11 research outputs found
Period-colour and amplitude-colour relations in classical Cepheid variables II: the Galactic Cepheid model
In this paper, we construct full amplitude non-linear hydrodynamical models
of fundamental mode Galactic Cepheids and analyze the resulting theoretical
period-colour and amplitude-colour relations at maximum, mean and minimum
light. These theoretical relations match the general form of the observed
relations well. This agreement is, to some extent, independent of the
mass-luminosity relations used, pulsation code, numerical techniques, details
of the input physics and methods to convert theoretical quantities, such as
bolometric luminosity and temperature, to observational quantities, such as V
band magnitudes or colours. We show that the period-colour and
amplitude-colour properties of fundamental mode Galactic Cepheids with periods
such that can be explained by a simple application of the
Stefan-Boltzmann law and the interaction of the photosphere with the hydrogen
ionization front. We discuss the implications of our results for explaining the
behavior of Galactic Cepheid period-colour, and period-luminosity relations at
mean light.Comment: 13 pages, 11 figures and 5 tables. MNRAS submitte
New X-ray observations of the old nova CP Puppis and of the more recent nova V351 Pup
We present X-ray observations of the field containing Nova Puppis 1942 (CP
Pup) and Nova Puppis 1991 (V351 Pup), done with ASCA in 1998, and with
XMM-Newton in 2005. The X-ray and UV luminosity of CP Pup seem to have remained
approximately constant since the last X-ray observations of the 1980'ies, while
the optical luminosity has decreased. The X-ray properties of this nova are
explained by a high mass white dwarf accreting at low rate, in agreement with
the nova theory given the large amplitude and other characteristics of the 1942
outburst.
Assuming a distance of 1600 pc, the X-ray luminosity of CP Pup is L=2.2 x
10(33) erg/s in the 0.15-10 keV range covered with EPIC, compatible with a
magnetic system. The RGS grating spectrum shows a few prominent emission lines,
and it is fitted with a cooling flow with mass accretion rate mdot <= 1.6 x
10(-10) msol/year. We detected also the O VII complex at 21.6-21.8 A that does
not arise in the cooling flow. Most likely this feature originates in a wind or
in the nova shell. The RGS and EPIC spectra are fitted only with thermal models
with a very high shock temperature, T>60 keV, indicating a white dwarf with
M>1.1 M(sun). The X-ray flux is modulated with the spectroscopic period of 1.47
hours detected in the optical. Since CP Pup is not an eclipsing system, this is
better understood if magnetic accretion occurs: we discuss this possibility and
its implications in detail. V351 Pup (N Pup 1991) was detected with XMM-Newton,
but not with ASCA. It is a faint, non-super-soft X-ray source with luminosity
L(x) =~ 3 x 10(31) erg/s, a factor of 50 less than measured with ROSAT in 1993.Comment: in press on the Astrophysical Journa
Catalog of 93 Nova Light Curves: Classification and Properties
We present a catalog of 93 very-well-observed nova light curves. The light
curves were constructed from 229,796 individual measured magnitudes, with the
median coverage extending to 8.0 mag below peak and 26% of the light curves
following the eruption all the way to quiescence. Our time-binned light curves
are presented in figures and as complete tabulations. We also calculate and
tabulate many properties about the light curves, including peak magnitudes and
dates, times to decline by 2, 3, 6, and 9 magnitudes from maximum, the time
until the brightness returns to quiescence, the quiescent magnitude, power law
indices of the decline rates throughout the eruption, the break times in this
decline, plus many more properties specific to each nova class. We present a
classification system for nova light curves based on the shape and the time to
decline by 3 magnitudes from peak (t3). The designations are S for smooth light
curves (38% of the novae), P for plateaus (21%), D for dust dips (18%), C for
cusp-shaped secondary maxima (1%), O for quasi-sinusoidal oscillations
superposed on an otherwise smooth decline (4%), F for flat-topped light curves
(2%), and J for jitters or flares superposed on the decline (16%). Our
classification consists of this single letter followed by the t3 value in
parentheses; so for example V1500 Cyg is S(4), GK Per is O(13), DQ Her is
D(100), and U Sco is P(3).Comment: Astronomical Journal, in press, 19 figures, 73 page
The Star Formation History of the Large Magellanic Cloud
We present the first-ever global, spatially-resolved reconstruction of the
star formation history (SFH) of the Large Magellanic Cloud (LMC), based on the
application of our StarFISH analysis software to the multiband photometry of
twenty million of its stars from the Magellanic Clouds Photometric Survey. The
general outlines of our results are consistent with previously published
results: following an initial burst of star formation, there was a quiescent
epoch from approximately 12 to 5 Gyr ago. Star formation then resumed and has
proceeded until the current time at an average rate of roughly 0.2 solar
masses/yr, with temporal variations at the factor-of-two level. The re-ignition
of star formation about 5 Gyr ago, in both the LMC and SMC, is suggestive of a
dramatic event at that time in the Magellanic system. Among the global
variations in the recent star formation rate are peaks at roughly 2 Gyr, 500
Myr, 100 Myr and 12 Myr. The peaks at 500 Myr and 2 Gyr are nearly coincident
with similar peaks in the SFH of the Small Magellanic Cloud, suggesting a joint
history for these galaxies extending back at least several Gyr. The chemical
enrichment history recovered from our StarFISH analysis is in broad agreement
with that inferred from the LMC's star cluster population, although our
constraints on the ancient chemical enrichment history are weak. We conclude
from the concordance between the star formation and chemical enrichment
histories of the field and cluster populations that the field and cluster star
formation modes are tightly coupled.Comment: 20 pages, with color figures. Accepted for publication in A
Activity cycle of the giant star of Z Andromedae and its spin period
We have reanalyzed the long-term optical light curve (LC) of the symbiotic
star Z Andromedae, covering 112--yr of mostly visual observations. Two strictly
periodic and one quasi-periodic cycles can be identified in this LC. A P1=7550
d quasi periodicity characterizes the repetition time of the outburst episodes
of this symbiotic star. Six such events have been recorded so far. During
quiescence states of the system, i.e. in time intervals between outbursts, the
LC is clearly modulated by a stable coherent period of P2=759.1 d. This is the
well known orbital period of the Z And binary system that have been measured
also spectroscopically. A third coherent period of P3=658.4 d is modulating the
intense fluctuations in the optical brightness of the system during outbursts.
We attribute the trigger of the outbursts phenomenon and the clock that drives
it, to a solar type magnetic dynamo cycle that operates in the convection and
the outer layers of the giant star of the system. We suggest that the intense
surface activity of the giant star during maximum phases of its magnetic cycle
is especially enhanced in one or two antipode regions, fixed in the atmosphere
of the star and rotating with it. Such spots could be active regions around the
North and the South poles of a general magnetic dipole field of the star. The
P3 periodicity is half the beat of the binary orbital period of the system and
the spin period of the giant. The latter is then either 482 or 1790 d. If only
one pole is active on the surface of the giant, P3 is the beat period itself,
and the spin period is 352 d. It could also be 5000 d if the giant is rotating
in retrograde direction. We briefly compare these findings in the LC of Z And
to similar modulations that were identified in the LC of two other prototype
symbiotics, BF Cyg and YY Her.Comment: 9 pages, 4 figures, Accepted for publication in MNRA