18 research outputs found
G 112-29 (=NLTT 18149), a Very Wide Companion to GJ 282 AB with a Common Proper Motion, Common Parallax, Common Radial Velocity and Common Age
We have made a search for common proper motion (CPM) companions to the wide
binaries in the solar vicinity. We found that the binary GJ 282AB has a very
distant CPM companion (NLTT 18149) at a separation s=1.09 \arcdeg. Improved
spectral types and radial velocities are obtained, and ages determined for the
three components. The Hipparcos trigonometric parallaxes and the new radial
velocities and ages turn out to be very similar for the three stars, and
provide strong evidence that they form a physical system. At a projected
separation of 55733AU from GJ 282AB, NLTT 18149 ranks among the widest physical
companions known.Comment: 13 pages, 3 figures, submmited to Ap
On the Reported Death of the MACHO Era
We present radial velocity measurements of four wide halo binary candidates
from the sample in Chaname & Gould (2004; CG04) which, to date, is the only
sample containing a large number of such candidates. The four candidates that
we have observed have projected separations >0.1 pc, and include the two widest
binaries from the sample, with separations of 0.45 and 1.1 pc. We confirm that
three of the four CG04 candidates are genuine, including the one with the
largest separation. The fourth candidate, however, is spurious at the 5-sigma
level. In the light of these measurements we re-examine the implications for
MACHO models of the Galactic halo. Our analysis casts doubt on what MACHO
constraints can be drawn from the existing sample of wide halo binaries.Comment: 6 Pages, 4 Figures, Accepted for MNRAS Letter
Disk and Halo Wide Binaries from the Revised Luyten Catalog: Probes of Star Formation and MACHO Dark Matter
We present a catalog of 1147 candidate common proper motion binaries selected
from the revised New Luyten Two-Tenths Catalog. Among these, we identify 999
genuine physical pairs using the measured proper-motion difference and the
relative positions of each binary's components on a reduced proper-motion (RPM)
diagram. The RPM positions also serve to classify them as either disk
main-sequence (801), halo subdwarf (116), or pairs containing at least one
white dwarf (82). The disk and halo samples are complete to separations of
\theta=500" and \theta=900", which correspond to ~0.1 pc and ~1 pc,
respectively. At wide separations, both distributions are well described by
single power laws, dN/d\theta ~ \theta^{-\alpha}: \alpha=1.67+-0.07 for the
disk and \alpha=1.55+-0.10 for the halo. The fact that these distributions have
similar slopes (and similar normalizations as well) argues for similarity of
the star-formation conditions of these two populations. The fact that the halo
binaries obey a single power law out to ~1 pc permits strong constraints on
halo dark-matter candidates. At somewhat closer separations (10"<\theta<25"),
the disk distribution shows a pronounced flattening, which is detected at very
high statistical significance and is not due to any obvious systematic effect.
We also present a list of 11 previously unknown halo stars with parallaxes that
are recognized here as companions of Hipparcos stars.Comment: 56 pages, 16 figures; replaced with version accepted for publication
in Ap
Wide binaries as a critical test of Classical Gravity
Modified gravity scenarios where a change of regime appears at acceleration
scales have been proposed. Since for systems the
acceleration drops below at scales of around 7000 AU, a statistical
survey of wide binaries with relative velocities and separations reaching
AU and beyond should prove useful to the above debate. We apply the
proposed test to the best currently available data. Results show a constant
upper limit to the relative velocities in wide binaries which is independent of
separation for over three orders of magnitude, in analogy with galactic flat
rotation curves in the same acceleration regime. Our results are
suggestive of a breakdown of Kepler's third law beyond
scales, in accordance with generic predictions of modified gravity theories
designed not to require any dark matter at galactic scales and beyond.Comment: accepted for publication in EPJ
Primordial Black Holes: sirens of the early Universe
Primordial Black Holes (PBHs) are, typically light, black holes which can
form in the early Universe. There are a number of formation mechanisms,
including the collapse of large density perturbations, cosmic string loops and
bubble collisions. The number of PBHs formed is tightly constrained by the
consequences of their evaporation and their lensing and dynamical effects.
Therefore PBHs are a powerful probe of the physics of the early Universe, in
particular models of inflation. They are also a potential cold dark matter
candidate.Comment: 21 pages. To be published in "Quantum Aspects of Black Holes", ed. X.
Calmet (Springer, 2014
Atypical Mg-poor Milky Way Field Stars with Globular Cluster Second-generation-like Chemical Patterns
We report the peculiar chemical abundance patterns of 11 atypical Milky Way (MW) field red giant stars observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). These atypical giants exhibit strong Al and N enhancements accompanied by C and Mg depletions, strikingly similar to those observed in the so-called second-generation (SG) stars of globular clusters (GCs). Remarkably, we find low Mg abundances ([Mg/Fe] < 0.0) together with strong Al and N overabundances in the majority (5/7) of the metal-rich ([Fe/H] gsim −1.0) sample stars, which is at odds with actual observations of SG stars in Galactic GCs of similar metallicities. This chemical pattern is unique and unprecedented among MW stars, posing urgent questions about its origin. These atypical stars could be former SG stars of dissolved GCs formed with intrinsically lower abundances of Mg and enriched Al (subsequently self-polluted by massive AGB stars) or the result of exotic binary systems. We speculate that the stars Mg-deficiency as well as the orbital properties suggest that they could have an extragalactic origin. This discovery should guide future dedicated spectroscopic searches of atypical stellar chemical patterns in our Galaxy, a fundamental step forward to understanding the Galactic formation and evolution