72 research outputs found
Helium Nova on a Very Massive White Dwarf -- A Light Curve Model of V445 Puppis (2000) Revised
V445 Pup (2000) is a unique object identified as a helium nova. Color indexes
during the outburst are consistent with those of free-free emission. We present
a free-free emission dominated light curve model of V445 Pup on the basis of
the optically thick wind theory. Our light curve fitting shows that (1) the
white dwarf (WD) mass is very massive (M_WD \gtrsim 1.35 M_\sun), and (2) a
half of the accreted matter remains on the WD, both of which suggest that the
increasing WD mass. Therefore, V445 Pup is a strong candidate of Type Ia
supernova progenitor. The estimated distance to V445 Pup is now consistent with
the recent observational suggestions, 3.5 < d < 6.5 kpc. A helium star
companion is consistent with the brightness of m_v=14.5 mag just before the
outburst, if it is a little bit evolved hot (\log T (K) \gtrsim 4.5) star with
the mass of M_He \gtrsim 0.8 M_\sun. We then emphasize importance of
observations in the near future quiescent phase after the thick circumstellar
dust dissipates away, especially its color and magnitude to specify the nature
of the companion star. We have also calculated helium ignition masses for
helium shell flashes against various helium accretion rates and discussed the
recurrence period of helium novae.Comment: 8 pages including 12 figures, to appear in Ap
Dust rings and filaments around the isolated young star V1331 Cygni
We characterize the small and large scale environment of the young star V1331
Cygni with high resolution HST/WFPC2 and Digitized Sky Survey images. In
addition to a previously known outer dust ring (~30'' in diameter), the
HST/WFPC2 scattered light image reveals an inner dust ring for the first time.
This ring has a maximum radius of 6.5'' and is possibly related to a molecular
envelope. Large-scale optical images show that V1331 Cyg is located at the tip
of a long dust filament linking it to the dark cloud LDN 981. We discuss the
origin of the observed dust morphology and analyze the object's relation to its
parent dark cloud LDN 981. Finally, based on recent results from the
literature, we investigate the properties of V1331 Cyg and conclude that in its
current state the object does not show suffcient evidence to be characterized
as an FU Ori object.Comment: 15 pages ApJ preprint style including 3 figures, accepted for
publication in ApJ (Feb. 2007
The secondary minimum in YY Her: Evidence for a tidally distorted giant
We present and analyze quiescent UBVRI light curves of the classical
symbiotic binary YY Her. We show that the secondary minimum, which is clearly
visible only in the quiescent VRI light curves, is due to ellipsoidal
variability of the red giant component. Our simple light curve analysis, by
fitting of the Fourier cosine series, resulted in a self-consistent
phenomenological model of YY Her, in which the periodic changes can be
described by a combination of the ellipsoidal changes and a sinusoidal changes
of the nebular continuum and line emission.Comment: 5 pages, 2 figures, to appear in Astronomy & Astrophysic
Flickering in FU Orionis
We analyze new and published optical photometric data of FU Orionis, an
eruptive pre-main sequence star. The outburst consists of a 5.5 mag rise at B
with an e-folding timescale of roughly 50 days. The rates of decline at B and V
are identical, 0.015 +- 0.001 mag per yr. Random fluctuations superimposed on
this decline have an amplitude of 0.035 +- 0.005 mag at V and occur on
timescales of 1 day or less. Correlations between V and the color indices U-B,
B-V, and V-R indicate that the variable source has the optical colors of a G0
supergiant. We associate this behavior with small amplitude flickering of the
inner accretion disk.Comment: 19 pages of text, 3 tables, and 6 figures to be published in the
Astrophysical Journal, 10 March 200
Observations of the 6 Centimeter Lines of OH in Evolved (OH/IR) Stars
Recent observational and theoretical advances have called into question
traditional OH maser pumping models in evolved (OH/IR) stars. The detection of
excited-state OH lines would provide additional constraints to discriminate
