323 research outputs found
A photometric and spectroscopic study of the brightest northern Cepheids. III. A high-resolution view of Cepheid atmospheres
We present new high-resolution (R=40000) spectroscopic observations of 18
bright northern Cepheids carried out at David Dunlap Observatory, in 1997. The
measurements mainly extend those of presented in Paper I adding three more
stars (AW Per, SV Vul, T Mon). The spectra were obtained in the interval of
5900 A and 6660 A. New radial velocities determined with the cross-correlation
technique and the bisector technique are presented. We found systematic
differences between the spectroscopic and CORAVEL-type measurements as large as
1-3 km/s in certain phases. We performed Baade-Wesselink analysis for CK Cam
discovered by the Hipparcos satellite. The resulting radius is 31+/-1 Ro, which
is in very good agreement with recent period-radius relation by Gieren et al.
(1999). Observational pieces of evidence of possible velocity gradient
affecting the individual line profiles are studied. The FWHM of the metallic
lines, similarly to the velocity differences, shows a very characteristic phase
dependence, illustrating the effect of global compression in the atmosphere.
The smallest line widths always occur around the maximal radius, while the
largest FWHM is associated with the velocity reversal before the minimal
radius. Three first overtone pulsators do not follow the general trend: the
largest FWHM in SU Cas and SZ Tau occurs after the smallest radius, during the
expansion, while in V1334 Cyg there are only barely visible FWHM-variations.
The possibility of a bright yellow companion of V1334 Cyg is briefly discussed.
The observed line profile asymmetries can be partly associated with the
velocity gradient, which is also supported by the differences between
individual line velocities of different excitation potentials.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Validating Continuum Lowering Models via Multi-Wavelength Measurements of Integrated X-ray Emission
X-ray emission spectroscopy is a well-established technique used to study
continuum lowering in dense plasmas. It relies on accurate atomic physics
models to robustly reproduce high-resolution emission spectra, and depends on
our ability to identify spectroscopic signatures such as emission lines or
ionization edges of individual charge states within the plasma. Here we
describe a method that forgoes these requirements, enabling the validation of
different continuum lowering models based solely on the total intensity of
plasma emission in systems driven by narrow-bandwidth x-ray pulses across a
range of wavelengths. The method is tested on published Al spectroscopy data
and applied to the new case of solid-density partially-ionized Fe plasmas,
where extracting ionization edges directly is precluded by the significant
overlap of emission from a wide range of charge states
A semi-analytical light curve model and its application to type IIP supernovae
The aim of this work is to present a semi-analytical light curve modeling
code which can be used for estimating physical properties of core collapse
supernovae (SNe) in a quick and efficient way. To verify our code we fit light
curves of Type II SNe and compare our best parameter estimates to those from
hydrodynamical calculations. For this analysis we use the quasi-bolometric
light curves of five different Type IIP supernovae. In each case we get
appropriate results for the initial pre-supernova parameters. We conclude that
this semi-analytical light curve model is useful to get approximate physical
properties of Type II SNe without using time-consuming numerical hydrodynamic
simulations.Comment: accepted for publication in Astronomy \& Astrophysics; corrected
Fig.2, 3,
Possible detection of singly-ionized oxygen in the Type Ia SN 2010kg
We present direct spectroscopic modeling of 11 high-S/N observed spectra of
the Type Ia SN 2010kg, taken between -10 and +5 days with respect to B-maximum.
The synthetic spectra, calculated with the SYN++ code, span the range between
4100 and 8500 \r{A}. Our results are in good agreement with previous findings
for other Type Ia SNe. Most of the spectral features are formed at or close to
the photosphere, but some ions, like Fe II and Mg II, also form features at
~2000 - 5000 km s above the photosphere. The well-known high-velocity
features of the Ca II IR-triplet as well as Si II 6355 are also
detected.
