New Elemental Abundances for V1974 Cygni Vanlandingham, K. M; Schwarz, G. J; Shore, S. N ...
The Astrophysical journal,
05/2005, Letnik:
624, Številka:
2
Journal Article
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We present a new analysis of existing optical and ultraviolet spectra of the ONeMg nova V1974 Cygni 1992. Using these data and the photoionization code Cloudy, we have determined the physical ...parameters and elemental abundances for this nova. Many of the previous studies of this nova have made use of incorrect analyses, and hence a new study was required. Our results show that the ejecta are enhanced, relative to solar, in helium, nitrogen, oxygen, neon, magnesium, and iron. Carbon was found to be subsolar. We find an ejected mass of 6 2 x 10 super(-4) M sub( ). Our model results fit well with observations taken at IR, radio, submillimeter, and X-ray wavelengths.
Aims. The neutral oxygen resonance λ1302 Å line can, if the optical depth is sufficiently high, de-excite by an intercombination transition at λ1641 Å to a metastable state. This has been noted in a ...number of previous studies but never systematically investigated as a diagnostic of the neutral red giant wind in symbiotic stars and symbiotic-like recurrent novae. Methods. We used archival IUE high resolution, and HST GHRS and STIS medium and high resolution, spectra to study a sample of symbiotic stars. The integrated fluxes were measured, where possible, for the O I λ1302 Å and O I λ1641 Å lines. Results. The intercombination λ1641 Å line is detected in a substantial number of symbiotic stars with optical depths that give column densities comparable with direct eclipse measures (EG And) and the evolution of the recurrent nova RS Oph 1985 in outburst. In four systems (EG And, Z And, V1016 Cyg, and RR Tel), we find that the O I variations are strongly correlated with the optical light curve and outburst activity. This transition can also be important for the study of a wide variety of sources in which an ionization-bounded H II region is imbedded in an extensive neutral medium, including active galactic nuclei, and not only for evaluations of extinction.
The discovery of very high energy (VHE) gamma-ray emitting X-ray binaries has triggered an intense effort to better understand the particle acceleration, absorption, and emission mechanisms in ...compact binary systems, which provide variable conditions along eccentric orbits. Despite this, the nature of some of these systems, and of the accelerated particles producing the VHE emission, is unclear. To answer some of these open questions, we conducted a multiwavelength campaign of the VHE gamma-ray emitting X-ray binary LS I +61 303 including the MAGIC telescope, XMM-Newton, and Swift during 60% of an orbit in 2007 September. We detect a simultaneous outburst at X-ray and VHE bands, with the peak at phase 0.62 and a similar shape at both wavelengths. A linear fit to the simultaneous X-ray/VHE pairs obtained during the outburst yields a correlation coefficient of r = 0.97, while a linear fit to all simultaneous pairs provides r = 0.81. Since a variable absorption of the VHE emission towards the observer is not expected for the data reported here, the correlation found indicates a simultaneity in the emission processes. Assuming that they are dominated by a single particle population, either hadronic or leptonic, the X-ray/VHE flux ratio favors leptonic models. This fact, together with the detected photon indices, suggests that in LS I +61 303 the X-rays are the result of synchrotron radiation of the same electrons that produce VHE emission as a result of inverse Compton scattering of stellar photons.
New low-frequency 74 and 330 MHz observations of the Galactic center (GC) region reveal the presence of a large-scale (6 x 2) diffuse source of nonthermal synchrotron emission. A minimum-energy ...analysis of this emission yields a total energy of 6(h super(4/7) f super(3/7)) x 10 super(52) ergs and a magnetic field strength of 66(h/f) super(2/7) kG (where h is the proton to electron energy ratio and f is the filling factor of the synchrotron emitting gas). The equipartition particle energy density is 1.2(h/f) super(2/7) eV cm super(-3), a value consistent with cosmic-ray data. However, the derived magnetic field is several orders of magnitude below the 1 mG field commonly invoked for the GC. With this field the source can be maintained with the supernova rate inferred from the GC star formation. Furthermore, a strong magnetic field implies an abnormally low GC cosmic-ray energy density. We conclude that the mean magnetic field in the GC region must be weak, of order 10 kG (at least on size scales 125").
