536 research outputs found
Optical SETI: A Spectroscopic Search for Laser Emission from Nearby Stars
We have searched for nonastrophysical emission lines in the optical spectra
of 577 nearby F, G, K, and M main-sequence stars. Emission lines of
astrophysical origin would also have been detected, such as from a
time--variable chromosphere or infalling comets. We examined ~20 spectra per
star obtained during four years with the Keck/HIRES spectrometer at a
resolution of 5 km/s, with a detection threshold 3% of the continuum flux
level. We searched each spectrum from 4000-5000 angstroms for emission lines
having widths too narrow to be natural from the host star, as well as for lines
broadened by astrophysical mechanisms. We would have detected lasers that emit
a power, P>60 kW, for a typical beam width of ~0.01 arcsec (diffraction-limit
from a 10-m aperture) if directed toward Earth from the star. No lines
consisstent with laser emission were found.Comment: 27 pages, 11 figures, uses aastex.st
Hundreds of Low-Mass Active Galaxies in the Galaxy And Mass Assembly (GAMA) Survey
We present an entirely new sample of 388 low-mass galaxies () that have spectroscopic signatures indicating the presence of
massive black holes (BHs) in the form of active galactic nuclei (AGNs) or tidal
disruption events (TDEs). Of these, 70 have stellar masses in the dwarf galaxy
regime with . We identify the
active galaxies by analyzing optical spectra of a parent sample of 23,000
low-mass emission-line galaxies in the Galaxy and Mass Assembly (GAMA) Survey
Data Release 4, and employing four different diagnostics based on narrow
emission line ratios and the detection of high-ionization coronal lines. We
find that 47 of the 388 low-mass active galaxies exhibit broad H in
their spectra, corresponding to virial BH masses in the range with a median BH mass of . Our sample extends to higher redshifts () than previous samples of AGNs in low-mass/dwarf galaxies based
on Sloan Digital Sky Survey spectroscopy, which can be attributed to the
spectroscopic limit of GAMA being magnitudes deeper. Moreover, our
multi-diagnostic approach has revealed low-mass active galaxies spanning a wide
range of properties, from blue star-forming dwarfs to luminous "miniquasars"
powered by low-mass BHs. As such, this work has implications for BH seeding and
AGN feedback at low masses.Comment: Accepted for publication in The Astrophysical Journa
Neutrino-induced deuteron disintegration experiment
Cross sections for the disintegration of the deuteron via neutral-current
(NCD) and charged-current (CCD) interactions with reactor antineutrinos are
measured to be 6.08 +/- 0.77 x 10^(-45) cm-sq and 9.83 +/- 2.04 x 10^(-45)
cm-sq per neutrino, respectively, in excellent agreement with current
calculations. Since the experimental NCD value depends upon the CCD value, if
we use the theoretical value for the CCD reaction, we obtain the improved value
of 5.98 +/- 0.54 x 10^(-45) for the NCD cross section. The neutral-current
reaction allows a unique measurement of the isovector-axial vector coupling
constant in the hadronic weak interaction (beta). In the standard model, this
constant is predicted to be exactly 1, independent of the Weinberg angle. We
measure a value of beta^2 = 1.01 +/- 0.16. Using the above improved value for
the NCD cross section, beta^2 becomes 0.99 +/- 0.10.Comment: 22pages, 9 figure
Inelastic Scattering of Tritium-Source Antineutrinos on Electrons of Germanium Atoms
Processes of the inelastic magnetic and weak scattering of
tritium-beta-source antineutrinos on the bound electrons of a germanium atom
are considered. The results obtained by calculating the spectra and cross
sections are presented for the energy-transfer range between 1 eV and 18 keV.Comment: Latex, 7 pages, 8 ps figure
Reactor-based Neutrino Oscillation Experiments
The status of neutrino oscillation searches employing nuclear reactors as
sources is reviewed. This technique, a direct continuation of the experiments
that proved the existence of neutrinos, is today an essential tool in
investigating the indications of oscillations found in studying neutrinos
produced in the sun and in the earth's atmosphere. The low-energy of the
reactor \nuebar makes them an ideal tool to explore oscillations with small
mass differences and relatively large mixing angles.
In the last several years the determination of the reactor anti-neutrino flux
and spectrum has reached a high degree of accuracy. Hence measurements of these
quantities at a given distance L can be readily compared with the expectation
at L = 0, thus testing \nuebar disappearance.
