724 research outputs found
Proper Motions of Faint UV-Bright Sources in the Sandage Two-color Survey of the Galactic Plane
Proper motions with values >10 mas/yr or <-10 mas/yr have been extracted from
the USNO-B1.0 and Tycho II catalogues for all Lanning UV-bright sources
identified in the Sandage Two-color Survey of the Galactic Plane and presented
in Papers I-VI. Of the 572 sources examined, we find at least 213 which exhibit
a significantly large proper motion. Based on the location of the sources in a
reduced proper motion diagram, we demonstrate that about two thirds of the high
proper motion sources are likely or very likely to be heretofore unidentified
white dwarfs.Comment: 15 pages, to appear in Publications of the Astronomical Society of
the Pacifi
Hipparcos absolute magnitudes for metal rich K giants and the calibration of DDO photometry
Parallaxes for 581 bright K giants have been determined using the Hipparcos
satellite. We combine the trigonometric parallaxes with ground based
photometric data to determine the K giant absolute magnitudes. For all these
giants, absolute magnitude estimates can also be made using the intermediate
band photometric DDO system (Janes 1975, 1979). We compare the DDO absolute
magnitudes with the very accurate Hipparcos absolute magnitudes, finding
various systematic offsets in the DDO system. These systematic effects can be
corrected, and we provide a new calibration of the DDO system allowing absolute
magnitude to be determined with an accuracy of 0.35 mag in the range 2 > M_V >
-1. The new calibration performs well when tested on K giants with DDO
photometry in a selection of low reddening open-clusters with well-measured
distance moduli.Comment: Submitted to MNRAS. 7 pages, 6 figures, MNRAS style file also
available at http://astro.utu.fi/~cflynn/projects4.htm
Calibrated griz magnitudes of Tycho stars: All-sky photometric calibration using bright stars
Photometric calibration to 5% accuracy is frequently needed at arbitrary
celestial locations; however, existing all-sky astronomical catalogs do not
reach this accuracy and time consuming photometric calibration procedures are
required. I fit the Hipparcos B_T and V_T magnitudes along with the 2MASS J, H,
and K magnitudes of Tycho-2 catalog-stars with stellar spectral templates. From
the best fit spectral template derived for each star, I calculate the synthetic
SDSS griz magnitudes and constructed an all-sky catalog of griz magnitudes for
bright stars (V<12). Testing this method on SDSS photometric telescope
observations, I find that the photometric accuracy for a single star is usually
about 0.12, 0.12, 0.10 and 0.08 mag (1 sigma), for the g, r, i, and z-bands,
respectively. However, by using ~10 such stars, the typical errors per
calibrated field (systematic + statistical) can be reduced to about 0.04, 0.03,
0.02, and 0.02,mag, in the g, r, i, and z-bands, respectively. Therefore, in
cases for which several calibration stars can be observed in the field of view
of an instrument, accurate photometric calibration is possible.Comment: 3 pages, PASP, in pres
Roots in 3-manifold topology
Let C be some class of objects equipped with a set of simplifying moves. When
we apply these to a given object M in C as long as possible, we get a root of
M.
Our main result is that under certain conditions the root of any object
exists and is unique. We apply this result to different situations and get
several new results and new proofs of known results. Among them there are a new
proof of the Kneser-Milnor prime decomposition theorem for 3-manifolds and
different versions of this theorem for cobordisms, knotted graphs, and
orbifolds.Comment: This is the version published by Geometry & Topology Monographs on 29
April 200
Chandra Observations of Low Mass X-ray Binaries and Diffuse Gas in the Early-Type Galaxies NGC 4365 and NGC 4382 (M85)
(Abridged) We used the Chandra X-ray Observatory ACIS S3 to image the X-ray
faint elliptical galaxy NGC 4365 and lenticular galaxy NGC 4382. The
observations resolve much of the X-ray emission into 99 and 58 sources,
respectively, most of which are low-mass X-ray binaries (LMXBs) associated with
each of the galaxies. We identify 18 out of the 37 X-ray sources in a central
field in NGC 4365 with globular clusters. The luminosity functions of the
resolved sources for both galaxies are best fit with cutoff power-laws whose
cutoff luminosity is ergs s. These
luminosities are much larger than those previously measured for similar
galaxies; we do not find evidence for a break in the luminosity function at the
Eddington luminosity of a 1.4 neutron star. The spatial distributions
of the resolved sources for both galaxies are broader than the distribution of
optical stars. In both galaxies, a hard power-law model fits the summed
spectrum of all of the sources. The unresolved emission is best fit by the sum
of a soft mekal model representing emission from diffuse gas, and a hard
power-law, presumed to be from unresolved LMXBs. A standard beta model fits the
radial distribution of the diffuse gas in both galaxies. In the elliptical NGC
4365, the best-fit core radius is very small, while the S0 galaxy NGC 4382 has
a larger core radius. This may indicate that the gas in NGC 4382 is rotating
significantly.Comment: Astrophysical Journal, accepted: 38 pages with 20 embedded reduced
resolution Postscript figure
Helimagnetic thin films: surface reconstruction, surface spin-waves and magnetization
Quantum properties of a helimagnetic thin film of simple cubic lattice with
Heisenberg spin model are studied using the Green's function method. We find
that the spin configuration across the film is strongly non uniform. Using the
exactly determined spin configuration we calculate the spin-wave spectrum and
the layer magnetizations as functions of temperature T. We show the existence
of surface-localized modes which strongly affect the surface magnetization. We
also show that quantum fluctuations cause interesting spin contractions at T =
