219 research outputs found
Discovery of the Widest Very Low Mass Binary
We report the discovery of a very low mass binary system (primary mass <0.1
Msol) with a projected separation of ~5100 AU, more than twice that of the
widest previously known system. A spectrum covering the 1-2.5 microns
wavelength interval at R ~1700 is presented for each component. Analysis of the
spectra indicates spectral types of M6.5V and M8V, and the photometric distance
of the system is ~62 pc. Given that previous studies have established that no
more than 1% of very low mass binary systems have orbits larger than 20 AU, the
existence of such a wide system has a bearing on very low mass star formation
and evolution models.Comment: accepted ApJL, 4 page
Correlated Photon Emission from a Single II-VI Quantum Dot
We report correlation and cross-correlation measurements of photons emitted
under continuous wave excitation by a single II-VI quantum dot (QD) grown by
molecular-beam epitaxy. A standard technique of microphotoluminescence combined
with an ultrafast photon correlation set-up allowed us to see an antibunching
effect on photons emitted by excitons recombining in a single CdTe/ZnTe QD, as
well as cross-correlation within the biexciton ()-exciton ()
radiative cascade from the same dot. Fast microchannel plate photomultipliers
and a time-correlated single photon module gave us an overall temporal
resolution of 140 ps better than the typical exciton lifetime in II-VI QDs of
about 250ps.Comment: 4 pages, 3 figures, to appear in Appl. Phys. Let
New distant companions to known nearby stars: I. GJ 4047B, GJ 718B, GJ 747.2C, GJ 4100B, and GJ 4153B
In an ongoing survey for high proper motion stars at low galactic latitudes,
we have identified 5 previously uncatalogued common proper motion companions to
stars listed in the Preliminary Version of the Third Catalogue of Nearby Stars
(GJ stars). For each system, the relative proper motion between the components
is less than 5% of the common proper motion of the pair. Spectra of the pairs
have been obtained at the Lick 3-m Shane Telescope, confirming that the systems
are indeed wide separation binaries. The systems are classified as follows: GJ
4047AB = K5 V + M5 V, GJ 718AB = K5 V + M4.5 V, GJ 747.2ABC = (K7 V + K7 V) +
M4 Ve, GJ 4100AB = M1 V + M4.5 Ve, and GJ 4153AB = M0.5 V + M3.5 V. The total
area surveyed contains 346 Gliese stars, which suggests that approximately 1.5%
of the stars listed in the Preliminary Version of the Third Catalogue of Nearby
Stars have unrecognized proper motion companions. We predict that 15-50 more
new distant companions to GJ stars will be discovered in the Digitized Sky
Survey.Comment: 15 page, 5 figures, 2 tables, to appear in The Astronomical Journa
Visual Binaries in the Orion Nebula Cluster
We have carried out a major survey for visual binaries towards the Orion
Nebula Cluster using HST images obtained with an H-alpha filter. Among 781
likely ONC members more than 60" from theta-1 Ori C, we find 78 multiple
systems (75 binaries and 3 triples), of which 55 are new discoveries, in the
range from 0.1" to 1.5". About 9 binaries are likely line-of-sight
associations. We find a binary fraction of 8.8%+-1.1% within the limited
separation range from 67.5 to 675 AU. The field binary fraction in the same
range is a factor 1.5 higher. Within the range 150 AU to 675 AU we find that T
Tauri associations have a factor 2.2 more binaries than the ONC. The binary
separation distribution function of the ONC shows unusual structure, with a
sudden steep decrease in the number of binaries as the separation increases
beyond 0.5", corresponding to 225 AU. We have measured the ratio of binaries
wider than 0.5" to binaries closer than 0.5" as a function of distance from the
Trapezium, and find that this ratio is significantly depressed in the inner
region of the ONC. The deficit of wide binaries in the central part of the
cluster is likely due to dissolution or orbital change during their passage
through the potential well of the inner cluster region. Many of the companions
are likely to be brown dwarfs.Comment: 27 pages, 10 figures, 2 tables, accepted by the Astronomical Journa
The PHASES Differential Astrometry Data Archive. V. Candidate Substellar Companions to Binary Systems
The Palomar High-precision Astrometric Search for Exoplanet Systems monitored
51 subarcsecond binary systems to evaluate whether tertiary companions as small
as Jovian planets orbited either the primary or secondary stars, perturbing
their otherwise smooth Keplerian motions. Six binaries are presented that show
evidence of substellar companions orbiting either the primary or secondary
star. Of these six systems, the likelihoods of two of the detected
perturbations to represent real objects are considered to be "high confidence",
while the remaining four systems are less certain and will require continued
observations for confirmation.Comment: 16 Pages, Accepted to A
PHASES Differential Astrometry and Iodine Cell Radial Velocities of the kappa Pegasi Triple Star System
kappa Pegasi is a well-known, nearby triple star system. It consists of a
``wide'' pair with semi-major axis 235 milli-arcseconds, one component of which
is a single-line spectroscopic binary (semi-major axis 2.5 milli-arcseconds).
Using high-precision differential astrometry and radial velocity observations,
the masses for all three components are determined and the relative
inclinations between the wide and narrow pairs' orbits is found to be 43.8 +/-
3.0 degrees, just over the threshold for the three body Kozai resonance. The
system distance is determined to 34.60 +/- 0.21 parsec, and is consistent with
trigonometric parallax measurements.Comment: Accepted for publication in ApJ, complete versions of tables 2 and 4
can be found at http://stuff.mit.edu/~matthew1/kapPegTables
PHASES High Precision Differential Astrometry of delta Equulei
delta Equulei is among the most well-studied nearby binary star systems.
Results of its observation have been applied to a wide range of fundamental
studies of binary systems and stellar astrophysics. It is widely used to
calibrate and constrain theoretical models of the physics of stars. We report
27 high precision differential astrometry measurements of delta Equulei from
the Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES).
The median size of the minor axes of the uncertainty ellipses for these
measurements is 26 micro-arcseconds. These data are combined with previously
published radial velocity data and other previously published differential
astrometry measurements using other techniques to produce a combined model for
the system orbit. The distance to the system is determined to within a
twentieth of a parsec and the component masses are determined at the level of a
percent. The constraints on masses and distance are limited by the precisions
of the radial velocity data; we outline plans improve this deficiency and
discuss the outlook for further study of this binary.Comment: Accepted by AJ. Complete versions of tables 2-7 now available at
http://stuff.mit.edu/~matthew1/deltaEquTables/ (removed from astroph server
Using Nonlinear Response to Estimate the Strength of an Elastic Network
Disordered networks of fragile elastic elements have been proposed as a model
of inner porous regions of large bones [Gunaratne et.al., cond-mat/0009221,
http://xyz.lanl.gov]. It is shown that the ratio of responses of such
a network to static and periodic strain can be used to estimate its ultimate
(or breaking) stress. Since bone fracture in older adults results from the
weakening of porous bone, we discuss the possibility of using as a
non-invasive diagnostic of osteoporotic bone.Comment: 4 pages, 4 figure
- …