96 research outputs found
Early production of the passive in two Eastern Bantu languages
The passive construction is acquired relatively late by children learning to speak many languages, with verbal passives not fully acquired till age 6 in English. In other languages it appears earlier, around age 3 or before. Use of passive construction in young children was examined in two Eastern Bantu languages spoken in Kenya (Kiswahili and Kigiriama), both with frequent use of passive. The passive was used productively very early (2;1) in these languages, regardless of the method used to measure productivity. In addition non-actional passives, particularly rare in English and some other European languages, were seen at these early ages. The proportion of verbs that were passive varied between individuals, both in children's speech and in the input to children. Pragmatic and grammatical features of the passive in some languages have previously been suggested to drive early passive acquisition, but these features are not found consistently in the two languages studied here. Findings suggest that the relatively high frequency of input found in these languages is the most plausible reason for early productive use of the passive
A Bayesian approach to the analysis of time symmetry in light curves: Reconsidering Scorpius X-1 occultations
We present a new approach to the analysis of time symmetry in light curves,
such as those in the x-ray at the center of the Scorpius X-1 occultation
debate. Our method uses a new parameterization for such events (the bilogistic
event profile) and provides a clear, physically relevant characterization of
each event's key features. We also demonstrate a Markov Chain Monte Carlo
algorithm to carry out this analysis, including a novel independence chain
configuration for the estimation of each event's location in the light curve.
These tools are applied to the Scorpius X-1 light curves presented in Chang et
al. (2007), providing additional evidence based on the time series that the
events detected thus far are most likely not occultations by TNOs.Comment: 24 pages, 18 figures. Preprint typeset using LaTeX style emulateapj
v. 04/20/0
A major outburst from the X-ray binary RX J0520.5-6932
We report on the analysis of 8 years of MAssive Compact Halo Objects (MACHO)
data for the source RX J0520.5-6932. A regular period of 24.4 days has been
confirmed, however this is manifest almost entirely in the red part of the
spectrum. A major outburst, lasting approximately 200 days, was observed which
increased the apparent brightness of the object by approximately 0.15
magnitudes without significantly altering its V-R colour index. This outburst
was also seen in X-ray data. The evidence from this analysis points to the
identification of this object as a Be/X-ray binary with a periodically variable
circumstellar disk and a very early optical counterpart.Comment: Paper has been accepted by MNRA
Searching for periodicities in the MACHO light curve of LMC X-2
Using the exceptional long-term monitoring capabilities of the MACHO project,
we present here the optical history of LMC X-2 for a continuous 6-yr period.
These data were used to investigate the previously claimed periodicities for
this source of 8.15 h and 12.54 d : we find upper amplitude limits of 0.10 mag
and 0.09 mag, respectively.Comment: 4 pages, 4 figures. Minor changes, including title. MNRAS, in pres
Discovery of the optical counterpart to the X-ray pulsar SAX J2103.5+4545
We report optical and infrared photometric and spectroscopic observations
that identify the counterpart to the 358.6-s X-ray transient pulsar SAX
J2103.5+4545 with a moderately reddened V=14.2 B0Ve star. This identification
makes SAX J2103.5+4545 the Be/X-ray binary with the shortest orbital period
known, Porb= 12.7 days. The amount of absorption to the system has been
estimated to be Av=4.2+-0.3, which for such an early-type star implies a
distance of about 6.5 kpc. The optical spectra reveal major and rapid changes
in the strength and shape of the Halpha line. The Halpha line was initially
observed as a double peak profile with the ratio of the intensities of the blue
over the red peak greater than one (V/R > 1). Two weeks later this ratio
reversed (V/R< 1). Subsequently, in less than a month, the emission ceased and
Halpha appeared in absorption. This fast spectral variability is interpreted
within the viscous decretion disc model and demonstrates the significant role
of the neutron star on the evolution of the circumstellar disc around the Be
star. The implications of the small orbit and moderate eccentricity on the spin
