10,091 research outputs found
A Revised Geometry for the Magnetic Wind of theta^1 Orionis C
Theta^1 Ori is thought to be a hot analog of Bp variables because its optical
and UV line and X-ray continuum fluxes modulate regularly over the
magnetic/rotational period. A flattened magnetosphere surrounding co-rotates
with these stars, producing a periodic modulation of emission and absorption
components of the UV resonance lines, as well as of optical H and He lines. In
this paper we examine these modulations in detail and point out that the
far-blue and near-red wings of C IV and N V resonance lines exhibit
anticorrelated modulations, causing mild flux elevations at moderate redshifts
at edge-on phase (phi=0.5). However, the lines do not exhibit rest-frame
absorption features, the usual signatures of cool static disks surrounding Bp
stars. We suggest that this behavior can be explained by the existence of two
geometrically distinct wind regions separated by the local magnetic Alfven
radius. Wind streams emerging outside this point are forced outward by
radiative forces and eventually expand outward radially to infinity - this
matter produces the far-blue wing absorptions at phi=0.5. Interior streams
follow closed loops and collide at the magnetic equator with counterstreams.
There they coalesce and fall back to the star along their original field lines
- these are responsible for mild emissions at this same phase. The rapid
circulation of the interior wind component back to the star is responsible for
the absence of static disk features.Comment: 7 figure
Race, Class, And Gender In Boys\u27 Education: Repositioning Intersectionality Theory
Boys\u27 identities are distinctly gendered, racialized, and classed across disparate social and cultural contexts. Related intersectional identity processes are associated with boys\u27 academic success. While intersectionality has been utilized throughout boys\u27 education scholarship, a limited, light touch approach is often enacted. As a critical logic of interpretation, intersectionality theory accounts for race, class, and gender within equity-based empirical studies. The authors contend insufficient engagement with intersectionality may lead educational research on boys\u27 social and learner identities to become static. Examining boys\u27 identities through intersectional approaches reveals more complex insights particularly related to their school engagement. Critical of the recent boy crisis literature, this article strives to compel theorists of boys\u27 education to more fully leverage the history, constructs, and epistemologies of intersectionality
The (B0+?)+O6 system FN CMa: A case for tidal-pulsational interaction?
FN CMa is visually double with a separation of about 0.6arcsec. Sixty
high-cadence VLT/UVES spectra permit the A and B components to be disentangled,
as the relative contribution of each star to the total light entering the
spectrograph fluctuates between exposures due to changes in seeing. Component A
exhibits rapid line-profile variations, leading us to attribute the photometric
variability seen by HIPPARCOS (with a derived P=0.08866d) to this component.
From a total of 122 archival and new echelle spectra it is shown that component
A is an SB1 binary with an orbital period of 117.55 days. The eccentricity of
0.6 may result in tidal modulation of the pulsation(s) of component Aa.Comment: 2 pages, 1 figure, IAUS 272 - Active OB Stars: Structure, Evolution,
Mass Loss and Critical Limit
Dust Formation and He II 4686 emission in the Dense Shell of the Peculiar Type Ib Supernova 2006jc
We present evidence for the formation of dust grains in an unusual Type Ib SN
based on late-time spectra of SN 2006jc. The progenitor suffered an LBV-like
outburst just 2 yr earlier, and we propose that the dust formation is a
consequence of the SN blast wave overtaking that LBV-like shell. The key
evidence for dust formation is (a) the appearance of a red/near-IR continuum
source fit by 1600 K graphite grains, and (b) fading of the redshifted sides of
He I emission lines, yielding progressively more asymmetric blueshifted lines
as dust obscures receding material. This provides the strongest case yet for
dust formation in any SN Ib/c. Both developments occurred between 51 and 75 d
after peak, while other SNe observed to form dust did so after a few hundred
days. Geometric considerations indicate that dust formed in the dense swept-up
shell between the forward and reverse shocks, and not in the freely expanding
SN ejecta. Rapid cooling leading to dust formation may have been aided by
extremely high shell densities, as indicated by He I line ratios. The brief
epoch of dust formation is accompanied by He II 4686 emission and enhanced
X-ray emission. These clues suggest that the unusual dust formation in this
object was not due to properties of the SN itself, but instead -- like most
peculiarities of SN 2006jc -- was a consequence of the dense environment
created by an LBV-like eruption 2 yr before the SN.Comment: ApJ, accepted. added some discussion and 2 figures, better title,
conclusions same as previous version. 12 pages, 4 color fig
Eta Carinae across the 2003.5 Minimum: Analysis in the visible and near infrared spectral region
We present an analysis of the visible through near infrared spectrum of Eta
Carinae and its ejecta obtained during the "Eta Carinae Campaign with the UVES
at the ESO VLT". This is a part of larger effort to present a complete Eta
Carinae spectrum, and extends the previously presented analyses with the
