816 research outputs found
Direct Observation of the Fourth Star in the Zeta Cancri System
Direct imaging of the zeta Cnc system has resolved the fourth star in the
system, which is in orbit around zeta Cnc C. The presence of the fourth star
has been inferred for many years from irregularities in the motion of star C,
and recently from C's spectroscopic orbit. However, its mass is close to that
of C, making its non-detection puzzling. Observing at wavelengths of 1.2, 1.7,
and 2.2 microns with the adaptive-optics system of the CFHT, we have obtained
images which very clearly reveal star D and show it to have the color of an M2
star. Its brightness is consonant with its being two M stars, which are not
resolved in our observations but are likely to be in a short-period orbit,
thereby accounting for the large mass and the difficulty of detection at
optical wavelengths, where the magnitude difference is much larger. The
positions and colors of all four stars in the system are reported and are
consistent with the most recent astrometric observations.Comment: 7 pages including 3 tables, 1 figure; To appear in PAS
Extrasolar Planets in the Classroom
The field of extrasolar planets is still, in comparison with other
astrophysical topics, in its infancy. There have been about 300 or so
extrasolar planets detected and their detection has been accomplished by
various different techniques. Here we present a simple laboratory experiment to
show how planets are detected using the transit technique. Following the simple
analysis procedure describe we are able to determine the planetary radius to be
1.27 +/- 0.20 R_{J} which, within errors agrees with the establish value of
1.32 +/- 0.25 R_{J}.Comment: 7 pages, 2 figures, published in Physics Educatio
Properties and nature of Be stars: 27. Orbital and recent long-term variations of the Pleiades Be star Pleione = BU Tauri
Radial-velocity variations of the H-alpha emission measured on the steep
wings of the H-alpha line, prewhitened for the long-time changes, vary
periodically with a period of (218.025 +/- 0.022)d, confirming the suspected
binary nature of the bright Be star Pleione, a member of the Pleiades cluster.
The orbit seems to have a high eccentricity over 0.7, but we also briefly
discuss the possibility that the true orbit is circular and that the
eccentricity is spurious owing to the phase-dependent effects of the
circumstellar matter. The projected angular separation of the spectroscopic
orbit is large enough to allow the detection of the binary with large optical
interferometers, provided the magnitude difference primary - secondary is not
too large. Since our data cover the onset of a new shell phase up to
development of a metallic shell spectrum, we also briefly discuss the recent
long-term changes. We confirm the formation of a new envelope, coexisting with
the previous one, at the onset of the new shell phase. We find that the full
width at half maximum of the H-alpha profile has been decreasing with time for
both envelopes. In this connection, we briefly discuss Hirata's hypothesis of
precessing gaseous disk and possible alternative scenarios of the observed
long-term changes
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
Factors associated with usage of antimicrobials in commercial mink (Neovison vison) production in Denmark
AbstractThe American mink (Neovison vison) is used for commercial fur production in Denmark. In recent years, antimicrobial prescription for Danish mink has been increasing. In this study, the patterns and trends in antimicrobial use in mink were described and a multi-variable variance analysis was carried out with the objective of identifying risk factors for antimicrobial use on herd level. The study was based on register data for 2007–2012. Information on antimicrobial use was obtained from the national database VetStat, monitoring all medicinal products used for animals on prescription level. Data on microbiological feed quality was obtained from the Voluntary Feed Control under the Mink producers Organization, and data on herd size and the relation between farm and feed producer was obtained from the registers at Kopenhagen Fur, based on yearly reporting from the mink producers. Descriptive analysis showed a clear significant effect of season on antimicrobial use, with a peak in “treatment proportions”, TP (defined daily doses per kg biomass-days) in May, around the time of whelping, and a high level in the following months. In autumn, a minor peak in antimicrobial use occurred throughout the study period. From 2007 to 2011, a 102% increase in annual antimicrobial TP was noted; on herd level, the increase was associated with an increasing frequency of prescription, and a decrease in the amounts prescribed in months with prescription. A binomial model showed that on herd level, the annual number of months with antimicrobial prescription was significantly (p<0.01) affected by feed producer, veterinarian, disease (specific laboratory diagnosis) infection, herd size and year, with an interaction between feed producer and year. A log-normal model showed that in months with antimicrobial use, the TP on herd level was significantly (p<0.001) affected by year, month (season), feed producer, feed quality score, veterinarian, herd size and laboratory confirmed diagnosis of specific infections; additionally the interaction terms year×feed producer and herd size×month were significant (p<0.001).In conclusion, antimicrobial use on herd level was significantly associated with the microbiological food quality, the feed producer, and the veterinarian. The prescription patterns varied significantly between veterinarians, and some veterinarians were associated with both larger and more frequent prescriptions of antimicrobials at herd level. Herd size is associated with different prescription patterns. Finally, infection with Pseudomonas aeruginosa, astrovirus, influenza virus and Salmonella spp. was associated with an increase in antimicrobial use
A cross-sectional field study on potential associations between feed quality measures and usage of antimicrobials in commercial mink (Neovison vison)
New ground-based observational methods and instrumentation for asteroseismology
Space instrumentation like SOHO, MOST, CoRoT and Kepler has been and is being
built to attain very high precision data to be used for asteroseismic analysis.
