Masses and envelope binding energies of primary stars at the onset of a common envelope

We present basic properties of primary stars that initiate a common envelope (CE) in a binary, while on the giant branch. We use the population-synthesis code described in Politano et al. (2010) and follow the evolution of a population of binary stars up to the point where the primary fills its Roche lobe and initiates a CE. We then collect the properties of each system, in particular the donor mass and the binding energy of the donor's envelope, which are important for the treatment of a CE. We find that for most CEs, the donor mass is sufficiently low to define the core-envelope boundary reasonably well. We compute the envelope-structure parameter {\lambda_\mathrm{env}} from the binding energy and compare its distribution to typical assumptions that are made in population-synthesis codes. We conclude that {\lambda_\mathrm{env}} varies appreciably and that the assumption of a constant value for this parameter results in typical errors of 20--50%. In addition, such an assumption may well result in the implicit assumption of unintended and/or unphysical values for the CE parameter {\alpha_\mathrm{CE}}. Finally, we discuss accurate existing analytic fits for the envelope binding energy, which make these oversimplified assumptions for {\lambda_\mathrm{env}}, and the use of {\lambda_\mathrm{env}} in general, unnecessary.Comment: 6 pages, 3 figures, 1 table; to be published in the proceedings of the conference "Binary Star Evolution", in Mykonos, Greece, held in June 22-25, 201

A New and aberrant species of <i>Dugesia</i> (Platyhelminthes, Tricladida, Dugesiidae) from Madagascar

In this paper we report a new species of Dugesia of the family Dugesiidae from Madagascar, representing the fourth species of freshwater planarian known from this global biodiversity hotspot. In some respects the new species is aberrant, when compared with its congeners, being characterized by a head with smoothly rounded auricles, a peculiar course of the oviducts, including the presence of a common posterior extension, and by the asymmetrical openings of the vasa deferentia at about halfway along the seminal vesicle. Further, it is characterized by a ventral course of the ejaculatory duct with a terminal opening, very long spermiducal vesicles and unstalked cocoons. Its diploid chromosome complement with 18 chromosomes represents an uncommon feature among fissiparous species of Dugesia

New molecular sequences for two genera of marine planarians facilitate determination of their position in the phylogenetic tree, with new records for two species (Platyhelminthes, Tricladida, Maricola)

For the first time, molecular sequences of the 18S ribosomal DNA were generated for representatives of the genera Obrimoposthia Sluys &amp;amp; Ball, 1989 and Paucumara Sluys, 1989 of the suborder of the marine triclads, or Maricola, by analyzing the species Obrimoposthia wandeli (Hallez, 1906) and Paucumara trigonocephala (Ijima &amp;amp; Kaburaki, 1916). On the basis of this molecular data the phylogenetic position of these two genera in the phylogenetic tree of the Maricola was determined and compared with their position in the phylogeny based on the analysis of anatomical features. New records for these two species are documented and their taxonomic status is determined on the basis of histological studies

Black Hole Spin Evolution: Implications for Short-hard Gamma Ray Bursts and Gravitational Wave Detection

The evolution of the spin and tilt of black holes in compact black hole - neutron star and black hole - black hole binary systems is investigated within the framework of the coalescing compact star binary model for short gamma ray bursts via the population synthesis method. Based on recent results on accretion at super critical rates in slim disk models, estimates of natal kicks, and the results regarding fallback in supernova models, we obtain the black hole spin and misalignment. It is found that the spin parameter, a_spin}, is less than 0.5 for initially non rotating black holes and the tilt angle, i_tilt, is less than 45 deg for 50% of the systems in black hole - neutron star binaries. Upon comparison with the results of black hole - neutron star merger calculations we estimate that only a small fraction (~ 0.01) of these systems can lead to the formation of a torus surrounding the coalesced binary potentially producing a short-hard gamma ray burst. On the other hand, for high initial black hole spin parameters (a_spin>0.6) this fraction can be significant (~ 0.4). It is found that the predicted gravitational radiation signal for our simulated population does not significantly differ from that for non rotating black holes. Due to the (i) insensitivity of signal detection techniques to the black hole spin and the (ii) predicted overall low contribution of black hole binaries to the signal we find that the detection of gravitational waves are not greatly inhibited by current searches with non spinning templates. It is pointed out that the detection of a black hole - black hole binary inspiral system with LIGO or VIRGO may provide a direct measurement of the initial spin of a black hole.Comment: ApJ accepted: major revision

Integrative description of a new species of Dugesia (Platyhelminthes, Tricladida, Dugesiidae) from southern China, with its complete mitogenome and a biogeographic evaluation

A new species of freshwater flatworm of the genus Dugesia from Guangdong Province in China is described through an integrative approach, including molecular and morphological data, as well as mitochondrial genome analysis. The new species, Dugesia ancoraria Zhu &amp;amp; Wang, sp. nov., is characterised by: (a) a highly asymmetrical penis papilla, provided with a hunchback-like dorsal bump; (b) a short duct between seminal vesicle and ejaculatory duct; and (c) a postero-ventral course of the ejaculatory duct, which opens to the exterior at the subterminal, ventral part of the penis papilla. The molecular phylogenetic tree obtained from the concatenated dataset of four DNA markers (18S rDNA, ITS-1, 28S rDNA, COI) facilitated determination of the phylogenetic position of the new species, which shares a sister-group relationship with a small clade, comprising D. notogaea Sluys &amp;amp; Kawakatsu, 1998 from Australia and D. bengalensis Kawakatsu, 1983 from India. The circular mitogenome of the new species is 17,705 bp in length, including 12 protein coding genes, two ribosomal genes, and 22 transfer RNAs. Via analysis of gene order of mitochondrial genomes, the presently available pattern of mitochondrial gene rearrangement in the suborder Continenticola is discussed

