
magnification, without image splitting of the quasar itself, by some of these
maybe foreground galaxies cannot be excluded. The continuum fuzz (made of the
closest two objects, viz. A and D) is elongated in a direction orthogonal to
the E vector of the optical polarization, as in high-redshift radio-galaxies.
The spectrum of PKS 1610-771 appears strongly curved, in a convex way, with a
maximum of intensity at ~ 7,600 A (2,800 A rest frame), possibly indicating a
strong ultraviolet absorption by dust.Comment: 6 pages, uuencoded gziped tar file including TeX file + postscript
figures. Accepted for publication in A&A main journa
The atypical emission-line star Hen3-209
We analyse observations, spanning 15 years, dedicated to the extreme
emission-line object Hen3-209. Our photometric data indicate that the
luminosity of the star undergoes marked variations with a peak-to-peak
amplitude of 0.65mag. These variations are recurrent, with a period of
16.093+-0.005d. The spectrum of Hen3-209 is peculiar with many different lines
(HI, HeI, FeII,...) showing P Cygni profiles. The line profiles are apparently
changing in harmony with the photometry. The spectrum also contains [OIII]
lines that display a saddle profile topped by three peaks, with a maximum
separation of about 600km/s. Hen3-209 is most likely an evolved luminous object
suffering from mass ejection events and maybe belonging to a binary system.Comment: 6p, 5 fig, accepted for publication in MNRAS
(www.blackwell-synergy.com
HST Observations of the Gravitationally Lensed Cloverleaf Broad Absorption Line QSO H1413+1143: Modeling the Lens
We investigate gravitational lens models for the quadruply-lensed Cloverleaf
BAL QSO H1413+1143 based on the HST WFPC/WFPC2 astrometric and photometric data
of the system by Turnshek et al. and the HST NICMOS-2 data by Falco et al. The
accurate image positions and the dust-extinction-corrected relative
amplifications, along with a possible detection of the lensing galaxy in the
infrared, permit more accurate lens models than were previously possible. While
more recent models are qualitatively consistent with the HST data, none of the
previous models considered the dust-extinction-corrected relative
amplifications of the image components. We use the power-law elliptical mass
model to fit the HST data. We find that a single elliptical galaxy perturbed by
an external shear can fit the image positions within the observational
uncertainties; however, the predicted relative magnifications are only roughly
consistent with the observational relative amplifications. We find that a
primary galaxy combined with a secondary galaxy in the vicinity of the
Cloverleaf or a cluster centered (south-)west of the Cloverleaf can fit both
the image positions and relative amplifications within the observational
uncertainties. We discuss future observations which could be used to test
and/or further constrain lens models of the Cloverleaf.Comment: 23 pages (in aaspp.sty) including 5 tables and 3 figures, Accepted
for publication in the Astrophysical Journa
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