1,041 research outputs found
V348 Puppis: a new SW Sex star in the period gap
We present time-resolved optical spectroscopy and photometry of the nova-like
cataclysmic variable V348 Puppis. The system displays the same spectroscopic
behaviour as SW Sex stars, so we classify V348 Pup as a new member of the
class. V348 Pup is the second SW Sex system (the first is V795 Herculis) which
lies in the period gap. The spectra exhibit enhanced HeII 4686 emission,
reminiscent of magnetic cataclysmic variables. The study of this emission line
gives a primary velocity semi-amplitude of K1 ~= 100 km/s. We have also derived
the system parameters, obtaining: M1 ~= 0.65 Msun, M2 ~= 0.20 Msun (q ~= 0.31),
i ~= 80 deg and K2 ~= 323 km/s. The spectroscopic behaviour of V348 Pup is very
similar to that of V795 Her, with the exception that V348 Pup shows deep
eclipses. We have computed the ``0.5-absorption'' spectrum of both systems,
obtaining spectra which resemble the absorption spectrum of a B0 V star. We
propose that absorption in SW Sex systems can be produced by a vertically
extended atmosphere which forms where the gas stream re-impacts the system,
either at the accretion disc or at the white dwarf's magnetosphere (assuming a
magnetic scenario).Comment: 6 pages, 10 figures, accepted for publication in MNRA
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
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.
Brane-world Cosmologies with non-local bulk effects
It is very common to ignore the non-local bulk effects in the study of
brane-world cosmologies using the brane-world approach. However, we shall
illustrate through the use of three different scenarios, that the non-local
bulk-effect does indeed have significant impact on both the
initial and future behaviour of brane-world cosmologies.Comment: 17 pages, no figures, iopart.cls, submitted to CQ
Irradiation of the secondary star in X-ray Nova Scorpii 1994 (=GRO J1655--40)
We have obtained intermediate resolution optical spectra of the black-hole
candidate Nova Sco 1994 in June 1996, when the source was in an X-ray/optical
active state (R~15.05). We measure the radial velocity curve of the secondary
star and obtain a semi-amplitude of 279+/-10 km/s; a value which is 30 per cent
larger than the value obtained when the source is in quiescence. Our large
value for K_2 is consistent with 60 +9,-7 per cent of the secondary star's
surface being heated; compared to 35 per cent, which is what one would expect
if only the inner face of the secondary star were irradiated. Effects such as
irradiation-induced flows on the secondary star may be important in explaining
the observed large value for K_2.Comment: 5 pages, 2 figures, accepted by MNRA
The Gaia -ESO Survey : Empirical determination of the precision of stellar radial velocities and projected rotation velocities
Context. The Gaia-ESO Survey (GES) is a large public spectroscopic survey at the European Southern Observatory Very Large Telescope. Aims. A key aim is to provide precise radial velocities (RVs) and projected equatorial velocities (v sin i) for representative samples of Galactic stars, which will complement information obtained by the Gaia astrometry satellite. Methods. We present an analysis to empirically quantify the size and distribution of uncertainties in RV and v sin i using spectra from repeated exposures of the same stars. Results. We show that the uncertainties vary as simple scaling functions of signal-to-noise ratio (S/N) and v sin i, that the uncertainties become larger with increasing photospheric temperature, but that the dependence on stellar gravity, metallicity and age is weak. The underlying uncertainty distributions have extended tails that are better represented by Student's t-distributions than by normal distributions. Conclusions. Parametrised results are provided, which enable estimates of the RV precision for almost all GES measurements, and estimates of the v sin i precision for stars in young clusters, as a function of S/N, v sin i and stellar temperature. The precision of individual high S/N GES RV measurements is 0.22-0.26 kms-1, dependent on instrumental configuration.Peer reviewedFinal Accepted Versio
Late-epoch optical and near-infrared observations of the GRB000911 afterglow and its host galaxy
We present the results of an optical and near-infrared (NIR) monitoring
campaign of the counterpart of Gamma-Ray Burst (GRB) 000911, located at
redshift z=1.06, from 5 days to more than 13 months after explosion. Our
extensive dataset is a factor of 2 larger and spans a time interval about 4
times longer than the ones considered previously for this GRB afterglow; this
allows a more thorough analysis of its light curve and of the GRB host galaxy