period of the neutron star are discussed.Comment: 9 pages, 6 figures, accepted for publication in A&
The Proper Motion Field of the Small Magellanic Cloud: Kinematic Evidence for its Tidal Disruption
We present a new measurement of the systemic proper motion of the Small
Magellanic Cloud (SMC), based on an expanded set of 30 fields containing
background quasars and spanning a 3 year baseline, using the
\textit{Hubble Space Telescope} (\textit{HST}) Wide Field Camera 3. Combining
this data with our previous 5 \textit{HST} fields, and an additional 8
measurements from the \textit{Gaia}-Tycho Astrometric Solution Catalog, brings
us to a total of 43 SMC fields. We measure a systemic motion of =
0.02 (random) 0.10 (systematic) mas yr and
= 0.01 (random) 0.03 (systematic) mas yr. After
subtraction of the systemic motion, we find little evidence for rotation, but
find an ordered mean motion radially away from the SMC in the outer regions of
the galaxy, indicating that the SMC is in the process of tidal disruption. We
model the past interactions of the Clouds with each other based on the measured
present-day relative velocity between them of km s. We find
that in 97\% of our considered cases, the Clouds experienced a direct collision
Myr ago, with a mean impact parameter of kpc.Comment: 13 pages, 12 figures, 3 tables, accepted to Ap
The Proper Motion of the Large Magellanic Cloud using HST
We present a measurement of the systemic proper motion of the Large
Magellanic Cloud (LMC) from astrometry with the High Resolution Camera (HRC) of
the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). We
observed LMC fields centered on 21 background QSOs that were discovered from
their optical variability in the MACHO database. The QSOs are distributed
homogeneously behind the central few degrees of the LMC. With 2 epochs of HRC
data and a ~2 year baseline we determine the proper motion of the LMC to better
than 5% accuracy: mu_W = -2.03 +/- 0.08 mas/yr; mu_N = 0.44 +/- 0.05 mas/yr.
This is the most accurate proper motion measurement for any Milky Way satellite
thus far. When combined with HI data from the Magellanic Stream this should
provide new constraints on both the mass distribution of the Galactic Halo and
models of the Stream.Comment: 40 pages, 15 figures, submitted to Ap
Evidence for Companion-Induced Secular Changes in the Turbulent Disk of a Be Star in the LMC MACHO Database
The light curve of a blue variable in the MACHO LMC database (FTS ID
78.5979.72) appeared nearly unvarying for ~4 years (quasi-flat segment) but
then rapidly changed to become periodic with noisy minima for the remaining 4
years (periodic segment); there are no antecedent indications of a gradual
approach to this change. Lomb Periodogram analyses indicate the presence of two
distinct periods of ~61 days and 8 days in both the quasi-flat and the periodic
segments. Minima of the periodic segment cover at least 50% of the orbital
period and contain spikes of light with the 8-day period; maxima do not show
this short period. The system typically shows maxima to be redder than minima.
The most recent OGLE-III light curve shows only a 30-day periodicity. The
variable's V and R magnitudes and color are those of a Be star, and recent sets
of near infrared spectra four days apart, secured during the time of the
OGLE-III data, show H-alpha emission near and at a maximum, confirming its Be
star characteristics. The model that best fits the photometric behavior
consists of a thin ring-like circumstellar disk of low mass with four obscuring
sectors orbiting the central B star in unison at the 61-day period. The central
star peers through the three equi- spaced separations between the four sectors
producing the 8-day period. The remainder of the disk contains hydrogen in
emission making maxima appear redder. A companion star of lower mass in an
inclined and highly eccentric orbit produces an impulsive perturbation near its
periastron to change the disk's orientation, changing eclipses from partial to
complete within ~ 10 days.Comment: 42 pages, 14 figures, and 2 tables Submitted to AJ v3: Title changed,
figures added, model modifie
The X-ray off-state of the supersoft source CAL 83 and its interpretation
We consider simultaneous optical data obtained during the recent X-ray
turn-off of CAL83. Combining the optical behaviour with the observed X-ray
decay time, we show that a model of cessation of steady nuclear burning is
viable if the white dwarf is massive. Our model provides a natural explanation
for the subsequent return of the supersoft X-ray emission.Comment: 4 pages Latex, 1 figure, to appear in MNRA
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