Population Synthesis of Common Envelope Mergers: I. Giant Stars with Stellar or Substellar Companions

Using a population synthesis technique, we have calculated detailed models of the present-day field population of objects that have resulted from the merger of a giant primary and a main-sequence or brown dwarf secondary during common-envelope evolution. We used a grid of 116 stellar and 32 low-mass/brown dwarf models, a crude model of the merger process, and followed the angular momentum evolution of the binary orbit and the primary's rotation prior to merger, as well as the merged object's rotation after the merger. We find that present-day merged objects that are observable as giant stars or core-helium burning stars in our model population constitute between 0.24% and 0.33% of the initial population of ZAMS binaries, depending upon the input parameters chosen. The median projected rotational velocity of these merged objects is ~16 km/sec, an order of magnitude higher than the median projected rotational velocity in a model population of normal single stars calculated using the same stellar models and initial mass function. The masses of the merged objects are typically less than ~2 solar masses, with a median mass of 1.28 solar masses, which is slightly more than, but not significantly different from, their normal single star counterparts. The luminosities in our merged object population range from ~10-100 solar luminosities, with a strong peak in the luminosity distribution at ~60 solar luminosities, since the majority of the merged objects (57%) lie on the horizontal branch at the present epoch. The results of our population synthesis study are discussed in terms of possible observational counterparts either directly involving the high rotational velocity of the merger product or indirectly, via the effect of rotation on envelope abundances and on the amount and distribution of circumstellar matter.Comment: 16 pages, 12 figures, accepted for publication in the Astrophysical Journa

Cryptic species delineation in freshwater planarians of the genus Dugesia (Platyhelminthes, Tricladida): extreme intraindividual genetic diversity, morphological stasis, and karyological variability

The keystone of planarian taxonomy traditionally has been the anatomy of the copulatory apparatus. However, many planarian species comprise asexual fissiparous populations, with the fissiparous animals not developing a copulatory apparatus, thus precluding their morphological identification. Incorporation of molecular data into planarian systematics has been of great value, not only in the identification of fissiparous individuals but also as an additional source of information for determining species boundaries. Nevertheless, the discrepancy between morphological and molecular data has highlighted the need for extra sources of taxonomic information. Moreover, a recent study has pointed out that fissiparous reproduction may lead to high levels of intraindividual genetic diversity in planarians, which may mislead molecular analyses. In the present study we aim to test a new up-to-date integrative taxonomic procedure for planarians, including intraindividual genetic data and additional sources of taxonomic information, besides morphology and DNA, using Dugesia subtentaculata sensu lato as a model organism, a species with an intricate taxonomic history. First, we used three different methods for molecular species delimitation on single locus datasets, both with and without intraindividual information, for formulating Primary Species Hypotheses (PSHs). Subsequently, Secondary Species Hypotheses (SSHs) were formulated on the basis of three types of information: (1) a coalescent-based species delimitation method applied to multilocus data, (2) morphology of the copulatory apparatus, and (3) karyological metrics. This resulted in the delimitation of four morphologically cryptic species within the nominal species D. subtentaculata. Our results provide evidence that the analysis of intraindividual genetic data is essential for properly developing PSHs in planarians. Our study reveals also that karyological differentiation, rather than morphological differentiation, may play an important role in speciation processes in planarians, thus suggesting that the currently known diversity of the group could be highly underestimated

Genome sequence and rapid evolution of the rice pathogen Xanthomonas oryzae pv. oryzae PXO99A

Background: Xanthomonas oryzae pv. oryzae causes bacterial blight of rice (Oryza sativa L.), a major disease that constrains production of this staple crop in many parts of the world. We report here on the complete genome sequence of strain PXO99A and its comparison to two previously sequenced strains, KACC10331 and MAFF311018, which are highly similar to one another. Results: The PXO99 A genome is a single circular chromosome of 5,240,075 bp, considerably longer than the genomes of the other strains (4,941,439 bp and 4,940,217 bp, respectively), and it contains 5083 protein-coding genes, including 87 not found in KACC10331 or MAFF311018. PXO99A contains a greater number of virulence-associated transcription activator-like effector genes and has at least ten major chromosomal rearrangements relative to KACC10331 and MAFF311018. PXO99 A contains numerous copies of diverse insertion sequence elements, members of which are associated with 7 out of 10 of the major rearrangements. A rapidly-evolving CRISPR (clustered regularly interspersed short palindromic repeats) region contains evidence of dozens of phage infections unique to the PXO99A lineage. PXO99A also contains a unique, near-perfect tandem repeat of 212 kilobases close to the replication terminus. Conclusion: Our results provide striking evidence of genome plasticity and rapid evolution within Xanthomonas oryzae pv. oryzae. The comparisons point to sources of genomic variation and candidates for strain-specific adaptations of this pathogen that help to explain the extraordinary diversity of Xanthomonas oryzae pv. oryzae genotypes and races that have been isolated from around the world. © 2008 Salzberg et al; licensee BioMed Central Ltd

Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M&gt;70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0&lt;e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level