89 research outputs found
A High-Eccentricity Low-Mass Companion to HD 89744
HD 89744 is an F7 V star with mass 1.4 M, effective temperature 6166 K, age
2.0 Gy and metallicity [Fe/H]= 0.18. The radial velocity of the star has been
monitored with the AFOE spectrograph at the Whipple Observatory since 1996, and
evidence has been found for a low mass companion. The data were complemented by
additional data from the Hamilton spectrograph at Lick Observatory during the
companion's periastron passage in fall 1999. As a result, we have determined
the star's orbital wobble to have period P = 256 d, orbital amplitude K = 257
m/s, and eccentricity e = 0.7. From the stellar mass we infer that the
companion has minimum mass m2 sin i = 7.2 MJup in an orbit with semi-major axis
a2 = 0.88 AU. The eccentricity of the orbit, among the highest known for
extra-solar planets, continues the trend that extra-solar planets with
semi-major axes greater than about 0.15 AU tend to have much higher
eccentricities than are found in our solar system. The high metallicity of the
parent star reinforces the trend that parent stars of extra-solar planets tend
to have high metallicityComment: AASTEX-LateX v5.0, 7 pages w/ 3 figures, to be published in ApJ
An Eccentric Hot Jupiter Orbiting the Subgiant HD 185269
We report the detection of a Jupiter-mass planet in a 6.838 day orbit around
the 1.28 solar mass subgiant HD 185269. The eccentricity of HD 185269b (e =
0.30) is unusually large compared to other planets within 0.1 AU of their
stars. Photometric observations demonstrate that the star is constant to
+/-0.0001 mag on the radial velocity period, strengthening our interpretation
of a planetary companion. This planet was detected as part of our radial
velocity survey of evolved stars located on the subgiant branch of the H-R
diagram--also known as the Hertzsprung Gap. These stars, which have masses
between 1.2 and 2.5 solar masses, play an important role in the investigation
of the frequency of extrasolar planets as a function of stellar mass.Comment: 18 pages, 4 figures, 3 tables, ApJ in press (scheduled for Dec 2006,
v652n2
Ten Low Mass Companions from the Keck Precision Velocity Survey
Ten new low mass companions have emerged from the Keck precision Doppler
velocity survey, with minimum (msini) masses ranging from 0.8 mjup to 0.34
msun. Five of these are planet candidates with msini < 12 mjup, two are brown
dwarf candidates with msini ~30 mjup, and three are low mass stellar
companions. Hipparcos astrometry reveals the orbital inclinations and masses
for three of the (more massive) companions, and it provides upper limits to the
masses for the rest. A new class of extrasolar planet is emerging,
characterized by nearly circular orbits and orbital radii greater than 1 AU.
The planet HD 4208b appears to be a member of this new class. The mass
distribution of extrasolar planets continues to exhibit a rapid rise from 10
mjup toward the lowest detectable masses near 1 msat.Comment: 26 pages, TeX, plus 13 postscript figure
Precise Radial Velocities of Giant Stars II. Pollux and its Planetary Companion
It has long been speculated that the observed periodic radial velocity
pattern for the K giant Pollux might be explained in terms of an orbiting
planetary companion. We have collected 80 high-resolution spectra for Pollux at
Lick Observatory yielding precise radial velocities with a mean error of 3.8
m/s, providing the most comprehensive and precise data set available for this
star. Our data confirm the periodicity previously seen in the radial
velocities. We derive a period of 589.7+/-3.5 days and, assuming a primary mass
of 1.86 M_Sun, a minimum companion mass of 2.9+/-0.3 M_Jup, consistent with
earlier determinations. No evidence for any periodicities is visible in our
analysis of the shapes of the spectral lines via the bisector method, so that
we conclude that evidence is accumulating and compelling for a planet around
Pollux. However, some last doubt remains about this interpretation, because
non-radial pulsations which might be present in giant stars could in principle
also explain the observed radial velocities, while the accompanying bisector
variations might be too small to be detectable with current data.Comment: 13 pages, 4 figures, accepted by Ap
A Planet at 5 AU Around 55 Cancri
We report precise Doppler shift measurements of 55 Cancri (G8V) obtained from
1989 to 2002 at Lick Observatory. The velocities reveal evidence for an outer
planetary companion to 55 Cancri orbiting at 5.5 AU. The velocities also
confirm a second, inner planet at 0.11 AU. The outer planet is the first
extrasolar planet found that orbits near or beyond the orbit of Jupiter. It was
drawn from a sample of ~50 stars observed with sufficient duration and quality
to detect a giant planet at 5 AU, implying that such planets are not rare. The
properties of this jupiter analog may be compared directly to those of the
Jovian planets in our Solar System. Its eccentricity is modest, e=0.16,
compared with e=0.05 for both Jupiter and Saturn. Its mass is at least 4.0
jupiter masses (M sin i). The two planets do not perturb each other
significantly. Moreover, a third planet of sub-Jupiter mass could easily
survive in between these two known planets. Indeed a third periodicity remains
in the velocity measurements with P = 44.3 d and a semi-amplitude of 13 m/s.
