177 research outputs found
PACS and SPIRE range spectroscopy of cool, evolved stars
Context: At the end of their lives AGB stars are prolific producers of dust
and gas. The details of this mass-loss process are still not understood very
well. Herschel PACS and SPIRE spectra offer a unique way of investigating
properties of AGB stars in general and the mass-loss process in particular.
Methods: The HIPE software with the latest calibration is used to process the
available PACS and SPIRE spectra of 40 evolved stars. The spectra are convolved
with the response curves of the PACS and SPIRE bolometers and compared to the
fluxes measured in imaging data of these sources. Custom software is used to
identify lines in the spectra, and to determine the central wavelengths and
line intensities. Standard molecular line databases are used to associate the
observed lines. Because of the limited spectral resolution of the spectrometers
several known lines are typically potential counterparts to any observed line.
To help identifications the relative contributions in line intensity of the
potential counterpart lines are listed for three characteristic temperatures
based on LTE calculations and assuming optically thin emission. Result: The
following data products are released: the reduced spectra, the lines that are
measured in the spectra with wavelength, intensity, potential identifications,
and the continuum spectra, i.e. the full spectra with all identified lines
removed. As simple examples of how this data can be used in future studies we
have fitted the continuum spectra with three power laws and find that the few
OH/IR stars seem to have significantly steeper slopes than the other oxygen-
and carbon-rich objects in the sample. As another example we constructed
rotational diagrams for CO and fitted a two-component model to derive
rotational temperatures.Comment: A&A accepte
An ALMA view of CS and SiS around oxygen-rich AGB stars
We aim to determine the distributions of molecular SiS and CS in the
circumstellar envelopes of oxygen-rich asymptotic giant branch stars and how
these distributions differ between stars that lose mass at different rates. In
this study we analyse ALMA observations of SiS and CS emission lines for three
oxygen-rich galactic AGB stars: IK Tau, with a moderately high mass-loss rate
of M yr, and W Hya and R Dor with low mass loss
rates of M yr. These molecules are usually
more abundant in carbon stars but the high sensitivity of ALMA allows us to
detect their faint emission in the low mass-loss rate AGB stars. The high
spatial resolution of ALMA also allows us to precisely determine the spatial
distribution of these molecules in the circumstellar envelopes. We run
radiative transfer models to calculate the molecular abundances and abundance
distributions for each star. We find a spread of peak SiS abundances with
for R Dor, for W Hya, and for
IK Tau relative to H. We find lower peak CS abundances of
for R Dor, for W Hya and
for IK Tau, with some stratifications in the abundance
distributions. For IK Tau we also calculate abundances for the detected
isotopologues: CS, SiS, SiS, SiS, SiS,
SiS, and SiS. Overall the isotopic ratios we derive
for IK Tau suggest a lower metallicity than solar.Comment: 16 page
The unusual 3D distribution of NaCl around the AGB star IK Tau
NaCl is a diatomic molecule with a large dipole moment, which allows for its
detection even at relatively small abundances. It has been detected towards
several evolved stars, among which is the AGB star IK Tau, around which it is
distributed in several clumps that lie off-center from the star. We aim to
study the three-dimensional distribution of NaCl around the AGB star IK Tau,
and to obtain the abundance of NaCl relative to H for each of the clumps.
First, a new value for the maximum expansion velocity is determined. The
observed ALMA channel maps are then deprojected to create a three-dimensional
model of the distribution of NaCl. This model is then used as input for the
radiative transfer modelling code magritte, which is used to obtain the NaCl
abundances of each of the clumps by comparing the observations with the results
of the magritte simulations. Additionally, the rotational temperature of the
clumps is determined using population diagrams. We derive an updated value for
the maximum expansion velocity of IK Tau = 28.4 km/s. A
spiral-like shape can be discerned in our three-dimensional distribution model
of the NaCl. This spiral lies more or less in the plane of the sky. The
distribution is also flatter in the line-of-sight direction than in the plane
of the sky. We find clump abundances between and relative to H, where the relative abundance is typically lower for
clumps closer to the star. For the first time, we used deprojection to
understand the three-dimensional environment of an AGB star and calculated the
fractional abundance of NaCl in clumps surrounding the star.Comment: Accepted for publication in A&
New observations and models of circumstellar CO line emission of AGB stars in the Herschel SUCCESS programme
CONTEXT: Asymptotic giant branch (AGB) stars are in one of the latest
evolutionary stages of low to intermediate-mass stars. Their vigorous mass loss
has a significant effect on the stellar evolution, and is a significant source
of heavy elements and dust grains for the interstellar medium. The mass-loss
rate can be well traced by carbon monoxide (CO) line emission.
AIMS: We present new Herschel HIFI and IRAM 30m telescope CO line data for a
sample of 53 galactic AGB stars. The lines cover a fairly large range of
excitation energy from the line to the line, and even the
line in a few cases. We perform radiative transfer modelling for 38
of these sources to estimate their mass-loss rates.