Nonetheless, there is a very strong need for providing additional information,
especially on mode identification. With this contribution I will review the
efforts been put on new ground-based instrumentation and the methodology that
can be used to achieve this aim.Comment: 6 pages. Review contribution to be published in Astrophysics and
Space Science Proceedings series (ASSP), in the proceedings of "20th Stellar
Pulsation Conference Series: Impact of new instrumentation and new insights
in stellar pulsations", 5-9 September 2011, Granada, Spai
An atomic circumnuclear disk in Cygnus A
ABSTRACT We present Very Long Baseline Array (VLBA) H i absorption observations of the core region of the powerful radio galaxy Cygnus A. These data show both broad (FWHM = 244 ± 22km s −1 ) and narrow (FWHM < 30km s −1 ) velocity components. Modeling of the broad velocity absorption shows high opacity on the counter-jet, low opacity against the core and no absorption on the jet side; we argue this is most naturally explained by a circumnuclear H i disk orientated roughly perpendicular to the jet axis. We estimate that the H i absorbing gas lies at a radius of ∼ 80 pc and has a scale height of about 20 pc. We estimate this gas has a minimum density n > 10 4 cm −3 and a total column density in the range 10 23 − 10 24 cm −2 ; we cannot however determine whether it is primarily an atomic or molecular phase. We find that this gas component does not cover the radio core in Cygnus A and therefore does not contribute to the total gas column that blocks our view of the hidden quasar nucleus. If however we were observing Cygnus A from a different direction it could add significantly. This implies that in some radio galaxies gas on ∼ 100 pc scales may contribute to the obscuration of the central engine. We argue that the circumnuclear torus in Cygnus A contains too little mass to power the AGN over > 10 7 yr but that material in the outer H i absorbing gas disk can provide a reservoir to fuel the AGN and replenish torus clouds. The second narrow H i absorption component is significantly redshifted (by 180km s −1 ) with respect to the systemic velocity and probably traces infalling gas which will ultimately fuel the source. This component could arise either within a tidal tail structure associated with a recent (minor) merger or be associated with an observed infalling giant molecular cloud
The Challenge of Wide-Field Transit Surveys: The Case of GSC 01944-02289
Wide-field searches for transiting extra-solar giant planets face the
difficult challenge of separating true transit events from the numerous false
positives caused by isolated or blended eclipsing binary systems. We describe
here the investigation of GSC 01944-02289, a very promising candidate for a
transiting brown dwarf detected by the Transatlantic Exoplanet Survey (TrES)
network. The photometry and radial velocity observations suggested that the
candidate was an object of substellar mass in orbit around an F star. However,
careful analysis of the spectral line shapes revealed a pattern of variations
consistent with the presence of another star whose motion produced the
asymmetries observed in the spectral lines of the brightest star. Detailed
simulations of blend models composed of an eclipsing binary plus a third star
diluting the eclipses were compared with the observed light curve and used to
derive the properties of the three components. Our photometric and
spectroscopic observations are fully consistent with a blend model of a
hierarchical triple system composed of an eclipsing binary with G0V and M3V
components in orbit around a slightly evolved F5 dwarf. We believe that this
investigation will be helpful to other groups pursuing wide-field transit
searches as this type of false detection could be more common than true
transiting planets, and difficult to identify.Comment: To appear in ApJ, v. 621, 2005 March 1
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