TY  - JOUR
A1  - Mantzouki, Evanthia
A1  - Campbell, James
A1  - van Loon, Emiel
A1  - Visser, Petra
A1  - Konstantinou, Iosif
A1  - Antoniou, Maria
A1  - Giuliani, Gregory
A1  - Machado-Vieira, Danielle
A1  - de Oliveira, Alinne Gurjao
A1  - Maronic, Dubravka Spoljaric
A1  - Stevic, Filip
A1  - Pfeiffer, Tanja Zuna
A1  - Vucelic, Itana Bokan
A1  - Zutinic, Petar
A1  - Udovic, Marija Gligora
A1  - Plenkovic-Moraj, Andelka
A1  - Tsiarta, Nikoletta
A1  - Blaha, Ludek
A1  - Geris, Rodan
A1  - Frankova, Marketa
A1  - Christoffersen, Kirsten Seestern
A1  - Warming, Trine Perlt
A1  - Feldmann, Tonu
A1  - Laas, Alo
A1  - Panksep, Kristel
A1  - Tuvikene, Lea
A1  - Kangro, Kersti
A1  - Haggqvist, Kerstin
A1  - Salmi, Pauliina
A1  - Arvola, Lauri
A1  - Fastner, Jutta
A1  - Straile, Dietmar
A1  - Rothhaupt, Karl-Otto
A1  - Fonvielle, Jeremy Andre
A1  - Grossart, Hans-Peter
A1  - Avagianos, Christos
A1  - Kaloudis, Triantafyllos
A1  - Triantis, Theodoros
A1  - Zervou, Sevasti-Kiriaki
A1  - Hiskia, Anastasia
A1  - Gkelis, Spyros
A1  - Panou, Manthos
A1  - McCarthy, Valerie
A1  - Perello, Victor C.
A1  - Obertegger, Ulrike
A1  - Boscaini, Adriano
A1  - Flaim, Giovanna
A1  - Salmaso, Nico
A1  - Cerasino, Leonardo
A1  - Koreiviene, Judita
A1  - Karosiene, Jurate
A1  - Kasperoviciene, Jurate
A1  - Savadova, Ksenija
A1  - Vitonyte, Irma
A1  - Haande, Sigrid
A1  - Skjelbred, Birger
A1  - Grabowska, Magdalena
A1  - Karpowicz, Maciej
A1  - Chmura, Damian
A1  - Nawrocka, Lidia
A1  - Kobos, Justyna
A1  - Mazur-Marzec, Hanna
A1  - Alcaraz-Parraga, Pablo
A1  - Wilk-Wozniak, Elzbieta
A1  - Krzton, Wojciech
A1  - Walusiak, Edward
A1  - Gagala, Ilona
A1  - Mankiewicz-Boczek, Joana
A1  - Toporowska, Magdalena
A1  - Pawlik-Skowronska, Barbara
A1  - Niedzwiecki, Michal
A1  - Peczula, Wojciech
A1  - Napiorkowska-Krzebietke, Agnieszka
A1  - Dunalska, Julita
A1  - Sienska, Justyna
A1  - Szymanski, Daniel
A1  - Kruk, Marek
A1  - Budzynska, Agnieszka
A1  - Goldyn, Ryszard
A1  - Kozak, Anna
A1  - Rosinska, Joanna
A1  - Szelag-Wasielewska, Elzbieta
A1  - Domek, Piotr
A1  - Jakubowska-Krepska, Natalia
A1  - Kwasizur, Kinga
A1  - Messyasz, Beata
A1  - Pelechata, Aleksandra
A1  - Pelechaty, Mariusz
A1  - Kokocinski, Mikolaj
A1  - Madrecka, Beata
A1  - Kostrzewska-Szlakowska, Iwona
A1  - Frak, Magdalena
A1  - Bankowska-Sobczak, Agnieszka
A1  - Wasilewicz, Michal
A1  - Ochocka, Agnieszka
A1  - Pasztaleniec, Agnieszka
A1  - Jasser, Iwona
A1  - Antao-Geraldes, Ana M.
