Near-Infrared Constraints on the Presence of Warm Dust at Metal-Rich, Helium Atmosphere White Dwarfs

Here, we present near-infrared spectroscopic observations of 15 helium atmosphere, metal-rich white dwarfs obtained at the NASA Infrared Telescope Facility. While a connection has been demonstrated between the most highly polluted, hydrogen atmosphere white dwarfs and the presence of warm circumstellar dust and gas, their frequency at the helium atmosphere variety is poorly constrained. None of our targets show excess near-infrared radiation consistent with warm orbiting material. Adding these near-infrared constraints to previous near- and mid-infrared observations, the frequency of warm circumstellar material at metal-bearing white dwarfs is at least 20% for hydrogen-dominated photospheres, but could be less than 5% for those effectively composed of helium alone. The lower occurrence of dust disks around helium atmosphere white dwarfs is consistent with Myr timescales for photospheric metals in massive convection zones. Analyzing the mass distribution of 10 white dwarfs with warm circumstellar material, we search for similar trends between the frequency of disks and the predicted frequency of massive planets around intermediate mass stars, but find the probability that disk-bearing white dwarfs are more massive than average is not significant.Comment: AJ, in pres

Post-processing of the HST STIS coronagraphic observations

In the past 20 years, the Hubble Space Telescope (HST) STIS coronagraphic instrument has observed more than 100 stars, obtaining more than 4,000 readouts since its installment on HST in 1997 and the numbers are still increasing. We reduce the whole STIS coronagraphic archive at the most commonly observed positions (Wedge A0.6 and A1.0) with new post-processing methods, and present our results here. We are able to recover all of the 32 previously reported circumstellar disks, and obtain better contrast close to the star. For some of the disks, our results are limited by the over subtraction of the methods, and therefore the major regions of the disks can be recovered except the faintest regions. We also explain our efforts in the calibration of its new BAR5 occulting position, enabling STIS to explore inner regions as close as 0.2".Comment: 14 pages, 9 figures, 2 tables. Proceedings of the SPIE, 10400-2

Approaches to overcome flow cytometry limitations in the analysis of cells from veterinary relevant species

BACKGROUND: Flow cytometry is a powerful tool for the multiparameter analysis of leukocyte subsets on the single cell level. Recent advances have greatly increased the number of fluorochrome-labeled antibodies in flow cytometry. In particular, an increase in available fluorochromes with distinct excitation and emission spectra combined with novel multicolor flow cytometers with several lasers have enhanced the generation of multidimensional expression data for leukocytes and other cell types. However, these advances have mainly benefited the analysis of human or mouse cell samples given the lack of reagents for most animal species. The flow cytometric analysis of important veterinary, agricultural, wildlife, and other animal species is still hampered by several technical limitations, even though animal species other than the mouse can serve as more accurate models of specific human physiology and diseases. RESULTS: Here we present time-tested approaches that our laboratory regularly uses in the multiparameter flow cytometric analysis of ovine leukocytes. The discussed approaches will be applicable to the analysis of cells from most animal species and include direct modification of antibodies by covalent conjugation or Fc-directed labeling (Zenon™ technology), labeled secondary antibodies and other second step reagents, labeled receptor ligands, and antibodies with species cross-reactivity. CONCLUSIONS: Using refined technical approaches, the number of parameters analyzed by flow cytometry per cell sample can be greatly increased, enabling multidimensional analysis of rare samples and giving critical insight into veterinary and other less commonly analyzed species. By maximizing information from each cell sample, multicolor flow cytometry can reduce the required number of animals used in a study

Perspective acceleration and gravitational redshift. Measuring masses of individual white dwarfs using Gaia + SIM astrometry

According to current plans, the SIM/NASA mission will be launched just after the end of operations for the Gaia/ESA mission. This is a new situation which enables long term astrometric projects that could not be achieved by either mission alone. Using the well-known perspective acceleration effect on astrometric measurements, the true heliocentric radial velocity of a nearby star can be measured with great precision if the time baseline of the astrometric measurements is long enough. Since white dwarfs are compact objects, the gravitational redshift can be quite large (40-80 km/s), and is the predominant source of any shift in wavelength. The mismatch of the true radial velocity with the spectroscopic shift thus leads to a direct measure of the Mass--Radius relation for such objects. Using available catalog information about the known nearby white dwarfs, we estimate how many masses/gravitational redshift measurements can be obtained with an accuracy better than 2%. Nearby white dwarfs are relatively faint objects (10 < V < 15), which can be easily observed by both missions. We also briefly discuss how the presence of a long period planet can mask the astrometric signal of perspective acceleration.Comment: 3 pages, 2 Figures. Proceedings of the IAU Symposium 261 : Relativity in Fundamental Astronomy. 27 April - 1 May 2009, Virginia Beach, VA, USA. refereed and accepted versio

