7,713 research outputs found
Serendipitous discovery of a projected pair of QSOs separated by 4.5 arcsec on the sky
We present the serendipitous discovery of a projected pair of quasi-stellar
objects (QSOs) with an angular separation of arcsec. The
redshifts of the two QSOs are widely different: one, our programme target, is a
QSO with a spectrum consistent with being a narrow line Seyfert 1 AGN at
. For this target we detect Lyman-, \ion{C}{4}, and
\ion{C}{3]}. The other QSO, which by chance was included on the spectroscopic
slit, is a Type 1 QSO at a redshift of , for which we detect
\ion{C}{4}, \ion{C}{3]} and \ion{Mg}{2}. We compare this system to previously
detected projected QSO pairs and find that only about a dozen previously known
pairs have smaller angular separation.Comment: 4 pages, 3 figures. Accepted for publication in A
Determining the fraction of reddened quasars in COSMOS with multiple selection techniques from X-ray to radio wavelengths
The sub-population of quasars reddened by intrinsic or intervening clouds of
dust are known to be underrepresented in optical quasar surveys. By defining a
complete parent sample of the brightest and spatially unresolved quasars in the
COSMOS field, we quantify to which extent this sub-population is fundamental to
our understanding of the true population of quasars. By using the available
multiwavelength data of various surveys in the COSMOS field, we built a parent
sample of 33 quasars brighter than mag, identified by reliable X-ray to
radio wavelength selection techniques. Spectroscopic follow-up with the
NOT/ALFOSC was carried out for four candidate quasars that had not been
targeted previously to obtain a 100\% redshift completeness of the sample. The
population of high quasars (HAQs), a specific sub-population of quasars
selected from optical/near-infrared photometry, is found to contribute
of the parent sample. The full population of bright spatially
unresolved quasars represented by our parent sample consists of
reddened quasars defined by having , and
of the sample having assuming the extinction
curve of the Small Magellanic Cloud. We show that the HAQ selection works well
for selecting reddened quasars, but some are missed because their optical
spectra are too blue to pass the color cut in the HAQ selection. This is
either due to a low degree of dust reddening or anomalous spectra. We find that
the fraction of quasars with contributing light from the host galaxy is most
dominant at . At higher redshifts the population of spatially
unresolved quasars selected by our parent sample is found to be representative
of the full population at mag. This work quantifies the bias against
reddened quasars in studies that are based solely on optical surveys.Comment: 22 pages, 10 figures, accepted for publication in A&A. The ArXiv
abstract has been shortened for it to be printabl
Formation Scenario for Wide and Close Binary Systems
Fragmentation and binary formation processes are studied using
three-dimensional resistive MHD nested grid simulations. Starting with a
Bonnor-Ebert isothermal cloud rotating in a uniform magnetic field, we
calculate the cloud evolution from the molecular cloud core (n=10^4 cm^-3) to
the stellar core (n \simeq 10^22 cm^-3). We calculated 147 models with
different initial magnetic, rotational, and thermal energies, and the
amplitudes of the non-axisymmetric perturbation. In a collapsing cloud,
fragmentation is mainly controlled by the initial ratio of the rotational to
the magnetic energy, regardless of the initial thermal energy and amplitude of
the non-axisymmetric perturbation. When the clouds have large rotational
energies in relation to magnetic energies, fragmentation occurs in the
low-density evolution phase (10^12 cm^-3 < n < 10^15 cm^-3) with separations of
3-300 AU. Fragments that appeared in this phase are expected to evolve into
wide binary systems. On the other hand, fragmentation does not occur in the
low-density evolution phase, when initial clouds have large magnetic energies
in relation to the rotational energies. In these clouds, fragmentation only
occurs in the high-density evolution phase (n > 10^17 cm^-3) after the clouds
experience significant reduction of the magnetic field owing to Ohmic
dissipation in the period of 10^12 cm^-3 < n < 10^15 cm^-3. Fragments appearing
in this phase have separations of < 0.3 AU, and are expected to evolve into
close binary systems. As a result, we found two typical fragmentation epochs,
which cause different stellar separations. Although these typical separations
are disturbed in the subsequent gas accretion phase, we might be able to
observe two peaks of binary separations in extremely young stellar groups.Comment: 45 pages,12 figures, Submitted to ApJ, For high resolution figures
see
http://www2.scphys.kyoto-u.ac.jp/~machidam/protostar/proto/main-astroph.pd
Debris disks in main sequence binary systems
We observed 69 A3-F8 main sequence binary star systems using the Multiband
Imaging Photometer for Spitzer onboard the Spitzer Space Telescope. We find
emission significantly in excess of predicted photospheric flux levels for
9(+4/-3)% and 40(+7/-6)% of these systems at 24 and 70 microns, respectively.
