548 research outputs found
Mass and Angular Momentum Transfer in the Massive Algol Binary RY Persei
We present an investigation of H-alpha emission line variations observed in
the massive Algol binary, RY Per. We give new radial velocity data for the
secondary based upon our optical spectra and for the primary based upon high
dispersion UV spectra. We present revised orbital elements and an estimate of
the primary's projected rotational velocity (which indicates that the primary
is rotating 7 times faster than synchronous). We use a Doppler tomography
algorithm to reconstruct the individual primary and secondary spectra in the
region of H-alpha, and we subtract the latter from each of our observations to
obtain profiles of the primary and its disk alone. Our H-alpha observations of
RY Per show that the mass gaining primary is surrounded by a persistent but
time variable accretion disk. The profile that is observed outside-of-eclipse
has weak, double-peaked emission flanking a deep central absorption, and we
find that these properties can be reproduced by a disk model that includes the
absorption of photospheric light by the band of the disk seen in projection
against the face of the star. We developed a new method to reconstruct the disk
surface density distribution from the ensemble of H-alpha profiles observed
around the orbit, and this method accounts for the effects of disk occultation
by the stellar components, the obscuration of the primary by the disk, and flux
contributions from optically thick disk elements. The resulting surface density
distribution is elongated along the axis joining the stars, in the same way as
seen in hydrodynamical simulations of gas flows that strike the mass gainer
near trailing edge of the star. This type of gas stream configuration is
optimal for the transfer of angular momentum, and we show that rapid rotation
is found in other Algols that have passed through a similar stage.Comment: 39 pages, 12 figures, ApJ in press, 2004 June 20 issu
Observables in Topological Yang-Mills Theories
Using topological Yang-Mills theory as example, we discuss the definition and
determination of observables in topological field theories (of Witten-type)
within the superspace formulation proposed by Horne. This approach to the
equivariant cohomology leads to a set of bi-descent equations involving the
BRST and supersymmetry operators as well as the exterior derivative. This
allows us to determine superspace expressions for all observables, and thereby
to recover the Donaldson-Witten polynomials when choosing a Wess-Zumino-type
gauge.Comment: 39 pages, Late
Three-dimensional topologically gauged N=6 ABJM type theories
In this paper we construct the conformal supergravity in three
dimensions from a set of Chern-Simons-like terms one for each of the graviton,
gravitino, and R-symmetry gauge field and then couple this theory to the
superconformal ABJM theory. In a first step part of the coupled
Lagrangian for this topologically gauged ABJM theory is derived by demanding
that all terms of third and second order in covariant derivatives cancel in the
supersymmtry variation of the Lagrangian. To achieve this the transformation
rules of the two separate sectors must be augmented by new terms. In a second
step we analyze all terms in that are of first order in covariant
derivatives. The cancelation of these terms require additional terms in the
transformation rules as well as a number of new terms in the Lagrangian. As a
final step we check that all remaining terms in which are bilinear
in fermions cancel which means that the presented Lagrangian and transformation
rules constitute the complete answer. In particular we find in the last step
new terms in the scalar potential containing either one or no structure
constant. The non-derivative higher fermion terms in that have not
yet been completely analyzed are briefly discussed.Comment: 26 pages, v.2 minor corrections, comment on relation to chiral
gravity added
Multiwavelength Monitoring of the Narrow-Line Seyfert 1 Galaxy Akn 564. II. Ultraviolet Continuum and Emission-line Variability
We present results of an intensive two-month campaign of approximately daily
spectrophotometric monitoring of the narrow-line Seyfert 1 galaxy Akn 564 with
HST. The fractional variability amplitude of the continuum variations between
1365-3000 A is ~6%, about a factor 3 less than that found in typical Seyfert 1
galaxies over a similar period of time. However, large amplitude, short
time-scale flaring behavior is evident, with trough-to-peak flux changes of
about 18% in approximately 3 days. We present evidence for wavelength-dependent
continuum time delays, with the variations at 3000 A lagging behind those at
1365 A by about 1 day. These delays may be interpreted as evidence for a
stratified continuum reprocessing region, possibly an accretion-disk structure.
The Lyman-alpha 1216 emission-line exhibits flux variations of about 1%
amplitude.Comment: 27 pages, 14 figures. Accepted by Astrophysical Journa
Secular changes in the quiescence of WZ Sge: the development of a cavity in the inner disk
We find a dimming during optical quiescence of the cataclysmic variable WZ
Sge by about half a magnitude between superoutbursts. We connect the dimming
with the development of a cavity in the inner part of the accretion disk. We
suggest that, when the cavity is big enough, accretion of material is governed
by the magnetic field of the white dwarf and pulsations from the weakly
magnetic white dwarf appear. The time scale of forming the cavity is about a
decade, and it persists throughout the whole quiescent phase. Such a cavity can
be accommodated well by the proposed magnetic propeller model for WZ Sge, where
during quiescence mass is being expelled by the magnetic white dwarf from the
inner regions of the accretion disk to larger radii.Comment: 10 pages, 4 figures, accepted for publication in Astronomy and
Astrophysics; following referee report, many textual changes, figures
improved, more historic data added, conclusions unchange
Impact of age norms and stereotypes on managers' hiring decisions of retirees
Purpose -Our study investigates the role of managers in the re-employment of early retirees and asks what the effect is of managersâ age norms and stereotypes on managersâ employment decisions.
