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

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

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 $\rm O^+$ ionization ($\rm T_{eff} \approx 30,000 \, K$). 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 $\rm O^{+}$. The central star evolves to higher temperatures at a rate of $\rm 45 \pm 7\,K\, yr^{-1}$. The heating rate is consistent with a final mass of $\rm 0.626 ^{+0.003}_{-0.005} \, M_{\odot}$ or $\rm 0.645 ^{+0.008}_{-0.008} \, M_{\odot}$ 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&

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

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

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