METHODS: We used a radiative transfer code based on the Monte Carlo method to
model the CO line emission. We assume spherically symmetric circumstellar
envelopes that are formed by a constant mass-loss rate through a smoothly
accelerating wind.
RESULTS: We find models that are consistent across a broad range of CO lines
for most of the stars in our sample, i.e., a large number of the circumstellar
envelopes can be described with a constant mass-loss rate. We also find that an
accelerating wind is required to fit, in particular, the higher-J lines and
that a velocity law will have a significant effect on the model line
intensities. The results cover a wide range of mass-loss rates (
to ) and gas expansion
velocities (2 to km s), and include M-, S-, and C-type AGB stars.
Our results generally agree with those of earlier studies, although we tend to
find slightly lower mass-loss rates by about 40%, on average. We also present
"bonus" lines detected during our CO observations.Comment: 36 page
An ALMA view of SO and SO around oxygen-rich AGB stars
We present and analyse SO and SO, recently observed with high angular
resolution and sensitivity in a spectral line survey with ALMA, for two
oxygen-rich AGB stars: the low mass-loss rate R Dor and high mass-loss rate IK
Tau. We analyse 8 lines of SO detected towards both stars, 78 lines of
SOdetected towards R Dor and 52 lines of SO detected towards IK Tau. We
detect several lines of SO, SO and SO towards both
stars, and tentatively SO towards R Dor, and hence derive isotopic
ratios for these species. The spatially resolved observations show us that the
two sulphur oxides are co-located towards R Dor and trace out the same wind
structures in the circumstellar envelope (CSE). Much of the emission is well
reproduced with a Gaussian abundance distribution spatially centred on the
star. Emission from the higher energy levels of SO and SO towards R Dor
provide evidence in support of a rotating inner region of gas identified in
earlier work. The new observations allow us to refine the abundance
distribution of SO in IK Tau derived from prior observations with single
antennas, and confirm the distribution is shell-like with the peak in the
fractional abundance not centred on the star. The confirmation of different
types of SO abundance distributions will help fine-tune chemical models and
allows for an additional method to discriminate between low and high mass-loss
rates for oxygen-rich AGB stars.Comment: Accepted for publication in MNRA
Rotational spectra of vibrationally excited AlO and TiO in oxygen rich stars
Rotational transitions in vibrationally excited AlO and TiO -- two possible
precursors of dust -- were observed in the 300 GHz range (1 mm wavelength)
towards the oxygen rich AGB stars R Dor and IK Tau with ALMA, and vibrationally
excited AlO was observed towards the red supergiant VY CMa with the SMA. The
transition of TiO in the levels, and the transition in the level of AlO were identified towards R Dor;
the line of TiO was identified in the level towards IK Tau;
and two transitions in the levels of AlO were identified
towards VY CMa. The newly-derived high vibrational temperature of TiO and AlO
in R Dor of K, and prior measurements of the angular extent
confirm that the majority of the emission is from a region within
of the central star. A full radiative transfer analysis of
AlO in R Dor yielded a fractional abundance of 3% of the solar abundance
of Al. From a similar analysis of TiO a fractional abundance of % of
the solar abundance of Ti was found. The observations provide indirect evidence
that TiO is present in a rotating disk close to the star. Further observations
in the ground and excited vibrational levels are needed to determine whether
AlO, TiO, and TiO are seeds of the AlO dust in R Dor, and perhaps
in the gravitationally bound dust shells in other AGB stars with low mass loss
rates.Comment: Accepted for publication in Ap
Отдаленные исходы реваскуляризации миокарда и мозга при помощи чрескожных коронарных вмешательств и каротидной эндартерэктомии в гибридном и поэтапном режимах
Aim To evaluate in-hospital and long-term outcomes of myocardial and cerebral revascularization with combined or staged PCI and carotid endarterectomy.Methods.263 myocardial and cerebral revascularizations with PCI and CEA in patients with combined cerebral and coronary artery lesions in the period from 2011 to 2017 were performed. Patients were divided into two groups depending on the surgical strategy. Patient (n = 133) who underwent a staged intervention (CEA and PCI) were included in Group 1, whereas patients (n = 130) who underwent a hybrid intervention (CEE+PCI CA) were included in Group 2. The mean follow-up was 3.5 years.Results.100% of patients in Group 2 underwent coronary and internal carotid revascularization according to the results of in-hospital and long-term follow-up. 81.35% of patient in Group 1 underwent PCI and CEA, whereas 3.01% of patients underwent only PCI and 6.77% of patients – CEA. 1.5% of patients in Group 1 did not receive any surgical treatment. The most common causes of incomplete revascularization were the subsequent change of the initially defined treatment for myocardial (6.02%) or cerebral revascularization (0.75%). The rest refused the second stage, or it was associated with extremely high risk and the strategy was switched to the conservative therapy.Conclusion.100% of patients received hybrid myocardial and cerebral revascularization during one hospitalization. It allowed reducing mortality from MI and stroke during the waiting period for the next stage of the treatment in Group 1 (almost 5%). Hybrid interventions can be used in patients with high risk for open-heart surgery, severe comorbidities (obesity, diabetes, renal dysfunction), significant coronary and cerebral artery lesions with high risk of MI and stroke. However, hybrid approach was associated with high rate (almost 7%) of non-fatal MI in the long-term follow-up.