| 1. |
- Chandra, Poonam, et al.
(författare)
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Radio and x ray observations of sn 2006jd : another strongly interacting type iin supernova
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 755:2, s. 110-
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Tidskriftsartikel (refereegranskat)abstract
- We report four years of radio and X-ray monitoring of the Type IIn supernova SN 2006jd at radio wavelengths with the Very Large Array, Giant Metrewave Radio Telescope, and Expanded Very Large Array; at X-ray wavelengths with Chandra, XMM-Newton, and Swift-XRT. We assume that the radio and X-ray emitting particles are produced by shock interaction with a dense circumstellar medium. The radio emission shows an initial rise that can be attributed to free-free absorption by cool gas mixed into the nonthermal emitting region; external free-free absorption is disfavored because of the shape of the rising light curves and the low gas column density inferred along the line of sight to the emission region. The X-ray luminosity implies a preshock circumstellar density similar to 10(6) cm(-3) at a radius r similar to 2 x 10(16) cm, but the column density inferred from the photoabsorption of X-rays along the line of sight suggests a significantly lower density. The implication may be an asymmetry in the interaction. The X-ray spectrum shows Fe line emission at 6.9 keV that is stronger than is expected for the conditions in the X-ray emitting gas. We suggest that cool gas mixed into the hot gas plays a role in the line emission. Our radio and X-ray data both suggest the density profile is flatter than r(-2) because of the slow evolution of the unabsorbed emission.
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| 2. |
- Immler, Simone, et al.
(författare)
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Resolving variation in the reproductive tradeoff between sperm size and number
- 2011
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 108:13, s. 5325-5330
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Tidskriftsartikel (refereegranskat)abstract
- Spermatozoa are amongst the most variable cells, and three factors are thought to account for this variation in design: fertilization mode, phylogeny, and postcopulatory sexual selection. In addition, it has long been assumed that a tradeoff exists between sperm size and number, and although postcopulatory sexual selection affects both traits, empirical evidence for a tradeoff has so far been elusive. Our recent theoretical model predicts that the nature of a direct tradeoff between sperm size and number varies with sperm competition mechanism and sperm competition risk. We test these predictions using a comparative approach in two very different taxa with different sperm competition mechanisms: passerine birds (mechanism: simple raffle) and Drosophila fruit flies (sperm displacement). We show that in both groups, males increase their total ejaculate investment with increasing sperm competition risk, but whereas passerine birds allocate disproportionately to sperm number, drosophilids allocate disproportionately to sperm size. This striking difference between the two groups can be at least partly explained by sperm competition mechanisms depending on sperm size relative to the size of the female reproductive tract: in large animals (passerines), sperm numbers are advantageous in sperm competition owing to dilution inside the female tract, whereas in small animals (drosophilids), large spermare advantageous for physical competition (sperm displacement). Our study provides two important results. First, we provide convincing evidence for the existence of a sperm size-number tradeoff. Second, we show that by considering both sperm competition mechanism and dilution, can we account for variation in sperm size between different taxa.
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| 3. |
- Levine, Hagai, et al.
(författare)
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Male reproductive health statement (XIIIth international symposium on Spermatology, may 9th-12th 2018, Stockholm, Sweden
- 2018
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Ingår i: Basic and Clinical Andrology. - : Springer Science and Business Media LLC. - 2051-4190. ; 28:1
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Tidskriftsartikel (refereegranskat)abstract
- On the occasion of the XIIIth International Symposium on Spermatology held from 9 to 13 May 2018 in Stockholm (Sweden), participants (guest speakers and audience) collectively felt the need to make a public statement on the general issue of male reproductive health. Our intention is to raise awareness of what we believe is a neglected area of research despite alarming situations around the world. The disclosure strategy desired by the co-authors is to bring it to the attention of the greatest number partly by considering co-publication in the various periodicals dealing with Reproductive Biology and Andrology. BaCA's editorial office accepted this mission and found it natural that our periodical, the official journal of the French Andrology Society (SALF), should carry this message.
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| 4. |
- Stritzinger, Maximilian, et al.
(författare)
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The He-Rich Core-Collapse Supernova 2007Y : Observations from X-Ray to Radio Wavelengths
- 2009
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 696:1, s. 713-728
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Tidskriftsartikel (refereegranskat)abstract
- A detailed study spanning approximately a year has been conducted on the Type Ib supernova (SN) 2007Y. Imaging was obtained from X-ray to radio wavelengths, and a comprehensive set of multi-band (w2m2w1u'g'r'i'UBVYJHKs ) light curves and optical spectroscopy is presented. A virtually complete bolometric light curve is derived, from which we infer a 56Ni mass of 0.06 M sun. The early spectrum strongly resembles SN 2005bf and exhibits high-velocity features of Ca II and Hα during late epochs the spectrum shows evidence of an ejecta-wind interaction. Nebular emission lines have similar widths and exhibit profiles that indicate a lack of major asymmetry in the ejecta. Late phase spectra are modeled with a non-LTE code, from which we find 56Ni, O, and total-ejecta masses (excluding He) to be 0.06, 0.2, and 0.42 M sun, respectively, below 4500 km s-1. The 56Ni mass confirms results obtained from the bolometric light curve. The oxygen abundance suggests that the progenitor was most likely a ≈3.3 M sun He core star that evolved from a zero-age-main-sequence mass of 10-13 M sun. The explosion energy is determined to be ≈1050 erg, and the mass-loss rate of the progenitor is constrained from X-ray and radio observations to be lsim10-6 M sun yr-1. SN 2007Y is among the least energetic normal Type Ib SNe ever studied. Partly based on observations collected at the European Southern Observatory, La Silla and Paranal Observatories, Chile (ESO Programme 078.D-0048 and 380.D-0272).
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