Twenty two systems total have excess emission, including four systems that show
excess emission at both wavelengths. A very large fraction (nearly 60%) of
observed binary systems with small (<3 AU) separations have excess thermal
mission. We interpret the observed infrared excesses as thermal emission from
dust produced by collisions in planetesimal belts. The incidence of debris
disks around main sequence A3-F8 binaries is marginally higher than that for
single old AFGK stars. Whatever combination of nature (birth conditions of
binary systems) and nurture (interactions between the two stars) drives the
evolution of debris disks in binary systems, it is clear that planetesimal
formation is not inhibited to any great degree. We model these dust disks
through fitting the spectral energy distributions and derive typical dust
temperatures in the range 100--200 K and typical fractional luminosities around
10^-5, with both parameters similar to other Spitzer-discovered debris disks.
Our calculated dust temperatures suggest that about half the excesses we
observe are derived from circumbinary planetesimal belts and around one third
of the excesses clearly suggest circumstellar material. Three systems with
excesses have dust in dynamically unstable regions, and we discuss possible
scenarios for the origin of this short-lived dust.Comment: ApJ, in press. 57 pages, including 7 figures (one of which is in
color
Spectroscopy at B-factories Using Hard Photon Emission
The process of hard photon emission by initial electrons (positrons) at
B-factories is discussed. It is shown that studies of the bottomonium
spectroscopy will be feasible for the planned integrated luminosity of the
B-factory experiments.Comment: 9 pages, Latex, 1 fugure, Submitted to Int.Jour.Mod.Phys.
Towards a better understanding of somatic embryogenesis in Cyclamen persicum
Somatic embryogenesis in Cyclamen persicum was first reported in 1984 and has potential applications for propagation and breeding of this economically important ornamental crop. This in vitro regeneration system can be used for vegetative propagation of parental lines of F1 hybrids and elite plants, production of artificial seeds, Agrobacterium tumefaciens-mediated genetic transformation, long-term cryopreservation, protoplast to plant regeneration and somatic hybridization. Somatic embryogenesis was shown to be a powerful propagation system for some C. persicum genotypes, but commercial application in large scale so far is hindered by several limitations, i.e., asynchronous development, malformations or secondary somatic embryogenesis. However, recent molecular approaches by transcriptomic and proteomic analyses were undertaken in order to better understand and control this in vitro regeneration system and to overcome these problems. Our studies aim at comparing somatic embryos to their zygotic counterparts regarding their proteomes. Protein separation by two dimensional isoelectric focusing - sodium do-decyl sulfate polyacrylamide gel electrophoresis led to a resolution of about 1000 protein spots per gel, of which the first 253 were identified by mass spectrometry. Most were found to be involved in glycolysis/gluconeogenesis and stress response pathways. A proteome reference map of zygotic embryos will be publicly released soon and may serve as a basis for further investigations and improvements of somatic embryogenesis
The orbit of the brown dwarf binary Gl 569B
We present photometric, astrometric and spectroscopic observations of the
nearby (9.8 pc) low-mass binary Gl 569Bab (in turn being a companion to the
early-M star Gl 569A), made with the Keck adaptive optics facility. Having
observed Gl 569Bab since August 1999, we are able to see orbital motion and to
determine the orbital parameters of the pair. We find the orbital period to be
892 +/- 25 days, the semi-major axis to be 0.90 +/- 0.02 AU, the eccentricity
to be 0.32 +/- 0.02 and the inclination of the system to be 34+/- 3 degrees
(1-sigma). The total mass is found to be 0.123 (-0.022/+0.027) Msun (3-sigma).
