The Life of Michael the Synkeltos. Text, Translation and Commentary ed. By M. B. Cunningham

Berger, Albrecht

doi:10.1515/bz-1992-1-216

Cited by 3 publications

(3 citation statements)

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“…Walker (1981) found the visual spectrum of LS IV +10 • 9 to be similar to that of CD-31 • 4800 and concluded that it must be of the same spectral type as CD-31 • 4800. Berger & Fringant (1980) observed low resolution UV spectra from the TD1 satellite and from a comparison with other sdO stars (including CD-31 • 4800) concluded that [CW83] 0904−02 is a sdO star similar to CD-31 • 4800. LSS 1274 was first described as a sdO star by Drilling & Heber (1987).…”

Section: The Sample and Spectral Observationsmentioning

confidence: 99%

A quantitative NLTE analysis of visual and ultraviolet spectra of four helium-rich subdwarf O stars

Schindewolf

Németh

Heber

et al. 2018

A&A

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Aims. Hot subdwarf stars represent a poorly understood late phase of stellar evolution. While binary evolution plays an important role for the formation of B-type subdwarfs (sdB), the origin of the helium dominated subclass of O-type subdwarfs (He-sdO) is still unknown. We search for chemical signatures of their genesis by means of quantitative spectral analyses of high-quality visual and ultraviolet spectra. Methods. Four prototypical He-sdO stars, one belonging to the nitrogen-rich and three to the C-rich subclass, were selected for which archival FUV spectra from the FUSE satellite as well as high-resolution visual and UVA spectra taken with the ESO-UVES/FEROS spectrographs are available. Using Tlusty200/Synspec49 to compute line blanketed-non-local thermodynamic equilibrium (NLTE) model atmospheres and synthetic spectra, atmospheric parameters and the abundances patterns have been derived. The final models included H, He, C, N, O, Ne, Mg, Al, Si, P, S, Fe, and Ni represented by the most detailed model atoms available. Because of the enrichment of either nitrogen or carbon, it turned out, that models including these elements at the appropriate high abundance provide sufficiently accurate approximations to the temperature stratification of full models. Results. No indications for binarity were found, neither radial velocity variations nor photometric evidence for the presence of a companion could be detected. All stars have helium-dominated atmospheres almost free of hydrogen and temperatures between 42 000 K and 47 000 K while their surface gravities lie between log g = 5.4 and 5.7. The abundance pattern of CD-31 • 4800 displays the signatures of CNO burning, while heavier elements are subsolar by about 0.4 dex, except for Ne and Si which are close to solar. The abundance patterns of the C-rich He-sdOs are more complex. A slightly subsolar metallicity is accompanied by N-enrichment and O-deficiency, less pronounced than in CD-31 • 4800. Neon is mildly to strongly enriched, up to a factor of ten with respect to the sun in LS IV +10 • 9. The nickel-to-iron ratio is significantly super-solar. Using spectral energy distributions and Gaia parallaxes the masses of the stars were determined. They are found to scatter around the canonical mass for the core helium flash, although the uncertainties are large. Conclusions. The abundance pattern observed for CD-31 • 4800 is consistent with predictions of models for slow (cold) mergers of pairs of equal mass helium WDs except for the low oxygen abundance observed. Models for composite mergers were considered for the C-rich stars, but predict abundance pattern dissimilar to those determined. [CW83] 0904−02, though, may be a candidate for a composite He-WD merger, as it rotates and appears to be more massive than the other program stars. New evolutionary models for the hot flasher scenario predict abundance patterns similar to those determined for the C-rich stars. Hence, C-rich He-sdO may well result from late He flashes with deep-mixing episodes.Article number, page 2 of 3...

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Section: The Sample and Spectral Observationsmentioning

confidence: 99%

A quantitative NLTE analysis of visual and ultraviolet spectra of four helium-rich subdwarf O stars

Schindewolf

Németh

Heber

et al. 2018

A&A

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“…HW Vir (BD-07 o 3477, HIP 62157, GSC 5528-0629) was first classified as a subdwarf B (sdB) star by Berger & Frigant (1980) and was discovered to be a very short-period eclipsing variable with a period of about 2.8 hours, T 1 =26,000 K and T 2 =4,500 K, and relative polar radii (in units of the separation) of r 1 =0.203 and r 2 =0.207 by Menzies & Marang (1986). Since then, the binary system has been the topic of several investigations and its observational history was reviewed in a recent paper byİbanoglu et al (2004).…”

