87 research outputs found
Historic Light Curve and Long-term Optical Variation of BL Lacertae 2200+420
In this paper, historical optical(UBVRI) data and newly observed data from
the Yunnan Observatory of China(about100 years) are presented for BL Lacertae.
Maximum variations in UBVRI: 5.12, 5.31, 4.73, 2.59, and 2.54 and color indices
of U-B = -0.11 +/- 0.20, B-V= 1.0 +/- 0.11, V-R= 0.73 +/- 0.19, V-I= 1.42 +/-
0.25, R-I= 0.82 +/- 0.11, and B-I= 2.44 +/- 0.29 have been obtained from the
literature; The Jurkevich method is used to investigate the existence of
periods in the B band light curve, and a long-term period of 14 years is found.
The 0.6 and 0.88 year periods reported by Webb et al.(1988) are confirmed. In
addition, a close relation between B-I and B is found, suggesting that the
spectra flattens when the source brightens.Comment: 21 pages, 6 figures, 2 table, aasms4.sty, to be published in ApJ,
Vol. 507, 199
A spectroscopic analysis of the chemically peculiar star HD207561
In this paper we present a high-resolution spectroscopic analysis of the
chemically peculiar star HD207561. During a survey programme to search for new
roAp stars in the Northern hemisphere, Joshi et al. (2006) observed significant
photometric variability on two consecutive nights in the year 2000. The
amplitude spectra of the light curves obtained on these two nights showed
oscillations with a frequency of 2.79 mHz [P~6-min]. However, subsequent
follow-up observations could not confirm any rapid variability. In order to
determine the spectroscopic nature of HD207561, high-resolution spectroscopic
and spectro-polarimetric observations were carried out. A reasonable fit of the
calculated Hbeta line profile to the observed one yields the effective
temperature (Teff) and surface gravity (log g) as 7300 K and 3.7 dex,
respectively. The derived projected rotational velocity (vsin i) for HD207561
is 74 km/sec indicative of a relatively fast rotator. The position of HD207561
in the H-R diagram implies that this is slightly evolved from the main-sequence
and located well within the delta-Scuti instability strip. The abundance
analysis indicates the star has slight under-abundances of Ca and Sc and mild
over-abundances of iron-peak elements. The spectro-polarimetric study of
HD207561 shows that the effective magnetic field is within the observational
error of 100 gauss (G). The spectroscopic analysis revealed that the star has
most of the characteristics similar to an Am star, rather than an Ap star, and
that it lies in the delta-Scuti instability strip; hence roAp pulsations are
not expected in HD207561, but low-overtone modes might be excited.Comment: 8 pages, 7 figures, 3 tables. Accepted for pubblication in MNRA
Classical novae from the POINT-AGAPE microlensing survey of M31 -- I. The nova catalogue
The POINT-AGAPE survey is an optical search for gravitational microlensing
events towards the Andromeda Galaxy (M31). As well as microlensing, the survey
is sensitive to many different classes of variable stars and transients. Here
we describe the automated detection and selection pipeline used to identify M31
classical novae (CNe) and we present the resulting catalogue of 20 CN
candidates observed over three seasons. CNe are observed both in the bulge
region as well as over a wide area of the M31 disk. Nine of the CNe are caught
during the final rise phase and all are well sampled in at least two colours.
The excellent light-curve coverage has allowed us to detect and classify CNe
over a wide range of speed class, from very fast to very slow. Among the
light-curves is a moderately fast CN exhibiting entry into a deep transition
minimum, followed by its final decline. We have also observed in detail a very
slow CN which faded by only 0.01 mag day over a 150 day period. We
detect other interesting variable objects, including one of the longest period
and most luminous Mira variables. The CN catalogue constitutes a uniquely
well-sampled and objectively-selected data set with which to study the
statistical properties of classical novae in M31, such as the global nova rate,
the reliability of novae as standard-candle distance indicators and the
dependence of the nova population on stellar environment. The findings of this
statistical study will be reported in a follow-up paper.Comment: 21 pages, 13 figures, re-submitted for publication in MNRAS, typos
corrected, references updated, figures 5-9 made cleare
WEBT multiwavelength monitoring and XMM-Newton observations of BL Lacertae in 2007-2008. Unveiling different emission components
In 2007-2008 we carried out a new multiwavelength campaign of the Whole Earth
Blazar Telescope (WEBT) on BL Lacertae, involving three pointings by the
XMM-Newton satellite, to study its emission properties. The source was
monitored in the optical-to-radio bands by 37 telescopes. The brightness level
was relatively low. Some episodes of very fast variability were detected in the
optical bands. The X-ray spectra are well fitted by a power law with photon
index of about 2 and photoelectric absorption exceeding the Galactic value.
