1,039 research outputs found
Progenitors of Supernovae Type Ia
Despite the significance of Type Ia supernovae (SNeIa) in many fields in
astrophysics, SNeIa lack a theoretical explanation. The standard scenarios
involve thermonuclear explosions of carbon/oxygen white dwarfs approaching the
Chandrasekhar mass; either by accretion from a companion or by a merger of two
white dwarfs. We investigate the contribution from both channels to the SNIa
rate with the binary population synthesis (BPS) code SeBa in order to constrain
binary processes such as the mass retention efficiency of WD accretion and
common envelope evolution. We determine the theoretical rates and delay time
distribution of SNIa progenitors and in particular study how assumptions affect
the predicted rates.Comment: 6 pages, 6 figures, appeared in proceedings for "The 18th European
White Dwarf Workshop
Population synthesis for double white dwarfs. II. Semi-detached systems: AM CVn stars
We study two models for AM CVn stars: white dwarfs accreting (i) from a
helium white dwarf companion and (ii) from a helium-star donor. We show that in
the first model possibly no accretion disk forms at the onset of mass transfer.
The stability and the rate of mass transfer then depend on the tidal coupling
between the accretor and the orbital motion. In the second model the formation
of AM CVn stars may be prevented by detonation of the CO white dwarf accretor
and the disruption of the system. With the most favourable conditions for the
formation of AM CVn stars we find a current Galactic birth rate of 6.8 10^{-3}
yr^{-1}. Unfavourable conditions give 1.1 10^{-3} yr^{-1}. The expected total
number of the systems in the Galaxy is 9.4 10^{7} and 1.6 10^{7}, respectively.
We model very simple selection effects to get some idea about the currently
expected observable population and discuss the (quite good) agreement with the
observed systems.Comment: Accepted by A&
Time-resolved optical photometry of the ultra-compact binary 4U0614+091
We present a detailed optical study of the ultra-compact X-ray binary
4U0614+091. We have used 63 hrs of time-resolved optical photometry taken with
three different telescopes (IAC80, NOT and SPM) to search for optical
modulations. The power spectra of each dataset reveals sinusoidal modulations
with different periods, which are not always present. The strongest modulation
has a period of 51.3 mins, a semi-amplitude of 4.6 mmags, and is present in the
IAC80 data. The SPM and NOT data show periods of 42 mins and 64 mins
respectively, but with much weaker amplitudes, 2.6 mags and 1.3 mmags
respectively. These modulations arise from either X-ray irradiation of the
inner face of the secondary star and/or a superhump modulation from the
accretion disc, or quasi-periodic modulations in the accretion disc. It is
unclear whether these periods/quasi-periodic modulations are related to the
orbital period, however, the strongest period of 51.3 mins is close to earlier
tentative orbital periods. Further observations taken over a long base-line are
encouraged.Comment: Accepted for publication in PAS
Phase resolved spectroscopy and Kepler photometry of the ultracompact AM CVn binary SDSS J190817.07+394036.4
{\it Kepler} satellite photometry and phase-resolved spectroscopy of the
ultracompact AM CVn type binary SDSS J190817.07+394036.4 are presented. The
average spectra reveal a variety of weak metal lines of different species,
including silicon, sulphur and magnesium as well as many lines of nitrogen,
beside the strong absorption lines of neutral helium. The phase-folded spectra
and the Doppler tomograms reveal an S-wave in emission in the core of the He I
4471 \AA\,absorption line at a period of \,sec
identifying this as the orbital period of the system. The Si II, Mg II and the
core of some He I lines show an S-wave in absorption with a phase offset of
compared to the S-wave in emission. The N II, Si III and some
helium lines do not show any phase variability at all. The spectroscopic
orbital period is in excellent agreement with a period at \,sec detected in the three year {\it Kepler} lightcurve. A
Fourier analysis of the Q6 to Q17 short cadence data obtained by {\it Kepler}
revealed a large number of frequencies above the noise level where the majority
shows a large variability in frequency and amplitude. In an O-C analysis we
measured a xs\,s for some of
the strongest variations and set a limit for the orbital period to be
s\,s. The shape of the phase folded
lightcurve on the orbital period indicates the motion of the bright spot.
