1,821 research outputs found
Optical Monitoring of Quasars: I. Variability
We present an analysis of quasar variability from data collected during a
photometric monitoring of 50 objects carried out at CNPq/Laboratorio Nacional
de Astrofisica, Brazil, between March 1993 and July 1996. A distinctive feature
of this survey is its photometric accuracy, ~ 0.02 V mag, achieved through
differential photometry with CCD detectors, what allows the detection of faint
levels of variability. We find that the relative variability, delta = sigma /
L, observed in the V band is anti-correlated with both luminosity and redshift,
although we have no means of discovering the dominant relation, given the
strong coupling between luminosity and redshift for the objects in our
sample.We introduce a model for the dependence of quasar variability on
frequency that is consistent with multi-wavelength observations of the nuclear
variability of the Seyfert galaxy NGC 4151. We show that correcting the
observed variability for this effect slightly increases the significance of the
trends of variability with luminosity and redshift. Assuming that variability
depends only on the luminosity, we show that the corrected variability is
anti-correlated with luminosity and is in good agreement with predictions of a
simple Poissonian model. The energy derived for the hypothetical pulses, ~
10^50 erg, agrees well with those obtained in other studies. We also find that
the radio-loud objects in our sample tend to be more variable than the
radio-quiet ones, for all luminosities and redshifts.Comment: 17 pages, 12 figures, accepted for publication in MNRAS (uses MNRAS
style
A Qualitative Exploration of Emerging Adultsâ and Parentsâ Perspectives on Communicating Adulthood Status
In this study the authors examine parent - child communication in Emerging Adulthood. Thirty - seven college students and one or both of their parents completed written questionnaires assessing whether the parent had verbally communicated or did some action to acknowledge the Emerging Adultâs maturity. Communication about changes in the parent - child relationship, as well as the Emerging Adultâs decision - making abilities, obligations to the family, and financial responsibilities were also assessed. The responses to the open ended questions were qualitatively analyzed using grounded theory. The findings indicated that the Emerging Adultsâ and parentsâ responses were very similar, and the overwhelming majority reported that there had indeed been an acknowledgment from the parents to indicate Emerging Adulthood status, although this was not always verbally communicated; sometimes it was indicated through the parentsâ behavior.
Spectral atlas of massive stars around He I 10830 A
We present a digital atlas of peculiar, high-luminosity massive stars in the near-infrared region (10470-11000 A) at medium resolution (R~7000). The spectra are centered around He I 10830 A, which is formed in the wind of those stars, and is a crucial line to obtain their physical parameters. The instrumental configuration also sampled a rich variety of emission lines of Fe II, Mg II, C I, N I and Pa gamma. Secure identifications for most spectral lines are given, based on synthetic atmosphere models calculated by our group. We also propose that two unidentified absorption features have interstellar and/or circumstellar origin. For the strongest one (10780 A) an empirical calibration between E(B-V) and equivalent width is provided. The atlas displays the spectra of massive stars organized in four categories, namely Be stars, OBA Iape (or luminous blue variables, LBV candidates and ex/dormant LBVs), OB supergiants and Wolf-Rayet stars. For comparison, the photospheric spectra of non emission-line stars are presented. Selected LBVs were observed in different epochs from 2001 to 2004, and their spectral variability reveals that some stars, such as Eta Car, AG Car and HR Car, suffered dramatic spectroscopic changes during this time interval
Correlated radial velocity and X-ray variations in HD 154791/4U 1700+24
We present evidence for approximately 400-d variations in the radial velocity
of HD 154791 (V934 Her), the suggested optical counterpart of 4U 1700+24. The
variations are correlated with the previously reported approximately 400 d
variations in the X-ray flux of 4U 1700+24, which supports the association of
these two objects, as well as the identification of this system as the second
known X-ray binary in which a neutron star accretes from the wind of a red
giant. The HD 154791 radial velocity variations can be fit with an eccentric
orbit with period 404 +/- 3 d, amplitude K=0.75 +/- 0.12 km/s and eccentricity
