448 research outputs found
Recurrent Nova IM Normae
We detected the second historical outburst of the 1920 nova IM Nor. Accurate
astrometry of the outbursting object revealed the true quiescent counterpart
having a magnitude of R=17.0 mag and B=18.0 mag. We show that the quiescent
counterpart shows a noticeable variation. From the comparison of light curves
and spectroscopic signatures, we propose that IM Nor and CI Aql comprise a new
class of recurrent novae bearing some characteristics similar to those of
classical novae. We interpret that the noticeable quiescent variation can be a
result of either high orbital inclination, which may be also responsible for
the low quiescent brightness, or the presence of high/low states. If the second
possibility is confirmed by future observations, IM Nor becomes the first
recurrent nova showing state changes in quiescence. Such state changes may
provide a missing link between recurrent novae and supersoft X-ray sources.Comment: 4 pages, 3 figures, submitted to Astronomy and Astrophysics Letter
Evidence from stellar rotation of enhanced disc dispersal: (I) The case of the triple visual system BD-21 1074 in the Pictoris association
The early stage of stellar evolution is characterized by a star-disc locking
mechanism. The disc-locking prevents the star to spin its rotation up, and its
timescale depends on the disc lifetime. Some mechanisms can significantly
shorten this lifetime, allowing a few stars to start spinning up much earlier
than other stars. In the present study, we aim to investigate how the
properties of the circumstellar environment can shorten the disc lifetime. We
have identified a few multiple stellar systems, composed of stars with similar
masses, which belong to associations with a known age. Since all parameters
that are responsible for the rotational evolution, with the exception of
environment properties and initial stellar rotation, are similar for all
components, we expect that significant differences among the rotation periods
can only arise from differences in the disc lifetimes. A photometric timeseries
allowed us to measure the rotation periods of each component, while
high-resolution spectra provided us with the fundamental parameters,
and chromospheric line fluxes. The rotation periods of the components differ
significantly, and the component B, which has a closer companion C, rotates
faster than the more distant and isolated component A. We can ascribe the
rotation period difference to either different initial rotation periods or
different disc-locking phases arising from the presence of the close companion
C. In the specific case of BD21 1074, the second scenario seems to be more
favored. In our hypothesis of different disc-locking phase, any planet orbiting
this star is likely formed very rapidly owing to a gravitational instability
mechanism, rather than core accretion. Only a large difference of initial
rotation periods alone could account for the observed period difference,
leaving comparable disc lifetimes.Comment: Accepted by Astronomy & Astrophysics on July 31, 2014; Pages 12,
Figs.
ThomX : un dĂ©monstrateur dâune source Compton compacte de rayonnement X
International audienceâThomXâ est le nom dâun projet de source intense et compacte de rayons X, prĂ©sentant lâoriginalitĂ© de combiner un anneau de stockage dâĂ©lectrons Ă une cavitĂ© optique de stockage de photons. La rĂ©trodiffusion des photons entrant en collision avec les Ă©lectrons que seront produits les rayons X dâĂ©nergie rĂ©glable entre 45 et 90 keV. Il sâagit dâun projet pluridisciplinaire visant diverses applications, notamment dans le domaine biomĂ©dical (imagerie etthĂ©rapie), dans celui de lâhĂ©ritage culturel (identification et prĂ©servation) et en science des matĂ©riaux (caractĂ©risation). Des rĂ©pliques de cet appareil sont susceptibles dâĂȘtre implantĂ©es dans un laboratoire, un hĂŽpital ou un musĂ©e, oĂč un tel Ă©quipement serait complĂ©mentaire des sources de rayonnement synchrotron dont lâaccĂšs est beaucoup plus difficile
Photometric study of southern SU UMa-type dwarf novae and candidates -- III: NSV 10934, MM Sco, AB Nor, CAL 86
We photometrically observed four southern dwarf novae in outburst (NSV 10934,
MM Sco, AB Nor and CAL 86). NSV 10934 was confirmed to be an SU UMa-type dwarf
nova with a mean superhump period of 0.07478(1) d. This star also showed
transient appearance of quasi-periodic oscillations (QPOs) during the final
growing stage of the superhumps. Combined with the recent theoretical
interpretation and with the rather unusual rapid terminal fading of normal
outbursts, NSV 10934 may be a candidate intermediate polar showing SU UMa-type