We present the result of the observation of the ultrafaint dwarf galaxy Willman 1 performed with the 17 m MAGIC telescope during 15.5 hr between March and May 2008. No significant gamma -ray emission ...was found. We derived upper limits of the order of 10-12 ph cm-2 s-1 on the integral flux above 100 GeV, which we compare with predictions from several of the established neutralino benchmark models in the mSUGRA parameter space. The neutralino annihilation spectra are defined after including the recently quantified contribution of internal bremsstrahlung from the virtual sparticles that mediate the annihilation. Flux boost factors of three orders of magnitude are required even in the most optimistic scenario to match our upper limits. However, uncertainties in the dark matter intrinsic and extrinsic properties (e.g., presence of substructures, Sommerfeld effect) may significantly reduce this gap.
An elementary model is developed for grain growth during the expansion stage of nova ejecta. Rather than suppressing grain formation, we argue that agglomeration of atoms by dust nuclei proceeds ...kinetically through induced dipole reactions in a partially ionized medium. Ionization of a cluster increases once the ejecta become transparent in the ultraviolet which triggers runaway grain growth. This mechanism may also be important in other dust-forming hot stars such as Luminous Blue Variables and Wolf-Rayet systems.
New Findings
What is the central question of this study?
It is well recognized that there are disparities in cardiovascular disease outcomes between ethnic groups. Are there ethnic differences in ...microvascular function between healthy, young men and women of different ethnicities? This study used laser Doppler imagery and iontophoresis of acetylcholine and sodium nitroprusside to compare microvascular function between different ethnic groups and to understand the role of skin resistance in this methodology.
What is the main finding and its importance?
Endothelium‐independent microvascular function remained attenuated after correcting for skin resistance in the Black African and mixed ancestry groups, suggesting that differences in smooth muscle function may be an important factor contributing to ethnic differences in disease risk.
Microvascular dysfunction precedes the clinical manifestations of cardiovascular disease. Given the ethnic disparities in cardiovascular disease, we aimed to investigate ethnic differences in microvascular endothelial function in a group of young (18–33 years old), apparently healthy individuals (n = 33, nine Black African, 12 mixed ancestry and 12 Caucasian). Microvascular endothelium‐dependent and ‐independent function was assessed by laser Doppler imagery and iontophoresis of ACh and sodium nitroprusside (SNP), respectively, adjusting for skin resistance. Microvascular reactivity was expressed as maximum absolute perfusion, percentage change from baseline and area under the curve (AUC). Skin resistance was significantly lower in the Caucasian group in response to ACh (Caucasian, mean 0.16 ± 0.03 Ω versus Black, 0.21 ± 0.04 Ω and mixed ancestry, 0.20 ± 0.02 Ω, P < 0.01) and SNP (Caucasian, 0.08 ± 0.01 Ω versus Black, 0.11 ± 0.02 Ω and mixed ancestry, 0.12 ± 0.01 Ω, P < 0.01). Microvascular function in response to ACh was significantly higher in the Caucasian group compared with the other two groups; however, after adjusting for skin resistance these differences were no longer significant. Conversely, the microvascular SNP response remained significantly higher in the Caucasian group, even after adjusting for skin resistance (P < 0.01). Diastolic blood pressure was inversely associated with the AUC of ACh (r = −0.4) and all SNP responses (r = −0.3 to −0.6). Skin resistance was inversely associated with AUC and maximum absolute ACh response (r = −0.59 and −0.64, respectively) and all SNP responses (r = −0.37 to −0.79). Ethnic differences in endothelium‐independent microvascular function may contribute to ethnic disparities in cardiovascular disease. Moreover, skin resistance plays a significant role in the interpretation of the microvascular response to outcomes of iontophoresis in a multiethnic group.
Aims.We present an analysis of the exceptionally turbulent velocity field in the high Galactic latitude cirrus cloud MBM 3. As in the other translucent clouds in our study (MBM 16 and MBM 40), there ...is no evidence for internal star formation. However, the large scale velocity variation in this cloud is more pronounced. Methods.We have mapped the cloud in 12CO and 13CO (1-0) at high spatial (0.03 pc) and velocity (0.06 km s-1) resolution. We constructed several velocity probability density functions (PDFs), estimated the turbulent transfer rate, and analyzed the linewidths as a function of the size of randomly chosen regions within the cloud. Results.We find strong shear flows throughout the cloud that can easily power the turbulent motions. The wings of the PDFs are well approximated by a lorentzian distribution. Such distributions, related to Levy processes that are well known to be produced by correlated processes, are an unambiguous diagnostic of the turbulent intermittency. Conclusions.We find that the linewidth-size relation frequently used to indicate the role of turbulence in molecular clouds is not an unambiguous signature of its presence.
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