256 research outputs found
SCHNELLE BERECHNUNG DER IMPEDANZ VON PARALLELEN, VON STROMVERDRĂNGUNGS- (VOM HAUPTSTROM NICHT DURCHFLOSSENEN) SOWIE VON REIHENSCHLUSS-(NORMALEN) STĂBEN MIT HILFE KOMPLEXER FUNKTIONSKURVEN
Theoretical Modeling of the Thermal State of Accreting White Dwarfs Undergoing Classical Novae
White dwarfs experience a thermal renaissance when they receive mass from a
stellar companion in a binary. For accretion rates < 10^-8 Msun/yr, the freshly
accumulated hydrogen/helium envelope ignites in a thermally unstable manner
that results in a classical novae (CN) outburst and ejection of material. We
have undertaken a theoretical study of the impact of the accumulating envelope
on the thermal state of the underlying white dwarf (WD). This has allowed us to
find the equilibrium WD core temperatures (T_c), the classical nova ignition
masses (M_ign) and the thermal luminosities for WDs accreting at rates of
10^-11 - 10^-8 Msun/yr. These accretion rates are most appropriate to WDs in
cataclysmic variables (CVs) of P_orb <~ 7 hr, many of which accrete
sporadically as dwarf novae. We have included ^3He in the accreted material at
levels appropriate for CVs and find that it significantly modifies the CN
ignition mass. We compare our results with several others from the CN
literature and find that the inclusion of ^3He leads to lower M_ign for
>~ 10^-10 Msun/yr, and that for below this the particular author's
assumption concerning T_c, which we calculate consistently, is a determining
factor. Initial comparisons of our CN ignition masses with measured ejected
masses find reasonable agreement and point to ejection of material comparable
to that accreted.Comment: 14 pages, 11 figures; uses emulateapj; accepted by the Astrophysical
Journal; revised for clarity, added short discussion of diffusio
The 2005 July Superoutburst of the Dwarf Nova 2QZ J021927.9-304545: the SU UMa Nature Confirmed
We report on time-resolved photometry of the 2005 July superoutburst of the
dwarf nova, 2QZ J021927.9-304545. The resultant light curves showed conspicuous
superhumps with a period of 0.081113(19) days, confirming the SU UMa nature of
the object. Although we missed the maximum phase of the outburst, the amplitude
of the superoutburst well exceeded 5 mag. This value is slightly larger than
that of typical SU UMa-type dwarf novae. The superhump period decreased as time
elapsed, as can be seen in most SU UMa-type dwarf novae. Based on the archive
of ASAS-3, the recurrence time of a superoutburst of the variable turned out to
be about 400 days. This value is typical of well known SU UMa stars. The
distance to this system was roughly estimated as 370(+20, -60) pc using an
empirical relation.Comment: 6 pages, 7 figures, accepted for publication in PAS
A cyclical period variation detected in the updated orbital period analysis of TV Columbae
The two CCD photometries of the intermediate polar TV Columbae are made for
obtaining the two updated eclipse timings with high precision. There is an
interval time \sim 17yr since the last mid-eclipse time observed in 1991. Thus,
the new mid-eclipse times can offer an opportunity to check the previous
orbital ephemerides. A calculation indicates that the orbital ephemeris derived
by Augusteijn et al. (1994) should be corrected. Based on the proper linear
ephemeris (Hellier, 1993), the new orbital period analysis suggests a cyclical
period variation in the O-C diagram of TV Columbae. Using Applegate's mechanism
to explain the periodic oscillation in O-C diagram, the required energy is
larger than that a M0-type star can afford over a complete variation period
\sim 31.0(\pm 3.0)yr. Thus, the light travel-time effect indicates that the
tertiary component in TV Columbae may be a dwarf with a low mass, which is near
the mass lower limit \sim 0.08Msun as long as the inclination of the third body
high enough.Comment: 10 pages, 5 figure
Solar-like oscillations in the metal-poor subgiant nu Indi: II. Acoustic spectrum and mode lifetime
Convection in stars excites resonant acoustic waves which depend on the sound
speed inside the star, which in turn depends on properties of the stellar
interior. Therefore, asteroseismology is an unrivaled method to probe the
internal structure of a star. We made a seismic study of the metal-poor
subgiant star nu Indi with the goal of constraining its interior structure. Our
study is based on a time series of 1201 radial velocity measurements spread
over 14 nights obtained from two sites, Siding Spring Observatory in Australia
and ESO La Silla Observatory in Chile. The power spectrum of the high precision
velocity time series clearly presents several identifiable peaks between 200
and 500 uHz showing regularity with a large and small spacing of 25.14 +- 0.09
uHz and 2.96 +- 0.22 uHz at 330 uHz. Thirteen individual modes have been
identified with amplitudes in the range 53 to 173 cm/s. The mode damping time
is estimated to be about 16 days (1-sigma range between 9 and 50 days),
substantially longer than in other stars like the Sun, the alpha Cen system or
the giant xi Hya.Comment: 5 pages, 7 figures, A&A accepte
Outbursts on normal stars. FH Leo misclassified as a novalike variable
We present high resolution spectroscopy of the common proper motion system FH
Leo (components HD 96273 and BD+07 2411B), which has been classified as a
novalike variable due to an outburst observed by Hipparcos, and we present and
review the available photometry. We show from our spectra that neither star can
possibly be a cataclysmic variable, instead they are perfectly normal late-F
and early-G stars. We measured their radial velocities and derived the
atmospheric fundamental parameters, abundances of several elements including
Fe, Ni, Cr, Co, V, Sc, Ti, Ca and Mg, and we derive the age of the system. From
our analysis we conclude that the stars do indeed constitute a physical binary.
However, the observed outburst cannot be readily explained. We examine several
explanations, including pollution with scattered light from Jupiter, binarity,
microlensing, background supernovae, interaction with unseen companions and
planetary engulfment. While no explanation is fully satisfactory, the scattered
light and star-planet interaction scenarios emerge as the least unlikely ones,
and we give suggestions for further study.Comment: 8 pages, 7 figures. Accepted for publication in A&
Magnetic Interaction in Ultra-compact Binary Systems
This article reviews the current works on ultra-compact double-degenerate
binaries in the presence of magnetic interaction, in particular, unipolar
induction. The orbital dynamics and evolution of compact white-dwarf pairs are
discussed in detail. Models and predictions of electron cyclotron masers from
unipolar-inductor compact binaries and unipolar-inductor white-dwarf planetary
systems are presented. Einstein-Laub effects in compact binaries are briefly
discussed.Comment: invited review, accepted for publication in Research in Astronomy and
Astrophysics (RAA
Swift X-ray Observations of Classical Novae
The new gamma-ray burst mission Swift has obtained pointed observations of
several classical novae in outburst. We analyzed all the observations of
classical novae from the Swift archive up to 30 June, 2006. We analyzed usable
observations of 12 classical novae and found 4 non-detections, 3 weak sources
and 5 strong sources. This includes detections of 2 novae exhibiting spectra
resembling those of Super Soft X-ray binary Source spectra (SSS) implying
ongoing nuclear burning on the white dwarf surface. With these new Swift data,
we add to the growing statistics of the X-ray duration and characteristics of
classical novae.Comment: Accepted for ApJ; this version contains additional material: 18
pages, 16 figure
CAFF CBMP Report No. 9: Community-based Monitoring â a discussion paper
Community-based Monitoring â a discussion paper. Supporting publication to the CAFF Circumpolar Biodiversity Monitoring Program â Framework Document. CAFF CBMP Report No.
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