Models of the system were constructed to see whether the phases of the radial
velocity curves and the lightcurve variation can be combined to a coherent
picture. However, from the measured phases neither the absorption nor the
emission can be explained to originate in the bright spot.Comment: Accepted for publication in MNRAS, 15 pages, 14 figures, 5 table
The ESO supernovae type Ia progenitor survey (SPY) : The radial velocities of 644 DA white dwarfs
Accepted for publication in A&A. 59 pages.Close double degenerate binaries are one of the favoured progenitor channels for type Ia supernovae, but it is unclear how many suitable systems there are in the Galaxy. We report results of a large radial velocity survey for double degenerate (DD) binaries using the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surveY - SPY). Exposures taken at different epochs are checked for radial velocity shifts indicating close binary systems. We observed 689 targets classified as DA (displaying hydrogen-rich atmospheres), of which 46 turned out to possess a cool companion. We measured radial velocities (RV) of the remaining 643 DA white dwarfs. We managed to secure observations at two or more epochs for 625 targets, supplemented by eleven objects meeting our selection criteria from literature. The data reduction and analysis methods applied to the survey data are described in detail. The sample contains 39 double degenerate binaries, only four of which were previously known. 20 are double-lined systems, in which features from both components are visible, the other 19 are single-lined binaries. We provide absolute RVs transformed to the heliocentric system suitable for kinematic studies. Our sample is large enough to sub-divide by mass: 16 out of 44 low mass targets (0.45 Msun are double. Although the detected fraction amongst the low mass objects (36.4 +/- 7.3%) is significantly higher than for the higher-mass, carbon/oxygen-core dominated part of the sample (3.9 +/- 0.8%), it is lower than the detection efficiency based upon companion star masses >= 0.05 Msun. This suggests either companion stars of mass <0.05 Msun, or that some of the low mass white dwarfs are single.Peer reviewe
Personality development across adolescence and young adulthood:The role of life transitions and self-concept clarity
Personality develops across the lifespan, but most development occurs in adolescence and young adulthood. Life transitions to new social roles may be important drivers of mean-level personality development. The present study examined mean-level personality development in adolescence and young adulthood, and the role of the transition to tertiary education and working life therein in a sample of Dutch young people that were followed across 14 years (N = 497, Age(W1) = 13.03 years). We explored whether young people's self-concept clarity moderated these associations. Our hypotheses and analytical plan were pre-registered. Findings from Latent Growth Models showed support for maturation in personality across adolescence and young adulthood, but not a maturity dip. Having the role of employee was associated with higher conscientiousness, but no associations were found of the transition to tertiary education and the transition to work with mean-level development of any of the personality traits. Self-concept clarity did not moderate the role of transitions in mean-level personality development. Our findings suggest that socialization effects may not explain associations between life transitions and personality development in adolescence and young adulthood
On the Theory of Gamma Ray Bursts and Hypernovae: The Black Hole Soft X-ray Transient Sources
We show that a common evolutionary history can produce the black hole
binaries in the Galaxy in which the black holes have masses of ~ 5-10 M_sun. In
with low-mass, <~ 2.5 M_sun, ZAMS (zero age main sequence) companions, the
latter remain in main sequence during the active stage of soft X-ray transients
(SXTs), most of them being of K or M classification. In two intermediate cases,
IL Lupi and Nova Scorpii with ZAMS ~ 2.5 M_sun companions the orbits are
greatly widened because of large mass loss in the explosion forming the black
hole, and whereas these companions are in late main sequence evolution, they
are close to evolving. Binaries with companion ZAMS masses >~ 3 M_sun are
initially "silent" until the companion begins evolving across the Herzsprung
gap. We provide evidence that the narrower, shorter period binaries, with
companions now in main sequence, are fossil remnants of gamma ray bursters
(GRBs). We also show that the GRB is generally accompanied by a hypernova
explosion (a very energetic supernova explosion). We further show that the
