Iron in Hot DA White Dwarfs

We present a study of the iron abundance pattern in hot hydrogen-rich (DA) white dwarfs. The study is based on new and archival far ultraviolet spectroscopy of a sample of white dwarfs in the temperature range 30,000 K < T_eff < 64,000 K. The spectra obtained with the Far Ultraviolet Spectroscopic Explorer along with spectra obtained with the Hubble Space Telescope Imaging Spectrograph and the International Ultraviolet Explorer sample FeIII to FeVI absorption lines enabling a detailed iron abundance analysis over a wider range of effective temperatures than previously afforded. The measurements reveal abundance variations in excess of two orders of magnitude between the highest and the lowest temperatures probed, but also show considerable variations (over one order of magnitude) between objects with similar temperatures and surface gravities. Such variations in cooler objects may be imputed to accretion from unseen companions or so-called circumstellar debris although the effect of residual mass-loss and selective radiation pressure in the hottest objects in the sample remain dominant.Comment: Accepted for publication in Ap

Arthroscopic repair of subscapularis tear: Surgical technique and results

SummaryIntroductionArthroscopic management of extensive subscapularis tendon lesions was reported more recently than for the supra- and infra-spinatus tendons. Extensive tears create technical problems requiring an extra-articular approach. The few results so far reported have been encouraging.Study designSurgical techniques adapted to each type of tear according to our subscapularis lesion classification are described, with the preliminary results from our cohort.Patients and methodsBetween January 2006 and December 2008, 74 patients were operated on for extensive subscapularis tear. Twenty-three were assessed over a minimum 2 years’ follow-up (mean, 32 months) on UCLA, ASES and Constant scores, comparative dynamometric Bear-Hug test, visual analog pain scale and self-assessed shoulder function.ResultsPostoperative clinical results for the 23 patients followed up showed an improvement in shoulder function from 58 to 86%, in UCLA score from 16.4 to 30.9 points and in weighted Constant score from 48.6 to 75.2%.DiscussionIn case of severe tear, we recommend visualizing the subscapularis tendon along its main axis from above, on a lateral approach allowing the intra- and extra-articular parts to be controlled, so as to check the reduction achieved by traction wire and anatomic fixation by anchors and sutures via an anterior access of varying height but systematically kept under tension. Biceps tenodesis is often required. Results show a clear improvement on all scores: pain, strength and function. The failure rate was 9% (two cases). There were no complications.Level of evidenceIV (retrospective study)

Essays on marketing and online social networks

Based on unique datasets of the world's largest music and audio platform, this dissertation sets out (1) to investigate optimal seeding policies (e.g., as a creator of music) and (2) to create a managerial framework for early-stage investments in creators (e.g., as a record label)

Argon Abundances in the Solar Neighborhood: Non-LTE Analysis of Orion Association B-type Stars

Argon abundances have been derived for a sample of B main-sequence stars in the Orion association. The abundance calculations are based on NLTE metal line-blanketed model atmospheres calculated with the NLTE code TLUSTY and an updated and complete argon model atom. We derive an average argon abundance for this young population of A(Ar) = 6.66 +- 0.06. While our result is in excellent agreement with a recent analysis of the Orion nebula, it is significantly higher than the currently recommended solar value which is based on abundance measurements in the solar corona. Moreover, the derived argon abundances in the Orion B stars agree very well with a measurement from a solar impulsive flare during which unmodified solar photospheric material was brought to flare conditions. We therefore argue that the argon abundances obtained independently for both the Orion B stars and the Orion nebula are representative of the disk abundance value in the solar neighborhood. The lower coronal abundance may reflect a depletion related to the FIP effect. We propose a new reference value for the abundance of argon in the solar neighborhood, A(Ar) = 6.63 +- 0.10, corresponding to Ar/O = 0.009.Comment: to appear in Astrophysical Journal, 24 pages, 3 figures; minor corrections after referee's repor

