146,957 research outputs found
Light and Motion in SDSS Stripe 82: The Catalogues
We present a new public archive of light-motion curves in Sloan Digital Sky
Survey (SDSS) Stripe 82, covering 99 deg in right ascension from RA = 20.7 h to
3.3 h and spanning 2.52 deg in declination from Dec = -1.26 to 1.26 deg, for a
total sky area of ~249 sq deg. Stripe 82 has been repeatedly monitored in the
u, g, r, i and z bands over a seven-year baseline. Objects are cross-matched
between runs, taking into account the effects of any proper motion. The
resulting catalogue contains almost 4 million light-motion curves of stellar
objects and galaxies. The photometry are recalibrated to correct for varying
photometric zeropoints, achieving ~20 mmag and ~30 mmag root-mean-square (RMS)
accuracy down to 18 mag in the g, r, i and z bands for point sources and
extended sources, respectively. The astrometry are recalibrated to correct for
inherent systematic errors in the SDSS astrometric solutions, achieving ~32 mas
and ~35 mas RMS accuracy down to 18 mag for point sources and extended sources,
respectively.
For each light-motion curve, 229 photometric and astrometric quantities are
derived and stored in a higher-level catalogue. On the photometric side, these
include mean exponential and PSF magnitudes along with uncertainties, RMS
scatter, chi^2 per degree of freedom, various magnitude distribution
percentiles, object type (stellar or galaxy), and eclipse, Stetson and Vidrih
variability indices. On the astrometric side, these quantities include mean
positions, proper motions as well as their uncertainties and chi^2 per degree
of freedom. The here presented light-motion curve catalogue is complete down to
r~21.5 and is at present the deepest large-area photometric and astrometric
variability catalogue available.Comment: MNRAS accepte
The mass of Albireo Aa and the nature of Albireo AB: New aspects from Gaia DR2
Aims: We aim to clarify the nature of Albireo AB and specifically to decipher
whether it is an optical or physical pair. We also try to determine the mass of
Albireo Aa. Methods: We scrutinize and compare the available absolute
astrometric data (from Hipparcos and Gaia DR2) of Albireo A and B, and we
investigate the relative orbit of the pair Albireo Aa,Ac using orbit solutions
based on ground-based interferometric measurements. Results: The mass of
Albireo Aa (K3 II) is surprisingly small; only an upper limit of about 0.7
solar masses could be derived. The systemic proper motion of Aa,Ac differs from
that of component B by about 10 mas/year with an uncertainty of less than 2
mas/year. Albireo AB is therefore most probably an optical double. Conclusions:
Specific astrometric and spectroscopic follow-up observations clarifying the
surprising mass estimate for Albireo Aa are recommended.Comment: 4 pages, 3 figures, accepted by Astron. Astrophy
Evolution of massive binary black holes
Since many or most galaxies have central massive black holes (BHs), mergers
of galaxies can form massive binary black holes (BBHs). In this paper, we study
the evolution of massive BBHs in realistic galaxy models, using a
generalization of techniques used to study tidal disruption rates around
massive BHs. The evolution of BBHs depends on BH mass ratio and host galaxy
type. BBHs with very low mass ratios (say, \la 0.001) are hardly ever formed
by mergers of galaxies because the dynamical friction timescale is too long for
the smaller BH to sink into the galactic center within a Hubble time. BBHs with
moderate mass ratios are most likely to form and survive in spherical or nearly
spherical galaxies and in high-luminosity or high-dispersion galaxies; they are
most likely to have merged in low-dispersion galaxies (line-of-sight velocity
dispersion \la 90 km/s) or in highly flattened or triaxial galaxies. The
semimajor axes and orbital periods of surviving BBHs are generally in the range
10^{-3}-10 pc and 10-10^5 yr; and they are larger in high-dispersion galaxies
than in low-dispersion galaxies, larger in nearly spherical galaxies than in
highly flattened or triaxial galaxies, and larger for BBHs with equal masses
than for BBHs with unequal masses. The orbital velocities of surviving BBHs are
generally in the range 10^2-10^4 km/s. The methods of detecting surviving BBHs
are also discussed. If no evidence of BBHs is found in AGNs, this may be either
because gas plays a major role in BBH orbital decay or because nuclear activity
switches on soon after a galaxy merger, and ends before the smaller BH has had
time to spiral to the center of the galaxy.Comment: 32 pages, including 14 figures, submitted to MNRA
Prospects of constraining the dense matter equation of state from the timing analysis of pulsars in double neutron star binaries: the cases of PSR J0737-3039A and PSR J1757-1854
The Lense-Thirring effect from spinning neutron stars in double neutron star
binaries contribute to the periastron advance of the orbit. This extra term
involves the moment of inertia of the neutron stars. Moment of inertia, on the
other hand, depends on the mass and spin of the neutron star as well as the
equation of state of the matter. If at least one member of the double neutron
star binary (better the faster one) is a radio pulsar, then accurate timing
analysis might lead to the estimation of the contribution of the Lense-Thirring
effect to the periastron advance, which will lead to the measurement of the
moment of inertia of the pulsar. Combination of the knowledge on the values of
the moment of inertia, the mass, and the spin of the pulsar, will give a new
constraint on the equation of state. Pulsars in double neutron star binaries
are the best for this purpose as short orbits and moderately high
eccentricities make the Lense-Thirring effect substantial, whereas tidal
effects are negligible (unlike pulsars with main sequence or white-dwarf
binaries). The most promising pulsars are PSR J0737-3039A and PSR J1757-1854.
The spin-precession of pulsars due to the misalignment between the spin and the
orbital angular momentum vectors affect the contribution of the Lense-Thirring
effect to the periastron advance. This effect has been explored for both PSR
J0737-3039A and PSR J1757-1854, and as the misalignment angles for both of
these pulsars are small, the variation in the Lense-Thirring term is not much.
However, to extract the Lense-Thirring effect from the observed rate of the
periastron advance, more accurate timing solutions including precise proper
motion and distance measurements are essential.Comment: To appear in the special issue of `Universe' dedicated to the
conference: "Compact Stars in the QCD Phase Diagram VI" held at The Joint
Institute for Nuclear Research (JINR), Dubna, Russia; during 26 - 29
September, 201
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