The single absorption feature at ~4400 \r{A}, which usually has been
identified as due to Si III, is poorly fit with Si III in SN 2010kg. We find
that the fit can be improved by assuming that this feature is due to either C
III or O II, located in the outermost part of the ejecta, ~4000 - 5000 km
s above the photosphere. Since the presence of C III is unlikely,
because of the lack of the necessary excitation/ionization conditions in the
outer ejecta, we identify this feature as due to O II. The simultaneous
presence of O I and O II is in good agreement with the optical depth
calculations and the temperature distribution in the ejecta of SN 2010kg. This
could be the first identification of singly ionized oxygen in a Type Ia SN
atmosphere.Comment: Submitted to MNRA
Zadovoljstvo z delom gospodarskih kriminalistov na policijskih upravah Ljubljana – Maribor in nekateri vzroki za fluktuacijo
An average person spends almost a third of his life at work. It is therefore very important that the person is satisfied with their job.We could define job satisfaction as a factor with an important influence on increased quality in both professional and private life. The dissatisfaction of employees with their jobs is usually followed by fluctuation. This can be very damaging to an organization since employees are one of the most important resources. This article presents the results of various surveys on the satisfaction of police officers and detectives with their work, on fluctuation as a phenomenon and some of the reasons for it. In the empirical part of this article, the authors present a study done among the economic crime detectives working in the police directorates of Ljubljana and Maribor. The study showed that economic crime detectives are somewhat satisfied with their work but are still willing to change their jobs and leave the police for a better salary. The main factor for dissatisfaction is the low pay for their performance.Povprečen človek preživi skoraj tretjino življenja na delovnem mestu. Zaradi tega je zelo pomembno, če je pri delu, ki ga opravlja zadovoljen. Tako lahko zadovoljstvo pri delu označimo, kot dejavnik, ki pomembno vpliva na večjo kakovost delovnega in zasebnega življenja. Nezadovoljstvo zaposlenih pri delu običajno spremlja fluktuacija, ki lahko povzroči organizaciji veliko škodo, saj tudi zaposleni predstavljajo za organizacijo določen kapital. V prispevku so predstavljeni rezultati nekaterih raziskav o zadovoljstvu policistov in kriminalistov pri njihovem delu ter fluktuacija kot pojav in najpogostejši vzrok zanjo. V empiričnem delu prispevka je predstavljena raziskava, opravljena med kriminalisti, ki preiskujejo gospodarsko kriminaliteto na policijskih upravah Ljubljana in Maribor. Ta je postregla z rezultati, da so gospodarski kriminalisti srednje zadovoljni z delom, ki ga opravljajo in so pripravljeni zamenjati svojo službo za boljše plačano službo izven policije. Kot enega večjih dejavnikov nezadovoljstva pri delu so opredelili prav slabo plačo, prejeto za delo, ki ga opravljajo
Extreme Supernova Models for the Superluminous Transient ASASSN-15lh
The recent discovery of the unprecedentedly superluminous transient
ASASSN-15lh (or SN 2015L) with its UV-bright secondary peak challenges all the
power-input models that have been proposed for superluminous supernovae. Here
we examine some of the few viable interpretations of ASASSN-15lh in the context
of a stellar explosion, involving combinations of one or more power inputs. We
model the lightcurve of ASASSN-15lh with a hybrid model that includes
contributions from magnetar spin-down energy and hydrogen-poor circumstellar
interaction. We also investigate models of pure circumstellar interaction with
a massive hydrogen-deficient shell and discuss the lack of interaction features
in the observed spectra. We find that, as a supernova ASASSN-15lh can be best
modeled by the energetic core-collapse of a ~40 Msun star interacting with a
hydrogen-poor shell of ~20 Msun. The circumstellar shell and progenitor mass
are consistent with a rapidly rotating pulsational pair-instability supernova
progenitor as required for strong interaction following the final supernova
explosion. Additional energy injection by a magnetar with initial period of 1-2
ms and magnetic field of 0.1-1 x 10^14 G may supply the excess luminosity
required to overcome the deficit in single-component models, but this requires
more fine-tuning and extreme parameters for the magnetar, as well as the
assumption of efficient conversion of magnetar energy into radiation. We thus
favor a single-input model where the reverse shock formed in a strong SN
ejecta-CSM interaction following a very powerful core-collapse SN explosion can
supply the luminosity needed to reproduce the late-time UV-bright plateau.Comment: 8 pages, 3 figure
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