61 research outputs found
Ordinary morality does not imply atheism
Many theist as well as many atheist philosophers have maintained that if
God exists, then every instance of undeserved, unwanted suffering ultimately
benefits the sufferer. Recently, several authors have argued that this implication of
theism conflicts with ordinary morality. I show that these arguments all rest on a
common mistake. Defenders of these arguments overlook the role of merely
potential instances of suffering in determining our moral obligations toward
suffering
Stellar model atmospheres with magnetic line blanketing. III. The role of magnetic field inclination
Context. See abstract in the paper.
Aims. In the last paper of this series we study the effects of the magnetic
field, varying its strength and orientation, on the model atmosphere structure,
the energy distribution, photometric colors and the hydrogen Balmer line
profiles. We compare with the previous results for an isotropic case in order
to understand whether there is a clear relation between the value of the
magnetic field angle and model changes, and to study how important the
additional orientational information is. Also, we examine the probable
explanation of the visual flux depressions of the magnetic chemically peculiar
stars in the context of this work.
Methods. We calculated one more grid of the model atmospheres of magnetic A
and B stars for different effective temperatures (Teff=8000K, 11000K, 15000K),
magnetic field strengths (B=0, 5, 10, 40 kG) and various angles of the magnetic
field (Omega=0-90 degr) with respect to the atmosphere plane. We used the
LLmodels code which implements a direct method for line opacity calculation,
anomalous Zeeman splitting of spectral lines, and polarized radiation transfer.
Results. We have not found significant changes in model atmosphere structure,
photometric and spectroscopic observables or profiles of hydrogen Balmer lines
as we vary the magnetic field inclination angle Omega. The strength of the
magnetic field plays the main role in magnetic line blanketing. We show that
the magnetic field has a clear relation to the visual flux depressions of the
magnetic CP stars.
Conclusions. See abstract in the paper.Comment: 10 pages, 5 figure
Search for low instability strip variables in the young open cluster NGC 2516
In this paper we revise and complete the photometric survey of the
instability strip of the southern open cluster NGC 2516 published by Antonello
and Mantegazza (1986). No variable stars with amplitudes larger than
were found. However by means of an accurate analysis based on a new statistical
method two groups of small amplitude variables have been disentangled: one with
periods (probably Scuti stars) and one with periods
. The position in the HR diagram and the apparent time-scale may
suggest that the stars of the second group belong to a recently discovered new
class of variables, named Dor variables. They certainly deserve
further study. We also present a comparison between the results of the
photometric survey and the available pointed ROSAT observations of this
cluster.Comment: 7 pages, 2 ps figures. Accepted for P.A.S.
Stellar model atmospheres with magnetic line blanketing
Model atmospheres of A and B stars are computed taking into account magnetic
line blanketing. These calculations are based on the new stellar model
atmosphere code LLModels which implements direct treatment of the opacities due
to the bound-bound transitions and ensures an accurate and detailed description
of the line absorption. The anomalous Zeeman effect was calculated for the
field strengths between 1 and 40 kG and a field vector perpendicular to the
line of sight. The model structure, high-resolution energy distribution,
photometric colors, metallic line spectra and the hydrogen Balmer line profiles
are computed for magnetic stars with different metallicities and are discussed
with respect to those of non-magnetic reference models. The magnetically
enhanced line blanketing changes the atmospheric structure and leads to a
redistribution of energy in the stellar spectrum. The most noticeable feature
in the optical region is the appearance of the 5200 A depression. However, this
effect is prominent only in cool A stars and disappears for higher effective
temperatures. The presence of a magnetic field produces opposite variation of
the flux distribution in the optical and UV region. A deficiency of the UV flux
is found for the whole range of considered effective temperatures, whereas the
``null wavelength'' where flux remains unchanged shifts towards the shorter
wavelengths for higher temperatures.Comment: accepted by Astronomy & Astrophysic
vbyCaHbeta CCD Photometry of Clusters. VI. The Metal-Deficient Open Cluster NGC 2420
CCD photometry on the intermediate-band vbyCaHbeta system is presented for
the metal-deficient open cluster, NGC 2420. Restricting the data to probable
single members of the cluster using the CMD and the photometric indices alone
generates a sample of 106 stars at the cluster turnoff. The average E(b-y) =
0.03 +/- 0.003 (s.e.m.) or E(B-V) = 0.050 +/- 0.004 (s.e.m.), where the errors
refer to internal errors alone. With this reddening, [Fe/H] is derived from
both m1 and hk, using b-y and Hbeta as the temperature index. The agreement
among the four approaches is reasonable, leading to a final weighted average of
[Fe/H] = -0.37 +/- 0.05 (s.e.m.) for the cluster, on a scale where the Hyades
has [Fe/H] = +0.12. When combined with the abundances from DDO photometry and
from recalibrated low-resolution spectroscopy, the mean metallicity becomes
[Fe/H] = -0.32 +/- 0.03. It is also demonstrated that the average cluster
abundances based upon either DDO data or low-resolution spectroscopy are
consistently reliable to 0.05 dex or better, contrary to published attempts to
establish an open cluster metallicity scale using simplistic offset corrections
among different surveys.Comment: scheduled for Jan. 2006 AJ; 33 pages, latex, includes 7 figures and 2
table
Searching for links between magnetic fields and stellar evolution. II. The evolution of magnetic fields as revealed by observations of Ap stars in open clusters and associations
The evolution of magnetic fields in Ap stars during the main sequence phase
is presently mostly unconstrained by observation because of the difficulty of
assigning accurate ages to known field Ap stars.
