We present an analysis of the UV spectra of the fast ONeMg nova V693 Coronae Austrinae 1981. Observations with IUE began on 1981 April 10 and continued until 1981 November 14. We find the reddening ...for the nova to be E (B — V) ≃ 0.2 ±0.1. Using the photoionization code cloudy 90.02 and the minimization routine minuit, we derive elemental abundances for the ejecta. We find the following abundances, relative to solar material: He = 1.3, C = 2.5, N = 132, O = 14, Ne = 247, Mg = 7.9, Al = 60 and Si = 22. These results are based on independent fits to three different dates of observation, spanning six months. We find a high N/O ratio which is indicative of an outburst on a massive white dwarf.
V838 Her and V4160 Sgr were two of the fastest classical novae ever observed, exhibiting light curve declines of 2 mag in less than 2 days. Both novae also showed strong neon emission lines, ...indicative of an outburst occurring on an oxygen-neon-magnesium white dwarf. Being the brighter of the two, V838 Her has an extensive set of X-ray to radio observations obtained during its first year after outburst. V4160 Sgr has a more modest set of ultraviolet and optical spectra, which show it to be similar to V838 Her, not just in its light curve evolution but also in its spectral development. The observed attributes imply that these novae occurred on extremely massive white dwarfs. This paper uses the Cloudy photoionization code to fit multiple epochs of emission line spectra to determine the elemental abundances of the ejecta of V838 Her and V4160 Sgr.
We present an analysis of optical and UV spectra of the fast nova V838 Herculis 1991. IUE observations began on 1991 March 25 and continued through 1991 August 20, while optical observations began on ...1991 March 29 and continued through 1991 August 20. We determine a value for the reddening of E (B − V) ~ 0.5 ± 0.1 and a distance of ~ 3 ± l kpc based both on our own observations and on those of other groups. This nova was remarkable in being both fast and optically thick in the UV at maximum light. Our spectra show strong lines of helium, neon, sulphur and nitrogen. In contrast, oxygen lines were never present in our UV spectra and very weak in our optical spectra. We use a new optimization method to perform an abundance analysis of the spectra, and find that carbon, nitrogen, neon, silicon and sulphur are overabundant with respect to solar material by factors ranging from 5 to 37, while helium and oxygen are both underabundant by a factor of 0.3. Our best model is obtained with a luminosity for the central source of 5.1 × 1036 erg s−1, indicating that this nova may have turned off by two months after outburst. We also find an ejected mass for this nova of Mej ~ 1.8 × 10−4 M⊙. Based on both the characteristics of the outburst and our observed abundances, we suggest that this outburst occurred on a very massive ONeMg white dwarf.
We report the detection of a new source of very high energy (VHE; unk greater than or equal to 100 Gev) Y-ray emission located close to the Galactic plane, MA J0616+225, which is spatially coincident ...with supernova remnant IC 443. The observations were carried out with the MAGIC telescope unk 2005 December-2006 January and 2006 December-2007 January. Here we present results from this source, leading to a VHE Y-ray unk statistical significance of 5.7 sigma in the 2006/2007 data and a measured differential Y-ray flux consistent with a power law, described as unk(dAdtdE) = (1.0 plus or minus 0.2) x 10 super(11)(E/0.4TeV)-3.1 plus or minus 0.3 cm super(-2) s super(-1) Tev super(-1). we briefly discuss the observational technique used and the unk implemented for the data analysis. The results are placed in the context of the multiwavelength emission and the molecular environment region of IC 443.
This paper reports the observation and interpretation of the ultraviolet spectrum variations of nine helium-strong stars: HD 36485, 37017, 37479, 37776, 58260, 60344, 64740, 96446, and 133518. A ...unified model is developed to account for the observed correlation among three stellar properties: the line profile characteristics of the C IV and Si IV resonance doublets, the variations in the strength of these lines, and the inferred magnetic field geometry. It is proposed that circumstellar plasma is trapped in the stellar magnetosphere near the magnetic equator or is channeled to form jetlike outflows from the magnetic polar regions. These results, together with those of a previous study of the helium-weak sn stars, show that both helium-weak and helium-strong stars can possess magnetospherically trapped plasma, notwithstanding their different photospheric properties. New results for radii and temperatures of the helium-strong stars in Ori OB 1 and for HD 64740 from low-dispersion IUE spectra are also presented.