e=0.26 +/- 0.15. There are also indications of variations on longer time scales
>~ 2000 d. We have re-examined all available ASM data following an unusually
large X-ray outburst in 1997-98, and confirm that the 1-d averaged 2-10 keV
X-ray flux from 4U 1700+24 is modulated with a period of 400 +/- 20 d. The mean
profile of the persistent X-ray variations was approximately sinusoidal, with
an amplitude of 0.108 +/- 0.012 ASM count/s (corresponding to 31% rms). The
epoch of X-ray maximum was approximately 40 d after the time of periastron
according to the eccentric orbital fit. If the 400 d oscillations from HD
154791/4U 1700+24 are due to orbital motion, then the system parameters are
probably close to those of the only other neutron-star symbiotic-like binary,
GX 1+4. We discuss the similarities and differences between these two systems.Comment: 6 pages, 2 figures; accepted by Ap
A Technique for Narrowband Time Series Photometry: the X-ray Star V2116 Oph
We have used innovative features of the Taurus Tunable Filter instrument on
the 3.9-m Anglo-Australian Telescope to obtain nearly-continuous,
high-throughput, linear photometry of V2116 Oph in a 7 Angstrom bandpass at the
center of the O I 8446 emission line. This instrumental technique shows promise
for applications requiring precise, rapid, narrowband photometry of faint
objects. The spectrum of V2116 Oph, the counterpart of GX 1+4 (=X1728-247), is
exotic, even among the unusual spectra of other optical counterparts of compact
Galactic X-ray sources. The second strongest emission line is an unusual one,
namely extremely prominent O I 8446, which is likely to result from pumping by
an intense Ly beta radiation field. As the X-radiation from GX 1+4 is steadily
pulsed, with typical pulsed fractions of 0.4, the O I 8446 emission in V2116
Oph may also be strongly modulated with the current 127 s period of the X-ray
source. If so, this may well allow us to obtain high signal-to-noise radial
velocity measurements and thus to determine the system parameters. However, no
such pulsations are detected, and we set an upper limit of ~1% (full-amplitude)
on periodic 8446 oscillations at the X-ray frequency. This value is comparable
to the amplitude of continuum oscillations observed on some nights by other
workers. Thus we rule out an enhancement of the pulsation amplitude in O I
emission, at least at the time of our observations.Comment: 9 pages including 4 figures and no tables. Accepted for publication
in PASP; to appear in Volume 110, August 199
Family communication predicts the decisions of adolescents to engage in sexual behaviors
This study investigated whether family communication predicted adolescent decision-making about sexual behaviors, as well as gender differences in whether adolescents prefer talking with their mother or father about sex. Male and female college students (n =148) retrospectively answered questions on a survey pertaining to their family communication about sex when they were going through puberty. Results demonstrated that females reported better communication with their mothers about sex than males, and males reported better communication with their fathers about sex than females. It also was found that the better the communication with mothers, the more informed about sex the adolescents reported to be, the more likely the adolescents reported their relationship with their parents to have an effect on their decision to have sex, and the greater the likelihood of the adolescents to inform their parent if they hypothetically had been diagnosed with a sexually transmitted infection
Beyond Control-Flow: Extending Business Process Configuration to Roles and Objects
A configurable process model is an integrated representation of multiple variants of a business process. It is designed to be individualized to meet a particular set of requirements. As such, configurable process models promote systematic reuse of proven or common practices. Existing notations for configurable process modeling focus on capturing tasks and control-flow dependencies, neglecting equally important aspects of business processes such as data flow, material flow and resource management. This paper fills this gap by proposing an integrated meta-model for configurable processes with advanced features for capturing resources involved in the performance of tasks (through task-role associations) as well as flow of data and physical artifacts (through task-object associations). Although embodied as an extension of a popular process modeling notation, namely EPC, the meta-model is defined in an abstract and formal manner to make it applicable to other notations
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