Section: History Of Hw Virginismentioning

confidence: 99%

THE sdB+M ECLIPSING SYSTEM HW VIRGINIS AND ITS CIRCUMBINARY PLANETS

Lee

Kim

et al. 2009

The Astronomical Journal

210

196

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For the very short-period sdB eclipsing binary HW Vir, we present new CCD photometry made from 2000 through 2008. In order to obtain consistency of the binary parameters, our new light curves, showing sharp eclipses and a striking reflection effect, were analyzed simultaneously with previously published radial-velocity data. The secondary star parameters of M 2 =0.14 M ⊙ , R 2 =0.18 R ⊙ , and T 2 =3,084 K are consistent with those of an M6-7 main sequence star. A credibility issue regarding bolometric corrections is emphasized. More than 250 times of minimum light, including our 41 timings and spanning more than 24 yrs, were used for a period study. From a detailed analysis of the O-C diagram, it emerged that the orbital period of HW Vir has varied as a combination of a downward-opening parabola and two sinusoidal variations, with cycle lengths of P 3 =15.8 yr and P 4 =9.1 yr and semi-amplitudes of K 3 =77 s and K 4 =23 s, respectively. The continuous period decrease with a rate of −8.28×10 −9 d yr −1 may be produced by angular momentum loss due to magnetic stellar wind braking but not by gravitational radiation. Of the possible causes of the cyclical components of the period change, apsidal motion and magnetic period modulation can be ruled out. The most reasonable explanation of both cyclical variations is a pair of light-travel-time effects driven by the presence of two substellar companions with projected masses of M 3 sin i 3 =19.2 M Jup and M 4 sin i 4 =8.5 M Jup . The two objects are the first circumbinary planets known to have been formed in a protoplanetary disk as well the first ones discovered by using the eclipse-timing method. The detection implies that planets could be common around binary stars just as are planets around single stars and demonstrates that planetary systems formed in a circumbinary disk can survive over long time scales.Depending on the thermal inertia of their massive atmospheres, the hemispheres of the planets turned toward the stars can experience substantial reciprocating temperature changes during the minutes-long primary eclipse intervals.

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“…The star, known variously as TD1 31206 = TD1 32707 (Thompson et al 1978) = UVO 0825+15 (Berger & Fringant 1980) = [CW83] 0825+15 (Carnochan & Wilson 1983) = TYC 808-490-1 = GALEX J082832.8+145205 = 2MASS J08283287+1452024 = EPIC 211623711, was classified "sdO" by Berger & Fringant (1980) and Kilkenny (1988). The equatorial coordinates for epoch J2000 and equinox 2000 are α = 08h28m32.876s, δ = +14 • 52 02.51 .…”

Section: Introductionmentioning

confidence: 99%

Discovery of a variable lead-rich hot subdwarf: UVO 0825+15

Jeffery

Baran

Behara

et al. 2016

Mon. Not. R. Astron. Soc.

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UVO 0825+15 is a hot bright helium-rich subdwarf which lies in K2 Field 5 and in a sample of intermediate helium-rich subdwarfs observed with Subaru/HDS. The K2 light curve shows low-amplitude variations, whilst the Subaru spectrum shows Pbiv absorption lines, indicative of a very high lead overabundance. UVO 0825+15 also has a high proper motion with kinematics typical for a thick disk star. Analyses of ultraviolet and intermediate dispersion optical spectra rule out a short-period binary companion, and provide fundamental atmospheric parameters of T eff = 38 900±270 K, log g/cm s −2 = 5.97 ± 0.11, log n He /n H = −0.57 ± 0.01, E B−V ≈ 0.03, and angular radius θ = 1.062±0.006×10−11 radians (formal errors). The high-resolution spectrum shows that carbon is > 2 dex subsolar, iron is approximately solar and all other elements heavier than argon are at least 2 -4 dex overabundant, including germanium, yttrium and lead. Approximately 150 lines in the blue-optical spectrum remain unidentified. The chemical structure of the photosphere is presumed to be determined by radiatively-dominated diffusion. The K2 light curve shows a dominant period around 10.8 h, with a variable amplitude, its first harmonic, and another period at 13.3 h. The preferred explanation is multi-periodic non-radial oscillation due to g-modes with very high radial order, although this presents difficulties for pulsation theory. Alternative explanations fail for lack of radial-velocity evidence. UVO 0825+15 represents the fourth member of a group of hot subdwarfs having helium-enriched photospheres and 3-4 dex overabundances of trans-iron elements, and is the first lead-rich subdwarf to show evidence of pulsations.

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The Life of Michael the Synkeltos. Text, Translation and Commentary ed. By M. B. Cunningham

Cited by 3 publications

References 0 publications

A quantitative NLTE analysis of visual and ultraviolet spectra of four helium-rich subdwarf O stars

A quantitative NLTE analysis of visual and ultraviolet spectra of four helium-rich subdwarf O stars

THE sdB+M ECLIPSING SYSTEM HW VIRGINIS AND ITS CIRCUMBINARY PLANETS

Discovery of a variable lead-rich hot subdwarf: UVO 0825+15

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