A1  - Leira, Manel
A1  - Hernandez, Armand
A1  - Vasconcelos, Vitor
A1  - Morais, Joao
A1  - Vale, Micaela
A1  - Raposeiro, Pedro M.
A1  - Goncalves, Vitor
A1  - Aleksovski, Boris
A1  - Krstic, Svetislav
A1  - Nemova, Hana
A1  - Drastichova, Iveta
A1  - Chomova, Lucia
A1  - Remec-Rekar, Spela
A1  - Elersek, Tina
A1  - Delgado-Martin, Jordi
A1  - Garcia, David
A1  - Luis Cereijo, Jose
A1  - Goma, Joan
A1  - Carmen Trapote, Mari
A1  - Vegas-Vilarrubia, Teresa
A1  - Obrador, Biel
A1  - Garcia-Murcia, Ana
A1  - Real, Monserrat
A1  - Romans, Elvira
A1  - Noguero-Ribes, Jordi
A1  - Parreno Duque, David
A1  - Fernandez-Moran, Elisabeth
A1  - Ubeda, Barbara
A1  - Angel Galvez, Jose
A1  - Marce, Rafael
A1  - Catalan, Nuria
A1  - Perez-Martinez, Carmen
A1  - Ramos-Rodriguez, Eloisa
A1  - Cillero-Castro, Carmen
A1  - Moreno-Ostos, Enrique
A1  - Maria Blanco, Jose
A1  - Rodriguez, Valeriano
A1  - Juan Montes-Perez, Jorge
A1  - Palomino, Roberto L.
A1  - Rodriguez-Perez, Estela
A1  - Carballeira, Rafael
A1  - Camacho, Antonio
A1  - Picazo, Antonio
A1  - Rochera, Carlos
A1  - Santamans, Anna C.
A1  - Ferriol, Carmen
A1  - Romo, Susana
A1  - Soria, Juan Miguel
A1  - Hansson, Lars-Anders
A1  - Urrutia-Cordero, Pablo
A1  - Ozen, Arda
A1  - Bravo, Andrea G.
A1  - Buck, Moritz
A1  - Colom-Montero, William
A1  - Mustonen, Kristiina
A1  - Pierson, Don
A1  - Yang, Yang
A1  - Verspagen, Jolanda M. H.
A1  - Domis, Lisette N. de Senerpont
A1  - Seelen, Laura
A1  - Teurlincx, Sven
A1  - Verstijnen, Yvon
A1  - Lurling, Miquel
A1  - Maliaka, Valentini
A1  - Faassen, Elisabeth J.
A1  - Latour, Delphine
A1  - Carey, Cayelan C.
A1  - Paerl, Hans W.
A1  - Torokne, Andrea
A1  - Karan, Tunay
A1  - Demir, Nilsun
A1  - Beklioglu, Meryem
A1  - Filiz, Nur
A1  - Levi, Eti E.
A1  - Iskin, Ugur
A1  - Bezirci, Gizem
A1  - Tavsanoglu, Ulku Nihan
A1  - Celik, Kemal
A1  - Ozhan, Koray
A1  - Karakaya, Nusret
A1  - Kocer, Mehmet Ali Turan
A1  - Yilmaz, Mete
A1  - Maraslioglu, Faruk
A1  - Fakioglu, Ozden
A1  - Soylu, Elif Neyran
A1  - Yagci, Meral Apaydin
A1  - Cinar, Sakir
A1  - Capkin, Kadir
A1  - Yagci, Abdulkadir
A1  - Cesur, Mehmet
A1  - Bilgin, Fuat
A1  - Bulut, Cafer
A1  - Uysal, Rahmi
A1  - Koker, Latife
A1  - Akcaalan, Reyhan
A1  - Albay, Meric
A1  - Alp, Mehmet Tahir
A1  - Ozkan, Korhan
A1  - Sevindik, Tugba Ongun
A1  - Tunca, Hatice
A1  - Onem, Burcin
A1  - Richardson, Jessica
A1  - Edwards, Christine
A1  - Bergkemper, Victoria
A1  - Beirne, Eilish
A1  - Cromie, Hannah
A1  - Ibelings, Bastiaan W.