The Survival Rate of Ejected Terrestrial Planets with Moons

During planet formation, a gas giant will interact with smaller protoplanets that stray within its sphere of gravitational influence. We investigate the outcome of interactions between gas giants and terrestrial-sized protoplanets with lunar-sized companions. An interaction between a giant planet and a protoplanet binary may have one of several consequences, including the delivery of volatiles to the inner system, the capture of retrograde moons by the giant planet, and the ejection of one or both of the protoplanets. We show that an interesting fraction of terrestrial-sized planets with lunar sized companions will likely be ejected into interstellar space with the companion bound to the planet. The companion provides an additional source of heating for the planet from tidal dissipation of orbital and spin angular momentum. This heat flux typically is larger than the current radiogenic heating of the Earth for up to the first few hundred million years of evolution. In combination with an atmosphere of sufficient thickness and composition, the heating can provide the conditions necesary for liquid water to persist on the surface of the terrestrial mass planet, making it a potential site for life. We also determine the possibility for directly detecting such systems through all-sky infrared surveys or microlensing surveys. Microlensing surveys in particular will directly measure the frequency of this phenomenon.Comment: 4 pages, 2 figures, Accepted to ApJ

Chemotaxis of T cell subsets ex vivo

Titelblatt, Inhaltsverzeichnis, Lebenslauf 1\. Einleitung 2\. Material und Methoden 3.1 Ergebnisse Teil 1 3.2 Ergebnisse Teil 2 3.3 Ergebnisse Teil 3 4\. Diskussion 5\. Zusammenfassung / Summary 6\. Tabellenanhang LiteraturverzeichnisChemokine sind wichtig in der Homýostase und Regulation des Immunsystems.Neben ihrer Fýhigkeit Lymphozyten in lymphatische Organe und distinkte Gewebskompartimente zu locken,erfýllen sie wichtige Funktionen in Entzýndung. Von Studien mit in vitro erzeugten Th1-und Th2-Zellen ist bekannt,dass diese Zellen differentiell auf chemotaktische Einflýsse reagieren.Um zu klýren,ob dies auch fýr CD4 + Effektor/Memory T-Zellen gilt,die in vivo entstanden sind,wurden solche Zellen aus Milzen unbeeinflusster und immunisierter Mýuse gewonnen und ex vivo im Chemotaxisassay eingesetzt.Hierbei wurde die Migration zu verschiedenen induzierbaren und homýostatischen Chemokinen getestet. Die Ergebnisse zeigen,dass IL-4 produzierende T-Zellen die hýchste Antwortfýhigkeit gegenýber dem ýTh2-Chemokin"CCL17 zeigten,wýhrend das ýTh1-Chemokin"CXCL9 prýferentiell,aber nicht ausschlieýlich,IFN-? -produzierende T-Zellen anlockte. CXCL13,ein Chemokin,das fýr die Verteilung von T-und B-Zellen in den B-Zell-Follikel lymphatischer Organe verantwortlich ist,hat bevorzugt IL-10-produzierende T-Zellen angelockt,wohingegen andere Zytokinproduzenten weniger reagierten.Nach Immunisierung ýnderte sich dieses Migrationsprofil und IL-4 + T-Zellen waren die am stýrksten reaktive Fraktion zu CXCL13. Der korrespondierende Rezeptor fýr CCL21 und CCL19,CCR7 wurde,wie in der Literatur berichtet,hauptsýchlich auf der in vitro erzeugten Th1-Subpopulation gefunden.Im Gegensatz dazu,konnte ex vivo eine starke Migration von IL-4 und/oder IFN-? - produzierenden T-Zellen zu CCL21 detektiert werden. CCR7 wurde zuvor beschrieben humane Memory T-Zellen in zwei funktionell unterschiedliche Subpopulationen zu trennen,wobei alle Zytokinproduzenten innerhalb der CCR7-negativen Fraktion liegen sollten.In der vorliegenden Studie migrierten dagegen die meisten der murinen oder humanen Effektor/Memory T-Zellen zu CCR7-Liganden.Im Einklang dazu,zeigten die Zellen auch eine positive Oberfýchenfýrbung fýr den Rezeptor. Durch Versuche mit CCR7 -/- -Mýusen konnte gezeigt werden,dass CCR7 der einzige Rezeptor ist,der fýr die Chemotaxis zu CCL21 verantwortlich ist.CCR7-defiziente Th1- Zellen