55 research outputs found
Spectroscopic Analysis of Hot (Pre-) White Dwarfs
In this work, different kinds of hot (pre-) white dwarfs were analyzed by means
of static and expanding non-LTE model atmospheres to obtain a better understanding
of the late, hot stages of stellar evolution
Discovery of two bright DO-type white dwarfs
We discovered two bright DO-type white dwarfs, GALEXJ053628.3+544854
(J0536+5448) and GALEX231128.0+292935(J2311+2929), which rank among the eight
brightest DO-type white dwarfs known. Our non-LTE model atmosphere analysis
reveals effective temperatures and surface gravities of
and
for J0536+5448 and and for J2311+2929. The latter shows a significant amount
of carbon in its atmosphere (, by mass), while for
J0536+5448 we could derive only an upper limit of . Furthermore, we
calculated spectroscopic distances for the two stars and found a good agreement
with the distances derived from the Gaia parallaxes.Comment: 7 pages, 4 figures, accepted for publication in MNRA
Post-red-giant-branch Planetary Nebulae
Common envelope events have been associated with the formation of a planetary
nebulae since its proposition more than forty five years ago. However, until
recently there have been doubts as to whether a common envelope while the donor
is ascending the red giant branch, rather than the subsequent asymptotic red
giant branch, would result in a planetary nebula. There is now strong
theoretical and observational evidence to suggest that some planetary nebulae
are, indeed, the products of common envelope phases which occurred while the
nebular progenitor was on the red giant branch. The characterisation of these
systems is challenging but has the potential to reveal much about the common
envelope -- a critical evolutionary phase in the formation of a plethora of
interesting astrophysical phenomena.Comment: 6 pages, to appear in Highlights of Spanish Astrophysics XI,
Proceedings of the XV Scientific Meeting of the Spanish Astronomical Society
held on September 4 0 9, 2022, in La Laguna, Spain. M. Manteiga, L. Bellot,
P. Benavidez, A. de Lorenzo-Caceres, M. A. Fuente, M. J. Martinez, M.
Vazquez- Acosta, C. Dafonte (eds.), 202
The rapid evolution of the central star of the Stingray Nebula - latest news from the HST
SAO 244567 is an unusually fast evolving star. Within twenty years only, it had turned from a B-type supergiant into the central star of the Stingray Nebula. Space- and ground-based observations obtained over the last decades have revealed that its spectrum changes noticeably over just a few years, showing stellar evolution in real time. The low mass of SAO 244567 is, however, in strong contradiction with canonical post-asymptotic giant branch evolution. Thus, its fast evolution has been a mystery for decades. We present preliminary results of the non-LTE spectral analyis of the recently obtained HST/COS observations, which finally allow us to shed light on the evolutionary history of this extraordinary object.Facultad de Ciencias AstronĂłmicas y GeofĂsicasInstituto de AstrofĂsica de La Plat
The photospheres of the hottest fastest stars in the Galaxy
We perform nonlocal thermodynamic equilibrium (NLTE) model atmosphere
analyses of the three hottest hypervelocity stars (space velocities between
1500-2800 km s) known to date, which were recently discovered
spectroscopically and identified as runaways from Type Ia supernovae. The
hottest of the three (J05460836, effective temperature =
95,000 15,000 K, surface gravity log g = ) has an
oxygen-dominated atmosphere with a significant amount of carbon (C = , O = , mass fractions). Its mixed absorption+emission line
spectrum exhibits photospheric absorption lines from O V and O VI as well as O
III and O IV emission lines that are formed in a radiation-driven wind with a
mass-loss rate of the order of yr.
Spectroscopically, J05460836 is a [WC]-PG1159 transition-type pre-white
dwarf. The second object (J09276335) is a PG1159-type white dwarf with a
pure absorption-line spectrum dominated by C III/C IV and O III/O IV. We find
= 60,000 5000 K, log g = , and a carbon-
and oxygen-dominated atmosphere with C = , O = ,
and possibly a minute amount of helium (He = ). Comparison with
post-AGB evolutionary tracks suggests a mass of for
both objects, if such tracks can safely be applied to these stars. We find the
third object (J13323541) to be a relatively massive ()
hydrogen-rich (DAO) white dwarf with = 65,657 2390 K,
log g = , and abundances H = and He = . We discuss our results in the context of the "dynamically driven
double-degenerate double-detonation" (D) scenario proposed for the origin
of these stars.Comment: Accepted for publication in A&
Vorkurse in Bayern. Zwischenbericht einer regionalen Befragung von Erzieherinnen und GrundschullehrkrÀften im Raum Regensburg
Vorkurse in Bayern. Zwischenbericht einer regionalen Befragung von Erzieherinnen und GrundschullehrkrÀften im Raum Regensburg
Der Vorkurs Deutsch in Bayern ist eine SprachfördermaĂnahme fĂŒr Kinder mit Migrationshintergrund im Elemen-
tarbereich. Er wird in Zusammenarbeit zwischen Kindergarten und Grundschule durchgefĂŒhrt. Im Beitrag werden ausgewĂ€hlte
Ergebnisse einer Befragung von LehrkrÀften und Erzieherinnen im Raum Regensburg vorgestellt. Aus der Auswertung gehen
Empfehlungen fĂŒr die Weiterentwicklung des Vorkurses hervor
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