HST/STIS in the UV (1240-3159 A) to 10,430 A. The spectrum in the mid and near
UV is characterized by the ejecta absorption. At longer wavelengths, stellar
wind features from the central source and narrow emission lines from the
Weigelt condensations dominate the spectrum. However, narrow absorption lines
from the circumstellar shells are present. This paper provides a description of
the spectrum between 3060 and 10,430 A, including line identifications of the
ejecta absorption spectrum, the emission spectrum from the Weigelt
condensations and the P-Cygni stellar wind features. The high spectral
resolving power of VLT/UVES enables equivalent width measurements of atomic and
molecular absorption lines for elements with no transitions at the shorter
wavelengths. However, the ground based seeing and contributions of nebular
scattered radiation prevent direct comparison of measured equivalent widths in
the VLT/UVES and HST/STIS spectra. Fortunately, HST/STIS and VLT/UVES have a
small overlap in wavelength coverage which allows us to compare and adjust for
the difference in scattered radiation entering the instruments' apertures. This
paper provides a complete online VLT/UVES spectrum with line identifications
and a spectral comparison between HST/STIS and VLT/UVES between 3060 and 3160
A.Comment: 13 pages, 11 figures + atlas. The paper accepted for the ApJS and is
accompanied with an atlas in the online edition pape
Spectroscopic and photometric oscillatory envelope variability during the S Doradus outburst of the Luminous Blue Variable R71
To better understand the LBV phenomenon, we analyze multi-epoch and
multi-wavelength spectra and photometry of R71. Pre-outburst spectra are
analyzed with the radiative transfer code CMFGEN to determine the star's
fundamental stellar parameters. During quiescence, R71 has an effective
temperature of and a luminosity of
log = 5.78 and is thus a classical LBV, but at the lower
luminosity end of this group. We determine its mass-loss rate to yr. We present R71's spectral energy distribution
from the near-ultraviolet to the mid-infrared during its present outburst.
Mid-infrared observations suggest that we are witnessing dust formation and
grain evolution. Semi-regular oscillatory variability in the star's light curve
is observed during the current outburst. Absorption lines develop a second blue
component on a timescale twice that length. The variability may consist of one
(quasi-)periodic component with P ~ 425/850 d with additional variations
superimposed. During its current S Doradus outburst, R71 occupies a region in
the HR diagram at the high-luminosity extension of the Cepheid instability
strip and exhibits similar irregular variations as RV Tau variables. LBVs do
not pass the Cepheid instability strip because of core evolution, but they
develop comparable cool, low-mass, extended atmospheres in which convective
instabilities may occur. As in the case of RV Tau variables, the occurrence of
double absorption lines with an apparent regular cycle may be due to shocks
within the atmosphere and period doubling may explain the factor of two in the
lengths of the photometric and spectroscopic cycles.Comment: 18 pages, 14 figures, submitted to A&
Discovery and quantitative spectral analysis of an Ofpe/WN9 (WN11) star in the Sculptor spiral galaxy NGC 300
We have discovered an Ofpe/WN9 (WN11 following Smith et al.) star in the
Sculptor spiral galaxy NGC 300, the first object of this class found outside
the Local Group, during a recent spectroscopic survey of blue supergiant stars
obtained at the ESO VLT. The light curve over a five-month period in late 1999
displays a variability at the 0.1 mag level. The intermediate resolution
spectra (3800-7200 A) show a very close resemblance to the Galactic LBV AG Car
during minimum. We have performed a detailed non-LTE analysis of the stellar
spectrum, and have derived a chemical abundance pattern which includes H, He,
C, N, O, Al, Si and Fe, in addition to the stellar and wind parameters. The
derived stellar properties and the He and N surface enrichments are consistent
with those of other Local Group WN11 stars in the literature, suggesting a
similar quiescent or post-LBV evolutionary status.Comment: 9 pages, 4 figures, 2 tables. Accepted for publication in the
Astrophysical Journal Letter
Chandra HETGS Multi-Phase Spectroscopy of the Young Magnetic O Star theta^1 Orionis C
We report on four Chandra grating observations of the oblique magnetic
rotator theta^1 Ori C (O5.5 V) covering a wide range of viewing angles with
respect to the star's 1060 G dipole magnetic field. We employ line-width and
centroid analyses to study the dynamics of the X-ray emitting plasma in the
circumstellar environment, as well as line-ratio diagnostics to constrain the
spatial location, and global spectral modeling to constrain the temperature
distribution and abundances of the very hot plasma. We investigate these
diagnostics as a function of viewing angle and analyze them in conjunction with
new MHD simulations of the magnetically channeled wind shock mechanism on
theta^1 Ori C. This model fits all the data surprisingly well, predicting the
temperature, luminosity, and occultation of the X-ray emitting plasma with
rotation phase.Comment: 52 pages, 14 figures (1 color), 6 tables. To appear in the
Astrophysical Journal, 1 August 2005, v628, issue 2. New version corrects
e-mail address, figure and table formatting problem
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