Hot Subdwarfs in Resolved Binaries

In the last decade or so, there have been numerous searches for hot subdwarfs in close binaries. There has been little to no attention paid to wide binaries however. The advantages of understanding these systems can be many. The stars can be assumed to be coeval, which means they have common properties. The distance and metallicity, for example, are both unknown for the subdwarf component, but may be determinable for the secondary, allowing other properties of the subdwarf to be estimated. With this in mind, we have started a search for common proper motion pairs containing a hot subdwarf component. We have uncovered several promising candidate systems, which are presented here.Comment: 6 pages, 4 figures. Proceedings of The Fourth Meeting on Hot Subdwarf Stars and Related Objects held in China, 20-24 July 2009. Accepted for publication in Astrophysics and Space Scienc

Spitzer Observations of the North Ecliptic Pole

We present a photometric catalog for Spitzer Space Telescope warm mission observations of the North Ecliptic Pole (NEP; centered at $\rm R.A.=18^h00^m00^s$, $\rm Decl.=66^d33^m38^s.552$). The observations are conducted with IRAC in 3.6 $\mu$m and 4.5 $\mu$m bands over an area of 7.04 deg$^2$ reaching 1$\sigma$ depths of 1.29 $\mu$Jy and 0.79 $\mu$Jy in the 3.6 $\mu$m and 4.5 $\mu$m bands respectively. The photometric catalog contains 380,858 sources with 3.6 $\mu$m and 4.5 $\mu$m band photometry over the full-depth NEP mosaic. Point source completeness simulations show that the catalog is 80% complete down to 19.7 AB. The accompanying catalog can be utilized in constraining the physical properties of extra-galactic objects, studying the AGN population, measuring the infrared colors of stellar objects, and studying the extra-galactic infrared background light.Comment: 10 pages, 11 figures and 3 tables. Accepted to the ApJ

Evolution of X-ray spectra and light curves of V1494 Aquilae

We present six Chandra X-ray spectra and light curves obtained for the nova V1494 Aql (1999 #2) in outburst. The first three observations were taken with ACIS-I on days 134, 187, and 248 after outburst. The count rates were 1.00, 0.69 and 0.53 cps, respectively. We found no significant periodicity in the ACIS light curves. The X-ray spectra show continuum emission and lines originating from N and O. We found acceptable spectral fits using isothermal APEC models with significantly increased elemental abundances of O and N for all observations. On day 248 after outburst a bright soft component appeared in addition to the fading emission lines. The Chandra observations on days 300, 304, and 727 were carried out with the HRC/LETGS. The spectra consist of continuum emission plus strong emission lines of O and N, implying a high abundance of these elements. On day 300, a flare occurred and periodic oscillations were detected in the light curves taken on days 300 and 304. This flare must have originated deep in the outflowing material since it was variable on short time scales. The spectra extracted immediately before and after the flare are remarkably similar, implying that the flare was an extremely isolated event. Our attempts to fit blackbody, Cloudy, or APEC models to the LETG spectra failed, owing to the difficulty in disentangling continuum and emission line components. The spectrum extracted during the flare shows a significant increase in the strengths of many of the lines and the appearance of several previously undetected lines. In addition, some of the lines seen before and after the flare are not present during the flare. On day 727 only the count rate from the zeroth order could be derived, and the source was too faint for the extraction of a light curve or spectrum.Comment: 7 pages, 6 figures, 3 Table

SHOCKED POSTSTARBURST GALAXY SURVEY. II. the MOLECULAR GAS CONTENT and PROPERTIES of A SUBSET of SPOGs

We present CO(1–0) observations of objects within the Shocked POststarburst Galaxy Survey taken with the Institut de Radioastronomie Millimétrique 30 m single dish and the Combined Array for Research for Millimeter Astronomy interferometer. Shocked poststarburst galaxies (SPOGs) represent a transitioning population of galaxies, with deep Balmer absorption $({\mathrm{EW}}_{{\rm{H}}\delta }\gt 5\,{\mathring{\rm{A}}} )$, consistent with an intermediate-age (A-star) stellar population, and ionized gas line ratios inconsistent with pure star formation. The CO(1–0) subsample was selected from SPOGs detected by the Wide-field Infrared Survey Explorer with 22 μm flux detected at a signal-to-noise ratio (S/N) > 3. Of the 52 objects observed in CO(1–0), 47 are detected with S/N > 3. A large fraction (37%–46% ± 7%) of our CO-SPOG sample were visually classified as morphologically disrupted. The H2 masses detected were between ${10}^{8.7-10.8}$ ${M}_{\odot }$, consistent with the gas masses found in normal galaxies, though approximately an order of magnitude larger than the range seen in poststarburst galaxies. When comparing the 22 μm and CO(1–0) fluxes, SPOGs diverge from the normal star-forming relation, having 22 μm fluxes in excess of the relation by a factor of $\langle {\epsilon }_{{\rm{MIR}}}\rangle ={4.91}_{-0.39}^{+0.42}$, suggestive of the presence of active galactic nuclei (AGNs). The Na i D characteristics of CO-SPOGs show that it is likely that many of these objects host interstellar winds. Objects with large Na i D enhancements also tend to emit in the radio, suggesting possible AGN driving of neutral winds