We are carrying out a large survey of magnetic fields in cluster Ap stars
with the goal of obtaining a sample of these stars with well-determined ages.
In this paper we analyse the information available from the survey as it
currently stands.
We select from the available observational sample the stars that are probably
(1) cluster or association members and (2) magnetic Ap stars. For the stars in
this subsample we determine the fundamental parameters T_eff, log(L/L_o), and
M/M_o. With these data and the cluster ages we assign both absolute age and
fractional age (the fraction of the main sequence lifetime completed). For this
purpose we have derived new bolometric corrections for Ap stars.
Magnetic fields are present at the surfaces of Ap stars from the ZAMS to the
TAMS. Statistically for the stars with M > 3 M_o the fields decline with
advancing age approximately as expected from flux conservation together with
increased stellar radius, or perhaps even faster than this rate, on a time
scale of about 3 10^7 yr. In contrast, lower mass stars show no compelling
evidence for field decrease even on a timescale of several times 10^8 yr.
Study of magnetic cluster stars is now a powerful tool for obtaining
constraints on evolution of Ap stars through the main sequence. Enlarging the
sample of known cluster magnetic stars, and obtaining more precise RMS fields,
will help to clarify the results obtained so far. Further field observations
are in progress.Comment: Accepted by Astronomy & Astrophysic
Searching for links between magnetic fields and stellar evolution III. Measurement of magnetic fields in open cluster Ap stars with ESPaDOnS
We are carrying out a survey of magnetic fields in Ap stars in open clusters
in order to obtain the first sample of magnetic upper main sequence stars with
precisely known ages. These data will constrain theories of field evolution in
these stars. Using the new spectropolarimeter ESPaDOnS at CFHT, we have
obtained 44 measurements of the mean longitudinal fields of 23 B6 - A2 stars
that have been identified as possible Ap stars and that are possible members of
open clusters, with a median uncertainty of about 45 G. Of these stars, 10 have
definite field detections. Nine stars of our sample are found not to be
magnetic Ap stars. The ESPaDOnS data contain a large amount of useful
information not readily obtained from lower resolution spectropolarimetry. With
the new observations we are able to expand the available data on fields of
low-mass, relatively evolved Ap stars, and identify more robustly which
observed stars are actually magnetic Ap stars and cluster members. Re-analysis
of the enlarged data set of cluster Ap stars indicates that such stars with
masses in the range of 2 -- 5 \mo show RMS fields larger than about 1 kG only
when they are near the ZAMS. The time scale on which these large fields
disappear varies strongly with mass, ranging from about 250 Myr for stars of 2
- 3 solar mass to 15 Myr for stars of 4 - 5 solar mass. Our data are consistent
either with emergent flux conservation for most (but not all) Ap stars, or with
modest decline in flux with age.Comment: accepted by Astronomy & Astrophysic
Multiplicity among chemically peculiar stars II. Cool magnetic Ap stars
We present new orbits for sixteen Ap spectroscopic binaries, four of which
might in fact be Am stars, and give their orbital elements. Four of them are
SB2 systems: HD 5550, HD 22128, HD 56495 and HD 98088. The twelve other stars
are : HD 9996, HD 12288, HD 40711, HD 54908, HD 65339, HD 73709, HD 105680, HD
138426, HD 184471, HD 188854, HD 200405 and HD 216533. Rough estimates of the
individual masses of the components of HD 65339 (53 Cam) are given, combining
our radial velocities with the results of speckle interferometry and with
Hipparcos parallaxes. Considering the mass functions of 74 spectroscopic
binaries from this work and from the literature, we conclude that the
distribution of the mass ratio is the same for cool Ap stars as for normal G
dwarfs. Therefore, the only differences between binaries with normal stars and
those hosting an Ap star lie in the period distribution: except for the case of
HD 200405, all orbital periods are longer than (or equal to) 3 days. A
consequence of this peculiar distribution is a deficit of null eccentricities.
There is no indication that the secondary has a special nature, like e.g. a
white dwarf.Comment: 31 pages, 15 figures, A&A accepte
Is diversity good?
Prominent ethical and policy issues such as affirmative action and female
enrollment in science and engineering revolve around the idea that diversity is
good. However, even though diversity is an ambiguous concept, a precise
definition is seldom provided. We show that diversity may be construed as a
factual description, a craving for symmetry, an intrinsic good, an instrumental
good, a symptom, or a side effect. These acceptions differ vastly in their
nature and properties. The first one cannot lead to any action and the second
one is mistaken. Diversity as intrinsic good is a mere opinion, which cannot be
concretely applied; moreover, the most commonly invoked forms of diversity
(sexual and racial) are not intrinsically good. On the other hand, diversity as
instrumental good can be evaluated empirically and can give rise to policies,
but these may be very weak. Finally, symptoms and side effects are not actually
about diversity. We consider the example of female enrollment in science and
engineering, interpreting the various arguments found in the literature in
light of this polysemy.
Keywords: ethics, policy, higher education, female students, minority
students, affirmative actionComment: 7 page
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