1,006 research outputs found
A comparison of the globular cluster luminosity functions of the inner and outer halo of the Milky Way and M31
We show that the globular cluster luminosity function (GCLF) of the inner
halo of the Milky Way is statistically different from the GCLF of the outer
halo. We also find a similar difference between the inner and outer halo
population of M31. We assert that this difference is evidence for some form of
dynamical evolution of the cluster population and/or a dependence of GCLF shape
on the environment in which the cluster population formed. We also find that
the turnover luminosity of the GCLF is unaffected by these differences and
further assert that this stability of the turnover luminosity affirms its
usefulness as an indicator of cosmic distance.Comment: 3 pages, 2 figures, submitted to MNRA
Investigating the pre-main sequence magnetic chemically peculiar system HD 72106
The origin of the strong magnetic fields observed in chemically peculiar Ap
and Bp stars stars has long been debated. The recent discovery of magnetic
fields in the intermediate mass pre-main sequence Herbig Ae and Be stars links
them to Ap and Bp stars, providing vital clues about Ap and Bp stars and the
origin and evolution of magnetic fields in intermediate and high mass stars. A
detailed study of one young magnetic B star, HD 72106A, is presented. This star
appears to be in a binary system with an apparently normal Herbig Ae star. A
maximum longitudinal magnetic field strength of +391 +/- 65 G is found in HD
72106A, as are strong chemical peculiarities, with photospheric abundances of
some elements ranging up to 100x above solar.Comment: 8 pages, 6 figures. Proceeding of the 2006 conference of the Special
Astrophysical Observatory of the Russian Academy of Science
Substructure in the Andromeda Galaxy Globular Cluster System
In the most prominent current scenario of galaxy formation, galaxies form
hierarchically through the merger of smaller systems. Such mergers could leave
behind dynamical signatures which may linger long after the event. In
particular, the globular cluster system (GCS) of a merging satellite galaxy may
remain as a distinct sub-population within the GCS of a massive galaxy. Using
the latest available globular cluster velocities and metallicities, we present
the results of a search for grouping in the GCS of our nearest large spiral
galaxy neighbor, M31. A modified friends-of-friends algorithm is used to
identify a number of possible merger remnants in projected position, radial
velocity and [Fe/H] parameter space. Numerical simulations are used to check
that such merger remnants are indeed plausible over the timescales of interest.
The identification of stellar streams associated with these groups is required
in order to confirm that they represent merger remnants.Comment: 19 pages, 3 figures, accepted for publication in the Ap
Searching for Weak or Complex Magnetic Fields in Polarized Spectra of Rigel
Seventy-eight high-resolution Stokes V, Q and U spectra of the B8Iae
supergiant Rigel were obtained with the ESPaDOnS spectropolarimeter at CFHT and
its clone NARVAL at TBL in the context of the Magnetism in Massive Stars
(MiMeS) Large Program, in order to scrutinize this core-collapse supernova
progenitor for evidence of weak and/or complex magnetic fields. In this paper
we describe the reduction and analysis of the data, the constraints obtained on
any photospheric magnetic field, and the variability of photospheric and wind
lines.Comment: IAUS272 - Active OB Stars: Structure, Evolution, Mass Loss and
Critical Limit
Critical evaluation of magnetic field detections reported for pulsating B-type stars in the light of ESPaDOnS, Narval and reanalyzed FORS1/2 observations
Recent spectropolarimetric studies of 7 SPB and Cep stars have
suggested that photospheric magnetic fields are more common in B-type pulsators
than in the general population of B stars, suggesting a significant connection
between magnetic and pulsational phenomena. We present an analysis of new and
previously published spectropolarimetric observations of these stars. New
Stokes observations obtained with the high-resolution ESPaDOnS and Narval
instruments confirm the presence of a magnetic field in one of the stars
( Lup), but find no evidence of magnetism in 5 others. A re-analysis
of the published longitudinal field measurements obtained with the
low-resolution FORS1/2 spectropolarimeters finds that the measurements of all
stars show more scatter from zero than can be attributed to Gaussian noise,
suggesting the presence of a signal and/or systematic under-estimation of error
bars. Re-reduction and re-measurement of the FORS1/2 spectra from the ESO
archive demonstrates that small changes in reduction procedure lead to
substantial changes in the inferred longitudinal field, and substantially
reduces the number of field detections at the 3 level. Furthermore, we
find that the published periods are not unique solutions to the time series of
either the original or the revised FORS1/2 data. We conclude that the reported
field detections, proposed periods and field geometry models for Pyx,
15 CMa, 33 Eri and V1449 Aql are artefacts of the data analysis and reduction
procedures, and that magnetic fields at the reported strength are no more
common in SPB/ Cep stars than in the general population of B stars.Comment: 10 pages, 5 figures, accepted for publication in ApJ, 2012, typo
correcte
A New Evolutionary Path to Type Ia Supernovae: Helium-Rich Super-Soft X-Ray Source Channel
We have found a new evolutionary path to Type Ia supernovae (SNe Ia) which
has been overlooked in previous work. In this scenario, a carbon-oxygen white
dwarf (C+O WD) is originated, not from an asymptotic giant branch star with a
C+O core, but from a red-giant star with a helium core of . The helium star, which is formed after the first common envelope
evolution, evolves to form a C+O WD of with transferring
a part of the helium envelope onto the secondary main-sequence star. This new
evolutionary path, together with the optically thick wind from mass-accreting
white dwarf, provides a much wider channel to SNe Ia than previous scenarios. A
part of the progenitor systems are identified as the luminous supersoft X-ray
sources or the recurrent novae like U Sco, which are characterized by the
accretion of helium-rich matter. The white dwarf accretes hydrogen-rich,
helium-enhanced matter from a lobe-filling, slightly evolved companion at a
critical rate and blows excess matter in the wind. The white dwarf grows in
mass to the Chandrasekhar mass limit and explodes as an SN Ia. A theoretical
estimate indicates that this channel contributes a considerable part of the
inferred rate of SNe Ia in our Galaxy, i.e., the rate is about ten times larger
than the previous theoretical estimates for white dwarfs with slightly evolved
companions.Comment: 19 pages including 12 figures, to be published in ApJ, 519, No.
The Globular Cluster Systems of NGC 1400 and NGC 1407
The two brightest elliptical galaxies in the Eridanus A group, NGC 1400 and
NGC 1407, have been observed in both the Washington T_1 and Kron-Cousins I
filters to obtain photometry of their globular cluster systems (GCSs). This
group of galaxies is of particular interest due to its exceptionally high M/L
value, previously estimated at ~3000h, making this cluster highly
dark-matter-dominated. NGC 1400's radial velocity (549 km/s) is extremely low
compared to that of the central galaxy of Eridanus A (NGC 1407 with =
1766 km/s) and the other members of the system, suggesting that it is a
foreground galaxy projected by chance onto the cluster. Using the shapes of the
globular cluster luminosity functions, however, we derive distances of 17.6 +/-
3.1 Mpc to NGC 1407 and 25.4 +/- 7.0 Mpc to NGC 1400. These results support
earlier conclusions that NGC 1400 is at the distance of Eridanus A and
therefore has a large peculiar velocity. Specific frequencies are also derived
for these galaxies, yielding values of S_N = 4.0 +/- 1.3 for NGC 1407 and S_N =
5.2 +/- 2.0 for NGC 1400. In this and other respects, these two galaxies have
GCSs which are consistent with those observed in other galaxies.Comment: 14 pages (AASTeX), 3 postscript figures, submitted to the
Astronomical Journa
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