3,958 research outputs found
Search for binary central stars of the SMC PNe
The Optical Gravitational Lensing Experiment (OGLE), originally designed to
search for microlensing events, provides a rich and uniform data set suitable
for studying the variability of certain types of objects. We used the OGLE data
to study the photometry of central stars of planetary nebulae (PNe) in the
Small Magellanic Cloud (SMC). In particular, we searched for close binary
central stars with the aim to constrain the binary fraction and period
distribution in the SMC. We also searched for PNe mimics and removed them from
the PNe sample. We identified 52 counterparts of PNe in the SMC in the I-band
images from the OGLE-II and OGLE-III surveys. We analysed the time-series
photometry of the PNe. Spectra of the photometric variables were obtained to
constrain the nature of the objects or search for additional evidence for
binarity. Eight variables were found. Of these, seven objects are PNe mimics,
including one symbiotic star candidate. One close binary central star of PN
with a period of 1.15 or 2.31 day was discovered. The obtained binary fraction
for the SMC PNe and the observational biases are discussed in terms of the OGLE
observations.Comment: Accepted for publication in A&A. 7 pages and 7 figures, table 4 is
only available at the CD
CKVul: evolving nebula and three curious background stars
We analyse the remnants of CK Vul (Nova Vul 1670) using optical imaging and
spectroscopy. The imaging, obtained between 1991 and 2010, spans 5.6% of the
life-time of the nebula. The flux of the nebula decreased during the last 2
decades. The central source still maintains the ionization of the innermost
part of the nebula, but recombination proceeds in more distant parts of the
nebula. Surprisingly, we discovered two stars located within 10 arcsec of the
expansion centre of the radio emission that are characterized by pronounced
long term variations and one star with high proper motion. The high proper
motion star is a foreground object, and the two variable stars are background
objects. The photometric variations of two variables are induced by a dusty
cloud ejected by CK Vul and passing through the line of sight to those stars.
The cloud leaves strong lithium absorption in the spectra of the stars. We
discuss the nature of the object in terms of recent observations.Comment: Published in MNRAS, available at
http://mnras.oxfordjournals.org/cgi/content/abstract/stt426
Accelerated post-AGB evolution, initial-final mass relations, and the star-formation history of the Galactic bulge
We study the star-formation history of the Galactic bulge, as derived from
the age distribution of the central stars of planetary nebulae that belong to
this stellar population. The high resolution imaging and spectroscopic
observations of 31 compact planetary nebulae are used to derive their central
star masses. The Bloecker tracks with the cluster IFMR result in ages, which
are unexpectedly young. We find that the Bloecker post-AGB tracks need to be
accelerated by a factor of three to fit the local white dwarf masses. This
acceleration extends the age distribution. We adjust the IFMR as a free
parameter to map the central star ages on the full age range of bulge stellar
populations. This fit requires a steeper IFMR than the cluster relation. We
find a star-formation rate in the Galactic bulge, which is approximately
constant between 3 and 10 Gyr ago. The result indicates that planetary nebulae
are mainly associated with the younger and more metal-rich bulge populations.
The constant rate of star-formation between 3 and 10 Gyr agrees with
suggestions that the metal-rich component of the bulge is formed during an
extended process, such as a bar interaction.Comment: accepted for publication in A&
Cognitive Status and Initiation of Lifestyle Changes Following Acute Coronary Heart Syndrome: A Dissertation
Background: Cognitive impairment is prevalent in survivors of acute coronary syndrome (ACS) and increases risk for poor outcomes. Lifestyle changes are recommended to patients after ACS to reduce their risk for recurrent events, but cognitively impaired patients may encounter difficulties initiating these changes. This dissertation had three aims: (1) to examine cognitive status as a predictor of lifestyle changes after ACS, (2) to examine whether caregiver support moderates the association of cognitive status and initiation of lifestyle changes, and (3) to assess the reliability of self-reported lifestyle changes in cognitively impaired patients through comparison of their reports of lifestyle change with those from their caregivers.
Methods: For aims 1 and 2, Poisson regression with robust error variance was used to examine the association of cognitive status and caregiver support with patient-reported initiation of five lifestyle changes (improving diet, increasing exercise, quitting smoking, reducing stress, and attending cardiac rehabilitation) in 881 patients from TRACE-CORE, a prospective longitudinal observational study of outcomes in ACS. For aim 3, pilot data from 78 patient-caregiver dyads from TRACE-CARE, an ancillary substudy, were used to examine whether patient-caregiver congruence on reports of lifestyle changes varied according to patients’ cognitive function.
Results: Patient-reported rates of lifestyle change did not vary according to cognitive status, except for participation in cardiac rehabilitation. Caregiver support improved patient-reported rates of lifestyle change among cognitively intact patients but not cognitively impaired patients. Patients’ cognitive function was positively associated with patient-caregiver congruence on reports of initiation of lifestyle changes and patients with decreased cognitive function tended to over-report initiation of lifestyle changes compared to reports by their caregivers.