T1  - Data Descriptor: A European Multi Lake Survey dataset of environmental variables, phytoplankton pigments and cyanotoxins
JF  - Scientific Data
N2  - Under ongoing climate change and increasing anthropogenic activity, which continuously challenge ecosystem resilience, an in-depth understanding of ecological processes is urgently needed. Lakes, as providers of numerous ecosystem services, face multiple stressors that threaten their functioning. Harmful cyanobacterial blooms are a persistent problem resulting from nutrient pollution and climate-change induced stressors, like poor transparency, increased water temperature and enhanced stratification. Consistency in data collection and analysis methods is necessary to achieve fully comparable datasets and for statistical validity, avoiding issues linked to disparate data sources. The European Multi Lake Survey (EMLS) in summer 2015 was an initiative among scientists from 27 countries to collect and analyse lake physical, chemical and biological variables in a fully standardized manner. This database includes in-situ lake variables along with nutrient, pigment and cyanotoxin data of 369 lakes in Europe, which were centrally analysed in dedicated laboratories. Publishing the EMLS methods and dataset might inspire similar initiatives to study across large geographic areas that will contribute to better understanding lake responses in a changing environment.
KW  - Climate-change ecology
KW  - Limnology
KW  - Water resources
Y1  - 2018
U6  - https://doi.org/10.1038/sdata.2018.226
SN  - 2052-4463
VL  - 5
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Rauch, Thomas
A1  - Quinet, P.
A1  - Hoyer, D.
A1  - Werner, K.
A1  - Richter, Philipp
A1  - Kruk, J. W.
A1  - Demleitner, M.
T1  - VII. New Kr IV - VII oscillator strengths and an improved spectral analysis of the hot, hydrogen-deficient DO-type white dwarf RE 0503-289
JF  - Plant physiology : an international journal devoted to physiology, biochemistry, cellular and molecular biology, biophysics and environmental biology of plants
N2  - Context. For the spectral analysis of high-resolution and high signal-to-noise (S/N) spectra of hot stars, state-of-the-art non-local thermodynamic equilibrium (NLTE) model atmospheres are mandatory. These are strongly dependent on the reliability of the atomic data that is used for their calculation. Aims. New Kr IV-VII oscillator strengths for a large number of lines enable us to construct more detailed model atoms for our NLTE model-atmosphere calculations. This enables us to search for additional Kr lines in observed spectra and to improve Kr abundance determinations. Methods. We calculated Kr IV-VII oscillator strengths to consider radiative and collisional bound-bound transitions in detail in our NLTE stellar-atmosphere models for the analysis of Kr lines that are exhibited in high-resolution and high S/N ultraviolet (UV) observations of the hot white dwarf RE 0503-289. Results. We reanalyzed the effective temperature and surface gravity and determined T-eff = 70 000 +/- 2000 K and log (g/cm s(-2)) = 7.5 +/- 0.1. We newly identified ten Kr V lines and one Kr vi line in the spectrum of RE 0503-289. We measured a Kr abundance of 3.3 +/- 0.3 (logarithmic mass fraction). We discovered that the interstellar absorption toward RE 0503-289 has a multi-velocity structure within a radial-velocity interval of -40 km s(-1) < upsilon(rad) < +18 km s(-1). Conclusions. Reliable measurements and calculations of atomic data are a prerequisite for state-of-the-art NLTE stellar-atmosphere modeling. Observed Kr V-VII line profiles in the UV spectrum of the white dwarf RE 0503-289 were simultaneously well reproduced with our newly calculated oscillator strengths.
