634 research outputs found
New light curves and ephemeris for the close eclipsing binary V963 PER
We have obtained CCD photometry in 2010-11 of V963 Per (=GSC3355 0394), which
is a recently identified close binary star with unequal eclipse depths. The
seven new eclipse timings yield an improved ephemeris, but we caution that
secondary eclipse can be affected by variation of the light curve. This
variation seems to be on a monthly timescale at the few percent level.Comment: 6 pages, 3 figure
Population Futures for Europe: An Analysis of Alternative Scenarios
Population projections using arbitrary assumptions are made by many agencies, national and international, and there is no obvious need for one more set. But what distinguishes the projections of this Working Paper is the extremely wide range of assumptions in regard to births, deaths and migration with which the authors experimented. Moreover, they give a more explicit rationale for their assumptions than is commonly presented.
In effect the paper answers such questions as "What if we have a new baby boom, short but intense, comparable to that of the 1950s?" "What if mortality improves spectacularly, not only at the ages to which people have lived up to now, but far beyond those ages, say though discovery of a magic drug?" On the other hand they also ask "What happens if some vast epidemic, such as AIDS, ravages the population of Europe?"
Its imaginative assumptions are unlikely to be fulfilled, but none of them is impossible. This new set of perspectives goes beyond the more conventional projections that are currently in print in displaying what may happen in the future
Demographic Aspects of Changes in the Soviet Pension System
The paper discusses the consequences of possible demographic changes in the USSR as a whole and at the regional level upon the pension system under different assumptions about retirement ages. Some general recommendations on changes in the pension system based on international experience are presented
All conformally flat pure radiation metrics
The complete class of conformally flat, pure radiation metrics is given,
generalising the metric recently given by Wils.Comment: 7 pages, plain Te
Discovery of a Very Young Field L Dwarf, 2MASS J01415823-4633574
While following up L dwarf candidates selected photometrically from the Two
Micron All Sky Survey, we uncovered an unusual object designated 2MASS
J01415823-4633574. Its optical spectrum exhibits very strong bands of vanadium
oxide but abnormally weak absorptions by titanium oxide, potassium, and sodium.
Morphologically such spectroscopic characteristics fall intermediate between
old, field early-L dwarfs (log(g)~5) and very late M giants (log(g)~0), leading
us to favor low gravity as the explanation for the unique spectral signatures
of this L dwarf. Such a low gravity can be explained only if this L dwarf is
much lower in mass than a typical old field L dwarf of similar temperature and
is still contracting to its final radius. These conditions imply a very young
age. Further evidence of youth is found in the near-infrared spectrum,
including a triangular-shaped H-band continuum reminiscent of young brown dwarf
candidates discovered in the Orion Nebula Cluster. Using the above information
along with comparisons to brown dwarf atmospheric and interior models, our
current best estimate is that this L dwarf has an age of 1-50 Myr and a mass of
6-25 M_Jupiter. The location of 2MASS 0141-4633 on the sky coupled with a
distance estimate of ~35 pc and the above age estimate suggests that this
object may be a brown dwarf member of either the 30-Myr-old Tucana/Horologium
Association or the ~12-Myr-old beta Pic Moving Group.Comment: Accepted for publication in the 10 March 2006 issue (volume 639) of
the Astrophysical Journa
V371 Per - A Thick-Disk, Short-Period F/1O Cepheid
V371 Per was found to be a double-mode Cepheid with a fundamental mode period
of 1.738 days, the shortest among Galactic beat Cepheids, and an unusually high
period ratio of 0.731, while the other Galactic beat Cepheids have period
ratios between 0.697 and 0.713. The latter suggests that the star has a
metallicity [Fe/H] between -1 and -0.7. The derived distance from the Galactic
Plane places it in the Thick Disk or the Halo, while all other Galactic beat
Cepheids belong to the Thin Disk. There are indications from historical data
that both the fundamental and first overtone periods have lengthened.Comment: Accepted for publication in MNRA
Photometry of GSC 762-110, a new triple-mode radially pulsating star
Stars pulsating in three radial modes are very rare; only three examples are
known in the Galaxy. These stars are very useful since their periods may be
measured very precisely, and this will constrain the global stellar parameters
and the models of the star's interior. The purpose of this paper is to present
a new example of the class of triple-mode radial pulsators. A search for
candidate multi-mode pulsators was carried out in public survey data.
Time-series photometry of one of the candidates, GSC 762-110, was performed.
GSC 762-110 was found to be a triple-mode radial pulsator, with a fundamental
period of 0.1945d and period ratios of 0.7641 and 0.8012. In addition two
non-radial modes were found, for which the amplitude has diminished
considerably over the last few years.Comment: Accepted for publication in Astronomy & Astrophysic
Interpreting a conformally flat pure radiation space-time
A physical interpretation is presented of the general class of conformally
flat pure radiation metrics that has recently been identified by Edgar and
Ludwig. It is shown that, at least in the weak field limit, successive wave
surfaces can be represented as null (half) hyperplanes rolled around a
two-dimensional null cone. In the impulsive limit, the solution reduces to a
pp-wave whose direction of propagation depends on retarded time. In the general
case, there is a coordinate singularity which corresponds to an envelope of the
wave surfaces. The global structure is discussed and a possible vacuum
extension through the envelope is proposed.Comment: 9 pages, Plain TeX, 2 figures. To appear in Class. Quantum Grav.
Reference adde
Fundamental parameters of RR Lyrae stars from multicolour photometry and Kurucz atmospheric models -- II. Adaptation to double-mode stars
Our photometric-hydrodynamic method is generalized to determine fundamental
parameters of multiperiodic radially pulsating stars. We report 302 UBV(RI)_C
Johnson-Kron-Cousins observations of GSC 4868-0831. Using these and published
photometric data of V372 Ser, their metallicity, reddening, distance, mass,
radius, equilibrium luminosity, effective temperature are determined. The
results underline the necessity of using multicolour photometry including an
ultraviolet band to classify properly subgroups of RR Lyrae stars: our U
observations could reveal that GSC 4868-0831 is a subgiant star pulsating in
two radial modes, V372 Ser is a giant star with size and mass of an RRd star.Comment: 10 pages, 4 figures, 5 tables. Accepted for publication in Monthly
Notices RA
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