Conclusion: Although cognitive status was not associated with initiation of most lifestyle changes and the influence of caregiver support on initiation of lifestyle changes was only beneficial to cognitively intact patients in this cohort of ACS patients, these null findings may be explained by the questionable validity of self-report in cognitively impaired patients. This dissertation yields new knowledge about secondary prevention in ACS patients and provides insight into the challenges of conducting patient-reported outcomes research in cognitively compromised populations
Status of the isophot detector development
ISOPHOT is one of the four focal plane experiments of the European Space Agency's Infrared Space Observatory (ISO). Scheduled for a 1993 launch, it will operate extrinsic silicon and germanium photoconductors at low temperature and low background during the longer than 18 month mission. These detectors cover the wavelength range from 2.5 to 200 microns and are used as single elements and in arrays. A cryogenic preamplifier was developed to read out a total number of 223 detector pixels
The evolving spectrum of the planetary nebula Hen 2-260
We analysed the planetary nebula Hen 2-260 using optical spectroscopy and
photometry. We compared our observations with the data from literature to
search for evolutionary changes. The nebular line fluxes were modelled with the
Cloudy photoionization code to derive the stellar and nebular parameters. The
planetary nebula shows a complex structure and possibly a bipolar outflow. The
nebula is relatively dense and young. The central star is just starting ionization (). Comparison of our
observations with literature data indicates a 50% increase of the [OIII] 5007
\AA\ line flux between 2001 and 2012. We interpret it as the result of the
progression of the ionization of . The central star evolves to
higher temperatures at a rate of . The heating rate
is consistent with a final mass of
or for two different sets of
post-AGB evolutionary tracks from literature. The photometric monitoring of Hen
2-260 revealed variations on a timescale of hours or days. The variability may
be caused by pulsations of the star. The temperature evolution of the central
star can be traced using spectroscopic observations of the surrounding
planetary nebula spanning a timescale of roughly a decade. This allows us to
precisely determine the stellar mass, since the pace of the temperature
evolution depends critically on the core mass. The kinematical age of the
nebula is consistent with the age obtained from the evolutionary track. The
final mass of the central star is close to the mass distribution peak for
central stars of planetary nebulae found in other studies. The object belongs
to a group of young central stars of planetary nebulae showing photometric
variability.Comment: accepted for publication in A&
Political stability and innovation in Africa
This paper examines the role of institutional factors, primarily, political stability, in shaping the dynamics of innovation activity in today’s modern society. Using panel data consisting of 26 African countries from the period between 1996 and 2016 as well as employing the negative binomial estimate, we model the impact of those factors on the number of applications for patents per resident. GDP per capita, education and also other institutional factors including the rule of law and financial freedom. The results reveal a strong positive effect of the rule of law on patenting activity. © Foundation of International Studies, 2020 © CSR, 2020.Deutscher Akademischer Austauschdienst, DAADMinistry of Education and Science of the Russian Federation, MinobrnaukaMinisterstwo Nauki i Szkolnictwa Wyższego, MNiSWThe authors are thankful to the Russian Ministry of Education and Science, DAAD, The Ministry of Science and Higher Education in Poland for financial support to carry out this research. Thanks (IOS, Regensburg) for hosting James Okrah for the period of his research internship with them, with special thanks to Dr Alexander Nepp (Supervisor), Dr. Olga Popova (IOS, Regensburg), Prof. Richard Frensch (IOS, Regensburg) and Dr Stefan Huber for their support
Nuclear ashes and outflow in the eruptive star Nova Vul 1670
CK Vulpeculae was observed in outburst in 1670-16721, but no counterpart was
seen until 1982, when a bipolar nebula was found at its location. Historically,
CK Vul has been considered to be a nova (Nova Vul 1670), but a similarity to
'red transients', which are more luminous than classical nova and thought to be
the result of stellar collisions, has re-opened the question of CK Vul's
status. Red transients cool to resemble late M-type stars, surrounded by
circumstellar material rich in molecules and dust. No stellar source has been
seen in CK Vul, though a radio continuum source was identified at the expansion
centre of the nebula. Here we report CK Vul is surrounded by chemically rich
molecular gas with peculiar isotopic ratios, as well as dust. The chemical
composition cannot be reconciled with a nova or indeed any other known
explosion. In addition, the mass of the surrounding gas is too high for a nova,
though the conversion from observations of CO to a total mass is uncertain. We
conclude that CK Vul is best explained as the remnant of a merger of two stars.Comment: an older version of an article that appeared in Nature; published in
Nature, online version, 23 March 201
Disk evaporation in a planetary nebula
We study the Galactic bulge planetary nebula M 2-29 (for which a 3-year
eclipse event of the central star has been attributed to a dust disk) using HST
imaging and VLT spectroscopy, both long-slit and integral field. The central
cavity of M 2-29 is filled with a decreasing, slow wind. An inner high density
core is detected, with radius less than 250 AU, interpreted as a rotating
gas/dust disk with a bipolar disk wind. The evaporating disk is argued to be
the source of the slow wind. The central star is a source of a very fast wind
(1000 km/s). An outer, partial ring is seen in the equatorial plane, expanding
at 12 km/s. The azimuthal asymmetry is attributed to mass-loss modulation by an
eccentric binary. M 2-29 presents a crucial point in disk evolution, where
ionization causes the gas to be lost, leaving a low-mass dust disk behind.Comment: 11 pages, accepted for publication in "Astronomy and Astrophysics
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