properties. The afterglow light curves show a single power-law temporal
decline, modified at late times by light from a host galaxy with moderate
intrinsic extinction, and possibly by an emerging supernova (SN). The afterglow
evolution is interpreted within the classical "fireball" scenario as a weakly
collimated adiabatic shock propagating in the interstellar medium. The presence
of a SN light curve superimposed on the non-thermal afterglow emission is
investigated: while in the optical bands no significant contribution to the
total light is found from a SN, the NIR J-band data show an excess which is
consistent with a SN as bright as the known hypernova SN1998bw. If the SN
interpretation is true, this would be the farthest GRB-associated SN, as well
as the farthest core-collapse SN, discovered to date. However, other possible
explanations of this NIR excess are also investigated. Finally, we studied the
photometric properties of the host, and found that it is likely to be a
slightly reddened, subluminous, extreme starburst compact galaxy, with
luminosity about 0.1 L*, an age of about 0.5 Gyr and a specific Star Formation
Rate (SFR) of approximately 30 Msol yr-1 (L/L*)-1. This is the highest specific
SFR value for a GRB host inferred from optical/NIR data.Comment: 13 pages, 6 figures, 3 tables. Accepted for publication in A&A, main
journa
Optical and near-infrared observations of the GRB020405 afterglow
(Abridged) We report on observations of the optical and NIR afterglow of
GRB020405. Ground-based optical observations started about 1 day after the GRB
and spanned a period of ~10 days; archival HST data extended the coverage up to
70 days after the GRB. We report the first detection of the afterglow in NIR
bands. The detection of emission lines in the optical spectrum indicates that
the GRB is located at z = 0.691. Absorptions are also detected at z = 0.691 and
at z = 0.472. The latter system is likely caused by clouds in a galaxy located
2 arcsec southwest of the GRB host. Hence, for the first time, the galaxy
responsible for an intervening absorption system in the spectrum of a GRB
afterglow is identified. Optical and NIR photometry indicates that the decay in
all bands follows a single power law of index alpha = 1.54. The late-epoch VLT
and HST points lie above the extrapolation of this power law, so that a plateau
is apparent in the VRIJ light curves at 10-20 days after the GRB. The light
curves at epochs later than day ~20 after the GRB are consistent with a
power-law decay with index alphaprime = 1.85. We suggest that this deviation
can be modeled with a SN having the same temporal profile as SN2002ap, but 1.3
mag brighter at peak, and located at the GRB redshift. Alternatively, a shock
re-energization may be responsible for the rebrightening. A polarimetric R-band
measurement shows that the afterglow is polarized, with P = 1.5 % and theta =
172 degrees. Optical-NIR spectral flux distributions show a change of slope
across the J band which we interpret as due to the presence of nu_c. The
analysis of the multiwavelength spectrum within the fireball model suggests
that a population of relativistic electrons produces the optical-NIR emission
via synchrotron in an adiabatically expanding blastwave, and the X-rays via IC.Comment: 17 pages, 10 figures, 4 tables, accepted for publication on A&A, main
journa
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Building WF16: construction of a PPNA pisé structure in Southern Jordan
The Pre-Pottery Neolithic A (PPNA) period in Southwest Asia is essential for our understanding of the transition to sedentary, agricultural communities. Developments in architecture are key to understanding this transition, but many aspects of PPNA architecture remain elusive, such as construction techniques, the selection of building materials, and the functional use of space. The primary aim of the research described within this contribution was to build a PPNA-like structure in order to answer questions about PPNA architecture in general, while specifically addressing issues raised by the excavation of structures at the site of WF16, Southern Jordan. The second aim was to display a âPPNAâ building to visitors in Wadi Faynan to enhance their understanding of the period. The experimental construction based on one of the WF16 structures showed that 1) required materials can be acquired locally; 2) a construction technique using mud layers as described in this paper was likely used; 3) flat, or very slightly dome-shaped, roofs are functional and can also be used as a solid working platform; 4) the WF16 small semi-subterranean buildings appear inappropriate for housing a nuclear family unit
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