Цель.Оценка госпитальных и отдаленных исходов реваскуляризации головного мозга и миокарда при помощи чрескожного коронарного вмешательства (ЧКВ) и каротидной эндартерэктомии (КЭЭ) в поэтапном и гибридном режимах.Материалы и методы.С 2011 по 2017 г. выполнено 263 реваскуляризации миокарда и головного мозга с использованием ЧКВ и КЭЭ у пациентов с мультифокальным атеросклерозом с сочетанным поражением церебральных и коронарных артерий. В зависимости от выбранных стратегий лечения пациенты были разделены на две группы: 1-я группа (n = 133) – поэтапные вмешательства (КЭЭ и ЧКВ); 2-я группа (n = 130) – гибридные вмешательства (КЭЭ + ЧКВ). Средний период наблюдения составил 3,5 года.Результаты.В группе гибридных операций реваскуляризация двух сосудистых бассейнов (коронарных и внутренних сонных артерий) выполнена в 100% случаев. В группе поэтапной тактики полный объем запланированной реваскуляризации получили лишь 81,35% пациентов, тогда как в 3,01% случаев выполнено только ЧКВ, в 6,77% случаев – только КЭЭ, а в 1,5% – не выполнен ни один этап реваскуляризации. Самыми распространенными причинами неполной реваскуляризации явились изменение тактики реваскуляризации миокарда (6,02%) или головного мозга (0,75%), в оставшихся случаях пациенты не являлись на второй этап лечения по субъективным причинам или его выполнение было сопряжено с крайне высоким риском, в связи с чем тактика была пересмотрена в пользу консервативной терапии.Заключение.Гибридные вмешательства продемонстрировали 100% доступность реваскуляризации миокарда и головного мозга в течение одной госпитализации, что значительно сокращало летальность пациентов от инфаркта миокарда и острого нарушения мозгового кровообращения в период ожидания следующего этапа лечения при поэтапной стратегии (почти на 5%). Гибридные вмешательства могут применяться у пациентов с высоким риском «открытых» операций на сердце, тяжелой сопутствующей патологией (ожирением, сахарным диабетом, нарушением функции почек), значимым поражением коронарных и церебральный артерий с высоким риском инфаркта миокарда и острого нарушения мозгового кровообращения. Недостатком гибридной стратегии явилась более высокая частота (почти на 7%) нефатального инфаркта миокарда в отдаленном периоде наблюдения
Compulsory reduced working time in Belarus: Incidence, operation and consequences
This article examines compulsory reduced working time (CRWT) in five Belarusian factories, to assess its impact on employment relationships and evaluate arguments about ‘Soviet legacies’ and labour ‘patience’. Local use of CRWT increased between 2001 and 2012, and took a form more inimical to worker interests, thereby differing from official macro statistics. Managers expressed discontent at being pushed by state policy to use CRWT, but used it as a disciplinary tool. Workers perceived worsening work relationships and threats of collective response were in evidence. Arguments about ‘Soviet legacies’ and labour’s ‘patience’ therefore currently appear inappropriate
Armenia and Belarus: caught between the EU's and Russia's conditionalities?
This article looks into Armenia's and Belarus’ engagement with the European Union's (EU) and Russia's conditionalities, the two EU Eastern Partnership (EaP) countries that are also members of the Russia-led Eurasian Economic Union (EAEU). While paying attention to political, economic (including energy and technical) as well as security dimensions of the EU's and Russia's approaches, as proposed in the present special section, the article demonstrates that the conditionalities extended by the EU and Russia to the two countries in question have differed. In their turn, Armenia and Belarus have reacted differently to Russia's and the EU's conditionalities. Against the backdrop of the changing significance ascribed to both the EU's and Russia's policies towards their common neighbourhood since the 1990s, the present contribution identifies and analyses factors that account for the diverging positions of Armenia and Belarus, including the type of regime, the geopolitical considerations, the stakes in the economic and energy spheres and the predisposition to integration. The article shows that in the resulting complex context, Armenia and Belarus have been able to influence the shape and content of the EU's and Russia's conditionalities, although in a different way and to a different extent.Ministry of Education and Science (UID/CPO/ 00758/2013
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