923 research outputs found
Multicolour Photometric Study of M31 Globular Clusters
We present the photometry of 30 globular clusters (GCs) and GC candidates in
15 intermediate-band filters covering from ~3000 to ~10000 \AA using the
archival CCD images of M31 observed as part of the Beijing - Arizona - Taiwan -
Connecticut (BATC) Multicolour Sky Survey. We transform these intermediate-band
photometric data to the photometry in the standard UBVRI broad-bands. These M31
GC candidates are selected from the Revised Bologna Catalogue (RBC V.3.5), and
most of these candidates do not have any photometric data. Therefore the
present photometric data are supplement to RBC V.3.5. We find that 4 out of 61
GCs and GC candidates in RBC V.3.5 do not show any signal on the BATC images at
their locations. By linear fit of the distribution in colour-magnitude diagram
of blue GCs and GC candidates using the data from RBC V.3.5, and in this study
we find the ``blue-tilt'' of blue M31 GCs with a high confidence at 99.95% or
3.47 sigma for the confirmed GCs, and >99.99% or 4.87 sigma for GCs and GC
candidates.Comment: Accepted for publication in RAA. 22 pages including 9 figures and 6
table
A Wide Field Survey of Satellite Galaxies around the Spiral Galaxy M106
We present a wide field survey of satellite galaxies in M106 (NGC 4258)
covering a 1.7\degr \times 2\degr field around M106 using
Canada-France-Hawaii Telescope/MegaCam. We find 16 satellite galaxy candidates
of M106.
Eight of these galaxies are found to be dwarf galaxies that are much smaller
and fainter than the remaining galaxies. Four of these galaxies are new
findings. Surface brightness profiles of 15 out of 16 satellite galaxies can be
represented well by an exponential disk profile with varying scale length. We
derive the surface number density distribution of these satellite galaxies. The
central number density profile (d kpc) is well fitted by a power-law
with a power index of , similar to the expected power index of
isothermal distribution. The luminosity function of these satellites is
represented well by the Schechter function with a faint end slope of
. Integrated photometric properties (total luminosity,
total colour, and disk scale length) and the spatial distribution of these
satellite galaxies are found to be roughly similar to those of the Milky Way
and M31.Comment: Accepted by MNRA
A 15.65 solar mass black hole in an eclipsing binary in the nearby spiral galaxy Messier 33
Stellar-mass black holes are discovered in X-ray emitting binary systems,
where their mass can be determined from the dynamics of their companion stars.
Models of stellar evolution have difficulty producing black holes in close
binaries with masses >10 solar masses, which is consistent with the fact that
the most massive stellar black holes known so all have masses within 1 sigma of
10 solar masses. Here we report a mass of 15.65 +/- 1.45 solar masses for the
black hole in the recently discovered system M33 X-7, which is located in the
nearby galaxy Messier 33 (M33) and is the only known black hole that is in an
eclipsing binary. In order to produce such a massive black hole, the progenitor
star must have retained much of its outer envelope until after helium fusion in
the core was completed. On the other hand, in order for the black hole to be in
its present 3.45 day orbit about its 70.0 +/- 6.9 solar mass companion, there
must have been a ``common envelope'' phase of evolution in which a significant
amount of mass was lost from the system. We find the common envelope phase
could not have occured in M33 X-7 unless the amount of mass lost from the
progenitor during its evolution was an order of magnitude less than what is
usually assumed in evolutionary models of massive stars.Comment: To appear in Nature October 18, 2007. Four figures (one color figure
degraded). Differs slightly from published version. Supplementary Information
follows in a separate postin
Spectral Energy Distributions and Age Estimates of 39 Globular Clusters in M31
This paper supplements Jiang et al. (2003), who studied 172 M31 globular
clusters (GCs) and globular cluster candidates from Battistini et al. (1987) on
the basis of integrated photometric measurements in the
Beijing-Arizona-Taiwan-Connecticut (BATC) photometric system. Here, we present
multicolor photometric CCD data (in the BATC system) for the remaining 39 M31
GCs and candidates. In addition, the ages of 35 GCs are constrained by
comparing our accurate photometry with updated theoretical stellar synthesis
models. We use photometric measurements from GALEX in the far- and
near-ultraviolet and 2MASS infrared data, in combination with optical
photometry. Except for two clusters, the ages of the other sample GCs are all
older than 1 Gyr. Their age distribution shows that most sample clusters are
younger than 6 Gyr, with a peak at ~3 Gyr, although the `usual' complement of
well-known old GCs (i.e., GCs of similar age as the majority of the Galactic
GCs) is present as well.Comment: Accepted for Publication in AJ, 18 pages, 5 figures, 5 table
Magnetic fields in barred galaxies I. The atlas
The total and polarized radio continuum emission of 20 barred galaxies was
observed with the Very Large Array (VLA) at 3, 6, 18 and 22 cm and with the
Australia Telescope Compact Array (ATCA) at 6 cm and 13 cm. Maps at 30 arcsec
angular resolution are presented here. Polarized emission (and therefore a
large-scale regular magnetic field) was detected in 17 galaxies. Most galaxies
of our sample are similar to non-barred galaxies with respect to the
radio/far-infrared flux correlation and equipartition strength of the total
magnetic field. Galaxies with highly elongated bars are not always
radio-bright. We discuss the correlation of radio properties with the aspect
ratio of the bar and other measures of the bar strength. We introduce a new
measure of the bar strength, \Lambda, related to the quadrupole moment of the
bar's gravitational potential. The radio surface brightness I of the barred
galaxies in our sample is correlated with \Lambda, I \propto \Lambda^0.4+/-0.1,
and thus is highest in galaxies with a long bar where the velocity field is
distorted by the bar over a large fraction of the disc. In these galaxies, the
pattern of the regular field is significantly different from that in non-barred
galaxies. In particular, field enhancements occur upstream of the dust lanes
where the field lines are oriented at large angles to the bar's major axis.