However, when taking into account the presence of a molecular cloud on the line
of sight, the data are best fitted by a double power law, implying a concave
X-ray spectrum. The spectral energy distributions (SEDs) built with
simultaneous radio-to-X-ray data at the epochs of the XMM-Newton observations
suggest that the peak of the synchrotron emission lies in the near-IR band, and
show a prominent UV excess, besides a slight soft-X-ray excess. A comparison
with the SEDs corresponding to previous observations with X-ray satellites
shows that the X-ray spectrum is extremely variable. We ascribe the UV excess
to thermal emission from the accretion disc, and the other broad-band spectral
features to the presence of two synchrotron components, with their related SSC
emission. We fit the thermal emission with a black body law and the non-thermal
components by means of a helical jet model. The fit indicates a disc
temperature greater than 20000 K and a luminosity greater than 6 x 10^44 erg/s.Comment: 11 pages, 7 figures, accepted for publication in A&
Optical Imaging of Nova Shells and the Maximum Magnitude-Rate of Decline Relationship
An optical imaging study of recent 30 novae has been undertaken using both
ground-based and space-based observations. Resolved shells have been detected
around 9 objects in the ground-based data, while another four objects have
shells detected by HST observations; for RW UMi, we fail to detect a shell
which was observed five years earlier. Images in H-alpha, and when appropriate
[O III], are shown, and finding charts for novae without shells are given if no
published chart is available. Expansion parallaxes for all systems with shells
are derived, and absolute magnitudes for a total of 28 objects are presented,
along with a discussion of the maximum magnitude-rate of decline relation. We
find that separate linear fits for fast and slow novae may be a better
representation of the data than a single, global fit. At minimum, most novae
have similar magnitudes as those of dwarf novae at maximum and novalike stars.Comment: 39 pages, 5 ps-figures, 13 jpg-figures. Accepted for publication in
the Astronomical Journal (October 2000
De la conception à l'exploitation des cuves industrielles d'électrolyse en sels fondus
Electrowinning in molten salts is a widely prospected industrial process. It is currently used in producing aluminium, fluorine, sodium and some refractory metals. Optimizing economics is carried out by smart conception of processes (bench scale, pilot, extrapolation) and monitoring working conditions (detecting and suppressing troubles). By wedding the different electrochemical approaches of PECHINEY, our corporate laboratory is aiming at :
-developing appropriate tools : acquisition of basic data, modelling well fit with electrochemical specificities (software Flux Expert ®), experimental validation ;
- carrying out sensors with associated electrochemical methods for pinpointing troubles and monitoring processes.L'électrolyse en sels fondus est un procédé industriel largement développé. C'est la technique utilisée pour produire l'aluminium, le fluor, le sodium, et certains métaux réfractaires multivalents. Pour optimiser cette production, il faut concevoir intelligemment le procédé (laboratoire, pilote, extrapolation) et maîtriser les conditions d'exploitation (analyse et suppression des dysfonctionnements). Le laboratoire de recherche central qui marie les différentes "cultures" électrochimiques des Sociétés du Groupe PECHINEY a pour vocation :
- de mettre au point les outils de conception : acquisition des données essentielles ; simulation numérique bien adaptée aux réacteurs électrochimiques complexes (Flux Expert®) ; validation expérimentale.
- de développer des capteurs associés aux techniques électrochimiques pour piloter les procédés et détecter les dysfonctionnements
Surveillance de la qualité des eaux de baignades : recherche et suivi du développement des dinoflagellés toxiques du genre Ostreopsis au niveau du littoral de Monaco. Eté 2009.
Rapport scientifiqueSurveillance de la qualité des eaux de baignades : recherche et suivi du développement des dinoflagellés toxiques du genre Ostreopsis au niveau du littoral de Monaco. Eté 2009
Caractérisation large bande et in-situ de couches minces de ZrO2 et HfO2 intégrées dans des capacités MIM
National audienc
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