This periodicity is caused either by a third planet at a=0.24 AU or by
inhomogeneities on the stellar surface that rotates with period 42 d. The
planet interpretation is more likely, as the stellar surface is quiet,
exhibiting log(R'_{HK}) = -5.0 and brightness variations less than 1 millimag,
and any hypothetical surface inhomogeneity would have to persist in longitude
for 14 yr. Even with all three planets, an additional planet of
terrestrial--mass could orbit stably at ~1 AU. The star 55 Cancri is apparently
a normal, middle-aged main sequence star with a mass of 0.95 solar masses, rich
in heavy elements ([Fe/H] = +0.27). This high metallicity raises the issue of
the relationship between its age, rotation, and chromosphere.Comment: 47 pages, 4 tables, 12 figures, uses AASTE
Retired A Stars and Their Companions. III. Comparing the Mass-Period Distributions of Planets Around A-Type Stars and Sun-Like Stars
We present an analysis of ~5 years of Lick Observatory radial velocity
measurements targeting a uniform sample of 31 intermediate-mass subgiants (1.5
< M*/Msun < 2.0) with the goal of measuring the occurrence rate of Jovian
planets around (evolved) A-type stars and comparing the distributions of their
orbital and physical characteristics to those of planets around Sun-like stars.
We provide updated orbital solutions incorporating new radial velocity
measurements for five known planet-hosting stars in our sample; uncertainties
in the fitted parameters are assessed using a Markov Chain Monte Carlo method.
The frequency of Jovian planets interior to 3 AU is 26 (+9,-8)%, which is
significantly higher than the ~5-10% frequency observed around solar-mass
stars. The median detection threshold for our sample includes minimum masses
down to {0.2, 0.3, 0.5, 0.6, 1.3} MJup within {0.1, 0.3, 0.6, 1.0, 3.0} AU. To
compare the properties of planets around intermediate-mass stars to those
around solar-mass stars we synthesize a population of planets based on the
parametric relationship dN ~ M^{alpha}P^{beta} dlnM dlnP, the observed planet
frequency, and the detection limits we derived. We find that the values of
alpha and beta for planets around solar-type stars from Cumming et al. fail to
reproduce the observed properties of planets in our sample at the 4 sigma
level, even when accounting for the different planet occurrence rates. Thus,
the properties of planets around A stars are markedly different than those
around Sun-like stars, suggesting that only a small (~ 50%) increase in stellar
mass has a large influence on the formation and orbital evolution of planets.Comment: Accepted by the Astrophysical Journal; 15 pages, 15 figure
MerTK inhibition in tumor leukocytes decreases tumor growth and metastasis
MerTK, a receptor tyrosine kinase (RTK) of the TYRO3/AXL/MerTK family, is expressed in myeloid lineage cells in which it acts to suppress proinflammatory cytokines following ingestion of apoptotic material. Using syngeneic mouse models of breast cancer, melanoma, and colon cancer, we found that tumors grew slowly and were poorly metastatic in MerTK–/– mice. Transplantation of MerTK–/– bone marrow, but not wild-type bone marrow, into lethally irradiated MMTV-PyVmT mice (a model of metastatic breast cancer) decreased tumor growth and altered cytokine production by tumor CD11b+ cells. Although MerTK expression was not required for tumor infiltration by leukocytes, MerTK–/– leukocytes exhibited lower tumor cell–induced expression of wound healing cytokines, e.g., IL-10 and growth arrest-specific 6 (GAS6), and enhanced expression of acute inflammatory cytokines, e.g., IL-12 and IL-6. Intratumoral CD8+ T lymphocyte numbers were higher and lymphocyte proliferation was increased in tumor-bearing MerTK–/– mice compared with tumor-bearing wild-type mice. Antibody-mediated CD8+ T lymphocyte depletion restored tumor growth in MerTK–/– mice. These data demonstrate that MerTK signaling in tumor-associated CD11b+ leukocytes promotes tumor growth by dampening acute inflammatory cytokines while inducing wound healing cytokines. These results suggest that inhibition of MerTK in the tumor microenvironment may have clinical benefit, stimulating antitumor immune responses or enhancing immunotherapeutic strategies
PTB Domain-Directed Substrate Targeting in a Tyrosine Kinase from the Unicellular Choanoflagellate Monosiga brevicollis