Polarized radio emission seems to be a good indicator of large-scale
non-axisymmetric motions.Comment: 29 pages with 66 PostScript figures. Accepted for publication in A&A.
Figures 5-24 also available at http://www.mpifr-bonn.mpg.d
Measurement of the branching fraction and CP content for the decay B(0) -> D(*+)D(*-)
This is the pre-print version of the Article. The official published version can be accessed from the links below. Copyright @ 2002 APS.We report a measurement of the branching fraction of the decay B0âD*+D*- and of the CP-odd component of its final state using the BABAR detector. With data corresponding to an integrated luminosity of 20.4ââfb-1 collected at the ΄(4S) resonance during 1999â2000, we have reconstructed 38 candidate signal events in the mode B0âD*+D*- with an estimated background of 6.2±0.5 events. From these events, we determine the branching fraction to be B(B0âD*+D*-)=[8.3±1.6(stat)±1.2(syst)]Ă10-4. The measured CP-odd fraction of the final state is 0.22±0.18(stat)±0.03(syst).This work is supported by DOE and NSF (USA), NSERC (Canada), IHEP (China), CEA and CNRS-IN2P3 (France), BMBF (Germany), INFN (Italy), NFR (Norway), MIST (Russia), and PPARC (United Kingdom). Individuals have received support from the A.P. Sloan Foundation, Research Corporation, and Alexander von Humboldt Foundation
Search for rare quark-annihilation decays, B --> Ds(*) Phi
We report on searches for B- --> Ds- Phi and B- --> Ds*- Phi. In the context
of the Standard Model, these decays are expected to be highly suppressed since
they proceed through annihilation of the b and u-bar quarks in the B- meson.
Our results are based on 234 million Upsilon(4S) --> B Bbar decays collected
with the BABAR detector at SLAC. We find no evidence for these decays, and we
set Bayesian 90% confidence level upper limits on the branching fractions BF(B-
--> Ds- Phi) Ds*- Phi)<1.2x10^(-5). These results
are consistent with Standard Model expectations.Comment: 8 pages, 3 postscript figues, submitted to Phys. Rev. D (Rapid
Communications
Measurement of D-s(+) and D-s(*+) production in B meson decays and from continuum e(+)e(-) annihilation at âs=10.6 GeV
This is the pre-print version of the Article. The official published version can be accessed from the links below. Copyright @ 2002 APSNew measurements of Ds+ and Ds*+ meson production rates from B decays and from qqÌ
continuum events near the ΄(4S) resonance are presented. Using 20.8 fb-1 of data on the ΄(4S) resonance and 2.6 fb-1 off-resonance, we find the inclusive branching fractions B(BâDs+X)=(10.93±0.19±0.58±2.73)% and B(BâDs*+X)=(7.9±0.8±0.7±2.0)%, where the first error is statistical, the second is systematic, and the third is due to the Ds+âÏÏ+ branching fraction uncertainty. The production cross sections Ï(e+e-âDs+X)ĂB(Ds+âÏÏ+)=7.55±0.20±0.34pb and Ï(e+e-âDs*±X)ĂB(Ds+âÏÏ+)=5.8±0.7±0.5pb are measured at center-of-mass energies about 40 MeV below the ΄(4S) mass. The branching fractions ÎŁB(BâDs(*)+D(*))=(5.07±0.14±0.30±1.27)% and ÎŁB(BâDs*+D(*))=(4.1±0.2±0.4±1.0)% are determined from the Ds(*)+ momentum spectra. The mass difference m(Ds+)-m(D+)=98.4±0.1±0.3MeV/c2 is also measured.This work was supported by DOE and NSF (USA), NSERC (Canada), IHEP (China), CEA and CNRS-IN2P3 (France), BMBF (Germany), INFN (Italy), NFR (Norway), MIST (Russia), and PPARC (United Kingdom). Individuals have received support from the Swiss NSF, A. P. Sloan Foundation, Research Corporation, and Alexander von Humboldt Foundation
Systematic differences in simple stellar population model results: Application to the M31 globular-like cluster system
Simple stellar population (SSP) synthesis models are useful tools for
studying the nature of unresolved star clusters in external galaxies. However,
the plethora of currently available SSP models gives rise to significant and
poorly documented systematic differences. Here we consider the outputs of the
commonly used Bruzual & Charlot and GALEV models, as well as a recently updated
SSP model suite which attempts to include the contributions of binary merger
products in the form of blue straggler stars (BS-SSP). We rederive the ages,
metallicities, extinction values and masses of 445 previously observed
globular-like clusters in M31 based on chi-square minimisation of their
spectral energy distributions with respect to these three different SSP models
and adopting a Chabrier-like stellar initial mass function. A comparison
between our new results and previous estimates of the same parameters shows
that the Bruzual & Charlot models yield the youngest ages and lowest masses,
while adoption of the BS-SSP models results in the oldest ages and highest mass
estimates. Similarly, the GALEV SSP models produce the lowest metallicities,
with the highest values resulting from the BS-SSP model suite. These trends are
caused by intrinsic differences associated with the models, and are not
significantly affected by the well-known age-metallicity degeneracy. Finally,
we note that the mass function of the massive M31 star clusters is similar to
that of the Milky Way's globular clusters, which implies that the two star
cluster systems likely formed under similar environmental conditions.Comment: 15 pages, 12 figures, 2 tables, accepted for publication in MNRA
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