While two experiments, Chooz and Palo Verde, with baselines of about 1 km and
thus sensitive to the neutrino mass differences associated with the atmospheric
neutrino anomaly, have collected data and published results recently, an
ambitious project with a baseline of more than 100 km, Kamland, is preparing to
take data. This ultimate reactor experiment will have a sensitivity sufficient
to explore part of the oscillation phase space relevant to solar neutrino
scenarios. It is the only envisioned experiment with a terrestrial source of
neutrinos capable of addressing the solar neutrino puzzle.Comment: Submitted to Reviews of Modern Physics 34 pages, 39 figure
Efficacy of escitalopram in the treatment of social anxiety disorder: A meta-analysis versus placebo
Escitalopram is the most selective of the serotonin reuptake inhibitor (SSRI) antidepressants. We conducted a meta-analysis of placebo-controlled studies where escitalopram was used to treat patients with social anxiety disorder (SAD). Data from all randomised, double-blind placebo-controlled studies in SAD with escitalopram from both specialist settings and general practice were used. Patients met the DSM-IV criteria for SAD, ?18 years old, Liebowitz Social Anxiety Scale (LSAS) ?60. The primary outcome measure was the estimated treatment difference in LSAS total score at Week 12. Secondary outcome measures included the estimated treatment difference in the Clinical Global Impression-Severity (CGI-S) score at Week 12. A total of 1598 patients from 3 randomised controlled trials were included in the analyses. Escitalopram (n=1,061) was superior to placebo (n=537), with an estimated treatment difference on the LSAS of ?9.2 points (95%CI: [?14.4; ?4.0], p<0.01) (escitalopram 5 mg/day), ?4.6 points (95%CI: [?8.1; ?1.0], p<0.01) (escitalopram 10 mg/day), ?10.1 points (95%CI: [?13.7; ?6.5], p<0.01) (escitalopram 20 mg/day) and ?7.3 points (95%CI: [?12.3; ?2.2], p<0.01) (escitalopram 10-20 mg/day). For the CGI-S, the corresponding values were ?0.55 points (95%CI: [?0.79; ?0.31], p<0.01) (escitalopram 5 mg/day), ?0.26 points (95%CI: [?0.42; ?0.10], p<0.01) (escitalopram 10 mg/day), ?0.48 points (95%CI: [?0.64; ?0.31], p<0.01) (escitalopram 20 mg/day) and ?0.29 points (95%CI: [?0.51; ?0.07], p<0.05) (escitalopram 10-20 mg/day). The withdrawal rate due to adverse events was 7.2% for escitalopram, compared with 4.3% for placebo (p<0.05). In this meta-analysis, all doses of escitalopram showed significant superiority in efficacy versus placebo in the treatment of patients with SAD
UV+IR Star Formation Rates: Hickson Compact Groups with Swift and Spitzer
We present Swift UVOT (1600-3000A) 3-band photometry for 41 galaxies in 11
nearby (<4500km/s) Hickson Compact Groups (HCGs) of galaxies. We use the
uvw2-band (2000A) to estimate the dust-unobscured component, SFR_UV, of the
total star-formation rate, SFR_T. We use Spitzer MIPS 24-micron photometry to
estimate SFR_IR, the dust-obscured component of SFR_T. We obtain
SFR_T=SFR_UV+SFR_IR. Using 2MASS K_s band based stellar mass, M*, estimates, we
calculate specific SFRs, SSFR=SFR_T/M*. SSFR values show a clear and
significant bimodality, with a gap between low (<~3.2x10^-11 / yr) and high
SSFR (>~1.2x10^-10 / yr) systems. All galaxies with MIR activity index a_IRAC
0) are in the high- (low-) SSFR locus, as expected if high levels of
star-formation power MIR emission from polycyclic aromatic hydrocarbon
molecules and a hot dust continuum. All elliptical/S0 galaxies are in the
low-SSFR locus, while 22 out of 24 spirals/irregulars are in the high-SSFR
locus, with two borderline cases. We divide our sample into three subsamples
(I, II and III) according to decreasing HI-richness of the parent galaxy group
to which a galaxy belongs. Consistent with the SSFR and a_IRAC bimodality, 12
out of 15 type-I (11 out of 12 type-III) galaxies are in the high- (low-) SSFR
locus, while type II galaxies span almost the full range of SSFR values. Unlike
HCG galaxies, galaxies in a comparison quiescent SINGS sub-sample are
continuously distributed both in SSFR and a_IRAC. Any uncertainties can only
further enhance the SSFR bimodality. These results suggest that an environment
characterized by high galaxy number-densities and low galaxy
velocity-dispersions, such as the one found in compact groups, plays a key role
in accelerating galaxy evolution by enhancing star-formation processes in
galaxies and favoring a fast transition to quiescence.(abridged)Comment: Accepted by ApJ. [8 Tables, 16 Figures. Color figures have reduced
size for ArXiv - emulateapj v. 2/16/10
The Infrared Properties of Hickson Compact Groups
Compact groups of galaxies provide a unique environment to study the
mechanisms by which star formation occurs amid continuous gravitational
encounters. We present 2MASS (JHK), Spitzer IRAC (3.5-8 micron) and MIPS (24
micron) observations of a sample of twelve Hickson Compact Groups (HCGs 2, 7,
16, 19, 22, 31, 42, 48, 59, 61, 62, and 90) that includes a total of 45
galaxies. The near-infrared colors of the sample galaxies are largely
consistent with being dominated by slightly reddened normal stellar
populations. Galaxies that have the most significant PAH and/or hot dust
emission (as inferred from excess 8 micron flux) also tend to have larger
amounts of extinction and/or K-band excess and stronger 24 micron emission, all
of which suggest ongoing star formation activity. We separate the twelve HCGs
in our sample into three types based on the ratio of the group HI mass to
dynamical mass. We find evidence that galaxies in the most gas-rich groups tend
to be the most actively star forming. Galaxies in the most gas-poor groups tend
to be tightly clustered around a narrow range in colors consistent with the
integrated light from a normal stellar population. We interpret these trends as
indicating that galaxies in gas-rich groups experience star formation and/or
nuclear actively until their neutral gas consumed, stripped, or ionized. The
galaxies in this sample exhibit a ``gap'' between gas-rich and gas-poor groups
in infrared color space that is sparsely populated and not seen in the Spitzer
First Look Survey sample. This gap may suggest a rapid evolution of galaxy
properties in response to dynamical effects. These results suggest that the
global properties of the groups and the local properties of the galaxies are
connected.Comment: 34 pages, 26 figures, accepted for publication in AJ, higher quality
images available in publicatio
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