amongst these theoretical models. In this Letter, we report on VLA observations
of the 4750 MHz and 4765 MHz lines of OH toward 45 sources, mostly evolved
stars. We detect 4765 MHz emission in the star forming regions Mon R2 and LDN
1084, but we do not detect excited-state emission in any evolved stars. The
flux density and velocity of the 4765 MHz detection in Mon R2 suggests that a
new flaring event has begun.Comment: 4 pages, to appear in ApJ
Влияние способа поддержания проходимости дыхательных путей при эндоскопических риносинусохирургических вмешательствах на кровоточивость в области операционного поля
The objective: to conduct a comparative assessment of the severity of intraoperative bleeding with different methods of airway management (using a laryngeal mask and endotracheal tube) during endoscopic rhinosinussurgical procedures.Subjects and Methods. A prospective randomized cohort single-center study of 160 cases of endoscopic rhinosinussurgical procedures under general anesthesia was conducted.Tracheal intubation (TI) was used in 79 cases (Group 1), a laryngeal mask (LM) – in 81 (Group 2). The evaluation criteria in the groups included the bleeding intensity (BI) by 6-point scale of average categories (Fromme-Boezaart Score), indicators characterizing the state of blood circulation during surgery: HR, BPsys., BPdiast., MAP, and perfusion index.Results. Significantly lower BI values were observed in Group 2 at all time points of the study (at the 10th, 30th and 60th minute of surgery). This was due both to using a laryngeal mask, and to lower HR, BPsys., BPdiast, and MAP.Conclusion. The use of a laryngeal mask for airway management during general anesthesia in endoscopic rhinosinussurgical procedures helps to reduce the intensity of surgical field bleeding.Управление степенью интраоперационного кровотечения играет ведущую роль в улучшении видимости операционного поля и снижении риска осложнений при эндоскопических риносинусохирургических (ЭРСХ) вмешательствах.Цель: провести сравнительную оценку выраженности интраоперационного кровотечения при разных способах поддержания проходимости дыхательных путей (с помощью ларингеальной маски и эндотрахеальной трубки) во время ЭРСХ-вмешательств.Материалы и методы. Проспективное рандомизированное когортное одноцентровое исследование 160 случаев ЭРСХ-вмешательств в условиях общей анестезии. Интубация трахеи (ИТ) использована в 79 случаях (1-я группа), ларингеальная маска (ЛМ) – в 81 (2-я группа). Критерии оценки в группах включали интенсивность кровотечения по 6-балльной шкале средних категорий (Fromme ‒ Boezaart Score) и показатели, характеризующие состояние кровообращения в ходе оперативного вмешательства (ЧСС, АДсист, АДдиаст, САД, перфузионный индекс).Результаты. Значимо меньшие показатели интенсивности кровотечения во всех точках исследования (на 10, 30 и 60-й мин операции) наблюдали во 2-й группе. Это было связано как с самим фактом использования ларингеальной маски, так и с более низкими значениями показателей ЧСС, АДсист, АДдиаст и САД.Вывод. Использование ларингеальной маски для поддержания проходимости дыхательных путей во время общей анестезии при ЭРСХ-вмешательствах способствует уменьшению локальной кровоточивости
Near infrared and the inner regions of protoplanetary disks
We examine the ``puffed-up inner disk'' model (Dullemond, Dominik & Natta
2001), proposed for explaining the near-IR excess radiation from Herbig Ae/Be
stars. Detailed model computations show that the observed near-IR excess
requires more hot dust than is contained in the puffed-up disk rim. The rim can
produce the observed near-IR excess only if its dust has perfectly gray
opacity, but such dust is in conflict with the observed 10m spectral
feature. We find that a compact ( 10 AU) tenuous (\tau_V \la 0.4) dusty
halo around the disk inner regions contains enough dust to readily explain the
observations. Furthermore, this model also resolves the puzzling relationship
noted by Monnier and Millan-Gabet (2002) between luminosity and the
interferometric inner radii of disks.Comment: 14 pages, 10 figures, accepted in Ap
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