binaries with evolved companions are good models for some of the ultraluminous
X-ray sources (ULXs) recently seen by Chandra in other galaxies. The great
regularity in our evolutionary history, especially the fact that most of the
companions of ZAMS mass <~ 2.5 M_sun remain in main sequences as K or M stars
can be explained by the mass loss in common envelope evolution to be Case C;
i.g., to occur only after core He burning has finished. Since our argument for
Case C mass transfer is not generally understood in the community, we add an
appendix, showing that with certain assumptions which we outline we can
reproduce the regularities in the evolution of black hole binaries by Case C
mass transfer.Comment: 59 pages, 12 figures, review articl
Theoretical Black Hole Mass Distributions
We derive the theoretical distribution function of black hole masses by
studying the formation processes of black holes. We use the results of recent
2D simulations of core-collapse to obtain the relation between remnant and
progenitor masses and fold it with an initial mass function for the
progenitors. We examine how the calculated black-hole mass distributions are
modified by (i) strong wind mass loss at different evolutionary stages of the
progenitors, and (ii) the presence of close binary companions to the black-hole
progenitors. Thus, we are able to derive the binary black hole mass
distribution. The compact remnant distribution is dominated by neutron stars in
the mass range 1.2-1.6Msun and falls off exponentially at higher remnant
masses. Our results are most sensitive to mass loss from winds which is even
more important in close binaries. Wind mass-loss causes the black hole
distribution to become flatter and limits the maximum possible black-hole mass
(<10-15Msun). We also study the effects of the uncertainties in the explosion
and unbinding energies for different progenitors. The distributions are
continuous and extend over a broad range. We find no evidence for a gap at low
values (3-5Msun) or for a peak at higher values (~7Msun) of black hole masses,
but we argue that our black hole mass distribution for binaries is consistent
with the current sample of measured black-hole masses in X-ray transients. We
discuss possible biases against the detection or formation of X-ray transients
with low-mass black holes. We also comment on the possibility of black-hole
kicks and their effect on binaries.Comment: 22 pages, submitted to Ap
Psychometric qualities of the Educational Identity Processes Scale (EIPS)
In the educational domain, the development of identity becomes especially salient during school transition phases. To assess the specific identity processes that match the adolescents' experiences before and after the school transition, the Educational Identity Processes Scale (EIPS) was developed. The present study aimed to test the psychometric qualities of the EIPS by examining its factor structure, the internal and convergent validity of the identity dimensions, and whether the questionnaire was measurement invariant over time. The pre-transition version was tested in a Dutch sample (N = 242 early adolescents) and the post-transition version was tested in a Lithuanian sample (N = 1,268 mid-adolescents). Findings indicated good psychometric qualities for both the pre- and post-transition versions of the EIPS. Additionally, context dependencies were observed, as distance to the transition influenced the meaning of specific identity processes and determined whether specific processes could be considered as part of normative development
Variability of Optical Counterparts in the Chandra Galactic Bulge Survey
We present optical lightcurves of variable stars consistent with the
positions of X-ray sources identified with the Chandra X-ray Observatory for
the Chandra Galactic Bulge Survey. Using data from the Mosaic-II instrument on
the Blanco 4m Telescope at CTIO, we gathered time-resolved photometric data on
timescales from hr to 8 days over the of the X-ray survey
containing sources from the initial GBS catalog. Among the lightcurve
morphologies we identify are flickering in interacting binaries, eclipsing
sources, dwarf nova outbursts, ellipsoidal variations, long period variables,
spotted stars, and flare stars. of X-ray sources have at least one
potential optical counterpart. of these candidate counterparts are
detectably variable; a much greater fraction than expected for randomly
selected field stars, which suggests that most of these variables are real
counterparts. We discuss individual sources of interest, provide variability
information on candidate counterparts, and discuss the characteristics of the
variable population.Comment: Accepted for publication in the Astrophysical Journal Supplement
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