Adalbert W. A. Pauldrach

Spitzer observations of M83 and the hot star, H ii region connection

We have undertaken a programme to observe emission lines of [Siv] 10.51, [NeII] 12.81, [Ne III] 15.56, and [S III] 18.71 μm in a number of extragalactic HII regions with the Spitzer Space Telescope. Here we report our results for the nearly face-on spiral galaxy M83. A subsequent paper will present our data and analysis for another substantially face-on spiral galaxy M33. The nebulae selected cover a wide range of galactocentric radii (R G ). The observations were made with the infrared spectrograph in the short wavelength, high dispersion configuration. The above set of four lines is observed cospatially, thus permitting a reliable comparison of the fluxes. From the measured fluxes, we determine the ionic abundance ratios including Ne ++ /Ne + , S 3+ /S ++ and S ++ /Ne + and find that there is a correlation of increasingly higher ionization with larger R G . By sampling the dominant ionization states of Ne and S for Hit II regions, we can approximate the Ne/S ratio by (Ne + + Ne ++ )/(S ++ + S 3+ ). Our findings of ratios that significantly exceed the benchmark Orion Nebula value, as well as a decrease in this ratio with increasing R G , are more likely due to other effects than a true gradient in Ne/S. Two effects that will tend to lower these high estimates and to flatten the gradient are first, the method does not account for the presence of S + and second, S but not Ne is incorporated into grains. Both Ne and S are primary elements produced in α-chain reactions, following C and O burning in stars, making their yields depend very little on the stellar metallicity. Thus, it is expected that Ne/S remains relatively constant throughout a galaxy. We stress that this type of observation and method of analysis does have the potential for accurate measurements of Ne/S, particularly for H II regions that have lower metallicity and higher ionization than those here, such as those in M33. Our observations may also be used to test the predicted ionizing spectral energy distribution (SED) of various stellar atmosphere models. We compare the ratio of fractional ionizations / and / versus / with predictions made from our photoionization models using several of the state-of-the-art stellar atmosphere model grids. The overall best fit appears to be the nebular models using the supergiant stellar atmosphere models of Pauldrach, Hoffmann & Lennon and Sternberg, Hoffmann & Pauldrach. This result is not sensitive to the electron density and temperature range expected for these M83 nebulae. Considerable computational effort has gone into the comparison between data and models, although not all parameter studies have yet been performed on an ultimate level (e.g. in the present paper the stellar atmosphere model abundances have been fixed to solar values). A future paper, with the benefit of more observational data, will continue these studies to further discriminate how the ionic ratios depend on the SED and the other nebular parameters.

Spitzer observations of extragalactic H ii regions - III. NGC 6822 and the hot star, H ii region connection

Using the short-high module of the Infrared Spectrograph on the Spitzer Space Telescope, we have measured the [S iv] 10.51, [Ne ii] 12.81, [Ne iii] 15.56, and [S iii] 18.71-mu m emission lines in nine H ii regions in the dwarf irregular galaxy NGC 6822. These lines arise from the dominant ionization states of the elements neon (Ne++, Ne+) and sulphur (S3+, S++), thereby allowing an analysis of the neon to sulphur abundance ratio as well as the ionic abundance ratios Ne+/Ne++ and S3+/S++. By extending our studies of H ii regions in M83 and M33 to the lower metallicity NGC 6822, we increase the reliability of the estimated Ne/S ratio. We find that the Ne/S ratio appears to be fairly universal, with not much variation about the ratio found for NGC 6822: the median (average) Ne/S ratio equals 11.6 (12.2 +/- 0.8). This value is in contrast to Asplund et al.s currently best estimated value for the Sun: Ne/S = 6.5. In addition, we continue to test the predicted ionizing spectral energy distributions (SEDs) from various stellar atmosphere models by comparing model nebulae computed with these SEDs as inputs to our observational data, changing just the stellar atmosphere model abundances. Here, we employ a new grid of SEDs computed with different metallicities: solar, 0.4 solar, and 0.1 solar. As expected, these changes to the SED show similar trends to those seen upon changing just the nebular gas metallicities in our plasma simulations: lower metallicity results in higher ionization. This trend agrees with the observations.