In addition, we have obtained low resolution (R=1500-1700) near-infrared
spectra of each of the components in the J- and K-bands. We determine the
spectral types of the objects to be M8.5V (Gl 569Ba) and M9V (Gl 569Bb) with an
uncertainty of half a subclass. We also present new J- and K-band photometry
which allows us to accurately place the objects in the HR diagram. Most likely
the binary system is comprised of two brown dwarfs with a mass ratio of 0.89
and with an age of approximately 300 Myr.Comment: Accepted for publication in ApJ, 28 pages, figures include
Orbital parameters, masses and distance to Beta Centauri determined with the Sydney University Stellar Interferometer and high resolution spectroscopy
The bright southern binary star beta Centauri (HR 5267) has been observed
with the Sydney University Stellar Interferometer (SUSI) and spectroscopically
with the ESO CAT and Swiss Euler telescopes at La Silla. The interferometric
observations have confirmed the binary nature of the primary component and have
enabled the determination of the orbital parameters of the system. At the
observing wavelength of 442 nm the two components of the binary system have a
magnitude difference of 0.15. The combination of interferometric and
spectroscopic data gives the following results: orbital period 357 days,
semi-major axis 25.30 mas, inclination 67.4 degrees, eccentricity 0.821,
distance 102.3 pc, primary and secondary masses M1 = M2 = 9.1 solar masses and
absolute visual magnitudes of the primary and secondary M1V = -3.85 and M2V =
-3.70. The high accuracy of the results offers a fruitful starting point for
future asteroseismic modelling of the pulsating binary components.Comment: 10 pages, 4 figures. Accepted for publication in MNRA
Chandra spectroscopy of the hot star beta Crucis and the discovery of a pre-main-sequence companion
In order to test the O star wind-shock scenario for X-ray production in less
luminous stars with weaker winds, we made a pointed 74 ks observation of the
nearby early B giant, beta Cru (B0.5 III), with the Chandra HETGS. We find that
the X-ray spectrum is quite soft, with a dominant thermal component near 3
million K, and that the emission lines are resolved but quite narrow, with
half-widths of 150 km/s. The forbidden-to-intercombination line ratios of Ne IX
and Mg XI indicate that the hot plasma is distributed in the wind, rather than
confined near the photosphere. It is difficult to understand the X-ray data in
the context of the standard wind-shock paradigm for OB stars, primarily because
of the narrow lines, but also because of the high X-ray production efficiency.
A scenario in which the bulk of the outer wind is shock heated is broadly
consistent with the data, but not very well motivated theoretically. It is
possible that magnetic channeling could explain the X-ray properties, although
no field has been detected on beta Cru. We detected periodic variability in the
hard (hnu > 1 keV) X-rays, modulated on the known optical period of 4.58 hours,
which is the period of the primary beta Cep pulsation mode for this star. We
also have detected, for the first time, an apparent companion to beta Cru at a
projected separation of 4 arcsec. This companion was likely never seen in
optical images because of the presumed very high contrast between it and beta
Cru in the optical. However, the brightness contrast in the X-ray is only 3:1,
which is consistent with the companion being an X-ray active low-mass
pre-main-sequence star. The companion's X-ray spectrum is relatively hard and
variable, as would be expected from a post T Tauri star.Comment: Accepted for publication in MNRAS; 19 pages, 15 figures, some in
color; version with higher-resolution figures available at
http://astro.swarthmore.edu/~cohen/papers/bcru_mnras2008.pd
Constraints on a Massive Dirac Neutrino Model
We examine constraints on a simple neutrino model in which there are three
massless and three massive Dirac neutrinos and in which the left handed
neutrinos are linear combinations of doublet and singlet neutrinos. We examine
constraints from direct decays into heavy neutrinos, indirect effects on
electroweak parameters, and flavor changing processes. We combine these
constraints to examine the allowed mass range for the heavy neutrinos of each
of the three generations.Comment: latex, 29 pages, 7 figures (not included), MIT-CTP-221
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