KW  - atomic data
KW  - line: identification
KW  - stars: abundances
KW  - stars: individual: RE 0503-289
KW  - virtual observatory tools
KW  - stars: individual: RE 0457-281
Y1  - 2016
U6  - https://doi.org/10.1051/0004-6361/201628131
SN  - 1432-0746
VL  - 590
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Reindl, Nicole
A1  - Rauch, Thomas
A1  - Parthasarathy, M.
A1  - Werner, K.
A1  - Kruk, J. W.
A1  - Hamann, Wolf-Rainer
A1  - Sander, Andreas Alexander Christoph
A1  - Todt, Helge Tobias
T1  - The rapid evolution of the exciting star of the Stingray nebula
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. SAO 244567, the exciting star of the Stingray nebula, is rapidly evolving. Previous analyses suggested that it has heated up from an effective temperature of about 21 kK in 1971 to over 50 kK in the 1990s. Canonical post-asymptotic giant branch evolution suggests a relatively high mass while previous analyses indicate a low-mass star.
 Aims. A comprehensive model-atmosphere analysis of UV and optical spectra taken during 1988-2006 should reveal the detailed temporal evolution of its atmospheric parameters and provide explanations for the unusually fast evolution.
 Methods. Fitting line profiles from static and expanding non-LTE model atmospheres to the observed spectra allowed us to study the temporal change of effective temperature, surface gravity, mass-loss rate, and terminal wind velocity. In addition, we determined the chemical composition of the atmosphere.
 Results. We find that the central star has steadily increased its effective temperature from 38 kK in 1988 to a peak value of 60 kK in 2002. During the same time, the star was contracting, as concluded from an increase in surface gravity from log g = 4.8 to 6.0 and a drop in luminosity. Simultaneously, the mass-loss rate declined from log(M/M-circle dot yr(-1)) = -9.0 to -11.6 and the terminal wind velocity increased from v(infinity) = 1800 km s(-1) to 2800 km s(-1). Since around 2002, the star stopped heating and has cooled down again to 55 kK by 2006. It has a largely solar surface composition with the exception of slightly subsolar carbon, phosphorus, and sulfur. The results are discussed by considering different evolutionary scenarios.
 Conclusions. The position of SAO 244567 in the log T-eff-log g plane places the star in the region of sdO stars. By comparison with stellar-evolution calculations, we confirm that SAO 244567 must be a low-mass star (M < 0.55 M-circle dot). However, the slow evolution of the respective stellar evolutionary models is in strong contrast to the observed fast evolution and the young planetary nebula with a kinematical age of only about 1000 years. We speculate that the star could be a late He-shell flash object. Alternatively, it could be the outcome of close-binary evolution. Then SAD 244567 would be a low-mass (0.354 M-circle dot) helium pre-white dwarf after the common-envelope phase, during which the planetary nebula was ejected.
KW  - stars: abundances
KW  - stars: evolution
KW  - stars: AGB and post-AGB
KW  - stars: individual: SAO 244567
KW  - stars: fundamental parameters
KW  - planetary nebulae: individual: Stingray nebula (Henize 3-1357)
Y1  - 2014
U6  - https://doi.org/10.1051/0004-6361/201323189
SN  - 0004-6361
SN  - 1432-0746
VL  - 565
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Reindl, Nicole
A1  - Rauch, Thomas
A1  - Werner, Klaus
A1  - Kruk, J. W.
A1  - Todt, Helge Tobias
T1  - On helium-dominated stellar evolution: the mysterious role of the O(He)-type stars
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. About a quarter of all post-asymptotic giant branch (AGB) stars are hydrogen-deficient. Stellar evolutionary models explain the carbon-dominated H-deficient stars by a (very) late thermal pulse scenario where the hydrogen-rich envelope is mixed with the helium-rich intershell layer. Depending on the particular time at which the final flash occurs, the entire hydrogen envelope may be burned. In contrast, helium-dominated post-AGB stars and their evolution are not yet understood.
 Aims. A small group of very hot, helium-dominated stars is formed by O(He)-type stars. A precise analysis of their photospheric abundances will establish constraints to their evolution.