0 and give rise to a cross-over between layer magnetizations at low T .Comment: To appear in JMMM. arXiv admin note: substantial text overlap with
arXiv:1412.018
Tricriticality of the Blume-Emery-Griffiths Model In Thin Films of Stacked Triangular Lattices
We study in this paper the Blume-Emery-Griffiths model in a thin film of
stacked triangular lattices.The model is described by three parameters:
bilinear exchange interaction between spins , quadratic exchange interaction
and single-ion anisotropy . The spin at the lattice site
takes three values .This model can describe the mixing phase of He-4
() and He-3 () at low temperatures.Using Monte Carlo
simulations, we show that there exists a critical value of below (above)
which the transition is of second-(first-)order.In general, the temperature
dependence of the concentrations of He-3 is different from layer by layer. At a
finite temperature in the superfluid phase, the film surface shows a deficit of
He-4 with respect to interior layers. However, effects of surface interaction
parameters can reverse this situation. Effects of the film thickness on
physical properties will be also shown as functions of temperature.Comment: To appear in Modern Physics Letters B (2015
Comparing Tycho-2 Astrometry with UCAC1
The Tycho-2 Catalogue, released in February 2000, is based on the ESA
Hipparcos space mission data and various ground-based catalogs for proper
motions. An external comparison of the Tycho-2 astrometry is presented here
using the first U.S. Naval Observatory CCD Astrograph Catalog (UCAC1). The
UCAC1 data were obtained from observations performed at CTIO between February
1998 and November 1999, using the 206 mm aperture 5-element lens astrograph and
a 4k x 4k CCD. Only small systematic differences in position between Tycho-2
and UCAC1 up to 15 milliarcseconds (mas) are found, mainly as a function of
magnitude. The standard deviations of the distributions of the position
differences are in the 35 to 140 mas range, depending on magnitude. The
observed scatter in the position differences is about 30% larger than expected
from the combined formal, internal errors, also depending on magnitude. The
Tycho-2 Catalogue has the more precise positions for bright stars (V <= 10 mag)
while the UCAC1 positions are significantly better at the faint end (11 mag <=
V <= 12.5 mag) of the magnitude range in common. UCAC1 goes much fainter (to
R=16) than Tycho-2; however complete sky coverage is not expected before mid
2003.Comment: LaTeX, 8 pages, 3 PS figures, accepted by AJ (Aug 2000) see also
http://ad.usno.navy.mil/ad/ucac/ request for UCAC1 CD-ROM: e-mail to
[email protected] request for Tycho-2 CD-ROM: e-mail to
[email protected] or [email protected]
Revised Coordinates and Proper Motions of the Stars in the Luyten Half-Second Catalogue
We present refined coordinates and proper motion data for the high proper
motion (HPM) stars in the Luyten Half-Second (LHS) catalogue. The positional
uncertainty in the original Luyten catalogue is typically >10" and is often
>30". We have used the digital scans of the Palomar Observatory Sky Survey
(POSS) I and POSS II plates to derive more accurate positions and proper
motions of the objects. Out of the 4470 candidates in the LHS catalogue, 4323
objects were manually re-identified in the POSS I and POSS II scans. A small
fraction of the stars were not found due to the lack of finder charts and
digitized POSS II scans. The uncertainties in the revised positions are
typically ~2", but can be as high as ~8" in a few cases; this is a large
improvement over the original data. Cross-correlation with the Tycho-2 and
Hipparcos catalogues yielded 819 candidates (with m_R < 12). For these brighter
sources, the position and proper motion data have been replaced with the more
accurate Tycho/Hipparcos data. In total, we have revised proper motion
measurements and coordinates for 4040 stars and revised coordinates for 4330
stars, which are presented here.Comment: 108 pages. Accepted for Publication in ApJ Suppl. Some errors caused
by the transcription errors in the original LHS catalogue have been corrected
in this resubmission. The most current version of the catalogue is also
available online at http://www.stsci.edu/~ksahu/lh
Secure Identification of Free-Floating Planets
Among the methods proposed to detect extrasolar planets, microlensing is the
only technique that can detect free-floating planets. Free-floating planets are
detected through the channel of short-duration isolated lensing events.
However, if a seemingly isolated planetary event is detected, it is difficult
to firmly conclude that the event is caused by a free-floating planet because a
wide-separation planet can also produce an isolated event. There were several
methods proposed to break the degeneracy between the isolated planetary events
produced by the free-floating and wide-separation planets, but they are
incomplete. In this paper, we show that free-floating planets can be securely
identified by conducting astrometric follow-up observations of isolated events
to be detected in future photometric lensing surveys by using high-precision
interferometers to be operated contemporarily with the photometric surveys. The
method is based on the fact that astrometric lensing effect covers much longer
range of the lens-source separation than the photometric effect. We demonstrate
that several astrometric follow-up observations of isolated planetary events
associated with source stars brighter than by using the {\it Space
Interferometry Mission} with an exposure time of for
each observation will make it possible to measure the centroid shift induced by
primaries with projected separations up to . Therefore, the
proposed method is far more complete than previously proposed methods that are
flawed by the limited applicability only to planets with projected separations
or planets accompanied by bright primaries.Comment: 5 pages including 2 figure
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