properties. The mean superhump periods of MM Sco and AB Nor were determined to
be 0.06136(4) d and 0.08438(2) d, respectively. We suggest that AB Nor belongs
to a rather rare class of long-period SU UMa-type dwarf novae with low
mass-transfer rates. We also observed an outburst of the suspected SU UMa-type
dwarf nova CAL 86. We identified this outburst as a normal outburst and
determined the mean decline rate of 1.1 mag/d.Comment: 13 pages, 23 figures, to appear in MNRAS. For more information, see
http://www.kusastro.kyoto-u.ac.jp/vsnet
Absolute Fluorescence Spectrum and Yield Measurements for a wide range of experimental conditions
For the JEM-EUSO CollaborationThe fluorescence yield is a key ingredient in cosmic ray energy determination. It is sensitive to pressure, temperature and humidity. Up to now the fluorescence yield of the brightest line at 337 nm has been measured in an absolute way in one set of conditions, whereas fluorescence yields at the other wavelengths have been relatively measured for different conditions. Thus, absolute calibration for all the lines is unclear. We will do all measurements at once using the same apparatus: all the lines will be measured absolutely and not relatively for all conditions. For that we will use the 3-5 MeV electron beam of the PHIL accelerator (Photon Injector at LAL), shooting in a box filled with air at varying pressures, temperatures and humidity. Delta rays resulting from the beam collisions with Nitrogen are responsible for the light yield. The light detection probability should be independent of its emission point especially at the delta ray stopping point. The idea is to use an integrating sphere, encapsulated in a vessel where pressure, temperature and humidity can be varied. This sphere will have two ports for the beam (in and out), one more port dedicated to a NIST photodiode for calibration and another port feeding optical fibers going to: A) a grating spectrometer equipped with cooled CCD. B) a photomultiplier with BG3 filters to measure directly the integrated yield. Calibrations at the percent level, will give each line spectrum yields with a precision between 2 to 5%. A special issue will be to estimate the leakage due to "high energy" delta rays. Thus, we the air density will be increased, the beam energy will be lowered until the beam stops inside the sphere. Then, the energy loss will be precisely derived from the Bethe-Bloch formula. We will present the set-up
A laser triggered electron source for pulsed radiolysis
We present the design of a photo-injector based accelerator for pulsed radiolysis applications. This machine is destined to meet the needs of the physical chemistry community at the Universite de Paris XI. A 4 MeV Energy electron pulse of a few picoseconds duration and with a charge in the range of 1 to 10 nC is produced from a Cs/sub 2 /Te photocathode. The photocathode is placed in the half energy spread cell of a 1-1/2 cell, 3 GHz RF gun, whose design is based on the gun used for the drive beam of the CERN CLIC Test facility. A 4 cell "booster" cavity is then used to accelerate the beam to an energy of 9 MeV. The transport system consists of a quadrupole triplet downsteam of the booster, two rectangular, 30 degree bend, dipoles with a pair of quadrupoles between them and a second triplet downstream of the second dipole. Energy dependent path length effects in the two dipoles allow the possibility of magnetic bunch compression depending on the phase-energy correlation of the bunch exiting the booster cavity. The beam envelope and the bunch length have been calculated through the transport line using TRACE-3d and PARMELA. These codes allow us to verify the required beam parameters at the experimental areas. We discuss the adjustment of the optics, aimed at producing the minimum electron bunch length at the experimental targets. (4 refs)
Two X-Ray Bright Cataclysmic Variables with Unusual Activities: GZ Cnc and NSV 10934
We report on a discovery of unexpected activities in two X-ray bright dwarf novae. GZ Cnc showed an anomalous clustering of outbursts in 2002, in contrast to a low outburst frequency in the past record. The activity resembles an increased activity seen in some intermediate polars or candidates. We identified NSV 10934, X-ray selected high-amplitude variable star, as a dwarf nova with unusually rapid decline. The outburst characteristics make NSV 10934 a twin of recently discovered intermediate polar (HT Cam) with dwarf nova-type outbursts. We propose that these activities in X-ray strong dwarf novae may be a previously overlooked manifestation of outburst activities in magnetic cataclysmic variables
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