Very high energy (VHE) Delta *g-ray emission from the flat spectrum radio quasar (FSRQ) PKS 1222+21 (4C 21.35, z = 0.432) was detected with the MAGIC Cherenkov telescopes during a short observation ...(~0.5 hr) performed on 2010 June 17. The MAGIC detection coincides with high-energy MeV/GeV Delta *g-ray activity measured by the Large Area Telescope (LAT) on board the Fermi satellite. The VHE spectrum measured by MAGIC extends from about 70 GeV up to at least 400 GeV and can be well described by a power-law dN/dE E -- Delta *G with a photon index Delta *G = 3.75 ? 0.27stat ? 0.2syst. The averaged integral flux above 100 GeV is (4.6 ? 0.5) X 10--10 cm--2 s--1 (~1 Crab Nebula flux). The VHE flux measured by MAGIC varies significantly within the 30 minute exposure implying a flux doubling time of about 10 minutes. The VHE and MeV/GeV spectra, corrected for the absorption by the extragalactic background light (EBL), can be described by a single power law with photon index 2.72 ? 0.34 between 3 GeV and 400 GeV, and is consistent with emission belonging to a single component in the jet. The absence of a spectral cutoff constrains the Delta *g-ray emission region to lie outside the broad-line region, which would otherwise absorb the VHE Delta *g-rays. Together with the detected fast variability, this challenges present emission models from jets in FSRQs. Moreover, the combined Fermi/LAT and MAGIC spectral data yield constraints on the density of the EBL in the UV-optical to near-infrared range that are compatible with recent models.
We determine the elemental abundances for the ejecta of the slow nova PWVul 1984. Our technique uses a minimization of the emission-line fits of a photoionization model to available ultraviolet, ...optical and infrared spectra. We find the following abundances (by number) with respect to solar: He/H = 1.0 ± 0.4, C/H = 7.−4+7, N/H = −41+59 and O/H = 6−2+7. In addition, there is weak evidence for solar Ne and Mg, and for twice solar Fe. Previous studies of PW Vul by Saizar et al. and Andreä et al. yielded considerable differences in their derived elemental abundances for the ejecta. Our abundances fall in between those found in the previous studies. To explain the discrepant abundances, we analyse in detail the data and methods used to obtain the previous results. The abundances found by Saizar et al. are significantly smaller than our values because of the lower electron temperature used by them in deriving elemental abundances from ion abundances. Andreä et al. used an ionization correction method to obtain their abundances and later verified their results with a photoionization model. Our analysis of their data shows that the absolute fluxes of the optical emission lines used by Andreä et al. are underestimated by 15 per cent, leading to a factor of 2 increase in their derived abundances. We also find that the photoionization model used by Andreä et al. predicts twice as much carbon as the photoionization code we used even when fitting the same data with similar model parameters.
Elemental abundances for Nova LMC 1990#1 Vanlandingham, Karen M.; Starrfield, Sumner; Shore, Steven N. ...
Monthly notices of the Royal Astronomical Society,
09/1999, Letnik:
308, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present our analysis of the UV spectra of the fast ONeMg Nova LMC 1990#1. Observations with the IUE began on 1990 January 18 and continued through to 1990 March 15. We have analysed these spectra, ...and determined line fluxes and physical parameters as a function of time. Using both He ii lines and the Balmer decrement, we find the reddening for the nova to be E(B−V)≃0.22. Using the photoionization code cloudy 90.03b and the minimization routine minuit, we derive elemental abundances for the ejecta. We find the following abundances, relative to solar material: He=1, C=8, N=109, O=20, Ne=62, Mg=16, Al=257 and Si=41. These results are based on independent fits to different data sets acquired three weeks apart. These abundances are extremely similar to those found for V693 Corona Austrinae 1981. Given the position of V693 CrA in the Galaxy and the range of distances found for it, the similar abundances imply that the V693 CrA outburst took place on an older population white dwarf. The high N/O ratio implies an outburst on a massive white dwarf.
Context. We present the results of a multi-year monitoring campaign of the Galactic center (GC) with the MAGIC telescopes. These observations were primarily motivated by reports that a putative gas ...cloud (G2) would be passing in close proximity to the super-massive black hole (SMBH), associated with Sagittarius A*, located at the center of our galaxy. This event was expected to give astronomers a unique chance to study the effect of in-falling matter on the broad-band emission of a SMBH. Aims. We search for potential flaring emission of very-high-energy (VHE; ≥100 GeV) gamma rays from the direction of the SMBH at the GC due to the passage of the G2 object. Using these data we also study the morphology of this complex region. Methods. We observed the GC region with the MAGIC Imaging Atmospheric Cherenkov Telescopes during the period 2012–2015, collecting 67 h of good-quality data. In addition to a search for variability in the flux and spectral shape of the GC gamma-ray source, we use a point-source subtraction technique to remove the known gamma-ray emitters located around the GC in order to reveal the TeV morphology of the extended emission inside that region. Results. No effect of the G2 object on the VHE gamma-ray emission from the GC was detected during the 4 yr observation campaign. We confirm previous measurements of the VHE spectrum of Sagittarius A*, and do not detect any significant variability of the emission from the source. Furthermore, the known VHE gamma-ray emitter at the location of the supernova remnant G0.9+0.1 was detected, as well as the recently discovered VHE source close to the GG radio arc.
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