waren in ihrer Fýhigkeit in Lymphknoten und Peyer´sche Plaques zu migrieren stark beeintrýchtigt,aber in der Lage in eine Hautentzýndung einzudringen. Die Ergebnisse weisen daraufhin,dass Effektor/Memory T-Zellen zwar subpopulationsspezifische Prýferenzen fýr induzierbare Chemokine besitzen,diese aber weniger streng ausfallen,als fýr in vitro differenzierte Effektorzellen.Auýerdem behalten in vivo erzeugte Effektor/Memory T-Zellen ihre Fýhigkeit in sekundýre lymphatische Organe durch CCR7 zu rezirkulieren.Chemokines are important in the homeostasis and regulation of the immune system.Besides their capability of targeting lymphocytes into lymphoid organs and respective tissue compartments they fulfill specialized roles in inflammation. It is known from studies with in vitro generated Th1 and Th2 cells that these cells respond differentially to chemotactic agents.To clarify whether this also applies for in vivo primed effector/memory T cells,we isolated them from spleens of untreated and immunized mice and analyzed their migratory properties to various inducible and lymphoid chemokines ex vivo in a chemotaxis assay. The results show,that IL-4 producing T cells exhibited the highest response to the "Th2 chemokine"CCL17,whereas the "Th1 chemokine"CXCL9 preferentially,but not exclusively,attracted IFN-? producing cells. CXCL13 a chemokine that attracts T and B cells into the B cell-follicle of lymphoid tissues was found to preferentially attract IL-10-producing T cells,whereas other cytokine subsets reacted at lower levels.Interestingly,after immunization this migration pattern changed and IL-4-positive T cells exhibited the strongest response toward CXCL13. The corresponding receptor for CCL21 and CCL19 CCR7 was found,as reported,to be dominantly expressed by murine in vitro polarized Th1 cells.Conversely,we detected ex vivo a strong migratory response of IL-4 and/or IFN-? positive T cells toward CCL21. In the human system CCR7 was described to discriminate between two functional subsets of memory T cells,with all effector cytokine-producing T cells within the CCR7-negative subset.In contrast to that,we found the majority of mouse and human cytokine producing T cells responsive toward CCR7 ligands and in addition they also stained on the cell surface for the receptor. By using CCR7 -/- mice we were able to show that CCR7 is the only responsible receptor on CCL21-responsive murine T cells.Th1 cells generated from CCR7 -/- mice were reduced in their capacity to enter lymph nodes and Peyer´s patches,but did enter a site of inflammation. These findings indicate that CD4 + cells producing effector cytokines upon stimulation exhibit subset specific preferences for inducible chemokines,which are less restricted than for in vitro primed effector cells.Additionally,in vivo differentiated effector/memory T cells retain the capacity to recirculate through lymphoid tissues via CCR7

How to Make a Singleton sdB Star via Accelerated Stellar Evolution

Many hot subdwarf B stars (sdBs) are in close binaries, and the favored formation channels for subdwarfs rely on mass transfer in a binary system to strip a core He burning star of its envelope. However, these channels cannot account for sdBs that have been observed in long period binaries nor the narrow mass distribution of isolated (or "singleton") sdBs. We propose a new formation channel involving the merger of a helium white dwarf and a low mass, hydrogen burning star, which addresses these issues. Hierarchical triples whose inner binaries merge and form sdBs by this process could explain the observed long period subdwarf+main sequence binaries. This process would also naturally explain the observed slow rotational speeds of singleton sdBs. We also briefly discuss the implications of this formation channel for extreme horizontal branch morphology in globular clusters and the UV upturn in elliptical galaxies.Comment: 5 pages, 3 figures, accepted for publication ApJ