Design/methodology/approach- A combination of a factorial study and a survey was conducted. First, information on the age norms and stereotypes was collected. Secondly, profiles of hypothetical retired job applicants were presented to the employers, who were asked to make a specific hiring decision. The information collected during both studies was combined in the analysis and multilevel models were estimated.
Findings -The results indicate that higher age norms result in a higher propensity to hire an early retiree. Stereotypes, by contrast, do not influence managersâ decisions. Early retireesâ chances for re-employment are also related to their own circumstances (physical appearance and relevant experience) and organisational forces, as they are hired when organisations face labour force shortages.
Research limitation / implications â with the use of vignettes study we deal with hypothetical hiring situation.
Originality value- Although the effect of age norms and age stereotypes has been often suggested, not much empirical evidence was presented to support this notion. Our study estimates the effect of age norms and stereotypes on hiring decision.
key words: bridge employment; early retirees; age norms; age stereotypes; multilevel models.
Higgsing M2 to D2 with gravity: N=6 chiral supergravity from topologically gauged ABJM theory
We present the higgsing of three-dimensional N=6 superconformal ABJM type
theories coupled to conformal supergravity, so called topologically gauged ABJM
theory, thus providing a gravitational extension of previous work on the
relation between N M2 and N D2-branes. The resulting N=6 supergravity theory
appears at a chiral point similar to that of three-dimensional chiral gravity
introduced recently by Li, Song and Strominger, but with the opposite sign for
the Ricci scalar term in the lagrangian. We identify the supersymmetry in the
broken phase as a particular linear combination of the supersymmetry and
special conformal supersymmetry in the original topologically gauged ABJM
theory. We also discuss the higgsing procedure in detail paying special
attention to the role played by the U(1) factors in the original ABJM model and
the U(1) introduced in the topological gauging.Comment: 53 pages, Late
Reverberation Mapping of the Seyfert 1 Galaxy NGC 7469
A large reverberation mapping study of the Seyfert 1 galaxy NGC 7469 has
yielded emission-line lags for Hbeta 4861 and He II 4686 and a central black
hole mass measurement of about 10 million solar masses, consistent with
previous measurements. A very low level of variability during the monitoring
campaign precluded meeting our original goal of recovering velocity-delay maps
from the data, but with the new Hbeta measurement, NGC 7469 is no longer an
outlier in the relationship between the size of the Hbeta-emitting broad-line
region and the AGN luminosity. It was necessary to detrend the continuum and
Hbeta and He II 4686 line light curves and those from archival UV data for
different time-series analysis methods to yield consistent results.Comment: 9 Pages, 7 figures, 6 tables. Accepted for publication in The
Astrophysical Journa
Dwarf novae in the Hamburg quasar survey : rarer than expected
Aims. We report the discovery of five new dwarf novae that were spectroscopically identified in the Hamburg Quasar Survey (HQS),and discuss the properties of the sample of new dwarf novae from the HQS.
Methods. Follow-up time-resolved spectroscopy and photometry have been obtained to characterise the new systems.
Results. The orbital periods determined from analyses of the radial velocity variations and/or orbital photometric variability are Porb 105.1min or Porb 109.9min for HS 0417+7445, Porb = 114.3 ± 2.7min for HS 1016+3412, Porb = 92.66 ± 0.17 min for HS 1340+1524, Porb = 272.317 ± 0.001 min for HS 1857+7127, and Porb = 258.02 ± 0.56 min for HS 2214+2845. HS 1857+7127 is found to be partially eclipsing. In HS 2214+2845 the secondary star of spectral type M3 ± 1 is clearly detected, and we estimate the distance to the system to be d = 390 ± 40 pc. We recorded one superoutburst of HS 0417+7445, identifying the system as a SUUMatype
dwarf nova. HS 1016+3412 and HS 1340+1524 have rare outbursts, and their subtype is yet undetermined. HS 1857+7127 frequently varies in brightness and may be a ZCam-type dwarf nova. HS 2214+2845 is a UGem-type dwarf nova with a most likely cycle length of 71 d.
Conclusions. To date, 14 new dwarf novae have been identified in the HQS. The ratio of short-period (3 h)systems of this sample is 1.3, much smaller compared to the ratio of 2.7 found for all known dwarf novae. The HQS dwarf novae display typically infrequent or low-amplitude outburst activity, underlining the strength of spectroscopic selection in identifying new
CVs independently of their variability. The spectroscopic properties of short-period CVs in the HQS, newly identified and previously known, suggest that most, or possibly all of them are still evolving towards the minimum period. Their total number agrees with the predictions of population models within an order of magnitude. However, the bulk of all CVs is predicted to have evolved past the minimum period, and those systems remain unidentified. This suggests that those post-bounce systems have markedly weaker HÎČ emission lines compared to the average known short-period CVs, and undergo no or extremely rare outbursts
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