 Methods. We performed a detailed spectral analysis of ultraviolet and optical spectra of four O(He) stars by means of state-of-the-art non-LTE model-atmosphere techniques.
 Results. We determined effective temperatures, surface gravities, and the abundances of H, He, C, N, O, F, Ne, Si, P, S, Ar, and Fe. By deriving upper limits for the mass-loss rates of the O(He) stars, we found that they do not exhibit enhanced mass-loss. The comparison with evolutionary models shows that the status of the O(He) stars remains uncertain. Their abundances match predictions of a double helium white dwarf (WD) merger scenario, suggesting that they might be the progeny of the compact and of the luminous helium-rich sdO-type stars. The existence of planetary nebulae that do not show helium enrichment around every other O(He) star precludes a merger origin for these stars. These stars must have formed in a different way, for instance via enhanced mass-loss during their post-AGB evolution or a merger within a common-envelope (CE) of a CO-WD and a red giant or AGB star.
 Conclusions. A helium-dominated stellar evolutionary sequence exists that may be fed by different types of mergers or CE scenarios. It appears likely that all these pass through the O(He) phase just before they become WDs.
KW  - stars: AGB and post-AGB
KW  - stars: evolution
KW  - stars: fundamental parameters
KW  - stars: abundances
Y1  - 2014
U6  - https://doi.org/10.1051/0004-6361/201423498
SN  - 0004-6361
SN  - 1432-0746
VL  - 566
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Löbling, Lisa
A1  - Rauch, Thomas
A1  - Bertolami Miller, Marcelo Miguel
A1  - Todt, Helge Tobias
A1  - Friederich, F.
A1  - Ziegler, M.
A1  - Werner, Klaus
A1  - Kruk, J. W.
T1  - Spectral analysis of the hybrid PG 1159-type central stars of the planetary nebulae Abell 43 and NGC7094
JF  - Monthly notices of the Royal Astronomical Society
N2  - Stellar post asymptotic giant branch (post-AGB) evolution can be completely altered by a final thermal pulse (FTP) which may occur when the star is still leaving the AGB (AFTP), at the departure from the AGB at still constant luminosity (late TP, LTP) or after the entry to the white-dwarf cooling sequence (very late TP, VLTP). Then convection mixes the Herich material with the H-rich envelope. According to stellar evolution models the result is a star with a surface composition of H approximate to 20 per cent by mass (AFTP), approximate to 1 per cent (LTP), or (almost) no H (VLTP). Since FTP stars exhibit intershell material at their surface, spectral analyses establish constraints for AGB nucleosynthesis and stellar evolution. We performed a spectral analysis of the so-called hybrid PG 1159-type central stars (CS) of the planetary nebulae Abell 43 and NGC7094 by means of non-local thermodynamical equilibrium models. We confirm the previously determined effective temperatures of T-eff = 115 000 +/- 5 000K and determine surface gravities of log (g /(cm s(-2))) = 5.6 +/- 0.1 for both. From a comparison with AFTP evolutionary tracks, we derive stellar masses of 0.57(-0.04)(+0.07)M(circle dot) and determine the abundances of H, He, and metals up to Xe. Both CS are likely AFTP stars with a surface H mass fraction of 0.25 +/- 0.03 and 0.15 +/- 0.03, respectively, and an Fe deficiency indicating subsolar initial metallicities. The light metals show typical PG 1159-type abundances and the elemental composition is in good agreement with predictions from AFTP evolutionary models. However, the expansion ages do not agree with evolution time-scales expected from the AFTP scenario and alternatives should be explored.
KW  - stars: abundances
KW  - stars: AGB and post-AGB
KW  - stars: atmospheres
KW  - stars: evolution
KW  - stars: individual: WD1751+106
KW  - stars: individual: WD2134+125
Y1  - 2019
U6  - https://doi.org/10.1093/mnras/stz1994
SN  - 0035-8711
SN  - 1365-2966
VL  - 489
IS  - 1
SP  - 1054
EP  - 1071
PB  - Oxford Univ. Press
CY  - Oxford
ER  -