Choanoflagellates are considered to be the closest living unicellular relatives of metazoans. The genome of the choanoflagellate Monosiga brevicollis contains a surprisingly high number and diversity of tyrosine kinases, tyrosine phosphatases, and phosphotyrosine-binding domains. Many of the tyrosine kinases possess combinations of domains that have not been observed in any multicellular organism. The role of these protein interaction domains in M. brevicollis kinase signaling is not clear. Here, we have carried out a biochemical characterization of Monosiga HMTK1, a protein containing a putative PTB domain linked to a tyrosine kinase catalytic domain. We cloned, expressed, and purified HMTK1, and we demonstrated that it possesses tyrosine kinase activity. We used immobilized peptide arrays to define a preferred ligand for the third PTB domain of HMTK1. Peptide sequences containing this ligand sequence are phosphorylated efficiently by recombinant HMTK1, suggesting that the PTB domain of HMTK1 has a role in substrate recognition analogous to the SH2 and SH3 domains of mammalian Src family kinases. We suggest that the substrate recruitment function of the noncatalytic domains of tyrosine kinases arose before their roles in autoinhibition
Structure and Evolution of Nearby Stars with Planets II. Physical Properties of ~1000 Cool Stars from the SPOCS Catalog
We derive detailed theoretical models for 1074 nearby stars from the SPOCS
(Spectroscopic Properties of Cool Stars) Catalog. The California and Carnegie
Planet Search has obtained high-quality echelle spectra of over 1000 nearby
stars taken with the Hamilton spectrograph at Lick Observatory, the HIRES
spectrograph at Keck, and UCLES at the Anglo Australian Observatory. A uniform
analysis of the high-resolution spectra has yielded precise stellar parameters,
enabling systematic error analyses and accurate theoretical stellar modeling.
We have created a large database of theoretical stellar evolution tracks using
the Yale Stellar Evolution Code (YREC) to match the observed parameters of the
SPOCS stars. Our very dense grids of evolutionary tracks eliminate the need for
interpolation between stellar evolutionary tracks and allow precise
determinations of physical stellar parameters (mass, age, radius, size and mass
of the convective zone, etc.). Combining our stellar models with the observed
stellar atmospheric parameters and uncertainties, we compute the likelihood for
each set of stellar model parameters separated by uniform time steps along the
stellar evolutionary tracks. The computed likelihoods are used for a Bayesian
analysis to derive posterior probability distribution functions for the
physical stellar parameters of interest. We provide a catalog of physical
parameters for 1074 stars that are based on a uniform set of high quality
spectral observations, a uniform spectral reduction procedure, and a uniform
set of stellar evolutionary models. We explore this catalog for various
possible correlations between stellar and planetary properties, which may help
constrain the formation and dynamical histories of other planetary systems.Comment: 28 pages, 19 figures, 5 tables, Accepted for publication in ApJS; the
catalog of stellar parameters is available at
http://exoplanets.org/SPOCS_evol.htm
Implications For The Origin Of GRB 051103 From LIGO Observations
We present the results of a LIGO search for gravitational waves (GWs)
associated with GRB 051103, a short-duration hard-spectrum gamma-ray burst
(GRB) whose electromagnetically determined sky position is coincident with the
spiral galaxy M81, which is 3.6 Mpc from Earth. Possible progenitors for
short-hard GRBs include compact object mergers and soft gamma repeater (SGR)
giant flares. A merger progenitor would produce a characteristic GW signal that
should be detectable at the distance of M81, while GW emission from an SGR is
not expected to be detectable at that distance. We found no evidence of a GW
signal associated with GRB 051103. Assuming weakly beamed gamma-ray emission
with a jet semi-angle of 30 deg we exclude a binary neutron star merger in M81
as the progenitor with a confidence of 98%. Neutron star-black hole mergers are
excluded with > 99% confidence. If the event occurred in M81 our findings
support the the hypothesis that GRB 051103 was due to an SGR giant flare,
making it the most distant extragalactic magnetar observed to date.Comment: 8 pages, 3 figures. For a repository of data used in the publication,
go to: https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=15166 . Also see
the announcement for this paper on ligo.org at:
http://www.ligo.org/science/Publication-GRB051103/index.ph
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