Infra-red Radiative Cooling/Heating of the Mesosphere and Lower Thermosphere Due to the Small-Scale Temperature Fluctuations Associated with Gravity Waves

We address the effect of an additional infrared radiative cooling/heating of the mesosphere and lower thermosphere (MLT) in the infrared bands of CO2, O3 and H2O due to small-scale irregular temperature fluctuations associated with gravity waves (GWs). These disturbances are not well resolved by present general circulation models (GCMs), but they alter the radiative transfer and cooling rates significantly. A statistical model of gravity wave-induced temperature variations was applied to large-scale temperature profiles, and the corresponding direct radiative calculations were performed with accounting for the breakdown of the local thermodynamic equilibrium (non-LTE). We show that temperature fluctuations can cause an additional cooling of up to 4 K day−1 near the mesopause. The effect is produced mainly by the fundamental 15 μm band of the main CO2 isotope 12C16O2 (626). A simple parametrization has been derived that computes corrections depending on the temperature fluctuations variance, which need to be added in radiative calculations to the mean temperature and the volume mixing ratios (VMRs) of CO2 and O(3P) to account for additional cooling/heating caused by the unresolved disturbances. Implementation of this scheme into the LIMA model resulted in a colder and broader simulated summer mesopause in agreement with recent lidar measurements at Spitsbergen.

Masse und Energie formen ihr Umfeld bis zur Unkenntlichkeit

Man sollte meinen, dass uns eigentlich nichts mehr uberraschen kann, nachdem wir gesehen haben, dass Materie so gut wie keine Masse und nahezu keine raumliche Ausdehnung hat und dass diese Spuren von Masse zudem nur eine spezielle Form von Energie sind, wobei das ominose Higgs-Feld fur die Formgebung zustandig ist. Des Weiteren erinnern wir uns, dass uns nahezu alle Absolutgrosen, die uns im alltaglichen Leben mit einer bodenstandigen Selbstverstandlichkeit begleiten, zwischen den Fingern zerronnen sind. Was wir aus unserer eigenen Erfahrung heraus nie und nimmer erwartet hatten, ist geschehen: Die Zeit und der Raum haben sich als relativ erwiesen und in deren Schlepptau auch die Masse und der Impuls.

Das Universum: stur statisch oder entwickelbar?

In einem gewissen Rahmen haben wir uns nun das erforderliche Rustzeug erarbeitet, um, auf dem anerkannten Stand des Wissens basierend, den Ursprung und die fruhe Entwicklung des Universums zu durchleuchten.

Der Primus inter Pares

Es ist Strahlungsenergie, was wir beobachten und woraus wir unsere Erkenntnisse und nahezu alle weiterfuhrenden Schlussfolgerungen ziehen! Durch die Beobachtung der im ganzen heutigen Universum umtriebigen Strahlung hat die Astrophysik Zugang zu den unzahligen Experimenten, die im gesamten Kosmos permanent von selbst und ohne jeglichen Kostenaufwand ablaufen. Und das betrifft nicht nur auch, sondern vor allem „Experimente“, die das Universum in seiner tiefsten Vergangenheit durchgefuhrt hat.

Das Standardmodell wird angezählt

Die Dunkle Energie liefert das Fehlende frei Haus, und dennoch gerat das Standardmodell ins Wanken!

Die Suche nach dem „expansionsauslösenden“ Gaspedal

Dass das Universum an einem bestimmten Punkt gleich mit Vollgas in die Gange gekommen ist, um den Expansionszustand, in dem es sich bis heute befindet, zu erzeugen, wissen wir bereits.

Das grundlegende Inventar: Raum und Zeit – oder doch Raumzeit?

Dass Zeit und Raum das grundlegende Inventar unseres Universums sind, ist fraglos unstrittig. Aber wie viel Raum benotigt das Universum eigentlich, und wie viel Zeit ist dem Universum gegeben?

Das Universum hat es gut versteckt – zumindest „das Meiste“!

Das Wissen um die wesentlichen physikalischen Zusammenhange war der entscheidende Faktor, der uns das Universum begleitend ins „Hier“ und „Jetzt“ gebracht hat. Obwohl es zugegebenermasen nicht einfach war, alles Erforderliche zumindest in seinen Grundzugen zu verstehen, hat es sich gelohnt, denn wir sehen jetzt auch aus physikalischer Sicht um uns herum ein Universum, das seine „Dunklen Jahre“ beendet und sich daraufhin annehmbar entwickelt hat. Um das zu sehen, war es allerdings vordringlich wichtig, dass wir uns auf eine von George Gamow bereits im Jahr 1948 vorgegebene Spur begeben.