Flash Mixing on the White Dwarf Cooling Curve: FUSE Observations of three He-rich sdB Stars

We present FUSE spectra of 3 He-rich sdB stars. Two of these stars, PG1544+488 and JL87, reveal extremely strong C III lines at 977 and 1176A, while the carbon lines are quite weak in the third star, LB1766. We have analyzed the FUSE data using TLUSTY NLTE line-blanketed model atmospheres, and find that PG1544+488 has a surface composition of 96% He, 2% C, and 1% N. JL87 shows a similar surface enrichment of carbon and nitrogen, but some significant fraction of hydrogen still remains in its atmosphere. LB1766 has a surface composition devoid of hydrogen and strongly depleted of carbon, indicating that its surface material has undergone CN-cycle processing. We interpret these observations with new evolutionary calculations which suggest that He-rich sdB stars with C-rich compositions are the progeny of stars which underwent a delayed He-core flash on the white-dwarf cooling curve. During such a flash the interior convection zone will penetrate into the H envelope, thereby mixing the envelope with the He- and C-rich core. Such `flash-mixed' stars will arrive on the extreme horizontal branch (EHB) with He- and C-rich surface compositions and will be hotter than the hottest canonical (i.e., unmixed) EHB stars. Two types of flash mixing are possible: `deep' and `shallow', depending on whether the H envelope is mixed deeply into the site of the He flash or only with the outer layers of the core. Based on both their stellar parameters and surface compositions, we suggest that PG1544+488 and JL87 are examples of `deep' and `shallow' flash mixing, respectively. Flash mixing may therefore represent a new evolutionary channel for producing the hottest EHB stars. However, flash mixing cannot explain the abundance pattern in LB1766, which remains a challenge to current evolutionary models.Comment: 32 pages, 6 figures; minor additions; to appear in Astrophys. J., February 200

Hot subdwarfs from the ESO Supernova Ia Progenitor Survey: II. Atmospheric parameters of subdwarf O stars

We address the origin and evolutionary status of hot subdwarf stars by studying the optical spectral properties of 58 subdwarf O (sdO) stars. Combining them with the results of our previously studied subdwarf B (sdB) stars, we aim at investigating possible evolutionary links. We analyze high-resolution ESO VLT UVES spectra from the ESO Supernova Ia Progenitor Survey (SPY). Effective temperatures, gravities, and helium abundances are determined simultaneously by fitting the profiles of H and He lines using dedicated synthetic spectra in NLTE. Evidence for cool companions to 8 sdOs as well as a binary consisting of two sdO stars is found. A correlation between He abundances and the presence of carbon and/or nitrogen lines emerges: below solar He abundance, no sdO shows C or N lines. In contrast, C and/or N lines are present in ALL sdOs with super- solar He abundance. We thus use the solar He abundance to divide our sample into He-deficient and He-enriched sdOs. While He-deficient sdOs are scattered in a wide range of the Teff-log(g)-diagram, most of the He-enriched sdOs cluster in a narrow region at Teff = 40,000 ... 50,000K and log(g)=5.5 ... 6.0. An evolu- tionary link between sdBs and sdOs appears plausible only for the He-deficient sdOs indicating that they are the likely successors to sdBs. The properties of He-enriched sdOs cannot be explained with canonical single star evolutionary models. Alternative scenarios (late hot flasher) as well as for binary evolution (white dwarf merger; post-RGB evolution) are tested. While we regard the post-RGB scenario as inappropriate, the white dwarf merger and the late hot flasher scenarios remain viable to explain the origin of He-enriched sdOs.Comment: 14 pages, 10 figures, Astronomy & Astrophysics accepte